vascular plant experiment

Plants don’t get the admiration they deserve.

I mean, sure, lots of people enjoy gardening.  Some may even have a favorite flower. But when it comes time to learn about plant science, most people tune out.  In all my years of teaching, I have yet to witness a student get excited about reaching the portion of our biology course when we learn about plants.  

Plants just don’t seem to be very exciting.  Well, looks can be deceiving. Plants are much more fascinating than we give them credit for.

Without plants, life as we know it wouldn’t exist. 

Plants are able to capture energy from the sun and use it to convert carbon dioxide and water into sugar in a process called photosynthesis.  Plants and other organisms capable of performing photosynthesis form the basis of nearly every food chain on the planet.  

Plants are able to keep track of the seasons. 

Have you ever stopped to consider how a plant knows when to grow and when to go dormant?  How plant bulbs know when to emerge in the spring , and what triggers a tree to drop its leaves in the fall ? How plants know the optimal time to produce flowers ?  Like humans and animals, plants have circadian rhythms : internal “clocks” that read and respond to environmental cues.

Plants have developed tricky ways to attract pollinators.

Like all living things, plants need a way to pass their genes from one generation to the next. Flowering plants (angiosperms) rely on pollination to reproduce. To solve the problem of attracting pollinators to their flowers, members of the plant kingdom utilize a variety of clever methods .

Plants can communicate, both with other plants and with other organisms.

Recent studies have shown that plants can communicate with each other, even over vast distances.  How? If injured or under stress, plants can release chemical messages into the air (in the form of Volatile Organic Compounds , or VOCs), and these messages can be transmitted to other plants up to a mile away.

Plants can also communicate to each other underground through what has become known as the Wood Wide Web . The roots of many plants share a symbiotic relationship with fungi by forming mycorrhizae. In this relationship, plants provide the fungi with food (made through photosynthesis) while the fungi provide the plants with nutrients acquired by decomposing organic matter. Impressively, the vast networks of mycorrhizae can connect plants to each other, akin to the way the World Wide Web connects people who may be far apart.  Studies have shown that plants can use the mycorrhizae to transmit chemical signals (warning nearby plants of insect attack, for example) and to distribute resources (sugar or nutrients) from plant to plant.

The more I learn about plants, the more fascinated I become.  

Have you ever stopped to wonder how water is transferred from a plant’s roots to the rest of the plant’s tissues?  Consider a tree: water needs to travel from beneath the ground to reach leaves and branches that may be hundreds of feet above the soil.  How does that happen?

And how does the sugar produced within the leaves during photosynthesis get to other parts of the plant so that it can be broken down for energy needed to fuel cellular processes?

Let’s explore a cool aspect of plant science that is fun to experiment with: the plant vascular system.

The Plant Vascular System

I’m sure you’re familiar with the human cardiovascular* system: the series of vessels responsible for transporting necessary substances to and from all of the cells of the body. You may not have known that plants  also use a system of tubes to transport essential components throughout the plant. This is called the plant vascular system.  

*This post contains affiliate links

Xylem and Phloem

There are two major types of transport vessels within the plants vascular system: xylem and phloem (pronounced zy-lem and flo-em). 

Xylem tubes carry water and minerals obtained from the roots of the plant to the tissues above ground.  Phloem tissue transport the sugars produced in the leaves to the tissues in the rest of the plant. How does this transport take place?

Within xylem, water and minerals travels in one direction–against gravity–as it is transported from the roots up and throughout the plant.  What drives this process? 

Have you ever placed a corner of a paper towel in water, and watched how the water is instantly absorbed and transferred across the expanse of the towel?  The water is wicked from the wet part of the towel to the dry parts. This happens because water molecules are naturally “sticky”: the molecules stick to each other, and they stick to other objects.The movement of water through xylem occurs in much the same way. The water in the wet part of the xylem within the roots is wicked up to the dryer parts farther up the plant.

Plants continually lose water through their leaves.  In order for photosynthesis to occur, leaves need access to sunlight, water, and carbon dioxide.  How do they get the carbon dioxide? The answer may surprise you.  

Leaf Stomata

Each leaf has tiny holes called stomata (stoma is the singular form).  The word stoma comes from the Greek word for mouth, and perhaps knowing that will help you remember the purpose of leaf stomata. It is through the stomata that  leaves “breathe” Leaves don’t actually breathe in the same way we do, but they do perform gas exchange. Through stomata, leaves take in carbon dioxide and release oxygen.

During the day when the sun is shining, the stomata of leaves are kept open to allow gas exchange so that photosynthesis can occur. You can watch the process of stomata opening in this video.

Transpiration

While the stomata are open, water loss occurs from the leaves in a process called transpiration. In fact, transpiration of water from plants back into the air is actually a part of the water cycle!

The water loss from leaves due to transpiration is what drives the movement of water through the xylem through wicking action, as shown in the following video. 

Unlike the one-way transport that occurs within xylem, movement of sugars and other compounds through phloem can occur in either direction (up or down).  This process, called translocation, delivers sugars from the leaves (the source) to the tissues of the plant that need energy to grow (the sink). Translocation depends on a series of cells within the phloem and requires an expenditure of energy.

Within plants, xylem and phloem tissue exist side by side in what is called vascular bundles. These vascular bundles are organized in different ways depending on the part of the plant. Learn more in the following video.

Hands-On Activities to Study Transpiration and the Plant Vascular System

View transpiration in living leaves.

It’s easy to view transpiration for yourself.  All you need to do is take a clear, sealable plastic bag and use it to enclose a single green leaf.  Make sure that the entire leaf is inside the bag, and that the bag is sealed around the leaf stem as closely as possible to prevent water loss.

Depending on how hot and sunny the location of your plant is, you should begin seeing water vapor accumulate within the bag in no time.  

You could take this experiment further and compare how much water transpires from different types of leaves or at different times of day.

View Leaf Stomata Using a Microscope

Speaking of leaves, would you like to view stomata? 

All you need is a microscope , blank slides , and items you likely already have at home.  While it’s possible to see leaf stomata directly using a microscope, you can create a permanent impression of leaf stomata using a simple procedure. 

You can find the instructions for this easy lab here.

Using Celery to View the Vascular System

If you’d like to get a good look at vascular bundles, all you need is some celery stalks (with leaves attached), a glass, water, and food coloring. 

Take a stalk of celery and cut off a small slice at the bottom to remove any hardened tissue. Place the celery in a glass containing water (approximately ⅓ cup) and food coloring of your choice.  (You’ll want to go heavy on the food coloring if using liquid food coloring. You may not need as much if you’re using food coloring gels).

Within an hour or so, you may notice that the celery leaves have started to change color as the colored water makes its way up the stalk.

After a few hours, remove the celery from the water.  Cut a slice off of the bottom of the celery and examine the slice.  You should be able to see that as the colored water traveled up through the xylem, it left color behind in the vascular bundles.

If you make a thin cut lengthwise along the celery stalk, you may be able to get another view of the vascular bundles.

Create Your Own Colored Flowers

As long as you have those glasses full of colored water, why not use it to make something pretty? 

Most grocery store floral departments sell white (or light-colored) flowers. Buy some, cut a bit off the stems (to remove hardened tissue) and place them in the colored water.  The colored water will make its way up the xylem and into the flower petals.  

I’ve done this over the years with carnations and chrysanthemums.  I’ve seen others have success using white roses as well. You can take this further by cutting the bottom of the stem of a single flower lengthwise and placing each end in a different color of water. This will allow you to create a flower with petals that are two different colors.

I hope I’ve started to convince you that there’s more to plants than meets the eye.

In fact, the reason that leaves change color and fall each autumn is related to the plant vascular system and transpiration.

It is estimated that up to 95% of a plant’s water loss occurs through transpiration from stomata. Recall that stomata open to allow gas exchange to occur so that photosynthesis can happen.

As the days shorten and temperatures drop in the fall in winter, conditions for photosynthesis are no longer conducive. To prevent water loss through leaf stomata, plants seal off the leaves from the rest of plant. Without access to water and minerals from the soil, the leaves stop conducting photosynthesis. Over time, chlorophyll—the bright green pigment that drives photosynthesis—begins to break down, and the other leaf pigments are revealed. Those brilliant yellows and oranges that we associate with fall foliage are actually present in the leaves year-round, but are masked by the bright green chlorophyll.

If you’d like to learn more about the Science of Autumn Leaves , I have created a free, self-paced, online mini course. It contains instructions for a fun, hands-on experiment that uses simple paper chromatography to separate the different pigments in leaves. By comparing the pigments present in green, red, yellow, and orange leaves, students can visualize what happens inside a leaf during the fall color change. You can access the free course here .

Further Information

Water Uptake and Transport in Vascular Plants

Evapotranspiration and the Water Cycle

Process of How Trees Absorb and Evaporate Water via Roots and Leaves

Why Do Leaves Change Color in the Fall?

The Science of Spring

Carnivorous Plants: Why Do They “Eat” Meat?

Colorful Walking Water Science

My online high school biology students learn all about the plant vascular system as we study cellular energy, ecology, and Kingdom Plantae: one of the six biological kingdoms of life. If you’re looking for a fun, engaging class with plenty of opportunities for hands-on exploration, check out the classes I have to offer here: High School Science Classes Taught by Dr. Kristin Moon

*The cardiovascular system is also referred to as the circulatory system

*As an affiliate for Amazon and Home Science Tools, I may earn a commission if you use my affiliate link to make a purchase. This doesn’t affect your price in any way, but helps me with the cost of maintaining my website so that I may continue to share resources to help you understand, teach, and love science.

5 thoughts on “Hands-on Activities to Study the Plant Vascular System”

excellent study. Saving for when my lad reaches the vascular system of plants in his biology course. 🙂

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Author Kristin Moon acts as a real person and passed all tests against spambots. Anti-Spam by CleanTalk.

Thank you! Best of luck to you both. Biology is so much fun!

This is so cool! Our kiddos will be excited to give this a try.

I’m so glad you found it useful! I hope your kids are amazed with their results!

Absolutely! These terms can definitely be confusing!

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Xylem and Phloem – Plant Vascular System

The vascular system of plants consists of the xylem and phloem. They are somewhat like blood vessels in animals, but plants transport materials using two tissues rather than one. Here is a look at what xylem and phloem are, what they transport, and how they work.

What are Xylem and Phloem?

Xylem and phloem are the two types of transport tissue found in vascular plants. They form a complex network running throughout the plant, carrying resources to different parts and disposing of waste products.

• Xylem primarily transports water and mineral nutrients from the roots to the rest of the plant, and it also plays a role in physical support.
• Phloem transports organic substances, such as sugars produced during photosynthesis, from the leaves to other parts of the plant.

Importance of the Vascular System in Plants

The vascular system allows plants to grow taller and larger, enabling them to inhabit a wide variety of environments. Without these conduits, plants only grow to a small size. Non-vascular plants, such as mosses and liverworts, lack xylem and phloem and rely on diffusion and osmosis for the distribution of nutrients. Vascular plants, including trees, flowering plants, and ferns, use xylem and phloem to efficiently transport nutrients, even against gravity.

The term “xylem” comes from the Greek word “xylon,” which means “wood.” This reflects the role of xylem tissue in contributing to the structural strength of plants, particularly woody ones.

Function and Structure of Xylem

Xylem transports water and dissolved minerals absorbed from the soil by the roots to the above-ground parts of the plant. The plant uses the water transported by the xylem photosynthesis and transpiration. Additionally, the xylem also provides structural support to the plant.

The xylem tissue consists of four main types of cells: tracheids, vessel elements, xylem parenchyma, and xylem fibers. The vessel elements and tracheids are the water-conducting cells. Vessel elements are wider and shorter than tracheids and connect together at the ends. The ends have perforation plates that permit water transfer between cells. Tracheids are long, thin, and tapered at the ends. The secondary cell walls of the tracheids contain lignin. The parenchyma stores food and helps in the repair and growth of xylem, while xylem fibers provide support.

In most plants, the xylem is in the center of the stem, forming a core of rigid, woody material. Mature xylem consists of dead vessel element and tracheid cells connected by hollow ends.

Transportation in Xylem

The mechanism of water transport in xylem primarily involves a process known as cohesion-tension theory. Here, the evaporative pull of transpiration from the leaves creates a tension or negative pressure that pulls water upward from the roots through the xylem tissue. Also, root pressure also plays a role. Here, water enters roots from the soil via osmosis, generating a positive pressure that forces water upward into the plant.

The term “phloem” comes from the Greek word “phloios,” meaning “bark.” This name is fitting, as phloem is often found just beneath the bark in trees.

Function and Structure of Phloem

Phloem transports organic nutrients, particularly sugars synthesized during photosynthesis, from the leaves to all other cells of the plant, including the roots.

Phloem tissue is composed of sieve-tube elements, companion cells, phloem fibers, and phloem parenchyma. The sieve-tube elements, along with their companion cells, primarily control the transportation of food. Phloem fibers provide support, and phloem parenchyma assists with food storage and the secretion of plant resins.

In most plants, the phloem is towards the exterior of the plant, just below the bark in stems and roots. The sieve-tube cells are alive, but they lack a nucleus and have less cytoplasm than other plant cells . The companion cells are living cells with a normal composition.

Transportation in Phloem

The transport mechanism in phloem is known as translocation. It involves an active process where sugars load into sieve tubes in the leaves (source) and unload where they are needed (sink), such as roots or developing shoots. This differential in sugar concentration results in water moving from xylem to phloem, building a pressure that drives the sap down the plant.

Differences in Xylem and Phloem in Monocots and Dicots

Monocots and dicots differ in the arrangement and structure of their xylem and phloem.

In dicot plants, the vascular system is organized in a ring, with the xylem typically inside, surrounded by phloem. There is often a region of meristematic cambium cells, which divide to produce more xylem or phloem cells, allowing the stem or root to increase in diameter.

In monocot plants, the xylem and phloem are paired into bundles scattered throughout the stem. Monocots do not have a vascular cambium, meaning they typically do not increase in diameter after growth.

Girdling and Its Impacts

Girdling is a practice that removes a ring of bark (the phloem layer) from around the entire circumference of a tree or plant stem. This disrupts the downward transportation of sugars and other metabolites from the leaves through the phloem. Girdling can cause the death of a tree because it interrupts the supply of food from leaves to the roots, essentially starving the plant.

However, girdling also has a deliberate use in horticulture. It encourages the plant to produce larger fruits or to direct the plant’s energy towards certain branches. By disrupting the flow of nutrients, the plant overcompensates in the remaining portions, often leading to increased yield or size of the produce.

• Lucas, William; et al. (2013). “”The Plant Vascular System ” Evolution, Development and Functions”. Journal of Integrative Plant Biology . 55 (4): 294–388. doi: 10.1111/jipb.12041
• McCulloh, Katherine A.; John S. Sperry; Frederick R. Adler (2003). “Water transport in plants obeys Murray’s law”. Nature . 421 (6926): 939–942. doi: 10.1038/nature01444
• Raven, Peter A.; Evert, Ray F.; Eichhorn, Susan E. (1999). Biology of Plants . W.H. Freeman and Company. ISBN 978-1-57259-611-5.
• Roberts, Keith (ed.) (2007). Handbook of Plant Science . Vol. 1 (Illustrated ed.). John Wiley & Sons. ISBN 9780470057230.
• Slewinski, Thomas L.; Zhang, Cankui; Turgeon, Robert (2013-07-05). “Structural and functional heterogeneity in phloem loading and transport”. Frontiers in Plant Science . 4: 244. doi: 10.3389/fpls.2013.00244

Related Posts

Practical: Observing Vascular Tissue in Celery

Introduction:

We all know that plants need water – after all, it is an input for photosynthesis. But, in the scheme of things, most of the water that plants absorb from the soil is lost to the atmosphere via tiny pores in the leaves called stomata. This process is called transpiration, and it is vital for transportation of nutrients, cooling the plant, and prevention of cell damage and wilting. Transpiration works due to capillary action, cohesion of water molecules, and differences in pressure between different regions of the plant and the environment.

While transpiration is important, too much transpiration can lead to excessive water loss from the plant, and even plant death. Certain environmental factors such as high temperatures, wind, and low humidity can increase the rate of transpiration. Some plants have evolved mechanisms to help regulate transpiration and prevent water loss in these conditions. In this investigation, you will measure the rate of transpiration in celery that is in humid or standard environments. By doing so, you will discover if celery can regulate its rate of transpiration, and identify how quickly celery transpires water. You will also be able to visualise the process of transpiration and observe the structures through which water moves. In Part B of the investigation, you have the opportunity to improve on the original method outlined in Part A, and test if other factors influence the rate of transpiration in celery.

Aim: To observe and record the movement of water through a celery stalk in a humid, closed environment compared to a stalk that is exposed to a less humid, open environment.

Hypothesis: Hypothesis needs to be written in, 'If...then.. because' format. The because part needs to have clear links to content from last lesson.

• 4 × celery stalks with leaves attached

• 2 × beakers (or glasses or cups)

• red or blue food colouring

• single-edge razor blades or scalpels

• cling wrap

• clear, sealable plastic container that is large enough to fit an upright celery stalk

• 1 × ruler

1. Fill two beakers with 150 mL of water and add 2-3 drops of food colouring to each.

2. Select four celery stalks of similar size and with a similar number of leaves (you can break the stalks off the celery bunch if necessary). Carefully use a scalpel to make a clean cut to remove the base of each stalk. After removing the base, the four stalks should be of a similar height.

3. Set two stalks into each beaker. Use the cling wrap to ensure that the stalks are upright and that the beaker is sealed (you could also pour a layer of oil over the top of the water to prevent evaporation). Be sure to support all stalks in the same fashion.

4. Add 50–100 mL of room temperature water to the bottom of the plastic container. Place one of the celery beakers into the container and seal the lid to create a humid, closed environment.

5. Place the two celery apparatuses next to each other. Make sure that both are exposed to the same amount of sunlight and temperatures.

6. Write a hypothesis for this investigation. How do you expect the independent variable to affect the dependent variable, and why?

7. Set up the apparatus again (but with only one, un-tampered celery stalk in each beaker) and leave overnight.

8. The next day, remove the last two celery stalks and cling wrap and record the volume of solution in each beaker. Carefully use a scalpel to slice the stalks open longitudinally. Once more, measure the distance that the dyed water has travelled from the base of the celery. Make observations about the colours of the leaves.

9 . Take a very thin transect cut of each of the cut celery stalks. You should be able to see that the dye has travelled through certain parts of the stem, and avoided other parts. Prepare a scientific drawing of the transects and label all key structures.

Discussion:

Use the following questions to help you write a discussion response in paragraph format.

 Describe transpiration, including its purpose and mechanism.

 Compare and contrast phloem and xylem.

 Identify the independent and dependent variables in this investigation.

 Identify any controlled variables in this experiment.

 Identify any possible errors that may have affected your results. Be sure to state whether it was a personal, systematic, or random error.

 State what this investigation tested, and describe your main results.

 Using your understanding of transpiration, explain your results.

 Explain the role of the cling wrap in this experiment.

 Explain the importance of using similarly sized celery stalks in this experiment.

Conclusion:

Summarise the findings of this experiment. Be sure to:

 state whether the hypothesis was supported or refuted, and justify your choice

 identify limitations in the experiment

 identify potential ways to improve the experiment.

suggest further study that could be complete on the hypothesis

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A-level set practicals: dissection and microscopy of a plant stem

This experiment provides a quick and eye-catching way to teach about the vascular tissue in plants and the structure of plant stems. It provides students with the opportunity to develop (and demonstrate) their scientific drawing skills as well as their use of a light microscope and eye-piece graticule.

The viewed specimen clearly shows the location of vascular bundles and the xylem, phloem and sclerenchyma or collenchyma. The use of the stain toluidine blue provides a colour difference between lignified and non-lignified cell walls, clearly highlighting specialised cells and one adaptation they have.

Simple extensions to the basic protocol would allow students to collect data in cell diameters of different specialised cells, or from different plant species very quickly. Student could also explore modifications to the protocol to try to get clearer images of the vascular tissue, thereby developing their skills of experimental design.

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Please be aware that resources have been published on the website in the form that they were originally supplied. This means that procedures reflect general practice and standards applicable at the time resources were produced and cannot be assumed to be acceptable today. Website users are fully responsible for ensuring that any activity, including practical work, which they carry out is in accordance with current regulations related to health and safety and that an appropriate risk assessment has been carried out.

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• Post Secondary

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Plant Transport: Changing the colour of a flower

Meta Description

Learning Objectives

The main goal of this experiment is to show how plants can take up water from the environment and circulate it throughout the plant.

Stomata These are pores in the leaf that allow gaseous exchange between oxygen and carbon dioxide. The opening and closing of the stomata is under the control of specialized cells called guard cells.

Xylem The vascular tissue is responsible for the conduction of water (and dissolved nutrients) from the roots in the soil to the aerial parts of the plant.

Transpiration The process which allows water to travel up the plant against the action of gravity.

Step 1 Decide what colour you want the flowers to be.

Step 2 Place around 20 drops (or until the water colour is a reasonably strong colour) of food colouring in a jar containing water.

Step 3 Cut the stalk of a white flower such that it fits comfortably in the jar.

Step 4 Leave the flower for a couple of hours or even overnight.

Step 5 Observe the new colour of the flower and the movement of the dye within it.

Be creative and reuse old plastic bottles instead of buying glassware. Don`t forget to recycle them at the end of the experiment!

You might also want to use beakers, test tube or boiling tube instead of a jar.

Make the experiment more fun by placing highlighter fluid in the water to create a magical looking glow in the dark flower.

Using a scalpel, carefully split the stem in two and place each end of the stem in different colours of water. What will happen to the flower?

Be careful when using a scalpel/scissors to cut the stalk of the flower. An adult /demonstrator should preferably cut the flower to prevent any injuries.

Food colouring carries little risk but it does stain so keep tissues close by. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957945/

Plant sap may be an irritant to some people so if it`s the case try using another plant so that the you can still be able to enjoy this fun experiment. http://www.medscape.com/viewarticle/706404_3 , or if you have sensitive skin use disposable gloves.

Transpiration is the process by which plants take up the water present in the soil and move it up the stem until it eventually reaches the leaves. It is here that the water can move out into the atmosphere again through small openings. This is a necessary process since water (together with the sun) is vital for the plant so it can perform photosynthesis, this allows plants to make up their own food.

To visualize this process imagine a relay race involving a baton. The baton represents the water molecules while the athletes represent the different plant organs. The first athlete (the roots) passes the baton to the next one (the stem) which in turn passes it to the next (the leaves). At the end of the race, the baton then is placed back in its container (back into the environment).

What do you think will happen to the colour of the white flower after some hours in the water-containing food colouring? Flower takes up the colour of the food colouring.

Why is the flower taking up the colour of the food colouring? Process of transpiration which causes the coloured water to move up the stem to the petals.

Why do dark spots develop on the flower petals? This is where the stomata are present.

How would you make a multicoloured flower? By putting the plant in one colour of water for a few hours, and then placing the plant in another colour.

What is the structure that water and the dye pass to travel up the plant? Xylem

In this experiment, the plant stem was placed in the water containing the food colouring. After some time the coloured solution was then noted to be taken up by the plant. This is due to a pulling force created by a phenomenon known as transpiration. http://www.markedbyteachers.com/gcse/science/transport-in-flowering-plants-dye-experiment-2-aim-to-find-a-the-tissue-responsible-for-the-transport-of-water-b-the-rate-of-transport-of-water-in-a-leafy-shoot.html

Transpiration is the process by which water first evaporates through the small pores (stomata) present in the leaves and then moves out of the leaf into the atmosphere.

This causes the water molecules to move out of the xylem cells into the inside of the leaf to replace the lost water. This causes a pulling force that is known as capillary action to take place which allows water to move up the plant in a continuous stream.

http://www.science-sparks.com/2016/03/31/transport-in-plants/

In our experiment, the food colouring dissolved in the water is also moved through the plant up the stem and into the leaves through transpiration. When the water evaporates and is removed from the leaf’s stomata, the dye is left behind, resulting in a colour change in the leaves.

Transpiration is the process which allows water to travel up the plant against the action of gravity. Water is then lost from the upper parts of the plant by evaporation through the stomata. http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1092853841&topicorder=6

Water gets absorbed by the roots from the soil (or in the case of our experiment from the stem) and gets transported to the leaves via the xylem. The roots of plants usually have hair like extensions protruding outwards into the soil. This allows for an increase in the surface area available for water absorption. https://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1092853841

The entrance of carbon dioxide in the leaf through the stomatal pore is necessary for the process of photosynthesis which can be represented by the following equation:

6 CO2 + 6 H2O → C6H12O6 + 6 O2 Carbon Dioxide +Water → Glucose + Oxygen

Water evaporates and diffuses out of the leaf’s stomata and into the air. This in turn creates a pulling force, pulling water out of the xylem into the leaf to replace the evaporated water. This forms an unbroken column of water in the xylem vessels of the plant, which moves upwards towards the leaves against the downward force of gravity.

Transpiration also causes the coloured water to travel up into the flower, the water eventually evaporates but the food colouring does not and remains, causing the flower to change coloured.

Applications

An innovative way of producing green energy is via the process of transpiration. This is being done using artificial glass leaves in an effort to combat global warming. This technology uses the air bubbles in the water column to generate an electric current which is then harvested. http://inhabitat.com/fern-power-artificial-glass-leaves-produce-energy-via-transpiration/

Controlling transpiration in a greenhouse allows the air moisture to be controlled. Moisture can present a problem in greenhouses since warm air and the high humidity promotes the growth of pathogenic fungi. This fungi can reduces crop yield. By controlling transpiration levels and improving air circulation within the greenhouse reduced the humidity and can help control the prevalence of these fungal pests. https://ag.umass.edu/greenhouse-floriculture/fact-sheets/reducing-humidity-in-greenhouse

Another use of transpiration was found in Japan in 2016. This research made use of an artificial root systems created to combat the problem of shallow slope instability. Using what is known as transpiration-induced soil suction to enhance the stability of a slope using artificial roots. https://www.researchgate.net/profile/Viroon_Kamchoom/publication/292213007_A_new_artificial_root_system_to_simulate_the_effects_of_transpiration-induced_suction_and_root_reinforcement/links/56c15e1308aee5caccf683ee/A-new-artificial-root-system-to-simulate-the-effects-of-transpiration-induced-suction-and-root-reinforcement.pdf

Increase the temperature and observe as to whether the flower uptakes colour at a faster rate.

Check if the experiment would provide the same results if conducted in a very dark area (inside a cabinet for example).

See if exposure to wind would cause the flower to take up the colour faster. This can easily be demonstrated by placing the plant next to an open window.

Investigate other species of plants having white flowers and see if they uptake colour at a faster or perhaps a slower rate.

Preparation: 30mins

Conducting: 2 days

Clean Up: 5mins

Number of People

1 participant

Food colouring Jar Scissors/Scalpel White flower e.g. carnation Water Tape

Contributors

Transport in plants

http://www.nuffieldfoundation.org/practical-biology/investigating-transport-systems-flowering-plant

Transport in flowering plants- Dye Experiment 2. Aim: To find (a) the tissue responsible for the transport of water. (b) the rate of transport of water in a leafy shoot.

http://www.markedbyteachers.com/gcse/science/transport-in-flowering-plants-dye-experiment-2-aim-to-find-a-the-tissue-responsible-for-the-transport-of-water-b-the-rate-of-transport-of-water-in-a-leafy-shoot.html

TRANSPORT IN PLANTS – CAPILLARY ACTION

https://www.science-sparks.com/transport-in-plants/

DYED FLOWERS SCIENCE EXPERIMENT

https://theimaginationtree.com/dyed-flowers-science-experiment/

Staining Science: Capillary Action of Dyed Water in Plants

https://www.scientificamerican.com/article/bring-science-home-capillary-action-plant/

Colored flowers | Color changing flower experiment | Science experiments for kids | Elearnin

The Color-Changing Celery Experiment!

Science – Transportation in plants -xylem, phloem, transpiration pull – English

Additional Content

Attracting pollinators (Beginner)

How Plants Can Change Our Climate (Intermediate)

>LEAF POWER: Artificial Glass Leaves Produce Energy via Transpiration (Expert)

Cite this Experiment

Aquilina, M. C., & Styles, C. (2020, May 04). Plant Transport: Changing the colour of a flower. Retrieved from http://steamexperiments.com/experiment/plant-transport-changing-the-colour-of-a-flower/

First published: May 4, 2020 Last modified: April 22, 2022

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Celery transpiration

Follow FizzicsEd 150 Science Experiments:

You will need

• One bunch of Celery
• One cup of Water (roughly 400mL)
• Food Colouring
• One sharp Knife and chopping board (adult help please!)
• Somewhere to leave the experiment undisturbed

• Instruction

Use adult help when cutting the celery

Take one stick of celery off the bunch and cut the bottom 2 cm off of the stick. Careful; choose a length of celery that won’t tip over your cup of water when it’s placed in the cup.

Add some food colouring to the cup of water (make the colour quite dark).

The celery should be able to lean against the cup without tipping it over.

Put the cut end of the stick of celery into the cup of darkly coloured water.

Leave the cup and celery for at least half an hour. Check on the leaves regularly to see if there is any discolouration at the ends of the leaves.

The celery changes to a shade of blue…

Observe the differences in the celery.

How did this happen? Did the food colouring cause this?

Look near the outside of the cut celery stem…

Cut the celery stick around halfway up, and have a look at the inside of the stem. Can you see where the food colouring went?

Try testing different variables (different colours, different plant types, sugar or salt in the water etc).

Get the Unit of Work on Plant Biology here!

• Learn about the parts of a flower
• Discover how vascular tissue transports water & sugars around the plant
• Learn about plant pigments and adaptations to the environment
• From photosynthesis to transpiration & more, there’s a heap covered!

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Why Does This Happen?

You should have seen that the food coloured water travelled up the stem of the celery and into the leaves. How does food colour get up there? Gravity should be holding the water down, right?

Water is found all the way through the celery: in the stems, the leaves and the roots. The water in the leaves of the celery evaporates through the surface of the leaves, and this leaves space inside the leaves where the water was. This process is called transpiration. That new empty space inside the leaves creates a low pressure, and like a drinking straw, this low pressure allows water below the leaf to travel up the stem. You’ll see the little tubes the water travels up when you cut the celery stem, and you can see the colour up in the leaves. These tubes are called Xylem and are part of the plant’s vascular system. This how plants transport the water and nutrients from the soil up to the very highest leaves. By the way, the tubes that transport sugars from the leaves downwards are called phloem).

Variables to test

More on variables

• Does warm vs cold food colouring influence the speed of the experiment?
• Try flowers in food colouring
• Run this experiment on a hot vs a cold day
• Does cutting off the leaves at the top of the celery make a difference?

Learn more!

From  basic ecology  and  digital microscopy  to  plants for life , we’ve got your living things unit covered! Get in touch with FizzicsEd to find out how we can work with your class.

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2 thoughts on “ Celery transpiration ”

the experiment was fun and it was wicked

Awesome! Glad you enjoyed this science activity 🙂

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Tamara Horne

How to Reveal a Plant’s Vascular System

Are you looking for a WOW-factor experiment? Then this is the one! For maximum impact, I suggest the next-level option with the highlighter and black light.

Plants are more complicated than they appear on the surface. But did you know you can reveal the framework of plant’s physiology in a simple experiment at home?

What You Need:

• Cups or Test Tubes

• Leafy Celery or Carnations (other options: lettuce, gerberas & argyranthemums)

In a cup, mix 15 drops of food coloring of your choice with a half cup of water.

Cut at least two inches off the ends of the celery stalks or carnation stems.

Note: Hold the carnation stems under water while trimming them, and then quickly place them in the glass of water. This prevents air bubbles from forming in the plant’s vascular system. Learn more about why this is important in the explanation below.

Leave the plants in the dyed water overnight. Check on them the following day and you’ll see the plant’s inner transport system of water revealed.

Optional/Next Level Experiment

If you want to take your experiment to the next level, then you can use highlighter ink instead of food coloring. Pull the plug out of a highlighter with pliers. Drop the ink sponge tube in a half cup of water. Leave the plants in the water until nighttime, except this time you’ll reveal the plant’s vascular system by shining a black light flashlight on the plant. The phosphors in the highlighter ink that the plants pulled into their system will glow under ultra violet light!

Explanation

The vascular system of plants is made of straw-like tubes called xylem and phloem. Phloem transports the food made by chlorophyll in the leaves throughout the plant. Xylem moves the water and nutrients from the roots to the stems and leaves.

The human vascular system has a heart to pump our blood, but plants have a different mechanism to move fluids and nutrients. The water defies gravity and travels upward because of the properties of water and capillary action.

Water molecules are attracted to one another and as a single molecule evaporates from the leaf, each water molecule in the chain moves up in line and the roots pull in another water molecule to replace each one lost.  This continuous chain of water is key to the process, and is the reason you don’t want an air bubble sucked up by a flower stem in your bouquet.

How did your colorful, glowing plant experiments turn out? Share your photos on my Tamawi Facebook page or on Instagram with #tamawi.

Here are more experiments to try at home!

Join the Conversation

41 Comments

This was absolutely amazing. I am a student, and I have to come up with something good. This really helped me out!

You’re welcome! Good luck with your project.

My son is going to love this!!!!

Great – have fun!

hello, I am a student who needs to come up with something. I and my mom thought that the first one was boring but when we looked at the other one (the glowing one) and we thought it was perfect and can’t wait to try it

Hooray! I think you’ll have a blast trying it.

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when was this made? thanks

A few years ago.

Can the highlighter sponge be left in overnight? I want to do this one with my kids in my after-school program.

You should be able to leave the sponge in there overnight. Carnations flower longer than most other cut flowers.

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Article Contents

Introduction, linking xylem structural components and their functions, functionality of the xylem network: bottleneck for efficiency or smart design for safety, what is the appropriate approach to investigate the regulation of sap flow dynamics, toward real-time imaging of flow dynamics in the xylem network, future directions, acknowledgements.

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Investigating water transport through the xylem network in vascular plants

• Article contents
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• Supplementary Data

Hae Koo Kim, Joonghyuk Park, Ildoo Hwang, Investigating water transport through the xylem network in vascular plants, Journal of Experimental Botany , Volume 65, Issue 7, April 2014, Pages 1895–1904, https://doi.org/10.1093/jxb/eru075

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Our understanding of physical and physiological mechanisms depends on the development of advanced technologies and tools to prove or re-evaluate established theories, and test new hypotheses. Water flow in land plants is a fascinating phenomenon, a vital component of the water cycle, and essential for life on Earth. The cohesion-tension theory (CTT), formulated more than a century ago and based on the physical properties of water, laid the foundation for our understanding of water transport in vascular plants. Numerous experimental tools have since been developed to evaluate various aspects of the CTT, such as the existence of negative hydrostatic pressure. This review focuses on the evolution of the experimental methods used to study water transport in plants, and summarizes the different ways to investigate the diversity of the xylem network structure and sap flow dynamics in various species. As water transport is documented at different scales, from the level of single conduits to entire plants, it is critical that new results be subjected to systematic cross-validation and that findings based on different organs be integrated at the whole-plant level. We also discuss the functional trade-offs between optimizing hydraulic efficiency and maintaining the safety of the entire transport system. Furthermore, we evaluate future directions in sap flow research and highlight the importance of integrating the combined effects of various levels of hydraulic regulation.

In land plants, water and minerals are taken up from the soil by the roots and transported through the xylem network to the leaves. Some trees can lift water over distances of more than 100 metres from the roots to the uppermost leaves ( Ryan et al. , 2006 ). This ability has fascinated scientists through the centuries and the study of plant hydraulics remains an active topic of research open to new methods of investigation ( Tyree, 2003 ). Independent of plant size, water movement is at the crossroads of all plant growth and development processes, from transpiration and photosynthesis to the distribution of organic and inorganic molecules throughout the plant.

When Einstein formulated the equation for the interconversion of matter and energy in 1905, it inspired decades of research and the revision of the law of conservation of energy. In plant physiology, the cohesion-tension theory (CTT) represents a similar conceptual breakthrough; however, some aspects of the CTT still require experimental validation. The CTT originated at the end of the 19th century, when Boehm (1893) proposed an initial framework, based on the cohesion and adhesion properties of water, to explain water transport in plants. The CTT attributes the main driving force for water transport to the tension (i.e. negative hydrostatic pressure) generated at the leaf surface by evaporation. The fundamental principles of the CTT summarized by Dixon and Joly (1894) have withstood persistent challenges ( Zimmermann et al. , 1994 ; Canny, 1995 ; Milburn, 1996 ; Meinzer et al. , 2001 ; Zimmermann et al. , 2004 ) and remain the most comprehensive explanation of water transport in plants ( Angeles et al. , 2004 ). The CTT is based on the physical properties of water: cohesion between dipolar water molecules gives water its high tensile strength, which maintains hydraulic continuity throughout the plant vasculature. The negative pressure that causes water to move up through the xylem develops at the surface of cell walls, which act as a very fine capillary wick. Water molecules adhere to the cellulose microfibrils and other hydrophilic components of the wall ( Somerville et al. , 2004 ; Oda and Hasezawa, 2006 ). As water evaporates from a thin film permeating through an extensive system of intercellular air spaces in the substomatal chambers of leaves, cohesive forces result in the formation of curved air/water interfaces. The surface tension at the interface induces a negative pressure and that generates the motive force that drives sap ascent in the xylem ( Zimmermann, 1983 ). Ultimately, the surface tension generated at the air/water interfaces of cell walls is assumed to be transmitted through a continuous water column to the roots. However, this system is highly prone to cavitation owing to the metastable state of water ( Tyree and Sperry, 1989 ; Hacke and Sperry, 2001 ; Meinzer et al. , 2001 ; Zimmermann et al. , 2004 ; Herbert et al. , 2006 ). Cavitation in the xylem can lead to a major reduction in hydraulic conductivity. Such a disruption in water flow poses a serious threat to photosynthetic efficiency and plant survival.

The first extensive integration of water transport and xylem structure was proposed by Zimmermann ( Zimmermann et al. , 1971 ; Zimmermann, 1983 ) and was updated by Tyree and Zimmerman (2002) . The overview presented by Holbrook and Zwieniecki (2005) is probably the most comprehensive formulation of vascular transport in plants. However, new conceptual models and experimental methods that emerged in the past decade have brought new insights. Many research groups now examine the plant-water relationship at various scales, from the level of the cellular water exchange to that of the whole-plant canopy. In that respect, although the discovery of aquaporins ( Murata et al. , 2000 ) represent a significant advance in our understanding of intercellular water flow, we will restrict our review to water flow in the xylem network. Numerous tools have been developed to probe the mechanism underlying the passive transport of water in plants. During the past two decades, the concept of passive water transport has been heatedly debated in the scientific community ( Zimmermann et al. , 1994 ; Canny, 1995 ; Milburn, 1996 ; Meinzer et al. , 2001 ; Zimmermann et al. , 2004 ). In this review, we highlight the major experimental tools that have provided insight into sap flow through the xylem network. From the broader perspective of the Blue Revolution ( Pennisi, 2008 ), understanding how water is transported from the soil through the intricate plant xylem network to the atmosphere can lead to innovative ways to optimize each drop of water in applied scientific fields such as molecular biology and agronomy, and in breeding programmes that seek to improve drought-resistance in crop plants. Some industrial applications based on our understanding of microfluidics and nanofluidics have already started to emerge in the form of plant-inspired devices, such as synthetic trees ( Wheeler and Stroock, 2008 ). In recent reviews, Pittermann (2010) presented an integrated approach of the evolution of the plant vascular system, and Lucas et al. (2013) summarized our current understanding of plant vascular biology and emphasized the major impact of the tracheophyte-based vascular system on all terrestrial organisms. Two recent international meetings (the 9th International Workshop on Sap Flow, 2013, and the Third International Conference on Plant Vascular Biology, 2013) demonstrated that sap flow is an area of prolific and inspiring research. However, there is no agreement as to which methods are best for examining sap flow or how the new results contribute to unravel sap flow dynamics in vascular plants.

In this review, we briefly retrace the scientific investigation of water transport in vascular plants, and evaluate basic concepts and theories in light of new experimental methods. We will assess our current understanding of the structure/function relationships of the xylem hydraulic architecture and provide an overview of experimental tools and methods used to unravel sap flow dynamics through the xylem network. Real-time imaging emerges as the most promising approach for integrating the xylem network structure and its multiple layers of regulation.

Our understanding of xylem hydraulic properties has evolved with the development of theoretical modelling and novel experimental tools to visualize the cross-sectional and three-dimensional structure of xylem. Tracheary elements (TEs) are the elementary units of xylem. After a complex process of differentiation, TEs lose their nuclei and cell contents, leaving behind a central lumen surrounded by secondary cell walls, which together form tracheids or vessels ( Fukuda, 1997 ). The structural characteristics of tracheids in conifers and vessel elements in angiosperms have been well characterized using optical and electron microscopy. The diameter of TEs varies from a few micrometres to a few hundred micrometres. Their association in series to form long-distance pathways can attain a few millimetres up to several metres. Torus-margo or pit membranes integrated in the secondary cell wall provide various levels of subcellular resistance to water flow ( Schulte and Castle, 1993 ; Hacke et al. , 2006 ; Sperry et al. , 2007 ). Although the structural characteristics of TEs are well established, our understanding of water flow dynamics is limited to the tissue or organ level. From a bottom-up perspective, water and minerals from the soil are absorbed through apoplastic and symplastic pathways into protoxylem vessels of the roots ( Passioura, 1988 ). Then, long-distance transport in the stem is generally attributed to large metaxylem vessels. The vascular bundles in leaves become highly branched reducing the distance of most leaf cells to less than a few hundred micrometres from a vessel ( Fig. 1 ). The mesophyll at the interface with air represents the highest resistance to water flow ( Cochard et al. , 2004 ; Sack et al. , 2008 ).

Main characteristics of the xylem network. Organization and characteristics of the xylem network: water flow throughout the plants depends on characteristics of the xylem in different organs. Water absorbed by the roots moves radially from small protoxylem vessels, which have high hydraulic resistance, to larger metaxylem vessels, with reduced hydraulic resistance. In the stem, the number and organization of vessels vary along the height of the plant height. Packing and tapering functions can be used to characterize each level of organization. In the leaves, water travels through small xylem vessels. During transpiration, negative hydrostatic pressure is generated at the interface between mesophyll cells and air.

In analogy with Ohm’s law, water uptake and transport are associated with a hydraulic flow process that is controlled by resistance and hydraulic gradients ( van den Honert, 1948 ). The overall resistance is determined by soil water potential, conducting vessels, transpiration rate, plant height, and gravity. In this physical conceptualization of the soil-plant-atmosphere continuum, the tension of the driving force of sap ascent continuously decreases in the direction of flow, and the pressure gradient is proportional to the evaporative flux density from the leaves ( Tyree, 1997 ). The xylem provides a low-resistance pathway for long-distance water movement by minimizing the pressure gradients required to transport water from the soil to the leaves ( Jeje and Zimmermann, 1979 ). In its most simplified representation, the xylem is often modelled as an assemblage of ‘unit pipes’ ( Shinozaki et al. , 1964 ) and water flow is generally approximated with the Hagen-Poiseuille equation ( Dimond, 1966 ; Schulte et al. , 1989 ; Lewis and Boose, 1995 ). The pipe model has contributed to the estimation of canopy-level parameters by incorporating variations in vessel size and number at the tissue and organ levels, and was also used to understand tree growth, resource allocation, and plant biomechanics ( Niklas et al. , 2006 ). However, the functionalities of the xylem network integrate different structural organization at the tissue and organ levels that cannot be supported by this simplified model. Hydraulic resistance is highly variable depending on the species and organ. Unravelling how water is collected from all the vessels in the roots, passes through the stem, and is distributed in the leaves requires an integrated functional approach at the whole-plant level ( Sperry, 2003 ; Loepfe et al. , 2007 ; Page et al. , 2011 ).

At the tissue level, the hydraulic conductivity per unit of cross-sectional area generally defines efficiency. The constraints on the maximum diameter, length, and number of xylem vessels for a given cross-sectional area limit efficiency: this is related to a species-dependent limit on conduit frequency. For instance, vessel lumens in angiosperms occupy less than 10% of the cross-sectional wood area at the mid-point of their diameter range, whereas tracheid lumens in conifers can occupy over 40% ( Sperry et al. , 2008 ). Such variation is due to the lower investment in mechanical strength in angiosperms, which rely on wood fibres, whereas conifer tracheids provide both transport and support functions. Conduit diameter and frequency are not the only factors determining efficiency of water flow, because the conductivity of conduits of a given diameter can also vary. In angiosperms, simple or schalariform perforation plates and conduit end walls create differences in actual conductivity compared with the theoretical maximum set by the Hagen-Poiseuille equation. Lumen and end-wall resistance is relatively constant and flow resistance through pits does not increase with cavitation safety. Pit membrane porosity does not seem to be related to cavitation pressure ( Hacke et al. , 2006 ). Despite difference in size, the end wall resistance at a given diameter seems to be relatively similar between conifers and angiosperms. The presence of specialized structures, such as the torus-margo in conifers, greatly reduces the resistance of inter-tracheid water flow ( Pittermann et al. , 2005 ).

In summary, the most important structural features of the xylem at the cellular level are conduit diameter, length, wall features (i.e. annular, spiral, or reticulate thickening or pits), and the presence or absence of end walls (simple or scalariform). At the tissue level, inter-conduit pitting (determined by the density and size of torus-margo or pit membrane) and the number of conduits define the connectivity of the xylem network.

The two main functions of the xylem hydraulic network in vascular plants are (i) to supply water and minerals to all tissues and (ii) to provide mechanical support. In living organisms, similar functions are generally carried out by similar structures. A large diversity in xylem hydraulic architecture exists between organs and among species, and the initial structures are even modified during growth and development. Among seed plants, coniferous, diffuse-porous, and ring-porous trees have radically different xylem anatomy ( McCulloh et al. , 2010 ). Within angiosperms, the vascular bundles of dicot and monocot plants have distinct organizations that vary in different organs. These differences in organization are ultimately due to differences in conduit tapering and packing of similar elementary structures. However, the functional consequences of these distinct organizations are not well understood at either the conduit or the whole-organism level. The integration of organ-level variation in xylem architecture at the whole-plant level is essential for unravelling the mechanisms that maintain the integrity of water transport from roots to leaves. The elementary elements of the system (i.e. tracheids or vessel elements) are organized to withstand strong physical constraints and simultaneously achieve efficient water transport with minimal resistance, while protecting against cavitation ( Tyree and Sperry, 1989 ). To integrate structural characteristics into functional roles, it requires determining how the dynamic hydraulic properties at the cellular level are incorporated into tissue and organ levels. For example, the hydraulic efficiency per conduit diameter and length is higher for conifer tracheids than for angiosperm vessel elements; however, the wider diameter and greater length of angiosperm vessels provide greater conductivity per xylem area.

In terms of the biophysical mechanisms underlying these processes, the major challenge is to understand how the trade-off between efficiency and safety is achieved at different levels of organization. The hydraulic regulation attributed to the xylem is generally considered to depend on the specific organization in each organ; however, the respective contributions are difficult to integrate into the entire network ( Fig. 1 ). Unravelling the relationship between the structural complexity of hydraulic architecture and efficiency/safety functions remains one of the main issues in understanding plant-water relations. In leaves, direct pressure-drop measurements confirmed that mesophyll cells are the major component of hydraulic resistance, even though the vascular system accounts for the longest distance ( Cochard et al. , 2004 ). From the soil to the atmosphere, the relationship between hydraulic resistance and stomatal conductance is a key component ( Cruiziat et al. , 2002 ) as environmental factors can influence the efficiency of water absorption and uptake. When transpiration is high, maintaining the continuity of flow in individual vessels is seriously challenged owing to cavitation risks ( Cochard, 2006 ). However, cavitation can be reduced by the hydraulic capacitance of the xylem and the water storage capacity of each organ, and the network organization can also provide alternative pathways to avoid disruption of water flow ( Tyree and Ewers, 1991 ; Sperry et al. , 2008 ; Höltta et al. , 2009 ). Ultimately, water transport and gas exchange in the leaves have a major physiological effect on the photosynthetic capacity of the plant ( Tyree and Ewers, 1991 ).

The structural model of the hydraulic transport system proposed by West, Brown, and Enquist (WBE model; 1999) has been widely used to explain the maintenance of a constant flow rate along the entire flow path. In this model, it is assumed that plants minimize the effect of hydraulic resistance imposed by increasing height and total path-length conductance by tapering the xylem conduits. Plant size is related to the geometry of the branching architecture and metabolism. Based on the fact that all living organisms contain a transport system for aqueous materials, the plant vascular system should minimize the hydrodynamic resistance of nutrient transport, while maximizing the exchange surface with the environment ( Petit and Anfodillo, 2009 ). The ideas that (i) all plants adopt a universal architecture of the xylem transport system, and (ii) hydraulic efficiency is independent of plant height are very attractive. Although a wide range of plants seemed to comply with these assumptions ( West et al. , 1999 ), numerous studies challenged the validity of a universal rule given the diversity of vascular plants ( Dodds et al. , 2001 ; Coomes, 2006 ; Apol et al. , 2008 ), and hydraulic constraints seem to increase with plant height ( Koch et al. , 2004 ). Despite controversies, the WBE model highlights the value of architectural modelling in simplifying plant diversity and stimulated prolific empirical research. Now, complementary models of the vascular system not only include a more realistic view of the hydraulic architecture ( Savage et al. , 2010 ), but also incorporate physiological considerations ( von Allmen et al. , 2012 ).

Although the plant xylem is non-living tissue, there is an extraordinary degree of coordination between the hydraulic capacity and photosynthetic assimilation because both of these pathways intersect at stomata during the exchange of water and CO 2 at the leaf surface ( Brodribb, 2009 ). The rate of transpiration and gas exchange via stomata are limited by the xylem hydraulic system. Packing and taper functions are the backbone of a robust framework for modelling network transport ( Sperry et al. , 2008 ; McCulloh et al. , 2010 ). Strength and storage requirements set a packing limit and influence the conducting capacity ( Zanne et al. , 2010 ). Theoretically, a small number of wide conduits are more efficient than a large number of narrow ones. This is reflected by the more efficient networks of ring-porous trees compared with conifers ( McCulloh et al. , 2010 ). Without tapering of the xylem conduits, branches would have the highest conductivity in a tree. In other words, tapering counterbalances the decline in conductance due to increasing path length, but maintaining similar conductivity requires an increase in the number of xylem vessels per unit cross-sectional area as conduits become narrower. The organization of the xylem network thus defines the functional trade-off between efficiency and safety in each organ.

Building on these concepts, Höltta et al. (2011) proposed a carbon-cost gain model, which calculates the xylem structure that maximizes carbon-use efficiency while simultaneously accounting for intervessel pit structures that increase flow resistance. As the water potential is lower at the plant apex, fewer pores in the pits near the apex would also restrict the spreading of embolisms. An optimal hydraulic structure would have conduits that decrease in size from the base to the apex (defining tapering function). In parallel, the vulnerability to cavitation can be reduced by increasing conduit number (defining the packing function). Indeed, whole-plant carbon-use efficiency demands that conduit size decreases and conduit number increases simultaneously ( Lancashire and Ennos, 2002 ; Choat et al. , 2003 ; Höltta et al. , 2009 ).

The theoretical and conceptual bases of water transport and xylem hydraulic architecture have been examined by various experimental methods ( Fig. 2 ). Technical reliability of new methodology is of prime importance in investigating the processes of water transport. Moreover, subsequent results are rarely cross-validated with those obtained using other methods. A difficulty in making proper comparisons is that the measurement techniques do not address the same level of the xylem network. For instance, the technical limitations of new methods in measuring internal pressure or vulnerability to cavitation have sometimes resulted in a misunderstanding of the elementary processes and have given erroneous interpretations. The invasive methods using excised tissues do not change the internal xylem structure, but water flow generated artificially in isolated leaves, stems or roots does not accurately reflect water flow in intact plants.

Methods and instruments used to analyse sap flow in plants. A. Schematic representation of different methods used to measure sap flow velocity. In heat-based methods, heat sensors (heat pulse velocity, heat field deformation, or thermal dissipation) are installed radially into a segment. In radioisotope or dye methods, tracers are injected into the xylem or uptaken from a cut segment. B. Methods used to measure negative pressure in the xylem. The observation scale and measurement target (i.e. cell, tissue, or organ) differ between indirect (i.e. pressure bomb, centrifugation) or direct (i.e. cell pressure probe) methods. C. Simultaneous visualization of xylem structure and sap flow using magnetic resonance, neutron or synchrotron X-ray imaging methods. The temporal and spatial resolutions vary for each imaging method.

Three categories of methods are currently available for investigating xylem sap flow: (i) continuous measurement of sap flow velocity (to confirm the relationship between transpiration and water uptake); (ii) internal pressure measurement (to confirm that negative hydrostatic pressure is the main driving force of sap flow); and (iii) visualization of sap flow through the xylem. Experimental data obtained using these different methods were frequently not in agreement, because the scale of the xylem architecture examined (from the whole-plant network to individual vessels) generally differed. Futhermore, sap flow dynamics were not always measured with the same hydraulic parameters. Therefore, it is crucial to understand the advantages and limitations of different techniques to compare the characteristics of sap flow across different species.

Continuous sap-flow monitoring has been most commonly used to measure water flux through the stems and branches of trees, but the resolution is not sufficient for determining leaf-level responses to environmental changes. Flow monitoring techniques using tracers and histological sections enabled the identification of the water-conducting vessels of the xylem network and provided a snapshot of how they function under different environmental conditions. The injection of different dyes (e.g. fuchsin or safranin) is the most common method used to visualize water-conducting pathways at the tissue level in conifers ( Harris, 1961 ; Kozlowski and Winget, 1963 ; de Faÿ et al. , 2000 ), dicotyledonous trees ( Kramer and Kozlowski, 1960 ; Ellmore and Ewers, 1986 ), and herbaceous plants ( Hargrave et al. , 1994 ; Tang and Boyer, 2002 ). Recently, a number of concerns have been raised in interpreting the results of dye injection ( Umebayashi et al. , 2007 ). First, the type of dye and the method used for sample preparation greatly affect the distribution and diffusion of the dye through the xylem. Second, the diversity in plant size, and vessel size and organization do not generally allow extrapolation of the results obtained for a stem, root, or leaf sections to other organs. Third, it is difficult to compare the results of studies conducted at the whole-plant level under various environmental conditions with those obtained from the isolated tissues. Using improved preparation methods, stabilized dye can enable the identification of water-conducting vessels in trees at the cellular level ( Sano et al. , 2005 ); however, it remains technically challenging to visualize sap flow at the subcellular level ( Geitmann, 2006 ). Dye injection is a relatively easy technique, but it gives misleading interpretations about the functional water-conducting pathways if the procedures are not well defined and standardized ( Umebayashi et al. , 2007 ).

More accurate modelling of leaf and plant-level responses to abiotic stresses is essential to predict the canopy response to future climate change. In forest ecosystems, water fluxes in trees can be monitored at the stem or leaf level ( Fig. 2A ). Heat-balance and heat-pulse methods estimate whole-plant water flow using heat-based sensors ( Smith and Allen, 1996 ). In both cases, probes inserted into the stem of a tree generate heat that is used as a tracer. The heat-balance method calculates the mass flow of sap in the stem from the amount of heat taken up by the moving sap stream. In the heat-pulse method short pulses of heat are applied, and the mass flow of sap is determined from the velocity of the heat pulses moving along the stem ( Cohen et al. , 1981 ; Burgess et al. , 2001 ). The thermal dissipation method, which is based on the propagation of heat pulses and was initially developed by Huber (1932) and refined by Vieweg and Ziegler (1960) , is also widely used to estimate sap flow rates. The direction of volume flow is derived from the asymmetry of thermal dissipation; however, reliable estimates of the sap-conducting surface area and size are essential to compare the deduced sap flow rates with the actual sap flow rates ( Green et al. , 2003 ). One of the major limitations of theses techniques is that the inserted probes disrupt the sap stream, which alters the thermal homogeneity of the sapwood. Recently, mathematical corrections of sap velocity include effects due to heat-convection ( Vandegehuchte and Steppe, 2012 b ) or natural temperature gradients ( Lubczynski et al. , 2012 ). In ecophysiological studies, technically improved probes are now available for continuous sap flow measurements in trees ( Burgess et al. , 2001 ). A sophisticated four-needle, heat-pulse sap flow probe even permits measurement of non-empirical sap flux density and water content ( Vandegehuchte and Steppe, 2012 a ).

Measurements of sap flow alone do not provide sufficient spatial resolution to evaluate the variations in xylem water transport properties. Spatial variations in xylem structure and hydraulic properties have to be compared with the actual patterns of in vivo water flow dynamics. Measuring the sap flow (i.e. the velocity and amount of water transported through the xylem) and pressure (i.e. the driving force responsible for the transport) are technically and conceptually challenging. A reliable interpretation of instrumentation outputs requires an integrated understanding of both the structural complexity and technical limits of each measurement method. In particular, the velocity or pressure measurements should be evaluated with respect to the hydraulic architecture of the xylem network. Tension measured using pressure bombs and xylem pressure probes were only in accordance for non-transpiring leaves and differed considerably for transpiring leaves ( Melcher et al. , 1998 ). The deviations were later attributed to technical limitations, as the range of sensitivity of the initially developed pressure probes was below 0.8MPa, and insertion of the glass tip of the probe frequently disrupted a vessel under tension ( Wei et al. , 1999 a , b ; Wei et al. , 2001 ) ( Fig. 2B ). Pressure probes can now be used to measure negative pressures; however, theoretical values of up to –10MPa cannot be verified. The existence of negative hydrostatic pressure is no longer a question. Meanwhile, how this pressure is transmitted through the xylem network requires a better understanding of the relationship between changes in pressure and network architecture.

A lack of consistency between results obtained using tracer dyes and probes called into question which velocity component each method measures. Flow velocities obtained from heat-pulse or particle-type tracers, such as radioisotopes, probably differ owing to the way in which axial and radial flow components are measured. Vessels involved in the flow and the total lumen area are generally not known and it is technically difficult to insert the glass tip of a pressure probe into a vessel without causing cavitation ( Heine and Farr, 1973 ; Dye et al. , 1992 ). In a tropical forest canopy, axial long-distance flow and transport of radial water were affected by the internal water-exchange capacity and the transpiration stream ( James et al. , 2003 ). An inverse relationship between the internal water-exchange capacity and the specific hydraulic conductivity confirmed a trade-off between transport efficiency and water storage. By combining the thermal-dissipation technique with infrared gas analysis, sap flow and transpiration could be measured simultaneously ( Ziegler et al. , 2009 ).

Since the formulation of the CTT, multiple instruments and techniques have been developed to measure the negative pressure in xylem vessels. Inspired by Renner’s (1911) technique using a potometer attached to an excised leafy twig, Scholander et al. (1965) developed the pressure bomb technique. It rapidly became a reference tool to measure negative hydrostatic pressures in excised leaves. Despite initial disagreement between the results obtained from the pressure bomb, in situ psychrometry ( Turner et al. , 1984 ), and the root pressurization method ( Passioura and Munns, 1984 ; Passioura, 1988 ), the high negative value given by the pressure bomb was considered to be the decisive proof supporting the CTT. Later on, cell pressure probes developed by Balling and Zimmermann (1990) gave access to in vivo measurements of pressure in individual xylem vessels ( Pockman et al. , 1995 ). Measurements of xylem pressures, leaf balancing pressures, transpiration rates, and leaf hydraulic properties are now possible; however, the reasons behind the large variations in pressure obtained using different techniques need further investigation. Better integration of the hydraulic regulation at each level of organization of the xylem network should thus be the next step ( Fig. 2B ). How is water from individual vessels in the roots transmitted to a network of vessels in the stem? How is long-distance water transport redistributed to vessels in the leaves? How is each level of hydraulic regulation coordinated at the whole-plant level?

Visualization of in vivo water flow dynamics using magnetic resonance imaging (MRI) and synchrotron X-ray imaging provided the first tools for examining flow regulation and a specific level of structural organization. In particular, it is now possible to visualize the functionality of individual xylem vessels under different environmental conditions. Nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) is the least invasive method to investigate sap flow, and provide spatially and temporally resolved information on sap flow at the level of membrane, cell-to-cell, and long-distance transport ( Witsuba et al. , 2000 ; Scheenen et al. , 2007 ). Relative differences in flow volume in different vascular bundles suggested that each vascular bundle is under different tension. Also, root pressure can be estimated non-destructively by taking continuous measurement of sap flow and variations in root segments of different stem diameter and integrating this information with a mechanistic flow and storage model ( De Swaef et al. , 2013 ) ( Fig. 2C ).

Numerous studies examine sap flow as a combination of flow velocity and pressure measurements under different environmental conditions ( Witsuba et al. , 2000 ). A wide range of devices are available to measure pressure and flow at different scales: mobile MRI systems for outdoor tree measurements ( Kimura et al. , 2011 ), patch-clamp pressure-probes to monitor leaf water status non-invasively and record variations in turgor pressure gradients in leaves ( Zimmermann et al. , 2008 ), and even simultaneous dendrometer and leaf patch-clamp pressure-probe measurements for the effects of microclimate and soil moisture on diurnal variations in leaf turgor pressure and water in stems ( Ehrenberger et al. , 2012 ). Now, measurements of sap flow velocity, xylem pressure at the level of individual vessels and in-vivo real-time visualization are required to completely unravel the dynamics of sap flow regulation in the xylem network.

Real-time imaging methods, such as synchrotron X-ray imaging, have recently revealed that radial flow of water can occur during refilling of dehydrated xylem vessels in monocot leaves ( Kim and Lee, 2010 ) and in the roots of Arabidopsis plants ( Lee et al. , 2013 b ). A major challenge for plants under high evaporative demand or low soil water availability is to resist cavitation and/or recover from the reduction in water transport ( Hacke and Sperry, 2001 ; Lens et al. , 2013 ). Embolism of xylem vessels reduces hydraulic conductivity, and the percentage loss of conductivity (PLC) is used to estimate cavitation and embolism repair ( Zwieniecki and Holbrook, 1998 ). For a long time, the experimental research was focused on trying to identify how frequently embolism occurred and how it could be repaired, especially in trees. The refilling of embolized vessels is not explained by thermodynamic laws ( Holbrook and Zwieniecki, 1999 ). However, the latest comparison of different methods used to measure the PLC showed that embolism repair is largely due to technical artefacts ( Wheeler et al. , 2013 ). The ability to limit embolism occurrence is a major component of hydraulic safety and the frequent cavitation reported in earlier studies was due to erroneous interpretations. In particular, inappropriate dehydration methods to generate vulnerability curves led to an overestimation of the vulnerability to cavitation ( Cochard et al. , 2013 ). Nonetheless, the ability of plants to refill embolized vessels during transpiration cannot be neglected and the biophysical mechanisms that enable plants to do so remain to be elucidated ( Zwieniecki and Holbrook, 2009 ). Synchrotron X-ray computed tomography is an extremely promising method to visualize and quantify refilling dynamics ( Brodersen et al. , 2010 ; Brodersen et al. , 2013 ). In grapevines, water influx in the embolized vessels has been attributed to adjacent vessels or the surrounding living tissue. These advances in imaging techniques provide sufficient spatial and temporal resolution to visualize axial, radial, and reverse flow ( Lee et al. , 2013 a ; Lens et al. , 2013 ). Although such methods cannot be used on trees due to limitations in sample size and field of view, the experimental results obtained from model plants can be integrated into a broader framework to understand the hydraulic regulation of active water flow. If refilling under tension is indeed a physical process, we need to re-evaluate the reality of this phenomenon and identify the source of the driving force that draws water into embolized vessels, localize the origin of this water, and determine how embolized and functional vessels are hydraulically compartmentalized ( Holbrook and Zwieniecki, 1999 ). Real-time, high-resolution imaging methods are ideal for visualizing dynamic processes such as embolism repair ( Brodersen et al. , 2010 ; Brodersen et al. , 2013 ). Although these methods can only be used in some small model plants, the visualization of flow dynamics in the xylem network opens new insights in understanding the hydraulic efficiency/safety trade-offs ( Kim and Lee, 2010 ; Brodersen and McElrone, 2013 ). Ultimately, the different structural and functional components, such as sugar metabolism, capacitive effect ( Höltta et al. , 2009 ), the presence of bordered pit membranes ( Zwieniecki and Holbrook, 2009 ), venation architecture, and leaf size ( Scoffoni et al. , 2011 ) must be incorporated in a functional model to fully comprehend the hydraulic regulation at the entire plant level.

A multitude of tools and methods are now available to study water transport from the level of individual xylem vessels to the whole plant. It is crucial to consolidate our current knowledge in order to guide future research on plant water transport in the most relevant directions. Whereas plant physiologists are the ones who better understand the complexity of this transport system, they need support from physicists to validate the results obtained with new methods. Molecular biologists should also play a key role in incorporating the role of aquaporins in regulating plant water transport, especially in the roots and leaves. Ecologists, agronomists, and breeders can benefit tremendously by including the basic processes of water transport in their modelling and selection approaches. Currently, it is difficult to attribute structural characteristics of the xylem network to specific functions related to efficiency or safety. Developing new tools and methods that connect flow and structure at different scales is probably the most promising approach for gaining new insight into hydraulic regulation along the transpiration stream. Using a combination of structural and functional methods, it is now possible to distinguish between water-conducting and non-functional vessels. However, given the diversity of plant hydraulic architecture and dimensions, the same methods cannot be applied to all plants.

Advanced high-resolution imaging methods such as MRI, synchrotron X-ray imaging, and neutron-based imaging, now allows the analysis of flow dynamics at the organ level, as reported for rice leaves, grapevine stems, or Arabidopsis roots ( Kim and Lee, 2010 ; Brodersen, 2013 ; Lee et al. , 2013 a ; Warren et al. , 2013 ). The next major step will be to reconstitute a realistic 3D map of the hydraulic network of the whole organism starting with small model plants, such as Arabidopsis . At the subcellular level, the combination of scanning electron microscopy (nano-scale) and macroscopic techniques will enable investigations of the relationship between cell wall characteristics and the xylem network ( McCully et al. , 2009 ; Zehbe et al. , 2010 ; Page et al. , 2011 ). Atomic force microscopy will provide information about the surface chemistry of xylem cell walls. Confocal microscopy of leaves can provide insight into the relationship between leaf water dynamics and transpiration ( Botha et al. , 2008 ; Fitzgibbon et al. , 2010 ; Wuyts et al. , 2010 ). On the other hand, portable devices such as portable MRI are being developed to measure sap flow under real-field conditions. Infrared imaging techniques can provide a detailed map of surface temperatures and promote insight into water distribution, evaporation, ice formation, and sap flow. The development of enhanced computing power will also give rise to more realistic models and simulations of sap flow.

Transport of water and minerals is at the centre of all metabolic processes in plants, yet many variables and parameters related to this transport are unknown. In a broader perspective, a functional framework of the xylem network that integrates water flow dynamics at various levels of organizations can lead the development of bio-inspired technologies based on sap flow in plants. For decades, research on water transport in plants has hinged on a reference theory. To move forward, the research should now focus on unravelling how water transport through the xylem network is regulated using ingenious combinations of advanced techniques that probe the structure-function relationships of this fascinating transport system.

This work was supported by the Advanced Biomass R&D Center of the Global Frontier Project funded by the MEST (ABC-2011-0028378) to Ildoo Hwang.

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Vascular Plant Circulation Experiment

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Kathleen is a homeschooling mom of four boys with a serious case of the Wanderlust bug. Her love of travel extends to her children, and has resulted in the family visiting 48 states to date, and traveling nearly a third of the year. She is the owner of LifeWith4Boys.com where you will find information on Family Travel, recipes, reviews, lifestyle and more.

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16 comments.

we just did some experiments at home on Monday since the boys had a snow day.

This is so cool! Pinned it to try with my dauther!

That is so neat! We never did this one, but we've done plenty of "kitchen chemistry" in our homeschool lessons.

I had no idea it changed color so fast. Very cool.

So pretty! I think I tried this experiment when I was in junior high. I have forgotten what colors I used, but it was so much fun. :)

That is COOL!

Noah would totally love this. He loves science experiments. Thanks for sharing

I like the blue one a lot. Cool project.

The look so pretty. :)

I loved doing this as a kid. It works great with Queen Ann's Lace.

I remember this experiment as a kid!

Super cool. I remember doing this when I was a kid.

I've never tried it, but it looks pretty cool!

Wow this would be so fun to do with M once she's older! :)

Ha just look at how clever that was . great experiement

That is SO cool! My dude's only three so he won't fully get this, but I totally want to do this with him anyway.

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Vascular Plants Facilitated Bryophytes in a Grassland Experiment

2005, Plant Ecology

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Annika K. Jägerbrand , J.M Alatalo

Due to the climate change, vegetation of tundra ecosystems is predicted to shift toward shrub and tree dominance, and this change may influence bryophytes. To estimate how changes in growing environment and the dominance of vascular plants influence bryophyte abundance, we compared the relationship of occurrence of bryophytes among other plant types in a five-year experiment of warming (T), fertilization (F) and T + F in two vegetation types, heath and meadow, in a subarctic–alpine ecosystem. We compared individual leaf area among shrub species to confirm that deciduous shrubs might cause severe shading effect. Effects of neighboring functional types on the performance of Hylocomium splendens was also analyzed. Results show that F and T + F treatments significantly influenced bryophyte abundance negatively. Under natural conditions, bryophytes in the heath site were negatively related to the abundance of shrubs and lichens and the relationship between lichens and bryophytes strengthened after the experimental period. After five years of experimental treatments in the meadow, a positive abundance relationship emerged between bryophytes and deciduous shrubs, evergreen shrubs and forbs. This relationship was not found in the heath site. Our study therefore shows that the abundance relationships between bryophytes and plants in two vegetation types within the same area can be different. Deciduous shrubs had larger leaf area than evergreen shrubs but did not show any shading effect on H. splendens.

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• Published: 05 September 2024

Precise tracking of nanoparticles in plant roots

• Xiao-Dong Sun   ORCID: orcid.org/0000-0001-6449-5485 1 , 2 ,
• Jing-Ya Ma 1 , 2 ,
• Li-Juan Feng 3 ,
• Jian-Lu Duan 1 , 2 &
• Xian-Zheng Yuan   ORCID: orcid.org/0000-0002-7893-0692 1 , 2  

Nature Protocols ( 2024 ) Cite this article

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• Biogeochemistry
• Nanoparticles

One of the foremost challenges in nanobiotechnology is obtaining direct evidence of nanoparticles’ absorption and internalization in plants. Although confocal laser scanning microscopy (CLSM) or transmission electron microscopy (TEM) are currently the most commonly used tools to characterize nanoparticles in plants, subjectivity of researchers, incorrect sample handling, inevitable fluorescence leakage and limitations of imaging instruments lead to false positives and non-reproducibility of experimental results. This protocol provides an easy-to-operate dual-step method, combining CLSM for macroscopic tissue examination and TEM for cellular-level analysis, to effectively trace single particles in plant roots with accuracy and precision. In addition, we also provide detailed methods for processing plant materials before imaging, including cleaning, and staining, to maximize the accuracy and reliability of imaging. This protocol involves currently commonly used nanomaterial types, such as metal-based and doped carbon-based materials, and enables accurate localization of nanoparticles with different sizes at the cell level in Arabidopsis thaliana root samples either through contrast or element mapping analysis. It serves as a valuable reference and benchmark for scholars in plant science, chemistry and environmental studies to understand the interaction between plant roots and nanomaterials and to detect the distribution of nanomaterials in plants. Excluding plant culture time, the protocol can be completed in 4–5 d.

This protocol describes how to precisely track nanoparticles in plant roots, combining CLSM for macroscopic tissue examination and TEM for cellular-level analysis. It also introduces general methodologies for preparing plant materials before imaging.

The protocol provides a dual-step examination process to reduce the possibility of false positives and maximize the precision, reliability and reproducibility of nanoparticle localization in plant tissues.

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All data supporting this paper have been previously published 21 , 40 , 42 . The raw data are available from the corresponding author on reasonable request.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (U1906224, 22176114 and 22106095), Shandong Provincial Natural Science Foundation (ZR2019JQ18), Youth Interdisciplinary Science and Innovative Research Groups of Shandong University (2020QNQT014), the Postdoctoral Innovative Talent Support Program (BX20240211) and the Qilu Youth Talent Program of Shandong University.

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Shandong Key Laboratory of Environmental Processes and Health, School of Environmental Science and Engineering, Shandong University, Qingdao, Shandong, P. R. China

Xiao-Dong Sun, Jing-Ya Ma, Jian-Lu Duan & Xian-Zheng Yuan

Sino-French Research Institute for Ecology and Environment (ISFREE), Shandong University, Qingdao, Shandong, P. R. China

College of Geography and Environment, Shandong Normal University, Jinan, Shandong, P. R. China

Li-Juan Feng

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X.-D.S. and X.-Z.Y. designed and wrote the protocol and conceptualized and supervised the protocol development. All the co-authors contributed to developing the protocol.

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Correspondence to Xian-Zheng Yuan .

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Key references using this protocol

Sun, X.-D. et al. Nat. Nanotechnol . 15 , 755–760 (2020): https://doi.org/10.1038/s41565-020-0707-4

Xiao, F. et al. Environ. Sci. Technol . 56 , 4071–4079 (2022): https://doi.org/10.1021/acs.est.1c06595

Sun, X.-D. et al. Proc. Natl Acad. Sci. USA 120 , e2304306120 (2023): https://doi.org/10.1073/pnas.2304306120

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Supplementary Methods and Figs. 1–4

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Sun, XD., Ma, JY., Feng, LJ. et al. Precise tracking of nanoparticles in plant roots. Nat Protoc (2024). https://doi.org/10.1038/s41596-024-01044-5

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Received : 16 January 2024

Accepted : 19 June 2024

Published : 05 September 2024

DOI : https://doi.org/10.1038/s41596-024-01044-5

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