What Do These Creepy Plant Mouths Do? (Plant Tissues): Crash Course Botany #4

Summary

In this Crash Course Botany episode, Dr. Katherine Esau's discovery of how curly-top disease spreads in sugar beet plants is highlighted, emphasizing the importance of understanding plant anatomy. The video explores the three main plant tissues: dermal, vascular, and ground tissue. Dermal tissue acts as the plant's skin, vascular tissue transports nutrients and sugars, and ground tissue performs various supportive and photosynthetic functions. The script explains how these tissues collaborate to maintain plant health and resist diseases, with a call to action for viewers to appreciate the intricate relationship between plant structure and function.

Takeaways

• 🌿 Dr. Katherine Esau's research on sugar beet plants in 1924 led to the discovery of how the curly-top disease spread through the plant's vascular system.
• 🐝 The curly-top disease is transmitted by leafhoppers and causes abnormal growth and curly leaves in plants.
• 🔍 Esau's observation that the virus travels through the plant's food transport system was pivotal for understanding plant diseases.
• 🌱 The importance of understanding healthy plant anatomy is emphasized for diagnosing and treating plant diseases.
• 🍃 Plants are composed of tissues, which are organized groups of cells with similar structures and functions.
• 🌼 The three main types of plant tissues are dermal, vascular, and ground tissue, each with distinct roles in the plant's body.
• 🌳 Dermal tissue acts as the plant's skin, preventing water loss and protecting against harmful substances like viruses.
• 🚰 Vascular tissue, consisting of xylem and phloem, functions as the plant's circulatory system, transporting water, nutrients, and sugars.
• 🌾 Ground tissue includes parenchyma, collenchyma, and sclerenchyma cells, which perform various tasks such as photosynthesis, structural support, and protection.
• 🔬 Studying plant tissues under a microscope reveals the complex organization and interdependence of cells within plant organs.
• 🌳 The study of plant anatomy is crucial for understanding plant health and developing strategies to prevent and treat plant diseases.

Q & A

What was the name of the disease that affected sugar beet plants in California in 1924?

The disease was called curly-top disease.

Which insects are known to spread the curly-top disease in sugar beet plants?

The insects that spread the curly-top disease are called leafhoppers.

What was the significant discovery Dr. Katherine Esau made regarding the spread of the virus in plants?

Dr. Katherine Esau discovered that the virus spreads throughout the plant along the same pathway as the food moves, hijacking the cells that move sugar produced by photosynthesis.

How does the cuticle layer on the epidermis of plants function?

The cuticle layer prevents water from escaping and keeps viruses and other harmful substances from entering the plant.

What are stomata and what is their role in plants?

Stomata are tiny openings in the epidermis of leaves that allow carbon dioxide gas to enter, which is essential for photosynthesis.

What are trichomes and what functions do they serve?

Trichomes are little hairs that sprout out of a plant's skin, serving various functions such as protection against herbivores, acting as sunscreen, or helping to retain warmth.

How do xylem cells transport water and nutrients in plants?

Xylem cells transport water and nutrients from the roots to the leaves by dying on purpose and becoming hollow, with their strong cell walls forming perfect water-transporting pipes.

In what direction do phloem cells transport sugars in plants?

Phloem cells transport sugars in the opposite direction of xylem cells, moving the sugar produced by photosynthesis from the leaves to the rest of the plant.

What is the primary function of parenchyma cells in ground tissue?

Parenchyma cells are the main photosynthesizers in leaves and store starch, or extra sugar reserves, in roots.

How do sclerenchyma cells contribute to the structure of a plant?

Sclerenchyma cells provide structural support to organs that are fully mature and face too much weight or bending, similar to how xylem cells function.

What can be observed when examining a cross-section of a corn stem under a microscope?

In a corn stem cross-section, one can observe the dermal tissue layer, ground tissue filled with parenchyma cells, and vascular tissue bundles containing xylem and phloem cells.

Outlines

00:00

🌿 Dr. Katherine Esau's Discovery on Plant Viruses

In 1924, Dr. Katherine Esau was studying the curly-top disease affecting sugar beet plants on a Californian farm. She discovered that the disease, spread by leafhoppers, caused abnormal growth and curly leaves. By examining the plant's anatomy, she realized the virus used the plant's own system for transporting sugars, produced by photosynthesis, to spread throughout the plant. This system included the xylem and phloem, the plant's vascular tissues. Her findings were pivotal for botany, emphasizing the importance of understanding healthy plant anatomy to combat diseases. The video then transitions to an introduction of plant tissues by Crash Course Botany's host, Alexis, who explains that plant bodies are composed of tissues that form organs like stems, leaves, and roots.

05:02

🍃 Exploring Plant Tissues and Their Functions

The video script delves into the three main types of plant tissues: dermal, vascular, and ground. Dermal tissue forms the plant's skin, the epidermis, which is covered in a waxy cuticle to prevent water loss and protect against viruses. Stomata, tiny pores in the epidermis, allow for carbon dioxide intake, while trichomes serve various functions like protection and water absorption. Vascular tissue comprises xylem and phloem cells, which form the plant's circulatory system. Xylem cells, which transport water and nutrients, do so by dying and becoming hollow tubes. Phloem cells, in contrast, move sugars from the leaves to other parts of the plant and require companion cells for assistance. Ground tissue, the non-dermal and non-vascular part, includes parenchyma cells for photosynthesis and starch storage, collenchyma cells for structural support in growing organs, and sclerenchyma cells for support in mature organs.

10:03

🔬 Microscopic View of Plant Organs

The script describes the examination of plant organs under a microscope, starting with a corn stem cross-section. It highlights the neat arrangement of the dermal tissue, the parenchyma cells of the ground tissue that store water and nutrients, and the vascular tissue bundles containing xylem and phloem cells. A leaf cross-section reveals a central major vein with xylem and phloem cells, and the ground tissue packed with parenchyma cells rich in chloroplasts for photosynthesis. Stomata are found on the underside of the leaf to minimize water loss. Lastly, a root cross-section shows vascular tissue in the center, filtering incoming water, surrounded by ground tissue and the epidermis. The video concludes by emphasizing the importance of plant anatomy in understanding plant function and disease prevention, and hints at upcoming episodes on cellular respiration and photosynthesis.

Keywords

💡Curly-top disease

Curly-top disease is a plant virus that affects sugar beet plants, causing them to have unusually curly leaves and stunted growth. It is spread by insects called leafhoppers. In the context of the video, this disease serves as a starting point for discussing plant anatomy and how understanding it can help in disease prevention and treatment. Dr. Katherine Esau's research on this disease helped reveal how viruses spread within plants.

💡Anatomy

Anatomy, in the context of botany, refers to the internal structure of plants. The video emphasizes the importance of understanding plant anatomy for identifying diseases and their pathways within the plant. Dr. Esau's work on curly-top disease is highlighted as an example of how careful observation of plant anatomy can lead to significant discoveries.

💡Tissues

Tissues in plants are organized groups of cells with similar structures and functions, similar to tissues in the human body. The video explains that plant tissues are responsible for various functions, including nutrient transport and organ formation. Different types of tissues are discussed, such as dermal, vascular, and ground tissues, each playing a critical role in plant health and function.

💡Dermal tissue

Dermal tissue is the outermost layer of a plant, functioning as the plant's skin. It forms the epidermis and is coated with a wax layer called the cuticle, which prevents water loss and protects against pathogens like viruses. The video uses the concept of skincare to explain the protective role of the cuticle, emphasizing the importance of dermal tissue in plant health.

💡Vascular tissue

Vascular tissue forms the circulatory system of a plant, analogous to veins in humans. It is composed of xylem and phloem cells, which are specialized for transportation of water, nutrients, and sugars. The video explains how xylem cells die on purpose to become hollow tubes for water transport, while phloem cells move sugars from the leaves to the rest of the plant. This tissue is crucial for the distribution of resources within the plant.

💡Xylem

Xylem is a type of cell in vascular tissue that transports water and nutrients from the roots to the leaves. The video describes how xylem cells achieve this by digesting their own insides to become hollow tubes, forming an efficient water-transporting system. Xylem is vital for the upward movement of water and nutrients in plants.

💡Phloem

Phloem is another type of cell in vascular tissue that moves sugars, produced by photosynthesis, from the leaves to the rest of the plant. Unlike xylem, phloem cells do not die but clear out much of their cell contents to facilitate sugar transport. The video mentions that phloem cells often have companion cells to assist with tasks that would normally be done by organelles.

💡Ground tissue

Ground tissue comprises all the plant tissue that is neither dermal nor vascular, essentially the 'meaty' parts of the plant. It includes parenchyma, collenchyma, and sclerenchyma cells, each with different functions such as photosynthesis, structural support, and protection. The video uses the analogy of eating collenchyma cells in celery to illustrate the concept of ground tissue.

💡Stomata

Stomata are tiny pores in the epidermis of leaves that allow the exchange of gases, such as carbon dioxide for photosynthesis. The video likens stomata to 'creepy little mouths' and explains their role in gas exchange and water loss through a process akin to sweating in humans. Stomata are strategically placed to minimize water loss due to sun exposure.

💡Trichomes

Trichomes are hair-like structures that sprout from a plant's skin, serving various functions such as protection against herbivores, protection from solar radiation, or aiding in water absorption. The video uses the example of stinging nettles to illustrate the protective function of trichomes and mentions their length in rye plants to emphasize their abundance.

💡Cross-section

A cross-section, as used in the video, refers to a horizontal cut through a plant organ, such as a stem or leaf, allowing for microscopic examination of its internal structure. The video describes observing cross-sections under a microscope to understand the organization of tissues within plant organs, highlighting the collaboration of different tissues in plant function.

Highlights

Dr. Katherine Esau's discovery of how the curly-top disease spread in sugar beet plants in 1924.

The disease is spread by insects called leafhoppers, causing plants to have unusually curly leaves and stunt their growth.

Esau's realization that the virus moves in the plant along a pathway similar to how food is transported.

The importance of understanding healthy plant anatomy to combat plant diseases.

Plant bodies are made up of tissues, similar to human bodies.

Different tissues in plants work together to form organs like stems, leaves, and roots.

Dermal tissue covers the plant, forming the epidermis and preventing water loss and virus entry.

Stomata are tiny openings in leaves that let in carbon dioxide for photosynthesis.

Trichomes are plant hairs that serve various functions, including protection and water absorption.

Vascular tissue forms the circulatory system of the plant, with specialized cells for transportation.

Xylem cells transport water and nutrients from the roots to the leaves by dying on purpose.

Phloem cells move sugars produced by photosynthesis from the leaves to the rest of the plant.

Ground tissue is everything that isn't dermal or vascular, including parenchyma, collenchyma, and sclerenchyma cells.

Parenchyma cells are the main photosynthesizers in leaves and store starch in roots.

Collenchyma cells provide structural support to growing organs.

Sclerenchyma cells support mature organs and are often too tough to eat.

Plant tissues work together to form organs, showcasing the botanical magic of collaboration.

The study of plant anatomy helps prevent plant diseases and understand their impact on food supply and ecosystems.

Examining plant organs under a microscope reveals the highly organized structure of plants.

Plant form and function are inextricably linked, as shown by the work of plant anatomists like Dr. Esau.

Understanding the relationship between plant structure and function is crucial for plant conservation.

Transcripts

In 1924, Dr. Katherine Esau was working on a sugar beet farm in California,

where some of the beet plants were suffering from a strange virus called curly-top disease.

Spread by insects called leafhoppers,

it causes plants to have unusually curly leaves and stunts their growth.

By paying careful attention to the anatomy,

or the internal structure of these plants,

Esau discovered how the disease spread throughout the plant.

She wrote in her autobiography:

“I began to realize that the virus must enter and must move in the plant along a pathway.

I figured out that if the leaf-hopper passes the virus by feeding,

then the virus must be moving through the same system as the food moves.”

In other words, the very same group of cells  that move the sugar produced by photosynthesis

from the leaves to the rest of the plant was being hijacked

to transport the virus all throughout it.

This discovery was huge for the field of  botany

because it helped illustrate just how essential the knowledge of healthy plant anatomy is

for understanding unhealthy plants —and helping them get better.

So, stick out your tongue and say “ahhh,” plants.

Let’s explore what’s going on in there.

Hi! I’m Alexis, and this is Crash Course Botany.

[THEME MUSIC]

Just like human bodies, plant  bodies are made up of tissues,

which are organized groups of cells that have similar structures and functions.

They do everything from transporting nutrients throughout a plant’s body

to making fruit taste delicious.

And just like in our bodies,

different tissues work together to make organs function.

But in plant bodies, those organs aren’t hearts and lungs;

they’re stems, leaves, and roots.

So, let’s zoom in on the stars of today’s show.

Please welcome: dermal tissue, the plant’s skin;

vascular tissue, the plant’s veins;

and ground tissue — everything in between.

Let’s start with the skin.

The dermal tissue covers the entire outside of the plant,

forming the epidermis, which is coated in a layer of wax called a cuticle.

This outer layer prevents water from escaping,

and nasty things, like viruses, from getting inside.

In other words, the cuticle runs a constant skincare routine for the plant,

keeping it moisturized and free of gross stuff.

No wonder plants don’t get zits.

But they do have pores.

Tiny openings in the epidermis of leaves, called stomata,

let in carbon dioxide gas, a key part of photosynthesis.

And personally, I love that stomata  look like creepy little mouths.

I mean, they may look like aliens,

but this image could easily be from a tree in your backyard.

Plants also get little hairs sprouting out of their skin, called trichomes.

And like hairdos, there are trichomes for every occasion.

Some protect against plant-eating animals

by secreting itchy toxins from  the leaf or stem epidermis,

which, if you’ve ever run into a stinging nettle,

you are already painfully familiar with.

Others act like sunscreen and protect the plant from solar radiation,

or form a blanket to keep the plant warm during the freezing winter.

Meanwhile, the root epidermis produces billions of trichomes

to suck up water in the soil.

One study estimated that if you strung the root hairs of a single rye plant end-to-end,

it’d be eleven thousand kilometers long.

That’s a ponytail stretching a quarter of the way around the earth.

Ariana, who?

While we can observe a plant’s skin on the outside,

we’ll have to peer inside to explore its other tissues.

Next up: Vascular tissue, which forms the  circulatory system, or the veins, of the plant.

Its cells are specialized for transportation,

like how a subway system moves people where they need to go.

And there are two main types of cells that make up that vascular tissue:

xylem and phloem.

Xylem cells transport water and nutrients from the roots to the leaves.

And get this: the cells do this by dying on purpose.

They digest their own insides to become hollow,

and their strong cell walls make perfect water-transporting pipes.

As the plant grows, stem cell clusters called meristems

generate new xylem cells,

which form bigger pipes to suit the plant’s needs.

After water flows from the roots  to the leaves through the xylem,

it can exit the plant through the tiny stomata mouths.

This allows the plant to cool down.

In other words, it lets it sweat,  just like we do.

But unlike us, they never have to worry about pit stains.

Phloem cells, on the other hand,

transport stuff mostly in the opposite direction as xylem cells.

They move the sugar produced by photosynthesis from the leaves to the rest of the plant.

And while they don’t die on purpose like xylem does,

they do clear out a lot of their cell contents to pass that sugar around

—so much, in fact, that they need a buddy, called a companion cell,

to help them with the tasks their organelles

—or functional cell units —would normally do.

[Sings] We all need somebody to lean on.

Xylem and phloem are bundled together to form the veins of a plant

—the subway map that connects the leaves, stem, and roots.

You can actually see and feel these beautiful vein patterns when you pick up a leaf.

OK, so the third and final tissue type is ground tissue,

which is everything that isn’t dermal or vascular

— basically, the meaty bits of the plant.

Well, not meaty exactly.

But ground tissue does tend to be juicy and delicious.

The three types of cells that make up ground tissue all have similar

—but pretty funky-sounding—names.

Parenchyma cells are the most common ground tissue cell type in a plant.

When you bite into an apple,

the juicy part beneath the skin is  made up of these kinds of cells.

They’re the main photosynthesizers in leaves,

and they store starch, or extra sugar reserves,

in roots like sweet potatoes.

We sometimes eat collenchyma cells too.

They’re in the strings of plants like celery and rhubarb.

These cells provide structural support to organs that are still growing,

so they need to remain stretchy and flexible.

And lastly there’s sclerenchyma.

Sclerenchyma’s job is to support the plant when it faces too much weight or bending.

They’re like the folks at the bottom of the cheer pyramid.

We do occasionally eat these cells —

they give pears their gritty texture —

but they’re usually too tough to eat.

Like, I’m not trying to chow  down on a peach pit.

Sclerenchyma supports organs that are fully mature,

and similar to xylem, it has cells that are dead inside

(physically, not emotionally).

All this isn’t just fun trivia to plant-splain to your next date,

or fodder for your  next Scrabble game

— though “sclerenchyma” would definitely get you a new high score.

It’s also knowledge that, when applied,

can help prevent plant diseases, like those studied by Dr. Esau.

And plant diseases are often a big deal for more than just plants.

They could lead to losses in food supply, damaged ecosystems, and more.

So, all throughout this episode,

we’ve been yanking tissues out of the tissue box, one by one.

By which I mean — talking about dermal, vascular, and ground cells separately

when, of course, they don’t function separately.

Just like in our bodies, tissues work together in plants to form an organ.

And the real botanical magic happens when we can observe this collaboration in action.

So for that, we’ll need a microscope…

and some chopped-up plant organs.

Ahem.

Thank you.

We’ll start with a microscope slide of a corn stem.

This view is called a cross-section —

we’ve made a cut horizontally across the stem,

like a flat cucumber slice,

and we’re facing it head-on.

Check it out: the dermal tissue layer is the  perfectly neat row of cells all around the edges

— it’s giving the stem a tight hug.

The rest of the stem is filled with ground tissue —

those big, juicy parenchyma cells,

which help keep the plant upright and store water and nutrients.

And scattered throughout the ground tissue are the vascular tissue bundles, or veins,

which look weirdly like they’re screaming.

I mean, I guess I would be too if someone just cut a  chunk out of me and put me under a microscope.

The xylem cells, which are moving water and nutrients up through the stem,

are clumped toward the inside of the bundle,

and the phloem, which is transporting sugars down through the plant,

is clustered toward the outside.

The companion cells are the little guys scattered throughout the larger phloem cells.

There are even some sclerenchyma fibers helping out along the edges.

OK, next plant organ.

Chef, make me a leaf cross-section.

Thank you!

If you’ve doodled a leaf before,

chances are you’ve drawn a line going down its middle.

Well, here’s that line at the microscopic level.

That big honking circle in the center?

That’s the major vein that runs through the center of the leaf.

And if we zoom in,

we’ll notice its xylem and phloem cells snuggled together,

just like they were in the stem.

The blade of the leaf extends from either side of that big vein,

and smaller veins branch off from it that support the leaf and supply it with water and food.

So the xylem cells are transporting nutrients from the roots to the leaf,

and the phloem are taking the freshly made sugar from the leaf to the rest of the plant.

Packed around the veins is the ground tissue,

which is working so hard at photosynthesizing.

Each leaf parenchyma cell can hold hundreds of chloroplasts

— that’s where all the photosynthesis happens

and what gives leaves their signature green color.

And we’ll find those funky little stomata on the underside of the leaf.

Since water escapes  the plant through the stomata,

it’s best for the plant to have them on the side of the leaf  that does not get blasted by the sun all day.

Last but not least, let’s check out a root cross-section.

It’s got a similar vibe to the stem,

except its vascular tissue  is clustered in the center of the root.

This tissue acts as a filter for the  incoming water that the root is soaking up.

The vascular tissue is surrounded by a thick layer of ground tissue,

and the epidermis wraps around the whole thing.

So by examining these organs under a microscope,

we can recognize that plants aren’t just a mass  of cells—they’re highly organized.

Plants are made of organs, which are made of tissues,

which are made of complex cell structures that work together

and have a hand in everything that goes on in the plant,

from how it eats to how it sweats.

The work of plant anatomists like Dr. Esau

shows us that plant form and function are inextricably linked.

Without the intricacies of plant tissue,

plants wouldn’t be able to survive and thrive.

And viruses, unfortunately, know  this about as well as we do.  

But the more secrets we learn about the amazing relationship between

how plants are built and how they work,

the more we’ll be able to conserve them and all the types of life that rely on them.

Next time, we’ll be seeing these plants in action

as they accomplish some of their most important processes:

cellular respiration and photosynthesis.

Hey, before we go, let’s branch out!

At Dr. Esau’s first university job,

what did the students use to illuminate their microscope samples?

Find the answer in the comments!

Thanks for watching this episode of Crash Course Botany

which was filmed at the Damir Ferizović Studio

and was made in partnership  with PBS Digital Studios and Nature.

If you want to help keep Crash Course free for everyone, forever,

you can join our community on Patreon.