2.7 Molecular Biology of Plant Vision

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Из курса от партнера Tel Aviv University

Understanding Plants - Part I: What a Plant Knows

473 оценки

Tel Aviv University

Understanding Plants - Part I: What a Plant Knows

473 оценки

For centuries we have collectively marveled at plant diversity and form—from Charles Darwin’s early fascination with stems and flowers to Seymour Krelborn’s distorted doting in Little Shop of Horrors. This course intends to present an intriguing and scientifically valid look at how plants themselves experience the world—from the colors they see to the sensations they feel. Highlighting the latest research in genetics and more, we will delve into the inner lives of plants and draw parallels with the human senses to reveal that we have much more in common with sunflowers and oak trees than we may realize. We’ll learn how plants know up from down, how they know when a neighbor has been infested by a group of hungry beetles, and whether they appreciate the music you’ve been playing for them or if they’re just deaf to the sounds around them. We’ll explore definitions of memory and consciousness as they relate to plants in asking whether we can say that plants might even be aware of their surroundings. This highly interdisciplinary course meshes historical studies with cutting edge modern research and will be relevant to all humans who seek their place in nature. This class has three main goals: 1. To introduce you to basic plant biology by exploring plant senses (sight, smell, hearing, touch, taste, balance). 2. To introduce you to biological research and the scientific method. 3. To get the student to question life in general and what defines us as humans. Once you've taken this course, if you are interested in a more in-depth study of plants, check out my follow-up course, Fundamentals of Plant Biology (https://www.coursera.org/learn/plant-biology/home/welcome). In order to receive academic credit for this course you must successfully pass the academic exam on campus. For information on how to register for the academic exam – https://tauonline.tau.ac.il/registration Additionally, you can apply to certain degrees using the grades you received on the courses. Read more on this here – https://go.tau.ac.il/b.a/mooc-acceptance Teachers interested in teaching this course in their class rooms are invited to explore our Academic High school program here – https://tauonline.tau.ac.il/online-highschool

Из урока

What a Plant Sees?

This week we start a systematic review of a plant's sensory systems by starting with plant responses to light. We will cover an overview of human vision, plant responses to light, Darwin's experiments showing plant responses to light, phototropism, phytochrome and flowering, and modern research on phototropism. In other words, this week we get into more advanced concepts in plant sensory biology. The last module is especially advanced, and will be clearer for those of you with a strong biology background. But do not fret, aside from very basic concepts, this module will NOT be included in the exam (you will not be responsible for understanding the intricacies of the experimental methods, etc.). If you have not already, please review the Course Syllabus for general information about this course.

2.1 Introduction5:21

2.2 Darwin's Experiment6:50

2.3 Light and Flowering7:06

2.4 Phytochrome: A Light-Activated Switch7:35

2.5 Arabidopsis Blind Mutant8:42

2.6 What a Plant Sees?5:55

2.7 Molecular Biology of Plant Vision8:53

Познакомьтесь с преподавателями

Professor Daniel Chamovitz, Ph.D.
Dean, George S. Wise Faculty of Life Sciences
Director, Manna Center for Plant Biosciences

In this module of today's lecture, I wanna go into a little bit more of the advanced

biology that's involved in plant signaling, or in plant responses to light.

And I'm gonna assume a little bit of knowledge of basic biology.

And I'll try to explain some of the more advanced concepts.

So earlier on today's lecture we talked about, we learned about,

how a plant responds to blue light.

How there's phototrophism the plant absorbs the blue light and

bends towards that signal.

We didn't really talk about what's involved in this signaling,

how the plant is responding to the blue light.

Several decades ago, it was found out,

it was discovered that one of the first things that happens when a plant is

illuminated with blue light, is a change in a specific protein.

One protein in the membrane of the plant cell becomes phosphorylated.

What that means is that phosphate is added to this protein.

The way we can check this, the way that scientists check this is that we actually

add radioactive phosphate to the plant, isolates the proteins,

and then see which proteins have become radioactive.

Rather, which have absorbed the radioactive phosphate.

What we can see here in this picture, this is actually showing a specific

protein that when it's in the dark, it has a certain level of phosphorylation and

we see that by the width, or the size of this band in the gel.

And here are the same protein after it's illuminated with blue light,

it gets much stronger signal.

That means there's a lot more phosphate on this protein.

And this is induced only by the blue light, okay?

So here we have a protein that becomes phosphorylated in response to blue light.

Now in all of biology phosphorylation is one of the ways

that proteins signal to each other.

And this is true for all of Animal biology, all of bacterial biology, and

all of plant biology.

We also learned a little bit about the mutants that were isolated,

that were blind to blue light.

And it actually turns out that there was more than one mutant that were blind.

These mutants were called NPH at the time for non phototropic.

There's actually four mutants isolated.

Here we could see the normal, the wild type, which is bending to the light,

which is coming from the side here.

And mutations in four different genes and nph-1, nph-2,

nph-3, and nph-4, are all blind to the light.

These are mutants in different genes but

they all look the same, they're color blind.

So now the question could be,

what happens to these mutants in terms of phosphorylation of the same protein.

In other words, if I give the blue light Is the same protein still phosphorylated.

And in this experiment,

we can see that the results are different depending on the mutant.

For example, in nph-1, we can clearly

see that there is no change in phosphorylation in response to the light.

Again, I'll go through this slowly.

In the wild type, we see that when it's illuminated with a blue light,

there's a huge change in the amount of this band, a lot more phosphorylation.

In nph-1, a mutant that's blind to blue light.

There is no phosphorylation, but on the other hand,

in the other mutants, in nph-2 or nph-3 or

in nph-4, this protein is still phosphorylated.

Meaning we're seeing a difference.

We have two classes of proteins, two classes of mutants.

One mutant, nph-1, affects the original phosphorylation.

Whereas mutants in the other sub-units,

the phosphorylation still occurs, but the plant is still blind to the light.

So if I fast forward ahead now, 10 or

20 years, well we've now cloned the genes, my colleagues have cloned the genes.

We know what they're doing, here's what's happening.

So if we now take all the data that's accumulated for

these phototropic mutants, here's what we now know.

This is our paradigm right now, a blue light signaling for phototropism.

We now know that NPH1 encodes a protein which we now call phot 1,

or phototropin 1.

This is the blue light receptor necessary for phototropism.

When phot 1 absorbs blue light, it becomes phosphorolated.

A phosphate group is attached to it.

This is the first step in the blue light signaling.

Once volt one is phosphorolated, it can then interact with NPH3,

physically touch each other within the cell.

And then NPH3, somehow takes the information from phot 1 ,and

transduces this signal further into the plant.

The signal from NPH3 then effects a plant hormone that's called auxin.

We're gonna learn more about auxin later in this class.

But auxin is one of the main hormones that is important for phototropism.

The auxin signal is then modulated by NPH4,

which itself is a transcription factor.

What that means, this is a protein which directly effects

which genes are turned on and which genes are turned off.

And this then finally leads to phototropism.

So we could see that starting from a simple genetic screen

which isolated various mutants that are all blind to blue light.

We isolated a photoreceptor.

If this photoreceptor doesn't act or

doesn't exist, the plant is blind to blue light.

We isolated one of the proteins involved in the signal transduction,

in the transfer of the signal after light perception.

If this signalling component is missing, then you don't get phototropism.

And we also isolated a protein directly involved in the regulation of which genes

are turned on and turned off which will be very far downstream in the pathway.

And also, if this doesn't exist, the plant will be blind to blue light.

So we can affect light signaling at different levels, at the level of

perception, at the level of transduction or at the level of the response.

Just like in humans we can be blind because of a problem in the photoreceptor,

a problem in the transduction in the nerves, or

a problem of the response in the brain.

All three defects lead to blindness, but they're caused by different problems.

One last thing here, so we talked about blue light and phototropism.

We briefly talked about blue light and photomorphogenesis.

But blue light effects many, many process in the plant.

Phototropism.

But it also affects when plants

open the small holes on the leaves which are called stomata.

It affects how chloroplasts, the part of the plant that does photosynthesis,

actually move within the cell.

And in effect, how leaves follow the sun during the day.

In other words, blue light responses maximize the ability of

a plant to carry out its photosynthesis.

This thing about solar tracking is very important to me from a personal

level because the first class I ever learned in my signaling was taught by

Professor Dove Caldwell in Hebrew University,

who specialized in understanding how plants change the position of their

leaves in response to the direction of the sun.

Recently a book was published called the restless plant that Dov wrote, and

it was because of this class

that I took with Dov Koller that I started studying plant responses to light.

And the connection to this specific class is that Dov Koller is the father

of Professor Dofnick Koller who was one of the founders of Corcyra.

So if you're interested in learning more about the mechanisms by which

plants respond to light and move I highly recommend that you read this book.

So that ends today's lecture,

next week we're gonna be talking about what plants smell.

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