The changing world of plants

The presence of clouds and shadows mean plants live in a constantly changing world of light. Researchers have identified that plants can detect shadows but how do they do it and how do they maximize efficiency for capturing sunlight?

TRANSCRIPT

The presence of clouds and shadows mean plants live in a constantly changing world of light.

Researchers have identified that plants can detect shadows.

But how do they do it, and how do they maximize efficiency for capturing sunlight?

Here's the story.

It's not easy being a plant.

♪♪ That's because your world is constantly changing in providing one of the most important things needed to survive -- sunlight.

Watch this time-lapse video.

Once the sun rises, clouds come by.

Shadows move. Sunlight flickers.

The sun sets.

It's clear sunlight isn't always there, and plants use sunlight as energy to make food.

You can think of light as a nutrient, like water.

Plants need water.

Plants need nutrients like potassium and nitrogen.

We add fertilizer to our garden.

They need carbon dioxide.

And plants are competing for these things, and they're competing for light.

Plants need three basic things to live -- water from the soil, carbon dioxide from the air, and energy from the sun.

Plants combine those ingredients to make food in a process called photosynthesis.

It all happens in the plant's cells.

Plants capture sunlight using a compound called Chlorophyll.

Chlorophyll is found inside a structure called a chloroplast.

Photosynthesis converts sunlight into chemical energy which is used to make glucose, or sugar, along with oxygen.

Plants use glucose to live and grow.

They breathe out oxygen.

Now, let's go back to our time-lapse.

It turns out a plant's light-detection system is tied to the efficiency of photosynthesis.

They need to know right now, is it sunny? Is it dark?

Is this a shadow?

Is this flickering light important to me?

And so, in that way, they are smart.

So, this is your typical plant growth chamber.

Researchers at the University of North Carolina at Chapel Hill used a growth chamber to mimic the light changes a plant experiences throughout the day.

That led to the discovery of a protein in the plant called RGS1.

The protein detects changes in light and measures changes in glucose to control how efficiently photosynthesis works.

It knows when something is a shadow and what is a flicker of a light or the end of the day.

It kind of 'knows,' and I'm using 'know' in an anthropomorphic way because remember a plant is sessile, which means it just can't get up and go.

If the sun is too bright, it can't go into the shade like we do.

It has to stay where it's at.

And it has to become, let's say, inefficient at collecting the light because if it were too efficient, it would literally burn up.

♪♪

And so what we're trying to do is determine how a plant is going to change in response to a change in its environment.

In short, when light changes a plant needs to show restraint.

If a brief shadow forms, then the plant increases the efficiency of photosynthesis.

When the sun comes out of the shadows quickly, the plant will burn up.

The plant needs to determine, 'Is this a shadow or the end of the day?'

It can all be plotted in an equation.

And so we have a plant at some height.

So this is a tiny plant.

And we say, let's let the sun shine a lot of light on the plant.

And then if the sun shines a lot of light on the plant, what we observe is a tall plant.

So what we're going to do is write this all into equations.

And so, in our equation, we have our plant height at the beginning of our experiment, and then we add some light into our plant.

And then we measure how that plant height is going to change.

And then we can plot out the height of the plant as a function of time.

So, what does a plant considered to be a shadow?

The study found any change in light that was longer than 4 minutes was determined to be more than a flicker of light, and the efficiency of photosynthesis was increased.

And my model showed that if that duration is very short, like shorter than 4 minutes, then the plant won't react at all.

The sugar is the signal.

You can think of, you know, we all think of sugars as something important as a nutrient, right?

But it's also a signal.

It's also a signal, just like a hormone is a signal or light can be a signal or, you know, sound is a signal.

The amount of sugar and how it changes in time is also a signal.