「植物看得見你」公開課筆記／2.6 What a Plant Sees?

Humans have four photoreceptors, they can see between the blue to the red spectrum. Plants actually are much more complex than we are when it comes to light signaling.

Plants have upwards of 13 photoreceptors. They have UVR8, which allows the plant to detect UV light and respond.

Plants have upwards of five photo receptors that detect blue light. They have two, what we call phototropins, a photo receptor for flowering in blue light. And another photoreceptor for letting a plant know about seeding development called cryptochrome.

Plants also can detect green light. And they have multiple photoreceptors for red and for far red light. Actually Arabidopsis has five different types of phytochromes.

From a plant's perspective, humans actually may be somewhat visually dysfunctional, because plants can see much more.

While both animals and plants see blue and red light, photoreceptors that detect and respond to the light are completely different. Animals don't have phytochrome. They have erythrolabe, which allows them to see the red light. And they don't have phototropin. They have another of the blue cones, which allow them to see blue light. These are not the same photoreceptors. There's no evolutionary connection between them.

So why would a plant need to be so sensitive to light? Plants being unmovable, light is its ability to eat. Plants use sunlight, to power photosynthesis. A plant needs to know where the light is, so that it could do photosynthesis and make its own food. So a plant needs to know where the direction of its food is, what the intensity of its food is, and when it should be flowering in order to make its next generation. So because of the plant can't move, it's developed the ability to detect both the direction, and the intensity, and the type of light, which is much more complex than what animals have.

Light signaling is not evolescent, evolutionarily connected between plants and animals. Except for one molecule, that's this molecule here called cryptochrome. Cryptochrome is the blue light receptor, that allows a plant seedling to know how to develop in the light.

So while plant scientists had known that there should be a blue light receptor, they didn't know what it was. Johnny Gressel, Professor Johnny Gressel at the Weizmann Institute named it cryptochrome, because they didn't know what the receptor was.

Today we've cloned that gene, and we know where this blue light receptor is, what it looks like but the name has remained the same. Now you also have chryptochrome in your bodies. So what was the connection between cryptochrome and animals? We are influenced by light, the same way that plants are influenced by light, that's our biological clocks.

If you've ever gone through jet lag, you know that being out in the sun helps reset your clock. Through evolution, all organisms have biological clocks. And all organisms have to have the ability to have their clocks set by the light environment.

To summarize sight, what sight is for a plant than what it is for a person. We respond to about 400-700 nm whereas plants respond to a spectrum of 300 to about 750 nanometers, a wider spectrum of vision.

For us, light signals are sensed in the retina, whereas in plants, it's sensed in all cells. For us, it enables primarily identifying details that we see in pictures. Plants don't need to see the details, but for them it enables them to find food. Actually, the details also enable us to find food.