「植物看得見你」公開課筆記／2.5 Arabidopsis Blind Mutant

A color blind plant would keep growing straight since it wouldn't see the blue light coming from the side -- a very interesting hypothesis.

How could we actually find a color blind plant? Many plant biologist all over world use to answer such questions with a plant called Arabidopsis thaliana, a great plant for growing in the laboratory since its whole life cycle can be completed within eight weeks. The adult plant will produce so many seeds that we can get up to 20,000 seeds per plant. In our laboratories, we could grow literally thousands of these just in our room.

The second reason that Arabidopsis had a very small genome, a very small amount of DNA. In 2000, it was the first plant to have its genome sequenced.

The last reason is that it's so small, Arabidopsis is a great genetic system. We can make mutants, just like a lot of researchers have used fruit flies to study animal biology. We can take these seeds and treat them with chemicals that induce mutations and then try to find plants with different types of characteristics. We could maybe find plants that would be blind to blue light. We could put thousands of them that have been treated with a mutagen, treated with a chemical that will induce mutations. Put the blue light from the side and see if you can find the one plant that wouldn’t bend.

Even though the light is coming from the side, it keeps growing up straight. It's literally blind to the lateral light. Light effects plants more than just with phototropism, the ability to see light coming from the side.

A plant that grows in the light, the seedling is short -- a short hypocotyl. The stem has open and expanded cotyledons.

A plant that's germinated in the dark, will have an elongated hypocotyl. It's trying to find where the light is, and its first leaf/leaves like organs, the cotyledons remain closed, because it actually thinks it's under the soil and it's trying to push its way up.

When it grows in the light, we call this photomorphogenesis, because it's getting its structure, its development by the light, photo.

When it grows in the dark, we call this skotomorphogenesis. Once this plant that's grown in the dark get's a little bit of light, then it will initiate photomorphogenesis. Its leaves will open and it will continue on to adult development.

Scientists have utilized this system to further dissect light signaling in plants, because it ends up that photomorphogenesis can be induced by white + blue + red + constant far red light.

If you grow a plant in constant far red light not just flashes, but hours and hours and hours of high intensity far red light, it will also go through photomorphogenesis.

Now, many labs have isolated mutants that are defective in some of the light signalling. An experiment that was first performed in the laboratory of Martin Corniffe, in Vachenagen, Holland in the early 1980s, it's since been repeated in many other labs. Martin found several types of mutants.

The first type of mutant was wrong in white light. It was also long in red light, but was completely normal in blue light. It is defective in phytochrome. It's missing the photoreceptor that absorbs red light and transfers the signal to allow seeding development, which is why we get this elongated phenotype.

The second mutant was also long in white light, it was short looking at wild type and red light, but it was long in blue light. It is defective in the photoreceptor for blue light, which is necessary for seeding development.

The third mutant was long in white light. It was long in both red and blue light. One hypothesis could be that there's another photoreceptor, which is sensitive to both red and blue light. Another hypothesis could be downstream. Perhaps it is lacking something that transfers the light signal from the different photoreceptors. It may not detective in the photo receptor, but it is defective in the signalling of the light.