by Jason Amores Sumpter
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it should hopefully come as no surprise that one of the most important things for plants to be able to sense and respond Teoh is light as that is pretty much the basis for their survival. They need that sunlight to carry out photosynthesis, and they need to carry out photosynthesis in order to produce sugars to eat and survive. So Italy elation is going to be the general term for plant responses to the absence of sunlight. And these responses include growing towards the sun. Right. So if you detect an absence of sunlight, your response logically is a plant would be to grow towards the sun. Uh, one way they might accomplish this is by having longer inter nodes. Remember, that is the portion of the stem between leaves. So if you increase that, uh, that length the length of the inter notes, you're gonna have a lower density of leaves. But that doesn't matter because you're not getting enough sunlight anyways, right? These air responses to an absence of sunlight. So by having longer Internet nodes, you're going to have mawr vertical growth, right, and that's going to allow you to reach the sun now one of the last symptoms, if you wanna call it that is Clore ASUs. And this is a lack of chlorophyll. And you can see an example of that in this very sad looking plant right here. Now, the reason plants will experience sclerosis as a response to an absence of sunlight is actually kind of an energy conservation mechanism. Why would you wanna waste energy producing chloroplasts and chlorophyll if you're not going to be catching sunlight there and so not performing photosynthesis anyways? Now D Italy Elation is going to be the opposite of of Italy elation. It's responses to sunlight, and these were going to be in part regulated by some photo receptors called Fighter Chrome's. And we're gonna talk about fighter. Chrome's in just a little bit now just because I'm piling on the terminology right here. Photo more for Genesis is going to be a big focus in, uh in this lesson, and that is essentially plant growth in response to different spectrums of light. Hopefully, you recall from the section on photosynthesis that there are different types of light and plants selectively absorb specific wavelengths of that light, meaning that they're going to have responses. Two different types of light. So depending on the type of light they're able to receive, they will output different responses. And growth patterns based on these different spectrums of light is again called photo More Food Genesis and that's photo for light Morpho for form and Genesis for origin. So it's basically the origin of the form do toe light. You could think of it that way. Now, trope is, um trope ISMs are big category of plant responses and these air just movements of plants in response to something in the environment. Here we're focusing on photo trumpism, right growth toward or away from light. So essentially plants responding to light, however, in other lessons, will be looking at different types of trope ISMs. Now, photo trope is, um is going thio be, uh controlled or is going thio require, I should say, photo receptors thes air Gonna be proteins that respond to stimulation from certain wavelengths of light. Right. So if you're going to grow toward or away from light, you're going to need something to detect. That light and photo receptors is what plants are going to use Now. One type of photo receptor is or one class of photo receptor, I should say is photo trope ins. These are blue light photo receptors. Blue light, if you recall, is one of the main main lights that plants are going to absorb for photosynthesis. In addition, they also will absorb red light. And hopefully you also recall that blue light is what we consider higher energy light. That is to say, it's light of a higher frequency. Uh, this is kind of getting into physics. So, you know, don't worry about understanding. Uh, you know why Blue Light is higher energy and how frequency factors into that and all the mathematics just know that blue light is going to be higher Energy and red light is going to be lower energy light, And so blue light is very important for photosynthesis. And it's also important for photo trope is, um uh, additionally, it's actually involved in stem mata opening and closing, which will get back Thio. So here you can see a nice example of photo trope is, um so we have this plant here that is bending towards the light source it has here, which is lamp here. Obviously could be the son to now just as it's important for plants to be able to detect, uh, detect light they need for photosynthesis. They also need to detect when they're not getting great light for photosynthesis. So plants use red light and blue light for photosynthesis, as I've said, and, uh, red light is the red light, they preferably uses roughly in the range of 62 700 nanometers. Don't worry about memorizing these numbers. This is just, ah, detail for the sake of detail, in case you wanna look this up and blue light roughly around 4. 32 470 nanometers. So those were gonna be the main bands of light that plants want for photosynthesis. So it hopefully should seem logical that they are very sensitive to those particular wavelengths. They're gonna respond. Uh, they're going to have, you know, strong responses to those wavelengths. Now they also can detect what is called far red light. This is the range that plants want for photosynthesis, right light past that range further down the red spectrum is what we call far red light. You know, usually it's thought of his light of wavelength greater than 710 nanometers. This light is not absorbed by photosynthetic pigments, meaning it's not going to help photosynthesis. It actually passes through leaves, and it helps indicate shade. So what that means is high up leaves that far red light will actually pass through them and we'll hit light are sorry. Hit parts of the plant that are underneath those top leaves getting the direct sunlight. So it's a way for plants that are not in direct sunlight to detect that they are in shade, right, because the leaves above are gonna absorb those photosynthetic wavelengths. But that far red lights gonna make it through. So it's going to allow the plant Thio say, Oh, hey, I'm not I'm not getting the good son right now. I got a Hey, you get moving here. I got to do some photo Trope is, um Now plants will actually use that far red light for a really nifty thing called the Red Far Red Switch. This is kind of a hypothetical idea, and it's or I should say, it's a theoretical idea that Red Light will promote. See germination and far red light will inhibit it. And it's based on this particular type of photoreceptors mentioned earlier. Fight a chrome, which is a photo reversible photo receptor, meaning that it actually is a molecule that has two different forms. It has to alternate forms and each of those forms reacts to a different wavelength of light. And when it reacts to one of those wavelengths of light that actually changes its confirmation. So fighter chrome's are these photo reversible photo receptors that are sensitive to both red and far red wavelengths of light. So the way this works is basically light stimulation. If this fight a chrome, the red fighter chrome absorbs sunlight, it will change its confirmation and turn into the far red fighter chrome. And I mean red fighter chrome is infighter chrome that absorbs red light far red fighter chrome as in fighter chrome that absorbs far red light. So when this far red fighter chrome absorbs far red light that will switch it back Thio the fighter chrome red confirmation And you can see this is a nifty mechanism to detect light and shade or dark. However you want to think of it Now get my head out of the way here and behind my head you can see this, uh, nifty little graph showing you the wavelengths absorbed by the the red fighter chrome and the far red fighter chrome confirmations. So the red fighter chrome you can see has a strong response to light in groups light in this particular band right here. And while far Red Thief are red fighter, chrome confirmation can also absorb that particular band. It doesn't absorb it nearly a strongly and also but much more importantly, the far red fighter Chrome is able to absorb light past this particular wavelength and into this region here, right, the far red region now thes light stimulations are going thio cause phosphor relations and defrost for relations that will induce thes confirmation. All changes don't need to worry too much about the biochemistry. Just know that when the fight a chrome in the red confirmation absorbs red light, it switches to the far red confirmation. And when that far red confirmation absorbs far red light, it flips into the red absorbing confirmation. Now all of this is part of a behavior no nas shade avoidance, where far red light will actually cause plants to lengthen their stems or induce branching in an attempt to grow into direct light. So lengthening the stems is great if you just need to get up to the light, right, if the problem is your verticality. But it can also induce branching meaning, like making the plant get bushier. So it has a greater area of absorption, which is sometimes, uh, the behavior needed in order to absorb more light. And you can see that these are responses thio, far red, light or shade basically, right with that, let's flip the page.