Plant Development

hi in this video will be talking about plant development, which you'll see has many similarities. Toe animal development but also some key differences. Now embryo genesis is when the fertilized AV you'll develops into a seed containing a plant embryo, meaning that the seed is not the whole embryo. It actually contains the embryo and some support structures similar to like the placenta in mammals. Now. Another key difference is that plant cells don't migrate during development, like animal cells do. You might remember that when we're talking about animal development, we said that some animal cells will break away and move around the developing embryo to form specialized structures. Specifically, you might remember the Museo term. Those so mites had cell clusters that would break away to form. Specialized structures will plant cells don't migrate, they just don't move around at all. And it has to do with the fact that plant cells are different than animal cells. They have those cell walls, for example. Now, germination is the process by which a plant forms from a seed, and after germination, we have both vegetative development, which is the process that develops the roots, leaves and stems basically the non reproductive parts of the plant. There's also reproductive development, which is the process that develops reproductive parts of the plant. So essentially the process of plant development is how you can take a single plant cell like we see right here and turn that into you. He germinated seed like we see right there now, just like animal bodies have axes. Plant bodies also have axes, but they're different axes. Now you might remember that animals have a, uh, anterior posterior access axis. Well, this is similar to the A pickle basil axis of a plant which goes from the roots to the chutes and from the stem to the tips of leaves. So here we have our A pickle basil access. There's also a radial axis which, if you think of this, is a cross section of the stem of this plant. The radial axis is from the center of the stem outward. So this is our radio access. All right, let's flip the page

just like in animals After fertilization, the plants I go will undergo cell divisions. But here's where things get a little different. This I goat undergoes a symmetric cell divisions, meaning that the two resulting daughter cells don't get the same amount of cytoplasm and other stuff. And so they are different sizes, and we can see that happening in this image. So first we have our zygote, and then it divides unevenly, resulting in this to sell stage right here. And you can see that one is about twice the size of the other. Well, we call these cells the a pickle cell and the basal cell. And I bet you can guess why thinking back to that a pickle basil axis? Well, it turns out that the A pickle cell actually is what forms the plant itself. The basal cell forms what's known as the suspense, sir, which contributes to the support of structures of the embryo. Kind of like the placenta in mammals. So you could almost think of this parallel as like the inner cell mass versus the trophy blast. Now Onley one cell in the suspense er contributes to the plant embryo, just one so We can basically just say that the basal cell forms, um, the basal cell forms support structures and the A pickle sell forms the plant embryo. Of course, there's that one cell exception, but it's really not a big deal. So you know, it's okay for us to just make those generalities. In addition, thio these a pickle basil divisions. There are also radial divisions, so you can see going along this way, there are divisions in an outward fashion. See, we have these cells here dividing outward to form this pattern that is an example of a radial division dividing outward instead of just up and down. Now, in addition to these structures we've talked about the embryonic plant has some structures that we haven't given names too. Uh, namely, we have the Kotil Aidan's, which are basically embryonic leaves, and you can see them right here. The hypo coddle, which is basically the embryonic stem, could see that labeled right here. And there is thes shoot, which is made up of the hyper Kotal and the Kotil A dons. So this is our shoot, and then we have our route, which is the underground portion of the plant that forms from what's known as the radical and just you go back to our image up here, you can see that these two images are actually kind of like zoomed in pictures that air specifically looking at the the top of this developing embryo. But we can see the full image here right before we were kind of cutting it off like this and like this. But you can see that there's actually this long a string of cells coming off the bottom that's gonna form those support structures, whereas these colored cells on top will actually form the embryonic plant. Here we have what's known as the heart shape and here the torpedo and these air just names given to the particular shape that the developing plant embryo takes during the course of its development. Now let's get back to the merest M, which, if you recall the merest M, is where those plants stem cells are located, which can give rise to the various structures of the plant like the roots, the leaves, new stocks, what have you So before I said that there were more there was more than one mayor stem and that we'd get Thio What those specific mayor stems are. Well, now we're getting to it. So there is the shoot a pickle, merest m Sometimes abbreviated s am like that and you can see it located right here, denoted by this red dot You can see where it arises from during development. Right here. There's also the route a pickle mary stem, which you can see is highlighted in purple and is also present during development here and here. So the shoot a pickle merest, um, gives rise to Oregon's like flowers and leaves the route a pickle. Merest M gives rise to the roots as the name implies and marry stems. Ensure that plants can have lifelong growth, which is very important because many plants continue to grow throughout their entire lives. All right, let's turn the page.

embryonic tissues formed during plant development along the radial axis. And these embryonic tissues are kind of like the germ layers that form during animal development. So in animal development, we have the ectodermal Suderman endowed ERM In plant development, we have the epidermis, ground tissue and vascular tissue. The epidermis is the outermost layer of cells, and these air cells that are specialized to protect the organism. You can see them labeled here and represented by these bright green cells surrounding this cross section. Inside those, we have the ground tissue, and these are cells that will differentiate into specialized cells like photosynthetic cells. So these air going to be the cells that have a very wide range of differentiate differentiating possibilities. Now, within the ground tissue, we have vascular tissue, which you can see right here, and these air cells that are going to differentiate into specialize transport sells for the movement of food and water around the plant. You might know of xylem and flow. Um, those particular types of vascular tissues found in plants well thes arise from the vascular tissue. Embryonic tissue now plant embryos just like animals. Um, have their development governed by chemical signals which lead to differential expression. So just like we saw with the fly embryo where Bika Wade was released and diffused and developed, a concentration, radiant same thing happens in plants. And a nice example of that is with the hormone oxen, which is a common Morfogen that provides positional information in developing plants. And you can see in this image we have the diffusion of oxen at first upward and then eventually later in development downward. And, of course, remember that thes chemical signals are reused during development all the time Now. The major difference between plants and animals in terms of development is that, unlike animal cells, which have their fates sealed, you know they have that permanent differentiation. Some plant cells can actually d differentiate to become different types of cells. And this is why humans have been able to cultivate plants from clippings for so long. It's because of this ability for plant cells to d differentiate. So here, in our example, you can see we're cutting two portions of stem. Uh, call this portion one and portion, too. Here they are zoomed in, and you can see that the bottom of portion one has been marked by red dot and the top of portion to has been marked by a blue dot. So before we cut this stem that blue and red dot those were right next to each other. So those cells, we're basically the same types of cells, and they were right next to each other. However, we place our clippings differently so that the cells on the red dot end go into the ground and become the roots, whereas the cells from the blue dot end are placed out of the ground and grow into the shoot. So what does that mean? Well, because the red and blue, the cells near the red and blue dot were basically the same types of cells, but they, after the clipping, was made developed into different structures. This shows us that plant cells can d differentiate and then become different types of cells, which is very different from animals who have their cell fate sealed. All right, that's all I have for this lesson. I'll see you guys next time