Plant Development - Online Tutor, Practice Problems & Exam Prep

Plant development involves embryogenesis, where a fertilized ovule becomes a seed with an embryo and support structures. Unlike animals, plant cells do not migrate due to their rigid cell walls. Key stages include germination, vegetative development (roots, leaves, stems), and reproductive development. Asymmetric cell divisions create apical and basal cells, with the apical forming the embryo. Meristems, like the shoot and root apical meristems, enable continuous growth. Embryonic tissues differentiate into epidermis, ground tissue, and vascular tissue, with auxin acting as a morphogen guiding development.

Embryogenesis and Body Axes 4495

Hi. In this video, we'll be talking about plant development, which you'll see has many similarities to animal development, but also some key differences. Now, embryogenesis is when the fertilized ovule 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 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 were talking about animal development, we said that some animal cells would break away and move around the developing embryo to form specialized structures. Specifically, you might remember the mesoderm, the somites, had cell clusters that would break away to form specialized structures. Well, 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 from 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 the 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 a 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 an anterior-posterior axis. Well, this is similar to the apical-basal axis of a plant, which goes from the roots to the shoots, and from the stem to the tips of leaves. So here we have our apical-basal axis. There's also a radial axis, which, if you think of this as a cross-section of the stem of this plant, the radial axis is from the center of the stem outward. So this is our radial axis. Alright, let's flip the page.

Embryonic Plant Development

Just like in animals, after fertilization, the plant zygote will undergo cell divisions. But here's where things get a little different. This zygote undergoes asymmetric cell divisions, meaning that the two resulting daughter cells don't get the same amount of cytoplasm and other stuff, so they are different sizes and we can see that happening in this image. First, we have our zygote, and then it divides unevenly resulting in this 2-cell stage right here, and you can see that one is about twice the size of the other. We call these cells the apical cell and the basal cell. And I bet you can guess why thinking back to that apical basal axis. It turns out that the apical cell actually is what forms the plant itself. The basal cell forms what's known as the suspensor, which contributes to the supportive 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 trophoblast. Now, only one cell in the suspensor contributes to the plant embryo. Just one, so we can basically just say that the basal cell forms support structures and the apical cell forms the plant embryo. There's that one cell exception, but it's really not a big deal, so it's okay for us to just make those generalities. In addition to these apical-basal divisions, there are also radial divisions. So, you can see, going along this way, there are divisions in an outward fashion. We have these cells here dividing outward to form this pattern, which is an example of a radial division, dividing outward instead of just up and down.

Now, in addition to the structures we've talked about, the embryonic plant has some structures that we haven't given names to. Namely, we have the cotyledons, which are basically embryonic leaves, and you can see them right here. The hypocotyl, which is basically the embryonic stem, you can see that labeled right here. And, there is the shoot, which is made up of the hypocotyl and the cotyledons. So, this is our shoot. And, then we have our root, which is the underground portion of the plant that forms from what's known as the radicle. And, to go back to our image up here, you can see that these two images are actually like zoomed-in pictures that are specifically looking at the top of this developing embryo, but we can see the full image here, right? Before, we were kinda cutting it off like this and like this, but you can see that there's actually this long string of cells coming off the bottom that's going to 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 are just names given to the particular shapes that the developing plant embryo takes during the course of its development.

Now, let's get back to the meristem, which, if you recall, is where those plant stem cells are located, which can give rise to the various structures of the plant like the roots, the leaves, new stalks, what have you. So, before I said that there were more, there was more than one meristem and that we'd get to what those specific meristems are. Well, now we're getting to it. There is the shoot apical meristem, sometimes abbreviated SAM, like that, and you can see it located right here, denoted by this red dot, and you can see where it arises from during development right here. There's also the root apical meristem, which you can see is highlighted in purple and is present during development here and here. The shoot apical meristem gives rise to organs like flowers and leaves. The root apical meristem gives rise to the roots, as the name implies, and meristems ensure that plants can have lifelong growth, which is very important because many plants continue to grow throughout their entire lives.

Embryonic Tissues and Pattern Formation

Embryonic tissues form 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 ectoderm, mesoderm, and endoderm. In plant development, we have the epidermis, ground tissue, and vascular tissue. The epidermis is the outermost layer of cells and these are 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 are going to be the cells that have a very wide range of differentiating possibilities. Now, within the ground tissue, we have vascular tissue, which you can see right here. And these are cells that are going to differentiate into specialized transport cells for the movement of food and water around the plant. You might know of xylem and phloem. Those particular types of vascular tissues found in plants well, these arise from the vascular tissue and, embryonic tissue. Now, plant embryos, just like animals, have their development governed by chemical signals which lead to differential expression. So, just like we saw with the fly embryo where bicoid was released and diffused and developed a concentration gradient, the same thing happens in plants, and a nice example of that is with the hormone auxin, which is a common morphogen that provides positional information in developing plants. And you can see in this image, we have the diffusion of auxin at first upward and then, eventually, later in development, downward. And, of course, remember that these 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 dedifferentiate 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 dedifferentiate. So, here in our example, you can see we're cutting two portions, zoomed in, and you can see that the bottom of portion 1 has been marked by a red dot and the top of portion 2 has been marked by a blue dot. So, before we cut this stem, those blue and red dots were right next to each other, and those cells were, 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 dots, the cells near the red and blue dots 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 dedifferentiate and then become different types of cells, which is very different from animals who have their cell fate sealed. Alright. That's all I have for this lesson. I'll see you guys next time.

Here’s what students ask on this topic:

What is the process of plant embryogenesis?

Plant embryogenesis is the process by which a fertilized ovule develops into a seed containing a plant embryo and support structures. Unlike animal cells, plant cells do not migrate during development due to their rigid cell walls. The zygote undergoes asymmetric cell divisions, resulting in an apical cell and a basal cell. The apical cell forms the plant embryo, while the basal cell forms support structures similar to the placenta in mammals. Embryogenesis also involves the formation of embryonic tissues along the radial axis, including the epidermis, ground tissue, and vascular tissue. These tissues are analogous to the germ layers in animals and are crucial for the plant's development and growth.

How do plant cells differ from animal cells during development?

Plant cells differ from animal cells during development in several key ways. Firstly, plant cells do not migrate due to their rigid cell walls, whereas animal cells can move to form specialized structures. Secondly, plant cells undergo asymmetric cell divisions, resulting in different-sized daughter cells, unlike the typically symmetric divisions in animal cells. Additionally, plant cells can dedifferentiate, meaning they can revert to a less specialized state and then differentiate into different cell types. This ability allows plants to be propagated from clippings, a process not possible in animals due to their permanent cell differentiation.

What are meristems and their role in plant development?

Meristems are regions in plants where stem cells are located, allowing for continuous growth and development. There are two main types of meristems: the shoot apical meristem (SAM) and the root apical meristem (RAM). The SAM is responsible for the growth of organs like flowers and leaves, while the RAM gives rise to the roots. Meristems ensure that plants can grow throughout their entire lives by continuously producing new cells that differentiate into various tissues and organs. This lifelong growth capability is a significant difference between plants and animals.

What is the role of chemical signals like auxin in plant development?

Chemical signals like auxin play a crucial role in plant development by providing positional information to cells. Auxin is a common morphogen that diffuses through plant tissues, creating concentration gradients that guide the differentiation and growth of cells. For example, auxin helps establish the apical-basal axis and influences the formation of roots and shoots. These chemical signals are reused throughout development to ensure proper growth and organization of the plant. The ability of plant cells to respond to these signals and dedifferentiate makes plant development highly adaptable and efficient.

What are the key stages of plant development?

The key stages of plant development include embryogenesis, germination, vegetative development, and reproductive development. Embryogenesis is the formation of the plant embryo within the seed. Germination is the process by which a seed develops into a seedling. Vegetative development involves the growth of non-reproductive parts such as roots, leaves, and stems. Reproductive development includes the formation of flowers, fruits, and seeds. Each stage is regulated by genetic and environmental factors, ensuring the plant's successful growth and reproduction.