Plant cell wall: structure and biosynthesis

Published on January 1, 2014   58 min

Other Talks in the Series: Glycobiology

0:00
In our environment, we are surrounded by plants, our most abundant renewable resource. My name is Debra Mohnen, and in this presentation, Melani Atmodjo and I from the Complex Carbohydrate Research Center at the University of Georgia will summarize our current understanding of plant cell wall structure and synthesis.
0:23
Each year approximately 100 billion tons of carbon dioxide are fixed into biomass with roughly one-third of that produced by marine plants and microorganisms and two-thirds from land plants. In photosynthesis, plants use carbon dioxide and water taken up from the environment and energy from the sun to produce carbohydrates. The bulk of that fixed carbon ends up in the plant cell walls.
0:52
Plant cell walls are the carbohydrate-rich extracellular matrix that surrounds all plant cells. Plant cell walls and plant cells vary in shape and structure depending upon the cell type, as can be seen in these micrographs. Note the difference in shape and surface structure of the epidermis of Arabidopsis sepals, the leaf-like structure that supports petals, on the upper left versus the epidermis of petals on the upper right. Furthermore, note the intricate branch structure on the bottom left of single cell trichomes versus the elongated and pitted structure of pollen cells on the bottom right. Finally, note the round structure of suspension-cultured cells grown in liquid culture on the bottom middle versus the rigid and thicker wall structure of the large xylem cells, which make up water transporting vascular cells and cells in wood.
1:49
Plant cell walls have diverse and critical functions in the plant including providing structure to the plant and plant cells, being involved in plant growth, giving the plant flexibility, as you can see when plants sway in the wind. They provide hydration, as you may see when a seed germinates. They are a reservoir of defense and signaling molecules, and they provide cell adhesion between adjacent cells and are involved in development. If you look at the picture, what you will see is the wild-type Arabidopsis plant on the left compared to a mutant plant that is mutant in one of the plant cell wall biosynthetic enzymes, clearly showing that a knockdown in expression of a wall biosynthetic enzyme can lead to dwarfism.
2:34
Plant cell walls also have many uses for humans and animals. They provide clothing, wood, and lumber products. They are used for biomaterials including nanocomposites, nanocellulose fibers, biofuels, and chemicals. They are also used for animal and human food and fiber and as gelling and stabilizing agents in the food industry. And finally, cell walls have uses as nutraceuticals and pharmaceuticals.
3:02
So what are plant cell walls? Plant cell walls are extracellular matrices that are comprised of 80% to 90% carbohydrate and approximately 10% protein. Some cell walls also contain lignin. There are generally 2 types of plant cell walls, the primary wall versus the secondary wall. In the middle picture here, you can see an example of a secondary wall. This is a cross section of wood. The wall is thicker. If you look on the right, however, you see the primary wall. The primary wall is the first wall laid down around all dividing and growing cells. After that wall is produced, some cells go on to produce a secondary wall, and that primary wall is pushed outward. On the right-hand side, you see seedlings underneath callus culture and then finally suspension-cultured cells. All of these cells consist largely of cells made up of primary wall. There are 2 types of primary wall, dicots and non-grass monocots have a so called type 1 wall, as Arabidopsis on the bottom left. The grasses have a so called type 2 wall. Now finally, if you look at the bottom picture, you'll see a cross section of 4 contiguous cells. You have the plasma membrane, and outside the plasma membrane is the primary wall. And if you look at this primary wall, already at this level of viewing, you can see that it is fibrous. The wall that surrounds plant cells is cell type, developmental state, and to some extent species specific.
4:39
So let's review, primary walls are the first wall laid down, they surround meristematic and growing cells, they're prevalent in the succulent parts of the plant, they're found at the junction between cells, and they form the outer layer even of cells that have secondary walls, they're composed of roughly 90% carbohydrate and 10% protein, and there are 2 types— type 1 and type 2 primary walls. Secondary walls surround cells that differentiate to form specialized functions like wood cells, xylem cells, and fiber cells. They have a different polysaccharide composition than primary walls, and they are often lignified.
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Plant cell wall: structure and biosynthesis

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