BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

V. CYTOLOGY. CONCEPT OF THE CELL

Structure of the Plant Cell

Cell Wall

It protects The Cell contents from damage and gives the cell a definite shape. In addition, The Cell wall participates in the absorption and conduction of substances, Transpiration, and The excretion of substances from the cell.

In higher plants, the cell wall consists of the middle lamella, primary wall, and secondary wall. The cell wall contains pits, plasmodesmata, and perforations.

The middle lamella is an amorphous intercellular layer located between the primary walls of adjacent Cells. It is the first layer formed during Cell Division. It consists of pectic Polysaccharides, which chemically are polyuronic acids. They can be extracted from the cell wall with Water upon prolonged boiling.

The primary wall is deposited from the inside of the cell onto the middle lamella. It is capable of growth and thickening. It consists of Cellulose polymolecular fibers, known as microfibrils, embedded in a polysaccharide matrix, of which pectin is the main component.

The secondary wall consists of additional layers deposited on the inner side of the primary wall (facing the Cytoplasm). It is composed of cellulose microfibrils arranged in a polysaccharide matrix. The matrix is built of hemicellulose and a small amount of pectin.

In some cells (bast and wood fibers, sclereids), the secondary wall thickens to such an extent that it fills almost the entire intracellular space, which may lead to the death of the protoplast and cell autolysis.

Pits are unthickened areas of the primary wall (pit fields) where the secondary wall is not deposited. They facilitate communication between adjacent cells. Plasmodesmata—thin cytoplasmic strands connecting the protoplasts of neighboring cells—pass through these pits.

Perforations are continuous openings in the walls of plant cells that connect the cavities of adjacent cells (for example, the cavities between vessel elements or sieve tubes).

In addition to polysaccharides, the cell wall contains Proteins (particularly Enzymes) and water. During cell specialization, cell walls become impregnated with various substances, resulting in structural modifications: lignification (Lignin), suberinization (suberin), cutinization (cutin, wax), and mineralization (mineral salts). A special form of modification is cell wall mucilaginization, which is the transformation of its polysaccharides in an aqueous environment into a high-molecular-weight compound—mucilage. This can be observed in the seed coats of flax and pumpkin, as well as in the peripheral Cells of the ROOT cap.

Cell walls are of great importance for humans and the biosphere. Approximately one trillion tons of cell wall material are produced and broken down annually, of which 100 billion tons consist of cellulose. Stems and leaves, root crops, and tubers are rich in cell walls, making them essential components of animal feed.

Commercial timber and bast fibers consist almost entirely of cell walls. Pectic and mucilaginous substances are of great importance as medicinal remedies.