The principal effect of auxins in plants is cell enlargement. Explain,
Auxins are a group of plant hormones that play a crucial role in various aspects of plant growth and development. One of the primary effects of auxins is the promotion of cell enlargement, also known as cell elongation or elongation growth.
Auxins are produced in the apical meristem, which is the actively dividing area of plant cells located at the tips of shoots and roots. From there, auxins are transported downward throughout the plant in a polar manner. This means that auxins move from the shoot apex downward toward the roots, establishing a concentration gradient.
Once auxins reach a specific target tissue, they stimulate the elongation growth of cells in that region. This is achieved through several mechanisms:
1. Acidification of the cell wall: Auxins can promote the active transport of protons (H+) into the cell wall, leading to acidification. The acidic environment loosens the bonds between cellulose microfibrils in the cell wall, making it more flexible and allowing the cell to expand.
2. Activation of proton pumps: Auxins induce the activation of plasma membrane proton pumps, which increases the concentration of protons in the cell wall. Higher proton concentration leads to the activation of enzymes called expansins, which facilitate cell wall loosening.
3. Stimulation of water uptake: Auxins stimulate the uptake of water by increasing the expression of aquaporin proteins in the plasma membrane. Increased water uptake creates turgor pressure, causing the cell to expand and elongate.
4. Regulation of gene expression: Auxins influence the expression of genes involved in cell wall formation and modification. They activate specific genes that encode proteins involved in cell expansion or inhibit those involved in cell division, leading to more elongated cells.
In summary, auxins promote cell enlargement by acidifying the cell wall, activating proton pumps and expansins, stimulating water uptake, and modulating gene expression. These combined effects result in the elongation growth of cells, contributing to various developmental processes in plants, such as shoot and root growth, tropisms, and bending towards light.