. Explain the Functions of auxins
1. Cell elongation: Auxins promote elongations and growth of stems and roots and enlargement of many fruits by stimulating elongation of cells in all directions.
The auxins cause cell enlargement by solubilisation of carbohydrates, loosening of microfibrils and synthesis of more wall materials, increased membrane permeability and respiration.
2. Apical dominance: In many plants, the apical bud grows and the lower axillary buds are suppressed. Removal of apical bud results in the growth of lower buds. The auxin (IAA) of the terminal bud inhibits the growth of lateral buds. This phenomenon is known as apical dominance.
This property of auxins has found use in agriculture. Sprouting of lateral buds (eyes) of the potato tuber is checked by applying synthetic auxin (NAA).
3. Control of abscission layer: Auxin inhibits abscission of leaves and fruits. Abscission layer is produced when the auxin content falls below a minimum.
Premature drop of fruits such as apple, pear and citrus can be prevented to a great extent by spraying the trees with a dilute solution of IAA, NAA or some other auxin.
4. Weed control: Weeds are undesirable in a field with a crop. Weeds cause competition for water, mineral, light and space. This causes poor yield. By the spray of 2, 4-D, broad-leaved weeds can be destroyed but 2, 4 - D does not affect mature monocotyledonous plants.
5. Root differentiation: Many new plants are usually propagated by stem cutting e.g., Rose, Bougainvillea. If we dip the lower cut end of a cutting in dilute solution of auxins (especially IBA gives very good results) very soon large numbers of roots are developed on the cut ends due to which these cuttings develop into successful plants.