Functions of Auxins :
1. Cell enlargement: Auxins promote elongation and growth of stems and roots enlargement of many fruits by stimulating cell enlargement.
The auxins cause cell enlargement by solubilisation of carbohydrates, loosening of microfibrils, synthesis of more wall materials, increased membrane permeability and respiration.
2. Cell division in cambium : Auxin is responsible for initiation and promotion of cell division in cambium. The reactivation of cambium in the growing season is apparently trigerred by IAA moving from the developing shoot buds.
3. Cell division and tissue culture : In tissue culture auxins initate and promote cell division, and result in the formation of callus.
4. Root growth and root initiation : Auxins promote root growth only at extremely low concentration. At higher concentration of auxin which is suitable for shoot elongation.
5. Apical dominance : Apical dominance is the phenomenon by which presence of apical bud does not allow the nearly lateral buds to grow. Lateral buds start developing into branches when the apical bud is removed.
6. Inhibition of abscission : Auxins have inhibitory effect on the abscission of leaves and fruits i.e., shedding of mature leaves and ripe fruits from the plant. It has been found that abscission zone does not form when the concentration of auxins is high in the leaves or fruits.
7. Tropic movements : Some tropic movements in
plants such as phototropism and geotropism are caused due to differential distribution of indole 3-acetic acid (IAA).
8. Parthenocarpic fruits: Auxins are known to induce parthenocarpy. It has been observed that the
carpels producing parthenocarpic or seedless fruit (e.g., banana, grapes, etc.) have a higher internal
production of auxins.
Synthesis of ethylene : Higher concentration of IAA induces synthesis of ethylene.
10. Sex: Auxins have been reported to have a feminisind effect on some plants.
11. Membrane potential : IAA produces a negative potential on the cell membrane.