Question

What is the main function of auxin?

Answer 1

Auxin:

1. Auxins are a group of naturally occurring and artificially synthesized plant hormones.
2. They play an important role in the regulation of plant growth.
3. Auxins were initially isolated from human urine.

Main functions of auxin are:

1. Cell Elongation: Auxin promotes elongation in shoots and coleoptiles. Plasticity of the cell wall is increased by acidification.
2. Cell Division and Differentiation: Auxin promotes healing. It helps in cell differentiation and regeneration of vascular tissues (phloem, xylem).
3. Callus Formation and Morphogenesis: Auxin along with cytokinin induces callus formation in explant and stimulates morphogenesis.
4. Secondary Growth: Auxin promotes secondary growth and induces cell division in the vascular cambium.
5. Root Initiation on Cuttings: For asexual propagation, NAA is used to initiate root formation in the stem cuttings.
6. Apical Dominance: When the growth of apical meristem inhibits the growth of axillary buds, the phenomenon is known as apical dominance. When the shoot tip is removed, it induces the growth of lateral buds. This is used to promote branching, e.g. in hedge-making and tea plantations.
7. Parthenocarpy: When auxin is applied to some flowers, it induces parthenocarpy, i.e. ovary enlarges and develops into seedless fruit (unfertilized). Seedless tomatoes are widely produced by this method.
8. Fruit development: Auxin is produced by seeds and it stimulates fruit development with gibberellins and delays senescence.
9. Flowering: It delays the senescence of flowers. A high concentration of auxin promotes femaleness in some of the plants. It promotes flowering in litchi and pineapples.
10. Herbicides: Synthetic auxins, e.g. 2,4-D and 2,4,5-T are widely used to kill weeds. It does not affect grasses (monocotyledons).
11. Promotes Tropism: Auxin induces phototropism, gravitropism and thigmotropism, i.e. movement in response to light, gravity and touch, respectively.