Write a note on agricultural/horticultural applications of auxins.

Hint: Auxins are plant hormones that promote plant growth in different segments. It promotes the growth by the elongation of cells in the apical meristem. For this, auxins are used in horticulture and agricultural purposes for productive yields.

Complete answer:
Auxins are a class of plant hormones or growth regulators that can regulate the growth of parts of the plants and also various physiological processes.
- Examples of auxins are indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), indole-3-propionic acid (IPA), 2,4,5-trichlorophenoxyacetic acid (2,4,5,-T), etc.
- Auxins are widely used in agriculture and horticulture as they promote elongation of stem and coleoptile by promoting the growth by the elongation of cells in the apical meristem.
- The agricultural and horticultural applications are as follows.
- It is known that when the main shoot of a plant is growing, its lateral buds are inhibited. if the bud at the apex is cut off, the lateral buds begin to develop. The suppression of lateral bud growth due to apical bud due to auxins produced by apical bud is apical dominance. So, when the apical bud is cut off and IAA is applied, the lateral bud growth is inhibited. This property is thus used by gardeners to grow hedges.
- Auxins stimulate meristematic activity. They initiate and promote cell division in the cambium in woody plants.
- Artificial vegetative propagation of plant cuttings (pieces of stems, leaves, roots, etc.) treated with auxins are useful for producing genetically identical plants made from a single individual containing desirable traits.
- They are used for producing parthenocarpic or seedless fruits by initiating the development of fruit without pollination.
- They are also used in stimulating flowering in pineapple plants.
- They are used in large amounts for the prevention of premature fall of fruits especially in apples, pears, and citrus fruits.
- 2, 4-D (2, 4-Dichlorophenoxyacetic acid) is used as a herbicide, it is a weed killer while protecting wheat, sugarcane, and corn crops.
- Auxins are known to induce female sex expression in plants. Spraying auxins on cucurbits increases the number of female flowers.

Additional Information:
Auxins were discovered by Charles and Francis Darwin through experiments on coleoptiles of canary grass.
- Other plant growth regulators/hormones are gibberellins, cytokinins, abscisic acid, and ethylene.
- The physiological functions of auxins that are also used in horticulture and agriculture are apical dominance, control of abscission, root formation in stem cuttings, parthenocarpy, and differentiation of xylem and phloem.

Note: Auxin causes changes in the gene expression of the plant cell when it comes in contact with it. Auxins promote root growth but only at very low concentrations.