Question

List the five main groups of growth regulators. Write one physiological function and one agricultural application for each of them.

Answer 1

Plant hormones are signal molecules produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of growth and development, from embryogenesis, the regulation of organ size, pathogen defense, stress tolerance and through to reproductive development. Plant hormones affect gene expression and transcription levels, cellular division, and growth. They are naturally produced within plants, though very similar chemicals are produced by fungi and bacteria that can also affect plant growth. The five main groups of growth regulators are:

1. Auxins: Auxins help to initiate and enhance rooting in stem cuttings. They help induce parthenocarpy in plants like tomatoes.
2. Cytokinins: Cytokinins can mediate axillary bud release from apical dominance. It helps to modify branching during grafting technique.
3. Gibberellins: Gibberellins are growth hormone that stimulate cell elongation. Gibberellins stimulate bud and fruit formation on plants
4. Ethylene: Ethylene acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves. It helps to alter the growth pattern of plants or crops.
5. Abscisic acid: Abscisic acid helps stimulate stress response. It helps to close stomata during drought conditions.