Question

List five plant growth hormones and briefly describe their roles.

List five plant growth hormones and mention one important role of each.

Answer 1

	Plant growth hormones	Roles
1.	Auxins	Promote elongation and the growth of stems and roots. Promote elongation and the growth of stems and roots. Auxins of the apical bud inhibit the growth of lateral buds (apical dominance)
2.	Cytokinins	Stimulate cell division and prevent the onset of senescence in tissues. Stimulate cell division. Break the dormancy of seeds. Delay in the senescence of leaves and other organs. Promote the growth of lateral buds.
3.	Gibberellins	Enhance the longitudinal growth of the stem. Cause stem elongation and leaf expansion but have no effect on roots. Break the dormancy of buds and tubers. Cause delay in senescence. Promote elongation of internodes in sugarcane
4.	Ethylene	Inhibits the growth of lateral buds and causes apical dominance. Breaks the dormancy of buds and seeds. Associated with the process of ageing of plant organs, such as the yellowing of leaves.
5.	Abscisic acid	Induces dormancy in buds, stems and seeds It induces and maintains dormancy in many seeds. It inhibits flowering in short-day plants. Inhibits cell division and cell elongation.

Answer 2

Plant growth hormones and their roles:

1. Auxins: Auxins are plant hormones that facilitate cell differentiation and expansion in plants. Auxins also promote fruit growth. Auxin horinone regulates the response of a plant to gravity and light. In other words, the auxin hormone regulates the phototropic and geotropic responses of plants. Cells located at the extremities of stems and roots synthesize auxin. Auxin transitions from light to gravity. Auxin has an opposing impact on the growth of roots and stems. Auxin accelerates the development of stems, but it inhibits the growth of roots. Horticulture and agriculture employ synthetic auxins.
2. Gibberellins: Gibberellins are plant hormones that facilitate cell differentiation and enlargement in the presence of auxins. Gibberellins are important in the process of breaking the dormancy in seeds and blooms. In addition, they facilitate the development of crops. Mainly, the gibberellin hormone is responsible for the extension of shoots. Gibberellin induces the elongation of the branches in a variety of plants.
3. Cytokinins: On the other hand, cytokinins are plant hormones that facilitate cell division in plants. Seeds and seedlings are also assisted in breaking their dormancy by cytokinins. In leaves, they postpone the ageing process. Cytokines facilitate the opening of stomata. Additionally, they encourage the development of fruit.
4. Abscisic acid: Abscisic acid is mostly a growth inhibitor, a plant hormone. Abscisic acid has the opposite effect of disrupting dormancy by promoting dormancy in seeds and buds. The closure of the stomata is also facilitated. Abscisic acid facilitates leaf abscission, which is the wilting and collapsing process. Flowers and fruits are also detached from the plant as a result.
5. Ethylgine: Ethylgine is the sole hormone; it is a gas at standard temperature. It is extracted from fruits and is primarily found in the same fruit. Therefore, it is distinct from other hormones in that its site of synthesis and site of action are not distinct. A gas that induces fruit maturation was initially identified as emanating from oranges, which facilitated the ripening of bananas when they were stored in close proximity. R. Gane identified the gas as ethylene. In plants, ethylene induces two processes: a decrease in stem elongation and an acceleration of senescence. Ethylene is also beneficial in the following applications:
   • Ripening of fruit.
   • Initiating germination in peanut seeds.
   • Sprouting of potato tubers.
   • Promoting root growth and root-hair formation.
   • Inducing flowering in mango.