Question

What are plant hormones? Name the plant hormones responsible for the following:
(i) Growth of stem
(ii) Promotion of cell division
(iii) Inhibition of growth
(iv) Elongation of cell

Answer 1

Hint:-Plant hormones are signal molecules that are produced within plants. Plant hormones are responsible for controlling all aspects of plant growth and development. They are naturally produced within plants and are not the nutrients but chemicals that in less amount promote the growth.

Complete Answer:-The term hormone is derived from Greek which means in motion. In early study of plant hormones, “phytohormone” was the commonly used term. Plant hormones are not nutrients but these are mainly chemicals that in small amounts promote and influence the growth. Though very similar chemicals are produced by fungi and bacteria that can also affect growth in plants. Hormones control all aspects of plant growth and development, from embryogenesis to reproductive development. Unlike in animals each plant cell is capable of producing hormones. Early research of plant hormones identified five main classes: abscisic acid, auxins, cytokinins, ethylene and gibberellins. Later it was expanded more. The plants hormones responsible for the following:
I. Growth of the stem is regulated by Gibberellins. It breaks the dormancy of seeds and buds hence promotes growth.
II. Promotion of cell division is done by cytokinins
III. Abscisic acid in seed and auxins in lateral buds are responsible for inhibition of growth by closing stomata.
IV. Elongation of cells is regulated by auxins.

Note:- Unlike animals plants lack glands to produce and store hormones. Plants utilize simple chemicals as hormones which move easily through tissues. Not all plants respond to hormones. The cells that respond are programmed to respond at specific points in their growth cycle.