Question

Plant hormones are

• A. Growth regulators
• B. Growth promoters
• C. Growth inhibitors
• D. None of the above

Answer 1

The correct option is A Growth regulators

The early studies on phototropism provided the basis for subsequent research on plant hormones. Some major classes of plant hormones are auxin, cytokinins, gibberellins, brassina steroids, abscisic acid and ethylene. Many molecules in plants that function in defence against pathogens are probably plant hormones as well. Plant hormones are produced in very low concentrations, but a tiny amount of hormone can have a profound effect on the growth and development of a plant organ. This implies that the hormonal signal must be amplified in some way. A hormone may act by altering the expression of genes, by affecting the activity of existing enzymes, or by changing properties of membranes. Any of these actions could redirect the metabolism and development of a cell responding to a small number of hormone molecules. Signal transduction pathways amplify the hormonal signal and connect it to a cell's specific responses. In general, hormones control plant growth and development by affecting the division, elongation and differentiation of cells. Thus, they act as growth regulators. Some hormones also mediate shorter-term physiological responses of plants to environmental stimuli. Each hormone has multiple effects, depending on its site of action, its concentration, and the developmental stage of the plant. Response to a hormone usually depends not so much on the amount of that hormone as on its relative concentration compared with other hormones. It is hormonal balance, rather than hormones acting in isolation, that may control growth and development.

Thus, the correct answer is option A.