Question

_______ is a growth inhibitor hormone in plants.
A.Auxin
B.Cytokinin
C.Abscisic acid
D.Gibberellic acid

Answer 1

Inhibitors of natural growth are controlling substances that retard processes such as root and stem elongation, germination of seeds, and opening of buds. The growth of isolated stem sections is actively depressed by these regulators and function as antagonists to plant hormones such as auxin, gibberellin and cytokinin.

Complete answer:
Throughout the plant kingdom, and also in algae, phytohormones exist where they have similar roles to those seen in higher plants. In microorganisms, such as unicellular fungi and bacteria, certain phytohormones also exist, however they do not play a hormonal function in these cases and may best be considered as secondary metabolites. Plant hormones are chemicals that encourage or inhibit plant development. There are 5 major forms of hormones from plants. Auxin, commonly abbreviated as IAA, stimulates plant growth with both gibberellins and cytokinins. Abscisic acid and ethylene hinder development in plants. Abscisic acid can be synthesized through the leaves and then translocated through the phloem to stem apices. ABA is a strong inhibitor of growth. This induces a 50 per cent growth inhibition of the coleoptile oat at a particular concentration. ABA also inhibits growth induced by Gibberellin.

Hence, the correct answer is option (C)

Note: Throughout the plant kingdom, and also in algae, phytohormones exist where they have similar roles to those seen in higher plants. In microorganisms, such as unicellular fungi and bacteria, some phytohormones also exist, but they do not play a hormonal role in these cases and can best be treated as secondary metabolites.