Question

Explain the biological activity of cytokinins.

Answer 1

Biological actions of Cytokinins

1. Cell division: Cytokinins promote cell division even in non-meristematic cells. A low ratio of cytokinin to auxin induces root development but high cytokinin to auxin ratio causes buds and shoots also to develop.
2. Cell enlargement and differentiation: Under some conditions, cytokinins enhance the expansion of cells in leaf disks and cotyledons (which are usually mature and do not expand). As discussed above cytokinins control the development of the shoot and root meristems.
3. Delay in senescence: Cytokinins delay the senescence (aging) of leaves and other organs by controlling protein synthesis and mobilization of resources. If leaves are cut and dipped into cytokinins they remain green and fresh for a longer period of time
4. Antagonistic action of auxin and cytokinin: Cytokinins are antagonistic to auxins with respect to their control over apical dominance. Auxins are known to stimulate the growth of the apical bud, whereas, cytokinins trigger the growth of the lateral buds. Thus cytokinins are applied exogenously to counteract the usual dominance of the apical buds.
5. Role in germination: They can break the seed dormancy of various types and thus help in the process of germination.
6. Increasing endurance of plants: They increase the resistance of plants to high or low temperatures and diseases.
7. Stimulation of enzyme activity: They can stimulate the activity of some enzymes, especially those concerned with photosynthesis.