Physiological effects of Cytokinins

Physiological effects of Cytokinins:-

i. Cell Division:- Cytokinins are essential for cytokinesis though chromosome dou­bling can occur in their absence. In the presence of auxin, cytokinins bring about division even in permanent cells. Cell division in callus is found to require both the hormones.

ii. Morphogenesis:- Both auxin and cytokinins are essential for morphogenesis or dif­ferentiation of tissues and organs. Buds develop when cytokinins are in excess while roots are formed when their ratios are reversed.

iii. Differentiation:- Cytokinins induce formation of new leaves, chloroplasts in leaves, lateral shoot formation and adventitious shoot formation. They also bring about lignification and differentiation of inter-fascicular cambium.

iv. Senescence (Richmond-Lang Effect):- Cytokinins delay the senescence of leaves and other organs by mobilisation of nutrients.

v. Apical Dominance:- Presence of cytokinin in an area causes preferential movement of nutrients towards it. When applied to lateral buds, they help in their growth despite the presence of apical bud. They thus act antagonistically to auxin which promotes apical dominance.

vi. Seed Dormancy:- Like gibberellins, they overcome seed dormancy of various types, including red light requirement of Lettuce and Tobacco seeds.

vii. Resistance:- Cytokinins increase resistance to high or low temperature and disease.

viii. Phloem Transport:- They help in phloem transport.

ix. Accumulation of Salts:- Cytokinins induce accumulation of salts inside the cells.

x. Flowering:- Cytokinins can replace photoperiodic requirement of flowering in certain cases.

xi. Sex Expression:- Like auxins and ethylene, cytokinins promote femaleness in flow­ers.

xii. Parthenocarpy:- Crane (1965) has reported induction of parthenocarpy through cytokinin treatment.

xiii. Stomatal opening:- It has been shown that an increased cytokinin concentration in xylem sap promotes stomatal opening.