Question

Natural cytokines are synthesized in tissues for
(a) Differentiating
(b) Senescent
(c ) Dividing
(d) Storing food

Answer 1

Hint: Natural cytokines are the plant growth hormones or regulators that determine whether a plant will produce roots or shoots first depending upon its concentration with respect to another hormone. Their application produces bushy growth.

Complete answer:
Cytokines are plant growth hormones that are basic in nature due to the presence of amino purines or derivatives of phenyl urea. As their name signifies, they are involved in cytokinesis i.e cell division which they perform either alone or in conjunction with auxin.
Natural cytokinins are synthesised in regions where rapid cell divisions occur like root apices, developing shoot buds and young fruits. E.g. zeatin, the first natural cytokine obtained from unripe maize grains or kernels. It can also be found in coconut milk.
Other functions of cytokinins are:
- They delay the senescence of leaves by promoting nutrient mobilisation. This has been proved by the low concentrations of endogenous cytokinin in senescing tissues. Also, the application of exogenous cytokinins delays senescence.
- Application of cytokinin on apical buds stimulates the growth of lateral buds and thus overcome apical dominance.
- They help in the maturation of chloroplasts and chlorophyll synthesis.
- Cytokinin application is also useful in developing resistance in plants against pathogens and extremes of temperature.
- Along with auxin, it helps to stimulate morphogenesis i.e initiate root and shoot formation in the callus. The high concentration of auxin with respect to cytokines induces rooting while high cytokines concentration induce shoot formation.
So, the correct answer is ‘Dividing.’

Note:
- In most plants, auxin exhibits a phenomenon named as ‘apical dominance’ wherein growing apical bud inhibits the growth of lateral buds. Removal of the shoot apex results in the growth of lateral buds. This property is exploited by gardeners in ‘hedge making’ and ‘tea plucking’ to produce dense bushy growth.
- Other plant hormones like ethylene and abscisic acid are positive regulators of senescence i.e promotes senescence.