Question

A plant hormone used for inducing morphogenesis in plant tissue culture is
(a) Ethylene
(b) Gibberellin
(c) Cytokinin
(d) Abscisic acid

Answer 1

Hint: Morphogenesis means the generation of form. In the context of developmental Biology, it refers to generation of tissue organization and shape in animal and plant embryos. The hormones that stimulate cell division in plants are generally used to induce morphogenesis in plant tissue culture.

Complete answer:
The plant hormone cytokinin is used for inducing morphogenesis in plant tissue culture. Cytokinins are plant hormones which stimulate cell division. Chemically they are adenine derivatives. They are synthesized in meristematic tissues. Growing roots, developing fruits and endosperm and embryos of seeds are active sites of cytokinin synthesize. It is believed that cytokinins are translocated upwards from roots to shoots probably through xylem tubes. It promotes cell division and cell enlargement. They induce formation of intrafascicular cambium. They break seed dormancy and also promote their germination. They promote leaf growth and fruit growth. Delay leaf senescence and slow down ageing. They promote stomatal opening. Cytokinins were first discovered by Miller and Skoog in 1955. By heat treatment of DNA they separated a factor which promotes cell division.
So, the correct answer is ‘Cytokinin’.

Additional information:
- Cytokinin inhibits apical dominance and promotes lateral root growth and lateral bud growth. Hence cytokinins are antagonistic to auxins in its action.
- Cytokinin-auxin interaction control cell differentiation in shoot meristem and root meristem. If both are in equal concentrations, cells only divide but do not differentiate.
- Higher cytokinin concentration induces shooting, whereas higher auxin concentration induces rooting.

Note: Zeatin is the first chemically identified natural cytokinin. It was isolated from young maize.
- The term cytokinin was adopted on the basis of its role in cytokinesis. The naturally occurring cytokinin includes zeatin, isopentenyl adenine.
- Cytokinins are commercially applied to delay senescence, to retain the freshness of flowers and leaf crops and to break seed dormancy.