Tag: biology

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. Therefore, cytokinin can overcome apical dominance, caused by auxins.

ABA induces seed dormancy in unfavorable environmental condition, its function is antagonistic to gibberillin which promotes seed germination. It is regarded as the stress hormone as it brings about closure of stomata during water stress to prevent water loss from transpiration.

Cytokinins (Letham, 1963) are plant growth hormones which are basic in nature, either aminopurine or phenyl urea derivatives, That promote cytokinesis (= cell division) either alone or in conjunction with auxin. Coconut milk is a rich source of cytokinin.

ABA Is known as dormin as it induces dormancy in buds, underground stems and seeds in a variety of plants. e.g., ABA induces winter bud dormancy in duckweed plant.

Ethylene inhibits longitudinal growth but stimulates transverse or horizontal growth and swelling of axis. It decreases the sensitivity to gravity. Roots become Apo-geotropic while stems turn positively geotropic. Leaves and flowers undergo drooping. The phenomenon is called epinasty. Seedlings develop tight epicotyl hook. It hastens the senescence of leaves and flowers.Abscission of various parts (leaves, flowers, fruits) is stimulated by ethylene which induces the formation of hydrolases. It breaks the dormancy of buds, seeds and storage organs. Rhizomes, corms, tubers, seeds (e.g., Peanut) and other storage organs can be made to sprout early by exposing them to ethylene. Initiates germination in peanut seeds. 

So, the correct answer is 'Ethylene'

ABA (Absisic acid) is a stress hormone which is synthesised by the plant during drought or other stress conditions. It causes rapid movement of $K^+$ ions out of the guard cells, closes stomatal pores and thus reduces the transpiration rate.

A- GA or Gibberellic acid helps in promoting the growth and the elongation of cells.

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. the hormone enhances the respiration rate during ripening of the fruits. Ethylene helps fruits ripen by making them softer, through the breakdown components of the cell walls, and sweeter, through the conversion of starches to sugars.