Q163
General ScienceBiology
Growth inhibiting hormone of plant is
- a.Auxin
- b.Gibberellin
- c.Cytokinin
- d.Abscisic acid
Answer: (D) Abscisic acid
Abscisic acid (ABA) is the main growth-inhibiting plant hormone. It induces dormancy of seeds and buds, closes stomata during water shortage (hence 'stress hormone') and promotes ageing and shedding of leaves, acting against gibberellins. The other three are growth promoters: auxin (IAA) causes cell elongation, apical dominance and phototropism, and is used for rooting cuttings; gibberellin causes stem elongation and bolting and breaks dormancy (first found in the fungus Gibberella, which causes the 'foolish seedling' disease of rice); cytokinin promotes cell division and delays ageing. The fifth major hormone, ethylene, is a gas that ripens fruits.