19. Among the following which hormone can induce flowering in
    short day plants grown even under long duration of light
    (1) Gibberllic acid (2) Auxins

(3) Cytokinin                 (4) Abscisic acid

Correct answer: (1) Gibberellic acid.

Gibberellins can substitute for the short-day (long-night) requirement and induce flowering in some short day plants even when they are kept under long-day (long-light) conditions, by promoting floral transition at the shoot apex.

Brief explanation of each option:

• (1) Gibberllic acid – Correct. GA applications are known to promote flowering and can partially overcome unfavorable photoperiod in several species, including short day plants, by acting downstream of photoperiod perception in the flowering pathway.

• (2) Auxins – Auxin mainly regulates cell elongation, apical dominance, root formation, and tropic responses. It is not the classic hormone used to bypass photoperiod and induce flowering in short day plants.

• (3) Cytokinin – Cytokinins influence cell division, shoot branching, and delay of senescence. They can affect flowering in some systems but are not the standard hormone that allows short day plants to flower under long days.

• (4) Abscisic acid – ABA generally promotes dormancy and stress responses and often delays growth and flowering rather than inducing it, so it cannot replace the short-day requirement for flowering in these plants.