16. The dwarfing gene which was responsible for green revolution is involved in signaling of which plant hormone?
(1) Gibberlic acid (2) Cytokinin
(3) Absicic acid          (4) Ethylene

Correct answer: (1) Gibberellic acid.

Gibberellin (GA) dwarfing genes used in the Green Revolution (such as Rht in wheat and sd1 in rice) reduce plant height by altering gibberellin biosynthesis or GA signal transduction, making plants less responsive to GA and therefore semi-dwarf. This improved lodging resistance and yield under high fertilizer input.

Brief explanation of options:

• (1) Gibberlic acid – Correct. The classic Green Revolution dwarfing genes encode GA biosynthesis enzymes or GA-signaling repressors (DELLA proteins), so the trait is directly linked to gibberellin signaling.

• (2) Cytokinin – Important for cell division and shoot branching, but not the hormone whose signaling pathway is altered by the main Green Revolution dwarfing genes.

• (3) Abscisic acid – Central in stress responses and seed dormancy, not the primary pathway targeted by the historic dwarfing alleles in wheat and rice.

• (4) Ethylene – Regulates ripening and senescence; again, not the hormone whose signaling was modified by the Green Revolution dwarf genes.