31. Out of several gibberllins identified in plants, which one

of the following is NOT bioactive
(1) GA1           (2) GA3

(3) GA4           (4) GA5

Correct answer: (4) GA5

Explanation:

• Among the many gibberellins identified in plants, the main bioactive forms that regulate plant growth and development are GA1, GA3, and GA4.

• GA5 is considered a precursor or inactive form in the gibberellin biosynthetic pathway and is not bioactive.

• GA1, GA3, and GA4 actively promote growth responses such as seed germination, stem elongation, and flowering.

Option explanations:

• (1) GA1 – bioactive gibberellin promoting growth.

• (2) GA3 – bioactive gibberellin widely used in agriculture.

• (3) GA4 – bioactive gibberellin with strong physiological effects.

• (4) GA5 – non-bioactive form, precursor in biosynthesis.