Question

Which gibberellic acid was first gibberellin to be discovered?
A) Gibberellin 1
B) Gibberellin 2
C) Gibberellin 3
D) Gibberellin 4

Answer 1

Hint:Gibberellins was discovered by Kurosawa in Japan in the course of his studies on fungal diseases of rice. Kurosawa found that the abnormal growth promoted by the fungi was due to a compound produced by G. fujikuroi. This compound was first isolated in 1935 by Yabuta and Sumuki, from fungal strains, Gibberella fujikuroi.

Complete answer:
Yabuta named this isolate as gibberellin. All gibberellins are derived from ent-gibberellins skeleton.The gibberellins are named as gibberellins 1.....gibberellins in the order of their discovery. Gibberellin 1 is the first gibberellin to be discovered.The first higher plan gibberellin was then found in a variety of higher plants. There are 125 different gibberellins which have been isolated and chemically characterised.

Additional information: Role of gibberellin in stem elongation in plants: The effects of gibberellins on stem elongation is very dramatic. gibberellin 1 is the biologically active gibberellin controlling stem elongation. The precursor of gibberellin 1 (gibberellin 19 - gibberellins) in higher plants is gibberellin 1(gibberellin 19- gibberellins). Enzyme gibberellic acid 3-oxidase ( functions as 3 beta-hydroxylase) catalyses the conversion of gibberellin20 to gibberellin1, by hydroxylation of carbon -3. Hence lack of enzyme gibberellic acid 3-oxidase causes dwarfism in plants. The active gibberellic acid 3-oxidase is encoded by le (mutant form of the enzyme) and thus can convert gibberellin20 to gibberellin1.

Hence the correct answer is option ‘A’.

Note:Gibberellins are a group of tetracyclic diterpenoid compounds made up of four isoprene units with the ent-gibberellane eing skeleton that functions as plant growth regulators influencing a range of developmental processes in higher plants including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence.