- The dwarf pea mutant (le) used by Mendel was defective in which of the following enzyme involved in gibberellin biosynthesis?
(1) ent-Kaurene synthase.
(2) GA 3 beeta-hydroxylase.
(3) GA 20-oxidase.
(4) ent-Kaurenoic acid hydroxylase.
Correct answer: (2) GA 3 beta-hydroxylase
Explanation:
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The dwarf pea mutant (le) studied by Mendel is defective in the enzyme gibberellin 3-beta-hydroxylase (also called GA 3-oxidase), which catalyzes a key step in the biosynthesis of bioactive gibberellins by converting GA20 to GA1.
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This enzymatic deficiency leads to reduced levels of active gibberellins, causing the dwarf phenotype due to impaired stem elongation.
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Other enzymes listed such as ent-kaurene synthase, GA 20-oxidase, and ent-kaurenoic acid hydroxylase function at different earlier steps in the gibberellin biosynthesis pathway but are not mutated in the le dwarf pea mutant.
Option-wise:
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(1) ent-Kaurene synthase: Early step enzyme converting geranylgeranyl diphosphate to ent-kaurene; not mutated in le.
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(2) GA 3 beta-hydroxylase: Correct; mutated in le dwarf pea mutant affecting final bioactive GA synthesis.
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(3) GA 20-oxidase: Catalyzes GA12 to GA20, upstream of GA 3 beta-hydroxylase step; not mutant enzyme.
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(4) ent-Kaurenoic acid hydroxylase: Hydroxylates ent-kaurenoic acid, earlier in pathway; not involved in le mutation.
3 Comments
Sonal Nagar
November 28, 2025GA 3-oxidase
Manisha choudhary
November 29, 2025GA-1/3/4/7 most bioactive gibberellic acid h
GA-3 hydroxylase/GA-3. Oxidase GA-20 (19 C) Ko GA-1 m convert krte h is enzyme m mutation ho jaaye too gibberellic acid ki active concentration reduce ho jaayegi
Sakshi Kanwar
December 1, 2025GA 3 beta-hydroxylase enzyme converts the inactive precursor converting GA20 to GA1