Q.40 Which of the following plant hormones is a carotenoid-cleavage product?
(A) Phytosulfokine
(B) Brassinosteroid
(C) Methyl jasmonate
(D) Strigolactone
Strigolactone is the plant hormone derived as a carotenoid-cleavage product. The correct answer to the question is (D) Strigolactone.
Option Analysis
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(A) Phytosulfokine: This is a sulfated pentapeptide hormone processed from precursor proteins via tyrosine sulfation and proteolytic cleavage, not from carotenoids.
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(B) Brassinosteroid: These steroid hormones derive from campesterol through oxidation, hydroxylation, and other modifications in pathways like early or late C-6 oxidation, unrelated to carotenoid cleavage.
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(C) Methyl jasmonate: A derivative of jasmonic acid from the lipoxygenase pathway starting with linolenic acid, not carotenoids.
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(D) Strigolactone: Forms via oxidative cleavage of carotenoids like β-carotene by enzymes such as CCD7 and CCD8, producing intermediates like carlactone.
Strigolactone stands out as the key plant hormone that is a carotenoid-cleavage product, making it essential knowledge for CSIR NET Life Sciences aspirants tackling plant physiology MCQs.
Biosynthesis Pathways
Strigolactones arise from β-carotene via stereospecific cleavage: D27 isomerizes it to 9-cis-β-carotene, then CCD7 cleaves to 9-cis-10′-apocarotenal, and CCD8 forms carlactone, further modified to active forms. Other options lack this origin—phytosulfokine from peptide precursors, brassinosteroids from sterols, and methyl jasmonate from fatty acids.
Functions in Plants
These hormones regulate shoot branching, promote mycorrhizal symbiosis, and inhibit parasitic weed germination, adapting architecture to nutrient scarcity. Unlike abscisic acid (another cleavage product), strigolactones focus on rhizosphere signaling.
Exam Relevance
For competitive exams, recognize carotenoid cleavage dioxygenases (CCDs) link to strigolactones, distinguishing from peptide, steroid, or jasmonate pathways—key for scoring in molecular biology sections.
