Q.56 Which of the following statements are TRUE for plant growth regulators?
P. The release of cellulase and polygalacturonase into the cell wall is promoted by abscissic acid
Q. The early biosynthetic steps of gibberellic acid, up to the formation of ent–kaurene take place
in the plastid
R. The naturally occurring zeatin belongs to the aromatic group of cytokinins
S. Induction of protease inhibitors as a result of wounding and pathogen attack is activated by
jasmonic acid
(A) P, R (B) Q, S (C) Q, R (D) P, Q
Q and S are true statements about plant growth regulators.
Question Breakdown
This GATE Life Sciences question evaluates precise knowledge of plant hormone (phytohormone) actions and biosynthesis. Analyze each statement against established roles: ABA (stress), GA (growth), cytokinins (division), JA (defense).
Statement Analysis
P: ABA promotes cellulase/polygalacturonase release into cell wall
False. ABA induces stomatal closure and inhibits growth; ethylene promotes these cell wall-loosening enzymes for fruit ripening/abscission.
Q: Early GA biosynthesis to ent-kaurene occurs in plastid
True. From GGPP → ent-kaurene via CPS/KS enzymes localized in plastids.
R: Zeatin is aromatic cytokinin
False. Zeatin is isoprenoid cytokinin (side chain from DMAPP/mevalonate pathway); aromatic cytokinins have benzyl/phenyl side chains (e.g., kinetin).
S: JA activates protease inhibitors post-wounding/pathogen attack
True. JA signaling induces Pin2/proteinase inhibitors systemically after herbivory/wounding, independent of ABA.
Correct Choice
(B) Q, S
Plant growth regulators true statements clarify ABA stress role, GA plastid steps, cytokinin types, JA defense in GATE prep.
Hormone Functions Snapshot
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ABA: Closes stomata, dormancy.
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GA: Stem elongation; early steps plastid-bound.
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Cytokinins: Zeatin (isoprenoid) delays senescence.
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JA: Wound response, inhibitors activation.
Truth Table
| Statement | Content | True? | Reason |
|---|---|---|---|
| P | ABA → cellulase/PG release | No | Ethylene does |
| Q | GA to ent-kaurene in plastid | Yes | CPS/KS plastid |
| R | Zeatin aromatic cytokinin | No | Isoprenoid |
| S | JA → protease inhibitors wounding | Yes | Defense signaling |
GATE Exam Relevance
XL-Plant Physiology PYQ tests specifics. Key: Biosynthesis sites (plastids for terpenoids), signaling (JA vs SA/ABA). Review for matching questions.
