Indole-3-acetic acid (IAA / Auxin) — plant growth hormone responsible for cell elongation, phototropism, and gravitropism
Cues (Left Column)
- Chemical nature of each PGR?
- Who discovered each?
- Primary function?
- NEET trap distinction?
Notes (Right Column)
Five PGRs — Complete Table:
| PGR | Chemical Nature | Discovered by | Key Functions | NEET Point |
|---|---|---|---|---|
| Auxins (IAA, 2,4-D) | Indole compounds | F.W. Went (Avena) | Apical dominance, phototropism, elongation, parthenocarpy | Low conc. = promote; High conc. = inhibit |
| Gibberellins () | Terpenoids | Kurosawa (Gibberella) | Bolting, alpha-amylase in aleurone, breaks dormancy | Only hormone that causes bolting |
| Cytokinins (Kinetin, Zeatin) | Adenine derivatives | Skoog & Miller (herring sperm DNA) | Cell division, delays senescence (Richmond-Lang), lateral buds | Adenine derivative — not protein-based! |
| Ethylene () | Gaseous hydrocarbon | Cousins (gas burners) | Ripening, abscission, triple response, feminization | ONLY gaseous hormone |
| ABA | Terpenoid | Addicott & Carns | Stomatal closure, dormancy, inhibits growth | "Stress hormone"; antagonizes GA |
Summary (Bottom)
Mnemonic: "AGCEA — All Gardeners Can Enjoy Apples." Promoters: A, G, C. Inhibitor: ABA. Ethylene: both. Chemical natures: I-T-A-G-T (Indole, Terpenoid, Adenine, Gas, Terpenoid). Both GA and ABA are terpenoids.