PP-03 — Five-Bullet Last-Minute Summary

• Growth = irreversible permanent increase; three phases: Meristematic → Elongation → Maturation; sigmoid curve (Lag → Log → Stationary); arithmetic (Lt = $L_{0}$ + rt, one daughter divides); geometric ($W_{1}$ = $W_{0}$eʳᵗ, both daughters divide).

• Five PGRs: Auxin (indole, apical dominance, 2,4-D herbicide), Gibberellin (terpenoid, bolting, alpha-amylase in aleurone, breaks dormancy), Cytokinin (adenine, cell division, Richmond-Lang effect), Ethylene (gas, ripening, triple response), ABA (terpenoid, STRESS hormone, stomatal closure via $K^{+}$ efflux, antagonizes GA).

• Photoperiodism: SDP (rice, chrysanthemum — need long nights); LDP (wheat, spinach — need short nights); DNP (tomato, cucumber — no requirement); Pfr = active phytochrome: promotes LDP flowering, inhibits SDP flowering.

• Vernalization = cold (0–5°C) requirement for flowering in winter wheat and biennials; FLC epigenetically silenced → flowering enabled; perception at SHOOT APEX (unlike photoperiodism which is perceived in LEAVES).

• Key antagonisms: GA breaks dormancy ↔ ABA maintains dormancy; Auxin = apical dominance ↔ Cytokinin = lateral buds; Ethylene promotes abscission ↔ Auxin suppresses abscission.