How PGRs, Growth Phases, and Differentiation Connect

SEED
  │ ABA → dormancy maintained
  │ GA + water → ABA/GA ratio shifts → GERMINATION
  │
  ↓
SEEDLING
  │ Geometric growth: both daughters divide
  │ Auxin from shoot apex → polarity established
  │ Cytokinin from roots → cell division
  │
  ↓
VEGETATIVE GROWTH
  │ Meristematic → Elongation → Maturation (differentiation)
  │ Parenchyma can undergo DEDIFFERENTIATION
  │ → Cambium (secondary growth)
  │ → Wound healing (callus)
  │
  ↓
FLOWERING (Triggered by:)
  │ Photoperiodism → Phytochrome → Florigen → Meristem transition
  │ Vernalization → FLC silencing → GA → Bolting → Flowering
  │
  ↓
FRUIT/SEED DEVELOPMENT
  │ Auxin + GA → Parthenocarpy (seedless) OR normal seeds
  │ ABA → Seed dormancy in developing seeds
  │
  ↓
RIPENING / SENESCENCE
  │ Ethylene → Fruit ripening → Climacteric burst
  │ ABA + Ethylene → Leaf senescence, abscission
  │ Cytokinin (low) → Chlorophyll lost → Yellowing

Key Connections for NEET

1. GA and ABA: Opposite roles in dormancy. Both are terpenoids.
2. Auxin and Cytokinin: Opposite roles in apical dominance. Together control tissue culture organogenesis.
3. Ethylene and Auxin: Ethylene promotes abscission; auxin suppresses it. Ethylene inhibits auxin transport.
4. Phytochrome and Photoperiodism: Pr/Pfr ratio is the molecular clock for flowering time.
5. Dedifferentiation → Totipotency: Plants can regenerate whole organisms from single cells because differentiation is epigenetically reversible.