Saturday, 4 September 2010

Hormone in plants

Auxin (IAA)
  1. Cell enlargment/growth by vacuolation & elongation (acid growth hypothesis)
  2. Tropism (photo/geo)
  3. Stimulate production of meristem - callus tissue at injury
  4. Apical dorminance / Inhibit lateral bud
  5. Induce root initiation
  6. Promote fruit growth (parthenocarpy)
  7. Inhibit abscission in leaves & flowers
  8. Inhibit auxiliary bud growth - potato tube
  9. Defoliation - increase 2,4,5 trichlorophenoxyacetic acid - Vietnam war - fall of leaves
  10. Weed killer
Gibberellins
  1. Promote stem elongation
  2. Breaks dormancy in seed & buds - winter
  3. Promote fruiting & parthenocarpy
  4. Inhibit apical dominance - promote side shoot growth
  5. Promote flowering in long day plants
  6. Strengthen stem of wheat - bigger grapes , stimulate amylase production in barley (commercial)
Cytokinins
  1. Promote cell division only if have auxin
  2. Delay senescense (aging) in leaves
  3. Inhibit apical dominance - lateral buds
  4. Inhibit lateral roots
  5. Prolong leafy vegetable storage, cut flower fresh, germination in seed
Abscisic Acid (eg: abscisin or dormin)
  1. Promotes dormancy in buds & seeds
  2. Antagonise effect of auxin, GA & cytokinin - inhibit growth of stem & root
  3. Promotes leaf fall (autumn) (inhibit synthesis of RNA, DNA - induce senescence & yellowing)
  4. Closure of stomata (stress condition, X water)
  5. Use comercially to drop fruits (cherry)
Ethene (Ethylene) - gas
  1. Inhibit growth of stem & root
  2. Promote ripening of fruits
  3. Breaks bud dormancy
  4. Promote defoliation
  5. Promote etiolation / yellowing of plants (when shaded)
  6. Induced flowering & fruiting in pineapples, ripening of tomatoes & citrus fruits (commercial)
 Interaction Between Hormones

Apical / Apex Dominance
  • Auxin - promote, inhibit lateral buds
  • Gibberellins - enhance IAA
  • Kinetin breaks dormancy temporarily
  • Kinetin & IAA - break dormancy completely
Lateral Bud Growth
  • Gibberellins & cytokinns enhance each other (suppress apical dominance)
Roots
  • Auxin promote lateral roots & supperss apical dominance (antoginase with cytokinins)


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