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Plant hormones

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Plant hormones

  1. 1. PLANT HORMONESPROMOTE CELL DIVISION: CYTOKININS
  2. 2. WHERE IT PRODUCED ? Cytokinin are synthesized primarily in actively growing tissues, particular in roots, embryos and fruits and transported to other organs, although there are many minor sites of production as well. Cytokinin produced in the root reach to their target tissues by moving up the plant in the xylem sap.
  3. 3. HOW IT CONTROL CELL DIVISION Cytokinin will stimulate cell division and influenced the pathway of differentiation when acting with auxin hormone. In some experiment, a piece of parenchyma tissue from stem is cultured. This is some observation of the effect on cytokinin in cell tissue Abcent of cytokinin Added cytokinin & Added cytokinin only auxin The cell grow very The cell is grow and No effect large but do not divide divided
  4. 4. HOW IT CONTROL CELL DIVISION The ratio of cytokinins to auxin controls the cell differentiate. When the concentration of these 2 hormone are at certain level, the mass of cell continues to grow, but remains undifferentiated called a callus. Cytokinin level increase Auxin level increase Shoot buds develop from callus Root form
  5. 5. FUNCTION OF CYTOKININ A list of some of the known physiological effects caused by cytokinins are listed below Stimulates Stimulates the morphogenesis growth of lateral Stimulates cell (shoot initiation/bud buds-release of division. formation) in tissue apical dominance. culture. Stimulates leaf Cytokinins can slow expansion resulting Slow deterioration down the aging of from cell of leaves on intact some plant organs. enlargement. plant.
  6. 6. STIMULATES ABSCISION & THEREPENING OF FRUIT : ETHYLENE
  7. 7. WHERE IT PRODUCED? Ethylene is the gaseous hormone that can be produced by most all part of the plant. It produced in high concentrations during senescence, leaf abscission, and the ripening of some type of fruits. This hormone synthesis is also stimulated by wounding & stress (drought, flooding, mechanical pressure, injury, & infection).
  8. 8. The triple response to mechanical senescene stress Triple response is occur when Senescence is natural process aging ethylene initiate a seedling to in plants perform a growth maneuver Ethylene play importance role e.g In the triple response, stem shedding of a leaf in autumn, elongation is slow, the stem withering of flower, & death of an thicken & curvature causesthe annual after flowering stem to start growing horizontally Apoptosis = the onset of programmed cell death, It induced by mechanical stress on the stem tip During apoptosis , newly formed enzyme breakdown chemical compound
  9. 9. Leaf Fruitabscission ripening The process of abscission A burst of ethylene production in the occurs in autumn when a fruit help triggers the ripening process leaf falls A change in the ratio of A chain reaction occur during ripening ethylene to auxin controls is abscission. 1) ethylene trigger ripening. 2) ripening trigger more ethylene. E.g positive feedback in physiologi An aging leaf produces less & less auxin and this make the cell of the abscisssion Ethylene is gas , the signal to ripen to layer more sensitive to ripen spread from fruit to fruit.for ethylene example if you want to speed up fruit ripening, storing it in paper bag.
  10. 10. Promotes bud & seed dormancy abscisic
  11. 11. Where it produced?  Almost plant has ability to synthesize ABA.  It presence has been detected in every major organ & living tissue and may be transported in the phloem/xylem
  12. 12. ABSCISIC ACID (ABA) ABA is one of the hormone plant. Also called as abscisic II & dormin Function: inhibit growth, promote seed dormancy & inhibit early germination, promote stomatal closure during drought stress. ABA also promotes abscission of leaves and fruits ABA inhibits stem elongation probably by its inhibitory effect on gibberellic acid
  13. 13. EFFECT OF ABSCISIC ACID SEED DORMANCY DROUGHT TOLERANCE• One of major affect of ABA • ABA is the primary internal is seed dormancy. Seed signal dormancy has great survival - That enables plants to value because it ensure that withstand drought seed will germinate only - signaling turns on the when there are optimal expression of genes conditions of light, encoding proteins that temperature, & moisture. protect cells — in seeds as well as in vegetative tissues• Many types of dormant seed — from damage when they germinate when ABA is become dehydrated remove or inactive.
  14. 14. a) ABA in roots that b) ABA in the stem thatelongate the root for allow the stem to elongate water absorption to get sufficient light
  15. 15. Example of past year question
  16. 16. 1) Name three (3) common types of planthormones and discuss the main functions ofeach hormone (APR 2009) A. Cytokinin B. Ethylene C. Abscisic
  17. 17. • stem apex, auxillary buds  promotes cells division (release ofCytokinins apical dominance) • leaves  inhibits senescence Abscisic • Guard cells  close stomata • seed coat  inhibits seed acid germination •Stem  inhibits cell elongationEhtylene •fruits  promotes ripening
  18. 18. 2) Which plant hormones might be used to enhance stem elongation and fruit growth? (APR 2010) A. Auxins and gibberellins B. Ethylene and cytokinins C. Abscisic acid and phytochrome D. Phytochrome and flowering hormone

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