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Plant Hormones (Auxin (Cell Elongation (Promotes Proton Pumping into Wall…
Plant Hormones
Auxin
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- Promotes Proton Pumping into Wall by 2 mechanisms
A. Direct Activation of proton-pump enzymes (Bound auxin interacts directly with plasma membrane proton-ATPase AND/OR Second Messengers
b. New proton-pump enzymes synthesized (Auxin-induced messengers activate a gene expression with a synthesis of new plasma membrane proton-ATPase enzymes)
- Increases cell wall acidity so the cell wall becomes loosened due to the promotion expansion activity which breaks the H bonds between the polysaccharides in the wall.
- Longer term eefect include: Nutrient uptake and Synthesase of wall polysaccharides and proteins needed to maintain the walls thickness.
Phototropism (response to unilateral blue light by growing away from the light and cell elongation occurs in the shaded regions)
Gravitropism / GEotropism ( Response to gravity where auxin is distributed to the lower side of stem/ roots) Stemm bends upwards while roots bend down
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- Apical Dominance (Inhibition of Lateral (axillary) bud growth by shoot apex.. Auxin levels actually rise after apex removal (decapitation)
- Leaf Abscission (auxins from leaf prevents abscission so when the levels drop during senescence (ethylene promotion) abscission is triggered)
- Vascular Differentiation: This is induce by auxin in all organs in a polar manner Controls the regeneration of vascular tissue after wounding
- Lateral & Adventitious Root Formation Promoted (in roots can activate pericycle cells to develop into a lateral root)
- Fruit Development ( promoted by auxin and produced in pollen and developing seeds)
- Floral Bud Development ( required for normal floral development in Aarabidopsis)
Abscisic Acid
- Several Roles in the seed
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- Inhibits GA-induced enzyme production
- Closes stomata in response to water stress
- promtoes growth and inhibits shoot growth at low water potentials
- Promotes leaf senescence independently of ethylene.
Cytokinins
Stimulates Cell division and morphogenesis in tissue culture and the growth of lateral buds-release of apical dominance and leaf expansion resulting from cell enlargement
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Gibberellins
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Juvenility - external GAs regulates the transition fron juvenile to adult or reverse depending on the species.
Floral initiation & Sex Determination - GAs act as a mediator when the sex is determined by the genes and influenced by environmental factors. Interact with other PGR to regulate sex determination and stimulate a staminate flowers
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Ethylene
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Fruit ripening by softening the tissue and allowing enzymes to breakdown the cell walls. Hydrolysis of starch and sugar accumulation
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