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Produced in root tips transported via xylem action of

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Unformatted text preview: duced in root tips, transported via xylem. Action of Cytokinins Action Promote cell division. Delay senescence of leaves. Delay senescence Can release lateral buds from apical dominance. Promote shoot formation in tissue cultures. Cytokinin/ Auxin Interactions In Tissue Cultures (p. 646-647; 609-610) 609-610 Auxin alone: rapid cell expansion, giant cells. Cytokinin alone: minimal effect Equal cytokinin + auxin: rapid cell divisionformation of many small undifferentiated cells (callus). Cytokinin + high auxin: root formation. High cytokinin + auxin: bud, shoot formation. Ethylene (p. 647; 611) 611 Ethylene Simple hydrocarbon: C2H4. Simple Leaking gas from 19th C gaslights caused defoliation of shade trees. shade Produced in many tissues, as response to stress or Produced during senescence/ ripening. during Moves via simple diffusion. Commercial uses—ripen green-picked tomatoes, etc. Action of Ethylene Action Fruit ripening. Leaf & flower senescence. Abscission. Usually Inhibits cell expansion. Triggers rapid stem elongation in aquatic species (rice, Triggers water lilies) during flooding. water Causes air spaces to develop in submerged tissues of Causes flooded plants. flooded ABA (Abscisic Acid) p. 649; 612 612 Paul Wareing (1949) isolated a powerful growth inhibitor from dormant buds. inhibitor Despite name, no role in abscission (abbreviation Despite ABA is preferred). ABA • Prevents seed germination. • Keeps buds dormant. • Root to shoot signaling during stress. • Triggers stomata to close Transported via phloem & xylem. Action of Abscisic Acid Action Prevents seed germination: • Mutant corn grains germinate on cob. Induces stomatal closu...
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