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13.6 Control of Plant Growth and Development. Pages613-618. Photoperiod (page 608). Day length affects plants For example: flowering. Plant growth regulators. Chemicals that direct plant growth and differentiation. Tropism. External stimulus directs the change in a plant’s growth
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13.6 Control of Plant Growth and Development Pages613-618
Photoperiod (page 608) • Day length affects plants • For example: flowering
Plant growth regulators Chemicals that direct plant growth and differentiation.
Tropism • External stimulus directs the change in a plant’s growth For example: Phototropism-the bending of a plant towards the light
Gravitropism • Gravity affects growth • Roots grow downwards and shoots grow upwards
Thigmotropism • Objects influence plant growth For example: rocks, trellises
Auxins • Made in the shoot apical meristem • Stimulate cell elongation • Responsible for phototropism
Auxinscont… • Herbicide • Simultaneously ripens fruit in orchards • Promotes apical dominance • Promotes rooting, growth of vascular cambium and forms lateral buds
Apical dominance • Removing apical meristem (auxins) allows lateral meristem to grow
Gibberellins • Produced by young shoot tissues and developing seeds • Promote cell division and elongation • Promote flowering and fruit production • Help to access carbohydrate reserves
cytokinins • Promote cell division • Found in meristems, young leaves and growing seeds • Stimulates lateral meristem growth • Slows cell aging
Ethylene • Plant stress hormone • Drought…plant loses its leaves • Ozone…reduces plant yield • Lateral growth of roots around stones • Fruit ripening • Flower opening • Fruit and leaf drop
Abscisic Acid • (ABA) inhibits growth • Maintains dormancy in leaf buds and seeds • Closes stomata to conserve water