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Chapter 31.docx

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Tristan Long

Chapter31PlantGrowthandDevelopmentPlant growth and developmentto understand diversity of plant structures and life histories need to understand role that signal response pathways play in their growth and developmentSignal Response PathwaysHormones and environmental stimuli alter behavior of target cellsSignal molecules bind to receptors in target cellsElicit cellular response different response in different tissuesBy means of a response pathway signal can Induce changes in cells shape or internal structureInfluence cells metabolismAlter gene activation and rate of protein synthesisSet in motion events that modify existing cell proteinsSome hormones and growth factors bind to receptors at target cells plasma membrane on ER or in cytoplasmBinding triggers release of internal second messengers that diffuse through cytoplasm and provide main chemical signal that alters cell functioningReaction sequence amplifies cells response to signalPlant Hormones 7 major classes Auxins promote growthGibberellins stimulate growth including the elongation of stemsCytokinins enhance growth and retard agingEthylene regulates a range of responses including senescenceBrassinosteroids regulate plant growth responsesAbscisic acid suppresses growth and influences responses to environmental stressJasmonatesand oligosaccharins regulate growth and have roles in plant defenseAuxinsMainly indoleacetic acid IAA Synthesized primarily in shoot apical meristem and young stems and leavespromotes elongation of cells in shootsinhibits cell elongation in rootsGoverns growth responses to light and gravity Phototrophism in seedlingsrays from the sun strike one side of a shoot tipAuxins diffuses down from the shoot tip to cell on its shaded sideThe auxinstimulated cells elongate more quickly causing the seedling to bendAuxin Effects on Stems Frequently promotes axial elongation of stemsMaintain apical dominanceinhibits growth of lateral meristems branching
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