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1、Chapter16GrowthandDevelopmentTHEVEGETATIVEPHASEOFDEVELOPMENTbeginswithembryo-genesis,butdevelopmentcontinuesthroughoutthelifeofaplant.Plantdevelopmentalbiologistsareconcernedwithquestionssuchas,Howdoesazygotegiverisetoanembryo,anembryotoaseedling?Howdonewp
2、lantstructuresarisefrompreexistingstructures?Organsaregen-eratedbycelldivisionandexpansion,buttheyarealsocomposedoftis-suesinwhichgroupsofcellshaveacquiredspecializedfunctions,andthesetissuesarearrangedinspecificpatterns.Howdothesetissuesforminaparticularp
3、attern,andhowdocellsdifferentiate?Whatarethebasicprinciplesthatgovernthesizeincrease(growth)thatoccursthroughoutplantdevelopment?Understandinghowgrowth,celldifferentiation,andpatternforma-tionareregulatedatthecellular,biochemical,andmolecularlevelsistheult
4、imategoalofdevelopmentalbiologists.Suchanunderstandingalsomustincludethegeneticbasisofdevelopment.Ultimately,developmentistheunfoldingofgeneticallyencodedprograms.Whichgenesareinvolved,whatistheirhierarchicalorder,andhowdotheybringaboutdevelopmentalchange?
5、Inthischapterwewillexplorewhatisknownaboutthesequestions,beginningwithembryogenesis.Embryogenesisinitiatesplantdevelop-ment,butunlikeanimaldevelopment,plantdevelopmentisanongoingprocess.Embryogenesisestablishesthebasicplantbodyplanandformsthemeristemsthatg
6、enerateadditionalorgansintheadult.Afterdiscussingtheformationoftheembryo,wewillexaminerootandshootmeristems.Mostplantdevelopmentispostembryonic,anditoccursfrommeristems.Meristemscanbeconsideredtobecellfactoriesinwhichtheongoingprocessesofcelldivision,expan
7、sion,anddiffer-entiationgeneratetheplantbody.Cellsderivedfrommeristemsbecomethetissuesandorgansthatdeterminetheoverallsize,shape,andstruc-tureoftheplant.Vegetativemeristemsarehighlyrepetitive—theyproducethesameorsimilarstructuresoverandoveragain—andtheirac
8、tivitycancon-340Chapter16tinueindefinitely,aphenomenonknownasindeterminategenesisandseeddevelopmentarehighlyordered,inte-growth.Somelong-livedtrees,suchasbristleconepinesandgratedprocesses,bothofwhichareiniti
