400分求有关植物组织培养的英文文献资料

TheManyDimensionsofPlantTissueCultureResearch

R.DanielLineberger

ProfessorofHorticulture

TexasA&MUniversity

CollegeStation,TX77843

WebmasterofAggieHorticulture(http://aggie-horticulture.tamu.edu/)

INTRODUCTION

Thepracticeofplanttissueculturehaschangedthewaysomenurserymenapproachplantpropagation.Intherecentpast,theapplicabilityofthistechnologytothepropagationoftreesandshrubshasbeendocumented.Somefirmshaveestablishedtissueculturefacilitiesandcommercialscaleoperationsarepresentlyinoperationforthemasspropagationofapples,crabapples,rhododendrons,andafewotherselectedwoodyspecies.Theintentofthisresearchupdateistobrieflyexaminewhatisbeingdoneandtoexplorewhatcanbedonewithregardtothetissuecultureofornamentalplants.Suchaconsiderationnecessarilyincludesanoverviewoftissuecultureasapropagationtool.Themajorimpactofplanttissueculturewillnotbefeltintheareaofmicropropagation,however,butintheareaofcontrolledmanipulationsofplantsatthecellularlevelinwayswhichhavenotbeenpossiblepriortotheintroductionoftissueculturetechniques.

THEARTANDSCIENCEOFMICROPROPAGATION

Ofallthetermswhichhavebeenappliedtotheprocess,micropropagationisthetermwhichbestconveysthemessageofthetissueculturetechniquemostwidelyinusetoday.Theprefixmicrogenerallyreferstothesmallsizeofthetissuetakenforpropagation,butcouldequallyrefertothesizeoftheplantswhichareproducedasaresult.

Micropropagationallowstheproductionoflargenumbersofplantsfromsmallpiecesofthestockplantinrelativelyshortperiodsoftime.Dependingonthespeciesinquestion,theoriginaltissuepiecemaybetakenfromshoottip,leaf,lateralbud,stemorroottissue(Fig.1).Inmostcases,theoriginalplantisnotdestroyedintheprocess--afactorofconsiderableimportancetotheownerofarareorunusualplant.Oncetheplantisplacedintissueculture,proliferationoflateralbudsandadventitiousshoots(Fig.2)orthedifferentiationofshootsdirectlyfromcallus(Fig.3),resultsintremendousincreasesinthenumberofshootsavailableforrooting.Rootedmicrocuttingsorplantletsofmanyspecieshavebeenestablishedinproductionsituationsandhavebeensuccessfullygrownoneitherincontainersorinfieldplantings.Thetwomostimportantlessonslearnedfromthesetrialsarethatthismethodologyisameansofacceleratedasexualpropagationandthatplantsproducedbythesetechniquesrespondsimilarlytoanyown-rootedvegetativelypropagatedplant.Micropropagationoffersseveraldistinctadvantagesnotpossiblewithconventionalpropagationtechniques.Asingleexplantcanbemultipliedintoseveralthousandplantsinlessthanoneyear.Withmostspecies,thetakingoftheoriginaltissueexplantdoesnotdestroytheparentplant.Onceestablished,activelydividingculturesareacontinuoussourceofmicrocuttingswhichcanresultinplantproductionundergreenhouseconditionswithoutseasonalinterruption.Usingmethodsofmicropropagation,thenurserymancanrapidlyintroduceselectedsuperiorclonesofornamentalplantsinsufficientquantitiestohaveanimpactonthelandscapeplantmarket.

PLANTIMPROVEMENTTHROUGHTISSUECULTURE

Inintroducingthisresearchupdate,itwasmentionedthatthemajorimpactoftissueculturetechnologywouldnotbeintheareaofmicropropagation,butratherintheareaofcontrolledmanipulationsofplantgermplasmatthecellularlevel.Theabilitytounorganize,rearrange,andreorganizetheconstituentsofhigherplantshasbeendemonstratedwithafewmodelsystemstodate,butsuchbasicresearchisalreadybeingconductedonornamentaltreesandshrubswiththeintentofobtainingnewandbetterlandscapeplants.

SELECTIONOFPLANTSWITHENHANCEDSTRESSORPESTRESISTANCE

Perhapsthemostheavilyresearchedareaoftissueculturetodayistheconceptofselectingdisease,insect,orstressresistantplantsthroughtissueculture.Justassignificantgainsintheadaptabilityofmanyspecieshavebeenobtainedbyselectingandpropagatingsuperiorindividuals,sothesearchforthesesuperiorindividualscanbetremendouslyacceleratedusinginvitrosystems.Suchsystemscanattempttoexploitthenaturalvariabilityknowntooccurinplantsorvariabilitycanbeinducedbychemicalorphysicalagentsknowntocausemutations.

Allwhoarefamiliarwithbudsports,variegatedfoliageandothertypesofchimerashaveanappreciationforthenaturalvariabilityinthegeneticmakeuporexpressioninplants.Chimerasarethealteredcellularexpressionswhicharevisible,butforeachofthesewhichareobservedmanymoredifferencesprobablyexistbutaremaskedbytheoverallorganizationoftheplantasawhole.Forexample,eveninfrost-tenderspecies,certaincellsorgroupsofcellsmaybefrosthardy.However,becausemostoftheorganismiskilledbyfrost,thetolerantcellseventuallydiebecausetheyareunabletosupportthemselveswithouttheremainderoftheorganizedplant.Planttissuesgrowninvitrocanbereleasedfromtheorganizationofthewholeplantthroughcallusformation.Ifthesegroupsofcellsarethensubjectedtoaselectionagentsuchasfreezing,thenthosetolerantonescansurvivewhileallthosewhicharesusceptiblewillbekilled.Thisconceptcanbeappliedtomanytypesofstressaswellasresistancetofungalandbacterialpathogensandvarioustypesofphytotoxicchemicalagents.Thegoalofselectingsuchresistantcelllineswouldbetoreorganizewholeplantsfromthemwhichwouldretaintheselectedresistance(Fig.4).Currentresearchinthisareaextendsacrossmanyinterestsincludingattemptstoselectsalttolerantlinesoftomato,freezingresistanttobaccoplants,herbicideresistantagronomiccrops,andvariousspeciesofplantswithenhancedpathogenresistance.Imagine,ifyouwill,theimpactofafireblight-resistantBartlettpear,acloneofpinoakforalkalinesoils,oraselectionofsouthernmagnoliahardytozone4!

TISSUECULTUREANDPATHOGENFREEPLANTS

Anotherpurposeforwhichplanttissuecultureisuniquelysuitedisintheobtaining,maintaining,andmasspropagatingofspecificpathogen-freeplants.Theconceptbehindindexingplantsfreeofpestsiscloselyalliedtotheconceptofusingtissuecultureasaselectionsystem.Planttissuesknowntobefreeofthepathogenunderconsideration(viral,bacterial,orfungal)arephysicallyselectedastheexplantfortissueculture.Inmostcases,theapicaldomesofrapidlyelongatingshoottipsarechosen(Fig.5).Theseareallowedtoenlargeandproliferateunderthesterileconditionsofinvitroculture(Fig.6)withtheresultingplantletstestedforpresenceofthepathogen(aprocedurecalledindexing).Cultureswhichrevealthepresenceofthepathogenaredestroyed,whilethosewhichareindexedfreeofpathogenaremaintainedasastockofpathogen-freematerial.Proceduressimilartothesehavebeenusedsuccessfullytoobtainvirus-freeplantsofanumberofspeciesandbacteria-freeplantsofspeciesknowntohavecertainleafspotdiseases.Theimpactofobtainingpathogen-freenurserystockcanonlybespeculative,sincelittleresearchdocumentingviral,bacterial,orfungaldiseasestransmittedthroughpropagationofwoodyornamentalsisavailable.

SOMATICHYBRIDIZATION

Theabilitytofuseplantcellsfromspecieswhichmaybeincompatibleassexualcrossesandtheabilityofplantcellstotakeupandincorporateforeigngeneticcodesextendtherealmofplantmodificationsthroughtissueculturetothelimitsoftheimagination.Mostsuchmanipulationsarecarriedoutusingplantprotoplasts.Protoplastsaresinglecellswhichhavebeenstrippedoftheircellwallsbyenzymatictreatment.Asingleleaftreatedundertheseconditionsmayyieldtensofmillionsofsinglecells,eachtheoreticallycapableofeventuallyproducingawholeplant.Thisconcepthasfueledspeculationasdiverseasthepossibilitiesofobtainingnitrogen-fixingcornplantsontheoneextremetodiscoveringayellow-floweredAfricanvioletontheotherextreme.

Theobservationthathasprovidedtheimpetusformostofthisresearchisthatwhencellsarestrippedoftheircellwallsandbroughtintoclosecontact,theytendtofusewitheachother(Fig.7).Thissomatichybridizationisnotsubjecttothesameincompatibilityproblemsthatlimittraditionalplantbreedingstrategies.ItisconceivablethenthatonecouldhybridizeaJuneberrywithacrabappleoraplum,butthefundamentalresearchrequiredtodemonstratesuchaneventhasyettobeconducted.

ThepotentialuseofsomatichybridizationtobringaboutnovelcombinationsofgeneticmaterialhasbeendemonstratedinthegeneraPetuniaandNicotiana.ResearchfundedinpartbytheHorticulturalResearchInstituteattheUniversityofWisconsinisinvestigatingthefeasibilityofusingsuchtechniqueswithwoodyspecies.BrentMcGownandco-workershavesucceededinobtainingnakedcellsfromtissueculturesofBetulaandRhododendron,butasofyet,theyhaveneitherobtainedplantsfromsinglecellsnotachievedcellularfusion.However,furtherresearchinthisareapromisestohaveatremendousimpactonourconceptsofwoodyplantdiversity.Justasremarkableastheideaoffusingplantprotoplastsistheideaofincorporatingforeigngeneticmaterialintothegeneticcodeofplantcells.Suchtransformationshavebeencarriedoutintheso-calledgene-splicingexperimentswheretheinformationformakinginsulinwasincorporatedintobacteria.Notonlyisthedesiredinformationtransmittedtosucceedinggenerationsofbacteria,butthebacterialculturesbecomesynthesizersofinsulinaswell.Plantcellscanbemadetotakeupforeigngeneticcodes,butevidencethatthiscanbetransmittedintothedaughtercellsandservetheintendedfunctionislacking.Whatif,forexample,thegeneticinformationforaccumulatingaveryhighsugarcontentisincorporatedintoacloneofsugarmaples?Onecouldthinkofenoughwhatif誷inthiscategorytofillseveralvolumes!

SUMMARY

Planttissuecultureresearchismulti-dimensional.Whilemostnurserymenhavebeenintroducedtothetechniquesandadvantagesofmicropropagation,fewhaveventuredtouseitasapropagationtool.Theapplicabilityofmicropropagationforwoodytreeshasbeendemonstratedasfeasiblesinceallaspectsofthetechnologyhaveconfirmedthefactthattreesproducedbythismethodlooklikeandgrowliketheircounterpartsproducedbytraditionalmethodsofcloning.

Otherdimensionsoftissuecultureresearchhavebeenlesswellpublicized.Thepotentialforselectingpathogenfreeplants,forselectingstress-tolerantandpathogen-resistantclonesofplants,andthenovelgeneticcombinationstobeachievedthroughsomatichybridizationarealllinesofresearchwhichcanhaveaprofoundimpactonthenurseryindustry.