除草剂毒理学

PartI:Introduction,definition

FactorsaffectingitsactivityAbsorptionandTranslocationHerbicideMetabolismPartII:ModeofAction

HerbicideToxicology1PartIIntroductionAherbicideisapesticideusedtokillunwantedplants.Herbicidesarechemicalsthatinhibitorinterruptnormalplantgrowthanddevelopment.Weedicide

2PartIIntroductionWeedsareproductofhumansociety.Primitiveman,thegathererandhunter,wasnotconsciousofweedsinthemodernsense.Contemporarymanhascreatedtheconceptofweedasaplantinaplacewhereitisnotwanted.3PartIIntroduction2006年，生产农药130万吨（折100%），同比增长20%。其中杀虫剂50万吨，占39%；杀菌剂11万吨，占9%；除草剂39万吨，占30%。

4PartIIntroduction2006年我国进口农药4.3万吨,用汇2.1亿美元;出口农药保守估计39.8万吨,创外汇10.4亿美元.其中:除草剂出口22.3万吨(创外汇5.3亿美元),占出口的56%,占除草剂产量的57.6%.5PartIIntroductionSelectivity:Theherbicide’sabilitytokillcertainplantswithoutinjuringothersiscalledselectivity.SelectiveherbicideNon-selectiveherbicideContactherbicideSystemicherbicide61.Factorsaffectingherbicideactivity1).Soiltexture:Herbicideadsorptionisgreaterinfine-texturedsoilshighinorganicmatter

thanincoarse-texturedsoilslowinorganicmatter.Thus,alowerproportionofherbicideisavailableinthefine-texturedsoils,soahigherherbicideapplicationrateisrequiredtoprovidethesamelevelofweedcontrolasinacoarse-texturedsoil.71.Factorsaffectingherbicideactivity2).SoilmoistureSoilmoistureisimportantbecauseitinfluencesherbicideadsorptiontosoils.Therefore,theherbicideisunavailableforplantuptake.Adsorptionoccurswhenherbicidemoleculesadheretosoilparticlesandorganicmatter.Whileadsorbed,herbicidemoleculesareunavailableforabsorptionbyplants.81.FactorsaffectingherbicideactivityWatermoleculescompetewithherbicidemoleculesforadsorptionsitesonsoilparticlesandorganicmatter.Therefore,herbicideadsorptionishighestunderdrysoilconditions,andlowestinmoistsoils.Consequently,weedcontrolisgenerallybestwithmoistsoilconditionsbecausemoreherbicideisavailableforplantuptakeinthesoilsolutionorgaseousphase.91.Factorsaffectingherbicideactivity3).TemperatureSeedlingplantstendtobemoresusceptibletosoil-appliedherbicidesundercoolconditionsthanunderwarmtemperaturesbecauseplantemergenceisdelayedandmetabolismisslowed.Ontheotherhand,extremelyhightemperaturessometimesincreasecropinjurysimplybyplacingtheplantundermultiplestresses.101.FactorsaffectingherbicideactivityEnvironmentalsoinfluencesherbicideefficacybyaffectingplantgrowth.Plantsaregenerallymostsusceptibletopostemergenceherbicideswhenactivelygrowing.Extremeenvironmentalconditionsthatslowplantgrowthandthickenleafcuticlesoftenincreaseplanttolerancetoaherbicide.112.AbsorptionandTranslocationA)Foliarabsorption:cuticlewax(lipophilic):no-polarCuticlecutin(角质,hydrophilic):polarPectin(胶质):hydrophilic12a).Foliarabsorption13Foliarabsorption14a).FoliarabsorptionAbsorptionoffoliar-appliedherbicidesviathestomata(气孔)canalsobeanimportantrouteofentry.

15b).TranslocationinplantsContactherbicidesarenottranslocated.Contactherbicidesgenerallyareineffectiveforlong-termperennialweedcontrol.Systemicherbicidescanbetranslocatedtootherpartsoftheplanteitherinthexylem(木质部)orthephloem16b).TranslocationinplantsTheapoplastic(非原生质体)systemconstitutesthetotalcontinuumofintercellularspaces,cellwalls,andmaturexylem;itisconsideredtobenonliving.Apoplasticlymobileherbicides,whichareabsorbedbytheroots,followthesamepathwayaswater.17b).TranslocationinplantsThesymplastic(共质体)systemconstitutesthetotalcontinuumofprotoplasmthroughouttheplant,includingthecytoplasmofeachcell,theirinterconnectingplasmodesma(胞间连丝),andthephloem(韧皮部),itisconsideredtobeliving.18b).TranslocationinplantsSymplasticallymobileherbicides,whichareabsorbedbytheleaves,movealongwiththephotosynthate(光合作用产物)viathesamepathway.Phloem:injuredbyherbicide19Translocation20b).TranslocationinplantsHerbicidescanbetranslocatedinthexylem,thephloem,orboth.Herbicidestranslocatedonlyinthexylemaremosteffectiveassoil-appliedorearlypostemergencetreatmentsbecausetranslocationisonlyupward.Atrazine(莠去津)isagoodexampleofaherbicidethatistranslocatedonlyinthexylem.21b).TranslocationinplantsPhloemtranslocatedherbicidesthatmovedownwardandsuppressrootandrhizome(根茎)growth,aswellastopgrowth,providethebestperennialweedcontrol.2,4-Disexampleofsystemicherbicidesthatwilltranslocateinthephloemandprovidegood,long-termcontrolofcertainperennialweeds.223.HerbicideMetabolismMetabolismisoneofthemostimportantwaysaplantcanescapethetoxiceffectsofaherbicide.Herbicide-tolerantplantsoftenhavetheabilitytometabolizeorbreakdownthechemicaltononactivecompoundsbeforeitcanbuilduptotoxiclevelsatthesiteofaction.233.HerbicideMetabolismSusceptibleplantsareunabletodetoxifyherbicides.Selectivityofmanyherbicidesisbasedondifferingratesofmetabolism.

243.HerbicideMetabolismSiteexclusiontypeofherbicideresistance.Atrazine(莠去津)isineffectiveonresistantbiotypebecauseaconformationalchangeinthechloroplastpreventsitfrombindingatthesiteofaction.25PartII:HerbicideModeofActionHerbicidescanworkatvarioussitesinplants.Theygenerallyinterferewithaprocessessentialfornormalplantgrowthanddevelopment.Herbicidescanbeclassifiedbysiteofactionbasedonhowtheyworkandtheinjurysymptomstheycause.26PartII:HerbicideModeofActionTobeeffective,herbicidesmust1)adequatelycontactplants;2)beabsorbedbyplants;3)movewithintheplantstothesiteofaction,withoutbeingdeactivated;4)reachtoxiclevelsatthesiteofaction.27PotentialSitofActionPhotosynthesis(food)Respiration(energy)Aminoacids(proteins/growth)Lipids(cellmembranes)Pigments(energy/lightcapture)Mitosis(celldivision)28PartII:HerbicideModeofAction1).PhotosynthesisInhibitors2).PigmentInhibition3).AminoAcidSynthesisInhibition4).LipidSynthesisInhibition5).CellMembraneDisruption6).GrowthRegulators7).SeedlingGrowthInhibitors291.PhotosynthesisInhibitorsPhotosynthesisinhibitorsshutdownthephotosynthetic(foodproducing)processinsusceptibleplantsbybindingtospecificsiteswithintheplant'schloroplasts.Inhibitionofphotosynthesiscouldresultinaslowstarvationoftheplant.301.PhotosynthesisInhibitorsHowever,theplantexperiencesamorerapiddeaththatisbelievedtobeduetotheproductionofsecondarytoxicsubstances.Susceptibleplantstreatedwithaphotosyntheticinhibitordiefromabuildupofhighlyreactivemoleculesthatdestroycellmembranes.311.PhotosynthesisInhibitorsa、阻断电子由QA到QB的传递：取代脲类，三氮苯类b、抑制光合磷酸化：苯氟磺胺c、截获电子到NADP+的传递：百草枯。32331.PhotosynthesisInhibitorsTheselectiveactionoftriazine(三嗪类,如莠去津)herbicidesisprimarilydeterminedbydifferentialmetabolism.Plantspeciessuchascornandsorghumpossesstheglutathione-S-transferase(GST)enzymeandcanselectivelymetabolizetriazineherbicidesintonontoxicsubstances.341.PhotosynthesisInhibitorsSymptomologyInterveinalorveinal(叶脉)yellowingfollowedbydeathofplanttissuefromleafmarginsinwardPostemergenceapplicationscauserapidburningofplanttissueCropstoleranttopostappliedPI’smayexhibitspottedleafyellowingorbronzing351.PhotosynthesisInhibitorsSymptomBladex草净津;百得斯

Cotoran361.Symptom372.PigmentInhibitionThepigmentinhibitorherbicidesinterferewiththeproductionandprotectionofphotosyntheticpigments.Ultimately,chlorophyllproductionisinhibited,andplantfoliageturnswhite.382.PigmentInhibitionPigmentinhibitorspreventplantsfromformingphotosyntheticpigments.Asaresult,theaffectedplantpartsbecomewhitetotranslucent.ThenewlydevelopedfoliageofmanyplantspeciesissosensitivetoCommand(广灭灵)thatverysmallamountscanwhitennewplantgrowth.392.PigmentInhibitionTheseherbicidescausethegreenpigments(chlorophyll)inplantstobedestroyed.Withoutchlorophyll,plantscannotphotosynthesizeandwilldie.Theseherbicidesareprimarilyxylemtranslocated,sotheyaremosteffectiveaspreemergencetreatments.40Chlorophylsynthesisinhibition412.PigmentInhibitionAcifluorfen(杂草焚),fomesafen(虎威),Oxadiazon(恶草灵,农思它)Sunlightisnecessaryfortheseherbicidestokillorinhibitweeds.422.PigmentInhibition:SymptomologyPigmentinhibitorscausewhitefoliage(“albinogrowth”)insusceptibleplantsNewgrowthwillnotcontainthenormalgreenpigmentationnecessaryforphotosynthesisAlbino（白化）growthmaybeobservedwithinveinsandbetweenveins(primarilywithCommand)432.PigmentInhibition:SymptomologyCommandZorial443.AminoAcidSynthesisInhibitionTheseherbicidesinhibitaminoacidsynthesiswhichisnecessaryfortheformationofplantproteins.453.AminoAcidSynthesisInhibitionTheaminoacidsynthesisinhibitorsincludethefollowingherbicidefamilies:sulfonylureas(磺酰脲类),imidazolinones(咪唑啉酮类),sulfonamide(磺胺类),andaminoacidderivatives.Aminoacidsynthesisinhibitorsactonaspecificenzymetopreventtheproductionofspecificaminoacids,keybuildingblocksfornormalplantgrowthanddevelopment.463.AminoAcidSynthesisInhibition473.AminoAcidSynthesisInhibition(1)Theacetolactatesynthase(ALS乙酰乳酸合成酶)inhibitingherbicideshaveabroadspectrumofselectivityandareusedatlowratesassoil-appliedorpostemergencetreatmentsinavarietyofcrops.TheseherbicidesinhibittheactivityoftheALSenzyme,whichisinvolvedinthesynthesisofbranchchainaminoacids(leucine亮氨酸,ioleucineandvaline缬氨酸).483.AminoAcidSynthesisInhibitionAminoacidsareessentialbuildingblocksinproteinsandarerequiredforproductionofnewcells.ALSherbicidesarereadilyabsorbedbybothrootsandfoliageandtranslocatedinboththexylemandphloemtothesiteofactionatthegrowingpoints.Selectivityisbasedondifferentialmetabolismandsiteexclusion.493.AminoAcidSynthesisInhibition(2)TheEPSP(烯醇丙酮酰-莽草酸-磷酸合成酶)inhibitorherbicidesarereadilyabsorbedthroughplantfoliageandtranslocatedinthephloemtothegrowingpoints.TheseherbicidesinhibittheEPSPenzyme,whichisinvolvedinthesynthesisofthearomaticaminoacids(芳氨酸)(tyrosine酪氨酸,tryptophan色氨酸,andphenylalanine苯丙氨酸)503.AminoAcidSynthesisInhibitionGlyphosate(草甘膦,EPSP抑制剂)isarelativelynonselectivepostemergenceherbicidethatisinactiveinthesoilbecauseofadsorption.GlyphosateresistantcropswithanalternativeEPSPenzymehavebeendevelopedthroughgeneticengineering.513.AminoAcidSynthesisInhibition(3)Liberty(草铵磷,glufosinate)isabroad-spectrumpostemergenceherbicidethathasnosoilactivity.Libertyinhibitstheactivityoftheglutaminesynthetaseenzymethatisnecessaryfortheplanttoconvertammoniaintoothernitrogencompounds.523.AminoAcidSynthesisInhibitionConsequently,ammoniaaccumulatesandglutaminelevelsdecrease.Plantdamageprobablyoccursduetothecombinedeffectsofammoniatoxicityanddeficiencyofaminoacidsrequiredforothermetabolicprocesses.Libertyhaslimitedtranslocation,sothoroughspraycoverageofsmallweedsgenerallyprovidesthebestperformance.533.SymptomologyInjurysymptomsongrassincludestunting,purplecoloration,andinhibitedrootsystemswith“bottle-brush”appearanceBroadleafplantsymptomincludesformationofredorpurpleleafveins,yellowingofnewleaftissueandblackeningofterminalgrowthInitialyellowingfollowedbydeathofaffectedtissue543.SymptomologyCadre“yellowflash”553.Symptomology564.LipidSynthesisInhibitionTheseherbicidesactbydisruptinglipidbiosynthesisingrassplants.Plantcellsandcellularorganellesallcontainlipidmembranes.Therefore,theseherbicidesaffectcellmembraneintegrityinthemeristematic(分生组织的)areas.574.LipidSynthesisInhibitionLipidsynthesisinhibitorspreventtheformationoffattyacids,componentsessentialfortheproductionofplantlipids.Lipidsarevitaltotheintegrityofcellmembranesandtonewplantgrowth.Thelipidsynthesisinhibitorherbicidesinhibitasinglekeyenzymeinvolvedinfattyacidbiosynthesis.584.LipidSynthesisInhibitionThelipidsynthesisinhibitorherbicidesinhibitmeristematicactivitybyinhibitingtheacetyl-CoAcarboxylase(ACCase,乙酰辅酶A羧化酶)enzymethatisinvolvedinthesynthesisoflipidsandfattyacids.Fenoxiapro-p-ethyl骠马594.LipidSynthesisInhibition604.SymptomologyInitialinjuryinmeristematicregionsoccurswherenewestleavesaredevelopingTheseregionswillturnchlorotic,whichisfollowedbynecrosisTheaffectedareawillbecome“rotted”andwilleasilyseparatefromrestofplantInjurywilldevelopslowly(7to14days)614.Symptomology“rotted”meristem625.CellMembraneDisruptionCellmembranedisruptersarepostemergencecontactherbicidesthatareactivatedbyexposuretosunlighttoformoxygencompoundssuchashydrogenperoxide.Theseoxygencompoundsdestroyplanttissuebyrupturingplantcellmembranes.Destructionofcellmembranesresultsinarapidbrowning(necrosis)ofplanttissue.635.CellMembraneDisruptionThecellmembranedisruptorherbicidesdestroycellmembranes,causingcellcontentstoleakoutanddesiccationofplanttissue.Onabrightandsunnyday,herbicideinjurysymptomscanoccurin1to2hours.645.CellMembraneDisruptionThecellmembranedisruptersareprimarilynontranslocatedherbicidesthatarelightactivated.Paraquat(百草枯)anddiquat(敌草快)arerelativelynonselectivechemicalsusedtocontrolallexistingvegetationandaspreharvestdesiccants.Theseherbicidesquicklyformhighlyreactivecompoundsintheplantsthatrupturecellmembranes,causingthefluidstoleakout.655.CellMembraneDisruptionThoroughspraycoverageisessentialforgoodpostemergenceweedcontrol.Becausetheyarenottranslocatedtotheroots,theseherbicidesareineffectiveforlong-termperennialweedcontrol.665.SymptomologyRapidyellowingfollowedbydesiccationofaffectedplanttissueSymptomsgenerallyappearfirstonleaftips．Driftoroff-targetapplicationmayshowspeckledleafburn675.SymptomologyBlazerInjuryonPeanutValorInjuryonPeanut685.Symptomology696.GrowthregulatorherbicidesTheseherbicidesmimicnaturalgrowthhormones,andthus,upsetthenaturalhormonebalanceinplants.Theyaffectseveralplantprocessessuchascelldivision,cellenlargement,proteinsynthesisandrespiration.706.GrowthregulatorherbicidesThekillingactionofgrowth-regulatingchemicalsisnotcausedbyanysinglefactor,butratherbythedisruptionofseveralgrowthprocessesinsusceptibleplants.2,4-Disverysensitivetocottonplant716.SymptomologyBroadleafplantstemtwistingandcurlingLeavesonbroadleafplantsexhibitcupping,crinkling,strapping,ordrawstringaffectSymptomsongrassplantsincludeleafrolling,crinkling,bracerootfusionandmalformation.Also,flowersterilityandmissinggrainincrops.726.SymptomologyMalformedbracerootsBlastedgrainheads737.SeedlingGrowthInhibitorsSeedlinggrowthinhibitorsinterferewithnewplantgrowth,therebyreducingtheabilityofseedlingstodevelopnormallyinthesoil.Herbicidesinthesefamiliesmustbesoil-applied.Theseherbicidesareonlyeffectiveonseedlingofannualorperennialweeds.747.SeedlingGrowthInhibitorsTheseherbicidesincludebothseedlingrootinhibitorsand