干旱胁迫对玉米苗期叶片光合作用和保护酶的影响_张仁和

生态学报2011，31(5):1303—1311ActaEcologicaSinica．ecologica．cn基金项目:国家重点基础研究发展规划(973计划)项目(2009CB118604);国家自然科学基金项目(30971722);陕西省自然科学基金项目(2010JM3002)．收稿日期:2010-06-19;修订日期:2011-01-20*通讯作者Correspondingauthor．E-mail:[e-mail]．干旱胁迫对玉米苗期叶片光合作用和保护酶的影响张仁和，郑友军，马国胜，张兴华，路海东，史俊通，薛吉全*(西北农林科技大学农学院/黄土高原土壤侵蚀与旱地农业国家重点实验室，陕西杨凌712100)摘要:以玉米品种郑单958(抗旱性强)和陕单902(抗旱性弱)为材料，采用盆栽控水试验，设置3个干旱处理(轻度干旱，中度干旱，重度干旱)和正常灌水，研究了干旱胁迫对玉米苗期叶片光合速率、叶绿素荧光以及相关生理指标的影响。结果表明:(1)干旱胁迫下2个品种叶片净光合速率(Pn)和气孔导度(Gs)显著下降，胞间CO2浓度(Ci)出现了先下降后上升，而气孔限制值(Ls)上升后下降，说明中度干旱胁迫下叶片Pn下降是气孔因素引起的，重度干旱胁迫下Pn降低主要由非气孔因素引起的。(2)随着干旱胁迫的加剧，2个品种叶片光系统Ⅱ(PSⅡ)的实际量子产量(φPSⅡ)、电子传递速率(ETR)和光化学猝灭(qP)一直下降，而非光化学猝灭(qN)上升后下降，说明中度干旱下热耗散仍是植株重要光保护机制，重度干旱时叶片光合电子传递受阻，PSⅡ受到损伤。(3)干旱胁迫下2个品种叶片的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性先升高后降低，而丙二醛(MDA)含量一直升高，说明干旱胁迫初期对保护系统酶活性升高有诱导作用，重度胁迫下活性氧清除酶的活性下降，导致细胞膜伤害。这些结果暗示，轻度和中度干旱胁迫下2个玉米品种通过减少光捕获、热耗散和酶活性调节协同作用稳定了光合机构功能，是Pn下降的气孔限制因素;而重度干旱胁迫下光系统Ⅱ和抗氧化酶系统损伤，是Pn下降的非气孔限制因素;郑单958的各生理参数比陕单902受旱影响小，干旱胁迫下仍具有较高的光合效率和较强的保护酶活性是郑单958抗旱的主要生理原因。关键词:玉米;干旱胁迫;气体交换;叶绿素荧光;保护酶EffectsofdroughtstressonphotosynthetictraitsandprotectiveenzymeactivityinmaizeseedingZHANGRenhe，ZHENGYoujun，MAGuosheng，ZHANGXinghua，LUHaidong，SHIJuntong，XUEJiquan*CollegeofAgronomy，NorthwestA＆FUniversity/StateKeyLaboratoryofSoilErosionandDrylandFarmingontheLoessPlateau，，Yangling712100，ChinaAbstract:Droughtisamajorlimitingfactoraffectingmaizegrowth，developmentandyieldmainlyinaridandsemiaridregionsofChina．Butthephysiologicalmechanismrelatedtosimultaneouscomparisonofphotosyntheticresponseandprotectiveenzymeactivity，whichcouldbeusefulforidentifyingdifferencesinmaizecultivarsunderdroughtstress，remainsunclear．Theobjectiveofthisstudywastoinvestigatetheeffectsofdroughtstressonthephotosyntheticcharacteristicsofthedifferentmaizecultivarsattheseedlingstageandtoofferatheoreticalbasisandtechnicalparametersforsaving-waterandhighyieldcultivationofmaize．Twomaizecultivars，zhengdan958(droughttolerance)andshandan902(droughtsensitive)growninpotsexperimentingreenhouseweresubjectedtothreedifferentdroughttreatments(milddrought，moderatedrought，severedrought)andcomparedtonormalirrigation．Thegasexchange，chlorophyllfluorescence，andprotectiveenzymeactivityweretested．Theresultsshowedthat:(1)theonsetofdroughtstresscausedanincreaseofleaf'snetphotosyntheticrate(Pn)andstomatalconductance(Gs)，furthermore，intercellularCO2concentration(Ci)decreasedandthenincreased，butreversible，stomatallimits(Ls)increasedandthendecreasedunderdroughtstressintwocultivars．ThissuggestedthatreductionsinPnresultedfromstomatallimitationsundermildandmoderatedroughtstress;andfromnon-stomatallimitationsundertheseveredroughtstressinbothcultivars．(2)Inthechlorophyllfluorescenceparameters，．ecologica．cnleaf'sthequantumyield(φPSⅡ)，electrontransportrate(ETR)，photochemicalquenching(qP)decreasedwithincreasingdroughtstress，however，non-photochemicalquenching(qN)ofphotosystemⅡ(PSⅡ)activityincreasedsignificantlywiththedevelopingofdroughtstress，indicatingthatphotoprotectionwaseffective，whereasseverlydroughtstresscausedtheinhibitionofphotosyntheticelectrontransportleadingtodamageofPSⅡinthetwocultivars．(3)Underdroughtstresstheactivitiesofsuperoxidedismutase(SOD)，peroxidase(POD)，catalase(CAT)obviouslyincreasedandthendecreasedrapidly．Theincreaseofenzymeactivitiesindroughttolerancezhengdan958wasgreaterthanthatindroughtsensitiveshandan902．malondialdehyde(MDA)contentsincreasedcontinuously，beingsignificantlyhigherthanthatofthecontrol，theincreaseofMDAcontentsindroughtsensitiveshandan902wasgreaterthanthatindroughttolerancezhengdan958，whichcontributingtoregulateactivityoftheprotectionsystemduringtheinitialphaseofdroughtstress，andthenegativeeffectsofdroughtduringthestressperiodwereobserved．TheseresultsimpliedthatdroughtstressdepressedPnsignificantly，whichinducedbystomatallimitationandnon-stomatalfactorsatseedlingstage，underthemoderatedroughtstressthedecreasedPnweremainlyduetostomatallimitationsthroughstomatalregulation，theenhanceofthermaldissipationandantioxidantenzymejointly;undertheseveredroughtstressmajornon-stomatallimitationsresponsibleforreductioninPnwereassociatedwiththeimpairmentofPSⅡandantioxidantenzymesystem．Atsametime，thechangerangeofallphysiologicalparametersweresmallerinzhengdan958thaninshandan902．Basetheaboveresults，wespeculatethatzhengdan958maintainsthehigherphotosynthesisfunctionandthebetteroxidativeenzymedefensesystem'sabilitytoeliminatereactiveoxygencomparedtoshandan902underdroughtstress，whichcanbeconsideredasthemajorphysiologicaltraitsforitshigheryieldanddroughttolerance．KeyWords:maize;droughtstress;gasexchange;chlorophyllfluorescence;protectiveenzymeactivity干旱是抑制玉米生长和光合作用下降的重要原因［1-2］，阻碍CO2进入叶片，影响羧化中心对CO2的吸收，净光合速率(Pn)下降［3-4］。然而气孔关闭引起CO2同化量下降促使PSⅡ光化学活性与Pn电子需求不平衡［4-5］，吸收的过多光能导致光合机构的光抑制，严重时还可引起光破坏［6-7］。叶绿素荧光动力学参数可以较好地反映PSⅡ结构和功能变化［8］，作物在逆境条件下，耐性品种具有较高的耗散过多光能的能力，即具有较高的非光化学猝灭系数(qN)，以抵御不良环境［9］;但也存在相反的研究结果［10］，其原因是多仅从光合、荧光的角度研究干旱胁迫对作物光合性能的影响，其实逆境下植株除热耗散外，还可通过光呼吸、Mehler反应、叶黄素循环、活性氧清除系统等机制耗散过剩光能［11-6］。近年来已开始研究光氧化过程中叶片荧光特性和膜脂过氧化的关系，说明PSⅡ光能转化、活性氧代谢与逆境条件有密切联系［17-18］。因此，将光合作用与保护酶活性及其相互