Cd^(2+)胁迫对西瓜幼苗光合生理及活性氧代谢的影响

EFFECTS OF CADMIUM STRESS ON PHOTOSYNTHESIS AND ACTIVE OXYGEN METABOLISM IN THE LEAVES OF SMALL WATERMELON SEEDLINGS

通过盆栽试验,研究了土壤中Cd2+对西瓜(Citrullus vulgaris)幼苗光合特性及活性氧代谢的影响。结果表明:Cd2+降低了小型西瓜叶绿素总含量,改变了叶绿素a/b的值,其叶绿素总含量与土壤中Cd2+浓度极显著(P<0.01)负相关;减弱了西瓜幼苗的净光合速率(Pn),降低了胞间CO2浓度(Ci)、气孔导度(Gs)和蒸腾速率(Tr)。西瓜叶片中超氧阴离子自由基(·O2-)产生速率、过氧化氢(H2O2)和丙二醛(MDA)含量随着土壤中Cd2+浓度的升高而增加,且H2O2和MDA含量与Cd2+浓度极显著(P<0.01)正相关。在Cd2+胁迫下,过氧化氢酶(CAT)活性变化显著,其活性与H2O2含量、MDA含量极显著(P<0.01)负相关。Cd2+胁迫引起叶绿素等光合相关生理因子降低,是导致西瓜幼苗净光合速率降低的直接原因;活性氧代谢失调,脂膜过氧化加重是导致其净光合速率降低的另一重要原因。

Through pot experiment,the effects of cadmium stress on the leaf chlorophyll content,photosynthetic rate（Pn）,intercellular CO2 concentration（Ci）,stomatal conductance（Gs）,transpiration rate（Tr） and membrane lipid peroxidation of watermelon seedlings were studied.The results showed that cadmium stress reduced the chlorophyll content and changed the chlorophyll a /b ratio.It also reduced the Pn,Ci,Gs and Tr.There was significant negative correlation（P 0.01） between Cd2 ＋ concentration in the soil and total chlorophyll content of the watermelon leaves,and significant positive correlation（P 0.01） between Cd2 ＋ concentration in the soil to hydrogen peroxide（H2O2 ） and malondialdehyde（MDA） content.Samely,the positive correlation was significant（P 0.01） between catalase（CAT） activity and H2O2 content,CAT activity and MDA content.With the increasing of Cd2 ＋ concentration in the soil,superoxide anions（· O 2-）,H2O2 and MDA contents in watermelon leaves were elevated.Superoxid dismutase（SOD） and peroxidase（POD） activities varied similarly,but CAT activity changed remarkably under lower Cd2 ＋ concentration stress.It could be concluded that the direct reason of reduction of photosynthetic rate was that the cadmium stress reduced chlorophyll content and other relative photosynthetic physiological index,another reasons were the reduction of antioxidative enzymes activity and the membrane lipid peroxidation.