模拟酸雨对龙眼叶片PSⅡ反应中心和自由基代谢的影响

Effects of simulated acid rain stress on the PSⅡ reaction center and free radical metabolism in leaves of longan

酸雨对植物光合机构的伤害机理一直是生态学研究的热点之一,为了探讨叶面酸化导致的PSⅡ反应中心损伤和光合机构自由基累积之间的内在联系,以1年生龙眼(Dimocarpus longana Lour.)实生小苗为研究对象,采用盆栽试验,研究了模拟酸雨胁迫对龙眼叶片叶绿素荧光参数和自由基代谢的影响。结果表明:酸雨胁迫改变了龙眼叶片的快速叶绿素荧光诱导动力学曲线形状,伤害PSⅡ反应中心;pH2.5酸雨胁迫5d后最大光化学效率(Fv/Fm)、PSⅡ反应中心活性(1/FO-1/FM)、反应中心含量(RC/CSO)急剧下降;有活性反应中心的关闭程度(VJ)、失活反应中心的比例(Non-QA和Non-QB)显著增加,QA迅速还原;放氧复合体(OEC)被破坏;PSⅡ受体侧电子传递体数(Sm)、电子转化效率(ψO)和电子传递速率(φEo)明显降低,叶面酸化导致光系统线性电子传递受损。pH2.5酸雨胁迫5d后叶片超氧阴离子自由基(O.2-)、过氧化氢(H2O2)和丙二醛(MDA)含量显著增加;抗坏血酸(AsA)和谷胱甘肽(GSH)转化为氧化型,还原型减少;超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDAR)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)活性下降,叶绿体内自由基不能被及时清除,过多的自由基损伤光合器官,导致龙眼叶片PSⅡ受伤害。模拟酸雨胁迫伤害龙眼叶片PSⅡ反应中心供体侧和受体侧的电子传递体,造成同化力不足,清除自由基能力下降,导致叶绿体自由基累积,光合机构受到伤害。

Injury mechanism of acid rain on the photosynthetic apparatus of plants has been one of the hot spots of the ecological research. To elucidate the relationship between the damage of reaction center and the accumulation of free radicals in photosynthetic system due to foliar acidification, one-year old longan （Dimocarpus longana Lour. cv. Wulongling） seedlings grown in pots were used to study the effects of simulated acid rain stress on chlorophyll fluorescence parameters, free radical metabolism and their recovery. The results showed that, under acid rain stress, the curve of chlorophyll fluorescence was quickly changed and PS Ⅱ reaction center was damaged. Maximum photochemistry efficiency of PS Ⅱ （Fv/Fm）, the activity of PS Ⅱ reaction center （1/F0- 1/FM） and the density of active reaction center （RC/CS0） decreased significantly after 5d stress with acid rain of pH2.5. The closure degree of active reaction center （VJ） and the percentage of inactive reaction center （ Non-QA and Non-QB ） increased, whereas the QA was reduced rapidly. The oxygen releasing complexes were destructed, and the number of electron transducer of PS Ⅱ receptor （ Sm ）, the electronic conversion efficiency （ψ0）, the transduction rate of electron （ψEo） all decreased significantly. These results displayed that foliar acidification inhibited the linear electronic transduction of PS Ⅱ reaction center. The results of free radical metabolism of longan indicated the contents of O2-, H2O2 and MDA increased significantly after 5d stress with acid rain of pH2.5. AsA and GSH converted to oxidized form, the contents of reduced form decreased, and the activities of SOD, APX, MDAR, DHAR and GR all reduced significantly. The inability of scavenging the free radicals in chloroplast in time resulted in the attack of photosynthetic organs by the redundant free radicals and thus the damage of PS Ⅱ of longan leaves. Taken together, we concluded that acid rain stress damaged the oxidation and reduction sides of the reaction centers of PS Ⅱ of the leaves in longan, and further decreased the linear electronic transduction to result in the weakened the scavenging of free radicals, the accumulation of free radicals in apparatus more. shortage of assimilatory power which chloroplasts destructed photosynthetic