镉胁迫对菜豆叶片抗氰呼吸、抗氧化及PSⅡ光合特性的影响

Effects of cadmium stress on cyanide-resistant respiration, antioxidation, and PSⅡ photosynthetic characteristics of kidney bean leaves

为探究镉胁迫下抗氰呼吸(交替途径)对植物体的保护作用和可能存在的作用机制,以菜豆幼苗为研究材料,探讨镉胁迫对菜豆叶片抗氰呼吸、抗氧化和光系统Ⅱ(PSⅡ)光合特性的影响,以及抗氰呼吸对PSⅡ的影响是否与其参与抗氧化调节作用有关.结果显示:随镉处理浓度的增加,菜豆叶片抗氰呼吸能力和抗氧化酶[过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)、超氧化物歧化酶(SOD)]活性以及过氧化氢(H2O2)含量呈现先升高后降低趋势,而超氧阴离子自由基(O2^-)则逐渐显著上升;同时,菜豆幼苗叶片Fv′/Fm′(光适应下PSⅡ最大光化学效率)、Y(Ⅱ)(PSⅡ实际光化学效率)和qP(光化学淬灭系数)、ETR(PSⅡ光合电子传递速率)下降,而叶片非光化学荧光猝灭系数(NPQ)则上升.非镉胁迫条件下,叶面分别喷施H2O2、O2^-消除剂或抗氰呼吸抑制剂未对上述所测叶绿素荧光参数造成不良影响,且H2O2消除剂的施加使得qP和ETR显著提高.在镉胁迫下,叶面分别喷施H2O2或O2^-消除剂有效缓解了镉导致的PSⅡ光化学活性的降低,而抗氰呼吸抑制剂的施加则造成了镉胁迫造成的PSⅡ光化学活性的进一步下降以及H2O2和O2^-含量的进一步提高,并导致了CAT、POD、APX抗氧化酶活性水平的降低.上述研究结果表明,镉胁迫下抗氰呼吸可有效缓解镉胁迫导致的菜豆幼苗叶片活性氧的过量积累和抗氧化酶活性的上升以及PSⅡ光化学活性的下降;且抗氰呼吸对PSⅡ的保护作用可能与其调节抗氧化的功能有关.

To explore the protective effects and possible mechanisms of cyanide-resistant respiration(alternating pathway)of plants under cadmium stress, we investigated the effects of cadmium stress on cyanide-resistant respiration, antioxidation,and photosynthetic characteristics of photosystem Ⅱ(PS Ⅱ) in kidney bean leaves. We determined whether the effects of cyanide-resistant respiration on PS Ⅱ is related to its involvement in antioxidant regulation. The results showed that the ability of cyanide-resistant respiration, the activity of antioxidant enzymes [including superoxide dismutase(SOD), catalase(CAT), peroxidase(POD), and ascorbate peroxidase(APX)] and the content of hydrogen peroxide(H2O2) first increased but then decreased with the increase in cadmium concentration, whereas the superoxide anion radical(O2^-)) content significantly increased with the increase in cadmium concentrations. Simultaneously, the effective photochemical quantum yield of PS Ⅱ photosynthetic [Y(Ⅱ)], photochemical quenching coefficient(qP), and rate of non-cyclic electron transport through PS Ⅱ(ETR)of the leaves decreased. However, the non-photochemical quenching(NPQ) of leaves increased with the increase in cadmium concentration. Under conditions without cadmium stress, spraying with exogenous eliminator of H2O2 and O2^- or inhibitor of cyanide-resistant respiration on the leaf surface did not adversely affect chlorophyll fluorescence parameters, but qP and ETR significantly increased with the application of H2O2 eliminator. Under cadmium stress, treatment with the exogenous eliminator of H2O2 and O2^- could effectively alleviate the decrease in photochemical activity of PS Ⅱ, whereas treatment with the inhibitor of cyanide-resistant respiratory pathway caused further decrease in PS Ⅱ photochemical efficiency, increase in reactive oxygen species level, and decrease in antioxidant enzyme activities. The results showed that cyanide-resistant respiration can effectively alleviate the excessive accumulation of reactive oxygen species, increase of antioxidant enzyme activity, and decrease the PS Ⅱ photochemical activity in the kidney bean seedling leaves caused by cadmium stress. Furthermore, the function of the cyanide-resistant respiratory pathway in protecting the PS Ⅱ from Cd stress could be related to the ability of the cyanide-resistant respiratory pathway to regulate the antioxidant capacity of plants.