低钾对水稻不同叶位叶片光合特性及抗氧化系统的影响

研究了低钾条件下钾敏感型水稻品种"二九丰"不同叶位叶片的气体交换、荧光参数、色素和活性氧及抗氧化酶活性的变化。结果表明,随着叶位降低,对照和低钾处理的净光合速率(Pn)、气孔导度(Gs)、叶绿素(Chl)、类胡萝卜素(Car)、PSⅡ最大光化学量子产量(Fv/Fm)、PSⅡ实际光化学量子产量(ΦPSⅡ)、表观电子传递速率(ETR)、可溶性蛋白(SP)含量、超氧化物歧化酶(SOD)和过氧化物酶(POD)活性均显著下降,而胞间CO2浓度(Ci)、激发压(1-qP)、非光化学猝灭(qN)、超氧化物自由基(O2.-)产生速率、过氧化氢(H2O2)和丙二醛(MDA)含量却急剧升高。与对照相比,低钾胁迫加速了各叶位Pn的下降和Ci的上升,而Gs并无降低,说明Pn的降低主要是由非气孔引起的。低钾胁迫还明显降低Fv/Fm、ΦPSⅡ、ETR、Chl和SP含量、Chl/Car比率、及SOD和POD活性,促进了(1-qP)、O2.-产生速率、H2O2和MDA含量的升高。这些结果均说明低钾胁迫引起了PSⅡ光化学效率降低和能量耗散的不平衡,从而导致了叶片的早衰。相关性分析表明,PSⅡ的激发压的升高与Pn、Chl和SP的含量及SOD和POD活性呈极显著负相关,与O2.-产生速率、H2O2和MDA含量呈极显著的正相关。据此推测,激发压的升高可能介导了水稻在低钾条件下叶片早衰的起始过程。

EFFECTS OF LOW POTASSIUM STRESS ON PHOTOSYNTHETIC CHARACTERISTICS AND ANTIOXIDANT SYSTEMS IN DIFFERENT POSITION LEAVES OF RICE PLANTS

It was investigated that the alterations in characteristics of photosynthetic gas exchange and chlorophyll fluorescence parameters,contents of pigments,soluble proteins and reactive oxygen species(ROS),activities of antioxidant enzymes and malonyldialdehyde(MDA) content of leaves at different position of potassium-sensitive rice cultivar "Erjiufeng" plants grew under normal-or low-potassium conditions.The results showed that the net photosynthetic rate(Pn),stomatal conductance(Gs),chlorophyll(Chl),carotenoid(Car),PSⅡ maximum photochemical quantum yield(Fv/Fm),PSⅡ actual photochemical quantum yield(ΦPSⅡ),apparent electron transport rate(ETR),soluble protein content,superoxide dismutase(SOD) and peroxidase(POD) activities decreased significantly with lowering of leaf position in both plants,while intercellular CO_2 concentration(Ci),excitation pressure(1-qP),non-photochemical quenching(qN),superoxide radical(O_2~(·-)) generation rate,hydrogen peroxide(H_2O_2) and MDA contents significantly increased.Compared with the control plants,low potassium stress accelerated the decline of Pn and the increase of Ci,whereas Gs remained rather stable,which indicated that the decrease of Pn mainly resulted from the non-stomatal factors.Meanwhile,Fv/Fm,Φ_(PSⅡ),ETR,the contents of Chl and SP,the ratio of Chl/Car and the activities of SOD and POD were obviously reduced,whereas(1-qP),the generation rate of O_2~(·-)and the contents of H_2O_2 and MDA were drastically increased,indicating that low potassium stress caused the decline of PSⅡ photochemical efficiency and the imbalance of energy dissipation,therefore resulting in the pre-senescence of the leaves.Correlation analysis showed that PSⅡ excitation pressure was inversely correlated with Pn,the content of Chl and SP, and the activities of SOD and POD,and was positively correlated with the generation rate of O_2~(·-),the content of H_2O_2 and MDA.Therefore,it was hypothesized that the increase of excitation pressure in chlorophyll may mediate the onset of leaf pre-senescence in rice plants under low potassium condition.