镉对玉米叶片光系统活性的影响

Effect of Cadmium on Photosystem Activities of Maize(Zea mays L.) Leaves

【目的】研究Cd对玉米叶片光系统活性的影响及其抑制光合性能的作用位点与方式,为进一步解释Cd对玉米叶片光合机构伤害机理提供理论依据。【方法】以郑单958和登海661为供试材料,3叶期开始以Hoagland营养液为养分来源,设置4个不同浓度Cd处理连续培养40 d,选择第8片展开叶测定气体交换参数、叶绿素荧光诱导动力学曲线及820 nm光吸收曲线,分析Cd抑制玉米叶片光合机构性能的主要原因。【结果】Cd胁迫下,PSⅡ电子供体侧K点荧光(Wk)和受体侧J点荧光(Vj)明显增加,与受体侧相比,供体侧性能下降导致PSⅡ性能(Ψo)降低。Cd胁迫使RuBP羧化酶活性和光能产物(NADPH)利用率显著降低,PSI电子积累量上升,RuBP羧化酶活性的下降使PSI 820 nm光吸收量(ΔIR/Io)快速降低,PSⅡ与PSI性能下降比率不同,造成两光系统协调性(Φ(PSI/PSⅡ))降低。【结论】Cd抑制叶片Pn由非气孔因素引起。Cd降低羧化系统活性,导致光能转化为化学能过程受阻,使过剩电子大量积累于PSI处;随Cd浓度增加,PSI性能降幅显著高于PSⅡ,二者协调性降低,导致Pn降低。

[ Objective] The effect of Cd on photosystem activities of maize leaves, and the action site and ways of Cd to photosynthesis were studied in order to provide a theoretical foundation for understanding of the injury mechanisms of Cd to the photosynthetic apparatus. [Method] Two maize varieties were chosen as materials. One is the common variety mainly planted in northem China, Zhengdan 958 （ZD958）. Another is a new variety with higher yielding potential, Denghai 661 （DH661）. Maize seedling was continuously cultured with different Hoagland＇s solution containing 0, 10, 30 and 60 umol·L-1 of CdSO4 after 3-lear-stage. After 40 days of treatment, the parameters of gas exchange, chlorophyll a fluorescence transient and light absorbance at 820 nm of maize leaves were measured for analying the injury reason of Cd to the photosynthetic apparatus. [ Result ] It was found that the declines of Pn were not mainly related to stomatic factors under Cd stress. After Cd treatment, both fluorescence at K-step （Wk） of PS II electron donor side and the fluorescence at J-step （Vj） of acceptor side were increased. However, the decrease of activity of electron donor side was lager than the electron acceptor side, which caused the decline of ψo. With the increase of Cd concentration, the activity of RUBP （Ribulose 1,5-Biphosphate） decreased significantly, the utilization rate of NADPH was also decreased. They caused the electron accumulation in PSI increased and the 820 nm light absorption of PSI （△IR/Io） decrease. And then, which caused the activity declined of PS II was not in keeping with PS I, thus depressed the coordination between PS II and PSI （Ф（PSI/PS II））. [Conclusion] Under the Cd stress, the main reason of Pn declined was not caused by non-stomata limitation. Cd decreased the activity of PS II electron donor side, which resulted in the performance of PS II declined and reduced the amount of electron transport to PS I. The most importantly, the increased amount of electron accumulation in PSI fed back by the carboxylation system was more than the decreased amount of electron transport form PS II that resulted in the PSI performance declined sharply, which depressed the coordination ofPS II and PS I, and caused Pn declining.