Wang Peng, Duan Wei, Takabayashi Atsushi, Endo Tsuyoshi, Shikanai Toshiharu, Ye Ji-Yu, Mi Hualing
National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
Plant Physiol. 2006 Jun;141(2):465-74. doi: 10.1104/pp.105.070490. Epub 2006 Jan 20.
In this study, the function of the NAD(P)H dehydrogenase (NDH)-dependent pathway in suppressing the accumulation of reactive oxygen species in chloroplasts was investigated. Hydrogen peroxide accumulated in the leaves of tobacco (Nicotiana tabacum) defective in ndhC-ndhK-ndhJ (DeltandhCKJ) at 42 degrees C and 4 degrees C, and in that of wild-type leaves at 4 degrees C. The maximum quantum efficiency of PSII decreased to a similar extent in both strains at 42 degrees C, while it decreased more evidently in DeltandhCKJ at 4 degrees C. The parameters linked to CO(2) assimilation, such as the photochemical efficiency of PSII, the decrease of nonphotochemical quenching following the initial rise, and the photosynthetic O(2) evolution, were inhibited more significantly in DeltandhCKJ than in wild type at 42 degrees C and were seriously inhibited in both strains at 4 degrees C. While cyclic electron flow around PSI mediated by NDH was remarkably enhanced at 42 degrees C and suppressed at 4 degrees C. The proton gradient across the thylakoid membranes and light-dependent ATP synthesis were higher in wild type than in DeltandhCKJ at either 25 degrees C or 42 degrees C, but were barely formed at 4 degrees C. Based on these results, we suggest that cyclic photophosphorylation via the NDH pathway might play an important role in regulation of CO(2) assimilation under heat-stressed condition but is less important under chilling-stressed condition, thus optimizing the photosynthetic electron transport and reducing the generation of reactive oxygen species.
在本研究中，对依赖NAD(P)H脱氢酶（NDH）的途径在抑制叶绿体中活性氧积累方面的功能进行了研究。过氧化氢在42℃和4℃时在ndhC-ndhK-ndhJ（DeltandhCKJ）缺陷的烟草（Nicotiana tabacum）叶片中积累，在4℃时在野生型叶片中也有积累。在42℃时，两种菌株中PSII的最大量子效率均下降到相似程度，而在4℃时，DeltandhCKJ中的下降更为明显。与CO₂同化相关的参数，如PSII的光化学效率、初始上升后非光化学猝灭的降低以及光合O₂释放，在42℃时DeltandhCKJ中比野生型受到更显著的抑制，在4℃时两种菌株均受到严重抑制。而由NDH介导的围绕PSI的循环电子流在42℃时显著增强，在4℃时受到抑制。在25℃或42℃时，野生型中跨类囊体膜的质子梯度和光依赖的ATP合成高于DeltandhCKJ，但在4℃时几乎不形成。基于这些结果，我们认为通过NDH途径的循环光合磷酸化在热胁迫条件下对CO₂同化的调节中可能起重要作用，但在冷胁迫条件下不太重要，从而优化光合电子传递并减少活性氧的产生。
