In vivo changes of the oxidation-reduction state of NADP and of the ATP/ADP cellular ratio linked to the photosynthetic activity in Chlamydomonas reinhardtii
In vivo changes of the oxidation-reduction state of NADP and of the ATP/ADP cellular ratio linked to the photosynthetic activity in Chlamydomonas reinhardtii
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DOI：
10.1104/pp.102.018861
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发表时间：
2003-07-01
期刊：
影响因子：
7.4
通讯作者：
Finazzi, G
中科院分区：
文献类型：
--
作者：
Forti, G;Furia, A;Finazzi, G
测量了绿色莱茵衣藻全细胞提取物中ATP/ADP和NADP/NADPH的比值，以了解它们在体内通过卡尔文循环同化CO2的可用性。在需氧和厌氧细胞的暗光转换期间，在饱和或低光强度的照明下进行测量。观察到两种不同的行为模式：（a）在厌氧细胞中，在O-2进化之前的滞后期间，ATP的合成没有NADP/NADPH比率的变化，与循环电子流的操作一致。(b)在有氧，照明增加ATP/ADP比率独立的强度使用，而NADPH的量减少限制光子通量和饱和光子通量下恢复暗适应水平。此外，在这些条件下，除了低浓度的解偶联剂刺激光合O-2的演变。这些结果表明，光合作用产生的还原当量，而不是ATP的形成率限制了光合同化的CO2在C。reinhardtii细胞这种情况是C所特有的。reinhardtii，因为NADPH和ATP都不限制植物叶片中的这一过程，如大麦（Hordeum vulgare）叶片中光照后其增加所示，与光强度无关。实验的目的是评估不同的生理过程，可能会增加光合ATP/NADPH比率的Mehler反应，呼吸ATP供应后，通过苹果酸/草酰乙酸穿梭，和循环电子流周围的PSI，这种代谢情况下的还原当量的转移的贡献。
The ATP/ADP and NADP/NADPH ratios have been measured in whole-cell extract of the green alga Chlamydomonas reinhardtii, to understand their availability for CO2 assimilation by the Calvin cycle in vivo. Measurements were performed during the dark-light transition of both aerobic and anaerobic cells, under illumination with saturating or low light intensity. Two different patterns of behavior were observed: (a) In anaerobic cells, during the lag preceding O-2 evolution, ATP was synthesized without changes in the NADP/NADPH ratio, consistently with the operation of cyclic electron flow. (b) In aerobiosis, illumination increased the ATP/ADP ratio independently of the intensity used, whereas the amount of NADPH was decreased at limiting photon flux and regained the dark-adapted level under saturating photon flux. Moreover, under these conditions, the addition of low concentrations of uncouplers stimulated photosynthetic O-2 evolution. These observations suggest that the photosynthetic generation of reducing equivalents rather than the rate of ATP formation limits the photosynthetic assimilation of CO2 in C. reinhardtii cells. This situation is peculiar to C. reinhardtii, because neither NADPH nor ATP limited this process in plant leaves, as shown by their increase upon illumination in barley (Hordeum vulgare) leaves, independent of light intensity. Experiments are presented and were designed to evaluate the contribution of different physiological processes that might increase the photosynthetic ATP/NADPH ratio-the Mehler reaction, respiratory ATP supply following the transfer of reducing equivalents via the malate/oxaloacetate shuttle, and cyclic electron flow around PSI-to this metabolic situation.