Interaction between Starch Breakdown, Acetate Assimilation, and Photosynthetic Cyclic Electron Flow in Chlamydomonas reinhardtii
Interaction between Starch Breakdown, Acetate Assimilation, and Photosynthetic Cyclic Electron Flow in Chlamydomonas reinhardtii
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DOI：
10.1074/jbc.m112.370205
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发表时间：
2012-07-27
影响因子：
4.8
通讯作者：
Alric, Jean
中科院分区：
文献类型：
--
作者：
Johnson, Xenie;Alric, Jean
光合作用电子转移的光谱研究通常基于对电子转移链中从暗到亮的变化的监测。这些研究重点关注光合作用的光反应，也间接提供了黑暗中叶绿体氧化还原或代谢状态的信息。在这里，我们利用单细胞微藻莱茵衣藻，通过光系统 I 的光氧化初级电子供体 P700(+) 的分光光度检测，研究了异养/混合营养醋酸盐喂养对叶绿体碳代谢的影响。 P700(+)的动力学直接反映了叶绿体基质中还原剂(主要是NAD(P)H)的暗代谢产生。这样的结果可以与其他代谢研究相关：例如，在没有乙酸盐的情况下，P700（+）的还原率与之前报道的淀粉分解率相匹配，证实了衣藻糖酵解途径上游步骤的叶绿体定位。此外，还可以解决光合和非光合碳代谢之间相互作用的问题。我们发现，在用乙酸盐喂养的无淀粉突变体中，光系统 I 周围的循环电子流速度是 WT 中的两倍，并且我们涉及碳水化合物代谢中电子通量的变化如何通过氯呼吸调节黑暗中质体醌池的氧化还原平衡。
Spectroscopic studies on photosynthetic electron transfer generally are based upon the monitoring of dark to light changes in the electron transfer chain. These studies, which focus on the light reactions of photosynthesis, also indirectly provide information on the redox or metabolic state of the chloroplast in the dark. Here, using the unicellular microalga Chlamydomonas reinhardtii, we study the impact of heterotrophic/mixotrophic acetate feeding on chloroplast carbon metabolism by using the spectrophotometric detection of P700(+), the photooxidized primary electron donor of photosystem I. We show that, when photosynthetic linear and cyclic electron flows are blocked (DCMU inhibiting PSII and methylviologen accepting electrons from PSI), the post-illumination reduction kinetics of P700(+) directly reflect the dark metabolic production of reductants (mainly NAD(P)H) in the stroma of chloroplasts. Such results can be correlated to other metabolic studies: in the absence of acetate, for example, the P700(+) reduction rate matches the rate of starch breakdown reported previously, confirming the chloroplast localization of the upstream steps of the glycolytic pathway in Chlamydomonas. Furthermore, the question of the interplay between photosynthetic and non-photosynthetic carbon metabolism can be addressed. We show that cyclic electron flow around photosystem I is twice as fast in a starchless mutant fed with acetate than it is in the WT, and we relate how changes in the flux of electrons from carbohydrate metabolism modulate the redox poise of the plastoquinone pool in the dark through chlororespiration.