Differential use of two cyclic electron flows around photosystem I for driving CO2-concentration mechanism in C4 photosynthesis.
Differential use of two cyclic electron flows around photosystem I for driving CO2-concentration mechanism in C4 photosynthesis.
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DOI：
10.1073/pnas.0507095102
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发表时间：
2005-11
影响因子：
11.1
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中科院分区：
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光合作用中的线性电子流(LEF)同时产生ATP和NADPH，而围绕光系统I的循环电子流(CEF)被证明只产生ATP。CEF有两条可供选择的途径：NAD(P)H脱氢酶(NDH)和铁氧还蛋白：质醌氧化还原酶(FQR)依赖的流，但它们的生理相关性尚未详细阐明。同时，由于C(4)光合作用比C(3)光合作用需要更多的ATP来浓缩CO(2)，因此尚不清楚额外的ATP是如何产生的。在这项研究中，为了阐明CEF是否有助于C(4)光合作用所需的额外ATP，我们估计了四个C(4)物种中参与FQR依赖流的PGR5和NDH-H亚基的数量。尽管PGR5的表达谱与额外的ATP需求没有很好的相关性，但NDH在NAD-苹果酸酶(ME)物种的叶肉细胞和NADP-ME物种的束鞘细胞中大量表达，这些细胞对ATP的需求很强。我们的结果表明，通过NDH的CEF在驱动C(4)光合作用中CO(2)的浓缩机制中起着核心作用。
Whereas linear electron flow (LEF) in photosynthesis produces both ATP and NADPH, the cyclic electron flow (CEF) around photosystem I has been shown to produce only ATP. Two alternative routes have been shown for CEF; NAD(P)H dehydrogenase (NDH)- and ferredoxin:plastoquinone oxidoreductase (FQR)-dependent flows, but their physiological relevance has not been elucidated in detail. Meanwhile, because C(4) photosynthesis requires more ATP than does C(3) photosynthesis to concentrate CO(2), it has not been clear how the extra ATP is produced. In this study, to elucidate whether CEF contributes to the additional ATP needed in C(4) photosynthesis, we estimated the amounts of PGR5, which participates in FQR-dependent flow, and NDH-H, a subunit of NDH, in four C(4) species. Although the expression profiles of PGR5 did not correlate well with the additional ATP requirement, NDH was greatly expressed in mesophyll cells in the NAD-malic enzyme (ME) species, and in bundle-sheath cells in NADP-ME species, where there is a strong need for ATP in the respective cells. Our results indicate that CEF via NDH plays a central role in driving the CO(2)-concentrating mechanism in C(4) photosynthesis.