The pgr1 mutation in the Rieske subunit of the cytochrome b6f complex does not affect PGR5-dependent cyclic electron transport around photosystem I
The pgr1 mutation in the Rieske subunit of the cytochrome b6f complex does not affect PGR5-dependent cyclic electron transport around photosystem I
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DOI：
10.1074/jbc.m505703200
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发表时间：
2005-08-05
影响因子：
4.8
通讯作者：
Shikanai, T
中科院分区：
文献类型：
--
作者：
Okegawa, Y;Tsuyama, M;Shikanai, T
虽然光系统I(PSI)的循环电子传递对植物是必不可少的，但我们对电子所走的路线的了解非常有限。为了评估铁氧还蛋白(Fd)是直接给质酚(PQ)还是通过细胞色素(Cyt)b(6)f复合体中的Q循环给电子，我们研究了拟南芥突变体pgr1(质子梯度调节)中PSI循环电子传递的活性。在pgr1中，由于细胞色素b6f复合体Rieske亚基的氨基酸变化，Q周期活性对类囊体腔的酸化高度敏感，导致Q周期活性的条件性缺陷。用破裂的叶绿体进行的体外检测表明，FD对依赖于PGR5的PQ的还原活性没有任何差异，该活性在体内PSI循环电子传递中起作用。与pgr5缺陷相反，pgr1缺陷对ndh(NAD(P)H脱氢酶)活性降低的突变体crr2-2的光系统II的量子效率没有表现出任何协同效应。此外，两个光系统的量子产率的同时测定表明，pgr1的线性电子传递和psi循环电子传递的比率没有显著影响。以上结果表明，pgr1突变不影响FD对PGR5依赖的PQ的降低。Pgr1和pgr5之间的表型差异表明，维持线性和PSI循环电子传递的适当平衡对于防止间质过度减少是必不可少的。
Although photosystem I ( PSI) cyclic electron transport is essential for plants, our knowledge of the route taken by electrons is very limited. To assess whether ferredoxin (Fd) donates electrons directly to plastoquinone (PQ) or via a Q-cycle in the cytochrome (cyt) b(6)f complex in PSI cyclic electron transport, we characterized the activity of PSI cyclic electron transport in an Arabidopsis mutant, pgr1 (proton gradient regulation). In pgr1, Q-cycle activity was hypersensitive to acidification of the thylakoid lumen because of an amino acid alteration in the Rieske subunit of the cyt b6f complex, resulting in a conditional defect in Q-cycle activity. In vitro assays using ruptured chloroplasts did not show any difference in the activity of PGR5-dependent PQ reduction by Fd, which functions in PSI cyclic electron transport in vivo. In contrast to the pgr5 defect, the pgr1 defect did not show any synergistic effect on the quantum yield of photosystem II in crr2-2, a mutant in which NDH (NAD(P) H dehydrogenase) activity was impaired. Furthermore, the simultaneous determination of the quantum yields of both photosystems indicated that the ratio of linear and PSI cyclic electron transport was not significantly affected in pgr1. All the results indicated that the pgr1 mutation did not affect PGR5-dependent PQ reduction by Fd. The phenotypic differences between pgr1 and pgr5 indicate that maintenance of the proper balance of linear and PSI cyclic electron transport is essential for preventing over-reduction of the stroma.