Department of Agriculture, Kyushu University, Fukuoka, Japan.
Photosynth Res. 2010 Feb;103(2):111-23. doi: 10.1007/s11120-009-9525-0.
A transient in chlorophyll fluorescence after cessation of actinic light illumination, which has been ascribed to electron donation from stromal reductants to plastoquinone (PQ) by the NAD(P)H-dehydrogenase (NDH) complex, was investigated in Arabidopsis thaliana. The transient was absent in air in a mutant lacking the NDH complex (ndhM). However, in ndhM, the transient was detected in CO(2)-free air containing 2% O(2). To investigate the reason, ndhM was crossed with a pgr5 mutant impaired in ferredoxin (Fd)-dependent electron donation from NADPH to PQ, which is known to be redundant for NDH-dependent PQ reduction in the cyclic electron flow around photosystem I (PSI). In ndhM pgr5, the transient was absent even in CO(2)-free air with 2% O(2), demonstrating that the post-illumination transient can also be induced by the Fd- (or PGR5)-dependent PQ reduction. On the other hand, the transient increase in chlorophyll fluorescence was found to be enhanced in normal air in a mutant impaired in plastid fructose-1,6-bisphosphate aldolase (FBA) activity. The mutant, termed fba3-1, offers unique opportunities to examine the relative contribution of the two paths, i.e., the NDH- and Fd- (or PGR5)-dependent paths, on the PSI cyclic electron flow. Crossing fba3-1 with either ndhM or pgr5 and assessing the transient suggested that the main route for the PSI cyclic electron flow shifts from the NDH-dependent path to the Fd-dependent path in response to sink limitation of linear electron flow.
在光停止照射后，叶绿素荧光会出现一个短暂的瞬变，这个瞬变被归因于NAD(P)H 脱氢酶（NDH）复合物将基质还原剂中的电子传递给质体醌（PQ）。在拟南芥中，研究了这个瞬变。在缺乏 NDH 复合物（ndhM）的突变体中，这个瞬变在空气中不存在。然而，在 ndhM 中，在不含 CO2 的空气中检测到了这个瞬变，该空气含有 2%的 O2。为了研究原因，ndhM 与一个在依赖铁氧还蛋白（Fd）的电子从 NADPH 传递到 PQ 中受到损害的 pgr5 突变体杂交，已知该突变体在 PSI 周围的环式电子流中对 NDH 依赖的 PQ 还原是冗余的。在 ndhM pgr5 中，即使在不含 CO2 的空气中含有 2%的 O2，这个瞬变也不存在，表明该瞬变也可以由 Fd-（或 PGR5）依赖的 PQ 还原诱导。另一方面，在依赖质体果糖-1,6-二磷酸醛缩酶（FBA）活性的突变体中，发现正常空气中的叶绿素荧光瞬变增加。这个突变体称为 fba3-1，为检查两条途径（即 NDH 和 Fd-（或 PGR5）依赖的途径）对 PSI 环式电子流的相对贡献提供了独特的机会。将 fba3-1 与 ndhM 或 pgr5 杂交，并评估瞬变表明，在线性电子流的汇限制下，PSI 环式电子流的主要途径从 NDH 依赖的途径转移到 Fd 依赖的途径。
