Graduate School of Agricultural Science, Kobe University, Nada-ku, Kobe, Japan.
Planta. 2010 Apr;231(5):1077-88. doi: 10.1007/s00425-010-1112-2. Epub 2010 Feb 16.
Previously we observed that the oxygen-evolving complex 33 kDa protein (OEC33) which stabilizes the Mn cluster in photosystem II (PSII), was modified with malondialdehyde (MDA), an end-product of peroxidized polyunsaturated fatty acids, and the modification increased in heat-stressed plants (Yamauchi et al. 2008). In this study, we examined whether the modification of OEC33 with MDA affects its binding to the PSII complex and causes inactivation of the oxygen-evolving complex. Purified OEC33 and PSII membranes that had been removed of extrinsic proteins of the oxygen-evolving complex (PSIIOEE) of spinach (Spinacia oleracea) were separately treated with MDA. The binding was diminished when both OEC33 and PSIIOEE were modified, but when only OEC33 or PSIIOEE was treated, the binding was not impaired. In the experiment using thylakoid membranes, release of OEC33 from PSII and corresponding loss of oxygen-evolving activity were observed when thylakoid membranes were treated with MDA at 40 degrees C but not at 25 degrees C. In spinach leaves treated at 40 degrees C under light, maximal efficiency of PSII photochemistry (F(v)/F(m) ratio of chlorophyll fluorescence) and oxygen-evolving activity decreased. Simultaneously, MDA contents in heat-stressed leaves increased, and OEC33 and PSII core proteins including 47 and 43 kDa chlorophyll-binding proteins were modified with MDA. In contrast, these changes were to a lesser extent at 40 degrees C in the dark. These results suggest that MDA modification of PSII proteins causes release of OEC33 from PSII and it is promoted in heat and oxidative conditions.
先前我们观察到，在光合作用系统 II（PSII）中稳定锰簇的放氧复合物 33 kDa 蛋白（OEC33），会被丙二醛（MDA）修饰，MDA 是过氧化多不饱和脂肪酸的终产物，并且在受热胁迫的植物中这种修饰会增加（Yamauchi 等人，2008）。在这项研究中，我们研究了 MDA 对 OEC33 的修饰是否会影响其与 PSII 复合物的结合，并导致放氧复合物失活。我们分别用 MDA 处理纯化的 OEC33 和菠菜（Spinacia oleracea）PSII 膜，去除 PSII 中放氧复合物的外在蛋白（PSIIOEE）。当 OEC33 和 PSIIOEE 都被修饰时，结合减少，但当只有 OEC33 或 PSIIOEE 被处理时，结合不受损害。在使用类囊体膜的实验中，当类囊体膜在 40°C 下用 MDA 处理时，会观察到 OEC33 从 PSII 中释放出来，同时放氧活性丧失，但在 25°C 下则不会。在强光下 40°C 处理的菠菜叶片中，PSII 光化学的最大效率（叶绿素荧光的 F(v)/F(m) 比值）和放氧活性降低。同时，热胁迫叶片中的 MDA 含量增加，OEC33 和 PSII 核心蛋白（包括 47 和 43 kDa 的叶绿素结合蛋白）被 MDA 修饰。相比之下，在黑暗中 40°C 时这些变化程度较小。这些结果表明，MDA 修饰 PSII 蛋白导致 OEC33 从 PSII 中释放出来，并且在热和氧化条件下会促进这种释放。
