Garstka Maciej, Drozak Anna, Rosiak Małgorzata, Venema Jan Henk, Kierdaszuk Borys, Simeonova Ewa, van Hasselt Philip R, Dobrucki Jerzy, Mostowska Agnieszka
Department of Metabolic Regulation, Institute of Biochemistry, Warsaw University, Miecznikowa 1, PL-02-096 Warsaw, Poland.
Biochim Biophys Acta. 2005 Nov 15;1710(1):13-23. doi: 10.1016/j.bbabio.2005.08.006. Epub 2005 Sep 15.
Changes in chloroplast structure and rearrangement of chlorophyll-protein (CP) complexes were investigated in detached leaves of bean (Phaseolus vulgaris L. cv. Eureka), a chilling-sensitive plant, during 5-day dark-chilling at 1 degrees C and subsequent 3-h photoactivation under white light (200 mumol photons m(-2) s(-1)) at 22 degrees C. Although, no change in chlorophyll (Chl) content and Chl a/b ratio in all samples was observed, overall fluorescence intensity of fluorescence emission and excitation spectra of thylakoid membranes isolated from dark-chilled leaves decreased to about 50%, and remained after photoactivation at 70% of that of the control sample. Concomitantly, the ratio between fluorescence intensities of PSI and PSII (F736/F681) at 120 K increased 1.5-fold upon chilling, and was fully reversed after photoactivation. Moreover, chilling stress seems to induce a decrease of the relative contribution of LHCII fluorescence to the thylakoid emission spectra at 120 K, and an increase of that from LHCI and PSI, correlated with a decrease of stability of LHCI-PSI and LHCII trimers, shown by mild-denaturing electrophoresis. These effects were reversed to a large extent after photoactivation, with the exception of LHCII, which remained partly in the aggregated form. In view of these data, it is likely that dark-chilling stress induces partial disassembly of CP complexes, not completely restorable upon photoactivation. These data are further supported by confocal laser scanning fluorescence microscopy, which showed that regular grana arrangement observed in chloroplasts isolated from control leaves was destroyed by dark-chilling stress, and was partially reconstructed after photoactivation. In line with this, Chl a fluorescence spectra of leaf discs demonstrated that dark-chilling caused a decrease of the quantum yield PSII photochemistry (F(v)/F(m)) by almost 40% in 5 days. Complete restoration of the photochemical activity of PSII required 9 h post-chilling photoactivation, while only 3 h were needed to reconstruct thylakoid membrane organization and chloroplast structure. The latter demonstrated that the long-term dark-chilled bean leaves started to suffer from photoinhibition after transfer to moderate irradiance and temperature conditions, delaying the recovery of PSII photochemistry, independently of photo-induced reconstruction of PSII complexes.
研究了冷敏感植物菜豆（Phaseolus vulgaris L. cv. Eureka）离体叶片在1℃黑暗低温处理5天及随后在22℃白光（200 μmol光子m⁻² s⁻¹）下3小时光激活过程中叶绿体结构的变化以及叶绿素-蛋白（CP）复合物的重排。尽管所有样品的叶绿素（Chl）含量和Chl a/b比值均未观察到变化，但从黑暗低温处理叶片中分离的类囊体膜的荧光发射和激发光谱的总体荧光强度降低至约50%，光激活后保持在对照样品的70%。同时，在120 K时PSI和PSII的荧光强度之比（F736/F681）在低温处理后增加了1.5倍，光激活后完全恢复。此外，低温胁迫似乎导致120 K时LHCII荧光对类囊体发射光谱的相对贡献降低，而LHCI和PSI的贡献增加，这与轻度变性电泳显示的LHCI-PSI和LHCII三聚体稳定性降低相关。除LHCII部分仍以聚集形式存在外，这些效应在光激活后在很大程度上得到逆转。鉴于这些数据，黑暗低温胁迫可能诱导CP复合物的部分解离，光激活后不能完全恢复。共聚焦激光扫描荧光显微镜进一步支持了这些数据，该显微镜显示从对照叶片分离的叶绿体中观察到的规则基粒排列被黑暗低温胁迫破坏，光激活后部分重建。与此一致，叶盘的Chl a荧光光谱表明，黑暗低温处理在5天内使PSII光化学量子产率（F(v)/F(m)）降低了近40%。PSII光化学活性的完全恢复需要低温处理后光激活9小时，而重建类囊体膜组织和叶绿体结构仅需3小时。后者表明，长期黑暗低温处理的菜豆叶片在转移到适度光照和温度条件后开始遭受光抑制，延迟了PSII光化学的恢复，这与PSII复合物的光诱导重建无关。
