Litvín Radek, Bína David, Siffel Pavel, Vácha Frantisek
Department of Photosynthesis, Institute of Plant Molecular Biology, Branisovska 31, 37005 Ceske Budejovice, Czech Republic.
Photochem Photobiol Sci. 2005 Dec;4(12):999-1002. doi: 10.1039/b506166k. Epub 2005 Aug 23.
Accumulation of reduced pheophytin in photosystem II under illumination at low redox potential is known to be accompanied by a pronounced decrease of a chlorophyll fluorescence yield. Simultaneous measurement of this fluorescence quenching and absorbance changes in photosystem II reaction centres, in the presence of dithionite, showed each event to have a different temperature dependence. While fluorescence quenching was suppressed more than 20 times when measured at 77 K, pheophytin accumulation decreased only 5 times. At 77 K, the fluorescence was quenched considerably, but only in those reaction centres where reduced pheophytin had been accumulated at room temperature before sample freezing. This showed that the accumulation of reduced pheophytin above 240 K was accompanied by an additional, most probably conformational, change in the reaction centre that substantially enhanced non-radiative dissipation of excitation energy.
已知在低氧化还原电位光照下，光系统II中还原脱镁叶绿素的积累伴随着叶绿素荧光产量的显著下降。在连二亚硫酸盐存在的情况下，同时测量光系统II反应中心的这种荧光猝灭和吸光度变化，结果表明每个事件具有不同的温度依赖性。当在77 K下测量时，荧光猝灭被抑制了20倍以上，而脱镁叶绿素的积累仅下降了5倍。在77 K时，荧光被显著猝灭，但仅在样品冷冻前室温下已积累了还原脱镁叶绿素的那些反应中心中。这表明在240 K以上还原脱镁叶绿素的积累伴随着反应中心的另一种变化，很可能是构象变化，这大大增强了激发能的非辐射耗散。
