Hakala Marja, Tuominen Ilona, Keränen Mika, Tyystjärvi Taina, Tyystjärvi Esa
Department of Biology, Laboratory of Plant Physiology and Molecular Biology, Biocity A, University of Turku, FI-20014 University of Turku, Finland.
Biochim Biophys Acta. 2005 Jan 7;1706(1-2):68-80. doi: 10.1016/j.bbabio.2004.09.001.
Photoinhibition of PSII occurs at the same quantum efficiency from very low to very high light, which raises a question about how important is the rate of photosynthetic electron transfer in photoinhibition. We modulated electron transfer rate and light intensity independently of each other in lincomycin-treated pea leaves and in isolated thylakoids, in order to elucidate the specific effects of light and PSII electron transport on photoinhibition. Major changes in the rate of electron transport caused only small changes in the rate of photoinhibition, suggesting the existence of a significant photoinhibitory pathway that contains an electron-transfer-independent phase. We compared the action spectrum of photoinhibition with absorption spectra of PSII components that could function as photoreceptors of the electron-transfer-independent phase of photoinhibition and found that the absorption spectra of Mn(III) and Mn(IV) compounds resemble the action spectrum of photoinhibition, showing a steep decrease from UV-C to blue light and a low visible-light tail. Our results show that the release of a Mn ion to the thylakoid lumen is the earliest detectable step of both UV- and visible-light-induced photoinhibition. After Mn release from the oxygen-evolving complex, oxidative damage to the PSII reaction center occurs because the Mn-depleted oxygen-evolving complex cannot reduce P680+ normally.
从极低光强到极高光强，PSII的光抑制都以相同的量子效率发生，这就引发了一个问题，即光合电子传递速率在光抑制中究竟有多重要。我们在林可霉素处理的豌豆叶片和分离的类囊体中，彼此独立地调节电子传递速率和光强，以阐明光和PSII电子传递对光抑制的具体影响。电子传递速率的重大变化仅引起光抑制速率的微小变化，这表明存在一条重要的光抑制途径，其中包含一个与电子传递无关的阶段。我们将光抑制的作用光谱与可能作为光抑制电子传递无关阶段光感受器的PSII组分的吸收光谱进行了比较，发现Mn(III)和Mn(IV)化合物的吸收光谱与光抑制的作用光谱相似，从UV-C到蓝光急剧下降，可见光部分有一个低尾。我们的结果表明，Mn离子释放到类囊体腔是紫外线和可见光诱导的光抑制最早可检测到的步骤。Mn从放氧复合体释放后，PSII反应中心发生氧化损伤，因为缺Mn的放氧复合体不能正常还原P680+。
