Photoinhibition of Electron Transport Activity of Photosystem II in Isolated Thylakoids Studied by Thermoluminescence and Delayed Luminescence
Photosynthetic organisms exposed to higher light intensity than that required to saturate photosynthesis gradually lose their photosyn-thetic capacity. The phenomenon is called photoinhibition and related to a damage in photosystem II (PS II) [1–5]. However, the opinions differ concerning the exact site of photodamage. Works using algae cells suggest that the QB binding protein is injured [2,9]. On the other hand the majority of experiments on isolated chloroplasts advocate a primary site of photoinhibition in the P680-Pheo-QA section of the electron transport chain [3–5]. Recently thermoluminescence (TL) and delayed luminescence (DL) proved to be useful methods in the investigation of PS II photochemistry. Well characterized TL and DL signals are arising from the S2QA and S2QB charge recombinations [6–8]. Thus it is expected that the effect of photoinhibition on the QA and QB acceptors can be easily followed by these techniques. Recent TL investigation of photoinhibition in Chlamydomonas reinhardii cells led to the conclusion that in the first stage of photoinhibition the QB binding site is modified while the QA acceptor is only slightly influenced . Considering that in isolatea thylakoids the process of photoinhibition may differ from that occurring in intact cells we carried out TL and DL measurements of photoinhibited spinach thylakoids.
KeywordsElectron Transport Chain Alga Cell High Light Intensity Electron Transport Rate Charge Recombination
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