Thermoluminescence studies on the function of Photosystem II in the desiccation tolerant lichen Cladonia convoluta |
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Authors: | László Sass Zsolt Csintalan Zoltán Tuba Imre Vass |
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Affiliation: | (1) Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, Szeged, Hungary;(2) Plant Physiological Section, Department of Botany and Plant Physiology, Agricultural University of Gödöllö, Gödöllö, Hungary |
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Abstract: | The effect of desiccation and rehydration on the function of Photosystem II has been studied in the desiccation tolerant lichen Cladonia convoluta by thermoluminescence. We have shown that in functional fully hydrated thalli thermoluminescence signals can be observed from the recombination of the S2(3)QB– (B band), S2QA– (Q band), Tyr-D+QA– (C band) and Tyr-Z+(His+)QA– (A band) charge stabilization states. These thermoluminescence signals are completely absent in desiccated thalli, but rapidly reappear on rehydration. Flash-induced oscillation in the amplitude of the thermoluminescence band from the S2(3)QB– recombination shows the usual pattern with maxima after 2 and 6 flashes when rehydration takes place in light. However, after rehydration in complete darkness, there is no thermoluminescence emission after the 1 st flash, and the maxima of the subsequent oscillation are shifted to the 3rd and 7th flashes. It is concluded that desiccation of Cladonia convoluta converts PS II into a nonfunctional state. This state is characterized by the lack of stable charge separation and recombination, as well as by a one-electron reduction of the water-oxidizing complex. Restoration of PS II function during rehydration can proceed both in the light and in darkness. After rehydration in the dark, the first charge separation act is utilized in restoring the usual oxidation state of the water-oxidizing comples.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DT desiccation tolerant - PS II Photosystem II - TL thermoluminescence - P680 reaction center Chl of PS II - QA and QB puinone electron acceptors of PS II - S0,...,S4 the redox states of the water-oxidizing complex - Tyr-Z and Tyr-D redox-active tyrosine electron donors of PS II |
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Keywords: | thermoluminescence Photosystem II desiccation tolerance lichen |
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