Effects of High-Temperature Treatments on a Thermophilic Cyanobacterium Synechococcus vulcanus

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Effects of high-temperature treatments on a thermophilic cyanobacterium, Synechococcus vulcanus, were studied, and the following results were obtained. (1)Oxygen evolution and the PSII photochemical reaction were the most sensitive sites and started to be inactivated at temperatures slightly higher than the cultivating temperature. (2)The decrease in the fluorescence F_v value reflected the inactivation of the charge separation reaction of PSII as well as that of the oxygen evolution reaction. (3)The dark fluorescence level, F_o, showed an increase at around 70℃, which was partially reversed by further incubation at 50℃. This increase reflected the inactivation of PSII reaction centers and probably dissociation of phycobilisomes from the PSII reaction center complexes. (4)At higher temperatures, phycobiliproteins disassembled and denatured in a pH-dependent manner, causing a large F_o decrease. (5)Cell membranes became leaky to low-molecular-weight substances at around 72℃. (6)Inhibition of growth of the cells was recognized when the cells were pretreated at temperatures higher than 72℃. Reversibility of the high-temperature effects and relationship between viability of the cells and the degradation of the cell membranes are discussed.
日本植物生理学会の論文