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Authors: EDINA SZEKERES, VICTOR BERCEA, NICOLAE DRAGOȘ, BOGDAN DRUGĂ.
In this study the effect of microaerobiosis on photochemical activity in the cyanobacterium Synechococcus sp. PCC 7002 is presented, by measuring chlorophyll fluorescence. Microaerobiosis was achieved by argon bubbling for 120 minutes, with samples being taken in four specific time periods.In vitro measurements of absorption showed dominancy in chlorophyll a and the presence of carotenoids. Maximum fluorescence Fm decreased after 15 minutes of exposure to argon bubbling. Decline of Fm attests the large number of closed reaction centers, as well as plastoquinone reduction and growth of fluorescence emission. Variable fluorescence, expressing the difference between Fm and F0, showed positive values compared to the control, except after 60 minutes of argon treatment. Maximal quantum yield (Fv/Fm) of PS II photosynthesis was weakly stimulated by the argon treatment, except at 60 minutes of argon effect when negative values were observed. The coefficients of photochemical quenching, qP and qL, were maintained at higher values, except when 30 minute exposure to argon treatment. By exposure to argon, the Pm signal was high in the first 30 minutes, followed by a significant decrease towards the end of the stress treatment suggesting a decrease in the reduction state of P700 reaction center compared to oxidized state. Moreover, effective PS I photochemical quantum yield Y(I) dropped significantly in the first 30 minute compared to the control. The decrease in quantum yield Y(I) reveals decreased reduction state due to the lack of limitation by the acceptor, respectively, decrease in photochemical energy conversion in PS I. The interchange of oxidative/reduced state of the plastoquinone nuclei was revealed in the kinetics of the chlorophyll fluorescence induction by pulse saturation in control. Fluorescence kinetics showed on the logarithmic scale revealed important modifications in I – P spectrum due to reduction of the plastoquinone nuclei.
Keywords: Cyanobacteria, Synechococcus, photosynthesis, microaerobiosis, fluorescence
