文摘
Exposure of wild type (WT) and plastocyanin coding petE gene deficient mutant (¦¤petE) of Synechococcus cells to low iron growth conditions was accompanied by similar iron-stress induced blue-shift of the main red Chl a absorption peak and a gradual decrease of the Phc/Chl ratio, although ¦¤petE mutant was more sensitive when exposed to iron deficient conditions. Despite comparable iron stress induced phenotypic changes, the inactivation of petE gene expression was accompanied with a significant reduction of the growth rates compared to WT cells. To examine the photosynthetic electron fluxes in vivo, far-red light induced P700 redox state transients at 820 nm of WT and ¦¤petE mutant cells grown under iron sufficient and iron deficient conditions were compared. The extent of the absorbance change (¦¤A820/A820) used for quantitative estimation of photooxidizable P700+ indicated a 2-fold lower level of P700+ in ¦¤petE compared to WT cells under control conditions. This was accompanied by a 2-fold slower re-reduction rate of P700+ in the ¦¤petE indicating a lower capacity for cyclic electron flow around PSI in the cells lacking plastocyanin. Thermoluminescence (TL) measurements did not reveal significant differences in PSII photochemistry between control WT and ¦¤petE cells. However, exposure to iron stress induced a 4.5 times lower level of P700+, 2-fold faster re-reduction rate of P700+ and a temperature shift of the TL peak corresponding to S2/S3QB?/sup> charge recombination in WT cells. In contrast, the iron-stressed ¦¤petE mutant exhibited only a 40 % decrease of P700+ and no significant temperature shift in S2/S3QB?/sup> charge recombination. The role of mobile electron carriers in modulating the photosynthetic electron fluxes and physiological acclimation of cyanobacteria to low iron conditions is discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.