Sodium dependency of the photosynthetic electron transport in the alkaliphilic cyanobacterium Arthrospira platensis

摘要: Arthrospira (Spirulina) platensis (A. platensis) is a model organism for investigation of adaptation photosynthetic organisms to extreme environmental conditions: the cell functions in this cyanobacterium are optimized high pH and concentration (150–250 mM) Na+. However, mechanism possible fine-tuning these conditions and/or regulation cellular environment optimize poorly understood. In work we investigated effect Na-ions on different activities: linear electron transport reactions (measured by means polarography spectrophotometry), activity photosystem II (PS II) (thermoluminescence chlorophyll fluorescence induction), redox turnover cytochrome b6f complex (flash photolysis); measured changes intracellular (9-aminoacridine fluorescence). It was found that sodium deprivation cells dark at 10 inhibited, within 40 min, all reactions, led an alkalinization pH, which rose from physiological value about 8.3–9.6. These were partially totally restored readdition 2.5–25 mM 200 mM, respectively. The also sensitive monensin, exogenous Na+/H+ exchanger, collapses both proton gradients across cytoplasmic membrane. observations explain strict Na+-dependency extracellular provide experimental evidence alkalization environment, support hypothesized role antiport through plasma membrane homeostasis (Schlesinger et al. (1996). J. Phycol.32, 608–613). Further, show (i) specific site inactivation alkaline be water splitting enzyme; (ii) contrast earlier reports, occurs and, short periods, without detectable damage apparatus; (iii) Na+ dependency neutral range shown not originate PSII, but acceptor side PSI. data permit us conclude rather than machinery adjusted concentration.