Untitled

Abstract

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

A pilot-scale floating closed culture system for the multicellular cyanobacterium Arthrospira platensis NIES-39

“…7 ). The relationships between morphological changes of Arthrospira trichomes and NaCl concentration have been reported previously (Jeeji Bai 1985 ; Lewin 1980 ; Dhiab et al 2007 ; Pogoryelov et al 2003 ). In response to the increase of NaCl concentration, the shape of the trichomes of Arthrospira is changed to straight from the helical form.…”

“…6b ). According to previous studies, A. platensis shows high photosynthetic activity between pH 8.3 and 10.5 in a medium containing about 200 mM Na + and shows high Na dependency of oxygen evolution at high pH (Schlesinger et al 1996 ; Pogoryelov et al 2003 ). Generally, the sodium concentration of seawater is about 500 mM.…”

“…The glycogen content of A. platensis NIES-39 grown in modified seawater media was higher than in SOT medium (Table 2 ). Also, according to Pogoryelov et al ( 2003 ), A. platensis grown in seawater had higher carbohydrate content than in Zarrouk’s medium, which is a standard mineral medium and similar to SOT medium. It is known that as an osmotic response to the higher salinities in the media, A. platensis accumulates organic osmolytes such as low-molecular-weight carbohydrates, glucosyl-glycerol, and trehalose (Reed et al 1984 ; Vonshak et al 1988 ).…”

Characterization of the N-ATPase, a distinct, laterally transferred Na+-translocating form of the bacterial F-type membrane ATPase

“…In the view of several reports on the sodium dependence of energy-coupled reactions in cyanobacteria (Willey et al , 1987; Skulachev, 1988; Pogoryelov et al , 2003), we have searched cyanobacterial genomes for the Na + -translocating ATPases. We found several apparently Na + -dependent cyanobacterial ATPases, but always as second copies, in addition to the H + -translocating ATP synthases.…”

Detection of weed algae in open pond cultures of Cyanobacterium aponinum using PAM

“…/H ? -antiporter (Pogoryelov et al 2003). This and other physiological traits might lead to a competitive advantage of cyanobacteria at high pHs (Paerl et al 2001).…”