Energizing the plasmalemma of marine photosynthetic organisms: the role of primary active transport

Abstract

AbstractGeneration of ion electrochemical potential differences by primary active transport can involve energy inputs from light, from exergonic redox reactions and from exergonic ATP hydrolysis. These electrochemical potential differences are important for homoeostasis, for signalling, and for energizing nutrient influx. The three main ions involved are H+, Na+(efflux) and Cl−(influx). In prokaryotes, fluxes of all three of these ions are energized by ion-pumping rhodopsins, with one archaeal rhodopsin pumping H+intothe cells; among eukaryotes there is also an H+influx rhodopsin inAcetabulariaand (probably) H+efflux in diatoms. Bacteriochlorophyll-based photoreactions export H+from the cytosol in some anoxygenic photosynthetic bacteria, but chlorophyll-based photoreactions in marine cyanobacteria do not lead to export of H+. Exergonic redox reactions export H+and Na+in photosynthetic bacteria, and possibly H+in eukaryotic algae. P-type H+- and/or Na+-ATPases occur in almost all of the photosynthetic marine organisms examined. P-type H+-efflux ATPases occur in charophycean marine algae and flowering plants whereas P-type Na+-ATPases predominate in other marine green algae and non-green algae, possibly with H+-ATPases in some cases. An F-type Cl−-ATPase is known to occur inAcetabularia. Some assignments, on the basis of genomic evidence, of P-type ATPases to H+or Na+as the pumped ion are inconclusive.