Abstract
Diatoms are secondary symbiotic photoautotrophs that contribute approximetly 25% global primary productivity. Many diatom species inhabit in brackish water and seem to acclimate to broad range salt concentrations. It was shown previously that the marine diatom Phaeodactylum tricornutum grew in [NaCl] from 0.1 to 1.5 M. In this study, Na+ and Cl- fluxes were monitored under several ambient [NaCl] using ion-specific-fluorescence indicators. At [NaCl] below 0.5 M, both ions accumulated in periplastidal compartment, an intermembrane space of tetra-layered chloroplastic envelope of secondary endosymbionts, whereas only Na+ accumulated in chloroplast at 1.0 M NaCl. 360 μM ouabain and 100 μM EIPA, inhibitors respectively for Na+/K+-ATPase and Na+/H+-antiporter, completely abolished Na+ influx and dissipated periplastidal Cl- accumulation at 0.5 M NaCl. These observations indicated that the periplastidal compartment might play a crucial role during acclimation of cells to broad range [NaCl], and that these ion fluxes are driven by Na+/K+-ATPase and/or Na+/H+-antiporter.
