Arrest of cell division but not protein synthesis in sodium-deficient cells of the marine diatom Phaeodactylum tricornutum Bohlin

Abstract

Cell division in the marine diatom Phaeodactylum tricornutum was prevented when cultures were maintained in the absence of sodium, regardless of the nitrogen status of the cells or medium. Addition of 10 mM ammonium and 50 mM sodium to cultures preconditioned in nitrogen and sodium-deficient medium for 5 d led to a recovery in cell division and chlorophyll a, and net protein synthesis. Sodium added in the absence of ammonium led to a recovery in cell division, but not net protein synthesis. Ammonium added in the absence of sodium was partially assimilated (as NH3) and resulted in a small amount of protein synthesis, but without cell division. This effect was enhanced if the cells had lower protein quotas prior to ammonium addition, with total consumption of the added 1 mM ammonium and appreciable net protein synthesis. Respiration was enhanced by 1 or 10 mM ammonium or 10 mM methylammonium addition to nitrogen-deficient cultures maintained in the presence or absence of sodium. In contrast to respiration, photosynthesis was inhibited by these additions in sodium-replete cultures, but was enhanced in sodium-deficient cultures.