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

Abstract

Abstract. Cell division in the marine diatom Phaeodactylure 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.

CHANGES IN CELL COMPOSITION AND LIPID METABOLISM MEDIATED BY SODIUM AND NITROGEN AVAILABILITY IN THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

“…Cultures of the marine diatomPhaeodacl?llurii hicoriiutum Bohlin (NERC Culture Collection of Algae and Protozoa strain no. 1052/ 6) were grown for 3 d on modified ASP-2 medium and harvested as described previously (Larson and Rees 1994). Cells from these cultures were resuspended in one of two medium types: 1) modified ASP-2 medium without added nitrate or 2) modified ASP-2 medium without added nitrate or sodium salts.…”

“…Cells from these cultures were resuspended in one of two medium types: 1) modified ASP-2 medium without added nitrate or 2) modified ASP-2 medium without added nitrate or sodium salts. In this medium, 470 mM mannitol was substituted for NaCl to maintain osmolality, and potassium salts were substituted for the remaining sodium salts (Larson and Rees 1994). T h e requirement for an osmolality adjustment in the medium when sodium was omitted could also be met by raising the magnesium and calcium concentrations (Larson and Rees 1994).…”

“…It is thought to play an important role in regulating other aspects of cell metabolism in marine microalgae, including osmoregulation (Dickson and Kirst 1987) and photosynthesis (Zhao and Brand 1988). M'hen P. tricoruuturri is cultured in the absence of sodium, cell division ceases but resumes when sodium is resupplied, regardless of the presence or absence of a nitrogen source (Larson and Rees 1994). This provides a novel framework in which to study lipid metabolism; the effects of cell division on lipid metabolism can be separated from the effects of nitrogen assimilation.…”

In Situ Glutamine Synthetase Activity in a Marine Unicellular Alga (Development of a Sensitive Colorimetric Assay and the Effects of Nitrogen Status on Enzyme Activity)

“…Permeabilization was determined using Evans blue dye (Crippen and Perrier, 1974). Rates of ['4Clmethylamine uptake were determined as described by Rees (1995), and Chl a concentrations were determined as previously described (Larson and Rees, 1994).…”

“…Nitrogen-starved cells were routinely obtained by aseptically transferring nitrate-grown cells to nitrogen-deficient medium as previously described (Larson and Rees, 1994).…”