Vacuolar Ion Research Articles

Participation of vacuoles in regulation of levels of K+, Mg2+ and orthophosphate ions in cytoplasm of the yeast Saccharomyces carlsbergensis

Intracellular distributions of K+, Mg2+ and orthophosphate under various conditions of cultivation or incubation of the yeast Saccharomyces carlsbergensis were studied by differential extraction of ion pools. The decisive role of vacuolar compartmentation of ions in regulation of K+, Mg2+ and orthophosphate levels in the yeast cytoplasm was shown. The content of intracellular K+ and Mg2+ in yeast increased or decreased primarily depending on the increase or decrease in the vacuolar ion pool. The levels of K+ and Mg2+ in the cytoplasm were practically unchanged. Vacuoles were involved in regulation of Mn2+ concentration in the cytoplasm of the yeast S. carlsbergensis accumulating this ion in the presence of glucose. Alongside the vacuolar compartmentation, the chemical compartmentation, i. e. formation of bound Mg2+, Mn2+ and K+ was, evidently, also involved in the control of ion levels in the cytoplasm. The orthophosphate level in the yeast cytoplasm was regulated by its accumulation in vacuoles and biosynthesis of inorganic polyphosphates in these organelles. The biosynthesis of low-molecular weight polyphosphates occurred parallel to the accumulation of Mg2+ or Mn2+ in vacuoles, thus confirming the availability of the other mechanism for the transport of these ions through the tonoplast differing from the transport mechanism through the plasmalemma.

Role of vacuolar ion pool in Saccharomyces carlsbergensis: potassium efflux from vacuoles is coupled with manganese or magnesium influx

Saccharomyces carlsbergensis cells accumulated Mn2+ (or Mg2+) ions in the presence of glucose, fructose, or mannose, but not of deoxyglucose, 3-O-methylglucose, and sorbose. Accumulation of one equivalent of Mn/2+ was coupled with the efflux of two equivalents of K+ from the cells. Mg/2+ did not exit during Mn2+ uptake. Preliminary treatment of cells with various proton conductors or glucose led to the loss of K+ and to the proportional inhibition of Mn2+ uptake. Polyene antibiotic candicidin together with glucose elicited rapid efflux of K+ and completely inhibited Mn2+ accumulation. Exogenous K+ (more than 1 mM), 100 microM N,N'-dicyclohexylcarbodiimide, and 30 mM sodium arsenate inhibited both K+ efflux and Mn2+ influx. K+ efflux from S. carlsbergensis cells affected the vacuolar pool of K+ both during the accumulation of Mn2+ or Mg2+ and during glucose uptake.

Salt Stress and Comparative Physiology in the Gramineae. IV. Comparison of Salt Stress in Spartina × townsendii and Three Barley Cultivars

The possible significance of the compartmentation of major solutes between cytoplasm and vacuole is described. The barley cultivars appear to have a restricted ability, by comparison with S. × townsendii, to exploit Na+ and Cl- as major vacuolar ions and contributors to osmotic adjustment. They also appear less able to maintain a basal K- supply in the presence of Na+. The basal K+ supply to the shoot is interpreted as a requirement for a minimal cytoplasmic K+ concentration. The role of glycinebetaine and proline as cytoplasmic osmotic effectors is discussed. It is concluded that, in these hydroponic experiments, the synthesis of glycinebetaine and proline is not a limitation on the salt tolerance of these species.