Uptake of Cd2+ ions m the presence or absence of glucose by a brewing strain of Saccharomyces cerevisiae was examined in unbuffered, buffered and pH controlled systems. Levels of Cd2+ taken up, and K+ release were influenced by the degree of pH control in each system. A time-dependent component of uptake was observed in the absence of glucose which was attributed to a degree of metabolic activity Subcellulai localisation studies determined that Cd2+ was predominantly bound by insoluble cellular material (approximately 70%) whereas Mn2+ was localised to soluble pools, paiticularly the vacuole (less than 45% bound by insoluble cellular material). In the presence and absence of glucose, Sr2+ was sequestered mainly to bound (50-68%) or soluble (65- 85%) subcellular pools, respectively, but the converse was observed with Cu2+ localisation Perturbation of subcellular Mg2+ pools was observed in the presence of glucose only, and consisted of Mg displacement from vacuolar or bound pools to other subcellular compartments Vacuolar K+ loss was recorded during accumulation of all cations in the absence of glucose but only during Cd2+ uptake in the presence of glucose Growth inhibitory effects of Mn2+ on S c e re v is ia e NCYC 1383 weie eliminated by supplementing with excess Mg2+ ions but not with Ca2+ or K+ Intracellular Mg levels were amenable to manipulation and it was observed that Mg-ennched cells accumulated less Mn2+ (by approximately half) than their unsupplemented counterparts In addition, cells possessing low intracellular. Mg levels were more susceptible to Mn2+ toxicity Toxicity was dependent on the cellular Mg Mn ratio, a critical ratio of 2 0 was identified below which toxicity became acute. An alternative technique for differential extraction of subcellular ion pools was developed utilising specific biochemical markers to characterise separation of cytoplasmic and vacuolar ion pools, and the results obtained compared with the original method Some differences arose between levels of metal cations recovered but similar trends in subcellular localisation patterns were evident. It was concluded that either protocol could be used to characterise subcellular sequestration of accumulated metal cations
