Uptake of 35S-sulfur from Sulfate by Pinus radiata Pollen

The rates of uptake of 35S from sulfate solutions by Pinus radiata pollen were measured at a variety of extracellular concentrations (0.049—1.96 mM) of sulfate and over the temperature range 1—50°C. The transport process is not one of diffusion but appears to be carrier assisted by two carriers having dif ferent sulfate affinities. Values of Km for both carriers exhibit bell-shaped pro files when plotted against temperature. The temperature for maximum values of Km are 22 ° C and 35 ° C for the high affinity (low concentration) and low affin ity (high concentration) carriers, respectively. The activation energies for all concentrations of sulfate are greater than 147 kJ mol-1 and these high values are consistent with a carrier mediated process. The uptake of 35SO42- from a 0.196 mM sulfate solution was inhibited by the metabolic inhibitors cyanide, azide and carbonyl cyanide-m-chlorophenylhydrazone but enhanced by the metabolic energy source, adenosine-5'-triphosphate. These results support the proposal that SO42- transport is assisted by a carrier molecule. The rate of up take did not decrease in the presence of the structural isomer MoO42-, suggest ing that the high affinity carrier is specific for SO42-.

Effect of Temperature on the Uptake of 35S(-II) by Wine Yeasts

The rates of uptake of 35S from S(-II) solutions by wine yeasts, Saccharomyces cerevisiae strains R92 and R104 and Saccharomyces chevalieri strain R93, were measured at pH 3.1 and 7.2 over the temperature range 5 ° C to 80 ° C and at 0.3 (or 0.5) mM and 5.0 mM S(-II) concentrations. Three critical temperatures were observed; the first, at ca 20 ° C is attributed to a phase change of the yeast cell membrane from a crystalline to a liquid crystalline state; the second, at the temperature of maximum activity at 30 ° C to 40 ° C is thought to arise from a switch from a metastable to a thermodynamically more stable state which is less effective in supporting the transport functions; and the third, at tempera tures greater than 50 ° C correlates well with the thermal viability of the yeasts. Variation of the activation energy, Ea, with extracellular S(-II) concen tration was observed and Ea for the uptake of S(-II) from a solution of 5 mM S(-II) at pH 7.2 was higher than at pH 3.1. The values of Ea support the postulate of a simple diffusion of H2S(aq) and carrier mediated transport of HS-(aq) for the transport of S(-II).