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

Abstract

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-.