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

Department of Chemistry University of Auckland Private Bag Auckland, New Zealand

Kathryn P. Ashford

Department of Chemistry University of Auckland Private Bag Auckland, New Zealand

Ragina M.D. Singh

Department of Chemistry University of Auckland Private Bag Auckland, New Zealand

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 K_m for both carriers exhibit bell-shaped pro files when plotted against temperature. The temperature for maximum values of K_m 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 ³⁵SO₄^2- 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 SO₄^2- transport is assisted by a carrier molecule. The rate of up take did not decrease in the presence of the structural isomer MoO₄^2-, suggest ing that the high affinity carrier is specific for SO₄^2-.

Journal of Bioactive and Compatible Polymers, Vol. 1, No. 4, 437-447 (1986)
DOI: 10.1177/088391158600100402


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