Sulfate Transport in Normal and S-Deprived Chlorella fusca

Cation Stimulation, Chlorella fusca, Green Alga, Multiphasic Uptake, Sulfate Analogues, Sulfate Starvation Sulfate uptake into the unicellular green alga Chlorella fusca Shihira et Krauss strain 211-8 b was described as a pH-, temperatureand energy-dependent process. Transport followed triphasic kinetics with /^-values of 1.3 x 10-5, 3.9 x 105 and 2.8 x 10 4 m . The Hill plot showed coeffi­ cients of 1.0 for each uptake isotherm. Sulfate uptake was substantially inhibited by chromate, selenate, sulfite, thiosulfate and tetrathionate. Cysteine and other mercaptides diminished sulfate transport, whereas methionine was not inhibitory. Uptake was sensitive towards inhibitors of photosynthesis and respiration and towards SH-group reagents. Sulfate uptake could be strongly enhanced by polyvalent cations, apparently via reduction of the surface potential. Sulfate uptake in S-deprived algae was markedly different from constitutive sulfate uptake. Time kinetics was not linear but showed an initial rapid phase. Uptake was neither multiphasic nor conformed to simple Michaelis-Menten kinetics. Sulfate uptake was hardly affected by pH and temperature in the suboptimal range. The Arrhenius plot was biphasic with a discontinuity at 38 °C.