Characterization of Sulfate Transport in the Green AlgaChlorella ellipsoidea

摘要

A rapid induction of sulfate transport was observed in the green algaChlorella ellipsoideaduring sulfur-limited growth. Both affinity andVmaxincreased about five-fold within 6 h of transferring cells from Bold's basal medium with 350μM MgSO4to sulfur-deficient Bold's medium. High affinity sulfate transport was induced within 15 min and reached maximum rate within 3 h of transferring cells to sulfur-deficient condition, indicating that a new, high-affinity-sulfate transport system is induced by sulfur starvation inC. ellipsoidea. Eadie-Hofstee plots of initial rates of sulfate uptake indicated that theK½of sulfur-starved cells was about 17μM. Both sulfur-starved and unstarved cells grown in air had aVmaxof 1.5 times higher than that of high-CO2grown cells. Sulfate transport was completely inhibited by 30μM CCCP or 800μM KCN both in the light and the dark but transport in the light was not inhibited by 20μM DCMU. Treatment with 50μM or 500μM vanadate caused 50inhibition of uptake. The rate of sulfate uptake in the dark was twice that in the light and was stimulated by low pH. These results suggest that the sulfate transport system inC. ellipsoideais operated by proton symport across the plasmamembrane which is partially mediated by P-type ATPase and that these systems depend exclusively on energy derived from oxidative phosphorylation in the mitoc