Characteristics of Sulfite Transport by Chlorella vulgaris

Tbe rate of short-term accumulation of [S]su!fite in Chlorella vulgaris cells was found to be strongly dependent on the pH of the medium. The rate increased with decreased pH, and the increase in rate closely paralleled the increase in the concentration of the un-ionized form of sulfite. When the pH of the medium was increased, fast accumulation ceased immediately. The rate of accumulation showed a strong temperature dependence, with an apparent temperature coefficient of 1.93 per 10°C rise, between 10 and 25°C. Because pA"a values of sulfite shift with temperature, the rates were corrected by dividing by the concentration of the un-ionized form of sulfite present at the respective temperatures. The temperature coefficient was then found to decrease to 1.45. When cells which had been allowed to accumulate [S]sulfite for 20 min were transferred to a medium containing no sulfite, more than 50% of the accumulated [S] was released into the medium in 20 min. Our results are compatible with a simple diffusion model of SO2 transport into Chlorella cells.