Uptake and Efflux of [ S]Sulfite by Protoplasts and their Chloroplasts of Oat (Avena sativa L.)

A vena sativa , Chloroplasts, Protoplasts, Sulfite Efflux, Sulfite Uptake Processes of J5S-labelled sulfite uptake and efflux by oat protoplasts and their chloroplasts are very rapid: during the first minutes (or perhaps even seconds) after sulfite supply a state of equilibrium is established between the protoplasts and their chloroplasts and the incubation medium. Bicarbonate concentrations ranging from 1 to 5 mM in the medium had no significant effect on sulfite uptake. At pH 7.0 sulfite uptake is much greater than at pH 7.6. Light of low intensity (9 W m 2) had no significant effect on this uptake. The 35S concentration in chloroplasts was always much higher than in the whole protoplasts. One hour's incubation at sulfite concentra­ tions of 0.1 and 0.5 mM in the medium, concentrations slightly stimulating or inhibiting photosyn­ thesis, results in sulfite concentrations of 0.004 to 0.230 mM in chloroplasts. At a sulfite concentration photosynthesis, these values are 0.120 to 0.551 and 2