Chloride uptake in strains of Scenedesmus obliquus

Abstract

Summary Wild-type (#3) Scenedesmus obliquus, and mutants reported deficient in photosystem I (#8), photosystem II (#11) and cytochrome f (#50) were used to investigate the dependence of cellular chloride uptake on photosynthesis and respiration. The extent of the light-stimulation of chloride uptake rates from anaerobic solutions was in the same order as that of light-stimulation of O2 evolution, namely #3 ≫ #8 > #11 > #50. DCMU only partly inhibited the light-stimulated uptake in #3 and #8 and increased it in #11. The uptake rate by #3, #8 and #50 from aerobic solutions in the dark was the same, about 0.4–0.5 μmol (kg DW)−1 s−1; that of #11 was 0.13 μmol (kg DW)−1 s−1. O2 consumption under the same conditions was nearly equal in the four strains: 50–60 μmol (kgDW)−1 s−1. Sodium azide at 0.03–0.1 mM inhibited chloride uptake from dark, aerobic solutions and increased O2 consumption, in #3, #8 and #11. The results are discussed in terms of the mediation of chloride active transport by respiratory or photosynthetic ATP. Operation of Photosystem II does not seem essential and it is inferred that cyclic processes may support chloride uptake, in anaerobic solutions, in the light with DCMU present. An inhibition of chloride uptake from dark, anaerobic solutions, by sodium azide, may be a direct effect on a membrane-located transport mechanism or on substrate-level phosphorylation (an «energy limitation»).