METABOLISM OF ELEMENTAL SULFUR AND OXIDATION OF SULFITE BY WHEAT AND SPINACH-CHLOROPLASTS

Wheat or spinach chloroplasts were fed with S-35-labelled elemental sulphur (S-0). S-35-labelled compounds appearing thereafter were analysed. Five S-35-compounds were recovered, thiosulphate, sulphite, sulphate, cysteine and glutathione. The effect of environmental conditions was also studied. The measurement of S-0 metabolism rate was compared to the recovery of the introduced S-0 into other S compounds. The specific radioactivity of thiosulphate and sulphate was determined. The results obtained have permitted the elucidation of the precise biochemical pathway of S-0 oxidation. The oxidation of sulphite in wheat and spinach chloroplasts occurs via both non-enzymatic (in particular the operation of the photosynthetic electron transport chain) and enzymatic processes (sulphite oxidase activity).