Sulphite-induced changes of sulphur metabolism in the lichen alga Trebouxia sp

Solutions of sodium sulphite have been used to simulate the effect of gaseous sulphur dioxide on the lichen alga Trebouxia sp. The uptake and the metabolism of inorganic and organic [³⁵ S]compounds such as sulphate, sulphite, and cysteine were investigated in cells of Trebouxia under conditions of sulphite preincubation (sulphite-stressed cells: 3 d pretreatment with 50 mmol m^-3 and 5 mol m^-3 solutions of sodium sulphite). Metabolism was similar, regardless of whether the Trebouxia was provided with [³⁵ S]sulphate or -sulphite. In sulphite-stressed cells, uptake and incorporation into ethanol-soluble compounds, especially cysteine and methionine, was significantly decreased. In Trebouxia exogenous [³⁵ S]cysteine is metabolized only at a very low rate.