Some Effects of Sulphite on Photosynthesis in Lichens

SUMMARY Details of the effect of sulphite on H14CO3‐ fixation in the light were studied. The reduction of fixation by sulphite was rapid, taking place within 30 min of contact with the lichen. Parmelia physodes recovered in 24 h from almost total reduction of fixation caused by 1 h treatment with 0.4 mM sulphite but Usnea sp. did not. Studies with [35S] sulphite indicated that sulphite was taken up nonlinearly with time and that it was bound to protein. Algae isolated from Usnea sp., Parmelia physodes and Lecanora conizaeoides were similar in their response to sulphite, although the intact lichen L. conizaeoides is known to be more resistant. L. conizaeoides did not seem to be resistant to sulphite by causing rapid oxidation of sulphite to sulphate. There was no marked effect of temperature on the concentration of sulphite required to reduce fixation in Usnea sp.