STIMULATORY EFFECT OF SULFITE ON PHOTOSYNTHETIC (CO2)-C-14-FIXATION IN KALANCHOE-DIAGREMONTIANA HAMET ET PERRIER

Mesophyll cells of the CAM plant Kalanchoe daigremontiana exhibit a ve ry low sensitivity towards sulphite. Twenty mmolL(-1) sulphite concent ration in the presence of 10 mmolL(-1) bicarbonate does not bring abou t an inhibition of photosynthetic (CO2)-C-14-fixation, rather, it even stimulates this process. Sulphite also shifted the labelling pattern obtained by (CO2)-C-14-fixation in light in favour of malate. Acidifie d protoplasts compared with deacidified ones were found to be more act ive in photosynthetic O-2 production and sulphite oxidation. There is evidence that this effect is not the result of differences in the prod uction of oxygen free radicals. The results are discussed in terms of CAM as a mechanism that provides protection against damage by SO2.