EFFECTS OF AQUEOUS SULPHUR DIOXIDE ON CHLOROPHYLL DESTRUCTION IN PINUS CONTORTA

SUMMARY The effects of aqueous SO 2 on chlorophyll breakdown in lodgepole pine ( Pinus contorta Dougl. var. latifolia Engelm.) were determined under laboratory conditions. Aqueous SO 2 concentrations ranging from 100 to 500 ppm resulted in a sharp decrease in total chlorophyll content. Chlorophyll a was more sensitive to SO 2 than chlorophyll b. Quantitative determinations of various pigments suggested that's SO 2 causes the conversion of chlorophyll a into phaeophytin a (100–500 ppm SO 2 ) and chlorophyll b into chlorophyllide b (10–50 ppm SO 2 ). The suggested conversion of chlorophyll into chlorophyllide induced by SO 2 was supported by increased activity of pine needle chlorophyllase at low aqueous SO 2 concentrations (10–50 ppm). The breakdown of chlorophyll molecules by SO 2 as measured by loss of Mg ++ and total chlorophyll was accompanied by a decreased ability of pine needles to photosynthesize H 14 CO 3 . The effect of SO 2 on pigment breakdown and rate of photosynthesis was due mostly to the specific direct actions of SO 2 and was not a function of increased acidity.