Effects of Aqueous Sulphur Dioxide on Chlorophyll Destruction in Pinus Contorta

SUMMARY The effects of aqueous SO2 on chlorophyll breakdown in lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were determined under laboratory conditions. Aqueous SO2 concentrations ranging from 100 to 500 ppm resulted in a sharp decrease in total chlorophyll content. Chlorophyll a was more sensitive to SO2 than chlorophyll b. Quantitative determinations of various pigments suggested that's SO2 causes the conversion of chlorophyll a into phaeophytin a (100–500 ppm SO2) and chlorophyll b into chlorophyllide b (10–50 ppm SO2). The suggested conversion of chlorophyll into chlorophyllide induced by SO2 was supported by increased activity of pine needle chlorophyllase at low aqueous SO2 concentrations (10–50 ppm). The breakdown of chlorophyll molecules by SO2 as measured by loss of Mg++ and total chlorophyll was accompanied by a decreased ability of pine needles to photosynthesize H14CO3. The effect of SO2 on pigment breakdown and rate of photosynthesis was due mostly to the specific direct actions of SO2 and was not a function of increased acidity.