Sulphur dioxide metabolism in soy-bean, Glycine max var. biloxi

First-trifoliate leaves of soybeans Glycine max (L.) Merr. were exposed to 35SO2 in the light or dark, and the chemical distribution of the radioactivity in the source leaves and in the remainder of the plant was determined after 1.5 and 24 h. Only 35SO42- was found in leachates in the light but substantial quantities of 35SO32- were present in the dark. Radioactivity was present in all fractions of the source leaves examined (insoluble, centrifuge pellet, soluble protein, chloroform-soluble and water-soluble). The main water-soluble compounds labelled were sulphate >glutathione >cysteine. Small quantities of sulphite were also recovered in the dark but not in the light. The ratio of soluble: insoluble radioactivity in the sink tissues was influenced more by leaf age than by light treatment. Sulphate, glutathione and cysteine were labelled in the petioles of the source leaves and 35SO42- was found in the nutrient solution after 1.5 h in both treatments. It is concluded that light is not necessary for the reduction of internal 35SO2 products. The results are discussed in relation to current knowledge of SO2 metabolism. (author)