I. THE EFFECTS OF LIGHT AND DARK ON THE UPTAKE AND TRANSLOCATION OF 3'SO2

SUMMARY First-trifoliate leaves of four-leaved soybean plants were exposed to 3"SO2 in the light or dark, and the uptake and translocation of radioactivity measured. Nearly four times more 35S02 was taken up in the light (stomata open) than in the dark (stomata closed) but approximately 50% of the radioactivity was leached from the leaf surface in the dark compared with 5% in the light. A greater proportion of the source-leaf radioactivity was translocated in the dark but, in absolute terms, the quantity of radioactivity moved was less. Radioactive products were found in all parts of the plant after exposure in both light and dark. The expanding trifoliate leaf contained the greatest concentration of translocated radioactivity in both cases. Light and dark pre- and post-treatments had little effect on uptake of 35S02 or translocation of the products. 35SO42- was detected in the nutrient solution within 1 h of exposure of leaves to 35S02.