Absorption of 35SO2 and sulphur translocation in bean (Phaseolus vulgaris L.)

Absorption of 35SO2 by leaves of bean plants was found to depend both on the age of plants and the age of particular leaves. Differences in the ability of particular leaves to absorb sulphur were much greater in older than in younger plants. Sulphur translocation from source to sink leaves was mainly towards leaves higher up on the stem and side shoots and also to roots. Ungassed, rapidly developing leaves of side shoots had higher levels of radioactive sulphur than ungassed leaves of the main stem. Translocation to roots was greater when the lower leaves on the plant were the source. A week after gassing with 35SO2 a drop of radioactivity occurred in both source and sink leaves; the drop was greater in experiments with gassing individual leaves than whole plants. A week after the last exposure of leaves to 35SO2 labelled sulphur was found also in pods and its content increased the more the higher up on the plants were the source leaves. Sulphur dioxide absorption by leaves also depended on the degree of tissue hydration; under optimum soil moisture conditions 35SO2 absorption by leaves was greater than under soil drought conditions. (author)