Effect of H2S exposure on S-35-sulfate uptake, transport and utilization in curly kale

When Brassica oleracea L. was exposed to 0.2 mul l(-1) H2S the sulfate upta ke measured during a dark or light period was decreased to the same extent. Both the xylem loading and the net sulfate uptake rate were decreased by 4 2% after 6 days of exposure to 0.4 mul l(-1) H2S. This suggested that the x ylem loading was not the limiting factor in the uptake of sulfate by the ro ots. When Brassica oleracea L. was exposed to 0.4 mul l(-1) H2S and grown o n a nutrient solution containing S-35-sulfate, the specific radioactivity o f the labeled S of the insoluble fraction (mainly proteins) of the shoot an d roots was decreased more than the specific radioactivity of the labeled S of the soluble fraction (mainly sulfate). This demonstrated that the major proportion of the metabolized atmospheric H2S was incorporated into protei ns. The change in partitioning of the labeled sulfur upon H2S exposure was similar in the roots compared to the shoot, which suggested that the roots were dependent on the shoot for their organic sulfur supply.