INFLUENCE OF GLUTATHIONE (GSH) ON NET UPTAKE OF SULFATE AND SULFATE TRANSPORT IN TOBACCO PLANTS

Net uptake of sulphate by the roots, and its transport to the shoot was inhibited in intact tobacco plants by 1 h exposure of its roots to 0.1 or 1.0 mM GSH. The relative amount of sulphate taken up that was transported to the shoot was not affected by this treatment. Apparently, sulphate uptake, but not xylem loading of sulphate, was inhibited by GSH. Similar results were obtained when L-cysteine was used instead of GSH. As L-cysteine, mediated inhibition of sulphate, net uptake was counteracted by exposure of the roots to BSO, GSH synthesis seems to be required for inhibition of sulphate uptake by L-cysteine. However, exposure to 0.1 or 1.0 mM GSH did not result in an enhanced GSH level in roots or shoots. Also the cysteine contents remained unchanged. Small changes in metabolically active pools of GSH or cysteine seem to be responsible for the inhibition of sulphate uptake and its transport to the shoot. Flap-feeding of GSH to a mature leaf resulted in an inhibition of net uptake of sulphate by the roots and its transport to the shoot. These findings support the hypothesis that GSH produced in the leaves acts as a signal to control sulphur nutrition of plants.