Regulation of sulfate uptake, expression of the sulfate transporters Sultr1;1 and Sultr1;2, and APS reductase in Chinese cabbage (Brassica pekinensis) as affected by atmospheric HS nutrition and sulfate deprivation.

The activity and expression of sulfate transporters and adenosine 5'-phosphosulfate (APS) reductase (APR) in plants are modulated by the plant sulfur status and the demand for growth. To elucidate regulatory mechanisms in Chinese cabbage [Brassica pekinensis (Lour.) Rupr.], the interactions between atmospheric HS and sulfate nutrition and the impact on the activity and expression of the Group 1 sulfate transporters and APR were studied. At an ample sulfate supply, HS exposure of Chinese cabbage resulted in a partial decrease of the sulfate uptake capacity, and at concentrations ≥0.25 μL L a decreased expression of Sultr1;2 in the root and APR in the root and shoot. Upon sulfate deprivation there was a more than 3-fold increase in the sulfate uptake capacity of the root, accompanied by an induced expression of Sultr1;1 and an enhanced expression of Sultr1;2 in the root, along with an induction of Sultr1;2 in the shoot. The enhanced sulfate uptake capacity, the expression of the sulfate transporters in the root and the altered shoot-to-root partitioning appearing during sulfate deprivation were not alleviated upon HS exposure and not rapidly affected by sulfate re-supply. Expression of APR was strongly enhanced in the root and shoot of sulfate-deprived plants and decreased again upon HS exposure and sulfate re-supply. The significance of shoot-to-root interaction and sulfate and thiols as regulating signals in the activity and expression of Sultr1;1 and 1;2 is evaluated.