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 H2S 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, H2S exposure of Chinese cabbage resulted in a partial decrease of the sulfate uptake capacity, and at concentrations ≥0.25 μL L−1 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 H2S 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 H2S 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.

The uptake and distribution of sulfate in BRASSICA OLERACEA, a species characterised by its high sulfate content in root and shoot, are coordinated and adjusted to the sulfur requirement for growth, even at external sulfate concentrations close to the K (m) value of the high-affinity sulfate transporters. Plants were able to grow normally and maintain a high sulfur content when grown at 5 or 10 microM sulfate in the root environment. Abundance of mRNAs for the high affinity sulfate transporters, BolSultr1;1 and BolSultr1;2, were enhanced at

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