Copper exposure interferes with the regulation of the uptake, distribution and metabolism of sulfate in Chinese cabbage.

Exposure of Chinese cabbage (Brassica pekinensis) to enhanced Cu(2+) concentrations (1-10 microM) resulted in leaf chlorosis, a loss of photosynthetic capacity and lower biomass production at > or = 5 microM. The decrease in pigment content was likely not the consequence of degradation, but due to hindered chloroplast development upon Cu exposure. The Cu content of the root increased with the Cu(2+) concentration (up to 40-fold), though only a minor proportion (4%) was transferred to the shoot. The nitrate uptake by the root was substantially reduced at > or = 5 microM Cu(2+). The nitrogen content of the root was affected little at lower Cu(2+) levels, whereas that in the shoot was decreased at > or = 5 microM Cu(2+). Cu affected the uptake, distribution and metabolism of sulfate in Chinese cabbage. The total sulfur content of the shoot was increased at > or = 2 microM Cu(2+), which could be attributed mainly to an increase in sulfate content. Moreover, there was a strong increase in water-soluble non-protein thiol content in the root and, to a lesser extent, in the shoot at > or = 1 microM, which could only partially be ascribed to a Cu-induced enhancement of the phytochelatin content. The nitrate uptake by the root was substantially reduced at > or = 5 microM Cu(2+), coinciding with a decrease in biomass production. However, the activity of the sulfate transporters in the root was slightly enhanced at 2 and 5 microM Cu(2+), accompanied by enhanced expression of the Group 1 high affinity transporter Sultr1;2, and the Group 4 transporters Sultr4;1 and Sultr4;2. In the shoot, there was an induction of expression of Sultr4;2 at 5 and 10 microM Cu(2+). The expression of APS reductase was affected little in the root and shoot up to 10 microM Cu(2+). The upregulation of the sulfate transporters may be due not only to greater sulfur demand at higher Cu levels, but also the consequence of interference by Cu with the signal transduction pathway regulating the expression and activity of the sulfate transporters.

Expression and activity of sulfate transporters and APS reductase in curly kale in response to sulfate deprivation and re-supply.

Both activity and expression of sulfate transporters and APS reductase in plants are modulated by the sulfur status of the plant. To examine the regulatory mechanisms in curly kale (Brassica oleracea L.), the sulfate supply was manipulated by the transfer of seedlings to sulfate-deprived conditions, which resulted in an up to 3-fold increase in the sulfate uptake capacity by the root, accompanied by an induction of transcript abundances of the Group 1 and 4 sulfate transporters in root and shoot. Upon sulfate re-supply, there was no correlation between the activity and expression of the sulfate transporters. Despite the decrease in the abundance of the sulfate transporter transcripts, especially at the onset of the sulfate re-supply, the sulfate uptake capacity was affected very little for up to 96h. There was no relationship between changes in the sulfate or thiol content and activity and expression of the sulfate transporters. Thus, their significance as regulatory signal compounds remains unresolved. The activity and expression of APS reductase, which was enhanced strongly only in the shoots of sulfate-deprived plants, and rapidly decreased again upon sulfate re-supply, corresponded with changes in thiol content, consistent with this pool having a role as a regulatory signal.

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 H2S 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 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.

Regulation of sulfate uptake and expression of sulfate transporter genes in Brassica oleracea as affected by atmospheric H(2)S and pedospheric sulfate nutrition.

Demand-driven signaling will contribute to regulation of sulfur acquisition and distribution within the plant. To investigate the regulatory mechanisms pedospheric sulfate and atmospheric H(2)S supply were manipulated in Brassica oleracea. Sulfate deprivation of B. oleracea seedlings induced a rapid increase of the sulfate uptake capacity by the roots, accompanied by an increased expression of genes encoding specific sulfate transporters in roots and other plant parts. More prolonged sulfate deprivation resulted in an altered shoot-root partitioning of biomass in favor of the root. B. oleracea was able to utilize atmospheric H(2)S as S-source; however, root proliferation and increased sulfate transporter expression occurred as in S-deficient plants. It was evident that in B. oleracea there was a poor shoot to root signaling for the regulation of sulfate uptake and expression of the sulfate transporters. cDNAs corresponding to 12 different sulfate transporter genes representing the complete gene family were isolated from Brassica napus and B. oleracea species. The sequence analysis classified the Brassica sulfate transporter genes into four different groups. The expression of the different sulfate transporters showed a complex pattern of tissue specificity and regulation by sulfur nutritional status. The sulfate transporter genes of Groups 1, 2, and 4 were induced or up-regulated under sulfate deprivation, although the expression of Group 3 sulfate transporters was not affected by the sulfate status. The significance of sulfate, thiols, and O-acetylserine as possible signal compounds in the regulation of the sulfate uptake and expression of the transporter genes is evaluated.