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.