The Characteristic High Sulfate Content in Brassica oleracea is Controlled by the Expression and Activity of Sulfate Transporters

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 Km 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 μM sulfate in the root environment. Abundance of mRNAs for the high affinity sulfate transporters, BolSultr1;1 and BolSultr1;2, were enhanced at ≤ 25 μM sulfate, and this was accompanied with an up to three‐fold increase in the sulfate uptake capacity, whereas sulfate, organic sulfur, and thiol contents were only slightly affected. Upon sulfate deprivation, there was a much greater induction of the sulfate transporters, BolSultr1;1, BolSultr1;2, BolSultr1;3, BolSultr2;1, and BolSultr4;1, whilst the sulfate uptake capacity was only increased up to four‐fold. Plant growth and shoot to root biomass allocation were affected only upon sulfate‐deprivation and not at low external sulfate concentrations. From the current results it is suggested that the internal sulfate concentration may act as a determining factor in the regulation of activity and expression of sulfate transporters, and of shoot to root biomass allocation in B. oleracea.