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

Abstract

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 <or= 25 microM 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.