Expression Patterns of Genes Encoding Sugar and Potassium Transport Proteins are Simultaneously Up- or Downregulated When Carbon and Potassium Availability is Modified in Shiraz (Vitis vinifera L.) Berries.

A link between the accumulation of sugar and potassium has previously been described for ripening grape berries. The functional basis of this link has, as of yet, not been elucidated, but could potentially be associated with the integral role that potassium has in phloem transport. An experiment was conducted on Shiraz grapevines in a controlled environment. Berry sugar accumulation was curtailed by reducing the leaf photoassimilation rate and the availability of potassium was increased through soil fertilisation. The study characterises the relationship between the accumulation of sugar and potassium into the grape berry and describes how their accumulation patterns are related to the expression patterns of their transporter proteins. A strong connection was observed between sugar and potassium accumulation in the grape berry pericarp, irrespective of the treatment. The relative expression of proteins associated with sugar and potassium transport across the tonoplast and plasma membrane were closely correlated, suggesting transcriptional co-regulation leading to the simultaneous translocation and storage of potassium and sugar in the grape berry cell.