It is not all about sodium: revealing tissue specificity and signalling roles of potassium in plant responses to salt stress

Background: Salinity is a global issue threatening agricultural production systems across the globe. While the major focus of plant salinity stress tolerance research has been on sodium, the transport and physiological roles of K⁺ in plant salt stress response has received less attention. This review attempts to bridge this knowledge gap.

Scope: The major emphasis is on newly proposed K⁺ signalling roles and plant salt tolerance cell- and tissue specificity. In addition to summarizing the importance of K⁺ retention for plant salt tolerance, we focus on aspects that were not the subject of previous reviews including (1) the importance of HAK/KUP family of transporters in K⁺ uptake in salt stressed plants and its possible linkage with Ca²⁺ and ROS signalling; (2) control of xylem K⁺ loading in salt stressed plants, control of phloem K⁺ recirculation in salt stressed plants and the potential importance of plants' ability to efficiently coordinate K⁺ signals between root and shoot; (3) the buffering capacity of the vacuolar K⁺ pool; and (4) mechanisms of restoring the basal cytosolic K⁺ levels by coordinated activity of tonoplast K⁺-permeable channels.

Conclusions: Overall, this review emphasises the need to fully understand the newly emerging roles of K⁺ and regulation of its transport for improving salinity stress tolerance in plants.