Transport, signaling, and homeostasis of potassium and sodium in plants

Potassium (K+) is an essential macronutrient in plants and a lack of K+ significantly reduces the potential for plant growth and development. By contrast, sodium (Na+), while beneficial to some extent, at high concentrations it disturbs and inhibits various physiological processes and plant growth. Due to their chemical similarities, some functions of K+ can be undertaken by Na+ but K+ homeostasis is severely affected by salt stress, on the other hand. Recent advances have highlighted the fascinating regulatory mechanisms of K+ and Na+ transport and signaling in plants. This review summarizes three major topics: (i) the transport mechanisms of K+ and Na+ from the soil to the shoot and to the cellular compartments; (ii) the mechanisms through which plants sense and respond to K+ and Na+ availability; and (iii) the components involved in maintenance of K+/Na+ homeostasis in plants under salt stress.