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.