Abstract
Potassium is an essential macronutrient required for plant growth and development. Over the recent decade, an important signalling role of K(+) has emerged. Here, we discuss some aspects of such signalling at the various levels of plant functional organisation. The topic covered include: (1) mechanisms of long-distant K(+) transport in the xylem and phloem and the molecular identity and regulation of K(+) loading and unloading into plant vasculature; (2) essentiality and physiological roles of K(+) cycling between shoots and roots; (3) plant sensing and signalling of low K(+); (4) maintenance of K(+) homeostasis at the cellular level; (5) stress-induced modulation of cytosolic K(+) as a signal in plant adaptive responses to hostile environment; (6) stress-specific K(+) "signatures" and mechanisms of their decoding by regulation of purine metabolism and H(+)-ATPase activity; (7) cytosolic K(+) loss as a metabolic switch and a regulator of autophagy; and (8) vacuolar K(+) transport and sensing.