Abstract
Potassium (K) is the most abundant inorganic cation in plants. It is required for the activation of many enzymes, as a cellular osmoticum for rapidly expanding cells, and as a counter cation for anion accumulation and electrogenic transport processes. This chapter describes (1) the symptoms of potassium deficiency and the acclimatory responses of plants to potassium starvation, (2) the mechanisms by which roots acquire K+ from the soil and K+ is transported between tissues. and (3) the molecular biology of the transport proteins that catalyse influx and efflux across the plasma membrane and tonoplast of plant cells to effect K+ uptake and redistribution within the plant, cell expansion and shrinking, and cytoplasmic K+ homeostasis.