Biochemical and hormonal control of K+ homeostasis

Abstract

Cation antiporters of NHX family have been shown to increase the salt tolerance of various plants species and are thought to mediate compartmentation of Na+ in vacuoles. However, all isoforms characterized so far catalyze both Na+/H+ and K+/H+ exchange. Genetic evidence will be presented that NHX-type proteins are likely candidates for the H+-linked K+-transport that is thought to facilitate active K+ uptake at the tonoplast and the partitioning of K+ between vacuole and cytosol. This critical function should be taken into consideration for understanding the salt tolerance phenotype of plants overexpressing NHX-type exchangers. Recent findings show that ethylene and reactive oxygen species mediate the plant response to potassium deprivation. The transcriptional induction of the high-affinity K+ transporter gene HAK5 and changes in root morphology are among the adaptative responses to low K+ that regulated by ethylene.