K+Nutrition and Na+Toxicity: The Basis of Cellular K+/Na+Ratios

The capacity of plants to maintain a high cytosolic K⁺/Na⁺ratiois likely to be one of the key determinants of plant salt tolerance.Important progress has been made in recent years regarding theidentification and characterization of genes and transportersthat contribute to the cytosolic K⁺/Na⁺ratio. For K⁺uptake,K⁺efflux and K⁺translocation to the shoot, genes have been isolatedthat encode K⁺uptake and K⁺release ion channels and K⁺carriersthat are coupled to either a H⁺or Na⁺gradient. Although thepicture is less clear for the movement of Na⁺, one pathway,in the form of non-selective ion channels, is likely to playa role in Na⁺uptake, whereas Na⁺efflux and compartmentationare likely to be mediated by H⁺-coupled antiport. In addition,several proteins have been characterized that play prominentroles in the regulation of K⁺and/or Na⁺fluxes. In this BotanicalBriefing we will discuss the functions and interactions of thesegenes and transporters in the broader context of K⁺nutritionand Na⁺toxicity. Copyright 1999 Annals of Botany Company Salinty, K⁺/N⁺ratio, transporter, membrane.