High-affinity sodium uptake in land plants.

High-affinity Na(+) uptake in plants and its mediation by HKT transporters have been studied in very few species. This study expands the knowledge of high-affinity Na(+) uptake in land plants for both uptake characteristics and involvement of HKT transporters. In non-flowering plants, we analyzed the Na(+) content of wild mosses, carried out experiments on K(+) and Na(+) uptake in the micromolar range of concentrations with the moss Physcomitrella patens and the liverwort Riccia fluitans, studied a Deltahkt1 mutant of P. patens and identified the HKT genes of the lycopodiophyta (clubmoss) Selaginella moellendorffii. In flowering plants we studied Na(+) uptake in the micromolar range of concentrations in 16 crop plant species, identified the HKT transporters that could mediate high-affinity Na(+) uptake in several species of the Triticeae tribe, and described some characteristics of high-affinity Na(+) uptake in other species. Our results suggest that high-affinity Na(+) uptake occurs in most land plants. In very few of them, rice and species in the Triticeae and Aveneae tribes of the Poaceae family, it is probably mediated by HKT transporters. In other plants, high-affinity Na(+) uptake is mediated by one or several transporters whose responses to the presence of K(+) or Ba(2+) are fundamentally different from those of HKT transporters.