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SummaryNa uptake in the roots of K -starved seedlings of barley, rice, and wheat was found to exhibit fast rate, low OsHKT genes were fairly constant and insensitive to changes in the K and Na concentrations of the nutrient solution. In roots, the expressions were much lower than in shoots, except for OsHKT4 and OsHKT1 in K -starved plants. We propose that OsHKT transporters are involved in Na movements in rice, and that OsHKT1 speci®cally mediates Na uptake in rice roots when the plants are K de®cient. The incidence of HKT ESTs in several plant species suggests that the rice model with many HKT genes applies to other plants.

The gene ENA1 was cloned by its ability to complement the Li+ sensitivity of a low Li+‐efflux strain. The nucleotide sequence of the cloned DNA fragment showed that there are two almost identical genes in tandem, and predicts that they encode P‐ATPases. Disruption of both genes originated a strain defective in Na+ and Li+ effluxes, and sensitive to Na+, to Li+ and to alkaline pH. By transformation with ENA1 the defective effluxes and tolerances were repaired.

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Plants take up large amounts of K+ from the soil solution and distribute it to the cells of all organs, where it fulfills important physiological functions. Transport of K+from the soil solution to its final destination is mediated by channels and transporters. To better understand K+ movements in plants, we intended to characterize the function of the large KT-HAK-KUP family of transporters in rice (Oryza sativacv Nipponbare). By searching in databases and cDNA cloning, we have identified 17 genes (OsHAK1–17) encoding transporters of this family and obtained evidence of the existence of other two genes. Phylogenetic analysis of the encoded transporters reveals a great diversity among them, and three distant transporters, OsHAK1, OsHAK7, and OsHAK10, were expressed in yeast (Saccharomyces cerevisiae) and bacterial mutants to determine their functions. The three transporters mediate K+ influxes or effluxes, depending on the conditions of the experiment. A comparative kinetic analysis of HAK-mediated K+ influx in yeast and in roots of K+-starved rice seedlings demonstrated the involvement of HAK transporters in root K+ uptake. We discuss that all HAK transporters may mediate K+ transport, but probably not only in the plasma membrane. Transient expression of the OsHAK10-green fluorescent protein fusion protein in living onion epidermal cells targeted this protein to the tonoplast.