A high-affinity K+ transporter PutHKT2;1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. Expression of PutHKT2;1 was induced by both 300 mM NaCl and K+-starvation stress in roots, but only slightly regulated by those stresses in shoots. PutHKT2;1 transcript levels in 300 mM NaCl were doubled by the depletion of potassium. Yeast transformed with PutHKT2;1, like those transformed with PhaHKT2;1 from salt-tolerant reed plants (Phragmites australis), (i) were able to take up K+ in low K+ concentration medium or in the presence of NaCl, and (ii) were permeable to Na+. This suggests that PutHKT2;1 has a high affinity K+-Na+ symport function in yeast. Arabidopsis over-expressing PutHKT2;1 showed increased sensitivities to Na+, K+, and Li+, while Arabidopsis over-expressing OsHKT2;1 from rice (Oryza sativa) showed increased sensitivity only to Na+. In contrast to OsHKT2;1, which functions in Na+-uptake at low external K+ concentrations, PutHKT2;1 functions in Na+-uptake at higher external K+ concentrations. These results show that the modes of action of PutHKT2;1 in transgenic yeast and Arabidopsis differ from the mode of action of the closely related OsHKT2;1 transporter.

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Potassium channels are important for many physiological functions in plants, one of which is to regulate plant adaptation to stress conditions. In this study, a K(+) channel PutAKT1 cDNA was isolated from the salt-tolerant plant Puccinellia tenuiflora. A phylogenetic analysis showed that PutAKT1 belongs to the AKT1-subfamily in the Shaker K(+) channel family. PutAKT1 was localized in the plasma membrane and it was preferentially expressed in the roots. The expression of PutAKT1 was induced by K(+)-starvation stress in the roots and was not down-regulated by the presence of excess Na(+). Arabidopsis plants over-expressing PutAKT1 showed enhanced salt tolerance compared to wild-type plants as shown by their shoot phenotype and dry weight. Expression of PutAKT1 increased the K(+) content of Arabidopsis under normal, K(+)-starvation, and NaCl-stress conditions. Arabidopsis expressing PutAKT1 also showed a decrease in Na(+) accumulation both in the shoot and in the root. These results suggest that PutAKT1 is involved in mediating K(+) uptake (i) both in low- and in high-affinity K(+) uptake range, and (ii) unlike its homologs in rice, even under salt-stress condition.

The development of salinity tolerant varieties can be done by using doubled haploid technology. In the determination of the salinity tolerance trait, hydroponic screening at the seedling stage is the most common screening method. However, it needs improvement on the assignment of the tolerance traits. Cluster heatmap analysis has been reported to select lines by combining various data. The objective of the study was to select tolerant doubled-haploid rice lines to salinity stress at the seedling phase and evaluate the use of cluster heatmap analysis by combining tolerance score and growth characters. The study was conducted in a greenhouse using a nested factorial design (repetition nested in NaCl concentrations), with 3 replications. The plant materials used consisted of 62 genotypes and NaCl concentration levels consisted of 0 (1 dS/m) and 120 mM (13.3 dS/m). Hydroponic cultures used a Yoshida solution. Each container contained 14 experimental units and 2 units of check i.e. sensitive and tolerant controls. Observations was carried out on tolerance scoring and growth parameters. The results showed that tolerant and moderate genotypes have a lower pattern of decline than sensitive genotypes, especially in shoot-related characters. Based on the cluster heatmap analysis, there were 38 doubled haploid rice lines considered good tolerance traits under saline condition. The cluster heatmap assignment was considered more selective than only focused on tolerance score, especially in negative selection to sensitive lines.