Puccinellia tenuiflora maintains a low Na(+) level under salinity by limiting unidirectional Na(+) influx resulting in a high selectivity for K(+) over Na(+)

Puccinellia tenuiflora is a useful monocotyledonous halophyte that might be used for improving salt tolerance of cereals. This current work has shown that P. tenuiflora has stronger selectivity for K(+) over Na(+) allowing it to maintain significantly lower tissue Na(+) and higher K(+) concentration than that of wheat under short- or long-term NaCl treatments. To assess the relative contribution of Na(+) efflux and influx to net Na(+) accumulation, unidirectional (22)Na(+) fluxes in roots were carried out. It was firstly found that unidirectional (22)Na(+) influx into root of P. tenuiflora was significantly lower (by 31-37%) than in wheat under 100 and 150 mm NaCl. P. tenuiflora had lower unidirectional Na(+) efflux than wheat; the ratio of efflux to influx was similar between the two species. Leaf secretion of P. tenuiflora was also estimated, and found the loss of Na(+) content from leaves to account for only 0.0006% of the whole plant Na(+) content over 33 d of NaCl treatments. Therefore, it is proposed that neither unidirectional Na(+) efflux of roots nor salt secretion by leaves, but restricting unidirectional Na(+) influx into roots with a strong selectivity for K(+) over Na(+) seems likely to contribute to the salt tolerance of P. tenuiflora.