Calcium regulation of sodium hypersensitivities of sos3 and athkt1 mutants
2006
Horie, T.(University of California, San Diego (USA)) | Horie, R. | Chan, W.Y. | Leung, H.Y. | Schroeder, J.I.
T-DNA disruption mutations in the AtHKT1 gene have previously been shown to suppress the salt sensitivity of the sos3 mutant. However, both sos3 and athkt1 single mutants show sodium (Nasup(+)) hypersensitivity. In the present study we further analyzed the underlying mechanisms for these non-additive and counteracting Nasup(+) sensitivities by characterizing athkt1-1 sos3 and athkt1-2 sos3 double mutant plants. Unexpectedly, mature double mutant plants grown in soil clearly showed an increased Nasup(+) hypersensitivity compared with wild-type plants when plants were subjected to salinity stress. The salt sensitive phenotype of athkt1 sos3 double mutant plants was similar to that of athkt1 plants, which showed chlorosis in leaves and stems. The Nasup(+) content in xylem sap samples of soil-grown athkt1 sos3 double and athkt1 single mutant plants showed dramatic Nasup(+) over-accumulation in response to salinity stress. Salinity stress analyses using basic minimal nutrient medium and Murashige-Skoog (MS) medium revealed that athkt1 sos3 double mutant plants show a more athkt1 single mutant-like phenotype in the presence of 3 mM external Casup(2+), but show a more sos3 single mutant-like phenotype in the presence of 1 mM external Casup(2+). Taken together multiple analyses demonstrate that the external Casup(2+) concentration strongly impacts the Nasup(+) stress response of athkt1 sos3 double mutants. Furthermore, the presented findings show that SOS3 and AtHKT1 are physiologically distinct major determinants of salinity resistance such that sos3 more strongly causes Nasup(+) overaccumulation in roots, whereas athkt1 causes an increase in Nasup(+) levels in the xylem sap and shoots and a concomitant Nasup(+) reduction in roots.
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