| To provide insight into genetic mechanisms underlying salt tolerance in plants, T-DNA insertionally mutagenized seeds of Arabidopsis thaliana were screened on media containing 150–175 mM NaCl for an ability to germinate.; Two salt tolerant mutants, NN3 and NN143, were identified. Genetic analysis of the F1 and F2 generations indicated that the salt tolerance trait was recessive in NN3 and dominant in NN143.; When subjected to osmotic stress imposed by 175 mM NaCl for two weeks, mutants NN3 and NN143 attained germination levels of 97% and 65%, respectively. At this concentration of salt, the wild-type seeds were incapable of germination. On 300 mM mannitol, NN143, NN3 and wild type attained germination levels of 77%, 95% and 2% respectively. The biomass of NN3 seedlings grown on a medium containing 150 mM NaCl was significantly greater than that of the mutant NN143. Between 104 and 145 hours after germination on media containing 175 mM NaCl and 300 mM mannitol, germination levels of mutant NN3 were significantly higher than those of mutant NN143.; Mutant NN143 was capable of germination on a medium containing abscisic acid (ABA). After two weeks on 2 μM ABA, it attained 100% germination, and the wild type and NN3 did not germinate. The biomass of NN143 seedlings grown on ABA-free medium and those grown on 2 μM ABA were not significantly different. In presence of both 1 μM ABA and 250 mM mannitol, the ABA-insensitive mutant achieved 60% germination compared to 93% germination for seeds subjected only to 250 mM mannitol. Apparently, the hormone and the osmoticum exert a synergistic effect on its germination performance. Under these conditions, the wild type and NN3 did not germinate.; Phenotypic comparison of NN3 with the aba and abi mutants indicated that it must be a distinct gene. Genetic analysis of NN143 showed that it was not allelic to the only phenotypically similar abi mutant, abi3-1. The ABA levels in the seeds of NN143 and NN3 were 39% higher than and the same as in the wild type, respectively.; A putative salt tolerance gene of mutant NN143 was cloned by plasmid rescue and sequence data indicated the possible involvement of a protein phosphatase. The possible mechanisms underlying salt tolerance in mutants NN3 and NN143 are discussed. |
