Molecular and Cellular Biology
Genetic and physiological complexities associated with salt tolerance in plants have limited progress in the analysis of specific factors responsible for the salt-tolerant phenotype. We have used the homosporous fern Ceratopteris richardii as a model plant to investigate the physiological basis of salinity tolerance by selecting single gene mutants that confer tolerance in the gametophyte generation. The unique genetic system of homosporous ferns permits the generation of mutants in a genetic background nearly isogenic to the wildtype, such that comparative studies with the wildtype can identify specific physiological responses associated with salt tolerance. One of these mutations, stl2, confers a high level of tolerance to Na+ (I-50 approximate to 175 mM NaCl) and generates a complex suite of related phenotypes. For example, in addition to Na+ tolerance, stl2 exhibits tolerance to Mg2+salts, sensitivity to supplemented K+, higher K+-dependent efflux of K+, altered responses to Ca2+ supplementation and moderate tolerance to osmotic stresses. Based upon its physiological attributes, we have proposed that the mechanism of action for this mutation involves an enhanced influx of K+ and higher selectivity for K+ over Na+ in a KC channel. The direct and indirect consequences of this alteration can account for NaCl tolerance and the other phenotypes evident in stl2. The complex set of phenotypic responses from such a single gene mutation illustrates the potential for even more extreme pleiotropy in multigenic salt-tolerant strains.
International Journal of Plant Sciences