Regulation of sodium-inducible genes and efficient use of sodium ions determine the tolerance strategies of Cakile maritima and Brassica tournefortii in natural habitats

Abstract

One of the potential routes for improving the stress tolerance of crops is discovering the tolerance mechanisms of halophytes. Cakile maritima and Brassica tournefortii were collected from four sites with different salinity levels. Two populations for each species were collected from each site. The populations of C. maritima had different phenotypic traits, especially at high salinity levels. Meanwhile, the populations of B. tournefortii had approximately similar phenotypic traits at all sites. The present study aimed to compare the tolerance strategies used by C. maritima and B. tournefortii by examining the responses of different populations of each species to high salinity levels in their natural habitats. The evolutionary relationship among the populations of each species was recorded. Growth performance, pigment concentration, Rubisco protein content, ion concentration and regulation of salt-inducible genes were evaluated. At high salinity levels, the biomass of most C. maritima populations increased, but the reverse was true for B. tournefortii populations. The acclimation of B. tournefortii to salt stress depends on Na⁺ extrusion mechanisms. Meanwhile, C. maritima acclimated by a regulated and controlled ion uptake, regulated salt-inducible genes and efficient use of Na⁺ in osmotic adjustment. Hierarchical analysis revealed that the expression pattern of Na⁺-inducible genes was not only species-dependent but also organ-dependent. The expression pattern did not correspond to the profiles of promoter regulatory motifs of the examined genes. The study concluded that the tolerance mechanisms are not static among halophytes, but they are dependent on the species and even on the population of a species.