The differences in physiological responses, ultrastructure changes, and Na+ subcellular distribution under salt stress among the barley genotypes differing in salt tolerance

Plants adopt several strategies to maintain cellular ion homeostasis, including physiological, biochemical, cellular, subcellular, and molecular mechanisms for fighting against salt stress. We investigated the responses of tolerant Tibetan wild barley (XZ16), tolerant (CM72) and sensitive (Gairdner) barley cultivars at physiological, cellular, and molecular levels. The results revealed that salinity induced a significantly greater reduction in total root length, surface area, diameter, and total volume in Gairdner than in CM72 and XZ16. Analysis of gene expression using quantitative RT-PCR showed that transcripts of vacuolar H+-ATPase and inorganic pyrophosphatase (HvHVA/68 and HvHVP1) were more abundant in leaves and roots of XZ16 and CM72 than those of Gairdner. Observation of electron microscopy detected the difference in the damage of leaf and root ultrastructure among the three genotypes under salt stress, with XZ16 and Gairdner being least and most affected, respectively. Subcellular study showed that a primary strategy to protect the cytosol against sodium toxicity was compartmentalization of sodium ions into soluble fraction (vacuoles). Gairdner showed drastically stronger sodium-specific fluorescence visualized by CoroNa-Green, a sodium-specific fluorophore, than CM72 and XZ16.