Physiological and molecular mechanisms of salt tolerance in barley (Hordeum vulgare L.)

Abstract

Two isogenic barley cultivars Golden Promise and Maythorpe were used in this study to investigate physiological and molecular mechanisms of salt tolerance. Using the mRNA differential display technique, 21 cDNA fragments were cloned from young leaves, 10 of them had homologues from GenBank. A leucine zipper transcription factor gene (B 15/B20) was upregulated in Golden Promise and down-regulated in Maythorpe by both shortterm and long-term salt stress. The difference in the expression of this gene in response to salinity may regulate the expression of other genes identified from this study in response to salt stress, e. g. the Rubisco small subunit, cytochrome B6, chloroplast ATP synthase and V-ATPase B subunit. The V-ATPase B subunit was up-regulated in Golden Promise and down-regulated in Maythorpe under both short-term and long-term salt stress, which indicates the greater potential of Golden Promise in excluding excess Na+ from the cytoplasm and storage in the vacuoles when compared with Maythorpe. Other genes identified and associated with photosynthesis, e. g. genes encoding the Rubisco small subunit, cytochrome B6 and ATP synthase were down-regulated in Maythorpe by both short and long-term salt stress. However, in Golden Promise, the Rubisco small subunit was up-regulated by short-term salt stress and cytochrome B6 was up-regulated by both short and long-term salt stress. The differential expression of the above genes between Golden Promise and Maythorpe in response to salinity was closely related to measured differences in physiological characteristics. For instance, Golden Promise maintained significantly lower Na' concentrations and higher K+/Na+ and Cat+/ Na+ ratios than Maythorpe in the young leaves with increasing external NaCl concentrations. Golden Promise also showed higher comparative growth of shoot and significantly higher photosynthetic rates than Maythorpe under salt stress.