Tissue metabolic responses to salt stress in wild and cultivated barley

Abstract

A thorough understanding of the mechanisms underlying barley salt tolerance and exploitation of elite genetic resource are essential for utilizing wild barley germplasm in developing barley varieties with salt tolerance. In order to reveal the physiological and molecular difference in salt tolerance between Tibetan wild barley (Hordeum spontaneum) and cultivated barley (Hordeum vulgare), profiles of 82 key metabolites were studies in wild and cultivated barley in response to salinity. According to shoot dry biomass under salt stress, XZ16 is a fast growing and salt tolerant wild barley. The results of metabolite profiling analysis suggested osmotic adjustment was a basic mechanism, and polyols played important roles in developing salt tolerance only in roots, and high level of sugars and energy in roots and active photosynthesis in leaves were important for barley to develop salt tolerance. The metabolites involved in tolerance enhancement differed between roots and shoots, and also between genotypes. Tibetan wild barley, XZ16 had higher chlorophyll content and higher contents of compatible solutes than CM72, while the cultivated barley, CM72 probably enhanced its salt tolerance mainly through increasing glycolysis and energy consumption, when the plants were exposed to high salinity. The current research extends our understanding of the mechanisms involved in barley salt tolerance and provides possible utilization of Tibetan wild barley in developing barley cultivars with salt tolerance.

Figure 1. Shoot growth performance of the four barley genotypes (CM72, Gairdner, XZ16 and XZ169) under normal, moderate and high salinity conditions.

(A) shoot dry weight (g⁻¹ plant) at 35 days after salinity treatments and normal conditions (four biological replicates, bars show SE), * and ** indicates significant (P<0.05) and highly significant difference (P<0.01), respectively; (B) shoot relative dry weight (%) at 35 days after moderate (150 mM NaCl) and high (300 mM) salinity treatment; (C) pictures of shoot-plants of CM72, Gairdner, XZ16 and XZ169 at 35 days after salinity treatment and normal conditions.

Figure 2. The chlorophyll content (SPAD value) of the four barley genotypes (CM72, Gairdner, XZ16 and XZ169) at 35 days after salinity treatment and normal conditions (eight biological replicates, bars show SE).

Figure 3. Principal component analysis (PCA) of metabolic profiles in roots and leaves of CM72 and XZ16 under control and high salinity conditions (six biological replicates).

(A) PCA in roots; (B) PCA in leaves. CK: control; T: salt treatment; PC1, the first principal component; PC2, the second principal component.

Figure 4. Global comparison of metabolic profiles in roots and leaves between CM72 and XZ16 under control and high salinity conditions.

There are eighty-two metabolites identified in this study and the numbers in the figure indicate the numbers of metabolites with no significant difference in their contents for each comparison.

Figure 5. Change in metabolites of the metabolic pathways in roots of CM72 and XZ16 after 21 days of salinity treatment.

Numbers 1–4 on the X-axis indicate CM72-control, CM72-salt treatment, XZ16-control and XZ16-salt treatment, respectively. The concentration of metabolites on the Y-axis is presented as normalized values transformed by Metaboanalyst software (www.metaboanalyst.ca/), and the box plots show centered means and standard deviation of each variable. Metabolites in red indicate significant (P<0.05) up-accumulation in both CM72 and XZ16, in purple mean significant (P<0.05) up-accumulation in CM72 or XZ16, in light blue show significant (P<0.05) down-accumulation in CM72 or XZ16, and in dark blue represent significant (P<0.05) down-accumulation in CM72 and XZ16.

Figure 6. Change in metabolites of the metabolic pathways in leaves of CM72 and XZ16 after 21 days of salinity treatment.

Numbers 1–4 on the X-axis indicate CM72-control, CM72-salt treatment, XZ16-control and XZ16-salt treatment, respectively. The concentration of metabolites on the Y-axis is presented as normalized values transformed by Metaboanalyst software (www.metaboanalyst.ca/), and the box plots show centered means and standard deviation of each variable. Metabolites in red indicate significant (P<0.05) up-accumulation in both CM72 and XZ16, in purple mean significant (P<0.05) up-accumulation in CM72 or XZ16, in light blue show significant (P<0.05) down-accumulation in CM72 or XZ16, and in dark blue represent significant (P<0.05) down-accumulation in CM72 and XZ16.