Genotypic differences in physiological characteristics in the tolerance to drought and salinity combined stress between Tibetan wild and cultivated barley

Greenhouse pot experiments were conducted to investigate genotypic differences in response to individual and combined stresses of drought and salinity between Tibetan wild barley genotypes (XZ5, drought-tolerant; XZ16, salinity/aluminum tolerant) and cv. CM72 (salinity-tolerant). Either drought (D) or salinity (S) alone and in combination (D + S) stresses significantly decreased plant growth, chlorophyll content, net photosynthetic rate (Pn), maximal photochemical efficiency of PSII (Fv/Fm), water potential and osmotic potential, with the largest suppression under combined stress, and two wild genotypes showing more tolerance than CM72. Water use efficiency (WUE) increased significantly in XZ5 and XZ16 after D + S, but no significant change in CM72. XZ5 and XZ16 showed 30.9% and 12.1% higher K+ level and 30.5% and 24.1% lower Na+/K+ ratio in plants, compared with CM72, with increased metal nutrients as Ca, Fe and Mn under D + S. The peak accumulation in proline and glycine-beatine was recorded in combined stress with larger accumulation in two wild genotypes. Moreover, larger increases in the level of ASA and GSH, and the activities of Ca2+Mg2+-ATPase, and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), guaiacol peroxidase (POD) and glutathione reductase (GR) under D + S vs control were observed in XZ5 and XZ16 than CM72, with less accumulation of H2O2 and malondialdehyde. These results suggest that high tolerance to D + S stress of XZ5 and XZ16 is closely related to lower Na+/K+ ratio and enhanced Ca2+Mg2+-ATPase, proline, glycine-beatine and WUE, and improved capacity of antioxidative performance to scavenge reactive oxygen species and thus suppressed level of lipid peroxidation.

► Tibetan wild barley XZ5/XZ16 is more tolerant to drought + salinity stress than CM72.
► Tibetan barley recorded higher K+ level and lower Na+/K+ ratio in combined stress.
► Tibetan barley exhibited more enhanced ATPase, proline, glycine-beatine and WUE.
► Tibetan barley expresses enhanced antioxidative performance under combined stresses.
► Tibetan wild barley enjoys useful genes for drought and salinity stress tolerance.