Physiological and biochemical responses to drought stress in cultivated and Tibetan wild barley

Greenhouse pot experiments were conducted to investigate genotypic differences in response to drought stress between Tibetan wild barley genotypes (XZ5 and XZ150, drought-tolerant; XZ54 and XZ147, drought-sensitive) and cv ZAU3. Drought stress of 4 % soil moisture content (SMC) significantly decreased water potential (WP) and osmotic potential (OP), while increased water saturation deficit (WSD) and the bound water content (BWC) in leaves, with the least decrease/increase in XZ5, which recorded the highest levels in WP and OP but the lowest in WSD and BWC under 4 % SMC. Under 15 % SMC, when compared with control, XZ5 and XZ150 had more elevation in soluble sugar content relative to the other 3 genotypes, while XZ5 had the least increase in soluble protein. Under 4 % SMC, endogenous ABA content increased more in XZ5 and XZ150 than in the other three genotypes, but proline content increased least in XZ5. After rewatering, the transpiration rate increased in sensitive genotypes but decreased in tolerant genotypes. The less elevated MDA accumulation was observed in XZ5 and XZ150 with higher POD and CAT activities under 15 and 4 % SMC than in the other three genotypes. Drought stress of 4 % SMC significantly up-regulated the expression levels of CAT1 and Cu/ZnSOD in XZ5 and MnSOD in XZ150.Our results indicated that drought tolerance of wild barley XZ5 is mainly associated with the osmo-regulation of soluble sugar and stomatal regulation of ABA. This mechanism could be applied to improve the drought tolerance of cultivated barley and the further marker-assisted breeding.