Abstract
Soil salinity and drought are the two most common and frequently co-occurring abiotic stresses constraining crop growth and productivity. Greenhouse pot experiments were conducted to investigate the tolerance potential and mechanisms of Tibetan wild barley genotypes (XZ5, drought-tolerant; XZ16, salinity/aluminum tolerant) during anthesis compared with salinity-tolerant cv CM72 in response to separate and combined stresses (D+S) of drought (4% soil moisture, D) and salinity (S). Under salinity stress alone, plants had higher Na+ concentrations in leaves than in roots and stems. Importantly, XZ5 and XZ16 had substantially increased leaf K+ concentrations; XZ16 was more efficient in restricting Na+ loading in leaf and maintained a lower leaf Na+/K+ ratio. Moreover, a significant decrease in cell membrane stability index (CMSI) and an increase in malondialdehyde (MDA) were accompanied by a dramatic decrease in total biomass under D+S treatment. We demonstrated that glycine-betaine and soluble sugars increased significantly in XZ5 and XZ16 under all stress conditions, along with increases in protease activity and soluble protein contents. Significant increases were seen in reduced ascorbate (ASA) and reduced glutathione (GSH) contents, and in activities of H+K+-, Na+K+-, Ca++Mg++-, total- ATPase, and antioxidant enzymes under D+S treatment in XZ5 and XZ16 compared to CM72. Compared with control, all stress treatments significantly reduced grain yield and 1000-grain weight; however, XZ5 and XZ16 were less affected than CM72. Our results suggest that high tolerance to D+S stress in XZ5 and XZ16 is closely related to the lower Na+/K+ ratio, and enhanced glycine-betaine and soluble protein and sugar contents, improved protease, ATPase activities and antioxidative capacity for scavenging reactive oxygen species during anthesis. These results may provide novel insight into the potential responses associated with increasing D+S stress in wild barley genotypes.
Highlights
Drought and salinity are the most important abiotic stresses limiting agricultural production worldwide
Plant dry weight under drought, salinity, drought and salinity stress (D+S) treatments decreased by 12.6%, 15.5%, 26.6% in XZ5; 10.0%, 14.3%, 20.8% in XZ16 and 16.8%, 16.1%, 28.2% in CM72, respectively
Spike growth significantly differed among the genotypes under drought and D+S treatments during anthesis stage at a soil moisture level of 4%
Summary
Drought and salinity are the most important abiotic stresses limiting agricultural production worldwide. It is important to identify the genetic resources that have high tolerances and to understand the mechanisms of drought and salinity tolerance in plants. It is important to investigate the physiology of drought and salinity tolerance in well-adapted wild barley, to understand the limits and tradeoffs between drought and salinity tolerance, and to determine the traits that are associated with high tolerance to both factors [11,12]. We successfully identified Tibetan wild annual barley genotypes XZ5 and XZ16 that exhibited high tolerance to drought and salinity stress, respectively [13,14]. The underlying physiological and biochemical mechanisms involved in drought and salinity tolerance remain unclear, preventing the optimization of gene identification techniques and its further commercial applications
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