Phenolic compounds, antioxidant enzymes, and oxidative stress in barley (Hordeum vulgare L.) genotypes under field drought-stress conditions

Climate change has exacerbated drought, making water scarcity a significant constraint on crop production. This study aimed to evaluate drought stress responses of 21 barley cultivars and breeding lines, using various traits of leaf oxidative stress [DPPH radical scavenging, malondialdehyde (MDA), and hydrogen peroxide (H₂O₂)], antioxidants (enzymes and polyphenols), photosynthetic pigments and chlorophyll fluorescence (F) [carotenoid (Car), chlorophyll (Chl), F_m, F₀, and F_v/F_m], relative water content (RWC), electrolyte leakage (EL), proline (Pro), protein content (PC), and grain yield. Field experiments were conducted under both normal and drought stress conditions. Significant effects of moisture conditions were observed for most of the traits, except for Chla/b, carotenoids, and EL. Syringic acid, gallic acid, chlorogenic acid, ferulic acid, ellagic acid, caffeic acid, vanillic acid, and p-coumaric acid were the prominent phenolic acids in barley genotypes. The predominant leaf flavonoids were luteolin, apigenin, and rutin. There was significant genetic variation among genotypes for all traits except Chla/b. Drought stress caused significant increases in DPPH, MDA, H₂O₂, total phenolic content, total flavonoid content, peroxidase, and Pro. While catalase, ascorbate peroxidase, Chla, Chlb, Tchl, F_v/F_m, F₀, F_m, RWC, PC, and grain yield were significantly decreased due to water stress. These findings offer key insights into barley genotypes' drought stress response, aiding breeders in identifying key physiological and biochemical traits as markers for developing drought-tolerant cultivars.