Physio-Biochemical Changes Associated with the Response to Water Stress of Six Sunflower Inbred Lines at the Late Vegetative Growth Stage Reveal Their Differential Performance under Laboratory-Controlled Conditions

Water stress negatively impacts crop productivity worldwide, highlighting the need for a deeper understanding of plant-adaptive mechanisms to mitigate its effects. Our aim was to evaluate and compare the physiological and biochemical characteristics of six sunflower inbred lines subjected to water stress during late vegetative growth stage (V8) by quantifying endogenous phytohormones, oxidative metabolism compounds, and enzymatic antioxidant activity. Water stress was applied for 15 days to plants, which has reached their eighth-leaf stage grown under controlled conditions. Salicylic acid was abundant in shoots, while abscisic acid predominated in roots, and 28-norcastasterone was present in both organs. Under water stress, all lines showed high ferric-reducing antioxidant capacity in shoots and roots, lower hydrogen peroxide levels, and the highest ascorbate peroxidase activity in shoots. The lines employed different regulatory mechanisms to counteract the water stress. This knowledge may have important implications for sunflower breeding strategies aimed at developing drought-tolerant hybrids.