Short-term soil-waterlogging contributes to cotton cross tolerance to chronic elevated temperature by regulating ROS metabolism in the subtending leaf.

Chronic elevated temperature and soil-waterlogging events often occur concomitantly in the Yangtze River Valley; however, a clear understanding of the effects of aforementioned co-occurring stresses on antioxidant defense in cotton has not been attained. To address this, two temperature conditions during the whole flowering and boll development periods, and three soil-waterlogging levels (0, 3, 6 d) starting on the day of anthesis were established. In the current study, no siginificant difference was observed on plant performance for 3 d soil-waterlogging, whereas 6 d soil-waterlogging event and elevated temperature in isolation negatively affected plant performance (i.e. leaf area declined by 33.3% and 14.7% in AW6 (soil waterlogging for 6 d under ambient temperature regime) and EC (soil well-watered (SRWC(75 ± 5) %) under elevated temperature for 2-3 °C) relative to AC (soil well-watered (SRWC(75 ± 5) %) under ambient temperature regime)) and induced ROS (reactive oxygen species) production and scavenging mechanisms in the subtending leaf of cotton. SOD (superoxide dismutase), CAT (catalase), and POX (peroxidase) activities were increased, and ASA (ascorbic acid) concentration was enhanced due to higher H2O2 (hydrogen peroxide) and O2- accumulations. Whereas, APX (ascorbate peroxidase), DHAR (dehydroascorbate reductase) and GR (glutathione reductase) activities were inhibited under elevated temperature regime or waterlogging event, especially in the treatment of EW6 (soil waterlogging for 6 d under elevated temperature for 2-3 °C), which resulted in increasing H2O2 concentration and higher O2- generation rate. However, plants acclimated to a short-term waterlogging stress (3 d) performed a cross tolerance to chronic elevated temperature regime (leaf number increased by 11.4%, whereas the abscission rate decreased by 4.6% in EW3 (soil waterlogging for 3 d under elevated temperature for 2-3 °C) compared with EC (soil well-watered (SRWC(75 ± 5) %) under elevated temperature for 2-3 °C)). Moreover, plants undergone a brief soil-waterlogging (3 d) induced higher GR activity and increased ASA concentration, along with enhanced SOD, CAT, POX activities, limiting H2O2 and O2- accumulation and reducing oxidative damage to membrane lipids as evidenced by reduced MDA (malondialdehyde) concentration when cotton was subsequently exposed to chronic elevated temperature regime.