Oxidative damage and antioxidant mechanism in tomatoes responding to drought and heat stress

Abiotic stresses especially combined stress such as concurrence of drought and heat will influence crop production more seriously in the near future. Reactive oxygen species (ROS) worked as signal transduction molecule to accelerate plant response at abiotic stress conditions, the accumulation of which caused oxidative damage. Understanding the underlying effect of combined stress on the ROS metabolism and antioxidant mechanism in plant is a prerequisite for crop improvement in a changing climate. We aimed to explore the distinct response of the ROS production and its scavenging system in tomato at single and combined stress and to elucidate the crosstalk of tolerance mechanism. Thereby, dynamic changes in ROS metabolism and antioxidant mechanism in tomatoes at control, drought, heat and drought + heat (combined stress) were investigated. Two tomato cultivars (Sufen 14: CV1, Jinlingmeiyu: CV2) were applied to compare the cultivar difference. 6 days of drought and combined stress led to a sharp increase in H2O2 (hydrogen peroxide) content and O2·− (superoxide radicals) production speed of both cultivars even though there were fluctuations from day 1 to day 5. Dramatic increase of SOD and APX activity and significant decrease of CAT activity occurred in both cultivars at all stresses on day 3. In contrast, combined stress significantly depressed the POD and CAT activity in both cultivars on day 6. The significant increase in MDA content was observed in CV1 at drought and combined stress and in CV2 at three stresses. Meanwhile, combined stress induced significant decrease in proline content only in CV1. The canopy area and stem diameter of both cultivars at the combined stress were smaller than single stress. We found that there was cultivar variation in heat tolerance but not in drought and combined stress tolerance. In conclusion, the stress tolerance of tomatoes at drought and heat is closely associated with its ability to respond to oxidative damage and regulation of ROS scavenging system with unique ROS response induced by the combined stress. This study not only increases our understanding of the complex ROS responses in plants to abiotic stress, but also provides knowledge to improve crop tolerance.