Functional compartmentalization of oxidative stress and antioxidant defense in Nothofagus obliqua galls induced by Espinosa nothofagi

Galls induced by Espinosa nothofagi (Hymenoptera) on Nothofagus obliqua (Nothofagaceae) buds exhibit tissue compartmentalization, with an inner compartment (IC) specialized for larval nutrition and an outer compartment (OC) associated with defense and protection. Although previous studies have linked reactive oxygen species (ROS) to functional specialization in galls, comprehensive analyses of oxidative stress and antioxidant systems in distinct gall compartments are still limited. Additionally, N. obliqua is a deciduous species with active secondary growth in spring, which coincides with gall development and potentially influences host redox dynamics. This study evaluated ROS production, lipid peroxidation (MDA), and the activity of enzymatic and nonenzymatic antioxidant systems in gall compartments and nongalled stems (NGS). We hypothesized that ROS and antioxidant systems in galls are compartmentalized according to their function and that secondary growth in NGS leads to ROS accumulation, which is counteracted by antioxidant defenses. Both histochemical and quantitative analyses revealed low oxidative stress in the IC, which was supported by elevated dehydroascorbate reductase activity. The OC presented increased H₂O₂ levels and superoxide dismutase and glutathione reductase activities, indicating exposure to environmental stressors. NGS resulted in the highest ROS levels, which were associated with intense cambial activity, along with strong enzymatic antioxidant responses. The colocalization of H₂O₂ and flavonoids suggests that these compounds act as effective ROS scavengers in both galls and NGS. Although each organ relies on distinct strategies, all effectively prevent membrane damage through efficient enzymatic and flavonoid-based antioxidant mechanisms. These findings demonstrate the functional compartmentalization of oxidative stress and defense, highlighting the role of redox balance during secondary growth and gall development.