Coupling Mechanisms of Photosynthetic Downregulation and Enhanced Resistance in Maize Seedlings Under Ostrinia furnacalis Herbivory and Hormone Induction (SA and MeJA)

To clarify the photoacclimation and stress-resistance coupling strategies of maize (Zea mays L.) variety B73 under Ostrinia furnacalis (Guenée) herbivory, we compared herbivory with mechanical damage and exogenous salicylic acid (SA)/methyl jasmonate (MeJA) treatments, focusing on the relationship between photosynthesis and defense. Results showed that O. furnacalis herbivory significantly reduced chlorophyll fluorescence and gas-exchange parameters, impairing light energy capture and conversion, and induced a progressive shift in photosynthetic performance associated with dynamic changes in carbon acquisition and utilization. Although herbivory and MeJA elicitation induced similar phenotypic changes after 12 h, herbivory caused much stronger global downregulation of photosynthesis-related genes than mechanical damage and hormone treatments. All stress treatments increased total antioxidant capacity (T-AOC) and reactive oxygen species (ROS, H2O2 and O2·−) levels; notably, soluble protein (SP) explained 30.09% of the variance in the trade-off between photosynthetic pigment degradation and stress tolerance. Network modeling of photosynthetic genes, chlorophyll fluorescence parameters, gas-exchange parameters, and resistance-defense traits demonstrated robust modular connectivity, identifying chlorophyll fluorescence and gas-exchange parameters as core modulators of the resistance-defense trade-off. Collectively, maize adapts to external stress by balancing photosynthetic downregulation and defense enhancement through coordinated regulation of photosynthetic performance, antioxidant capacity, and core photosynthetic gene expression. These findings provide new insights into the mechanisms underlying plant stress tolerance.