Differential metabolic reprogramming and organ-specific antioxidant allocation in Oryza sativa and Echinochloa crus-galli under propanil-induced chemical stress

The physiological and metabolic mechanisms by which plants manage severe chemical stress during critical reproductive stages remain poorly understood. Here, we investigated the system-level phytotoxic responses and metabolic reprogramming of a tolerant species (Oryza sativa L.) and a susceptible species (Echinochloa crus-galli) exposed to the chemical stressor propanil using GC-MS/MS and LC-MS/MS. Under severe chemical stress, O. sativa maintained relatively stable antioxidant-related metabolism in grains, with α-tocopherol and phylloquinone showing only modest decreases of 0.86- and 0.90-fold, respectively. β-Sitosterol oryzanol was also preserved or increased in rice tissues, showing 1.05-fold in grain and 1.48-fold in husk, whereas it was not detected in E. crus-galli. In contrast, E. crus-galli exhibited stronger antioxidant perturbation, with α-tocopherol decreasing to 0.57-fold in grain and 0.72-fold in husk and (all-E)-zeaxanthin accumulating markedly in grain by 5.30-fold. Furthermore, the non-detection of oryzanol esters in E. crus-galli highlights a fundamental biochemical limitation in its oxidative stress defense. Ultimately, these findings suggest that resilience to chemical stressors may not rely solely on enzymatic detoxification, but may also involve coordinated, organ-specific metabolic buffering and targeted antioxidant reallocation.