Organic Soil Amendment Enhances Ascorbate Peroxidase-Mediated Antioxidant Defense in Water-Stressed Wheat

Drought stress remains a major constraint to wheat productivity, particularly in arid and semiarid regions where declining soil moisture disrupts photosynthetic efficiency, enzymatic regulation, and grain biochemical quality. In this study, the role of activated biochar as a soil amendment in enhancing drought resilience across selected wheat cultivars was evaluated. The study comprised three cultivars (C1, C2, C3) grown under five stress levels (DS0, DS1, DS2, DS3, DS4) with three levels of activated biochar as soil amendment (SA0, SA1, and SA2). Fourier transform infrared (FTIR) spectroscopy showed distinct peaks where C1 had calcium dihydroxide and amide groups, C2 showed allene, glyoxal, and C-H symmetric stretching, whereas C3 exhibited glyoxal, cyclopropane, and strong -OH/-NH stretches. The SA2 improved photosynthetic attributes across cultivars, with C2 and C3 showing the highest gains under DS4 when amended with SA2. The H₂O₂ and O₂ ^- production was reduced by 52% in C1 and C3 with SA2 when compared to SA0 under DS4. The ascorbate peroxidase (APX) and DPPH activity increased by 48-65% under SA2, while ABTS showed a slight suppression at DS4 in C2. Phenolic and flavonoid contents rose up to 2.4- and 2.2-fold, respectively, under SA2 at DS4, as compared to SA0 at DS4, notably in C1. Molecular docking revealed binding affinities between FTIR-predicted compound and APX protein interactions, revealing their coordinative role in stress resilience. This integrated physiological and molecular approach provides novel insights into the mechanistic role of organically amended soil and the APX enzyme in sustaining wheat performance under water-limited conditions.