Hydrogen Peroxide and Vitexin in the Signaling and Defense Responses of <i>Passiflora incarnata</i> Under Drought Stress

Hydrogen peroxide (H₂O₂) functions as a signaling molecule that triggers physiological and biochemical adjustments that help plants cope with environmental stress. This study evaluated the effects of foliar application of 1.5 mM H₂O₂ on the physiological and biochemical responses of <i>Passiflora incarnata</i> subjected to 14 days of drought stress followed by 5 days of rehydration. Drought reduced Fv/Fm and photochemical efficiency, as well as stomatal conductance and transpiration rates. H₂O₂ treatment under drought further reduced stomatal conductance and transpiration, suggesting enhanced water conservation. Drought-stressed plants treated with H₂O₂ exhibited increased concentrations of glucose, fructose, and mannose along with reduced sucrose levels, indicating osmotic adjustment and energy mobilization. Enzymatic antioxidant activity, particularly that of superoxide dismutase and catalase, increased with H₂O₂ treatment, while peroxidase activity remained low. The content of vitexin, arabinose, and trehalose decreased under drought, likely due to their roles in membrane protection, as MDA levels remained stable. After rehydration, Fv/Fm and ΦPSII recovered, and H₂O₂-treated plants showed higher carbon assimilation and carboxylation efficiency. These results indicate that H₂O₂ promotes drought acclimation and enhances post-stress recovery in <i>P. incarnata</i>. We conclude that H₂O₂ induces signaling pathways, with trehalose, arabinose, and vitexin contributing to the regeneration of the photochemical apparatus, as well as defense and acclimation under drought conditions.