Biochemical and transcriptomic analyses reveal the mechanisms underlying SNP and melatonin effects on antioxidant capacity and chlorophyll metabolism in postharvest okra

Okra fruit undergo rapid chemical deterioration after harvest. This study investigated how sodium nitroprusside (SNP) and melatonin (MT), alone or combined (MT+SNP), affect chemical stability, antioxidant capacity, and chlorophyll metabolism in okra stored at 20°C and 80-90% humidity. MT+SNP treatment most effectively preserved fruit quality by reducing weight loss, maintaining color parameters, decreasing oxidative stress markers (H₂O₂, MDA), enhancing antioxidant capacity, and regulating antioxidant enzymes (SOD, CAT, POD, APX). MT+SNP stabilized chlorophyll content by modulating chlorophyll-degrading enzymes (CLH, PPH, MDcase). Transcriptome analysis revealed differential expression of genes involved in antioxidant defense and chlorophyll metabolism, with synergistic effects from combined treatment. Weighted gene co-expression network analysis identified transcription factors (NAC86, ERF4, MYB24) connecting antioxidant and chlorophyll metabolism pathways. This combined treatment effectively preserves okra’s phytochemical integrity and nutritional quality by stabilizing redox homeostasis and pigment metabolism.