An animal-derived protein hydrolysate alleviates osmotic stress-induced oxidative damage in tomato by activating ascorbate and glutathione cycle

BACKGROUND: Protein hydrolysates, as a major group of biostimulants, have gained increasing attention because of their remarkable efficacy in enhancing plant stress resistance. However, the mechanism underlying protein hydrolysate-mediated tolerance to osmotic stress remains poorly understood. In this study, the alterations in oxidative damage and the ascorbate and glutathione (AsA-GSH) cycle were analyzed to investigate the potential effects of protein hydrolysates derived from pig blood (PP) against PEG-induced osmotic stress in tomato. RESULTS: ), leading to increased malondialdehyde (MDA), electrolyte leakage, and Evans blue uptake, which subsequently reduced photosynthetic efficiency, shoot fresh weight, and relative growth rate in tomato plants. Exogenous application of PP effectively alleviated the stress-induced negative effects by increasing the levels of AsA and GSH and ratios of AsA/DHA and GSH/GSSG. This protective effect was primarily attributed to the enhanced activity and gene expression of key AsA-GSH cycle enzymes, including glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), ascorbate peroxidase (APX), γ-glutamylcysteine synthetase (γ-ECS), glutathione peroxidase (GPX), and glutathione S-transferase (GST). In addition, treatment with L-buthionine-sulfoximine (BSO), a GSH biosynthesis inhibitor, significantly reduced AsA and GSH levels and aggravated oxidative damage and growth inhibition, while PP application partially reversed the above negative effects caused by BSO addition. Meanwhile, PP application increased the proline accumulation by enhancing the activities of ∆1-pyrroline-5-carboxylate synthase (P5CS) and ornithine-δaminotransferase (OAT), while reducing the activity of proline dehydrogenase (ProDH). CONCLUSION: Exogenous PP confers tolerance to PEG-induced osmotic stress in tomato plants by activating the AsA-GSH cycle and enhancing cellular redox homeostasis.