From waste to wonder: The potential of protein hydrolysates as plant biostimulants in agriculture

Protein hydrolysates (PHs) derived from plant and animal byproducts have emerged as promising biostimulants in sustainable agriculture. This comprehensive review investigates the production, composition, and mechanisms of action of PHs in promoting plant growth and stress resilience. PHs are obtained through enzymatic hydrolysis of protein-rich waste, yielding mixtures of amino acids and bioactive peptides. Commercial PHs exhibit diverse effects, including enhanced nutrient uptake, abiotic stress tolerance, and crop yield in various agricultural and horticultural species. The biostimulant activity of PHs is attributed to multiple interconnected pathways, such as hormone-like signalling, antioxidant defense, osmotic regulation, and gene expression modulation. Moreover, PHs influence the plant microbiome, potentially contributing to improved stress adaptation. Foliar and root application methods, along with factors like pH and transporters, govern PH absorption and translocation in plants. Transcriptomic and proteomic studies have provided insights into the molecular mechanisms underlying PH-mediated growth promotion and stress mitigation. Future research should focus on optimizing PH formulations, exploring synergies with other biostimulants, and elucidating the role of plant-microbe interactions. By harnessing the potential of these sustainable compounds, PH biostimulants offer a promising approach to enhance agricultural productivity and resilience in the face of global challenges.