Effect of two biostimulant on maize nitrogen metabolism.

Biostimulants belong to three major groups: humic substances (HS), seaweed extracts, and amino acid–containing products. Both HS and seaweed extracts, contain identifiable amounts of plant growth hormones and they affect the physiology of plants when applied in small quantities (1). Seaweed extracts, supplemented or not with humic acids and/or with FeSO4, promoted growth of plants, especially when grown under abiotic stress (2). In the case of small peptide-based products Kauffman III et al. (3) showed a growth-regulator activity of an array of free amino acids and other organic constituents on turf grass. Other authors have highlighted the positive role of amino acid–based biostimulants in plant nutrition as chelating agents, for boosting plant resistance to biotic and abiotic stress, and as admixture to pesticides or herbicides (4). The goal of this work was to study the chemical characteristics and biostimulant activity of two protein hydrolyzate–- based fertilizers (PHFs: alfalfa hydrolysate [AH] and meatflour hydrolyzate [MFH]) by evaluating their effect on plant growth and nitrate metabolism. We evaluated their effects on the activity of nitrate reductase (NR) and glutamine synthetase (GS), two key enzymes in N assimilation. A role of amino acids and small peptides as molecular signal interactions is suggested.