Alteration of aminoacid metabolism by humic substances during germination of in Pinus laricio seeds

Two humic fractions, characterized by different physical and chemical properties, were evaluated for their effects on Pinus laricio seed germination and amino acid metabolism. In seeds treated with the humic fractions, there was an alteration of the amino acid pool and an inhibition of pyruvate kinase (PK), phosphoenolpyruvate carboxylase (PEPC), urease (URE), arginase (ARG), glutamate dehydrogenase (GDH), aspartate aminotransferase (AAT) and glutamate synthase (GOGAT) activities. These results suggest that humic substances inhibit seed germination by affecting metabolic processes, and in particular the Krebs cycle, that provides the carbon skeleton necessary to synthesize aminoacids.