POSSIBLE MECHANISMS OF PEPTIDE-HYDROLASE ACTIVATION DURING THE COLD-ACCLIMATION OF WINTER-WHEAT SEEDLINGS

Activities of neutral proteinases and carboxypeptidases were studied during the cold acclimation of four cultivars of winter wheat (Triticum aestivum L.) with well-defined differences in their frost resistance. The peptide hydrolase activities of both neutral proteinases and carboxypeptidases increased during the first (2-degrees-C) and the second (-4-degrees-C) phases of cold acclimation, being the highest in the seedlings of frost-resistant cultivars after the second phase. Peptide hydrolase transition from the bound to the active, free state was hardly a reason for enzyme activation. None of endoproteinase inhibitors were found in the wheat seedlings, but a low-molecular-weight fraction capable of carboxypeptidase activation was revealed there. The content of amino acids and sugars in this fraction changed significantly in the course of cold acclimation, which implied that this activator participated in the control of carboxypeptidase activities under low-temperature stress.