Metabolism and translocation of allantoin in ureide-producing grain legumes

Abstract

Transfer of the nitrogen and carbon of allantoin to amino acids and protein of leaflets, stems and petioles, apices, peduncles, pods, and seeds of detached shoots of nodulated cowpea (Vigna unguiculata L. Walp. cv. Caloona) plants was demonstrated following supply of [2-(14)C], [1,3-(15)N]allantoin in the transpiration stream. Throughout vegetative and reproductive growth all plant organs showed significant ureolytic activity and readily metabolized [2-(14)C]allantoin to (14)CO(2). A metabolic pathway for ureide nitrogen utilization via allantoic acid, urea, and ammonia was indicated. Levels of ureolytic activity in extracts from leaves and roots of nodulated cowpea were consistently maintained at higher levels than in non-nodulated, NO(3) (-) grown plants.[(14)C]Ureides were recovered in extracts of aphids (Aphis craccivora and Macrosiphum euphorbieae) feeding at different sites on cowpea plants supplied with [2-(14)C]allantoin through the transpiration stream or to the upper surface of single leaflets. The data indicated that the ureides were effectively transferred from xylem or leaf mesophyll to phloem, and then translocated in phloem to fruits, apices, and roots.