Alterations in Arginase Activity and Polyamine Metabolism Contribute to the Mode of Action of Canavanine in Tomato Roots

Canavanine (CAN) is a nonproteinogenic amino acid, synthesised by many legumes (e.g., alfalfa, hairy vetch) and acts as a strong inhibitor of root growth. Thus, CAN may be considered as an allelopathic compound, influencing natural and agroecosystems. CAN is a structural analogue of arginine (Arg), so its toxicity results from its primary mode of action due to interference with Arg-dependent processes, especially incorporation into proteins instead of Arg. The aim of the work was to investigate the impact of CAN (10, 50 µM) treatment (24 or 72 h) on Arg catabolism and content of polyamines (PAs) in the roots of tomato (Solanum lycopersicum L.) seedlings. In the roots of plants cultured in the presence of CAN for 72 h, whosegrowth was completely inhibited, arginase activity and transcript levels of ARG1 and ARG2 were elevated, while ornithine (the product of Arg catabolism by arginase) content was low. CAN application resulted also in decreased total PAs level and increased relative contribution of spermine in the roots of tomato seedlings. CAN-induced alterations in PAs content in the roots were accompanied by changes in transcript levels of genes related to PAs synthesis (SPMS, SPDS) and PAs catabolism (PAO1).