There is a direct link between allantoin concentration and cadmium tolerance in Arabidopsis

Allantoin, an important intermediate of ureide metabolism, has been the subject of investigation recently due to its dual function in nitrogen recycling and abiotic stress response in plants. Allantoin appears to be the dominant ureide accumulating in response to different abiotic stresses, and mutants containing elevated allantoin concentrations exhibit a stress-tolerant phenotype due to limited reactive oxygen species (ROS) generation. Here we describe the involvement of allantoin in stress response and attempt to explain the regulatory mechanism(s) underlying allantoin function in plants. Growth of wild type Col-0 seedlings in the presence of exogenous allantoin improved root elongation in response to Cd treatment. Allantoin treatment of Col-0 seeds increases superoxide dismutase activity causing an enhanced seed germination and seedling growth following Cd exposure. Additionally, allantoinase-overexpressed (ALNox) lines, with lower levels of allantoin, exhibited more susceptibility to Cd treatment than Col-0 Arabidopsis, implying that there is a positive correlation between allantoin concentration and Cd resistance in plants. Growing ABA-insensitive (abi) mutants on allantoin-containing media and comparison between abi mutants and their wild-type backgrounds demonstrated that the potential regulatory function of allantoin does not require ABA at germination but may be ABA-dependent at later stages of seedling growth, suggesting a potential crosstalk between allantoin-mediated stress response and ABA signalling pathway in plants.