Ureide metabolism in Arabidopsis thaliana is modulated by C:N balance

Plants can respond and adapt to changes in the internal content of carbon and nitrogen by using organic compounds that widely differ in their carbon/nitrogen ratio. Among them, the amides asparagine and glutamine are believed to be preferred by most plants, including Arabidopsis. However, increases in the ureides allantoin and/or allantoate concentrations have been observed in different plant species under several environmental conditions. In this work, changes in the ratio between carbon skeletons and reduced nitrogen were investigated by varying the concentrations of nitrogen and sucrose in the growth media. Allantoin accumulation was observed when plants were grown in media with high ammonia concentrations. This increase was reverted by adding sucrose as additional carbon source. Moreover, mutant plants with a decreased capability to degrade allantoin showed a compromised growth compared to WT in ammonia supplemented media. Together, our results indicate that allantoin accumulation is induced by low carbon/nitrogen ratio and suggest that its degradation is critical for proper plant growth and development.