Abstract
Purine metabolism plays a central role in plant nitrogen metabolism. Unless salvaged to purine nucleotides, purines and their partial degradation products are converged to xanthine, the key starting compound of the catabolism which is consequently decomposed to inorganic nitrogen and carbon. To evaluate the physiological significance of purine catabolism, we constructed RNAi-silenced Arabidopsis in which the rate-limiting xanthine dehydrogenase (XDH) was downregulated. The RNAi plants displayed pleiotropic phenotype including retarded growth and overaccumulated xanthine. Excess xanthine didn't affect the growth of wildtype plants and the impaired growth of RNAi plants was reversed by a xanthine catabolite urate, suggesting that a block in purine catabolism possibly causes the growth defect of RNAi plants. Wildtype plants were able to use xanthine as sole nitrogen source whereas the growth of RNAi plants was severely impaired. Collectively, these data suggest the importance of purine catabolism and its catabolites in plant growth and physiology.
