Ureides and Enzymes of Ureide Synthesis in Flax (Linum usitatissimum) Plants and Seeds

Abstract

Xanthine oxidoreductase exhibiting a superoxide producing activity (Xanthine: O 2 Oxidoreductase, EC 1.2.3.2), uricase (Urate: O 2 oxidoreductase, EC 1.7.3.3), allantoinase (EC 3.5.2.5) and ureides were detected in leaves, stems, roots and seeds of flax plants. Allopurinol [4-hydroxypyrazolo(3,4-d)pyrimidine], an analogue of purine and tightly binding inhibitor of the xanthine oxidizing enzyme, was applied as soil drench at 0.4 mM starting 7-8 days after planting and reduced the concentration of allantoic acid in leaves and roots by 50%. No further inhibition was obtained using a higher concentration (1.6mM) of allopurinol. These findings indicate that in vivo inhibition of xanthine oxidoreductase took place and that the purine catabolic pathway is active in flax plants. However, since the higher inhibition obtained even at 1.6 mM was only 50%, and considering that no toxic effects were induced by applying 1.6 mM allopurinol, it is supposed that other route/s for ureide synthesis may be active in flax plants.