[Occurrence and localization of a flavonol-converting enzyme in plants]

The occurrence and distribution of an enzyme converting flavonols to 2,3-dihydroxy flavanones has been measured in various plants and found to occur in all plants tested.In garbanzo bean, Cicer arietinum L., the enzyme is found mainly in roots, hypocotyls, epicotyls and cytoledons while the other organs, rich in flavonols, possess much lower levels of the enzyme. In garbanzo seedlings the enzyme is formed between the second and sixth day after germination and appears parallel to the phenylalanine ammonia-lyase. The data indicate that the enzymes for both flavonol biosynthesis and turnover are formed simultaneously. These results further support earlier observations that regulation of flavonoid formation and regulation of turnover seem to be dependent on each other.The activity of the flavonol-converting enzyme does not increase in Cicer arietinum plants transferred to darkness though under such conditions flavonol turnover is accelerated.In Pisum sativum, Glycine max and Sinapis alba the flavonol converting enzyme is more evenly distributed over all organs, so that a correlation between flavonol content and enzyme is less obvious.The data are discussed with respect to intracellular regulation of flavonol turnover.