Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/1995
Publication Date: N/A
Interpretive Summary: Plants produce a wide variety of compounds which have important roles in both plant and animal health. The flavonoids are one such class of compounds. Not only are they critical to the plant's ability to deal with stress, but they have important pharmacological properties as well. However, specific functions have not been determined for individual flavonoids in either plant or animal systems. Simple and efficient techniques are needed to evaluate the formation and accumulation of these compounds in plant tissues. This paper describes improved methodology for the evaluation of an important class of enzymes involved in flavonoid synthesis, the glucosyltransferases. The method was then used to examine some of the properties of the flavonoid glucosyltransferases found in lemon (Citrus limon) leaves and flowers.
Technical Abstract: A routine method for the analysis of flavonoid glucosyltransferase activity in extracts from plant tissues using high-performance liquid chromatography (HPLC) is described. Cell-free extracts were prepared from young leaves of Eureka lemon and Meyer lemon for flavonoid glycosyltransferase assays. The remaining flavonoid substrates and the flavonoid reaction products in the ethyl acetate extracts of the assays were quantitatively analyzed by spectrophotometric detection at 285 nm on HPLC. The flavonoid aglycones naringenin, hesperetin, eriodictyol, homoeriodictyol (flavanones), apiginin, crysin (flavones), morin and kaempferol (flavonols) were used as substrates along with uridine diphospho-glucose and the corresponding glucosides that were formed were measured. The glucosyltransferase activity in the lemon preferentially glucosylated only the flavanone hesperetin, but glycosylated both the flavone and flavonol substrates. The eformation of flavonoid glucoside products were detectable down to levels o less than 0.5 micrograms per injection. Hesperetin 7-0-glucosyltransferase activity was evaluated in young, developing flowers and leaves of lemon trees.