UGT706D1 showed activities toward a broader
range of substrates, including flavanone, flavone,
flavonol, and isoflavone. Several UGTs that have
been studied so far show activities toward a broad
range of substrates. For example, a glucosyltransferase
from Medicago truncatula (UGT71G1)
showed activity not only for triterpene but also
for isoflavonoid and quercetin (Achnine et al.,
2005). UGT73G1 from onion also showed activities toward broad range of flavonoids, with the highest
preference for 7-O-methyl quercetin (rhamnetin)
(Kramer et al., 2003). In addition, glucosyltransferases
from Dorotheanthus bellidiformis exhibited
activity toward betanidin and quercetin (Vogt et
al., 1997). Thus, in order to assess the in vivo
function of UGTs, it will be necessary to know what
substrates are available in the cells that contain
the UGTs. Since the sugars and linkages of flavonoid
O-glycosides in rice are not known, in vitro
substrate specificity results are useful only as a
guide to the in vivo substrates.