The genetic control of the enzyme UDP-glucose: 3-0-flavonoïd-glucosyltransferase in flowers of Petunia hybrida

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Abstract
Four genes controlling the conversion of dihydroflavonols into anthocyanins have been investigated for their effect on UDP-Glucose: 3-0-flavonoïd glucosyltransferase activity, one of the enzymes involved in this conversion. An1 and An2 control the bulk of UFGT activity; a homozygous recessive for one of these genes shows an activity of 5–20% of the wildtype value. In a homozygous double recessive some 5% activity is still found while in mutants homozygous recessive for An6 or An9, UFGT activity is lower. In F2 progenies segregating for An6 or An9, however, no difference in UFGT activity was found between homozygous recessive and dominant plants. Mutants blocked in a biosynthesis step preceding the formation of dihydroflavonols show normal UFGT activity levels, indicating that no anthocyanidins are needed for UFGT induction. In addition to delphinidin, myricetin was used as a substrate. The results obtained indicate the probability that both substrates can be glucosylated by the same UFGT enzyme.