Institut für Biologie II, Lehrstuhl für Genetik, Universität Tübingen, Auf der Morgenstelle 28, D-7400, Tübingen, Federal Republic of Germany.
Theor Appl Genet. 1985 Aug;70(5):561-8. doi: 10.1007/BF00305991.
Chemogenetic investigations and precursor experiments on flowers of Petunia hybrida suggest that recessive alleles of the gene An3 block the biosynthetic pathway of flavonols and anthocyanins between the flavanone and dihydroflavonol step. In confirmation of this hypothesis, activity of the enzyme flavanone 3-hydroxylase, which catalyses the conversion of flavanones to dihydroflavonols, was readily demonstrated in enzyme preparations from flowers of lines with the dominant allele An3, whereas no or very low activity could be found in extracts from lines with recessive alleles (an3an3). A second genetic factor is described which clearly reduces the amount of flavonols in the flowers but not the amount of anthocyanins. Crossing experiments revealed that this factor represents a third allele of the An3 gene. It is referred to as an3-1. As expected, a residual flavanone 3-hydroxylase activity of about 10% could be found in enzyme extracts from plants with the an3-1 allele. The decreased level of dihydroflavonol formed under this condition is obviously still sufficient for anthocyanin formation but not for flavonol synthesis.Similar to flavanone 3-hydroxylases from other plants, the enzyme of Petunia is a soluble enzyme and belongs according to its cofactor requirements to the 2-oxoglutarate-dependent dioxygenases. The residual flavanone 3-hydroxylase activity found in plants with the an3-1 allele is identical to the activity extracted from An3-genotypes with regard to cofactors, substrate specificity and most of the inhibitors. The difference observed in the respective pH-optima and the genetic data suggest that the mutation providing the an3-1 phenotype is localized in the structural gene for flavanone 3-hydroxylase.
矮牵牛花朵的化学遗传学研究和前体实验表明，基因 An3 的隐性等位基因阻断了类黄酮和花色苷的生物合成途径，位于黄烷酮和二氢黄酮醇之间。该假说得到了证实，在具有显性等位基因 An3 的品系的酶制剂中，很容易证明催化黄烷酮转化为二氢黄酮醇的酶 flavanone 3-羟化酶的活性，而在具有隐性等位基因（an3an3）的品系提取物中则没有或很少发现活性。描述了第二个遗传因子，它明显降低了花朵中类黄酮的含量，但不影响花色苷的含量。杂交实验表明，该因子代表 An3 基因的第三个等位基因。它被称为 an3-1。正如预期的那样，在具有 an3-1 等位基因的植物的酶提取物中可以发现约 10%的残余 flavanone 3-羟化酶活性。在这种情况下形成的二氢黄酮醇水平降低显然仍然足以形成花色苷，但不足以合成类黄酮。与其他植物的 flavanone 3-羟化酶相似，矮牵牛的酶是一种可溶性酶，根据其辅因子要求属于 2-氧戊二酸依赖性加双氧酶。在具有 an3-1 等位基因的植物中发现的残余 flavanone 3-羟化酶活性与从 An3 基因型中提取的活性在辅因子、底物特异性和大多数抑制剂方面是相同的。观察到的在各自 pH 最优值和遗传数据方面的差异表明，提供 an3-1 表型的突变定位在 flavanone 3-羟化酶的结构基因中。
