Cytochrome P450.sub.II dependent monooxygenases and DNA molecules encoding these monooxygenases are provided, which are able to catalyze the biosynthethic conversion of aldoximes to nitrils and the conversion of said nitrils to the corresponding cyanohydrins, which are the presursors of cyanogenic glycosides. Moreover, the invention provides methods for obtaining DNA molecules according to the invention and methods for obtaining transgenic plants resistant to insects, acarids, or nematodes or plants with improved nutritive value.