Abstract Aucuparin is the most widely distributed biphenyl phytoalexin in the rosaceous subtribe Pyrinae, which includes the economically important fruit trees apple and pear. The biphenyl scaffold is formed by biphenyl synthase, which catalyzes biosynthesis of 3, 5- dihydroxybiphenyl. Conversion of this precursor to aucuparin (3, 5-dimethoxy-4- hydroxybiphenyl) was studied in cell cultures of Sorbus aucuparia after treatment with an ...