Isopentenyl diphosphate isomerase and prenyltransferase activities in rubiaceous and apocynaceous cultures

Abstract

Isopentenyl diphosphate (IPP) isomerase (EC 5.3.3.2) and farnesyl diphosphate (FPP) synthase (EC 2.5.1.10) activities were studied in plant cell cultures of Cinchona robusta, Morinda citrifolia, Rubia tinctorum, all belonging to the Rubiaceae, and Tabernaemontana divaricata and Catharanthus roseus, both belonging to the Apocynaceae. The presence of isoforms of IPP isomerase was detected after hydroxyapatite chromatography and by Western blotting using anti-IPP isomerase antibodies. The Rubiaceae cultures are able to accumulate anthraquinones, and for their biosynthesis isoprene C5-units are required. In a M. citrifolia cell line accumulating anthraquinones (AQ+), an almost two-fold higher IPP isomerase was observed compared with a cell line without accumulation of anthraquinones. In the Western blots three polypeptides were detected in the extracts from the AQ+ cells. In C. robusta cells the anthraquinone biosynthesis was induced by medium optimization and by elicitation. After both treatments, a specific isoform of IPP isomerase was induced. The C. roseus culture (not accumulating anthraquinones) expressed relatively low IPP isomerase activity, but two isoforms could be detected. The enzyme activities as observed in the different Rubiaceae cultures may indicate an efficient channelling of C5-units into anthraquinone biosynthesis.