The roles of latex and the vascular bundle in morphine biosynthesis in the opium poppy, Papaver somniferum

Abstract

The opium poppy, Papaver somniferum, is one of mankind's oldest medicinal plants. Opium poppy today is the commercial source of the narcotic analgesics morphine and codeine. Along with these two morphinans, opium poppy produces approximately eighty alkaloids belonging to various tetrahydrobenzylisoquinoline-derived classes. It has been known for over a century that morphinan alkaloids accumulate in the latex of opium poppy. With identification of many of the enzymes of alkaloid biosynthesis in this plant, biochemical data suggested involvement of multiple cell types in alkaloid biosynthesis in poppy. Herein the immunolocalization of five enzymes of alkaloid formation in opium poppy is reported: (R,S)-3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase central to the biosynthesis of tetrahydroisoquinoline-derived alkaloids, the berberine bridge enzyme of the sanguinarine pathway, (R,S)-reticuline 7-O-methyltransferase specific to laudanosine formation, and salutaridinol 7-O-acetyltransferase and codeinone reductase, which lead to morphine. In capsule and stem, both O-methyltransferases and the O-acetyltransferase are found predominantly in parenchyma cells within the vascular bundle, and codeinone reductase is localized to laticifers, the site of morphinan alkaloid accumulation. In developing root tip, both O-methyltransferases and the O-acetyltransferase are found in the pericycle of the stele, and the berberine bridge enzyme is localized to parenchyma cells of the root cortex. Laticifers are not found in developing root tip, and, likewise, codeinone reductase was not detected. These results provide cell-specific localization that gives a coherent picture of the spatial distribution of alkaloid biosynthesis in opium poppy.

Benzylisoquinoline alkaloid biosynthesis in opium poppy

“…However, SalAT and COR transcripts have also been reported in the cytoplasm, or latex, of laticifers (Decker et al 2000;Larkin et al 2007;Allen et al 2008), although in situ hybridization and immunofluorescence labeling failed to detect SalAT and COR mRNA and corresponding enzymes in laticifers (Bird et al 2003;weid et al 2004;Samanani et al 2006). Recently, the application of shotgun proteomics to determine the relative abundance of proteins in isolated latex, or in whole stem including latex, revealed that the final three steps in morphine biosynthesis, catalyzed by T6ODM, COR and CODM, occur primarily in laticifers (Onoyovwe et al 2013).…”

The Remarkable Pliability and Promiscuity of Specialized Metabolism

“…1B). Higher-order metabolons, involving direct physical interactions among enzymes, have also been implicated as key control points in many specialized metabolic pathways, including phenylpropanoid, isoprenoid, alkaloid, and cyanogenic glucoside biosyntheses in plants (Achnine et al 2004;Weid et al 2004;Winkel 2004;Jorgensen et al 2005;Leivar et al 2005;Nielsen et al 2008;Chen et al 2011b). Putative metabolons are postulated to facilitate metabolic channeling, thus exerting a level of kinetic control and specificity by localizing spe- cialized pathways within or on the surface of particular subcellular compartments or by balancing the stoichiometry of participating pathway enzymes.…”

Morphine Biosynthesis in Opium Poppy Involves Two Cell Types: Sieve Elements and Laticifers

“…Subsequently, alkaloids are transported to laticifers for storage in large vesicles of the latex. However, a similar study based on the use of polyclonal antibodies to localize BIA biosynthetic enzymes (4'OMT, SalAT, COR, and 7OMT) in resin-embedded tissue sections of opium poppy suggested that laticifers and cells defined as phloem parenchyma are the sites of alkaloid biosynthesis (Weid et al, 2004). An alternative model purported that the early stages of BIA biosynthesis occur in phloem parenchyma cells and that downstream intermediates leading to morphine are transported to laticifers for final biosynthetic transformations and product accumulation.…”