DEVELOPMENTAL REGULATION OF BENZYLISOQUINOLINE ALKALOID BIOSYNTHESIS IN OPIUM POPPY PLANTS AND TISSUE-CULTURES

Opium poppy (Papaver somniferum L.) contains a number of pharmaceutica lly important alkaloids of the benzylisoquinoline type including morph ine, codeine, papaverine, and sanguinarine. Although these alkaloids a ccumulate to high concentrations in various organs of the intact plant , only the phytoalexin sanguinarine has been found at significant leve ls in opium poppy cell cultures. Moreover, even sanguinarine biosynthe sis is not constitutive in poppy cell suspension cultures, but is typi cally induced only after treatment with a fungal-derived elicitor. The absence of appreciable quantities of alkaloids in dedifferentiated op ium poppy cell cultures suggests that benzylisoquinoline alkaloid bios ynthesis is developmentally regulated and requires the differentiation of specific tissues. In the 40 yr since opium poppy tissues were firs t cultured in. vitro, a number of reports on the redifferentiation of roots and buds from callus have appeared. A requirement for the presen ce of specialized laticifer cells has been suggested before certain al kaloids, such as morphine and codeine, can accumulate. Laticifers repr esent a complex internal secretory system in about 15 plant families a nd appear to have multiple evolutionary origins. Opium poppy laticifer s differentiate from procambial cells and undergo articulation and ana stomosis to form a continuous network of elements associated with the phloem throughout much of the intact plant. Latex is the combined cyto plasm of fused laticifer vessels, and contains numerous large alkaloid vesicles in which latex-associated poppy alkaloids are sequestered. T he formation of alkaloid vesicles, the subcellular compartmentation of alkaloid biosynthesis, and the tissue-specific localization and contr ol of these processes are important unresolved problems in plant cell biology. Alkaloid biosynthesis in opium poppy is an excellent model sy stem to investigate the developmental regulation and cell biology of c omplex metabolic pathways, and the relationship between metabolic regu lation and cell-type specific differentiation. La this review, we summ arize the literature on the roles of cellular differentiation and plan t development in alkaloid biosynthesis in opium poppy plants and tissu e cultures.