Early developmental onset of alkaloid biosynthesis in Mexican poppy (Argemone mexicana L) Papaveraceae

Abstract

The distribution of berberine and sanguinarine, two benzylisoquinolinic alkaloids, was analysed at early developmental phases in Argemone mexicana, including hypocotyls, cotyledonary seedlings and plantlets (displaying the first pair of true meristematic leaflets). Transcripts corresponding to genes involved in the synthesis of each of these alkaloids were also analysed. Even though most of the sanguinarine present in closed cotyledons of seedlings at the hypocotyl stage came from the original seeds, evidence for sanguinarine biosynthetic activity was also found in hypocotyls and closed cotyledons. Low levels of sanguinarine accumulated in hypocotyls, but evidence of a possible excretion mechanism in this tissue was detected. Transcripts related to sanguinarine synthesis continued accumulating in emerging hypocotyls, as well as in radicles of cotyledonary seedlings and plantlets, coinciding with alkaloid accumulation. In contrast, berberine required cotyledon unfolding to accumulate. This alkaloid was mostly found in aerial parts, even when biosynthetic related transcripts were mainly detected in radicles. These results suggest either the operation of a berberine transport system or the formation of berberine by different gene products, with similar catalytic properties, in underground and aerial tissues.