Figure 1.

Schematic representation of the multicell model for the biosynthesis and accumulation of BIAs in opium poppy involving the coordinated participation of companion cells (cc), sieve elements (se), and laticifers (la). Biosynthetic enzymes are synthesized in companion cells and transported to sieve elements, where alkaloid biosynthesis occurs. The bulk of synthesized alkaloids are stored in neighboring laticifer networks. Other abbreviations: phloem parenchyma (pp), vascular cambium (vc), xylem parenchyma (xp), and xylem vessels (xy).