A redox-dependent, G-protein-coupled phospholipase A of the plasma membrane is involved in the elicitation of alkaloid biosynthesis in Eschscholtzia californica

In cultured cells of Californian poppy formation of benzophenanthridine alkaloids can be triggered by a yeast elicitor preparation independently of the hypersensitive reaction. A plasma membrane (PM)bound phospholipase A (PLA)is likely to play a role in the signalling process: PLA activity was detectable in individual cells, cell suspensions and PM vesicles with the fluorogenic phospholipid bis-BODIPY FL C11-PC and was sensitive to known inhibitors of PLA2. In microscopic assays, enzyme activity increased after elicitor contact of cells that were pretreated with non-saturating concentrations of PLA2 inhibitors. In PM vesicles a PLA2-like protein as well as Ga- and Gß-proteins were detected immunologically. Anti-Ga or anti-Gß antisera or mastoparan stimulated PLA activity thus indicating a G-protein-controlled enzyme. Elicitation of alkaloid production was sensitive to aristolochic acid and enhanced by PLA2 products such as lysophosphatidylcholine and linolenic acid. Pretreatment of the cells with the artificial electron acceptors hexabromoiridate(V)or ferricyanide(III)reversibly abolished the effect of subsequent elicitation and reduced the activity of PLA both in intact cells and in PM vesicles. It appears, therefore, that PLA2 is a point of interference of redox control with the signal path.