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 alk aloids can be triggered by a yeast elicitor preparation independently of th e hypersensitive reaction. A plasma membrane (PM) bound phospholipase A (PL A) is likely to play a role in the signalling process: PLA activity was det ectable in individual cells, cell suspensions and PM vesicles with the fluo rogenic phospholipid bis-BODIPY FL C-11-PC and was sensitive to known inhib itors of PLA(2). In microscopic assays, enzyme activity increased after eli citor contact of cells that were pretreated with non-saturating concentrati ons of PLA(2) inhibitors. In PM vesicles a PLA(2)-like protein as well as G (alpha)- and G(beta)-proteins were detected immunologically, Anti-G(alpha) or anti-G(beta) antisera or mastoparan stimulated PLA activity thus indicat ing a G-protein-controlled enzyme. Elicitation of alkaloid production was s ensitive to aristolochic acid and enhanced by PLA(2) products such as lysop hosphatidylcholine and linolenic acid. Pretreatment of the cells with the a rtificial electron accepters hexabromoiridate(V) or ferricyanide(III) rever sibly abolished the effect of subsequent elicitation and reduced the activi ty of PLA both in intact cells and in PM vesicles. It appears, therefore, t hat PLA(2) is a point of interference of redox control with the signal path . (C) 1999 Elsevier Science B.V. All rights reserved.