Involvement of cAMP signaling in elicitor-induced phytoalexin accumulation in Cupressus lusitanica cell cultures

• An increasing body of evidence on plant electrophysiology, biochemistry, and molecular biology shows that cAMP exists in higher plants and plays a role in several physiological processes by affecting potassium (K ⁺) or calcium (Ca²⁺) fluxes. Our study here reports that cAMP is involved in elicitor-induced accumulation of a phytoalexin, β-thujaplicin, in Cupressus lusitanica cell cultures. • Treatment of C. lusitanica cultured cells with cAMP or its analogues stimulated β-thujaplicin accumulation. Cholera toxin and forskolin, activators of adenylyl cyclase, also stimulated β-thujaplicin accumulation. Enzyme immunoassay showed that after elicitor treatment, cAMP level in the elicited cells quickly increased to about three-to five-fold over the control. Cholera toxin and forskolin also stimulated cAMP accumulation in the absence of elicitor. • However, K⁺ and Ca²⁺ channel blockers inhibited the β-thujaplicin accumulation induced by cAMP analogues, suggesting that the cAMP-stimulated β-thujaplicin accumulation may involve Ca²⁺ and K⁺ fluxes. Several ionophores mimicked cAMP induction of β-thujaplicin accumulation. • Cross-talk between cAMP treatment and the ethylene signaling pathway was also observed to work in the cell cultures via Ca²⁺ signaling. The study also indicates an involvement of protein kinase cascades in cAMP signaling processes, leading to both phytoalexin and ethylene production.