Elicitor-induced indole alkaloid biosynthesis in Catharanthus roseus cell cultures is related to Ca 2+ influx and the oxidative burst

Abstract

Oxidative burst and lipid peroxidation occurred in fungal elicitor-treated Catharanthus roseus cell cultures before the expression of indole alkaloid biosynthesis. The activities of protective enzymes (superoxide dismutase, catalase, and peroxidase) involved in H 2O 2 metabolism and phenylalanine ammonia lyase were also activated to high levels in fungal elicited cell cultures due to the oxidative burst. H 2O 2 treatment alone could mimic the oxidative burst to stimulate alkaloid production, and NADPH pretreatment promoted elicitor-induced alkaloid biosynthesis. These results suggest that the oxidative burst or H 2O 2 production is closely related to indole alkaloid production. Further studies show that the fungal elicitor-induced oxidative burst and indole alkaloid accumulation could partially be inhibited by pretreatments of the cell cultures with calcium channel blockers (verapamil and LaCl 3) and Ca 2+ chelator EGTA, or by deleting calcium chloride from the medium, but could be recovered by re-addition of calcium chloride. These results suggest that the fungal elicitor-triggered oxidative burst and indole alkaloid biosynthesis involves Ca 2+ influx and Ca 2+-dependent signal transduction. This hypothesis was further strengthened by the observations that verapamil, LaCl 3, and EGTA pretreatments also partially blocked elicitor induced lipid peroxidation and increased protective or defense enzyme activities in C. roseus cell cultures.