Elicitor-induced indole alkaloid biosynthesis in Catharanthus roseus cell cultures is related to Ca2+ influx and the oxidative burst

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, c atalase. and peroxidase) involved in H2O2 metabolism and phenylalanine ammo nia lyase were also activated to high levels in fungal elicited cell cultur es due to the oxidative burst. H2O2 treatment alone could mimic the oxidati ve burst to stimulate alkaloid production, and NADPH pretreatment promoted elicitor-induced alkaloid biosynthesis. These results suggest that the oxid ative burst or H2O2 production is closely related to indole alkaloid produc tion. Further studies show that the fungal elicitor-induced oxidative burst and indole alkaloid accumulation could partially be inhibited by pretreatm ents of the cell cultures with calcium channel blockers (verapamil and LaCl 3) and Ca2+ chelator EGTA. or by deleting calcium chloride from the medium, but could be recovered by re-addition of calcium chloride. These results s uggest that the fungal elicitor-triggered oxidative burst and indole alkalo id biosynthesis involves Ca2+ influx and Ca2+-dependent signal transduction , This hypothesis was further strengthened by the observations that verapam il. LaCl3. and EGTA pretreatments also partially blocked elicitor induced l ipid peroxidation and increased protective or defense enzyme activities in C. roseus cell cultures. (C) 2001 Elsevier Science Ireland Ltd. Ali rights reserved.