Chitosan(CHN)specially induced the activities of 39 kD and 42 kD protein kinases in ginseng cells,which could be suppressed by an inhibitor of mitogen-activated protein kinase(MAPK)pathway,PD98059.The immunoprecipitation(IP)using MAPK antibody or kinase assay in vitro also showed that CHN-induced 42 kD and 39 kD protein kinases belonged to the MAPK family.PD98059 suppressed CHN-induced transcriptions of ginseng squalene synthase and ginseng squalene epoxidase genes(gss and gse),CHN-induced accumulation of β-Amyrin synthase(β-AS)and synthesis of saponin.These results showed that CHN-induced activities of MAPKs were necessary for the CHN-induced saponin synthesis.EGTA and LaCI3 suppressed CHN-induced 39 kD and 42 kD MAPK activities.Ruthenium red(RR)could suppress CHN-induced 39 kD activity.All of them suppressed CHN-induced saponin synthesis.These results indicated that CHN-induced increment of cytosolic calcium was necessary for CHN-induced saponin synthesis.PD98059 also suppressed CHN-induced oxidative burst(including the increment of activity of plasma membrane NADPH oxidase and production of H2O2),but diphenylene iodonium(DPI),dimethylthiourea(DMTU)and 2,5-dihydroxycinnamic acid methyl ester(DHC)could not suppress CHN-induced MAPK activities,which indicated that MAPK was possibly function upstream of CHN-induced oxidative burst.