Role of Jasmonic Acid as a Signaling Molecule in Copper Chloride-elicited Rice Phytoalexin Production

Phytoalexins are antimicrobial secondary metabolites which accumulate in plants against fungal invasion. Their production is triggered not only by fungal invasion, but also by a variety of elicitors. In rice plants, we have shown that CuCl2 is a potent abiotic elicitor. Jasmonic acid has recently become known to play an important role in secondary metabolite production in plants at the cellular level. This led us to speculate, in CuCl2-elicited rice leaves, that JA might also play an important role as a signal transducer for phytoalexin production. The endogenous level of JA increased rapidly in CuCl2-elicited rice leaves, and exogenously applied JA caused a large amount of phytoalexin production in rice leaves. This phytoalexin production by CuCl2 decreased when rice leaves were treated with JA biosynthesis inhibitors, but that by JA did not. JA is thus suggested to play an important role in the elicitation process leading to phytoalexin production in rice leaves.