Signal Mediators for Phytoalexin Production in Defense Response of Oats Elicited by Victorin as a Specific Elicitor

Signals mediating phytoalexin (PA) production were analyzed in primary leaves of oats cv. Iowa X469 treated with an elicitor victorin. Production of the PA avenanthramide A was inhibited by DPI, an inhibitor of NADPH oxidase/nitric oxide synthase (NOS) and the NOS inhibitors l-NMMA and 1,3-PBIT. However, catalase and superoxide dismutase (SOD) hardly suppressed it. From the data, NO functions as a major reactive oxygen species in signal transduction leading to PA production in the defense response of oats. EGTA, verapamil and ruthenium red inhibited PA production, suggesting that Ca²⁺ influx into the cytoplasm and intracellular Ca²⁺ movement are involved in the defense response. Trifluoperazine, a calmodulin function inhibitor, and K-252a, a serine/threonine kinase inhibitor, also suppressed the accumulation, whereas okadaic acid, a serine/threonine phosphatase inhibitor, did not suppress it, suggesting the involvement of calmodulin and protein kinase, but not of phosphatase in PA production.