INHIBITION OF PHYTOALEXIN ACCUMULATION IN POTATO-TUBER DISKS BY SUPEROXIDE SCAVENGERS

Non-steroidal anti-inflammatory drugs (NSAIDs) and nordihydroguaiaretic acid (NDGA) inhibited phytoalexin accumulation and browning in potato tuber tissue elicited by arachidonic acid, by sporangia of Phytophthora infestans, by two elicitors prepared from the fungus and by chitosan. Neither of the two fungal elicitors contained any detectable fatty acids. Since elicitation by arachidonic acid was also inhibited by superoxide dismutase, the ability of NSAIDs and NDGA to scavenge superoxide anions was investigated in vitro. Both types of compound reduced the levels of superoxide formed either enzymically by xanthine/xanthine oxidase or chemically by autoxidation of epinephrine or pyrogallol. The inhibitory effect of NSAIDs and NDGA on both browning and phytoalexin accumulation in tuber discs is most probably a consequence of their ability to scavenge superoxide anions. Moreover, other scavengers of oxygen free radicals inhibit the elicitation of phytoalexins by either arachidonic acid or chitosan. These results suggest that both fatty acid-containing and non-lipid elicitors have a similar mode of action, probably involving the production of superoxide anions or other active oxygen radicals.