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

Non-steroidal anti-inflammatory drugs (NSAIDs) and nordihydroguaiareti c acid (NDGA) inhibited phytoalexin accumulation and browning in potat o tuber tissue elicited by arachidonic acid, by sporangia of Phytophth ora infestans, by two elicitors prepared from the fungus and by chitos an. Neither of the two fungal elicitors contained any detectable fatty acids. Since elicitation by arachidonic acid was also inhibited by su peroxide dismutase, the ability of NSAIDs and NDGA to scavenge superox ide anions was investigated in vitro. Both types of compound reduced t he levels of superoxide formed either enzymically by xanthine/xanthine oxidase or chemically by autoxidation of epinephrine or pyrogallol. T he inhibitory effect of NSAIDs and NDGA on both browning and phytoalex in 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 a cid-containing and non-lipid elicitors have a similar mode of action, probably involving the production of superoxide anions or other active oxygen radicals.