Hydrogenperoxide exogenously administerd to the suspension-cultured cells of Pueraria lobata stimulated a rapid disappearance of the constitutive isoflavonoids (malonylglucosides of daidzein and genistein) from the methanol soluble fraction of the cells, in a similar manner as observed in the cells treated with yeast extract or glycoprotein preparation of Phytophthora megasperma f. sp. glycinea. Rapid generation of H2O2 was detected within 10 min after elicitation at the cell surface, presumably preceded by the activation of plasma membrane NAD(P)H-oxidases. Pretreatment of some representative NAD(P)H-oxidase inhibitors such as SHAM, DEDTC and KCN (1 mᴍ each) to the cells 1 h before elicitation resulted in almost complete inhibition of the elicitor-stimulated metabolism of isoflavonoids for 4 h, whereas treatment of the inhibitors at 1 h after elicitation showed no significant effect on the rapid isoflavonoid metabolism. These findings suggest that this type of response to elicitation could be regarded as a plausible initial defense strategy prior to the appearance of de novo synthesized defensive barriers such as phytoalexins and lignin in plant-pathogen interaction.
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