Induction of Phenylalanine Ammonia-Lyase Activation and Isoflavone Glucoside Accumulation in Suspension-Cultured Cells of Red Bean, Vigna angularis, by Phytoalexin Elicitors, Vanadate, and Elevation of Medium pH

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Abstract
Treatment of suspension-cultured cells of red bean, Vigna angularis, with nigeran resulted in an accumulation of isoflavone glucosides, such as daidzein 7-O-β-D-glucoside, daidzein 7,4′-di-O-β-D-glucoside, and 2′-hydroxydaidzein 7,4′-di-O-β-D-glucoside, which was accompanied by a transient increase in the activity of phenylalanine animonia-lyase (PAL). Similar effects were also seen with other phytoalexin elicitors, such as RNase A and cell wall components of Phytophthora megasperma var. sojae. Interestingly, the accumulation of isoflavone glucosides and the transient increase in PAL activity were induced also by vanadate, a specific inhibitor of plasma membrane adenosine triphosphatase. K3PO4 showed similar effects, but this was ascribed to the elevation of medium pH caused by adding this basic salt. In fact, merely raising the pH of the medium was found to be sufficient for the induction of PAL activity. Experiments using inhibitors showed that the induction depends on RNA and protein syntheses. The results are discussed in relation to the possible mechanism of action of phytoalexin elicitors.