Induction of Hydroxycinnamoyl-CoA: Hydroxyanthranilate N-Hydroxycinnamoyl-transferase (HHT) Activity in Oat Leaves by Victorin C

Abstract

Victorin C. a host-specific toxin produced by Helminthosporium victoriae, induced hydro-xycinnamoyl-CoAihydroxyanthranilate N-hydroxycinnamoyltransferase (HHT, EC 2.3.1) activity in oat leaves (Avena sativa L., a cultivar carrying Pc-2 gene). This enzyme activity catalyzes the final step of biosynthesis of oat phytoalexins, avenanthramides. The HHT activity was detected after 12 h of victorin C application and reached to a maximum by 18 h. The induction of HHT was dose-dependent. All of the putative precursors of avenanthramides acted as substrates for HHT. These findings indicate that the accumulation of avenanthramides by victorin C treatment is due to induction of HHT. The enzyme activity showed highest specificity to 5-hydroxyanthranilate for the anthranyl moiety, while feruloyl-CoA was most effective for cinnamoyl moiety. HHT induced by victorin C showed significantly lower affinity for anthranilic acid relative to the enzyme induced by oligo-N-acetylchitooligosaccharides, another elicitor. suggesting that isozymes of HHT occur in this plant. © 1997, Verlag der Zeitschrift für Naturforschung. All rights reserved.