Occurrence of Avenanthramides and Hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxycinnamoyltransferase Activity in Oat Seeds

Abstract

O at phytoalexins, avenanthram ides, occur as constitutive com ponents in seeds. The am ounts of each av en an th ram id e w ere analyzed. The com position of av en an th ram id es in dry seeds was d ifferent from th at in elicitor-treated leaves. In seeds, av en an th ram id e C was most ab u n d an t w ith an am o u n t tw o tim es larger than th at of aven an th ram id e A o r B. O n the o th er h and , av en an th ram id e A was the m ajor com ponent in elicitor-treated leaves. The total am ount of av en an th ram id es in seeds increased 2.5 tim es during im bibition for 48 h although the com position did n o t change. The hydroxycinnam oyl-C oA :hydroxyanthranilate /V-hydroxycinnam oyltransferase (H H T, E C 2.3.1.-) activity, which is responsible for th e final co n d en sation step in th e av en an th ram id e biosynthesis, was detected in dry seeds. T he activity was localized in e n d o sp erm and scutellum , and slightly increased during 48-h im bibition. The enzym e was partially purified by anion exchange chrom atography from b o th dry seeds and elicitor-treated leaves. TTie activity was separated into two peaks by chrom atography, indicat ing th at H H T consists of at least tw o isoforms. The substrate specificities o f H H T isoform s from seeds w ere differen t from each other.

New series of avenanthramides in oat seed

“…8,9) Enzyme activity is also detected in the oat seed extract, indicating the involvement of the same enzyme in the synthesis of avenanthramides in seeds. 10) The genes encoding HHTs have been cloned by Yang et al 11) Oats are usually consumed as whole grains and contain the highest levels of protein and fat of any of the cereal grains. 12) In ancient Rome, oat flour was topically applied to treat various dermatologic conditions.…”

Potential health benefits of avenanthramides of oats

“…Oats contain unique, low‐molecular‐weight, soluble phenolic compounds called avenanthramides (Avns), 13,14 which are not present in other cereal grains. These compounds are antipathogens (phytoalexins), which are produced by the plant in response to exposure to pathogens such as fungi 15,16 . Avns are conjugates of a phenylpropanoid with anthranilic acid or 5‐hydroxy anthranilic acid.…”

Phenols in spikelets and leaves of field‐grown oats (Avena sativa) with different inherent resistance to crown rust (Puccinia coronata f. sp. avenae)

“…It has been demonstrated that labelled anthranilate, phenylalanine and p ‐coumaric acid are incorporated into avenanthramides after elicitation 10, 12, 35, 36. Studies have also shown that the content of the avenanthramides, in some cases along with the activity of HHT, increases in grains during germination 37–39. However, when oat grain flour is steeped in water, the content of the avenanthramides decreases,40 probably a result of oxidation by peroxidase41 or PO (unpublished data).…”