In situ localization of avenanthramide A and its biosynthetic enzyme in oat leaves infected with the crown rust fungus, Puccinia coronata f. sp. avenae

We determined the temporal and spatial localization of the phytoalexin avenanthramide A, and its biosynthetic enzyme, hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxy-cinnamoyltransferase (AsHHT) in oat leaves infected with the crown rust fungus. Accumulation of avenanthramide A and AsHHT was first observed predominantly in hypersensitive response (HR) cells at 36 h post inoculation (hpi), and later in adjacent cells at 48 hpi. At 120 hpi, avenanthramide A was detected in a wider area of infected tissues, but AsHHT-positive signals were only observed in the HR and adjacent cells, suggesting that avenanthramide A was synthesized around the HR cells, and then transported to other parts of the infected tissues in a center-to-periphery manner.