Tissue distribution of avenanthramides and gene expression of hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxycinnamoyl transferase (HHT) in benzothiadiazole-treated oat (Avena sativa)1

Oats produce a group of natural products termed avenanthramides. These compounds are produced in both the vegetative tissue and the grain. They are produced in leaf tissue in response to crown rust infection and by chemical plant defense activators and likely other environmental stresses. Grain avenanthramide production tends to be constitutive but concentrations are highly variable and strongly influenced by environmental conditions. In this paper, we report the effect of a plant defense activator [benzothiadiazole (BTH)] on the temporal expression and tissue distribution of avenanthramides in the leaf, stem, root, panicle stem, glumes, lemma/palea, and filling grain in the oat plant. Hydroxycinnamoyl-CoA:hydroxyanthranilate N-hydroxycinnamoyl transferase (HHT, a member of the BAHD acyltransferase family and the final enzyme in the biosynthetic pathway to the avenanthramides) activity is also determined in these tissues, as well as the relative expression ratios of HHT mRNA resulting from BTH treatment. Evidence for phloem transport of the avenanthramides is also presented. In summary, following BTH treatment, leaf tissue is the predominant location for avenanthramide biosynthesis. However, significant amounts are also found in the upper and lower stems, roots, panicle stems, and glumes. The lemma/palea and filling grain contained demonstrable but substantially lower amounts of avenanthramides. Avenanthramides were also detected in the phloem sap, indicating a source to sink transport of these metabolites following BTH treatment.