Plants produce a large diverse array of organic compounds that may function in protection against pathogens. Diverse antifungal compounds were reported to exist in barley (Hordeum vulgare L.); the indole alkaloid, gramine, and the pathogenesis-related proteins are some of them. Both the N-methyltransferase that is involved in gramine biosynthesis and PR-17a were studied in barley upon infestation by the bird cherry-oat aphid (Rhopalosiphum padi).

The effect of infestation by R. padi on induction of PR-17a and N-methyltransferase was investigated in different barley lines, susceptible and resistant.

The gene expression of PR-17a was down-regulated in the susceptible cv. Golf and to some extent up-regulated at the first days in var. Lina and then down-regulated. The PR-17a was induced by the aphid infestation in the resistant line CI16145; the gene expression was stronger in the infested plants than in the controls. The different responses in resistant and susceptible lines indicate that the induced PR-17a may play a role in the resistance against aphid infestation. PR-17a was up-regulated systemically in the base in barley after infestation by R. padi.

In the susceptible varieties Lina and Golf, the accumulation of N-methyltransferase did not increase with time from 1 day to 7 days after infestation, as determined by western blots with antibody raised against NMT from barley. The NMT-gene was down-regulated after 7 days infestation in both variety Lina and Golf both locally in the first leaf and in the base. Barley line CI16145 had no accumulation of NMT as was seen by western blotting. There was no induction of NMT in barley upon aphid infestation.