Aphid infestation induces PR-proteins differently in barley susceptible or resistant to the birdcherry-oat aphid (Rhopalosiphum padi)

The effect of infestation by the birdcherry-oat aphid (Rhopalosiphum padi L.), on induction of PR-proteins was investigated in barley (Hordeum vulgare L.), using barley lines susceptible or resistant to R. padi, The PR-proteins PR-1a (unknown function), PR-5a (acidic thaumatin) and peroxidase (EC 1.11.1.7) were not affected, whereas one chitinase (EC 3.2.1.14) and four beta -1,3-glucanases (EC 3.2.1.39) were induced by the aphid treatment, In the resistant breeding line CI 16145, but not in the susceptible cultivar Golf, accumulation of one basic: chitinase and two acidic beta -1,3-glucanases increased with time from 2 until II days after infestation, as determined by western blots, with antibodies raised against purified chitinase (PR-3a) and beta -1,3-glucanase (PR-2a) from barley. By isoelectric focusing, two additional basic beta -1,3-glucanases were detected, which increased after infestation in both the resistant and the susceptible barley. The basic chitinase was only detected at days 7 and II in the susceptible cultivar, but already at day 2 in the resistant line. The induction was localized to the infested leaf. The PR-proteins PR-3a and PR-2a were also induced by the fungal pathogen (Blumeria [syn, Erysiphe] graminis f. sp, hordei), methyl salicylate and, to a lower extent, by wounding with tweezers and methyl jasmonate (MeJA). Needle mounding performed to mimic aphid stylet penetration did not induce chitinase or beta -1,3-glucanase, It is concluded that the fungal pathogen and the aphid infestation induce both similar and different responses, and that the aphid induction is not due to wounding only. The different responses in resistant and susceptible lines indicate that the induced enzymes may play a role in the resistance against aphid infestation.