Aphid infestation induces PR-proteins differently in barley susceptible orresistant 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-protei ns 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 bet a -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 b y western blots, with antibodies raised against purified chitinase (PR-3a) and beta -1,3-glucanase (PR-2a) from barley. By isoelectric focusing, two a dditional basic beta -1,3-glucanases were detected, which increased after i nfestation in both the resistant and the susceptible barley. The basic chit inase was only detected at days 7 and II in the susceptible cultivar, but a lready at day 2 in the resistant line. The induction was localized to the i nfested leaf. The PR-proteins PR-3a and PR-2a were also induced by the fung al pathogen (Blumeria [syn, Erysiphe] graminis f. sp, hordei), methyl salic ylate and, to a lower extent, by wounding with tweezers and methyl jasmonat e (MeJA). Needle mounding performed to mimic aphid stylet penetration did n ot induce chitinase or beta -1,3-glucanase, It is concluded that the fungal pathogen and the aphid infestation induce both similar and different respo nses, and that the aphid induction is not due to wounding only. The differe nt responses in resistant and susceptible lines indicate that the induced e nzymes may play a role in the resistance against aphid infestation.