Accumulation of pathogenesis-related proteins in the apoplast of a susceptible cultivar of apple (Malus domestica cv. Elstar) after infection by Venturia inaequalis and constitutive expression of PR genes in the resistant cultivar Remo

Leaves of apple ( Malus domestica cv. Elstar) were infected with a cloned isolate of the apple scab Venturia inaequalis. The intercellular washing fluid (IWF) of these plants was collected and the variation in the composition of proteins in the IWF was analysed by SDS-PAGE and two-dimensional gel electrophoresis during and after the infection with V. inaequalis, the causal agent of apple scab. The subsequent analysis of induced proteins by electron spray ionization quadrupole time of flight mass spectroscopy revealed the presence of beta-1,3-glucanase, chitinase, thaumatin-like protein and a cysteine-like protease in M. domestica leaves infected by V. inaequalis. These results were confirmed by immunoblotting with antibodies against some of these proteins. Moreover, a non-specific lipid transfer protein was identified in uninfected leaves: the amount declined to a non-detectable level within the first week after infection by V. inaequalis. The analysis of the IWF of M. domestica cv. Remo, bearing resistances to apple scab, powdery mildew and fire blight, showed a protein pattern comparable to that of the IWF from V. inaequalis infected leaves from cultivar Elstar indicating the constitutive production at least of some of the pathogenesis-related proteins in the resistant cultivar.