Expression of potential defense responses of Asian and European pears to infection with Venturia nashicola.

摘要

In order to determine if differences in timing or levels of gene and enzyme activations were likely to account for differences in resistance of pear cultivars against Japanese pear scab, time course analyses of several potential defense genes and enzymes as well as salicylic acid (SA) accumulation were carried out using leaf tissue of susceptible Japanese pear cv. 'Kousui' and resistant pear cvs. 'Kinchaku', 'Mamenashi 12' and 'Flemish Beauty' upon inoculation with the race 1 of Venturia nashicola. A phenylalanine-ammonia lyase gene (pal) expression was not significantly affected by pathogen regardless of the compatible or incompatible interaction. Accumulation of pathogenesis-related protein 1 (pr1) and chitinase (chi) transcripts was early and highly elicited in the host resistant cv. 'Kinchaku', while in the other interactions it was delayed. In general, enhancement of SA accumulation and increase in the expression of pr1 gene in 'Kinchaku' are positively correlated, suggesting that this resistance is SA-dependent. The activity of four antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)) was significantly enhanced only in resistant cultivars with a differential pattern of induction according to the cultivar. Superoxide anion (O2-) was highly detected in inoculated leaves of the resistant cvs. 'Kinchaku' and 'Mamenashi 12' when compared to the susceptible cv. 'Kousui'. The involvement of the oxidative burst as well as its relationship with the activity of the antioxidant enzymes and with resistance is discussed.