Components of C6-aldehyde-induced resistance in Arabidopsis thaliana against a necrotrophic fungal pathogen, Botrytis cinerea

Volatile C6-aldehydes, (E)-2-hexenal and (Z)-3-hexenal, enhance resistance against a necrotrophic pathogen (Botrytis cinerea) in Arabidopsis thaliana. We attempted to dissect the components involved in the induced resistance. The penetration of B. cinerea hyphae into Arabidopsis epidermis and the growth of hyphae after penetration were suppressed on the C6-aldehyde-treated leaves when compared with those on the control leaves. We found that after the volatile-treatment, the vascular bundles and cell walls of the leaves were intensely lignified. Higher lignification could be observed with (E)-2-hexenal-treatment compared to (Z)-3-hexenal-treatment, which coincided with the degree of overall resistance. When an extract was prepared from the treated leaves, and fractionated into high (>12,000) and low (<12,000) molecular weight fractions, high antifungal activities could be found with both fractions prepared from the treated leaves. We also found that C6-aldehydes-induced accumulation of PDF1.2 (plant defensin1.2) and PR-3 (chitinaseB) transcripts and camalexin. Taken together, these data suggest that C6-aldehydes made Arabidopsis resistant to the pathogen due to both volatile-treatment induced lignification, which formed a physical barrier to the penetration of the hyphae, and the accumulation of antifungal substances including PDF1.2, PR-3 and camalexin, which inhibited the growth of the hyphae in the plant cells.