Lipid peroxidation and the oxidative burst associated with infection of capsicum annuum by botrytis cinerea

A combination of electron paramagnetic resonance (EPR) spectroscopy and analytical chemistry has been used to study the changes in free radical content, transition metal ion status and lipid peroxidation following inoculation of fruits of sweet pepper (Capsicum annuum) with Botrytis cinerea. EPR detected a high concentration of an unidentified free radical associated with the spreading lesion that extends into the surrounding, healthy tissues. In addition, the EPR-detectable iron(III) was highest at the centre of the lesion, again displaying a gradient out into the surrounding tissues. Analyses for aldehydic products of lipid peroxidation were performed to assess the accumulation and potential of these compounds to contribute to the cell death associated with necrotrophic pathogens. In contrast to the spectrum of aldehydes typically observed within peroxidized biological samples, no accumulation of malondialdehyde nor n-hexanal was observed. Instead, high levels of two hydroxyalkenals (4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal) were detected at concentra- tions up to 4000 and 20 000 pmol g- 1, respectively, at the host-pathogen interface. These results are discussed in terms of the likely mechanisms of formation of these aldehydes.