Lipid peroxidation and the oxidative burst associated with infection of Capsicum annuum by Botrytis cinerea

A combination of electron paramagnetic resonance (EPR) spectroscopy and ana lytical chemistry has been used to study the changes in free radical conten t, transition metal ion status and lipid peroxidation following inoculation of fruits of sweet pepper (Capsicum annuum) with Botrytis cinerea. EPR det ected 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 le sion, again displaying a gradient out into the surrounding tissues. Analyse s for aldehydic products of lipid peroxidation were performed to assess the accumulation and potential of these compounds to contribute to the cell de ath associated with necrotrophic pathogens. In contrast to the spectrum of aldehydes typically observed within peroxidized biological samples, no accu mulation of malondialdehyde nor n-hexanal was observed. Instead, high level s 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), respective ly, at the host-pathogen interface. These results are discussed in terms of the likely mechanisms of formation of these aldehydes.