Oxidative effects in uninfected tissue in leaves of French bean (Phaseolus vulgaris) containing soft rots caused by Botrytis cinera

Several markers of oxidative processes have been measured in leaves of Phaseolus vulgaris infected with Botrytis cinerea, with the specific objective of investigating changes induced by this necrotrophic pathogen in tissue remote from the lesion. There was a progressive decrease with time in the contents of ascorbic acid (AA) in apparently healthy tissues from infected plants and non-inoculated plants grown under identical high-humidity conditions (abiotically stressed controls), and for periods >48 h this decrease was greater in the infected plants. This decline in AA content was accompanied by an elevation in the intensity of the electron paramagnetic resonance (EPR) signal from adducts of the spin trap a-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN), a destabilisation of the (monodehydro) ascorbate radical (Asc·) signal in the presence of POBN, and an increase in the ratio of Asc· to AA in samples studied in the absence of the spin trap. These results are consistent with a shift in redox status to more oxidising conditions in apparently healthy tissue of infected plants and indicate the prevalence of chemical processes that are distinctly different from those in uninfected plants. However, no differences in lipid peroxidation products or the single-peak free radical and Fe(III) (g = 4.27) EPR signals were observed between these tissues distant from the lesions and those from abiotically stressed controls. In addition, the pathogen-derived sesquiterpene toxin botrydial and a second Mn(II) EPR signal, both of which are associated with Botrytis infection, were not detected in these ‘apparently healthy’ tissues.
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