In vitro photodynamic lipid peroxidation of total lipophilic extracts from leaves of bean plants
1993
Ferrari-Iliou, R. | d'Arcy-Lameta, A. | Iliou, J.P. | Thi, A.T.P. | Monteiro de Paula, F. | Vieira da Silva, J. | Mazliak, P.
In vitro lipid peroxidation, induced by reactive oxygen species photochemically generated, was carried out on purified alpha-linolenic acid (18:3(n-3)) and on bean leaf total lipophilic extracts. The photosensitizer used was meso-tetraphenylporphine. The time-course of the reaction was evaluated by ultraviolet (UV) spectra analysis. The 18:3(n-3) photoperoxidation kinetics comprised three steps: monohydroperoxidation, characterized by the appearance of conjugated diene patterns; dihydroperoxidation, characterized by the appearance of conjugated triene patterns, oxidative cleavage of the mono- and dihydroperoxides, characterized by the disappearance of conjugated patterns. In contrast, for hydrated plant total lipophilic extract photoperoxidation, conjugated pattern appearance was slow and the maximum plateau was not obtained. In order to explain plant extract behaviour, we tested the effects of beta-carotene and quercetin (important components of the chloroplast membrane) on the time-course of 18:3(n-3) photoperoxidation. The first step was inhibited by beta-carotene implying that type II photoperoxidation involving singlet oxygen ((1)O2) was predominant. Whilst the two last steps were inhibited by quercetin implying that type I photoperoxidation involving free radicals, prevailed. Since 18:3(n-3) foliar content decreased under water deficit, we tested the behaviour of total lipophilic extracts from droughted plant leaves in presence of reactive oxygen species. In the case of droughted plants, the maximum of conjugated diene patterns was attained later than for hydrated plants, suggesting that drought affects the resistance capability of total lipophilic extracts from bean leaves to lipid photoperoxidation.
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