Photooxidative reactions in chloroplast thylakoids. Evidence for a Fenton-type reaction promoted by superoxide or ascorbate

Abstract

A methyl viologen (MV)(*) mediated Mehler reaction was studied using Type C and D chloroplasts (thylakoids) from spinach. The extent of photooxidative reactions were measured as (a) rate of ethylene formation from methional oxidation indicating the production of oxygen radicals, and (b) rate of malondialdehyde (MDA) formation as a measure of lipid peroxidation. Without added ascorbate, 1 μM FerricEDTA increased ethylene formation by greater than 4-fold, but had no effect on MDA production. Ascorbate (1 mM) produced a tripling of ethylene while it reduced MDA formation in the presence of iron. Radical scavengers diethyldithiocarbamate (DDTC), formate, 1,4-diazabicyclo (2.2.2octane) (DABCO), inhibited ethylene formation. Using 0,4 M mannitol to scavenge hydroxyl radicals, the rates of ethylene formation were reduced 40 to 60% with or without 1 μM Fe(III) EDTA. The strong oxidant(s) not scavenged by mannitol are hypothesized to be either alkoxyl radicals from lipid peroxidation, or 'site specific' formation of hydroxyl radicals in a lipophillic environment not exposed to mannitol. Singlet oxygen does not appear to be a significant factor in this system. Catalase strongly inhibited both ethylene and MDA synthesis under all conditions; 1 mM ascorbate did not reverse this inhibition. However, the strong superoxide dismutase (SOD) inhibition of ethylene and MDA formation was completely reversed by 1 mM ascorbate. This suggests that superoxide was functioning as an iron reducing agent and that in its absence, ascorbate was similarly promoting oxidations. Therefore, these oxidative processes were dependent on the presence of H2O2 and a reducing agent, suggesting the involvement of a Fenton-type reaction.

Growth inhibition and effect on photosystem by three imidazolium chloride ionic liquids in rice seedlings

“…Our former experiments showed that [OMIM]Cl may damage rice leaves and cause lipid peroxidation when applied at high concentrations which induced the increase of malondialdehyde (MDA) content [17]. Uphem [25] indicated that MDA would degrade chlorophyll. In this way the photosynthesis was affected by ILs and then the Hill reaction activity was decreased.…”

Analysis of differentially expressed genes and adaptive mechanisms of Prunus triloba Lindl. under alkaline stress

“…9h–i), indicating that plant damage was becoming more severe. MDA not only has a cytotoxic effect by damaging cell membrane structure, but it can also degrade chlorophyll, thereby reducing plant photosynthesis [55]. The Chl content in this study decreased gradually, from 5.492 to 2.304 mg/g, as the duration of alkaline stress increased (Fig.…”

A comparison of colorimetric assays detecting hydrogen peroxide in leaf extracts

“…Because of these characteristics, H 2 O 2 is considered as a signaling molecule in growth and development [7], cell cycle [8], flowering [9], senescence [10] and in stress responses [11]. On the other hand, travelling H 2 O 2 may spread oxidative damage as the source of highly reactive hydroxyl radicals via Fenton chemistry [12] or direct photo-cleavage by UV-B [13]. Consequently, assessing H 2 O 2 concentrations in leaves is of special interest as indicator of physiological status and stress responses.…”