Hydroxyl radicals are not the protagonists of UV-B-induced damage in isolated thylakoid membranes (original) (raw)

UV-B induced alteration of oxygen evolving reactions in pea thylakoid membranes as affected by scavengers of reactive oxygen species

Biologia Plantarum, 2014

The effect of UV-B irradiation at temperatures of 22 and 4 °C on flash induced oxygen yields, photochemical activity, and energy transfer in pea thylakoid membranes in the absence and presence of scavengers of reactive oxygen species (ROS) was studied. Three different scavengers were used: dimethyl sulfoxide (DMSO), histidine (His), and n-propyl gallate (nPG). As result of the UV-B treatment of isolated membranes, the flash oxygen yields were considerably affected -the amplitudes decreased and the oscillation pattern was lost. The analysis of the flash oxygen yields and initial oxygen burst showed alterations of a number of oxygen evolving centers in the S 0 state as well as changes of decay kinetics of the oxygen burst under continuous irradiation. ROS scavengers exhibited more or less expressed protective effects, nPG being the most effective against UV-B induced damages of the flash oxygen yields. At both the temperatures, photosystem II (PS II) mediated electron transport was more sensitive to the UV-B treatment in comparison with photosystem I (PS I). The analysis of 77 K fluorescence spectra showed that the fluorescence ratio F735/F685 increased by the UV-B treatment probably due to a redistribution of excitation energy between both photosystems most likely caused by partial unstacking and due to a decrease of PS II fluorescence resulting from reaction center-type quenching. The nPG was the most powerful scavenger which protected the oxygen evolution capacity of PS II in the absence and presence of an exogenous electron acceptor to the highest extent.

Uv-Induced Oxygen Free Radicals Production in Spinach Thylakoids

Besides being the ultimate driving force for photosynthesis and its important regulatory factor, solar light is also a major source of stress to photosynthetic organisms. The efficiency of the light induced damage increases with the wavelength decrease. Thus, from natural sunlight that reaches the Earth, the UV-A and UV-B (290–320 nm and 320 – 400 nm, respectively) spectral ranges have the highest damaging potential for photosynthetic organisms, mostly due to the UV-induced production of highly harmful reactive oxygen species (ROS) such as oxygen free radicals. The UV-induced oxygen free radicals production in aqueous suspensions of thylakoids (isolated photosynthetic organelles form spinach leaves), was investigated in this work by using the EPR-spin-trapping method. Two spin-traps, 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) and 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), were used for the simultaneous detection of various free radicals, as a conseque...

UV-B-INDUCED ALTERATIONS IN PRIMARY PHOTOSYNTHETIC REACTIONS IN ISOLATED THYLAKOID MEMBRANES OF ARABIDOPSIS THALIANA (C24)

Comptes rendus de l'Académie bulgare des sciences: sciences mathématiques et naturelles

The effect of UV-B irradiation on primary photosynthetic reactions of isolated thylakoid membranes from Arabidopsis thaliana (C24) has been investigated at low and room temperature. The energy distribution between the main pigment-protein complexes and oxygen evolving activity of PSII centres were strongly affected by UV-B treatment when irradiation was performed at room than at low temperature. The energy interaction in the pigment protein complex of PSII-core antenna is more affected by UV-B treatment at both temperatures than the energy distribution between both photosystems, as revealed by fluorescence rations of 77K spectra. The grana situated PSII centres are more sensitive to UV-B irradiation in respect to flash oxygen yields than PSII centres, situated in the stroma thylakoids.

The FAD-Enzyme Monodehydroascorbate Radical Reductase Mediates Photoproduction of Superoxide Radicals in Spinach Thylakoid Membranes

Plant and Cell Physiology, 1998

The photoreduction of dioxygen in spinach thylakoid membranes was enhanced about 10-fold by the FAD-enzyme monodehydroascorbate radical (MDA) reductase at 1 fM. The primary photoreduced product of dioxygen catalyzed by MDA reductase was the superoxide radical, as evidenced by the inhibition of photoreduction of Cytc by superoxide dismutase. The apparent K m for dioxygen of the MDA reductase-dependent photoreduction of dioxygen was 100 /JM, higher by one order of magnitude than that observed with thylakoid membranes only. Glutathione reductase, ferredoxin-NADP + reductase, and glycolate oxidase also mediated the photoproduction of superoxide radicals in thylakoid membranes at rates similar to those with MDA reductase. Among these flavoenzymes, MDA reductase is the most likely mediator stimulating the photoreduction of dioxygen in chloroplasts; its function in the protection from photoinhibition under excess light is discussed.

Production of superoxide in chloroplast thylakoid membranes

FEBS Letters, 2011

Accumulation of nitroxide radicals, DCP Å or TMT Å , under illumination of a thylakoid suspension containing either hydrophilic, DCP-H, or lipophilic, TMT-H, cyclic hydroxylamines that have high rate constants of the reaction with superoxide radicals, was measured using ESR. A slower accumulation of TMT Å in contrast with DCP Å accumulation was explained by re-reduction of TMT Å by the carriers of the photosynthetic electron transport chain within the membrane. Superoxide dismutase suppressed TMT Å accumulation to a lesser extent than DCP Å accumulation. The data are interpreted as evidencing the production of intramembrane superoxide in thylakoids.

Chapter 3 Ultraviolet-B Induced Changes in Gene Expression and Antioxidants in Plants

Advances in Botanical Research, 2009

The depletion of the stratospheric ozone layer leads to an increase in the level of ultraviolet-B radiations reaching the Earth's surface. UV-B radiations are known to have damaging effects on all forms of life. In plants, the UV-B exposure leads to the generation of reactive oxygen species (ROS), eventually resulting in oxidative stress. ROS induce lipid peroxidation of biological membranes, destroy the natural lipid-soluble antioxidants, and alter the expression of several genes through nonspecific signaling pathways. The integration of the thylakoid membrane appears to be much more sensitive than the activities of the photosynthetic components bound within. However, the decrease of mRNA transcripts in the photosynthetic complexes and other chloroplast proteins are among the early events of UV-B damage. Other genes, encoding defense-related proteins are rapidly upregulated under UV-B irradiation. UV-B radiation induced production of ROS, increased the antioxidant capacity and thus, minimized the magnitude of negative impact of UV-B on plants. Specific signaling pathway includes the UVR8 component that regulates the expression of a set of genes essential for the protection of plant against UV-B. This chapter comprises information regarding the UV-B perception, signal transduction, regulation of gene expression, ROS formation, and its metabolism from various studies performed under growth chamber, green house, and field conditions.

The first application of terephthalate fluorescence for highly selective detection of hydroxyl radicals in thylakoid membranes

Functional Plant Biology, 2007

Possibilities and limitations of the detection of hydroxyl radicals via the conversion of terephthalate (TPA) into the strongly fluorescent hydroxyterephthalate were investigated in order to adapt this method for chlorophyll-containing samples. Using model chemical sources of various reactive oxygen species, we confirmed that TPA detects hydroxyl radicals very sensitively, but is not reactive to either hydrogen peroxide or superoxide radicals. As a new result, we showed that the conversion of TPA to hydroxyterephthalate cannot be induced by singlet oxygen, which may be produced in photosynthetic systems under stress. Until now, the TPA method has not been used in photosynthesis research, so necessary adaptations to minimise the effects of chlorophyll and buffering sugars on hydroxyl radical detection were also explored and optimal conditions for using the method in thylakoid preparations are suggested. Anticipating further plant physiology applications, usefulness of the TPA method was tested in a wider range of pH than reported earlier. To demonstrate that this simple and highly specific method can be used as an alternative approach for the detection of hydroxyl radicals in plant samples, we measured these radicals in isolated thylakoid membranes exposed to 312 nm ultraviolet radiation.

Impact of High Light on Reactive Oxygen Species Production within Photosynthetic Biological Membranes

Journal of Biology and Life Science, 2015

In this study we describe the mechanisms of reactive oxygen species (ROS) production in the photosynthetic electron transport chain of higher plants chloroplasts under illumination. We implement an improved method for the measurement of hydrogen peroxide (H2O2) production in lipid phase of photosynthetic membranes of chloroplasts. Total rate of H2O2 production and the production within the thylakoid membrane under operation of photosynthetic electron transport chain is evaluated. Obtained data show that even in the presence of an efficient electron acceptor, methyl viologen, an increase in light intensity leads to an increase in H2O2 production mainly within the thylakoid membranes. The role of H2O2 produced within the photosynthetic biological membrane is discussed.