Peroxidation Of Thylakoid Lipids Research Articles

Close Relationships Between the PSII Repair Cycle and Thylakoid Membrane Dynamics.

In chloroplasts, a three-dimensional network of thylakoid membranes is formed by stacked grana and interconnecting stroma thylakoids. The grana are crowded with photosynthetic proteins, where PSII-light harvesting complex II (LHCII) supercomplexes often show semi-crystalline arrays for efficient energy trapping, transfer and use. Although light is essential for photosynthesis, PSII is damaged by reactive oxygen species that are generated from primary photochemical reactions when plants are exposed to excess light. Because PSII complexes are embedded in the lipid bilayers of thylakoid membranes, their functions are affected by the conditions of the lipids. Electron paramagnetic resonance (EPR) spin trapping measurements showed that singlet oxygen was formed through peroxidation of thylakoid lipids, suggesting that lipid peroxidation can damage proteins, including the D1 protein. After photodamage, PSII is restored by a specific repair system in thylakoid membranes. In the PSII repair cycle, phosphorylation and dephosphorylation of the PSII proteins control the timing of PSII disassembly and subsequent degradation of the D1 protein. Under light stress, stacked grana turn into unstacked thylakoids with bent grana margins. These structural changes may be closely linked to the mechanisms of the PSII repair cycle because PSII can move more easily from the grana core to the stroma thylakoids through an expanded stromal gap between each thylakoid. Thus, plants modulate the structure of thylakoid membranes under high light to carry out efficient PSII repair. This review focuses on the behavior of the PSII complex and the active role of structural changes to thylakoid membranes under light stress.

Differential Action of Toxic Metal Ions on Thylakoid Membrane Lipid Peroxidation

The peroxidation of thylakoid membrane lipids is one of the major degradative processes causing drastic modification of structural and functional characteristics of the photosynthetic organell. The peroxidation process is modulated by a number of exogenous factors like light, pH, toxic metal ions etc. Three toxic metal ions namely mercury, lead and cadmium are able to modify the process of thylakoid peroxidation and lower photochemical potential. Different mechanisms have been proposed to explain differential action of these metal ions on peroxidation process. The cation induced modulation has been explained in terms of binding of the cation to thylakoid surface, generation and entry of reactive oxygen species and stacking ability of the cations

Water stress-sensitized photoinhibition in senescing cotyledons of clusterbean: Changes in thylakoid structures and inactivation of photosystem 2

Seedlings of Cyamopsis tetragonoloba were grown on Petri dishes either in water or water plus 3 % PEG-6000 to induce water stress. The senescing cotyledons experiencing the stress exhibited loss in contents of leaf proteins and chlorophyll (Chl) and a decline in oxygen evolution. The effect of PEG treatment was more pronounced at moderate (MI) than low (LI) irradiance. The stress-induced loss in the activity of superoxide dismutase and increase in the thylakoid lipid peroxidation accompanied a change in the physical status of the bilayer membrane as demonstrated by an enhancement of room temperature Chl a fluorescence polarization and decrease in energy transfer efficiency in pigment assembly. This resulted in a sustained decrease in photosystem 2 activity blocking channels of energy utilization. The absorbed quanta, thus unutilized, were excess even at MI, leading to photoinhibitory response.

Response of senescing cotyledons of clusterbean to water stress in moderate and low light: Possible photoprotective role of beta-carotene.

Senescence of clusterbean (Cyamopsis tetragonoloba L.) cotyledons in moderate light (12 W m-2) brings about a loss in the pigments, enhanced lipid peroxidation and a decline in PS II photochemical activity without any loss either in Dl protein or in the level of beta-carotene. The senescence syndrome is aggravated in the cotyledons of water-stressed seedlings with an increase in thylakoid lipid peroxidation, a decline in the level of beta-carotene and a quantitative loss in the Dl protein. Loss of the protein, however, is arrested in the seedlings experiencing water stress at low light (3 W m-2) intensity that correlates with the stability in the level of beta-carotene and a slow rate of lipid peroxidation. Loss of the protein in moderate light is attributed to water-stress sensitized photoinhibitory damage. The data on changes in the components of xanthophyll cycle suggest the low activity of the cycle both during senescence and water stress. It is, therefore, concluded that beta-carotene may contribute to the assembly and stability of the Dl protein during senescence and water stress in clusterbean cotyledons.

Involvement of CDSP 32, a drought-induced thioredoxin, in the response to oxidative stress in potato plants

In animal cells, yeast and bacteria, thioredoxins are known to participate in the response to oxidative stress. We recently identified a novel type of plant thioredoxin named CDSP 32 for chloroplastic drought-induced stress protein of 32 kDa. In the present work, we measured comparable increases in the glutathione oxidation ratio and in the level of chlorophyll thermoluminescence, a specific marker for thylakoid lipid peroxidation in Solanum tuberosum plants subjected to drought or oxidative treatments (photooxidative stress, gamma irradiation and methyl viologen spraying). Further, substantial accumulations of CDSP 32 mRNA and protein were revealed upon oxidative treatments. These data show for the first time in plants the induction of a thioredoxin by oxidative stress. We conclude that CDSP 32 may preserve chloroplastic structures against oxidative injury upon drought.

Photoinduced Damage in Leaf Segments of Wheat ( Triticum aestivum L.) and Lettuce ( Lactuca sativa L.) Treated with 5-Aminolevulinic Acid I. Effect on Structural Components of the Photosynthetic Apparatus

Summary Two different plant species, wheat (Triticum aestivum L.) and lettuce (Lactuca sativa L.) were investigated for the sensitivity of thylakoid membrane structures to photoinduced damage caused by treatment with 5 mM 5-aminolevulinic acid (ALA) in the dark. At the end of a 16-h period in darkness lettuce leaves accumulated significantly lower amounts of protochlorophyllide (PChlide) per unit leaf area, however, when calculated on a protein basis, considerably higher amounts of PChlide compared to wheat. Additionally small amounts of Magnesium-protoporphyrin-IX (monomethylester) were found. Lettuce leaf segments were characterized, furtheron, by a higher ALA uptake and a higher endogenous pool of nonmetabolized ALA in comparison to wheat. PChlide and non-metabolized ALA that accumulated in darkness were strongly reduced after 1 h of illumination and disappeared nearly completely after a 5-h period of illumination with 120Wm-2. Light exposure to ALA-pretreated leaves revealed typical symptoms for the involvement of activated oxygen species in photodynamic action, to a greater extent in lettuce than in wheat. Photobleaching of pigments was accompanied by degradation of proteins and peroxidation of thylakoid lipids detected by the increase in the formation of thiobarbituric acid-reactive substances. The fluidity of the thylakoid membranes isolated from treated leaves decreased (as measured with 5-doxylstearic acid as spin label).

Chilling-induced Oxidative Stress in Cucumber ( Cucumis sativus L. cv. Calypso) Seedlings

One-week old cucumber (Cucumis sativus L. cv. Calypso) seedlings were chilled at 4 °C in the dark for up to 6 days, after which they were rewarmed at 13 °C in the light (16-h photoperiod) for 2 d to allow for recovery. Responses of these seedlings were compared to unchilled controls (13 °C) held in the dark or in the light with a 16-h photoperiod. Loss of viability in dark-chilled seedlings required more than 1 d of chilling and progressed to the point where it was complete after 4 d of chilling. Irreversible increases in cotyledon tissue electrolyte leakage of dark-chilled seedlings did not occur until after seedling collapse, indicating that increases in passive permeability are secondary responses to chilling injury. There were only minor differences in the temporal changes in the tissue antioxidants reduced glutathione, ascorbic acid, atocopherol, and β-carotene between chilled, unchilled, and chilled/rewarmed seedlings, with the exception that slightly lower levels of β-carotene and α-tocopherol may have been induced by dark-chilling. Peroxidation of thylakoid lipids was induced during the rewarming period, after only 1 to 2 d of chilling, as indicated by the accumulation of lipid fluorescent pigments (LFPs). LFPs accumulated in both the phospholipid and glycolipid fractions of thylakoid lipids extracted from rewarmed seedlings, whereas little evidence for lipid peroxidation was obtained for the unchilled controls. Our results indicate that chilling-induced oxidative stress may have a role in transducing chilling injury in cucumber seedlings.

Photosynthetic Activity and Peroxidation of Thylakoid Lipids during Photoinhibition and High Temperature Treatment of Isolated Wheat Chloroplasts

Summary Interactive effects of strong visible light and high temperature on isolated wheat ( Triticum aestivum ) chloroplasts were investigated by imposing them one after another and simultaneously. Both of the stresses were observed to impair photosystem II mediated electron transport activity. A concomitant reduction in chlorophyll fluorescence parameters and increase in thylakoid lipid peroxidation were also observed. Peroxidation of thylakoid lipids suggests the involvement of active oxygen species, which could be generated during photoinhibition. Our results demonstrate that the extent of damage to chloroplasts varied quantitatively upon reversing the order of imposition of strong light and high temperature stresses. Loss of electron transport activity, variable chlorophyll fluorescence (F v ) and increase in thylakoid lipid peroxidation were greater when photoinhibition treatment was given before heat stress. The reason for this differential damage upon changing the order of the two stresses is discussed on the basis of the, primary target site and the amount of potentially damaging active oxygen species generated under stress conditions.

The role of thylakoid lipids in the photodamage of photosynthetic activity

The effect of excess light at 10 or 30°C under aerobic or low O2 condition on peroxidation of thylakoid lipids and primary photochemistry of photoinsynthesis was studied in wheat (Triticum aestivum L. cv. HD 2329). Photoinhibitory damage to photosythesis was directly proportional to the peroxidation of thylakoid lipids. Photoinhibitory treatment given under low O2 conditions resulted in significantly less peroxidation of the primary photochemistry of photosythesis measured using chlorophyll fluorescence and photosythetic electron trasport. Short term recovery of Fv/Fm ratio was fast while thylakoid lipids did not show much recovry. However, recovery (of Fv/Fm ratio and thylakoid lipids) was almost complete within 12 h after photoinhibition treatment. A possible relationship between peroxidation of thylakoid lipids and photodamage to photosynthesis is discussed.

Protection of Wheat Chloroplasts from Lipid Peroxidation and Loss of Photosynthetic Pigments by Quercetin under strong Illumination

Summary Exposure of chloroplasts to strong visible light in the presence of DCMU and paraquat resulted in lipid peroxidation and pigment photobleaching, which could be because of increased rates of production of active oxygen species. Quercetin and its glycoside, rutin, protected the chloroplasts from thylakoid lipid peroxidation and pigment photo-oxidation. These flavonoids more effectively protected the chloroplasts when the light treatment was given in the presence of DCMU as compared with that in the presence of paraquat. This differential protection by the flavonoids was investigated by inhibition of crocin photobleaching by quercetin and rutin, which showed that both of the flavonoids effectively quenched singlet oxygen (1O2 On the basis of our results, we suggest that singlet oxygen may be one of the predominant active species produced during strong illumination of chloroplasts, which may further be accelerated in the presence of DCMU. However, strong illumination in the presence of paraquat may lead to production of species such as superoxide and hydroxyl free radicals, which may damage the thylakoid membrane but may not be efficiently quenched by quercetin and rutin.

Influence of photoinhibition on photosynthesis and lipid peroxidation

The effect of photoinhibition at 10 and 30 °C on photosynthetic electron transport, chlorophyll fluorescence and peroxidation of thylakoid lipids was studied in intact leaves, isolated chloroplasts and photosystem (PS) II and I particles. Photoinhibition impaired the photochemistry of PS II, whose activity was more significantly affected than that of PS I. The extent of the damage was greater at 30 °C than at 10 °C. Peroxidation of thylakoid lipids, measured in isolated chloroplasts and PS II particles, was also greater at 30 °C, but peroxidation of PS I particles was almost the same at the two temperatures. The recovery of thylakoid lipids and the F v/ F m ratio after 6 h of photoinhibition was complete within 12 h in intact leaves under the growth conditions.

Function of Photosynthetic Apparatus of Intact Wheat Leaves under High Light and Heat Stress and Its Relationship with Peroxidation of Thylakoid Lipids

Effects of high light and temperature stress on the structure and function of the photosynthetic apparatus of wheat (Triticum aestivum) were studied. There was a decrease in the electron transport activity of chloroplasts isolated from photoinhibited and heat-stressed leaves. Chlorophyll fluorescence was measured in photoinhibited and heat-stressed leaves and the decrease in variable fluorescence and variable to maximum fluorescence ratio of the stressed leaves indicated a loss in the quantum yield of photosynthesis. The decrease in electron transport activity was accompanied by an increase in peroxidation of thylakoid lipids. Lipid peroxidation indicated the oxidative degradation of polyunsaturated fatty acyl residues of the thylakoid lipids. A negative correlation was observed between electron transport activity and lipid peroxidation. The electron transport activity was completely lost as the peroxidation level reached a threshold equivalent to 0.6 micromoles malondialdehyde. The threshold of lipid peroxidation for complete loss of activity was the same for both photoinhibition and heat treatment, suggesting that the nature of the environmental stress may be less important with respect to the relationship between electron transport and lipid peroxidation. Thus, it seems likely that lipids are required for sustaining the photosynthetic activity under environmental stress, and a loss in activity is observed as the lipids are degraded either by high light or high temperature stress.

Proline enhances primary photochemical activities in isolated thylakoid membranes of Brassica juncea by arresting photoinhibitory damage

The presence of L-proline in the reaction mixture enhances the photosystem II (H 2O→DCPIP) and whole chain (H 2O→MV) catalysed electron transport activities of thylakoids isolated from the cotyledonary leaves of Brassica juncea seedlings raised in the absence and the presence of NaCl. The extent of stimulation in activities was higher in the thylakoids of NaCl raised plants than the controls. The extent of proline mediated stimulation was seen even in the presence of uncoupler NH 4Cl suggesting that this stimulation is not due to uncoupling. However, photosystem I (DCPIPH 2→MV) catalysed photoreaction remained almost insensitive to proline. The presence of proline in the incubation medium brought about a significant reduction in the time dependent loss in photochemical activity of thylakoids exposed to strong light suggesting that proline prevents photoinhibitory loss in chloroplast activity. Also, proline brought about a considerable reduction in the production of lipid peroxidation linked malodialdehyde during strong illumination. We suggest that proline protects the components involved in water oxidation capacity by reducing the production of free radicals and/or scavenging the free radicals and thereby reducing thylakoid lipid peroxidation.

Leaf senescence in fern: effect of duration, intensity and quality of light

Continuous white light at an intensity of 12 W/m 2 causes a mild retarding effect on chlorophyll loss during fern leaf senescence. Pigment loss is robustly retarded by continuous light of 6 W/m 2 and daily 1 or 4 hr pulses of light of 12 W/m 2. A 5-min red light pulse at 24 hr intervals retarded chlorophyll loss; this red light response was nullified with far-red pulses, suggesting the participation of phytochrome. Blue light pulses were similarly effective; the response was partially reversed by far-red pulses. This suggests that the blue light photoreceptor might be partially acting through phytochrome. Addition of sucrose during pulses of red or blue light did not result in any additional effect over the light pulses alone, suggesting non-involvement of photosynthesis in regulating chloroplast degradation. Since fern is a shade plant, its response to different light intensities is rather complex. The data suggest that moderate intensity light (12W/m 2) protects chloroplast degradation through phytochrome and blue light photoreceptors. In addition, light at this intensity may also photo-oxidize some pigments. This postulate appears to be supported by the relatively high level of thylakoid lipid peroxidation as indicated by the accumulation of MDA (malondialdehyde) during senescence of leaves exposed to 12W/m 2 light intensity. The apparent mild effect of continuous white light of 12W/m 2 to retard pigment loss, therefore, is due to a balance between photoprotection and light-induced oxidative processes.

Inhibition of Photosystem II Precedes Thylakoid Membrane Lipid Peroxidation in Bisulfite-Treated Leaves of Phaseolus vulgaris

Exposure of leaves to SO(2) or bisulfite is known to induce peroxidation of thylakoid lipids and to inhibit photosynthetic electron transport. In the present study, we have examined the temporal relationship between bisulfite-induced thylakoid lipid peroxidation and inhibition of electron transport in an attempt to clarify the primary mechanism of SO(2) phytotoxicity. Primary leaves of bean (Phaseolus vulgaris L. cv Kinghorn) were floated on a solution of NaHSO(3), and the effects of this treatment on photosynthetic electron transport were determined in vivo by measurements of chlorophyll a fluorescence induction and in vitro by biochemical measurements of the light reactions using isolated thylakoids. Lipid peroxidation in treated leaves was followed by monitoring ethane emission from leaf segments and by measuring changes in fatty acid composition and lipid fluidity in isolated thylakoids. A 1 hour treatment with bisulfite inhibited photosystem II (PSII) activity by 70% without modifying Photosystem I, and this inhibitory effect was not light-dependent. By contrast, lipid peroxidation was not detectable until after the inhibition of PSII and was strongly light dependent. This temporal separation of events together with the differential effect of light suggests that bisulfite-induced inhibition of PSII is not a secondary effect of lipid peroxidation and that bisulfite acts directly on one or more components of PSII.

Manganese induced peroxidation of thylakoid lipids and changes in chlorophyll-α fluorescence during aging of cell free chloroplasts in light

Photoinduced peroxidation of thylakoid lipids in wheat chloroplasts is correlated with thylakoid membrane disorganisation as probed by Chl. α fluorescence during aging of cell free organelles. Manganese, at its different redox states, modulates lipid peroxidation differently with its consequent effect on Chl. α fluorescence.