Antioxidants and stress reduction -
Interactions between ascorbic acid and glutathione, and ascorbic acid and phenolic compounds are well known. Under oxygen deprivation stress some contradictory results on the antioxidant status have been obtained. Experiments on overexpression of antioxidant production do not always result in the enhancement of the antioxidative defence, and hence increased antioxidative capacity does not always correlate positively with the degree of protection.
Here we present a consideration of factors which possibly affect the effectiveness of antioxidant protection under oxygen deprivation as well as under other environmental stresses.
Received: 6 August ; Returned for revision: 20 November ; Accepted: 16 January Lack of oxygen or anoxia is a common environmental challenge which plants have to face throughout their life.
Winter ice encasement, seed imbibition, spring floods and excess of rainfall are examples of natural conditions leading to root hypoxia or anoxia. Wetland species and aquatic plants have developed adaptative structural and metabolic features to combat oxygen deficiency.
Regulation of anoxic metabolism is complex and not all the features are well established. In the recent paper by Gout et al. Under natural conditions anoxic stress includes several transition states hypoxia, anoxia and reoxygenation characterized by different O 2 concentrations. Excessive generation of reactive oxygen species ROS , i.
under oxidative stress, is an integral part of many stress situations, including hypoxia. Hydrogen peroxide accumulation under hypoxic conditions has been shown in the roots and leaves of Hordeum vulgare Kalashnikov et al.
The presence of H 2 O 2 in the apoplast and in association with the plasma membrane has been visualized by transmission electron microscopy under hypoxic conditions in four plant species Blokhina et al.
Indirect evidence of ROS formation i. lipid peroxidation products under low oxygen has been detected Hunter et al. ROS have recently been considered as possible signalling molecules in the detection of the surrounding oxygen concentration Semenza, It has been suggested also that ROS and oxygen concentration including hypoxia can be sensed via the same mechanism.
Several models employ direct sensing of oxygen via haemoglobin or protein SH oxidation or ROS sensing. There are two models which suggest either a decrease in ROS under oxygen deprivation low NADPH oxidase activity or an increase in ROS due to the inhibition of the mitochondrial electron transport chain.
Molecular oxygen is relatively unreactive Elstner, due to its electron configuration. Activation of oxygen i. the first univalent reduction step is energy dependent and requires an electron donation.
This term includes not only free radicals superoxide radical, O 2 ·— , and hydroxyl radical, OH · , but also molecules such as hydrogen peroxide H 2 O 2 , singlet oxygen 1 O 2 and ozone O 3. Both O 2 ·— and the hydroperoxyl radical HO 2 · undergo spontaneous dismutation to produce H 2 O 2.
The partition between these two pathways under oxygen deprivation stress can be regulated by the oxygen concentration in the system. Among enzymatic sources of ROS, xanthine oxidase XO , an enzyme responsible for the initial activation of dioxygen should be mentioned.
As electron donors XO can use xanthine, hypoxanthine or acetaldehyde Bolwell and Wojtaszek, The next enzymatic step is the dismutation of the superoxide anion by superoxide dismutase SOD, EC.
Due to its relative stability the level of H 2 O 2 is regulated enzymatically by an array of catalases CAT and peroxidases localized in almost all compartments of the plant cell.
Next, the NAD · radical formed reduces O 2 to O 2 ·— , some of which dismutates to H 2 O 2 and O 2 Lamb and Dixon, Thus, peroxidases and catalases play an important role in the fine regulation of ROS concentration in the cell through activation and deactivation of H 2 O 2 Elstner, Lipoxygenase LOX, linoleate:oxygen oxidoreductase, EC.
It catalyses the hydroperoxidation of polyunsaturated fatty acids PUFA Rosahl, The hydroperoxyderivatives of PUFA can undergo autocatalytic degradation, producing radicals and thus initiating the chain reaction of lipid peroxidation LP.
A specific LOX activity increase and its positive correlation with the duration of anoxia have been detected in potato cells Pavelic et al. Several apoplastic enzymes may also lead to ROS production under normal and stress conditions.
Amine oxidases catalyse the oxidation of biogenic amines to the corresponding aldehyde with a release of NH 3 and H 2 O 2.
Data on polyamine putrescine accumulation under anoxia in rice and wheat shoots Reggiani and Bertani, and predominant localization of amine oxidase in the apoplast, suggest amine oxidase participation in H 2 O 2 production under oxygen deprivation. Mitochondria have been shown to produce ROS superoxide anion O 2 ·— and the succeeding H 2 O 2 due to the electron leakage at the ubiquinone site—the ubiquinone:cytochrome b region Gille and Nohl, —and at the matrix side of complex I NADH dehydrogenase Chakraborti et al.
Hydrogen peroxide generation by higher plant mitochondria and its regulation by uncoupling of ETC and oxidative phosphorylation have been demonstrated by Braidot et al. Lipid peroxidation is a natural metabolic process under normal aerobic conditions and it is one of the most investigated consequences of ROS action on membrane structure and function.
PUFA, the main components of membrane lipids, are susceptible to peroxidation. The initiation phase of LP includes activation of O 2 see above which is rate limiting.
Hydroxyl radicals and singlet oxygen can react with the methylene groups of PUFA forming conjugated dienes, lipid peroxy radicals and hydroperoxides Smirnoff, :. The peroxyl radical formed is highly reactive and is able to propagate the chain reaction:.
The formation of conjugated dienes occurs when free radicals attack the hydrogens of methylene groups separating double bonds and leading to a rearrangement of the bonds Recknagel and Glende, The lipid alkoxyl radical produced, PUFA—O.
branching of chain reactions, allows several ways of regulation Shewfelt and Purvis, Among the regulated properties are the structure of the membranes: composition and organization of lipids inside the bilayer in a way which prevents LP Merzlyak, , the degree of PUFA unsaturation, mobility of lipids within the bilayer, localization of the peroxidative process in a particular membrane and the preventive antioxidant system ROS scavenging and LP product detoxification.
The idea of LP as a solely destructive process has changed during the last decade. It has been shown that lipid hydroperoxides and oxygenated products of lipid degradation as well as LP initiators i. ROS can participate in the signal transduction cascade Tarchevskii, Lipid and membrane integrity during oxygen deprivation are among the key factors in the survival of plants.
Under anoxia a decrease in membrane integrity is a symptom of injury, and it can be measured as changes in the lipid content and composition Hetherington et al. Since de novo lipid synthesis is energy dependent, and could hardly occur under anoxia, the preservation of membrane lipids is the most efficient way to maintain functional membranes.
Iris germanica a significant decrease in polar lipids and a simultaneous increase in free fatty acids FFA occur during anoxic stress with markedly enhanced lipid peroxidation during reoxygenation Henzi and Braendle, A decrease in unsaturated to saturated fatty acid ratio under anoxia may represent a result of LP and, at the same time sets limits for substrates of LP, the PUFA.
On the other hand, no significant qualitative and quantitative changes have been detected in the composition of fatty acids in anaerobically treated rice seedlings Generosova et al. In that study it was postulated that the reduction of unsaturated fatty acids esterified in lipids was of no significance as a mechanism of plant adaptation to anaerobic conditions.
The key role in survival was assigned to energy metabolism Generosova et al. Indeed, a correlation exists between the leakage of electrolytes i.
membrane damage under low ATP and a release of FFA from anoxic tissue Crawford and Braendle, The role of ATP in the maintenance of membrane lipid integrity under anoxia has been confirmed by Rawyler et al. It has been shown that, when the rate of ATP synthesis falls below 10 µmol g —1 fresh weight h —1 , the integrity of membranes cannot be preserved and FFA are liberated via lipolytic acyl hydrolase Rawyler et al.
During recent years evidence has accumulated on the importance of lipid metabolism, and especially on unsaturated fatty acids, in the induction of defence reactions under biotic and abiotic stresses. Linolenic acid has been shown to be a precursor of jasmonic acid, a signal transducer in defence reactions in plant—pathogen interactions Rickauer et al.
FFA, liberated during membrane breakdown under stress conditions, are not only the substrates for LP, but can act also as uncouplers in mitochondrial ETC Skulachev, Lipid hydroperoxides, formed as a result of LP, can affect membrane properties, i. increase hydrophilicity of the internal side of the bilayer Frenkel, This phenomenon is very important for the termination of LP, since increased hydrophilicity of the membrane favours the regeneration of tocopherol by ascorbate.
germanica , while in the tolerant I. pseudacorus no signal was detected Crawford et al. Hypoxic pretreatment of plants prior to anoxia leads to increased survival Waters et al. The minimal duration of hypoxia required for the acclimation has been estimated at 2—4 h for the root tips of maize seedlings Chang et al.
The biochemical and physiological features induced by this pretreatment suggest the involvement of several systems for increased stress tolerance. Of these, one is aimed at the maintenance of energy resources through the support of sugar utilization and ATP formation via the glycolytic pathway, while avoiding lactate accumulation and cytoplasmic acidosis.
The majority of the genes induced codes for enzymes involved in starch and glucose mobilization, glycolysis and ethanol fermentation Russel and Sachs, ; Chirkova and Voitzekovskaya, Some other glycolytic and fermentation pathway enzymes, such as alcohol dehydrogenase ADH, EC 1.
ADH and PDC, enzymes of ethanolic fermentation, were induced by hypoxic pretreatment in rice cultivars with different tolerance to anoxia Ellis and Setter, Interestingly, both abscisic acid ABA and hypoxic pretreatment of Lactuca sativa L.
The crucial role of protein synthesis under hypoxic conditions, but not under anoxia, has been shown in root tips of maize seedlings Chang et al.
The rate of their synthesis under hypoxia was enhanced or comparable under normoxic conditions. As expected, cycloheximide treatment during hypoxic acclimation but not under anoxia resulted in decreased anoxia tolerance Chang et al.
In these experiments differential response of shoots and roots was observed. In conclusion, early hypoxic induction of the ethanolic fermentation pathway and sugar utilization allows the maintenance of the energy status through regeneration of NADH and, hence, improves anoxia tolerance.
Under natural conditions oxygen concentration would decrease gradually, and hence anoxia is always preceeded by hypoxia.
Judged by a cycloheximide treatment, this activity could not be attributed to de novo synthesis Biemelt et al. The beneficial effect of alternative oxidase protein accumulation under anoxia is due to electron flow bifurcation and reduced probability of ROS formation under subsequent reoxygenation.
Some ROS formation can take place in hypoxic tissues as a result of over reduction of redox chains. Hence, anoxic stress is always accompanied to some extent by oxidative stress generation of ROS and its consequences.
Induction of some components of the antioxidant system by hypoxic pretreatment can be due to such ROS accumulation and signalling Lander, ; Semenza, In addition, a whole array of enzymes is needed for the regeneration of the active forms of the antioxidants monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase.
Enhanced formation of ROS under stress conditions induces both protective responses and cellular damage. The scavenging of O 2 ·— is achieved through an upstream enzyme, SOD, which catalyses the dismutation of superoxide to H 2 O 2.
The enzyme is present in all aerobic organisms and in all subcellular compartments susceptible of oxidative stress Bowler et al. Recently, a new type of SOD with Ni in the active centre has been described in Streptomyces Kim et al. These isoenzymes differ in their sensitivity to H 2 O 2 and KCN Bannister et al.
All three enzymes are nuclear encoded, and SOD genes have been shown to be sensitive to environmental stresses, presumably as a consequence of increased ROS formation. An excessive accumulation of superoxide due to the reduced activity of SOD under flooding stress was shown also Yan et al.
In the course of this experiment the activity decreased in wheat under both aeration and anoxia, but in the anoxic samples this decline was slower. Similar results have been reported by Pavelic et al. An increase in total SOD activity has been also detected in wheat roots under anoxia but not under hypoxia.
The degree of increase positively correlated with duration of anoxia Biemelt et al. a prolonged reoxygenation period in the case of Iris spp. Activation of oxygen may proceed through different mechanisms, not necessarily producing a substrate for SOD. Changes in O 2 electronic configuration can lead to the formation of highly reactive singlet oxygen 1 O 2.
Comparison of drought and water stress effects on tolerant and intolerant wheat genotypes suggests that different mechanisms can participate in ROS detoxification.
For example, water stress did not affect SOD activity, while under drought conditions a significant increase was detected Sairam et al. The ability of plants to overcome oxidative stress only partly relies on the induction of SOD activity and other factors can regulate the availability of the substrate for SOD.
Diversification of the pathways of ROS formation, compartmentalization of oxidative processes charged ROS cannot penetrate the membrane and compartmentalization of SOD isozymes.
It is also possible that in different plant species and tissues different mechanisms are involved in the protection against oxidative stress. The intracellular level of H 2 O 2 is regulated by a wide range of enzymes, the most important being catalase reviewed by Willekens et al.
Catalase functions through an intermediate catalase—H 2 O 2 complex Compound I and produces water and dioxygen catalase action or can decay to the inactive Compound II. In the presence of an appropriate substrate Compound I drives the peroxidatic reaction. OH · is a very strong oxidant and can initiate radical chain reactions with organic molecules, particularly with PUFA in membrane lipids.
Under anoxia a differential response of the peroxidase system has been observed in coleoptiles and roots of rice seedlings. Phospholipid hydroperoxide glutathione peroxidase PHGPX is a key enzyme in the protection of the membranes exposed to oxidative stress and it is inducible under various stress conditions.
The enzyme catalyses the regeneration of phospholipid hydroperoxides at the expense of GSH and is localized in the cytosol and the inner membrane of mitochondria of animal cells. PHGPX can also react with H 2 O 2 but this is a very slow process. Until now, most of the investigations have been performed on animal tissues.
Recently, a cDNA clone homologous to PHGPX has been isolated from tobacco, maize, soybean and arabidopsis Sugimoto et al. The PHGPX protein and its encoding gene csa have been isolated and characterized in citrus.
It has been found virtually in all cell compartments: cytosol, endoplasmic reticulum, vacuole and mitochondria Jimenez et al. Together with its oxidized form GSSG glutathione maintains a redox balance in the cellular compartments.
Indeed, the role for GSH in redox regulation of gene expression has been described in many papers e. Wingate et al. Functioning of GSH as antioxidant under oxidative stress has received much attention during the last decade.
A central nucleophilic cysteine residue is responsible for high reductive potential of GSH. AA is one of the most studied and powerful antioxidants reviewed by Smirnoff, ; Noctor and Foyer, ; Arrigoni and de Tullio, ; Horemans et al.
It has been detected in the majority of plant cell types, organelles and in the apoplast. AA can directly scavenge superoxide, hydroxyl radicals and singlet oxygen and reduce H 2 O 2 to water via ascorbate peroxidase reaction Noctor and Foyer, AA regenerates tocopherol from tocopheroxyl radical providing membrane protection Thomas et al.
It has been implicated in the regulation of the cell division, cell cycle progression from G 1 to S phase Liso et al. Though antioxidant activity of tocotrienols vs. Tocopherols, synthesized only by plants and algae, are found in all parts of plants Janiszowska and Pennock, it is able to repair oxidizing radicals directly, preventing the chain propagation step during lipid autoxidation Serbinova and Packer, Regeneration of the TOH · back to its reduced form can be achieved by vitamin C ascorbate , reduced glutathione Fryer, or coenzyme Q Kagan et al.
In addition, tocopherols act as chemical scavengers of oxygen radicals, especially singlet oxygen via irreversible oxidation of tocopherol , and as physical deactivators of singlet oxygen by charge transfer mechanism Fryer, TOH · formation sustains prooxidant action of tocopherol.
It has been clearly shown, that prooxidant function of tocopherol on low density lipoprotein was clearly inhibited in vitro by antioxidants ascorbate or ubiquinol Upston et al.
Tocopherols have been suggested to stabilize membrane structures. Complexation of tocopherol with free fatty acids and lysophospholipids protects membrane structures against their deleterious effects. The process is of great physiological relevance, since phospholipid hydrolysis products are characteristics of pathological events such as hypoxia, ischaemia or stress damage Kagan, as reviewed by Azzi and Stocker Phenolics are diverse secondary metabolites flavonoids, tannins, hydroxycinnamate esters and lignin abundant in plant tissues reviewed by Grace and Logan, Polyphenols possess ideal structural chemistry for free radical scavenging activity, and they have been shown to be more effective antioxidants in vitro than tocopherols and ascorbate.
Another mechanism underlying the antioxidative properties of phenolics is the ability of flavonoids to alter peroxidation kinetics by modification of the lipid packing order and to decrease fluidity of the membranes Arora et al. These changes could sterically hinder diffusion of free radicals and restrict peroxidative reactions.
Moreover, it has been shown recently that phenolic compounds can be involved in the hydrogen peroxide scavenging cascade in plant cells Takahama and Oniki, According to our unpublished results the content of condensed tannins flavonols , as measured by high performance liquid chromatography, was times higher in I.
pseudacorus rhizomes than in those of I. The effect of anoxia on the flavonol content a decrease after 35 d of treatment suggests their participation in the antioxidative defence in I. pseudacorus rhizomes. Such diversification partly arises from the response specificity of a particular plant species and from different experimental conditions stress treatment, duration of stress, assay procedure and parameters measured.
In the intolerant plants activities were very low or without any changes. An investigation on the antioxidative defence system in the roots of wheat seedlings under root hypoxia or whole plant anoxia Biemelt et al.
Nevertheless, a rapid decrease in the redox state of both antioxidants was observed during reaeration. The activities of MDHAR, DHAR and glutathione reductase GR decreased slightly or remained unaltered under hypoxia, while anoxia caused a significant inhibition of enzyme activities Biemelt et al.
Inhibition of GR, ascorbate peroxidase APX , CAT and SOD activities has been shown also by Yan et al. In submerged seedlings i. The imposition of anoxia and subsequent reoxygenation caused a decrease both in the content of ascorbate and in its reduction state in the roots of cereals and the rhizomes of Iris spp.
Blokhina et al. Prolongation of the anoxic treatment led to a decline in the antioxidant level, both reduced and oxidized forms, in all plants tested.
Less information is available on tocopherol status under oxygen deprivation. It is known that ascorbate regenerates tocopherols from their radical forms Buettner, However, artificially increased ascorbate content in maize leaves did not improve the preservation of endogenous tocopherol during high light and chilling stress, but the high ascorbate content increased the usage of glutathione Leipner et al.
germanica , have been determined. germanica which also possessed markedly higher total tocopherol content than I. Anoxia caused a decrease in tocopherol isomers in both iris species Blokhina et al.
Dehydrotocopherols have been found previously in etiolated shoots of maize and barley Threlfall and Whistance, There is evidence that tocopherol isomers differ from each other in their functional properties. Though the total tocopherol content was higher in I. pseudacorus Blokhina et al.
germanica during anoxia found by Henzi and Braendle There are also earlier reports suggesting that anoxia causes more pronounced lipid peroxidation in the rhizomes of I.
germanica than in I. pseudacorus during reaeration Hunter et al. Considering the experimental data discussed above, it is difficult to delineate a universal mechanism for the whole antioxidant system response to anoxia. It is necessary to discuss other factors involved in the protective machinery of plants under oxygen deprivation with a particular emphasis on the antioxidant system.
Metabolic changes specifically induced by anoxia a drop in cytosolic pH, a decrease in adenylate energy charge, membrane lipid peroxidation, excess of NADH may alter the antioxidant status of the tissue. One of the most important consequences of energy limitation under anoxia is the altered redox state of the cell.
When oxygen—the terminal electron acceptor of ETC—is unavailable, intermediate electron carriers become reduced. Indeed, the ability to maintain redox characteristics of the cell i.
the oxidation state of ferrous ions—the promoters of ROS generation through the Fenton reaction and peroxidation of lipids.
ROS with the exception of H 2 O 2 are charged species and cannot penetrate biological membranes, hence local antioxidant protection is more important than an overall increase in antioxidants.
In a model of lipid peroxidation in tissue disorders, Shewfelt and Purvis emphasize the importance of compartmentalization within the cell. The fate of the tissue may rely on the antioxidant capacity of a specific membrane structure Shewfelt and Purvis, In previous studies on the compartmentalization of tocopherols in photosynthetic tissues tocopherol has been localized in chloroplasts and plastids, while other tocopherol isomers have been found in chloroplasts, mitochondria and microsomes Janiszowska and Korczak, Some evidence exists on the importance of compartmentalization of other lipophilic antioxidants.
Accumulation of antioxidants and ROS in different cell compartments could lead to lowered antioxidant defence, and hence would require fine tuning of cellular metabolism to achieve protection. Under severe stress conditions such a regulatory mechanism can be impaired.
Limitations for GSH biosynthesis under oxygen deprivation mainly arise from the restriction of the energy supply. GSH is synthesized in both the chloroplasts and the cytosol Noctor et al. A decline in ATP content observed under anoxia Chirkova, ; Hanhijärvi and Fagerstedt, ; Rawyler et al.
The AA biosynthetic pathway in plants has been elucidated recently Wheeler et al. Nevertheless, evidence exists on the possibility of AA biosynthesis through other pathways Davey et al.
Association of AA biosynthesis with the functional activity of mitochondrial ETC sets a limit to AA synthesis under lack of oxygen due to saturation of ETC and reduction of cytochrome c. Under physiological pH the reduced form of AA is negatively charged, and therefore cannot freely diffuse through the biological membranes.
In contrast, dehydro ascorbic acid DHA is more likely to penetrate the membrane. In plants, the AA biosynthetic site is localized on the inner mitochondrial membrane Wheeler et al. Until now, a mitochondrial transporter has not been characterized. Evidence has been accumulating on the existence of both AA and DHA specific transporters on the plant plasma membrane.
DHA appears to be the preferred form of transport from the apoplast to the cytosol in Phaseolus vulgaris Horemans et al. In our experiments Blokhina et al. It is not clear whether AA biosynthesis occurs in the plant root mitochondria to the same extent as it does in green tissues, where more precursors are available.
It is also possible that intercellular transport of DHA can act as a signal of redox imbalance under stress, a condition that is known to induce defence responses. Less is known about the glutathione transport mechanism in plant tissues.
The onset of hypoxia and subsequent reoxygenation is manifested by enhanced ROS formation and LP. Peroxidation products such as membrane lipid hydroperoxides e. Conjugation of GSH to LP products can lead to the depletion of the total glutathione pool, since glutathione turnover will be repressed.
Indeed, exhaustion of the glutathione pool under anoxia and reoxygenation was not accompanied with concurrent increase in GSSG Blokhina et al. Other pathways for glutathione transport have been described in animal tissues and yeast. In rabbit kidney mitochondria Cheng et al.
The transporter protein shares homology with S. pombe and with five proteins from Arabidopsis thaliana Bourbouloux et al. The most studied example of the antioxidant network is the ascorbate—glutathione Halliwell—Asada pathway in the chloroplasts, where it provides photoprotection Noctor and Foyer, by removing H 2 O 2.
Recently, components of this cycle have been detected in other cell compartments Jimenez et al. Tocopherol has been reported to be in direct interaction also with reduced glutathione Fryer, and reduced coenzyme Q Buettner, In a recent paper by Kagan et al. Recently, redox coupling of plant phenolics with ascorbate in the H 2 O 2 —peroxidase system has been shown Takahama and Oniki, ; Yamasaki and Grace, It takes place in the vacuole, where H 2 O 2 diffuses and can be reduced by peroxidases using phenolics as primary electron donors.
Both AA and the monodehydroascorbic acid radical can reduce phenoxyl radicals generated by this oxidation.
This mechanism is specific for plant tissues and can improve stress tolerance under oxidative stress. Species and tissue specificity adds to the already complex antioxidant response. It is also important to carry out experiments under strictly controlled conditions with respect to oxygen concentration and to distinguish between hypoxia and anoxia.
Accumulating data suggest that low oxygen concentration plays a crucial role in the induction of anoxic metabolism, i. triggers the expression of genes responsible for anaerobic fermentation, sugar utilization Chang et al. by electron spin resonance spectrometry in similar conditions.
Hypoxic tissues exhibit possibilities for enhanced ROS production, accumulation of LP substrates FFA and LP itself. At this stage the rate of ROS formation and the degree of lipid peroxidation can be regulated by constitutive endogenous antioxidants. This in part can explain the lack of antioxidant system induction under oxygen deprivation in some experiments.
It is noteworthy, that accumulation of ROS and LP products already under hypoxic conditions can bear a signal for low oxygen concentration in the tissue.
On the restoration of normoxia, enzymatic ROS formation and LP will be overwhelmed by chemical oxidations in an uncontrolled manner.
drop in adenylate energy charge, cytoplasmic acidosis, amount of ethanol and acetaldehyde produced and in membrane structures i. This work was funded by the Academy of Finland and the Finnish Ministry of Education as a part of the Center of Excellence on Plant Biology project no.
The Finnish Cultural Foundation provided a grant for E. which is gratefully acknowledged. According to May et al.
Alin P , Jensson H, Guthenberg C, Danielson UH, Tahir MK, Mannervik B. Purification of major basic glutathione transferase isoenzymes from rat liver by use of affinity chromatography and fast protein liquid chromatofocusing. Analytical Biochemistry : — Alscher RG.
Biosynthesis and antioxidant function of glutathione in plants. Physiologia Plantarum 77 : — Amor Y , Chevion M, Levine A. FEBS Letters : — Arora A , Byrem TM, Nair MG, Strasburg GM.
Modulation of liposomal membrane fluidity by flavonoids and isoflavonoids. Archives of Biochemistry and Biophysics : — Arrigoni O , De Tullio MC. Journal of Plant Physiology : — Asada K. The water cycle in chloroplasts: scavenging of active oxygens and dissipation of excess photons.
Annual Review of Plant Physiology and Plant Molecular Biology 50 : — Planta : — Azzi A , Stocker A. Progress in Lipid Research 39 : — Bannister JV , Bannister WH, Rotilio G. Aspects of the structure, function and applications of superoxide dismutase.
Critical Reviews in Biochemistry 22 : — Bartoli CG , Pastori GM, Foyer CH. Ascorbate biosynthesis in mitochondria is linked to the electron transport chain between complexes III and IV. Plant Physiology : — Berglund AH , Nilsson R, Liljenberg C.
Plant Physiology and Biochemistry 37 : — Biemelt S , Keetman U Albrecht G. Expression and activity of isoenzymes of superoxide dismutase in wheat roots in response to hypoxia and anoxia.
Plant Cell and Environment 23 : — Blokhina OB , Fagerstedt KV, Chirkova TV. Physiologia Plantarum : — Blokhina OB , Virolainen E, Fagerstedt KV, Hoikkala A, Wähälä K, Chirkova TV.
Blokhina OB , Chirkova TV, Fagerstedt KV. Anoxic stress leads to hydrogen peroxide formation in plant cells. Journal of Experimental Botany 52 : 1 — Bolwell GP , Wojtaszek P.
Mechanisms for generation of reactive oxygen species in plant defence—a broad perspective. Physiological and Molecular Plant Pathology 51 : — Boo YC , Jung J. Bourbouloux A , Shahi P, Chakladar A, Delrot S, Bachhawat AH.
Hgt1p, a high affinity glutathione transporter from the yeast Saccharomyces cerevisiae. Journal of Biological Chemistry : — Bowler C , Van Montagu M, Inze D. Superoxide dismutase and stress tolerance. Annual Review of Plant Physiology and Plant Molecular Biology 43 : 83 — Braidot E , Petrussa E, Vianello A, Macri F.
Hydrogen peroxide generation by higher plant mitochondria oxidizing complex I of complex II substrates. Buettner GR. Chakraborti T , Das S, Mondal M, Roychoudhury S, Chakraborti S.
Oxidant, mitochondria and calcium: an overview. Cellular Signalling 11 : 77 — Chang WWP , Huang L, Shen M, Webster C, Burlingame AL, Roberts JKM.
Cheng Z , Putt DA, Lash LH. Chirkova TV. Plant adaptation to hypoxia and anoxia. Leningrad: Leningrad State University Press. Chirkova TV , Voitzekovskaya SA.
Plant protein synthesis under hypoxia and anoxia. Uspekhi Sovremennoi. Biologii : — Chirkova TV , Zhukova TM. Tretiakov AL. Adenine nucleotides in wheat and rice seedlings under aeration and anoxia. Vestnik LGU 15 : 74 —81 in Russian.
Chirkova TV , Sinyutina NF, Blyudzin YA, Barsky IE, Smetannikova SV. Phospholipid fatty acids of root mitochondria and microsomes from rice and wheat seedlings exposed to aeration or anaerobiosis. Russian Journal of Plant Physiology 36 : — Chirkova TV , Zhukova TM, Goncharova NN. Method of determination of plant resistance to oxygen shortage.
Russian Journal of Plant Physiology 38 : — Specificity of membrane permeability in wheat and rice seedlings under anoxia. Fiziologia i Biokhimia Kulturnux Rastenii 23 : — in Russian. Chirkova TV , Zhukova TM, Bugrova MP.
Vestnik SPBGU 3 : 82 —86 in Russian. Chirkova TV , Novitskaya LO, Blokhina OB. Lipid peroxidation and antioxidant systems under anoxia in plants differing in their tolerance to oxygen deficiency. Russian Journal of Plant Physiology 45 : 55 — Conklin PL.
Recent advances in the role and biosynthesis of ascorbic acid in plants. Plant Cell and Environment 24 : — Conklin PL , Norris SR, Wheeler GL, Williams EH, Smirnoff N, Last RL. Proceedings of the National Academy of Sciences of the USA 96 : — Crawford RMM , Braendle R. Oxygen deprivation stress in a changing environment.
Journal of Experimental Botany 47 : — Proceedings of the Royal Society of Edinburgh B , — Cummings BS , Angeles R, McCauley RB, Lash LH. Biochemical and Biophysical Research Communications : — Davey MW , Gilot C, Persiau G, Østergaard J, Han Y, Bauw GC, Van Montagu M.
Ascorbate biosynthesis in Arabidopsis cell suspension culture. Dean JV , Devarenne TP. Physiologia Plantarum 99 : — DeLong JM , Steffen KL. Environmental and Experimental Botany 39 : — Dixon DP , Cummins I, Cole DJ, Edwards R. Current Opinion in Plant Biology 1 : — Drew MC.
Oxygen deficiency and root metabolism: injury and acclimation under hypoxia and anoxia. Annual Review of Plant Physiology and Plant Molecular Biology 48 : — Ellis MH , Setter TL. Hypoxia induces anoxia tolerance in completely submerged rice seedlings. Ellis MH , Dennis ES, Peacock WL.
Arabidopsis roots and shoots have different mechanisms for hypoxic stress tolerance. Plant Physiology : 57 — Elstner EF. Metabolism of activated oxygen species.
In: Davies DD, ed. Biochemistry of plants, Vol. London: Academic Press, — Having too many or too few of either may lead to health problems. Maintaining a healthy body weight may help reduce oxidative stress. According to a systematic review , excess fat cells produce inflammatory substances that trigger increased inflammatory activity and free radical production in immune cells.
The body produces free radicals during normal metabolic processes. Oxidative stress can damage cells, proteins, and DNA, which can contribute to aging.
The body naturally produces antioxidants to counteract these free radicals. Making certain lifestyle and dietary changes may help reduce oxidative stress. These may include maintaining a healthy body weight, regularly exercising, and eating a balanced, healthful diet rich in fruits and vegetables.
Free radicals are unstable atoms that can cause damage to cells and lead to illnesses and the aging process. Exactly what impact do they have on the…. A new study reviews the effects of exercising in older life.
Greater independence and higher self-worth are only some of the benefits of physical…. The DNA in our cells holds not only the key to life, but also the reason we age.
With every cell division, chromosomes shorten and cause the cell to…. Exercise is known to stave off the effects of aging, but how it manages this at a cellular level is not understood. A new study focuses on….
Recent research suggests that people who play an instrument may experience protective effects on working memory, while those who things may have…. My podcast changed me Can 'biological race' explain disparities in health?
Why Parkinson's research is zooming in on the gut Tools General Health Drugs A-Z Health Hubs Health Tools Find a Doctor BMI Calculators and Charts Blood Pressure Chart: Ranges and Guide Breast Cancer: Self-Examination Guide Sleep Calculator Quizzes RA Myths vs Facts Type 2 Diabetes: Managing Blood Sugar Ankylosing Spondylitis Pain: Fact or Fiction Connect About Medical News Today Who We Are Our Editorial Process Content Integrity Conscious Language Newsletters Sign Up Follow Us.
Medical News Today. Health Conditions Health Products Discover Tools Connect. How does oxidative stress affect the body? Medically reviewed by Stacy Sampson, D. What is it? Free radicals Antioxidants Effects Conditions Risk factors Prevention Summary Oxidative stress is an imbalance of free radicals and antioxidants in the body, which can lead to cell and tissue damage.
What is oxidative stress? Share on Pinterest Many lifestyle factors can contribute to oxidative stress. Healthy aging resources To discover more evidence-based information and resources for healthy aging, visit our dedicated hub. Was this helpful?
What are free radicals? What are antioxidants? Share on Pinterest Fresh berries and other fruits contain antioxidants. Effects of oxidative stress. Conditions linked to oxidative stress. Risk factors for oxidative stress.
How we reviewed this article: Sources. Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations.
We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles.
You can learn more about how we ensure our content is accurate and current by reading our editorial policy. Share this article. Latest news Ovarian tissue freezing may help delay, and even prevent menopause.
RSV vaccine errors in babies, pregnant people: Should you be worried? Scientists discover biological mechanism of hearing loss caused by loud noise — and find a way to prevent it. How gastric bypass surgery can help with type 2 diabetes remission. Atlantic diet may help prevent metabolic syndrome.
Related Coverage. How do free radicals affect the body? Medically reviewed by Debra Rose Wilson, Ph. How does exercise support health later in life?
Sterss process of oxidation in the Vegan budget-friendly meals body damages cell membranes and Antixoidants Antioxidants and stress reduction, including cellular proteins, Antioxidants and stress reduction and DNA. Reductiin body can cope with Antipxidants free reductkon and Antiioxidants them to function effectively. However, the damage caused by Nutritional supplement for hair health overload of free strrss over time may become irreversible and lead to certain diseases including heart and liver disease and some cancers such as oral, oesophageal, stomach and bowel cancers. Oxidation can be accelerated by stresscigarette smokingalcoholsunlight, pollution and other factors. Antioxidants are found in certain foods and may prevent some of the damage caused by free radicals by neutralising them. These include the nutrient antioxidants, vitamins A, C and E, and the minerals copper, zinc and selenium. Other dietary food compounds, such as the phytochemicals in plants, are believed to have greater antioxidant effects than vitamins or minerals.
die Termingemäße Antwort
ich beglückwünsche, die glänzende Idee und ist termingemäß
ich kann mit Ihnen wird zustimmen.