EnvironSciPollutRes(2015)22:4099–4121 DOI10.1007/s11356-014-3917-1 REVIEWARTICLE — Lipids and proteins major targets of oxidative modifications in abiotic stressed plants NaserA.Anjum&AdrianoSofo&AntonioScopa&AryadeepRoychoudhury& SarvajeetS.Gill&MuhammadIqbal&AlexanderS.Lukatkin&EduardaPereira& ArmandoC.Duarte&IqbalAhmad Received:13September2014/Accepted:24November2014/Publishedonline:5December2014 #Springer-VerlagBerlinHeidelberg2014 Abstract Stress factors provoke enhanced production of among these aspects. Based on recent reports, this article reactive oxygen species (ROS) in plants. ROS that escape (a) introduces ROS and highlights their relationship with antioxidant-mediated scavenging/detoxification react with abiotic stress-caused consequences in crop plants, (b) ex- biomolecules such as cellular lipids and proteins and cause amines critically the various physiological/biochemical as- irreversible damage to the structure of these molecules, pects of oxidative damage to lipids (membrane lipids) and initiate their oxidation, and subsequently inactivate key proteins in stressed crop plants, (c) summarizes the princi- cellular functions. The lipid- and protein-oxidation products ples of current technologies used to evaluate the extent of are considered as the significant oxidative stress biomarkers lipid and protein oxidation, (d) synthesizes major outcomes in stressed plants. Also, there exists an abundance of infor- of studies on lipid and protein oxidation in plants under mation on the abiotic stress-mediated elevations in the abiotic stress, and finally, (e) considers a brief cross-talk on generation of ROS, and the modulation of lipid and protein the ROS-accrued lipid and protein oxidation, pointing to oxidation in abiotic stressed plants. However, the available the aspects unexplored so far. literature reflects a wide information gap on the mecha- nisms underlying lipid- and protein-oxidation processes, major techniques for the determination of lipid- and Keywords Abioticstress .Lipidperoxidation .Oxidative protein-oxidation products, and on critical cross-talks modifications .Proteinoxidation .Reactiveoxygenspecies Responsibleeditor:PhilippeGarrigues : : : N.A.Anjum(*) E.Pereira A.C.Duarte I.Ahmad M.Iqbal(*) CESAM-CentreforEnvironmental&MarineStudiesand DepartmentofBotany,FacultyofScience,HamdardUniversity, DepartmentofChemistry,UniversityofAveiro,3810-193Aveiro, NewDelhi110062,India Portugal e-mail:[email protected] e-mail:[email protected] : A.Sofo A.Scopa A.S.Lukatkin SchoolofAgricultural,Forestry,FoodandEnvironmentalSciences, UniversityofBasilicata,Vialedell’AteneoLucano,10, DepartmentofBotany,PlantPhysiologyandEcology,N.P.Ogarev MordoviaStateUniversity,BolshevistskajaStr.,68,Saransk430005, 85100Potenza,Italy Russia A.Roychoudhury PostGraduateDepartmentofBiotechnology,St.Xavier’sCollege (Autonomous),30,MotherTeresaSarani,Kolkata700016,West Bengal,India I.Ahmad(*) CESAM-CentreforEnvironmental&MarineStudiesand S.S.Gill DepartmentofBiology,UniversityofAveiro,3810-193Aveiro, StressPhysiologyandMolecularBiologyLab,Centrefor Portugal Biotechnology,MDUniversity,Rohtak,Haryana124001,India e-mail:[email protected] 4100 EnvironSciPollutRes(2015)22:4099–4121 Introduction arbitrary exchange of solutes, whereas the regulation of ex- changeofsolutesorthetransductionofsignalsfromonesideof Abioticstress,reactiveoxygenspecies,andbiomolecules themembranetotheotheristightlyregulatedbythetransmem- braneproteins(Kleinschmidt2013).Notably,theperoxidation Abioticstresses(suchasdrought,salinity,radiations,extreme ofmembrane(phospho)lipidsandthedegradation/oxidationof temperatures including freezing/low and high temperatures, proteinsareamongthemostinvestigatedconsequencesofROS and chemicalssuch asmetals/metalloids) continue tohavea action on membrane structure and function (Blokhina et al. significantimpactonplantgrowthanddevelopment,limiting 2003;Davies2005;Rinalduccietal.2008;FoyerandNoctor the global crop production significantly (reviewed by 2009;FoyerandShigeoka2011).Regardingtheinteractionof •− Mahajan and Tuteja 2005; Gill and Tuteja 2010; Cramer ROSwithlipidsandproteins,superoxides(O )reactprimar- 2 etal.2011;Anjum etal. 2012,2014a;Krasensky and Jonak ily with protein Fe–S centers, while singlet oxygen (1O ) is 2 2012). Normal aerobic metabolism in plants results in the particularlypronetoreactwithconjugateddoublebondssuch •− generation of reactive oxygen species (ROS; such as O , as those found in polyunsaturated fatty acids (PUFAs) 2 • H O ,and OH),whereantioxidantdefensesystem(compris- (Rinalducci et al. 2008; reviewed by Braconi et al. 2011). 2 2 ing enzymes such as superoxide dismutase, SOD; catalase, Enhanced protein oxidation and lipid peroxidation may take CAT; guaiacol peroxidase, GPX; glutathione sulfo-transfer- placeinmembranesofthecellandtheorganelle,which,inturn, ase,GST;ascorbateperoxidase,APX;monodehydroascorbate canaffectthenormalcellularfunctioningandmetabolism.On reductase, MDHAR; dehydroascorbate reductase, DHAR; the one hand, oxidative stress may be aggravated by lipid glutathione reductase, GR; and non-enzymes such as ascor- peroxidationviatheproductionoflipid-derivedradicals(e.g., bate, AsA; glutathione, GSH; carotenoids; tocopherols;phe- alkyl, peroxyl, and alkoxyl radicals) that can react with and nolics)efficientlyscavengeROSandmaintaintheirlevelsat damagetheproteinsandtheDNA(reviewedbyGillandTuteja non-damaging levels (Mittler 2002; Gill and Tuteja 2010; 2010; Sharma et al. 2012). On the other hand, in the ROS- Anjumetal.2012).However,incapabilityofplantstoescape accruedproteinoxidation,theremayoccursite-specificamino- stress exposures makes them fall prey to previous abiotic acidmodification,fragmentationofpeptidechain,aggregation stresses.Inisolationorcombination,thesestressescancause of cross-linked reaction products, altered electric charge, and severedamagetoplants,eitherdirectlyorindirectly,bytrig- increasedsusceptibilityofproteinstoproteolysis.Nevertheless, gering an increased production of ROS and their reaction lipidperoxidationandproteinoxidationarecloselylinked,as products (Fig. 1). Although minimal levels of ROS may act theproteinscouldbemodifiedbytheirdirectconjugationwith asimportantsignaltransductionmoleculesandtriggerand/or the breakdown products offatty-acid (such as PUFA)peroxi- orchestrate plants’ responses to varied (abiotic) stresses, a dation in membrane (Yamauchi et al. 2008). Owing to the disturbance in the ROS/antioxidant homeostasis in any cell short-lived nature of toxic intermediates and ROS, and to the compartmentleadstoasituationcalledoxidativestress(Gill inefficiency of methodologies for their direct estimation, the and Tuteja 2010). Thus, oxidative stress (via unmetabolized quantification of stable end-products of reactions of the ROS and/orexcessROSandtheirreactionproductswithincells)can (andtheirreactionproducts)withcellularmacromoleculeshas causesignificantphysiologicalchallengesincludingcelldeath, beenadvocatedasanalternativeapproach(Orhanetal.2004). and the arrest of plant growth and development, mainly by In this context, plant-tissue contents of malondialdehyde provokingoxidativemodificationofvitalbiomoleculesinclud- (MDA,oneofthefinalproductsofperoxidationofunsaturated ingmembranelipids,cellularaminoacids,proteins,andDNA fatty acids in phospholipids) and carbonylated proteins [reac- (MahajanandTuteja2005;GillandTuteja2010;Anjumetal. tive carbonyls (RCs)] are considered as the biochemical 2012; Krasensky and Jonak 2012). The major metabolic markers of lipid peroxidation/cell-membrane damage sources(subcellularsites)ofROSinplantshavebeensumma- (Taulavuorietal.2001;Sochoretal.2012)andproteinoxida- rizedinFig.2,whereasFig.3presentsaschemeofthemajor tion(MøllerandKristensen2004),respectively.Increasedper- energy transfer by generation of the ROS and their reaction oxidation(degradation)oflipidsandtheelevatedproteinoxi- products, their chief characteristics, and the role they play in dation are common in plants growing under environmental theoxidativemodificationoflipidsandproteinsinplants. stresses (Romero Puertas et al. 2002; Han et al. 2009; Tanou Beingahighlyelaboratedstructure(withalipidbilayerand etal.2009;Mishraetal.2011;reviewedbySharmaetal.2012). the integral and peripheral proteins) and arguably the most This review (a) critically examines the various aspects of diverse membrane of the plant cell, plasma membrane func- oxidative damage to lipids (membrane lipids) and proteins in tionsasthepointofexchangewithadjoiningcells,cellwalls, abiotic-stressedplants,(b)summarizesthecurrenttechnologies andtheexternalenvironmentandhelpstheplanttodevelopand used to evaluate the extent of lipid and protein oxidation, (c) regulate plant–environment interactions (Barkla and Pantoja evaluatesthecross-talksoflipidandproteinoxidationandtheir 2011; Furt et al. 2011; Murphy et al. 2011). In particular, the oxidationproducts,and(d)highlightstheaspectsthatarerelevant lipid bilayer constitutes the hydrophobic barrier that prevents butsofarunexplored.Thediscussionisfocusedmainlyonthe EnvironSciPollutRes(2015)22:4099–4121 4101 CROP PRODUCTIVITY CONSEQUENCES Impaired:proteinsynthesisandchemistry; cellular redox homeostasis; oxidative ABIOTIC STRESSES modifications to cellular components (including lipids and proteins); uptake, translocation and assimilation of plant nutrients; root and shoot growth, chlorophyll-protein complexes; chlorophyll biosynthesis, and Oxidative photosyntheticmachinery. Stress HO HO 2 2 O2 .-2 O2.- 2 Peroxisomes Reactive Oxygen Species (ROS) 1O 2 H2O2 O2.-H2O2 O.- 2 Generation of ROS EXCEEDS Chloroplasts Mitochondria the induction of ROS- scavenging/antioxidant Antioxidants defense system ROS Fig.1 Schematicrepresentationofrelationshipsbetween abiotic-stress factors,and oxidativestress,their cumulativeconsequences in plants,and subsequentimpactoncropproductivity oxidationoflipidsandproteinsduetoROS(andtheirreaction environment(Lόpezetal.2011).Thylakoidmembranesofchlo- products)generatedbytheabove-mentionedabioticstresses. roplasts are an exception and contain primarily galactolipids, whicharealsoamphipathicandmoststableinabilayerconfig- uration (Tetlow et al. 2004; Robinson and Mant 2005). The Lipidperoxidationinplants amphipathic nature of membranes permits the formation of membranous sheets that self-anneal their edges into a sealed Plantlipids—anoverview compartment.Theinnerandoutersurfacesofbothplasmaand organelle membranesdiffer considerablyinchemicalcomposi- Plantlipidsincludefats,waxes,steroids,phospholipids,hydro- tion(Evert2006).Owingtothedynamicnatureofplantplasma carbons, and free higher fatty acids and their salts (soaps). membrane,andthesensitivityofitslipidcomposition/structure Membranelipidsconstituteamajorchemicalcomponentofall to the external environment cues (such as abiotic stresses), the cell membranes and are represented mainly by phospholipids changesinthemembranelipidsactasstressmarkersandhelpthe (themoreabundant)andsterols(particularlystigmasterol),which plantintuningwiththepotentialabioticstressimpacts(Barkla areamphipathicandspontaneouslyformbilayersinanaqueous andPantoja2011;Furtetal.2011;Murphyetal.2011). 4102 EnvironSciPollutRes(2015)22:4099–4121 Fig.2 Majormetabolicsources (subcellularsites)ofreactive oxygenspeciesinplants(based ondelRíoetal.2002;Corpas etal.2001;FoyerandNoctor 2009;Tayloretal.2009;Gilland Tuteja2010;Jaspersand Kangasjärvi2010) Basicmechanismsandestimationstrategies (withonedoublebond),PUFAsaremorevulnerabletoROS- mediated peroxidation because of the presence of greater Peroxidationoflipidscanbebroughtaboutbybothenzymatic number of double bonds in a fatty-acid chain, and the easy andnon-enzymatic(chemical)ways;theROS-mediatedlipid removalofahydrogenatom(Wagneretal.1994;Porteretal. peroxidationfallsunderthelattercategory.TheROS(suchas 1995).Owingtotheirunstablenature,lipoperoxidesdecom- freeoxygenradicals)havethetendencytocauseperoxidation posetoformawiderangeofcompoundsincludingthereac- oflipids,wherepolyunsaturatedfattyacids(PUFAs)oflipids tivecarbonylcompounds,especiallycertainaldehydes[such are chemicallydamaged byfreeradicalsand oxygen, giving as malondialdehyde (MDA) and 4-hydroxy-2-nonenal or way to lipoperoxides formation. Depending on the type of hydroxynonenal(4-HNE)],whichinturnfetchsevereconse- lipidsandoxidants,andontheseverityofoxidation,avariety quencestocellsbybindingfreeaminogroupsofaminoacids oflipid-peroxidationproductsareformed(Sharmaetal.2012; ofproteins(reviewedbySochoretal.2012).Withparticular Hameedetal.2013).Themajorproductsoflipidperoxidation referencetomitochondria,lipidperoxidationprincipallyrefers aremoietiescontaininghydroxyls,hydroperoxyls,aldehydes, toperoxidationofPUFAofmembranelipidssuchaslinoleic ketones, caroxylic acids,and trans doublebonds (Borchman acid,linolenicacidandarachidonicacid,wherevariouscyto- andSinha2002).Infact,incomparisontothesaturatedfatty toxicaldehydes,alkenals,andhydroxyalkenalscanbeyielded acids(withnodoublebonds)andmonounsaturatedfattyacids (Taylor et al. 2004). Nevertheless, among the ROS, mainly EnvironSciPollutRes(2015)22:4099–4121 4103 Fig. 3 Energy-transfer concept of reactive oxygen species (ROS) and their reaction products, their chief characteristics and the role in oxidative modificationoflipidsandproteinsinplants(basedonGillandTuteja2010;Sharmaetal.2012;SabaterandMartin2013) hydroxylradicalshavebeenreportedtoinitiatetheperoxida- the free-radical chain reactions; and (c) termination (cleav- tion of mitochondrial membrane PUFAs by abstracting a age),i.e.,theformationofnonradicalproducts(Fig.4). hydrogen atom and eventually leading to the formation of Enzymaticlipidperoxidationiscatalyzedbytheenzymes cytotoxic lipid aldehydes, alkenals, and hydroxyalkenals lipoxygenase(LOX,EC1.13.11.12)andcyclooxygenase(EC (such as HNE and MDA) (Rhoads et al. 2006). In general, 1.14.99.1), which are involved in the formation of eicosa- plant-lipidperoxidationismainlyduetoROSactivity,where noids, which represent a group of biologically active lipid the primary target of the ROS attack on lipids is the 1,4- compounds derived from unsaturated fatty acids containing pentadienestructureofPUFAs,whichareeitherfreeorester- 20carbonatoms(reviewedbySochoretal.2012).Inpartic- ifiedtocholesterolorglycerol(BrowneandArmstrong2002). ular, LOXs (linoleate/oxygen oxidoreductases) are ubiqui- The overall mechanism of the ROS (free radicals)-mediated tously occurring non-heme Fe-containing fatty acid lipid oxidation consistsof: (a) initiation(activation), i.e., the dioxygenases, soluble inwater, constituted bya singlepoly- formationoffreeradicals;(b)propagation(distribution),i.e., peptide associated with an atom of Fe(III), and catalyze the 4104 EnvironSciPollutRes(2015)22:4099–4121 Fig.4 Schematicrepresentation ofthebasicmechanismof reactiveoxygenspecies(ROS)- mediatedperoxidation(oxidative/ non-enzymaticmodification)of lipids(basedonGutteridge1995; Södergren2000;Mäkinen2002; Sochoretal.2012) additionofmolecularoxygentoPUFAsviaregio-andstereo- (Fig. 6) that can be quantified spectrophotometrically at specificoxygenation,andtherebyproducehydroperoxyfatty 532nm.Infact,thelevelofMDA/TBARSisfrequentlyutilized acidsandoxy-freeradicals(Garder1991;Sofoetal.2004a). asasuitablebiomarkerforlipidperoxidationinstressedplants Infact,owingtothepresenceofcis,cis-1,4-pentadienemoiety (Sofo et al. 2004a, b; Lόpez et al. 2011; Diwan et al. 2012; (–CH=CH–CH –CH=CH–),PUFAsbecomethemajortarget Hakeemetal.2012;Sorkhehetal.2012).However,ithasbeen 2 of LOX. LOX reactions exhibit high stereospecificity, with arguedthattheestimationofMDAviaTBARSmethod/TBA most lipoxygenases catalyzing the formation of (S)-config- assay may underestimate the actual extent of peroxidation ured fatty acid hydroperoxides (LOOHs) (Bannenberg et al. because (a) MDA can only be formed from fatty acids with 2009) (Fig. 5). Extensive reports including that of Feussner three or more double bonds (Halliwell and Gutteridge 1989, and Wasternack (2002), Liavonchanka and Feussner (2006), cited in Griffiths et al. 2000), and (b) the occurrence of high Skórzyńska-Polit et al. (2006), Vellosillo et al. (2007), and levelsofthepredominantacylconstituentsuchaslinoleicacid Lόpez et al. (2011) have evidenced the enzymatic modifica- [18:2(Δcis,9,12)]thatisthemajorPUFAandisusedassubstrate tion of these intermediates into oxylipins, bioactive com- byLOX,andhencecanrestricttheestimationofactualextent pounds involved in growth, development, and responses to of peroxidation (Leverentz et al. 2002). Additionally, TBA (a)bioticstressconditions.ThreeLOXisoenzymes,namely, assayyieldslittleinformationonthelevelsofLHPs. LOX-1, LOX-2, and LOX-3, were considered common in plants.However,LOX-3istheisoformwithmostabundance Ferrousoxidationinxylenol-orangeassay andhighestactivity(Sofoetal.2004a).Arabidopsisthaliana hasbeenreportedtoexhibitsixLOXisoforms(At-LOX-1to In general, total LHPs may be determined using the ferrous At-LOX-6)(Bannenbergetal.2009). oxidationinxylenolorange(FOX)assay,whichcanbeusedfor Contingent upon the lipid (per) oxidation-product types hydroperoxides present in the aqueous (FOX1) and the lipid (such as conjugated dienes and lipid hydroperoxides, LHP; (FOX2) phases (Wolff 1994; Nourooz-Zadeh et al. 1994). To or secondary products, such as MDA; alkanes or overcome the above-mentioned issue and correctly estimate isoprostanes), a number of methods/state-of-the-art equip- LHPs in plant samples, Griffiths et al. (2000) developed this mentsareemployedforestimationoflipid-oxidationlevelin spectrophotometric method, employing the FOX2-assay tech- plant samples. A brief description of the basic methods/ nique with some modification. Herein, the LHPs estimation principlesandtheirlimitationsfollows. was based on their reaction with the ferric-ion-indicator dye “xylenol orange” [o‐cresolsulphonphthalein‐3,3′‐bis Spectrophotometryassay (methyliminodiacetic acid) sodium salt] that binds ferric ion toproduceacolored(blue‐purple)complexwiththemaximum Spectrophotometry (UV–visible) is a simple, rapid, reproduc- absorbanceat560nm(a:Fe2++LOOH→Fe3++LO•+OH−;b: ible,andlow-costtechniquethatcanbeemployedforestimat- Fe3++XO→blue-purplecomplex).TodeterminetheLHPpres- ing MDA via the thiobarbituric acid reactive substances entinplanttissues,theauthorsfirstextractedtotallipidsinan (TBARS)method.Thismethodcanalsobeemployedtoesti- acidifiedchloroform–methanol-basedsolventsystem,andsub- mate the levels of lipid hydroperoxides (LHPs), the primary sequently, the isolated lipids were assayed spectrophotometri- oxygenated products of PUFAs, and the key intermediates in callywithFOX2reagents.Inanotherinstance,modifiedFOX2 the octadecanoid signalling pathway in plants. The principle andiodometricassayswereappliedtodetectLHPinmethanol underlying the TBARS method is that thiobarbituric acid extractofarangeofplanttissuesincludingthepericarp(avo- (TBA)reactswithMDAinacidicconditionsandformsapink cado; Persea americana; European pear, Pyrus communis), MDA-(TBA) 2 complex at a higher (100 °C) temperature periderm (potato; Solanum tuberosum), leaves (cabbage, EnvironSciPollutRes(2015)22:4099–4121 4105 Fig.5 Theprimaryreactioncatalyzedbylipoxygenase,usinglinoleicacidassubstrate,indicatestwopossibleproducts Brassicaoleraceaconvar.capitatavar.rubra;spinach,Spinacia where secondary products of lipid oxidation, such as MDA, oleracea), and fruits (red pepper; Capsicum annuum). The are not readily formed. Indeed, many plant lipids are highly impactof10–12daysexposureofexcisedpiecesoftheseplant unsaturated,containingasmanyassixC=Cbondsperhydro- speciesto83kJm−2day−1ofbiologicallyeffectiveultraviolet- carbonchain,andareverysensitivetolipidoxidation,partic- Birradiance(UV-BBE)onbothLHPandTBARSwasmoni- ularlyunderstressconditions. tored(DeLongetal.2002).TheFOXassaywasadvocatedto be employed for the detection of early membrane-associated Reverse-phasehigh-performanceliquidchromatography stresseventsinplanttissuesowingtoitsinsensivitytoambient assay O orlightlevels,itsefficiencytogenerateLHPmeasurements 2 rapidly(duringtheinitialratherthanmoreadvancedfatty-acid- Thistechniquecanseparateregioisomericspeciesoflipidhy- oxidationphase),anditsbeingrelativeinexpensive. droperoxides (LHP) and lipid hydroxide (LOH) derived from plant PUFA. Details of the reverse-phase high-performance Infraredspectroscopyassay liquidchromatography(RP-HPLC)assayhavebeendescribed byBrowneandArmstrong(2002)andArmstrong(2002). Infrared spectroscopy (IS) technique can detect the major products of lipid peroxidation and is uniquely sensitive in Lipidoxidationvs.abioticstresses detecting the lipid hydroxyl and hydroperoxyl groups (Borchman and Sinha 2002). The detection of these groups VariousabioticstressesleadtotheoverproductionofROSin is especially useful for quantifying the oxidation of mono- plants,whichcausedamagetolipidsthatultimatelyresultsin unsaturated lipids, such as those found in the ocular lens, oxidative stress (Nishida and Murata 1996; Gill and Tuteja 4106 EnvironSciPollutRes(2015)22:4099–4121 oflipidperoxidationinplantssincetheyhavebeenextensive- lyreportedtopromotetheformationofROS(GillandTuteja 2010;Anjumetal.2012).Notably,redoxactivemetals(such asCu,Cr,andFe)cancauselipidperoxidationviagenerating ROSthroughredoxcycling.However,redoxinactivemetals (such as As, Cd, Co, Hg, Al, Ni, Pb, Se, Zn, etc.) bring significant impairments in antioxidant defense components suchasthiol-containingantioxidantsandenzymes,andeven- tuallycauselipidperoxidation.Manystudiesonlipidperox- Thiobarbituric Acid (TBA) idationhaveshownthatCdproducesstrongalterationsinthe + functionality of membranes by inducing lipid peroxidation anddisturbancesinchloroplastmetabolismbyinhibitingchlo- rophyll biosynthesis and reducing the activity of enzymes involvedinCO fixation(Cuypersetal.2010,2011;Ahmad 2 et al. 2011; Gallego et al. 2012; Gill et al. 2013). Enhanced LOX activity has been reported in a number of Cd-exposed plants (Skórzyńska-Polit et al. 2006; Smeets et al. 2008; Tamas et al. 2009; Remans et al. 2010; Keunen et al. 2013; Liptákováetal.2013).Upregulationoflypoxigenase(LOX) was an important component of stress response of barley (Hordeumvulgare)rootstotoxicCd,butwasnotresponsible Malonaldehyde (MDA) for the Cd-induced harmful lipid peroxidation (Liptáková etal.2013).Cd-accruedenhancedLOXactivitycanmediate Cd-induced root growth inhibition (Tamas et al. 2009). Cd exposurecanalsocauseastrongupregulationinthetranscrip- tion level of the cytosolic LOX1 gene (Smeets et al. 2008; Remans et al. 2010). The Cd (25, 50, and 100 mg Cd kg−1 soil)-induced elevated TBARS production in Cd-tolerant mung bean (Vigna radiata) cv. Pusa 9531 was assumed to be the outcome of a strong cellular redox homeostasis, as compared with Cd-susceptible V. radiata cv. PS16 (Anjum etal.2011).Inanotherstudy,thesameCdtreatmentselevated the TBARS level in the leaves of mustard (Brassica campestris L.) cv. Pusa Gold, which was reduced by ROS TBA-MDA adduct scavengers such as ascorbate and glutathione (Anjum et al. 2008a).Organsofthesameplantmayexhibitdifferentlevels Fig. 6 The basic principle of thiobarbituric acid (TBA) test. TBA 2- of lipid peroxidation under Cd exposure. For example, an thiobarbituricacid,MDAmalonaldehyde) increased accumulation of MDA (a lipid-peroxidation prod- uct)wasmorepronouncedinshootsthaninrootsoftheCd- 2010; Miller et al. 2010; Foyer and Shigeoka 2011; Sharma exposed lentil (Lens culinaris) seedlings (Talukdar 2012). etal. 2012).Instancesofabiotic-stress-mediated lipid oxida- Plant species significantly differing in their tolerance to Cd tionviaROSproductionarebeingdiscussedhereunder,crit- mayexhibitdifferentextentofmembranelipidperoxidation; icallyanalyzingtheexperimentalresultsandsynthesizingthe Cd-induced increase in MDA level was lower in the less- basicunderlyingmechanisms. sensitivepea(Pisumsativum)genotypes3429and1658than inthemore-sensitivegenotypes4788and188.However,the Metals/metalloids maximumvalueoflipidperoxideswasassociatedwithgeno- type8456,whichshowedarelativelyhightolerancetoCd,as Oxidative stress caused in plants by exposure to elevated deduced from growth parameters (Metwally et al. 2005). metal concentrations in the environment coincides with a Thus,theCd-inducedoxidativestressvariedamongP.sativum constraint on plastidial and mitochondrial electron transport, genotypes.InarecentstudyofB.campestrisandV.radiata, whichenhanceslipidperoxidationinthesetwocompartments the difference in the Cd-accrued elevation in TBARS level and in the whole cell (Nagajyoti et al. 2010; Yadav 2010; wasattributedtothevariationintheCd-accumulationcapac- Keunenetal.2011).Metals/metalloidscanbepotentinducers ityofrootsandinthebalancedtuningbetweentheenzymatic EnvironSciPollutRes(2015)22:4099–4121 4107 and non-enzymatic components of the antioxidant defense Sharma 2000; Israr and Sahi 2006), as observed recently in system(Anjumetal.2014b). salt marsh macrophytes Halimione portulacoides (Anjum Lipidperoxidationappearedasanearlysymptomtriggered etal. 2014c) and Juncusmaritimus (Anjumet al. 2014d, e). byaluminium(Al)-inducedoxidativestress(Yamamotoetal. In environmentally exposed two grass species (Eriophorum 2001; Boscolo et al. 2003), but the major mechanisms angustifolium and Lolium perenne), a differential extent of underlining the Al toxicity remain unidentified. In this con- lipid peroxidation was argued as a result of a differential text, Yin et al. (2010) verified the participation of the lipid- efficiencyofROS-metabolizingsystem(Anjumetal.2013). peroxide-derived aldehydes (especially highly electrophilic Adose-dependentincreaseinTBARScontentcouldbeseen α,β-unsaturatedaldehydes,2-alkenals),inAltoxicity.Inthe inboron(B)-exposedwheat(Triticumaestivum;Gunesetal. rootsofAl-exposedtransgenictobacco (Nicotianatabacum) 2007) and Artemisia annua (Aftab et al. 2012) and Se- (overexpressing 2-alkenal reductase gene obtained from exposed H. vulgare seedlings (Akbulut and Çakır 2010). Se A.thaliana),N.tabacumcultivarSR1,andanemptyvector- at higher concentrations can elevate lipid peroxidation transformed control line (SR-Vec), ROS-led aldehydes such (Gomes-Junioretal.2007;AkbulutandÇakır2010). asMDAwereconsideredasthemajorcauseofinjurytoroot Notonlytheknowntoxicelementselevatelipidperoxida- cells(Yinetal.2010).InH.vulgareseedlings,Al(2.5,5,and tionbutevensuchelementsasCu,Fe,Ni,Se,andZn,which 10mM;6days)exposureresultedinadose-dependentsignif- arebeneficialinlowconcentrationforplantphysiologicaland icantincreaseinlipidperoxidation(Acharyetal.2012).Ina biochemical processes, may enhance lipid peroxidation recent study of peanut (Arachis hypogaea), the Al-induced (Cuypers et al. 2010, 2011; Sofo et al. 2013). Increasing lipid-peroxidationdamageofmitochondriawasmoreserious, concentration of Fe (40, 80, and 160 mM) enhanced lipid showing a significantly higher mitochondrial MDA content, peroxidation in Bacopa monnieri (Sinha and Basant 2009). inasensitive(Zhonghua2)cultivarthaninthetolerant(99– Similarly,elevationinlipidperoxidationinanumberofplants 1507)one(Zhanetal.2014).Lipidperoxidation(measuredas duetotheirexposuretoCu(Posmyketal.2009;Opdenakker MDAlevel)duetoAlexposurehasbeenreportedinanumber etal.2012;Singhetal.2012;Thounaojametal.2012;Elleuch of plants including barley (H. vulgare; Achary et al. 2012), et al. 2013; Ansari et al. 2013a), Ni (Kazemi et al. 2010; black soybean (Glycine max; Wu et al. 2013), cucumber Gajewska et al. 2012), Se (Malik et al. 2012), As (Ansari (Cucumis sativus; Pereira et al. 2010), maize (Zea mays; et al. 2013b), Pb (Qureshi et al. 2007; Maldonado-Magaña Giannakoula et al. 2010), pea (P. sativum; Yamamoto et al. et al. 2011), Cr (Diwan et al. 2008; 2010), and some other 2001),andrapeseed(B.campestris;Basuetal.2001),among heavymetals/metalloidswasreportedtobedependentontheir others. In contrast, no significant change in MDA level was doses and plant types (Sytar et al. 2013). The main site of observed in Plantago algarbiensis leaves and roots, while it attackbyanyredoxactivemetalinaplantcellisusuallythe decreased in Plantago almogravensis roots, exposed to Al cell membrane. Beinga redox active metal,Cu can catalyze (Martins et al. 2013), suggesting the existence of protective theformationofROSthroughFentonandHaber–Weiss-type mechanismsinthisspecies.InN.tabacumcells,Al-mediated reactions (Van Acker et al. 1995), which in turn can induce enhancedlipidperoxidaionwasconsideredasadirectcauseof lipid peroxidation (Valko et al. 2005). Cell membrane is cell death (Ikegawa et al. 2000). Contrarily, Boscolo et al. considered as the primary site of Cu toxicity in plants (2003) held that lipid peroxidation is not essential for cell (Thounaojam et al. 2012; Elleuch et al. 2013). At 2.0 and death in Al (6, 12, 36, and 60 μmol l−1)-exposed Z. mays 5.0μM,CucouldsignificantlystimulateMDAformationin andthattheoxidativestresscaninducecellinjurybyseveral the cyanobacteria Phormidium foveolarum and Nostoc other pathways, as pointed out by Halliwell and Gutteridge muscorum, after 24 h of experiment (Singh et al. 2012). Cu (1999)formammaliancells. treatment (200 and 500 μM) for a period of 1 and 7 days In the roots of Hg-exposed alfalfa (Medicago sativa), Hg initiatedtheprocessoflipidperoxidation(measuredasMDA ionsatlowconcentration(1.0μM)didnotcauseanysignif- level)intherootandshootofrice(Oryzasativa)seedlingsina icant lipid peroxidation; however, higher concentrations (5 dose-dependentmanner(Thounaojametal.2012).Enhanced and20μM)ingrowthmediumdiditmarkedly,asindicated levels of lipid peroxides (such as TBARS) were reported in by TBARS accumulation as well as lysil oxidase (LOX) B. oleracea tissues treated with 2.5 mM Cu2+; excess accu- activity,measuredinnon-denaturingpolyacrylamidegelelec- mulation of Cu caused the ROS-mediated oxidative damage trophoresis(Zhouetal.2007,2008).Alterationsinactivities toplasmamembrane(Posmyketal.2009).Inthreewild-type of antioxidant enzymes due to high Hg concentrations are plantspecies,namely, Daturastramonium, Malva sylvestris, ascribed to Hg-accrued differential lipid peroxidation. Addi- and Chenopodium ambrosioides, grown on Cu mine, a sig- tionally, owing to their transition property, mercuric ions nificant increase in the leaf MDA was corresponded to Cu induce oxidative stress by triggering generation of ROS in loadsaswellastoactivitiesofantioxidativeenzymes(Boojar plants,which can becorrelatedtotheHg-accrueddisruption and Goodarzi 2007). Lipid peroxidation (measured as of biomembrane lipids and cellular metabolism (Patra and TBARS)wasarguedasafirstindicationofoxidativedamage 4108 EnvironSciPollutRes(2015)22:4099–4121 observed under Cu (and also Cd) exposure (Cuypers et al. photosynthetic-capacity genotype (PS 16) (Anjum et al. 2011).ComparedtoCd,theexposureofplantswithCuledto 2008b). Interestingly, exogenous cinnamic acid and deriva- a higher cytotoxicity in A. thaliana roots, where a major tivesofjasmonicacidwereeffectivelyusedinimprovingthe increaseinlipidperoxidation(andalsoastrikingdecreaseof drought-stress tolerance of plants by modulating the the K content) was noted. Interactive effects of elements on membrane-lipid peroxidation and antioxidant activities (Sun MDAmaydifferfromthoseofisolatedelements.CuandZn et al. 2012). Arbuscular mychorriza could also alleviate the (10,50,and100μM)togetherincreasedtheMDAcontentin detrimental effect of drought by reducing the MDA content duckweed(Spirodelapolyrhiza)inadose-dependentmanner and membrane permeability and by increasing the proline (Upadhyay and Panda 2010). However, Zn supplementation contentandantioxidantenzymeactivities(Zhuetal.2011). hadadecliningeffectontheMDAlevels,reducingthelipid Salt stress, even at mild levels, is able to cause lipid peroxidation, thereby indicating that Zn has a property of peroxidationincereals(deAzevedoNetoetal.2006;Ashraf existing in a univalent state and being stable in a biological et al. 2010), vegetables (Sergio et al. 2012; Tayebimeigooni medium, and hence, the membrane-lipid packing was et al. 2012), and tree species (Ahmad et al. 2010; Ayala- protected from ROS (Teisseire and Guy 2000). Recently, AstorgaandAlcaraz-Meléndez2010).Indianmustard(Bras- Maleckaetal.(2014)reportedadifferentialcontentofMDA sica juncea) cultivars differing in ATP-sulfurylase activity inhydroponicallygrownP.sativumunderCd,Pb,Cu,andZn exhibitedadifferentialextentofTBARSlevelundersalinity alone and joint exposures.The observeddifference inMDA stress. Exhibition of low TBARS in B. juncea cv. Pusa Jai levelwasattributedtothevariationintheCd,Pb,Cu,Zn,as Kisan(vs.B.junceacv.SS2)wasarguedtobeduetohigher wellasCu+Pb,Cu+Cd,Cu+Zn,Pb+Cd,Zn+Pb,andZn+ activityofATP-sulfurylase,whichinturnincreasedthecon- Cd(25μMforeachmetalion)-accruedROSgenerationand tentofglutathione,areducedformofinorganicsulfurandan to the ROS-metabolizing components of the antioxidant de- essential component of cellular antioxidant defense system fensesystem. (Khanetal.2009).Plantsdifferinginsalinitytolerancecould exhibitavariedextentoflipidperoxidation.Increaseinlipid Droughtandsalinity peroxidation,expressedbyMDAcontent,isnormallysignif- icantly higher in salinity-sensitive cultivars than in salinity- Expression of the drought and/or salinity-induced metabolic tolerant ones, as for instance, in Brassica napus (Rasheed alteration in plants involves oxidative stress. In the drought- etal.2014).ThelowerlevelofTBARSinsalinity(50mM)- stressed plants, membranes are considered to be a primary exposedB.junceacv.Alankar(salt-tolerant)vs.B.junceacv. target of desiccation injury, and the ability of desiccation- PBM16 (salt-sensitive) was assumed to be due to its lower tolerant organisms to avoid membrane damage during a content of leaf Na+ and Cl− as well as the plant capacity to dehydration-rehydration cycle is related to changes in mem- maintaintuningamong the antioxidantdefense-systemcom- branefluidity.Membranebilayerstructureindrought-tolerant ponents(Syeedetal.2011).Similarconclusionwasdrawnin organismsisconsideredasbeingstabilizedduetointeractions thecaseofB.campestris,showingincreaseinTBARScontent of the polar head groups with sugars and proteins. Such withincreaseinthedegreeofsoilsalinity(Umaretal.2011). interactions create space between phospholipids and prevent Earlier, Sekmen et al. (2007) reported a similar differential membrane-phase changes. Membranes thus remain in the responseofsalt-tolerantPlantagomaritimeandsalt-sensitive liquid-crystalline phase when the hydration shell is lost Plantagomediaexposedto100and200mMNaCl. (Golovina and Hoekstra 2003). Moreover, under conditions of high vapor-pressure deficit, plants can reduce excessive Otherabioticstresses water loss by closing their stomata and thus enhancing the oxidativestressduetoexcessenergy.Droughtstressofvari- Themembranelipidperturbationcanalsobeperformedbya ousdegreescancausedamagetolipidstructureandfunction- range of other abiotic stress factors such as UV radiation, ing incereals(Fukaoetal.2011;Hameedetal.2011,2013; temperature extremes, nutrient deficiency, air pollution, and Csiszáretal.2012),treespecies(Štajneretal.2011),forage chemical toxicants (Gill and Tuteja 2010; Yan et al. 2010; plants (Slama et al. 2011), and medicinal plants (Tian et al. Tripathietal.2011;Lietal.2012;Szarkaetal.2012;Bashir 2012). etal.2014;Majidetal.2014).Thecontributionofmembrane Plants differing in photosynthetic capacity may exhibit lipids, particularly the unsaturated membrane lipids, in varied extent of lipid peroxidation under drought exposure. protectingthephotosyntheticmachineryfromphotoinhibition Inthiscontext,decreasingfieldcapacitywascorrelatedindi- undercoldconditionshasbeenintensivelydiscussed(Nishida rectlywithincreasedlipidperoxidation(intermsofTBARS) andMurata1996).Themembrane-lipidprofilesandphospho- in V. radiata genotypes, where high-photosynthetic-capacity lipases have a role in freezing-induced lipid changes in genotype (Pusa 9531) experienced less increase in TBARS Arabidopsis(Weltietal.(2002),contributingsignificantlyto andelectrolyteleakagethantherelativelymoresensitivelow- planttoleranceundercoldconditions.Exposureoftheexcised