Table Of ContentBhumi Nath Tripathi · Maria Müller
Editors
Stress Responses
in Plants
Mechanisms of Toxicity and Tolerance
Stress Responses in Plants
ThiSisaFMBlankPage
Bhumi Nath Tripathi (cid:129) Maria Mu¨ller
Editors
Stress Responses in Plants
Mechanisms of Toxicity and Tolerance
Editors
BhumiNathTripathi MariaMu¨ller
AcademyofInnovativeResearch InstituteofPlantSciences
Ambedkarnagar UniversityofGraz
India Graz
Austria
ISBN978-3-319-13367-6 ISBN978-3-319-13368-3 (eBook)
DOI10.1007/978-3-319-13368-3
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Contents
1 SaltStressinHigherPlants:MechanismsofToxicityandDefensive
Responses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
AnabellaFernandaLodeyroandNe´storCarrillo
2 PhysiologyandBiochemistryofAluminumToxicityandTolerance
inCrops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
AnjaliAggarwal,BunichiEzaki,AshokMunjal,
andBhumiNathTripathi
3 AdaptiveMechanismsofPhotosyntheticApparatusto
UVRadiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
A.A.Kosobryukhov,V.Yu.Lyubimov,andV.D.Kreslavski
4 SignalPerceptionandMechanismofSaltToxicity/Tolerance
inPhotosyntheticOrganisms:CyanobacteriatoPlants. . . . . . . . . . 79
ChhaviAgrawal,SoniaSen,AntraChatterjee,ShwetaRai,
ShivamYadav,ShilpiSingh,andL.C.Rai
5 PlantResponsestoSoilFlooding. . . . . . . . . . . . . . . . . . . . . . . . . . . 115
TamaraI.Balakhnina
6 MechanismofArsenicToxicityandToleranceinPlants:Role
ofSiliconandSignallingMolecules. . . . . . . . . . . . . . . . . . . . . . . . . 143
MeetuGuptaandEhsanullahKhan
7 ResponseofWheatSeedlingstoCombinedEffectofDrought
andSalinity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
AnatolyA.Ivanov
8 PlantResponsetoUV-B:FromTolerancetoToxicity. . . . . . . . . . 199
SuruchiSingh,S.B.Agrawal,andMadhoolikaAgrawal
v
vi Contents
9 MetabolicStrategyofAnnualDesertPlants:AdaptivePhenomenon
ofCAMandC PhotosynthesisFunctioninginaLeaf. . . . . . . . . . 217
4
ValeryYu.LyubimovandKarlYa.Biel
10 SalicylicAcidandDroughtStressResponse:Biochemical
toMolecularCrosstalk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
SonaliPandeyandDipjyotiChakraborty
11 DroughtResistanceinCrops:PhysiologicalandGeneticBasis
ofTraitsforCropProductivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
RenuKhanna-ChopraandKalpanaSingh
Chapter 1
Salt Stress in Higher Plants: Mechanisms
of Toxicity and Defensive Responses
AnabellaFernandaLodeyroandNe´storCarrillo
Abstract Soil salinity is a major constraint to crop performance. The main con-
tributors to salt toxicity at a global scale are Na+ and Cl(cid:1) ions which affect up to
50 % of irrigated soils. Effects of salt exposure occur at the organismic, cellular,
and molecular levels and are pleiotropic, involving (1) osmotic and water deficit
syndromes, (2) specific Na+ and Cl(cid:1) inhibitions, (3) nutritional imbalance, and
(4)oxidativestress.Wereviewhereintheresponseselicitedbysalt-stressedplants
to face all these challenges. With the only exception of halobacteria, all other
organismsarenothalotolerantatthemolecularlevel.Instead,theyhavedeveloped
strategiestokeepsaltsoutofthecell.Then,inductionofsystemsforsaltextrusion
totherhizosphereandsaltcompartmentationintothevacuoleplaykeyrolesinsalt
tolerance,aidedbythesynthesisandaccumulationofcompatibleosmolytesandof
antioxidantenzymesandmetabolites.Expressionoftheseeffectorgenesismodu-
lated by a complex network of salt-responsive transcription factors and signaling
molecules.Wediscusstheprogressmadetowardsincreasingsalttoleranceincrops
byengineeringgeneswhoseproductsoperateatallthesestages,fromsensingand
regulation to effector proteins, and identify key open questions that remain to be
addressed.
Keywords Salt tolerance • Oxidative stress • Nutritional imbalance • Osmotic
adjustment•Iontoxicity
1.1 Introduction
Earthisapredominantlysaltyplanet,withmostofitswatercontaining~600mM
NaCl.About7%ofthefirmland,20%ofthecultivatedland,andnearlyhalfofthe
irrigatedlandareaffectedbyhighsaltcontents(Zhu2001,2002,2003).Thethreats
of salinity are more obvious in arid and semiarid regions where limited rainfall,
highevapotranspiration,andextremetemperaturesassociatedwithpoorwaterand
A.F.Lodeyro•N.Carrillo(*)
InstitutodeBiolog´ıaMolecularyCelulardeRosario(IBR-CONICET)OcampoyEsmeralda,
FacultaddeCienciasBioqu´ımicasyFarmace´uticas,UniversidadNacionaldeRosario,
Suipacha531,2000Rosario,SantaFe,Argentina
e-mail:[email protected];[email protected]
©SpringerInternationalPublishingSwitzerland2015 1
B.N.Tripathi,M.Mu¨ller(eds.),StressResponsesinPlants,
DOI10.1007/978-3-319-13368-3_1
2 A.F.LodeyroandN.Carrillo
soilmanagement arethemaincontributingfactors(deAzevedoNetoetal.2006).
Whilevirtuallyallsaltsmayhavedeleteriouseffectsonplantwelfare,thetermsalt
stressusuallyreferstotheconsequencesofabnormalaccumulationofNa+andCl(cid:1)
ions, since this is by far the most extended environmental hardship related to
salinity.
Salinization might occur by natural causes, primarily by capillary water level
elevationandsubsequentevaporationofsalinegroundwater.However,theincrease
ofsalinizationataglobalscaleislargelyduetohumanintervention,particularlyin
arid regions. Irrigation practices lead to groundwater level elevation and a subse-
quentincreaseinevaporation.Saltsnotonlycausedirectdamageonplantsbutalso
provokesecondarynegativeeffects,suchasincreaseofthesoilpH.Mostplantsdo
not grow well at high pH due to iron starvation. Iron is found in nature mostly as
ferric oxides that are sparingly soluble, indicating that the main problem of Fe
acquisition is not of abundance but of bioavailability (Curie and Briat 2003). The
solubilityproductofferricoxidesdecreasesthreeordersofmagnitudeforeachpH
unitraise,whichrepresentsamajordeterrentforagricultureinalkaline,calcareous
soilsthatcovermorethanonethirdoftheplanet’scultivableland(MorelandPrice
2003).
Salt stress affects plant physiology at whole plant as well as cellular and
molecularlevelsandatallstagesofdevelopmentfromgerminationtosenescence
(Hasegawaetal.2000;Muranakaetal.2002;Murphyetal.2003;Ranjbarfordoei
etal.2002).Reportedeffectsincludechangesingrowthrate,iontoxicity,mineral
limitation,membraneinstability,photosynthesis,andincreasedrespiration(Ashraf
andShahbaz2003;Hasegawaetal.2000;Munns2002).Buildupofhighamounts
ofsaltsintheleafapoplastleadstodehydrationandturgorloss(Marschner1995),
whereas salt accumulation in the cytosol and organelles results in inhibition of
enzymes and metabolic pathways, including photosynthesis (de Lacerda
etal.2003).Thereductionofplantgrowthandbiomassaccumulationundersaline
conditionshasbeenreportedinseveralimportantcrops(Tejeraetal.2006).
Tofacilitateanalysis,theunfavorableeffectsofsaltstressareclassifiedinfour
major groups: (1) osmotically induced water stress, (2) specific salt toxicity
inhibiting enzymes and metabolic pathways, (3) nutrient ion imbalance due to
highlevelsofNa+andCl(cid:1)competingwiththeuptakeofotheressential ions,and
(4)increasedproductionofreactiveoxygenspecies(ROS)whichdamagealltypes
ofmacromolecules.Thesedifferentmodesofactionwillbebrieflydescribedinthe
forthcomingsections,followedbyasurveyoftheresponseselicitedbysalt-stressed
plants,theirregulation,andtheuseoftheknowledgegatheredinthelastdecadesto
designsalt-tolerantplants.Severalreviewsonsalt toxicity,sensing, andtolerance
have been published in recent years (Bose et al. 2014; Deinlein et al. 2014;
Golldack et al. 2011; Huang et al. 2012; Maathuis 2014). The reader is referred
tothemforamoreextensivetreatmentofthesesubjects.
1 SaltStressinHigherPlants:MechanismsofToxicityandDefensiveResponses 3
1.2 Osmotic Adjustment and Water Deficit
Salt accumulation in soils reduces the plant’s ability to take up water from the
rhizosphere,andthisleadstowaterlimitationandgrowthreduction.Thisprocessis
thefirsttooccurinasalt-stressedplantandisformallyanalogoustoawater-deficit
stress.Indeed,somecellularandmetabolicprocessesinvolvedinosmoticresponses
tosalinityarecommontodrought,includingstomatalclosure(seebelow).Therates
atwhichnewleavesareproduceddependlargelyonthewaterpotentialofthesoil
solution, in the same way as for a drought-stressed plant. At this stage, salts
themselves do not build up in the growing tissues at concentrations that could
inhibitgrowth,astherapidlyelongatingcellscanaccommodatethesaltthatarrives
inthexylemwithintheirexpandingvacuoles(Munns2005).Then,reductionsinthe
rateofleafandrootgrowthareduetowaterstressratherthanasalt-specificeffect
(Munns 2002), since Na+ and Cl(cid:1) are usually below toxic concentrations in the
growingcells.Forexample,inwheatexposedto120mMNaCl,Na+inthegrowing
tissues of leaves was at most 20 mM and only 10 mM in the rapidly expanding
zones (Hu et al. 2005). Results of experimental manipulation of shoot water
relationssuggestthathormonalsignals,probablyinducedbytheosmoticeffectof
thesaltontheroots,arecontrollingtherateofcellelongation(Munnsetal.1999).
Inhibition of plant growth due to salinity largely depends on the severity of the
stress. Mild osmotic challenges rapidly lead to growth inhibition of leaves and
stems,whereasrootsmaycontinuetoelongate(HsiaoandXu2000).Thedegreeof
growth inhibition due to this osmotic stress also depends on the time scale of the
responseforthe particulartissue andspeciesandonwhetherthestress treatments
areimposedabruptlyorgradually(Munnsetal.1999).
1.3 Specific Ion Toxicity
Assaltsaretakenupbyaplant,theytendtoconcentrateintheoldleaves.However,
continued transport into transpiring leaves over a long period of time eventually
exceedstheabilityofthecellstoexcludesaltsfromthecellortocompartmentalize
theminthevacuole(seebelow).Saltsthenwouldbuildupinthecytosolandinhibit
enzyme activity.Alternatively, they might accumulate inthe cellwallsand dehy-
drate the cell (Munns 2005). These specific effects of ions such as Na+ and Cl(cid:1)
followthewaterandosmoticstressesthatinitiatethesalinitysyndrome.
Undernormalgrowthconditions,rootcytosolicNa+concentrationsareprobably
in the order of 10–30 mM (Tester and Davenport 2003). Leaf Na+ cytosolic
concentrations are considered to be in the same range (Jones and Gorham 2002).
Roots mustexclude mostofthe Na+ andCl(cid:1)dissolvedinthe soilsolution,or the
salt concentration in the shoot will gradually increase to toxic levels. Plants
transpireabout50timesmorewaterthantheyretainintheirleaves(Munns2005).
