88OnthemechanismofsalttoleranceinoliveOleaeuropaea

Availableonlineat(2009)72–81Onthemechanismofsalttoleranceinolive(OleaeuropaeaL.)underlow-orhigh-Ca2+supplyMassimilianoTattini∗,MariaLauraTraversiIstitutoperlaValorizzazionedelLegnoedelleSpecieArboree,IVALSA,ConsiglioNazionaledelleRicerche,ViaMadonnadelPiano10,I-50019,SestoF.no,Firenze,ItalyReceived10January2008;accepted22January2008AbstractTheeffectofchangesinCa2+/Na+ratiosattherootzonehasbeenreportedinOleaeuropaea,aspeciesmostlycultivatedincalcareoussoils.Plantswereexposedtolow(2.0mM,low-Ca)orhigh-Ca2+supply(9.0mM,high-Ca)andsuppliedwith0or200mMNaCl.Measurementswereperformedonwaterrelations,gasexchangeandphotosyntheticperformances,ionfluxesatwhole-plantandleaflevel,Na+allocationatorganismallevel,theelementalandsolublecarbohydrateconcentrationintheleaf.Mostparameterswerealsomeasuredduringaperiodofrelieffromsalinitystress,asOleaeuropaeasuffersfromfluctuatingrootzoneNaClconcentrationsoverthewholegrowingseason.High-Ca2+supplydecreasedstomatalconductance,especiallyduringthefirsttwoweeksoftreatment.Inresponsetosalinitystress(i)leafturgorpotentialwasmoreseverelydepressedinhigh-Cathaninlow-Caplants,whereasnetCO2assimilationrateandrelativegrowthratewereunaffectedbyrootzoneCa2+concentrations(ii)high-CaplantshadamarkedlysuperiorabilitytobothexcludeNa+fromtheshootandtoselectivelytransportK+overNa+thanlow-Caplants;(iii)bothCO2carboxylationefficiencyandmaximalefficiencyofPSIIphotochemistry(Fv/Fm)weresignificantlysmallerinlow-Cathaninhigh-Caplants,likelyasaresultofagreateraccumulationoftoxicions.Consistently,whenosmoticstresswasrelievedbysupplyingplantswithgoodqualitywater(reliefperiod),bothphotosynthetic(+44%)andgrowthrates(+65%)recoveredtoamarkedlysuperiordegreeinhigh-Cathaninlow-Caplantswhichhadbeenpreviouslytreatedwith200mMNaCl.Weconcludethat(1)high-Ca2+supplyexposeoliveleavestoamoreseveredehydration,butallowedtorestrictboththeentryandtheallocationofpotentiallytoxicionstosensitiveshootorgans;(2)atransientrestrictionofwater-massflowtotheshootduringsalinizationmaybeofrelativelyminorsignificanceinOleaeuropaea,whichisverytoleranttodrought;(3)overallsalttoleranceinOleaeuropaea,asinmostevergreensclerophyllsinhabitingMediterraneanareas,tightlydependsupontheabilitytoreducewateruptakeandtranspirationduringthedry/warmperiodandtorecoverphotosyntheticandgrowthrateswhenlow-salinityfloodwaterisavailable.Therefore,datafromthepresentexperimentallowconcludethatanincreaseinrootzoneCa2+concentrationenhancestolerancetosalinitystressinoliveplants.©2008ElsevierB.V.Allrightsreserved.Keywords:Gasexchange;Ionfluxes;PhotosystemIIphotochemistry;Na+allocation;Relieffromsalinity;Waterrelations1.IntroductionSodium/calciuminteractionshavelongbeenreportedofcrucialsignificanceintheresponsesofbothglycophytesandhalophytestohighrootzoneNaClconcentrations(Epstein,1961;GreenwayandMunns,1980;Bush,1995;Cramer,2002;Zhu,2002;TesterandDavenport,2003).Onthewhole,anincreaseintheavailabilityofCa2+atrootzone(ingeneralnotgreaterthan10.0mM)hasbeenshowntoamelioratethedetrimentaleffectsofsalinitystressinmostspecies(Lynchand∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](M.Tattini).L¨auchli,1985;Davenportetal.,1997;Kinraide,1999;Cramer,2002;Tunaetal.,2007).Neverthelesssalttolerancedidnotvarybecauseofhigh-Ca2+supplyinsomespecies(AshrafandNaqvi,1991;Schmidtetal.,1993;Cramer,2002;Hern`andezetal.,2003;TesterandDavenport,2003),likelyduetobothdifferenttraitsusedto‘measure’tolerance(rootorwhole-plantgrowth,gasexchangeperformance,uptakeandallocationofNa+andCl−atorganismallevelMunns,2002;Shabalaetal.,2003)andmarkedchangesinexperimentalconditions(e.g.,actualrootzoneNa+andCa2+activitiesandintensityofsalinitystress,YeoandFlowers,1985;Cramer,2002;Husainetal.,2004).Basically,anincreaseinCa2+supplyunderexcesssoilsalin-ity(i)protectstheintegrityofcellmembranesandpreventsCa2+-deficiency(Epstein,1961;MaasandGrieve,1987;Reid0098-8472/$–seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.envexpbot.2008.01.005M.Tattini,M.L.Traversi/EnvironmentalandExperimentalBotany65(2009)72–8173andSmith,2000);(ii)enhancestheselectivityfortheuptakeandthetransportofK+overNa+,byinhibitingtheunidirectionalinfluxofNa+intotherootsanddecreasingtheNa+-stimulatedeffluxofK+(LiuandZhu,1998;Zhu,2002).Anincreaseincyto-plasmicCa2+mayactivatebothCa2+-dependentproteinkinasesandaCa2+-calmodulindependentPP-2BproteinphosphatasecapabletomodifytheNa+andK+uptakesystemstohaveahighaffinityforK+(Knightetal.,1997;Zhu,2001;Lecovrieuxetal.,2006).TheseCa2+-activatedmechanismsarethoughttobemostlyresponsiblefortheincreasedsalttoleranceinplantstreatedwithhigh-Ca2+(Bressanetal.,1998;Pardoetal.,1998).ChangesinCa2+supplymayalsoaffectotherkeymech-anismsofplant’sacclimationtoelevatedrootzoneNaClconcentrations,asthoselinkedtothesalt-inducedincreaseinABAbiosynthesis,whichisresponsibleforstomatalclo-sure(WilkinsonandDavies,2002).Anincreaseincytosolicfree-Ca2+intheguardcellsissuggestedtobeapartofthesignaltransductionchain(whichalsoincludesH2O2)