Responses of Batis maritima plants challenged with up to two-fold seawater NaCl salinity

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Batis maritima is a promising halophyte for sand-dune stabilization and saline-soil reclamation. This species has also applications in herbal medicine and as an oilseed crop. Here, we address the plant response to salinity reaching up to two-fold
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  © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com J. Plant Nutr. Soil Sci.  2010,  173,  291–299  DOI:  10.1002/jpln.200900222 291 Responsesof  Batis maritima  plants challenged with up to two-foldseawaterNaClsalinity Ahmed Debez 1,2 *, Dhouha Saadaoui 1 , InèsSlama 1 , BernhardHuchzermeyer 2 ,  and Chedly Abdelly 1 1 Laboratoire d’Adaptationdes Plantes aux Stress Abiotiques, Centre de Biotechnologie à la Technopolede Borj-Cedria, BP 901,Hammam-Lif 2050, Tunisia 2 Institut für Botanik, LeibnizUniversität Hannover, Herrenhäuser Str. 2, 30419Hannover, Germany Abstract Batis maritima   is a promising halophyte for sand-dune stabilization and saline-soil reclamation.This species has also applications in herbal medicine and as an oilseed crop. Here, we addressthe plant response to salinity reaching up to two-fold seawater concentration (0–1000 mMNaCl), with a particular emphasis on growth, water status, mineral nutrition, proline content, andphotosystem II integrity. Plant biomass production was maximal at 200 mM NaCl, and the plantssurvived even when challenged with 1000 mM NaCl. Plant water status was not impaired by thehigh accumulation of sodium in shoots, suggesting that Na + compartmentalization efficientlytook place in vacuoles. Concentrations of Mg 2+ and K + in shoots were markedly lower in salt-treated plants, while that of Ca 2+ was less affected. Soluble-sugar and chlorophyll concentra-tions were hardly affected by salinity, whereas proline concentration increased significantly inshoots of salt-treated plants. Maximum quantum efficiency ( F  v  /  F  m ), quantum yield of PSII( U PSII ), and electron-transport rate (ETR) were maximal at 200–300 mM NaCl. Both nonphoto-chemical quenching (NPQ) and photochemical quenching (qP) were salt-independent. Interest-ingly, transferring the plants previously challenged with supraoptimal salinities (400–1000 mMNaCl) to the optimal salinity (200 mM NaCl) substantially restored their growth activity. Al-together, our results indicate that  B. maritima   is an obligate halophyte, requiring high salt con-centrations for optimal growth, and surviving long-term extreme salinity. Such a performancecould be ascribed to the plant capability to use sodium for osmotic adjustment, selective absorp-tion of K + over Na + in concomitance with the stability of PSII functioning, and the absence ofphotosynthetic pigment degradation. Keywords: chlorophyll fluorescence / halophyte/ mineralnutrition / photosynthesis / proline Accepted January 21, 2010 1 Introduction About 20% of the world’s cultivated surfaces are consideredas nonfertile due to the increase of their salt content ( Sixto  et al., 2006). Semiarid and arid zones are particularly vulner-able to this increasing environmental issue ( Murillo-Amador  et al., 2006). Typically, salt stress triggers ion toxicity, osmoticstress, mineral deficiencies, and the combination of thesephysiological and biochemical disorders ( Netondo   et al.,2004). During the onset and development of salt stress withina plant, major processes, such as protein synthesis, energyand lipid metabolism, and photosynthesis are disrupted, ulti-mately resulting in the loss of plant productivity. Photosynth-esis is particularly sensitive to environmental hazards, suchas salinity. The salt-induced limitation of the photosyntheticperformance is commonly ascribed to lower stomatal conduc-tance for CO 2  ( Debez   et al., 2008), reduction in chlorophyllconcentration ( Lutts   et al., 1996), and impaired quenchingability of excessive energy through chlorophyll fluorescence( Lu   and  Vonshak  , 1999), leadingto photoinhibitionand photo-damage of photosystem II (PSII) ( Belkhodja   et al., 1994).Analysis of chlorophyll fluorescence is a nondestructive tech-nique allowing a rapid assessment of  in vivo   photosyntheticactivity ( Netondo   et al., 2004). In particular, fluorescence canfurnish precious insights regarding the ability of a plant to tol-erate abiotic stresses or the extent to which such constraintsmight have harmed PSII ( Murillo-Amador   et al., 2006), whichis of high relevance when assessing the response of photo-synthesis to environmental perturbations ( Baker  , 2008).Furthermore, chlorophyll-fluorescence data correlate withother physiological parameters, such as growth and yield( Debez   et al., 2008).Unlike almost all conventional crops, halophytes can growsuccessfully in salty soils owing to complex survival strate-gies ( Flowers   and  Colmer  , 2008). Halophytes, which re-present 1% of the world’s flora, thrive in a wide range of habi-tats, from arid regions to coastal marshes. Some halophytesrequire fresh water for germination and early establishmentbut can tolerate higher salt levels during later developmentalstages ( e.g. , vegetative and reproductive), whereas othersmay germinate at high salinities but require mild salinity for * Correspondence: Dr. A. Debez;e-mail: ahmed_debez@daad-alumni.de  maximum growth ( Debez   et al., 2003, 2004;  Koyro   and  Eisa  ,2008). In extreme cases (obligate or eu-halophytes), in-creased biomass production occurs only under increasedsalinity. Mechanisms that allow such an extraordinaryadapta-tion are still largely unknown. One of the key determinants ofsalt tolerance is the plant’s capacity to achieve osmoticadjustment by synthesizing and accumulating organicsolutes. These soluble compounds, which include solublecarbohydrates, glycine betaine, polyols, and amino acids,prevent osmotic stress by cellular osmotic adjustment, detox-ification of reactive oxygen species, protection of membraneintegrity, and stabilization of enzymes/proteins ( Ashraf   and Foolad  , 2007). Among the various organic osmolytes, prolineaccumulation in response to environmental stresses hasoften been considered as an adaptive component of stresstolerance. Besides contributing to osmotic adjustment, rolesof proline extend to maintaining intracellular redox potential( Hare   and  Cress  , 1997), cytosolic K + homeostasis ( Cuin   and Shabala  , 2005), and as protecting enzymes involved in chlor-ophyll biosynthesis ( Silva-Ortega   et al., 2008).A better understanding of how naturally adapted halophytestolerate salty soils is an important task, not only for plantbreeders and molecular biologists focusing on crop plants,but also in the perspective of promoting sustainable biosalineagriculture ( Koyro   et al., 2008). The utilization of salt-tolerantplants may be a suitable approach for the rehabilitationof sal-ine areas from both economic and environmental perspec-tives ( Galvani  , 2007). In this way, succulent species such as Salicornia bigelovii, Suaeda esteroa, Atriplex barclayana,Sesuvium portulacastrum,  and  Batis maritima   (Bataceae)have been suggested as potential candidates ( Brown   et al.,1999;  Milbrandt   and  Tinsley  , 2006;  Lokhande   et al., 2009). Batis maritima   is a C 3  perennial succulent shrub, native ofmuddy tidal-banks, mangrove swamps, salt-marshes, mud,and salt-flats in North and South America. It grows in saltmarshes at the upper edge of tidal flats, at the edge of man-grove stands, and between scattered mangroves ( Massimo  ,2003). Though not a water plant, it can endure brief floodingand long periods of waterlogged soils ( Nelson  , 1996). Owingto its significant biomass yield (up to 17 t ha –1 y –1 ),  B. mari- tima   is currently used for sand-dune stabilization, reclama-tion, and landscaping in the Middle East. Interestingly, thisspecies has applications in herbal medicine to treat eczema,psoriasis, and other skin conditions, rheumatism, gout, andblood and vein disorders ( Liogier  , 1990). Previous studiessuggested that  B. maritima   has interesting economical poten-tial as an oilseed crop with high concentrations of proteins(17%), essential amino acids, and tocopherol antioxidants.To our knowledge, data related to the behavior of  B. maritima  when exposed to extreme salinity are still scarce. In the pre-sent work, we address the response of this promising halo-phyte when challenged for 2 months with up to two-fold sea-water salinity and try to identify relevant traits that may beused as predictors of the plant performance. Furthermore, weassess the plant recovery potential following long-term expo-sure to extreme saline conditions. Plant growth, water andion relations, soluble sugar and proline concentrations, aswell as chlorophyll fluorescence (as indicator for PS II integ-rity) are considered. 2 Materials and methods 2.1 Culture conditions The experiments were performed in a greenhouse under thefollowing conditions: 300  l mol m –2 s –1 PAR, (22  ±  2)°C tem-perature, (45  ±  5)% relative humidity, and 14 h/10 h light/darkregime. Stem segments (5cm) with four opposite leaveswere taken from mother plants, disinfected for 5min in satu-rated calcium hypochlorite solution, and rinsed abundantlywith distilled water. They were then placed for 14 d in aerateddistilled water until rhizogenesis took place and transplantedinto 2 L plastic pots filled with vermiculite. The plants wereirrigated with Hoagland’s solution (pH 6.2–6.5) at the follow-ing NaCl concentrations: 0 (control), 100, 200, 300, 400, 600,800, and 1000 mM. Salinity levels were gradually increasedby 100 mM at 2 d intervals to reach the maximum level of1000 mM after 12 d of plant transplanting. Plants were har-vested after 60 d of salt treatment. Based on the resultsgained from this first experiment, the re-establishment ofplant growth under long-term exposure to high salinity wasassessed by transferring plants previously treated withsupraoptimal salinities to optimal salinity for two furthermonths. 2.2 Growth, water status, and ion relations Plants ( n   = 12 per treatment) were separated into shoots androots, and their fresh weights (FW) were determined. Sam-ples were then dried for 72 h at 65°C before dry-weight (DW)determination. Shoot and root water contents were deter-mined using the following equation:Tissue water content (mL [g DW] –1 ) = (FW – DW) / DW.Ions were extracted in HNO 3  (0.5%). Cation (Na + , K + , Ca 2+ ,and Mg 2+ ) concentrations were determined using a Varian220 FS atomic absorption spectrophotometer, whereas Cl – was assayed using coulometry (Büchler chloridometer). Theselectivity of ion accumulation for K + over Na + is of major sig-nificance for plants thriving in saline conditions. Therefore,we estimated the K + vs.  Na + selectivity ratio (S) from the ionconcentrations as:S = [([K + ] / ([K + ] + [Na + ])] shoots  / [[K + ] / ([K + ] + [Na + ])] medium .Shoot osmolality based on concentrations of Na + + K + plusthe associated anions (supposedly univalent and soluble)provides an indirect measure of the osmotic pressure in theseorgans ( Debez   et al., 2004). A minimal estimate of meanosmolality of plant tissues (mol m –3 ) was thus calculated asdescribed by  Glenn   and  Brown   (1998):2 ([Na + ] + [K + ]) / (H 2 O) (osmolmmol m –1 ),where brackets design amounts of ions ( l mol) or water (mL)per g DW. ©  2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com292 Debez, Saadaoui,Slama, Huchzermeyer, Abdelly  J. Plant Nutr. Soil Sci.  2010,  173,  291–299  2.3 Chlorophyll and proline Chlorophyll concentration was determined on fully expandedleaves ( n   = 4 per treatment) according to  Arnon   (1949).Chlorophyll a and b concentrations were calculated using theabsorbance values at 645 nm and 663 nm. Proline contentwas determined according to  Bates   et al. (1973). Leaf sam-ples (about 20 mg DW) were suspended in 1.5mL of 3%(w/v) sulfosalicylic acid to precipitate proteins and centrifugedat 14,000  g   for 10min. A 1mL aliquot of the supernatant wasthen incubated with 1mL of glacial acetic acid and 1mL ofninhydrin reagent (1.25 g ninhydrin in 30mL glacial aceticand 20mL phosphoric acid 6 M) for 1 h at 100°C before thereaction was stopped by cooling the tubes in ice. The pro-ducts were extracted with 2mL of toluene by vortex mixingand the upper (toluene) phase decanted into a glass cuvetteand absorbance read at 520 nm. Proline concentration ( n   = 4per treatment) was calculated from the absorbanceof a set ofproline standards (0–20 mg mL –1 ) assayed in an identicalmanner. Proline contribution to osmotic adjustment wasassessed by comparing the cytoplasmic concentration of thisamino acid with the ion vacuolar concentration (calculated astwice the sum of Na + and K + concentrations;  Slama   et al.,2007). It was assumed that the cytoplasmic volume repre-sents 5% of the total cell volume ( Flowers   and  Yeo  , 1986). 2.4 Chlorophyll fluorescence Modulated chlorophyll fluorescence was determinedwithintactplants in the greenhouse with a PAM-210 pulse-amplitude-modulated chlorophyll fluorometer (Heinz Walz GmbH, Effel-trich, Germany) connected to a notebook computer with data-acquisition software (DA 210). Measurements were made be-tween 10:00 a.m. and 01:00 p.m. on dark-adapted leaves for30min ( n   = 5 per treatment) using light-exclusion clips. Duringthedark-adaptedstate,allthereactioncentersandelectroncar-riersofthePSIIarere-oxidized,whichisessentialforrapidfluor-escence-induction kinetics. Minimal fluorescence ( F  o ) wasrecordedbyapplyingalow-intensityred-lightsourceof650nm,whereasmaximal fluorescence( F  m ) was measuredafter expo-sition to a saturating light pulse of 3500  l mol m –2 s –1 . Afterleaves had been continuously illuminated with actinic light, thesteady-statefluorescence( F  s )wasrecorded.Minimal( F  ′ o )andmaximal ( F  ′ m ) fluorescence of light-adapted leaves were alsoregistered using this method. The following fluorescence para-meterswerethencalculatedasdescribedby Maxwell  and John- son   (2000): maximum quantum efficiency [ F  v  /  F  m  = ( F  m  –  F  o ) /  F  m ],quantumyieldofPSII[ U PSII =( F  ′ m – F  s )/  F  ′ m ],photochemi-cal quenching [ qP   = ( F  ′ m  –  F  s ) / ( F  ′ m  –  F  ′ o )], and nonphoto-chemical quenching [ NPQ   = ( F  m  –  F  ′ m ) /   F  ′ m ]. Electron-trans-portrate(ETR)wascalculatedas ETR  = D F   /  F  ′ m × PPFD  ×0.5×0.84,withPPFD:photosyntheticphoton-fluxdensityincidentontheleaf;0.5:factorthatassumesequaldistributionofenergybe-tweenthetwophotosystems;0.84:assumedleafabsorbance. 2.5 Statistical analysis Data were subjected to one-way analysis of variance. Meanswere compared by least-significant-difference test at  p   <  5%level, using the SPSS for windows (Release 10.0, standardversion) software. 3 Results 3.1 Growth, mineral nutrition, and water status The survival rate of  B. maritima   plants challenged with up to1000 mM NaCl for 60 d was 100%. Low to moderate salinetreatments (100–300 mM NaCl) significantly enhanced shootDW, with an optimum at 200 mM NaCl (+122% of the controlvalue; Fig.1A). Further increasing salinity resulted in a pro-gressive decrease of this parameter (approximately –33%relative to the control at 1000 mM NaCl). Interestingly, rootDW was unaffected over the whole salinity range (Fig.1A).Root-to-shoot DW ratio significantly decreased with increas-ingsalinity, thelowestvaluesbeingregisteredat200–300mMNaCl (approximately –50% as compared to the control)(Fig.1B). At 1000 mM NaCl, the reduction was 21% of thecontrol, owing to the strong decline of shoot DW. Theresponses of both shoot height and root length to salinitywere similar to that of biomass production, with a significantenhancement up to 200 mM NaCl, followed by a progressivedecrease at salinities equal or higher than 300 mM NaCl(Fig.1C). Nevertheless, the values of both morphologicalparameters remained similar to those of the control. ©  2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 0.00.10.20.3da a ababcc c bcRoot length1.02.03.04.05.06.00.0 AB 1.02.03.04.05.06.00.0 AB 0.00.10.20.3    R  o  o   t   D   W  –   t  o  –  s   h  o  o   t   D   W  r  a   t   i  o  da a ab   abcc c bc1.02.03.04.05.06.0    D  r  y  w  e   i  g   h   t   /  g  p   l  a  n   t   –   1  b0.0 AB 1.02.03.04.05.06.0 RootsShoots dc baa acab b ab  ab aba a0.0 AB ab05101520250 100 200 300 400 600 800 1000 b caa a a a bc0510152025    L  e  n  g   t   h   /  c  m 0 100 200 300 400 600 800 1000 NaCl treatment (mM)  b caa a a a bccd d bcab bc C cda bc RootShoot 0.00.10.20.3da a ab   abcc c bcRoot length1.02.03.04.05.06.00.0 AB 1.02.03.04.05.06.00.0 AB 0.00.10.20.3da a ab   abcc c bc1.02.03.04.05.06.0 b0.0 AB 1.02.03.04.05.06.0 RootsShoots dc baa acab b ab  ab aba a0.0 AB ab05101520250 100 200 300 400 600 800 1000 b caa a a a bc05101520250 100 200 300 400 600 800 1000 b caa a a a bccd d bcab bc C cda bc RootShoot Figure 1:  Dry weight (A), Root-to-shoot DW ratio (B), andmorphological traits (C) of  B. maritima   plants exposed to differentsalinities for 2 months (see section 2;  n   = 12  ±  SE per treatment). Foreach plant tissue, values with at least identical letter were notsignificantly different at  p   <  5%. J. Plant Nutr. Soil Sci.  2010,  173,  291–299 Responses of  Batis maritima   to salinity 293  Sodium was significantly accumulated in shoots and to amuch lesser extent in roots following salt exposure (Fig.2A).For instance, shoot Na + concentration of 1000 mM–NaClsalt-treated plants was three-fold higher than that of the con-trol. The same pattern was found for Cl – (data not shown).The marked Na + accumulation in shoots at 1000 mM NaClwas concomitant with a significant reduction in K + and Mg 2+ concentrations (–62% and –53% relative to the control for K + and Mg 2+ , respectively; Figs. 2B and 2C). Shoot and rootCa 2+ concentrations were less affected by NaCl (Fig.2D).Interestingly,  B. maritima   displayed a pronounced selectivityfor K + uptake over Na + , as reflected by the significantincrease of the K + vs.  Na + selectivity ratio (S) with salt treat-ments (Fig.3A). For instance, S was 28-fold higher at1000 mM NaCl than in the control. Water content of bothshoots and roots were also significantly improved at 200 mMNaCl, but were significantly affected at supraoptimal sali-nities, especially in shoots (Fig.3B). Better shoot hydration atoptimal salinity was concomitant with significantly highershoot osmolarity relative to that of the medium, especially atNaCl concentrations exceeding200 mM NaCl (Fig.3C). 3.2 Proline and chlorophyll concentrations Proline accumulated more in shoots than in roots. Shoot pro-line concentration increased up to 600 mM–NaCl treatment(2.5-fold of the control value), before significantly decreasingwithin the 800 to 1000 mM–NaCl range (Fig.4A). On theother hand, the cytoplasmic concentration of proline was verylow for the 100 to1000 mM–NaCl–treated plants (about 15%)as compared to the vacuolar ion concentration (Fig.4B).Generally, chlorophyll a and b concentrations were hardlyaffected by 2 month exposure to 0–300 mM NaCl, butshowed a significant decline at 600–800 mM NaCl (Figs. 5Aand 5B, respectively). 3.3 Chlorophyll fluorescence F  v  /  F  m  was significantly enhanced up to 600 mM NaCl (+26%relative to the control at 600 mM NaCl) (Fig.6A). Both PSIIyield ( U PSII ) and ETR were significantly increased in the 200to 300 mM–NaCl range (+43% and +67% relative to the con-trol, respectively), before progressively decreasing at highersalinities (Figs. 6B and 6C). Yet, even at the highest salinity(1000 mM NaCl), the recorded values for these parameterswere close to that of the control. Neither qP (Fig.6D) norNPQ (Fig.6E) were significantly affected by the saline treat-ments. 4 Discussion Halophytes are plants that complete their life cycle in soilswith salinity concentrations above 200 mM NaCl ( Flowers  and  Colmer  , 2008). Yet, their natural biotopes are character-ized by spatial and/or temporal fluctuations in the salinitylevel. According to our findings,  B. maritima   can be consid-ered as an obligate halophyte, since 200 mM–NaCl salinitywas optimal for its growth activity, expressed in terms of bio-mass production and morphological traits (Figs. 1A and 1C).Further, the plant was able to maintain growth activity at sali-nity as high as 1000 mM NaCl and displayed a high aptitudeof growth recovery following long-term exposure to extremesalinities (up to two-fold seawater salt concentration; data notshown). Salt requirement for maximal growth has beenreported in several succulent halophytes, such as  Haloscaria pergranulata   (200 mM NaCl),  Sesuvium portulacastrum  ©  2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 02468a bcd cde edec c A 00.40.81.21.62 B edababc ab bc ca dc ba a 00.10.20.30.4dca a a abc ab a abc c abcabc bc abc 0 100 200 300 400 600 800 1000 C 00.10.20.30.40.50.6 D 0 100 200 300 400 600 800 1000 ba b b ab bc  baaa a b b b RootsShoots    N  a    +    c  o  n  c  e  n   t  r  a   t   i  o  n   /  m  m  o   l   (  g   D   W   )   –   1 02468   a bcd cde edec c a bc c ccd d e A 02 B edababc ab bc ca cd cdc 0dca a a abc bc0 100 200 300 400 600 800 1000 C 0 D 0 100 200 300 400 600 800 ba b b ab bc bRootsShoots   RootsShoots NaCl treatment (mM) 02468a bcd cde edec c A 02 B edababc ab bc ca dc ba a 0dca a a abc ab a abc c abcabc bc abc 0 100 200 300 400 600 800 1000 C 0 D 0 100 200 300 400 600 800 1000 ba b b ab bc  baaa a b b b   RootsShoots02468a bcd cde edec c a bc c ccd d e A 0 B edababc ab bc ca cd cdc 0dca a a abc bc0 100 200 300 400 600 800 1000 C 0 D 0 100 200 300 400 600 800 ba b b ab bc b   RootsShoots   RootsShoots    M  g    2   +    c  o  n  c  e  n   t  r  a   t   i  o  n   /  m  m  o   l   (  g   D   W   )   –   1    K    +    c  o  n  c  e  n   t  r  a   t   i  o  n   /  m  m  o   l   (  g   D   W   )   –   1    C  a    2   +    c  o  n  c  e  n   t  r  a   t   i  o  n   /  m  m  o   l   (  g   D   W   )   –   1 NaCl treatment (mM) Figure 2:  Na + (A), K + (B), Mg 2+ (C), and Ca 2+ (D)concentrations in shoots and roots of  B. maritima  plants exposed to different salinitiesfor 2 months(see section 2;  n   = 12  ±  SE per treatment). Foreach plant tissue, values with at least one sameletter were not significantly different at  p   <  5%. 294 Debez, Saadaoui,Slama, Huchzermeyer, Abdelly  J. Plant Nutr. Soil Sci.  2010,  173,  291–299  (400 mM NaCl), and  Cakile maritima   (100 mM NaCl) ( Short  and  Colmer  , 1999;  Messedi   et al., 2003;  Debez   et al., 2004).The positive effect of salt on biomass production at100–300 mM NaCl was more pronounced in shoots than inroots, resulting in significantly lower root DW–to–shoot DWratio (Fig.1B). This suggests that under favorable conditions,the root performance may sustain the shoot-biomass produc-tion of  B. maritima  , which is consistent with previous reportson salt-tolerant species such as  Sarcocornia fruticosa  ( Redondo-Gómez   et al., 2006) and  C. maritima   ( Debez   et al.,2008).Halophytes accumulate and compartmentalize large amountsof Na + and Cl – in vacuoles in order to lower the osmoticpotential, which enables them to thrive in salt-rich environ-ments ( Flowers   and  Colmer  , 2008). In  B. maritima  , themarked accumulation of Na + was concomitant (Fig.2A) withsignificantly higher shoot hydration at optimal salinity for plantgrowth (Fig.3B), whereas no significant impact on this para-meter was observed at supraoptimal salinities. Furthermore,shoot osmolality of salt-treated plants was significantly higherthan that of the external medium over the whole salinity range(Fig.3C). This is indicative of the efficient compartmentaliza-tion of salt inside shoot cells, away from the apoplast ( Munns  and  Passioura  , 1984), so that water supply was notdisrupted. Similarly, several euhalophytes including  Bassia hyssopifolia, Suaeda europaea, Atriplex occidentalis  , and C. maritima   succeededin maintainingsuch a constant osmol-ality gradient between their shoot tissues and the externalsolution, even when challenged with high salinity ( Glenn   and O’Leary  , 1985;  Debez   et al., 2004). The high Na + mean con-centrations (1.15 M on average, calculated by relating Na + content to water content) in shoot tissues of plants growing inthe 600 to 1000 mM–NaCl range did not appear to be harmfulfor the plant, with a reduction in shoot biomass of approxi-mately 30% as compared to the control, which provides afurther evidence for the includer character of  B. maritima.  Aspreviously shown in the halophytes  A. halimus   ( Debez   et al.,2003) and  S. portulacastrum   ( Messedi   et al., 2003), the inclu-der character is of vital eco-physiologicalsignificance for spe-cies such as  B. maritima   lacking morphological structures ofsalt removal on the leaf surface.The restriction of  B. maritima   growth observed at supraopti-mal salinities could result from salt-induced nutritional imbal-ances, as previously documented for  A. halimus   and  C. mari- tima   ( Debez   et al., 2003, 2004). Potassium and magnesium concentrations were severely depressed (Figs. 2B and 2C,respectively), whereas calcium concentration was less ©  2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com    O  s  m  o   l  a  r   i   t  y   /  o  s  m  o   l  m  o   l   –   3 01000200030000 100 200 300 400 800 1000600 NaCl treatment (mM) 4000 C a b bcc cdcdeeaa b bccdd bdaa a aaaMediumShootsRoots205101525    K    +    /   N  a    +    s  e   l  e  c   t   i  v   i   t  y  c  o  e   f   f   i  c   i  e  n   t ,   S 0 A  bacd df ef 2051015250 A  bacd df ef 01000200030000 100 200 300 400 800 10006004000 C a b bcc cdcd   eeaa b bccdd bdaa a aaaMediumShootsRoots    W  a   t  e  r  c  o  n   t  e  n   t   /  m   L   (  g   D   W   )   –   1 82468 B c bc bcaa bc dab cdeeed b baShootsRootsd82468 B c bc bcaa bc dab cdeeed b baShootsRootsd Figure 3:  Na +  /K + selectivity ratio (A), water content (B), and tissueosmolarity (C) of  B. maritima   plants exposed to different salinities for2 months (see section 2;  n   = 12  ±  SE per treatment). For eachparameter, values with at least one identical letter were notsignificantly different at  p   <  5%. cabcac bc bcabccacabcabcab3691215    P  r  o   l   i  n  e  c  o  n   t  e  n   t   /  μ  m  o   l   (  g   D   W   )   –   1 A ShootsRoots 050010001500200025003000    C  o  n  c  e  n   t  r  a   t   i  o  n   (  m   M   ) 100 200 300 400 600 800 1000 BNaCl treatment (mM) 2 (Na + +K  + )Cytoplasmic proline 0 cccabcac bc bcabccacabcabcab3691215 A ShootsRoots 050010001500200025003000100 200 300 400 600 800 1000 B  2 (Na + +K  + )Cytoplasmic proline2 (Na + +K  + )Cytoplasmic proline 0 cc Figure 4:  Proline concentration (A) and its concentration incomparison to tha Na and K concentration (B) in  B. maritima   plantsexposed to different salinities for 2 months (see section 2;  n   = 4  ±  SEper treatment). For each parameter, values with at least one identicalletter were not significantly different at  p   <  5%. J. Plant Nutr. Soil Sci.  2010,  173,  291–299 Responses of  Batis maritima   to salinity 295
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