JXB Advance Access originally published online on July 12, 2005
Journal of Experimental Botany 2005 56(419):2365-2378; doi:10.1093/jxb/eri229
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
RESEARCH PAPER |
Salt tolerance in wild Hordeum species is associated with restricted entry of Na+ and Cl– into the shoots
1School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
2CRC for Plant-Based Management of Dryland Salinity, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
3Genetic Resources Group, Department of Crop Sciences, Swedish University of Agricultural Sciences, SE-230 53 Alnarp, Sweden
* To whom correspondence should be addressed. Fax: +61 8 6488 1108. E-mail: tdcolmer{at}cyllene.uwa.edu.au
Received 15 September 2004; Accepted 16 May 2005
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Eight wild Hordeum species: H. bogdanii, H. intercedens, H. jubatum, H. lechleri, H. marinum, H. murinum, H. patagonicum, and H. secalinum, and cultivated barley (H. vulgare) were grown in nutrient solution containing 0.2 (control), 150, 300, or 450 mol m–3 NaCl. In saline conditions, the wild Hordeum species (except H. murinum) had better Na+ and Cl– ‘exclusion’, and maintained higher leaf K+, compared with H. vulgare. For example, at 150 mol m–3 NaCl, the K+:Na+ in the youngest, fully expanded leaf blades of the wild Hordeum species was, on average, 5.2 compared with 0.8 in H. vulgare. In H. marinum grown in 300 mol m–3 NaCl, K+ contributed 35% to leaf
, whereas Na+ and Cl– accounted for only 6% and 10%, respectively. By comparison, in H. vulgare grown at 300 mol m–3 NaCl, K+ accounted for 19% and Na+ and Cl– made up 21% and 25% of leaf , respectively. At 300 mol m–3 NaCl, glycinebetaine and proline together contributed almost 15% to in the expanding leaf blades of H. marinum, compared with 8% in H. vulgare. Decreased tissue water content under saline conditions made a substantial contribution to declines in leaf in the wild Hordeum species, but not in H. vulgare. A number of the wild Hordeum species were markedly more salt tolerant than H. vulgare. H. marinum and H. intercedens, as examples, had relative growth rates 30% higher than H. vulgare in 450 mol m–3 NaCl. Hordeum vulgare also suffered up to 6-fold more dead leaf material (as a proportion of shoot dry mass) than the wild Hordeum species. Thus, several salt-tolerant wild Hordeum species were identified, and these showed an exceptional capacity to ‘exclude’ Na+ and Cl– from their shoots. Key words: Asparagine, barley (Hordeum vulgare), Cl–, glycinebetaine, K+, Na+, proline, osmotic potential, salt tolerance, Triticeae, wild relatives
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Saline environments affect plant growth in two ways: (i) salts in the soil solution lower the external water potential, reducing cell turgor; and (ii) salts taken up by plants in the transpiration stream accumulate in leaves and become toxic (Greenway and Munns, 1980
; Munns and Termaat, 1986). Munns et al. (1995) have described the effect of these dual stresses on the growth of wheat and barley as a ‘two-phase growth response to salinity’. In the first ‘osmotic’ phase, salts in the external solution induce water stress which causes the large, almost immediate decrease in plant growth. In the second ‘salt-specific’ phase, ions accumulating in the leaves reach toxic levels, causing necrosis and reducing the photosynthetic area, and subsequently further declines in growth (Munns, 1993; Munns et al., 1995). The time between the first and second phases can be anything from hours to days to weeks, depending on the sensitivity of the plant to salt and its ability to ‘exclude’ Na+ and Cl– from the shoot (i.e. restrict rates of entry of these ions). Munns et al. (1995) suggest that the reduction in growth during the first phase is similar amongst genotypes of wheat or barley, and it is often not until the second phase that differences in salt tolerance become apparent. This variation amongst genotypes in tolerance of prolonged salinity was attributed to differences in ability to avoid ion toxicity in the shoot (Munns et al., 1995).
Tolerant members of the Triticeae avoid ion toxicity in the shoot by restricting the rate of entry of Na+ and Cl– and by minimizing the adverse affects of these ions when in shoot tissues. Bread wheat (Triticum aestivum), for example, restricts Na+ transport to leaf tissues (i.e. through Na+ ‘exclusion’) and maintains high selectivity of K+ over Na+ (Gorham et al., 1986; Gorham, 1993). Na+ ‘exclusion’ and K+/Na+ selectivity in barley (Hordeum vulgare ssp. vulgare) are poor by comparison (Gorham et al., 1990a; Munns et al., 2002); however, the adverse affects of Na+ within leaves of barley are minimized by its compartmentalization into vacuoles (with Cl–) and the production of organic solutes to osmotically ‘balance’ the cytosol (Greenway and Munns, 1980; Munns, 2002; Tester and Davenport, 2003). The importance to salt tolerance of restricting entry of Cl–, in addition to entry of Na+, is recognized (Munns, 2002), and barley genotypes differ in rates of Cl– uptake (Greenway, 1962); however, amongst Triticum species there appears to be much less variation in Cl– ‘exclusion’, as compared with Na+ ‘exclusion’ (Husain et al., 2004; Shah et al., 1987).
The difference in Na+ ‘exclusion’ and K+/Na+ selectivity between bread wheat and barley has been partially attributed to the presence of the ‘enhanced K+/Na+ discrimination’ character in bread wheat, but not in barley (Gorham et al., 1990a, b). This character has also been identified in some wild Triticeae species (Gorham, 1993). The genetics and physiology of this trait have been described for wheat and its ancestors (Gorham et al., 1990b; Gorham, 1993; Dvorák et al., 1994), leading to significant advances in the understanding of variation in salt tolerance amongst members of the genus Triticum. In the case of the genus Hordeum, Na+ ‘exclusion’ and K+ uptake have largely been investigated in species with the I genome (barley and H. vulgare ssp. spontaneum) (Greenway, 1962; Storey and Wyn Jones, 1978a; Gorham et al., 1990a; Forster et al., 1994), despite cytogenetical studies indicating that the genus Hordeum contains four distinct genomes; H, I, X, and Y (Jacobsen and von Bothmer, 1992; Svitashev et al., 1994). However, the limited data available on K+/Na+ discrimination in Hordeum species with the H, X, or Y genomes indicates there may be significant variation in this trait within the genus (Suhayda et al., 1992; Gorham, 1993; Huang and Redmann, 1995; Howes Keiffer and Ungar, 1997b). For example, Suhayda et al. (1992) reported that shoot Na+ concentrations in H. jubatum (H genome) were three to four times lower than those in H. vulgare, when plants were grown at 150 mol m–3 NaCl. The present study therefore evaluated a range of wild Hordeum species for salt tolerance and leaf ion concentrations and compared these with H. vulgare, under a range of external NaCl treatments.
Although H. vulgare is regarded as salt tolerant compared with bread wheat and other cultivated Triticeae, barley cultivars still experienced a 55–58% decline in biomass at 150 mol m–3 NaCl (i.e. less than one-third the NaCl concentration in sea water) (Greenway, 1962). However, an ecogeographical study of the genus Hordeum (von Bothmer et al., 1995) estimated that more than half of the wild, or non-cultivated, Hordeum species occupy habitats that are saline; ranging from mildly saline pastures occupied by the progenitor of H. vulgare, to salt lake environments habituated, for example, by species of H. patagonicum (von Bothmer et al., 1995). However, data are lacking to confirm the putative salt tolerance of these wild Hordeum species. The few studies that have been conducted on salt tolerance in wild Hordeum species have generally been ecological in nature, or focused upon germination or survival of seedlings (Nevo et al., 1993; Howes Keiffer and Ungar, 1997a; Mano and Takeda, 1998). However, the ability to germinate or survive in saline nutrient solution is a poor indicator of salt tolerance (Richards et al., 1987; Rawson et al., 1988), particularly for annual species where biomass production is a better predictor of yield (Munns, 2002). In addition, with the exception of work on H. jubatum (see above) (Suhayda et al., 1992; Huang and Redmann, 1995; Howes Keiffer and Ungar, 1997b), and a report summarizing shoot K+:Na+ ratios in some wild Hordeum species (Gorham, 1993), traits contributing to salt tolerance in wild Hordeum species are largely unexplored.
This study evaluated the tolerance of eight wild Hordeum species, and cultivated barley, to growth in nutrient solution containing 0.2 (control), 150, 300, or 450 mol m–3 NaCl. Osmotic potential () of expressed leaf sap, and Na+, Cl–, and K+ concentrations, in variously aged leaf tissues were compared for the various species. Concentrations of asparagine (Asn), glycinebetaine, and proline (Pro) were compared for leaf tissues of H. vulgare and H. marinum. The species originated from saline, intermediate, and non-saline habitats (R von Bothmer, unpublished field notes). Hordeum vulgare ssp. vulgare and H. jubatum were included since the responses of these species to saline conditions had been documented (Greenway, 1962; Gorham et al., 1990a; Suhayda et al., 1992). The study identified a number of Hordeum species that were markedly more salt tolerant than H. vulgare, and which demonstrated highly efficient Na+ and Cl– ‘exclusion’ and better maintenance of leaf K+ concentrations, at high external NaCl. The present findings are discussed in the context of understanding of salt tolerance in the Triticeae.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Plant materials and culture
Salt tolerance was evaluated in nine species from the genus Hordeum (Table 1). The species studied, represent: (i) the four taxonomic sections of the genus; Hordeum, Stenostachys, Anisolepis, and Critesion; (ii) include an example of each of the four genomic designations in the genus (I, Y, X, or H); and (iii) occupy habitats of varying salinities, ranging from non-saline meadows to salt marshes (von Bothmer et al., 1995
).
|
Seeds were obtained from the Hordeum Collection at the Nordic Gene Bank (Alnarp, Sweden), with the exception of Hordeum vulgare L. ssp. vulgare cv. ‘Golf’, that were provided by Svalöf Weibull AB. Germination of H. bogdanii was poor, only allowing a limited analysis of this accession.
Seeds were surface-sterilized with 0.04% (w/v) sodium hypochlorite for 45 s and rinsed thoroughly with deionized water. Seeds were then imbibed in aerated 0.5 mol m–3 CaSO4 for 3 h before being placed on plastic mesh floating on 0.1 concentration aerated nutrient solution in darkness in pots placed in a 20/15 °C (day/night) controlled environment chamber. The composition of the nutrient solution at full strength was (mol m–3): K+ 5.60, Ca2+ 4.00, Mg2+ 0.40, 
0.625, 
4.375, 
4.40, 
0.20, Na+ 0.20, 
0.10; and the micronutrients (mmol m–3): Cl– 50, B 25, Mn 2, Zn 2, Ni 1, Cu 0.5, Mo 0.5, ethylenediaminetetra-acetic acid ferric monosodium salt (Fe3+) 50. The solution also contained 2.5 mol m–3 2-[N-morpholino]ethanesulphonic acid (MES) and the pH was adjusted to 6.5 with KOH (the final K+ concentration as above). All chemicals used were analytical grade.
Germination of the species was scheduled based on a germination trial (data not shown) to provide plants at a similar developmental stage (2.0–2.5 leaves) at the onset of NaCl treatments. Hordeum bogdanii, H. jubatum, H. lechleri, and H. patagonicum were germinated (as described above) in darkness for 7 d and then exposed to 0.25 concentration nutrient solution and 490 µmol m–2 s–1 PAR (12 h light/dark) for an additional 6 d, before being transferred to pots of aerated, full-strength nutrient solution. Prior to being transferred to pots of aerated, full-strength nutrient solution, H. intercedens and H. secalinum were germinated in darkness for 7 d and then exposed to 0.25 concentration nutrient solution and 490 µmol m–2 s–1 PAR (12 h light/dark) for an additional 3 d. For H. marinum and H. murinum, it was 5 d and then 3 d. For H. vulgare it was 5 d and then 2 d. Each 4.5 dm3 plastic pot initially held four seedlings, with one removed at the time of the initial harvest when treatments were imposed (see below). Plants were held in the lids using flexible pieces of polystyrene foam. The pots and lids were covered with aluminium foil to ensure the roots were in darkness.
Experimental design and NaCl treatments
The plants were exposed to one of four NaCl concentrations: 0.2 (control), 150, 300, or 450 mol m–3. This range of concentrations was chosen to reflect the expected wide variation in salt tolerance amongst the diverse Hordeum species.
Each speciesxNaCl treatment combination was represented by three replicate pots. Pots were arranged in a randomized complete block design with three blocks. At the time treatments were imposed, an initial harvest was taken (i.e. leaving three plants per pot); shoot and root dry mass were measured and plant developmental stages recorded. NaCl treatments were initiated 7 d after the seedlings were transplanted into 4.5 dm3 plastic pots. NaCl concentrations were increased by 50 mol m–3 d–1 until the prescribed treatment concentrations were reached. The NaCl was added towards the end of each artificial day. After reaching the final NaCl concentrations, treatments were maintained for 16–21 d (plants were harvested as replicate blocks over the final 5 d). All nutrient solutions were renewed every 7 d throughout the experiment.
Harvest procedure
All pots in block one (i.e. the first replicate of each speciesxNaCl treatment combination) were harvested first (pots selected randomly), then block two and finally block three. The roots and stem base of each plant were rinsed three times, for 10 s each time, in deionized water. The roots were separated from the shoot, blotted dry, and set aside. All main tillers were divided into five leaf blade/tissue classes: (i) expanding leaf blades (the sheath was slit open to allow the entire leaf blade to be retrieved); (ii) youngest fully expanded leaf blades (no sheath); (iii) second youngest fully expanded leaf blades (no sheath); (iv) dead leaf tissues; (v) other, including stems, sheaths and all other ‘green’ and turgid leaf blades other than the three youngest (see above).
Fresh masses were recorded for the expanding and youngest fully expanded leaf blades to enable assessment of water content after the dry mass data were also taken. A subsample of each of these two tissues was taken immediately, sealed into an air-tight cryo-vial and frozen at –70 °C for subsequent measurement of sap (see below). The expanding leaf blades, the youngest fully expanded, and second youngest fully expanded leaf blades were wrapped in aluminium foil and frozen in liquid N2 and then lyophilized, after which dry masses were recorded. The roots, dead leaves, and ‘other’ tissues were placed in paper bags and dried at 60 °C and the dry masses recorded.
Growth analysis
The whole plant relative growth rate (RGR) was calculated from the dry mass data taken at initial and final harvests, using the formula given by Venus and Causton (1979). The percentage of dead leaf material of the whole shoot dry mass was assessed.
Analyses of Na+, Cl–, and K+ in variously aged leaf blades
The lyophilized tissues of the expanding, youngest fully expanded, and second youngest fully expanded leaf blades were ground to a fine powder in a ball mill and subsamples of approximately 0.02 g dry mass were used. Ions were extracted in 10 ml hot water (70 °C for 3 h) and samples were then shaken at room temperature for 2 d. The concentrations of Na+ and K+ in dilutions were determined by flame photometry (Flame Photometer 410; Corning Halstead, UK). Cl– concentrations were determined using a Buchler-Cotlove Chloridometer (Model 4-2000: Buchler Instruments, New Jersey USA). Recoveries of Na+, Cl–, and K+ from plant standards (State Chemistry Laboratory, Victoria, Australia) were, respectively, 85, 83, and 87%. The data presented have not been adjusted.
Determination of organic solute concentrations in leaf blades of H. vulgare and H. marinum
Lyophilized and ground subsamples of expanding, youngest fully expanded, and second youngest fully expanded leaf blades were used for the organic solute analyses. Tissues were extracted using the procedure described by Fan et al. (1993). In short, 3 ml of ice-cold 5% (v/v) perchloric acid was added to 
0.1 g of ground tissue, mixed, and centrifuged at 12 096 g for 30 min. Supernatant was collected and stored in a glass vial on ice. The pellet was again extracted in 3 ml of ice-cold 5% (v/v) perchloric acid, and the second supernatant was combined with that collected previously. pH of the supernatant was adjusted to 3.5±0.05 using K2CO3 to precipitate the perchlorate, after which the sample was again centrifuged, the supernatant collected, and the volume determined. The extract was passed through a 0.2 µm filter prior to injection into a HPLC system. The HPLC system (Waters Corporation, Milford, MA, USA) consisted of a 600E pump, 717 auto-sampler, 996 photodiode array detector, and Millennium Chromatography Manager software. The system was equipped with a Sugar-Pak column (300 mm lengthx6.5 mm diameter) (Waters Corporation) in a column heater maintained at 90 °C. The methods were as described by Naidu (1998), except that Ca-EDTA in the mobile phase was increased from 5 to 7.5 mg l–1. Recoveries of Asn, glycinebetaine, and Pro from spiked samples of Hordeum shoot tissue were, respectively, 82, 96, and 94%. The data presented have not been adjusted.
Expressed leaf sap osmotic potential ()
To determine for expanding and youngest fully expanded leaf blades, frozen leaf samples were allowed to thaw to room temperature while in their sealed vials, before being pressed. The expressed sap was analysed using a dew-point depression osmometer (WESCOR, Inc., Logan, UT, USA; C-52 sample chamber and HR-33T dew-point microvoltmeter).
Estimated contributions of ions and organic solutes to leaf sap in H. vulgare and H. marinum
The of a solution is given by –nRT/V, where n=number of solute molecules, R=the universal gas constant, T=temperature in °K, and V=volume in litres. In saline conditions, both solute accumulation and a lower water content can cause to become more negative. The contribution of reduced tissue water content was estimated by comparing leaf water content (ml g–1 dry mass) of plants grown in the non-saline and 300 mol m–3 NaCl solutions. The contributions of ions (Na+, Cl–, and K+) and organic solutes (Asn, glycinebetaine, and Pro) to were calculated for H. vulgare and H. marinum from the data on ion and organic solute concentrations in variously aged leaf blades (µmol g–1 dry mass) and leaf water contents (ml g–1 dry mass) of plants grown in the non-saline and 300 mol m–3 NaCl solutions.
Statistical analyses
An ANOVA was performed on the growth parameters (shoot and root dry masses, RGR, and proportion of dead leaf material) to determine whether species influenced responses of these parameters to the various NaCl treatments. The leaf , tissue Na+, Cl–, and K+ concentrations, K+:Na+ ratios, and organic solute concentrations were evaluated using ANOVA to determine the influence of species and NaCl treatment. The following regression analyses were performed to determine whether inherent growth rate (i.e. vigour) was related to salt tolerance: whole plant dry mass in 150, 300, or 450 mol m–3 NaCl (as % of control), against whole plant dry mass (control); RGR in 150, 300, or 450 mol m–3 NaCl (as % of control), against RGR (control). Means were compared using the LSD (P=0.05), and all means presented in the tables and figures are accompanied by standard errors (GenStat, 6th edn; VSN International; www.vsn-intl.com).
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Growth analyses
Shoot and root dry mass:
In the non-saline solution, H. vulgare had shoot and root dry masses approximately 5-fold higher than those of the other Hordeum species (Fig. 1; P <0.001). Hordeum murinum and H. marinum also had relatively high shoot (2.3 and 1.4 g, respectively) and root (0.8 and 0.5 g, respectively) dry masses, compared with the remaining species which ranged from 0.7 to 0.3 g for shoots, and 0.4 to 0.1 g for roots. The NaCl treatments caused shoot and root dry masses to decline in all species; however, H. murinum, H. marinum and, in particular, H. vulgare maintained the largest shoot and root dry masses throughout all NaCl concentrations. Hordeum bogdanii, H. lechleri, and H. jubatum had the lowest shoot and root dry masses in all the NaCl treatments.
|
In terms of percentage reductions in dry mass, compared with controls, the NaCl treatments affected H. marinum and H. intercedens least, with whole plant dry masses in the 150 mol m–3 NaCl reduced by 33% and 34%, respectively. In all the other species, the 150 mol m–3 NaCl solution caused a 50% or greater reduction in whole plant dry mass. In the 300 mol m–3 NaCl solution, H. marinum had the smallest reduction in dry mass, which was 58%, compared with the remaining species in which dry masses were reduced by 70–80%. In the 450 mol m–3 NaCl, the reduction in dry mass for H. marinum was 75%, while the reduction in dry mass ranged from 81–91% in the remaining species.
Regression analysis of whole plant dry mass (as % of control) in 150, 300, or 450 mol m–3 NaCl against whole plant dry mass (control) was not significant (not shown; P >0.05, r2=0.05); showing that the variation in salt tolerance (as % of control) was not merely due to inherent differences in size of the various species.
Relative growth rate:
Whole plant RGRs did not vary greatly amongst the species when in the non-saline solution, with the majority of the species having rates between 184 and 200 mg g–1 d–1 (Table 2). Hordeum murinum and H. intercedens were exceptions, having rates of 240 and 211 mg g–1 d–1, respectively, in the non-saline solution. NaCl caused a decline in RGR in all species (P <0.001).
|
In terms of the percentage reductions in RGRs when in the saline solution, compared with non-saline controls, H. marinum and H. intercedens had the smallest reductions (34% and 38% in the 450 mol m–3 NaCl solution, respectively) (Table 2; P <0.001). These two species also had the smallest reductions in RGR when in the 150 and 300 mol m–3 NaCl solutions; RGR in H. marinum, for example, was reduced by 10% and 21%, respectively. By contrast, H. vulgare, H. jubatum, and H. lechleri experienced the largest reductions in RGR in the NaCl treatments; for example, RGR decreased by
50% in the 450 mol m–3 NaCl solution. These species also experienced the largest reductions in RGR in the other NaCl treatments, with RGR in H. vulgare, for example, reduced by 17% and 39% in the 150 and 300 mol m–3 NaCl solutions, respectively. Regression analysis of RGR (as % of control) in 150, 300, or 450 mol m–3 NaCl against RGR (control) was not significant (not shown; P >0.05, r2=0.33); showing that the differences amongst the genotypes in salt tolerance (RGR as % of control) were not merely related to inherent differences in RGR.
Proportion of dead leaf material:
In the non-saline and 150 mol m–3 NaCl solutions, the amount of dead leaf material (as a percentage of shoot dry mass) on any of the genotypes was at most 4% (Fig. 2). In the 300 mol m–3 NaCl solution, the percentages of dead leaf material in H. vulgare and H. patagonicum (11% and 7%), were higher than for the majority of the other species (P <0.001). In the 450 mol m–3 NaCl, differences amongst the species were even larger, with the percentages of dead leaf material in H. vulgare, H. patagonicum, and H. murinum being approximately double those in any other species. In particular, the percentage of dead leaf material in H. vulgare in the 450 mol m–3 NaCl was 17%, almost six times that in H. marinum, the species with the lowest amount of dead leaf material, at 3% (P <0.001).
|
Concentrations of Na+, Cl–, and K+ in variously aged leaf blades
Na+:
For plants in the non-saline solution, there was no difference amongst species in leaf blade Na+ concentrations (Fig. 3). NaCl treatments increased the concentration of Na+ in leaf blades of all species, well above those in non-saline controls (P <0.001). With the exceptions of H. vulgare, H. murinum, and H. patagonicum, the other species showed relatively little variation in leaf blade Na+ concentrations in the 150, 300, or 450 mol m–3 NaCl solutions. For example, in the youngest fully expanded leaf blades of H. secalinum, Na+ concentrations in plants in the 150, 300, or 450 mol m–3 NaCl solutions were 387, 416, and 440 µmol g–1 dry mass, respectively. However, in H. vulgare and H. murinum (and to a lesser extent, H. patagonicum) increases in external NaCl to 300 mol m–3 or above, caused marked increases in Na+ concentrations in leaf tissues. For example in the youngest fully expanded leaf blades of H. murinum, Na+ concentrations in the plants in 150, 300, or 450 mol m–3 NaCl were 127, 438, and 1835 µmol g–1 dry mass, respectively.
|
In general, H. vulgare, H. murinum, and H. patagonicum had higher Na+ concentrations in all leaf tissues and at all NaCl treatments, compared with the other species. For plants in the 450 mol m–3 NaCl solution, for example, the expanding leaf blades of H. vulgare, H. murinum, and H. patagonicum contained 2132, 1286, and 497 µmol Na+ g–1 dry mass, respectively, whereas in the other species it ranged from 285 (H. bogdanii) to as low as 132 (H. marinum) µmol g–1 dry mass.
Na+ concentrations appeared to increase with leaf age in some species; however, the speciesxNaClxleaf age interaction was not significant in any NaCl treatment.
Cl–:
Cl– concentrations in the various leaf blades of all species under the three NaCl treatments showed trends very similar to those of Na+ (Fig. 4). The Na+:Cl– ratio (averaged for the species and variously aged leaf tissues) of plants grown in 150, 300, or 450 mol m–3 NaCl were 1.1, 0.9, and 0.8, respectively. As examples of genotypic differences, at 300 mol m–3 NaCl, Cl– concentrations in the youngest fully expanded leaf blades of H. vulgare and H. murinum were 2107 and 1050 µmol g–1 dry mass, respectively; whereas in this leaf in all other species, Cl– ranged from 452 µmol g–1 dry mass in H. patagonicum to as low as 181 µmol g–1 dry mass in H. secalinum.
|
In the plants grown in non-saline solution, however, leaf Cl– concentrations were higher than those of Na+ (the non-saline nutrient solution contained 0.2 mol m–3 Na+ and 0.05 mol m–3 Cl–). In H. vulgare and H. murinum grown in non-saline solution, Cl– concentrations in the expanding leaf blades were, on average, 5-fold higher than those of Na+. In all other species, Cl– concentrations were between 9- and 27-fold higher than those of Na+. This was paradoxical, since when the plants were exposed to 150 mol m–3 NaCl and above, H. vulgare and H. murinum had considerably higher concentrations of Cl– in the leaf tissues than all the other species (P <0.001).
As with the Na+ concentrations in leaves of plants in increasing NaCl, there was relatively little difference in Cl– concentrations in most species when external NaCl was increased to 150 mol m–3 and above; in the expanding leaf blades of H. marinum, for example, Cl– concentrations in the 150, 300, and 450 mol m–3 NaCl solutions were 205, 275, and 233 µmol g–1 dry mass, respectively. Hordeum vulgare, H. murinum, and H. patagonicum were again the exceptions, showing marked increases in Cl– concentrations with increasing external NaCl. In H. vulgare, in particular, Cl– concentrations in the expanding leaf blades rose from 26 µmol g–1 dry mass in the non-saline solution, to 491, 1039, and 1936 µmol g–1 dry mass in the 150, 300, and 450 mol m–3 NaCl treatments, respectively.
Cl– concentrations generally increased with leaf blade age in all NaCl treatments; for example at 450 mol m–3 NaCl, Cl– concentrations were 1.9-fold higher in the second youngest fully expanded leaf blades compared with those in the expanding leaf blades (P <0.001).
K+:
In the non-saline solution, H. marinum, H. patagonicum, and H. secalinum had higher leaf K+ concentrations than the other species, with 1336, 1297, and 1287 µmol g–1 dry mass, respectively, compared with an average for the others of 1027 µmol g–1 dry mass (P <0.001). When exposed to NaCl, leaf blade K+ concentrations (averaged for all species at all three NaCl treatments) declined by between 19% and 27% (P <0.001; Fig. 5). In the NaCl treatments, K+ concentrations were lower in H. vulgare than in the wild Hordeum species (with the exception of H. murinum). For example, K+ concentrations in the expanding leaf blades of the wild Hordeum species were 31% higher, on average, than in H. vulgare (P <0.001). More specifically, in H. marinum and H. vulgare, species with the lowest and highest Na+ and Cl– concentrations, respectively, K+ concentrations in the expanding leaf blades were, respectively, 1395 and 846 µmol g–1 dry mass in the non-saline solution, and these declined to 926 and 783 µmol g–1 dry mass in the 300 mol m–3 NaCl solution.
|
For plants in the non-saline or in the 150 mol m–3 NaCl treatments there was a general trend for leaf tissue K+ concentrations to decrease with increasing leaf age (Fig. 5); however, this trend was not observed in plants at the higher NaCl treatments and the speciesxNaClxleaf age interaction was not significant.
K+:Na+ ratio:
The pattern of K+:Na+ in leaf tissues versus increasing external NaCl was relatively similar for most of the Hordeum species, the exceptions being H. murinum and H. vulgare [calculated from data (not shown) in Figs 3 and 5; P <0.001]. For example, in the 150 mol m–3 NaCl solution, the K+:Na+ ratios in the expanding leaf blades of H. intercedens, H. jubatum, H. lechleri, H. marinum, H. patagonicum, and H. secalinum ranged from 9 to 13 and fell more or less linearly to between 2 and 7 in plants at 450 mol m–3 NaCl. Hordeum murinum and H. vulgare were the exceptions to this trend (P <0.001); in H. murinum, the K+:Na+ ratio remained relatively high in the expanding leaf blade of plants at 150 mol m–3 NaCl solution, but then fell to 3 and 0.5 in the 300 and 450 mol m–3 NaCl solutions, respectively; well below the values in the other species. By contrast, the K+:Na+ ratio in H. vulgare started well below the values in the other species; in the 150 mol m–3 NaCl solution, the value was 1.5 for expanding leaf blades, and it became even lower in plants at 300 and 450 mol m–3 NaCl, being 0.9 and 0.3, respectively. These genotypic differences in the K+:Na+ ratios were also evident for the next two youngest leaf blades, although the magnitude progressively declined.
Organic solute concentrations in leaf blades of H. vulgare and H. marinum
The tissue samples of many of the wild Hordeum species were too small to enable a complete analysis of organic solutes. Therefore, the two most contrasting species in the parameters discussed above (H. vulgare and H. marinum) were selected for this part of the study (Fig. 6).
|
Glycinebetaine:
There was no difference between H. vulgare and H. marinum in glycinebetaine concentrations in leaves of plants in the non-saline solution (Fig. 6). In both species, glycinebetaine concentrations increased in response to increases in external NaCl. The pattern of increase in glycinebetaine concentrations in response to NaCl treatment was similar in the expanding, and recently expanded leaf blades, although, generally glycinebetaine decreased with leaf age (P <0.01). In the 450 mol m–3 NaCl solution, for example, glycinebetaine concentrations in the expanding leaf blades of H. marinum and H. vulgare were 1.3–2.2-fold higher, respectively, than in the second youngest fully expanded leaf blades.
Proline:
Proline concentrations did not differ between leaves of H. vulgare and H. marinum in the non-saline solution (Fig. 6). Although increasing external NaCl concentrations caused an increase in Pro in both species, the increase was much larger in H. vulgare (being 17-fold in the expanding leaf blades) than in H. marinum (8-fold in the expanding leaf blades) at 450 mol m–3 NaCl. In H. vulgare, Pro concentrations were highest in the expanding leaf blade (P <0.05).
In H. marinum, Pro concentrations were lower than those of glycinebetaine in all NaCl treatments; being 13–79% of the glycinebetaine concentrations. In H. vulgare in the non-saline, 150 and 300 mol m–3 NaCl treatments, Pro concentrations were also lower than those of glycinebetaine. However, in H. vulgare in the 450 mol m–3 NaCl treatment, Pro concentrations were 1.6–2.8-fold higher than those of glycinebetaine.
Asparagine:
In plants in the non-saline solution, Asn concentrations in leaves of H. vulgare and H. marinum were below 8 µmol g–1 dry mass in both species (Fig. 6). With increasing NaCl in the external solution, Asn concentrations in the variously aged leaf blades of H. marinum did not significantly increase. In H. vulgare, Asn concentrations increased in all leaf blades with increased external NaCl concentration; for example, in the expanding leaf blades, Asn concentrations increased from 2 µmol g–1 dry mass in the non-saline solution to 15, 35, and 80 µmol g–1 dry mass in the plants in 150, 300, and 450 mol m–3 NaCl solutions, respectively.
In both species, and in all NaCl concentrations, Asn decreased with leaf age (P <0.001); for example, concentrations of Asn in the plants in 450 mol m–3 NaCl solution were 1.8- and 3.3-fold higher in the expanding leaf blades of H. marinum and H. vulgare, respectively, compared with those in the second youngest fully expanded leaf blades.
Asn concentrations were low compared with those of glycinebetaine and Pro in both species at all NaCl concentrations; being 2–36% of glycinebetaine, and 4–80% of Pro concentrations.
Expressed leaf sap osmotic potential ()
For plants in non-saline solution, there was no difference in leaf amongst the species (Fig. 7). The 150, 300, and 450 mol m–3 NaCl treatments decreased the of the nutrient solution (external) from –0.05 MPa to –0.69, –1.37, and –2.05 MPa, respectively. This resulted in a decline in leaf in all species (P <0.001). In general, this decline was approximately linear; except in H. vulgare and H. murinum, where the decline in leaf was larger than in the other species and increased sharply (i.e. almost doubling) from the 300 to the 450 mol m–3 NaCl treatment. At 450 mol m–3 NaCl (
external=–2.0 MPa), the leaf (salt treated minus control) was –3.52 and –3.02 MPa for H. vulgare and H. murinum, respectively, compared with –0.96 to –1.62 MPa for the other species. However, all of the species maintained leaf below external, suggesting that the much larger decline in leaf in H. vulgare and H. murinum exceeded that necessary for ‘osmotic adjustment’. Nevertheless, H. vulgare had the smallest reduction in tissue water content with the addition of NaCl. For example, in the expanding leaf blades of H. vulgare, the water content was reduced by 21% in the 300 mol m–3 NaCl (data not shown). Expanding leaf blades of H. marinum had a tissue water content in the non-saline solution of 5.6 ±0.1 ml g–1 dry mass, similar to that of H. vulgare (5.0 ±0.1 ml g–1 dry mass), but H. marinum showed a relatively large reduction in leaf tissue water content with increasing NaCl. For example, for H. marinum plants in the 300 mol m–3 NaCl treatment, leaf tissue water content was reduced by 46% in the expanding leaf blades (data not shown). The average reduction in tissue water content for expanding leaf blades of the other wild species, when treated with the 300 mol m–3 NaCl, was 43%, similar to that in H. marinum. This indicates that when exposed to NaCl, reduced tissue water content made a larger contribution to lowering leaf in H. marinum, and the other wild species, compared with H. vulgare.
|
Estimated contributions of ions and organic solutes to leaf sap
in H. vulgare and H. marinumThe contributions of selected ions (K+, Na+, and Cl–) and organic solutes (Asn, glycinebetaine, and Pro) to
in the expanding and youngest fully expanded leaf blades of H. vulgare and H. marinum treated with non-saline and 300 mol m–3 NaCl solution were calculated as described in the Materials and methods. K+ plus Na+ and Cl–, accounted for 65% of in the expanding leaf blades of H. vulgare grown in 300 mol m–3 NaCl solution, of which K+ accounted for 19%, Na+ for 21%, and Cl– for 25% (data not shown). By comparison, these three ions accounted for 51% of in the expanding leaf blades of H. marinum grown in 300 mol m–3 NaCl solution; with K+ contributing 35%, whereas Na+ and Cl– each accounted for only 6% and 10%, respectively. The contributions of these three ions to in the youngest fully expanded leaf blades were similar to those in the expanding leaves for both species. Although leaf blade organic solute concentrations (dry mass basis) were quite similar in H. vulgare and H. marinum in the 300 mol m–3 NaCl solution, organic solutes made a significantly larger contribution to in H. marinum (15% and 9% in the expanding and youngest fully expanded leaf blades, respectively), compared with H. vulgare (8% and 3%, respectively), due to the lower water content in H. marinum. In both H. marinum and H. vulgare, glycinebetaine made the largest contribution to in the 300 mol m–3 NaCl, at 8% and 6%, respectively, in the expanding leaves, followed by Pro (6% and 2%, respectively). These trends were similar for plants in the other NaCl concentrations; however, the contrasts between the two species became most prominent in the 450 mol m–3 NaCl solution. Asn contributed 
1% to in expanding leaf blades of both species at all NaCl concentrations. |
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
This study evaluated the tolerance of eight wild Hordeum species, and cultivated barley, to growth in salinized nutrient solution, and compared leaf tissue concentrations of Na+, Cl–, and K+, and leaf
. The wild Hordeum species had superior ‘exclusion’ of Na+ and Cl– from the leaves and better maintenance of tissue K+ concentrations, compared with H. vulgare, when exposed to NaCl salinity. A number of these wild Hordeum species also had lower reductions in growth when in saline conditions, compared with H. vulgare, indicating substantial variation in salt tolerance, and associated traits, within the genus Hordeum.
The Na+ and Cl– concentrations in the leaf tissues of the wild Hordeum species were markedly lower than those for H. vulgare. For plants grown at 150 mol m–3 NaCl, Na+ and Cl– concentrations in the youngest fully expanded leaf blades of the wild Hordeum species were, on average, similar to those found for H. jubatum (Suhayda et al., 1992; Huang and Redmann, 1995), and were significantly lower than those previously recorded for several wild Triticeae species when grown at 150 mol m–3 NaCl; being 76% and 72% lower, respectively, than those found in the progenitor of barley, Hordeum vulgare ssp. spontaneum (Gorham et al., 1990a; Forster et al., 1994), 45% and 34% lower, respectively, than in Thinopyrum elongatum (Greenway and Rogers, 1963), and 27% and 39% lower, respectively, than in Thinopyrum bessarabicum (Gorham et al., 1986). Na+ and Cl– concentrations in the wild Hordeum species were on average 62% and 57% lower, respectively, than in durum wheat (Triticum turgidum) (Munns et al., 2000; Rivelli et al., 2002; Husain et al., 2004), but Na+ was similar to that in bread wheat (Triticum aestivum) (Munns et al., 2000; Rivelli et al., 2002; Husain et al., 2004) for plants at 150 mol m–3 NaCl. Moreover, Na+ (and Cl–) ‘exclusion’ by several of the wild Hordeum species was still achieved even at high salinity (i.e. 300 and 450 mol m–3), which was in stark contrast to H. vulgare (Fig. 3).
Cl– concentrations in leaves of H. vulgare increased almost linearly with increasing salinity (Fig. 4). Greenway (1965) demonstrated that Cl– entered roots of H. vulgare via an ‘energy-independent’ flow at high external NaCl, whereas the ‘energy-dependent’ component of Cl– uptake, typical of all plants when exposed to low Cl– (White and Broadley, 2001), was decreased. The ‘energy-independent’ uptake of Cl– increased linearly with external concentration (Greenway, 1965). In contrast to the high concentrations of Cl– in H. vulgare, several of the wild Hordeum species still maintained relatively low concentrations of Cl– in leaves, even at high salinity (i.e. 300 and 450 mol m–3 NaCl). Leaf Cl– concentrations in the wild Hordeum species were also markedly lower than those reported for bread wheat. For example, the Cl–:Na+ ratio in the leaf tissues of bread wheat cv. ‘Janz’ was 5 (Husain et al., 2004) compared with 1.2 in the wild Hordeum species. This suggests that the genus Hordeum contains significant variation for ‘exclusion’ of both Na+ and Cl– under saline conditions, whereas there appears to be little variation in Cl– ‘exclusion’ between other species in the Triticeae (Shah et al., 1987; Husain et al., 2004).
As a result of superior Na+ ‘exclusion’ and better maintenance of leaf K+ concentrations in saline conditions, the wild Hordeum species exhibited higher leaf K+:Na+ ratios compared with H. vulgare. In the wild Hordeum species, the average K+:Na+ ratio in the youngest, fully expanded leaf blades of plants at 150 mol m–3 NaCl was 5.2, compared with 0.8 in H. vulgare. Many Triticum species have good Na+ ‘exclusion’ and better K+/Na+ selectivity compared with H. vulgare, as evidenced by high leaf K+:Na+ ratios (Gorham et al., 1990a; Gorham, 1993). For example, Gorham et al. (1990a) measured a K+:Na+ ratio of 5.9 in the youngest, fully expanded leaf blades of Triticum aestivum and one of its progenitors, Triticum tauschii, grown in 160 mol m–3 NaCl for 7 d. The high K+:Na+ ratio in leaves of T. aestivum and T. tauschii is partially attributed to the ‘enhanced K+/Na+ discrimination’ character (Gorham et al., 1990b; Gorham, 1993; Dvorák et al., 1994). Similarly high K+:Na+ ratios in leaves of the wild Hordeum species indicates mechanisms for Na+ ‘exclusion’ and K+/Na+ selectivity in these species. However, the wild Hordeum species (with the exception of H. murinum) appear to maintain K+/Na+ selectivity even at high salinity (i.e. 450 mol m–3 NaCl). By contrast, the K+/Na+ discrimination trait in T. aestivum and T. tauschii is most apparent at relatively low salinities (i.e. 50 mol m–3) (Gorham, 1993; Gorham et al., 1997).
The measurements of leaf for plants grown in the NaCl treatments indicated that all of the wild Hordeum species maintained below external, despite having relatively low Na+ and Cl– accumulation compared with H. vulgare (although H. murinum, with relatively high leaf Na+ and Cl– concentrations, was an exception) (Fig. 7). The response of the wild Hordeum species (except H. murinum), in which entry of Na+ and Cl– appears to be well-regulated so that leaf only declined by that required to maintain it below external, is similar to that of Thinopyrum bessarabicum (Gorham et al., 1985). The decline in leaf in H. marinum in the saline solution resulted from reduced tissue water content, and some entry of Na+ and Cl– with maintenance of K+ concentrations (dry mass basis) and increased production of organic solutes. Glenn (1987) found a similar response to NaCl stress amongst halophytic grasses compared with glycophytic grasses; several halophytes showed reduced tissue water contents and higher K+:Na+ ratios, while still maintaining growth in the saline conditions (Glenn, 1987). The consequences of this strategy for the plant are poorly understood. Some authors propose that reduced tissue water content may be regarded as an ameliorating factor that lowers osmotic potential whilst limiting Na+ and Cl– uptake (Glenn and O'Leary, 1984; Glenn, 1987). However, a reduction in leaf water content may affect turgor, depending on wall elasticity, although moderate reductions in turgor might not always impact on growth (Munns, 1993). Moreover, reduced tissue water content would itself increase the concentration of ions in the cellular fluids and this is what presumably determines toxicity. Data on concurrent changes in tissue elasticity (i.e. cell walls contracting as water is lost), and possible changes in wall extensibility under saline conditions as speculated by Greenway and Munns (1980), are limited for monocots [e.g. Spartina alterniflora (Drake and Gallagher, 1984), Ammophila arenaria and Elymus mollis (Pavlik, 1984)] and elasticity either did not change or decreased. Nevertheless, the common occurrence of reduced leaf water content and restricted ion uptake in halophytic monocots in response to NaCl stress makes the phenomenon worthy of further study.
Calculations of contributions of ions and organic solutes to leaf indicated that H. marinum has a higher proportion of organic solutes to osmotically ‘balance’ Na+ and Cl– (which are presumably sequestered in the vacuole) compared with H. vulgare. For example, when at 150 mol m–3 NaCl, the ratio of glycinebetaine to Na+ in expanding leaf blades of H. marinum was 1.1 compared with 0.2 in H. vulgare. Moreover, in expanding leaf blades of plants grown in 300 mol m–3 NaCl, organic solutes contributed 15% of in H. marinum, compared with 8% in H. vulgare. Interestingly, when exposed to salinity, Pro was higher in H. vulgare (dry mass basis) and also in several other species in the Triticeae [e.g. T. aestivum cv. ‘Chinese Spring’ (Gorham et al., 1986; Colmer et al., 1995), H. jubatum (Huang and Redmann, 1995), and Thinopyrum elongatum (Gorham et al., 1986)], than in H. marinum.
Hordeum marinum, H. intercedens, and to a lesser extent H. secalinum, were the most salt-tolerant species in this study, having the smallest reductions (% of control values) in shoot and root dry masses and RGR in the NaCl treatments. In comparison to non-saline controls, whole plant dry mass in H. marinum (the most tolerant species) was 67% in the 150 mol m–3 NaCl treatment, compared with 46% in H. vulgare. The value measured here for H. vulgare ssp. vulgare was similar to that previously found for a number of other cultivars (Greenway, 1962; Storey and Wyn Jones, 1978b), and its progenitor, H. vulgare ssp. spontaneum (dry mass in 150 mol m–3 NaCl was 40% of control) (Forster et al., 1994). However, the distinction between the wild Hordeum species and H. vulgare was less for growth parameters, compared with those for tissue ion concentrations, when in the NaCl treatments. Differences amongst the species for growth in saline conditions might become even larger in the longer term (NaCl exposure in the present experiment was up to 21 d). Na+ and Cl– accumulate as leaves age since ions are constantly delivered in the transpiration stream, hence salt concentrations will be highest in the older leaves (Greenway and Munns, 1980), which eventually die due to ion toxicity (Munns, 2002). Growth differences between closely related genotypes in saline conditions might take time to develop, as different rates of salt accumulation in the leaves impact on leaf area (Munns et al., 1995; Munns, 2002). The large difference in the proportion of dead leaf material between the wild Hordeum species and H. vulgare, when exposed to NaCl (Fig. 2), supports the suggestion that differences in growth might become even larger with time. In the 450 mol m–3 NaCl solution, the dead leaf material (as a % of shoot dry mass) in H. vulgare was 17%, compared with 3–11% in the other species. Munns et al. (1995) found for wheat that, when the percentage of dead leaves reached about 20% of the total, the rate of leaf production slowed down dramatically and some plants died. It is likely that the present experiments underestimate the actual variation in salt tolerance between the species studied.
In conclusion, the growth parameters and tissue Na+ and Cl– concentrations measured under NaCl treatments in this experiment indicate large differences in salt tolerance of several wild Hordeum species as compared with H. vulgare. The genus Hordeum is comprised of four genomes: H. vulgare has the I genome, H. murinum the Y genome, H. marinum the X genome and, the remaining species in this experiment, the H genome (von Bothmer et al., 1995). A study that evaluated waterlogging tolerance in Hordeum species (Garthwaite et al., 2003) found that tolerance to waterlogging and associated root aeration traits were related to genome type. Species with the I or Y genome were generally much less tolerant to waterlogging than those with the X or H genome (Garthwaite et al., 2003). The present findings on salinity tolerance in wild Hordeum species indicate that the X and H genomes are also of interest for traits associated with salt tolerance. The results provide evidence for the reputed salt tolerance of several wild species in the genus Hordeum, and demonstrate the significant diversity in salt tolerance amongst Hordeum species.
|
Acknowledgements |
|---|
We thank Dr Digby Short for assistance with the plant harvest, Professor Christian Jensen for use of an osmometer, Mr Greg Cawthray for excellent HPLC guidance, Dr Rana Munns for comments on a draft of this manuscript, and colleagues at the Department of Crop Science, Swedish University of Agricultural Sciences, Alnarp, for their kind support during the visit of AJG. The Grains Research and Development Corporation provided a scholarship to AJG.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Colmer TD, Epstein E, Dvorak J. 1995. Differential solute regulation in leaf blades of various ages in salt-sensitive wheat and a salt-tolerant wheatxLophopyrum elongatum (Host) A. Löve amphiploid. Plant Physiology 108, 1715–1724.[Abstract]
Drake BG, Gallagher JL. 1984. Osmotic potential and turgor maintenance in Spartina alterniflora Loisel. Oecologia 62, 368–375.[CrossRef]
Dvorák J, Noaman MM, Goyal S, Gorham J. 1994. Enhancement of the salt tolerance of Triticum turgidum L. by the Kna1 locus transferred from the Triticum aestivum L. chromosome 4D by homoeologous recombination. Theoretical and Applied Genetics 87, 872–877.
Fan TWM, Colmer TD, Higashi RM, Lane AN. 1993. Determination of metabolites by 1H NMR and GC: analysis for organic osmolytes in crude tissue extracts. Analytical Biochemistry 214, 260–271.[CrossRef][Web of Science][Medline]
Forster BP, Pakniyat H, Macaulay M, Matheson W, Phillips MS, Thomas WTB, Powell W. 1994. Variation in the leaf sodium content of the Hordeum vulgare (barley) cultivar Maythorpe and its derived mutant cv. Golden Promise. Heredity 73, 249–253.
Garthwaite AJ, von Bothmer R, Colmer TD. 2003. Diversity in root aeration traits associated with waterlogging tolerance in the genus Hordeum. Functional Plant Biology 30, 875–889.[CrossRef][Web of Science]
Glenn EP. 1987. Relationship between cation accumulation and water content of salt-tolerant grasses and a sedge. Plant, Cell and Environment 10, 205–212.
Glenn EP, O'Leary JW. 1984. Relationship between salt accumulation and water content of dicotyledonous halophytes. Plant, Cell and Environment 7, 253–261.
Gorham J. 1993. Genetics and physiology of enhanced K/Na discrimination. In: Randall PJ, ed. The fourth international symposium on genetic aspects of plant mineral nutrition. Canberra, Australia: Kluwer Academic Publishers, 151–158.
Gorham J, Bridges J, Dubcovsky J, Dvorak J, Hollington PA, Luo M-C, Khan JA. 1997. Genetic analysis and physiology of a trait for enhanced K+/Na+ discrimination in wheat. New Phytologist 137, 109–116.[CrossRef][Web of Science]
Gorham J, Bristol A, Young EM, Wyn Jones RG, Kashour G. 1990a. Salt tolerance in the Triticeae: K/Na discrimination in barley. Journal of Experimental Botany 41, 1095–1101.
Gorham J, Forster BP, Budrewicz E, Wyn Jones RG, Miller TE, Law CN. 1986. Salt tolerance in the Triticeae: solute accumulation and distribution in an amphiploid derived from Triticum aestivum cv. Chinese Spring and Thinopyrum bessarabicum. Journal of Experimental Botany 37, 1435–1449.
Gorham J, McDonnell E, Budrewicz E, Wyn Jones RG. 1985. Salt tolerance in the Triticeae: growth and solute accumulation in leaves of Thinopyrum bessarabicum. Journal of Experimental Botany 36, 1021–1031.
Gorham J, Wyn Jones RG, Bristol A. 1990b. Partial characterization of the trait for enhanced K+-Na+ discrimination in the D genome of wheat. Planta 180, 590–597.[CrossRef][Web of Science]
Greenway H. 1962. Plant response to saline substrates. I. Growth and ion uptake of several varieties of Hordeum during and after sodium chloride treatment. Australian Journal of Biological Sciences 15, 16–38.
Greenway H. 1965. Plant responses to saline substrates. IV. Chloride uptake by Hordeum vulgare as affected by inhibitors, transpiration, and nutrients in the medium. Australian Journal of Biological Sciences 18, 249–268.
Greenway H, Munns R. 1980. Mechanisms of salt tolerance in nonhalophytes. Annual Review of Plant Physiology 31, 149–190.[Web of Science]
Greenway H, Rogers A. 1963. Growth and ion uptake of Agropyron elongatum on saline substrates, as compared with a salt-tolerant variety of Hordeum vulgare. Plant and Soil 18, 21–30.[CrossRef]
Howes Keiffer C, Ungar IA. 1997a. The effect of extended exposure to hypersaline conditions on the germination of five inland halophyte species. American Journal of Botany 84, 104–111.[Abstract]
Howes Keiffer C, Ungar IA. 1997b. The effects of density and salinity on shoot biomass and ion accumulation in five inland halophytic species. Canadian Journal of Botany 75, 96–107.
Huang J, Redmann RE. 1995. Solute adjustment to salinity and calcium supply in cultivated and wild barley. Journal of Plant Nutrition 18, 1371–1389.
Husain S, von Caemmerer S, Munns R. 2004. Control of salt transport from roots to shoots of wheat in saline soil. Functional Plant Biology 31, 1115–1126.[CrossRef]
Jacobsen N, von Bothmer R. 1992. Supraspecific groups in the genus Hordeum. Heriditas 116, 21–24.
Mano Y, Takeda K. 1998. Genetic resources of salt tolerance in wild Hordeum species. Euphytica 103, 137–141.
Munns R. 1993. Physiological processes limiting plant growth in saline soils: some dogmas and hypotheses. Plant, Cell and Environment 16, 15–24.
Munns R. 2002. Comparative physiology of salt and water stress. Plant, Cell and Environment 25, 239–250.[CrossRef][Medline]
Munns R, Hare RA, James RA, Rebetzke GJ. 2000. Genetic variation for improving the salt tolerance of durum wheat. Australian Journal of Agricultural Research 51, 69–74.
Munns R, Husain S, Rivelli AR, James RA, Condon AG, Lindsay MP, Lagudah ES, Schachtman DP, Hare RA. 2002. Avenues for increasing salt tolerance of crops, and the role of physiologically based selection traits. Plant and Soil 247, 93–105.[CrossRef]
Munns R, Schachtman DP, Condon AG. 1995. The significance of a two-phase growth response to salinity in wheat and barley. Australian Journal of Plant Physiology 22, 561–569.[Web of Science]
Munns R, Termaat A. 1986. Whole-plant responses to salinity. Australian Journal of Plant Physiology 13, 143–160.[Web of Science]
Naidu BP. 1998. Separation of sugars, polyols, proline analogues, and betaines in stressed plant extracts by high performance liquid chromatography and quantification by ultra detection. Australian Journal of Plant Physiology 25, 793–800.[Web of Science]
Nevo E, Krugman T, Beiles A. 1993. Short communication: genetic resources for salt tolerance in the wild progenitors of wheat (Triticum dicoccoides) and barley (Hordeum spontaneum) in Israel. Plant Breeding 110, 338–341.[CrossRef]
Pavlik BM. 1984. Seasonal changes of osmotic pressure symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon, USA. Plant, Cell and Environment 7, 531–540.
Rawson HM, Richards RA, Munns R. 1988. An examination of selection criteria for salt tolerance in wheat, barley and triticale genotypes. Australian Journal of Agricultural Research 39, 759–772.[CrossRef][Web of Science]
Richards RA, Dennett CW, Qualset CO, Epstein E, Norlyn JD, Winslow MD. 1987. Variation in yield of grain and biomass in wheat, barley and triticale in a salt-affected field. Field Crops Research 15, 277–287.[CrossRef]
Rivelli AR, James RA, Munns R, Condon AG. 2002. Effect of salinity on water relations and growth of wheat genotypes with contrasting sodium uptake. Functional Plant Biology 29, 1065–1074.[CrossRef]
Shah SH, Gorham J, Forster BP, Wyn Jones RG. 1987. Salt tolerance in the Triticeae: the contribution of the D genome to cation selectivity in hexaploid wheat. Journal of Experimental Botany 38, 254–269.
Storey R, Wyn Jones RG. 1978a. Salt stress and comparative physiology in the Gramineae. I. Ion relations of two salt- and water-stressed barley cultivars, California Mariout and Arimar. Australian Journal of Plant Physiology 5, 801–816.
Storey R, Wyn Jones RG. 1978b. Salt stress and comparative physiology in the Gramineae. III. Effect of salinity upon ion relations and glycine betaine and proline levels in Spartinaxtownsendii. Australian Journal of Plant Physiology 5, 831–838.[Web of Science]
Suhayda CG, Redmann RE, Harvey BL, Cipywnyk AL. 1992. Comparative response of cultivated and wild barley species to salinity stress and calcium supply. Crop Science 32, 154–163.
Svitashev S, Bryngelsson T, Vershinin A, Pedersen C, Säll T, von Bothmer R. 1994. Phylogenetic analysis of the genus Hordeum using repetitive DNA sequences. Theoretical and Applied Genetics 89, 801–810.
Taketa S, Ando H, Takeda K, von Bothmer R. 1999. Brief report: detection of Hordeum marinum genome in three polyploid Hordeum species and cytotypes by genomic in situ hybridization. Heriditas 130, 185–188.[CrossRef][Web of Science][Medline]
Tester M, Davenport R. 2003. Na+ tolerance and Na+ transport in higher plants. Annals of Botany 91, 503–527.
Venus JC, Causton DR. 1979. Plant growth analysis: a re-examination of the methods of calculation of relative growth rate and net assimilation rates without using fitted functions. Annals of Botany 43, 633–638.
von Bothmer R, Giles BE, Jacobsen N. 1986. Crosses and genome relationships in the Hordeum patagonicum group. Genetica 71, 75–80.[CrossRef]
von Bothmer R, Jacobsen N, Baden C, Jørgensen RB, Linde-Laursen I. 1995. An ecogeographical study of the genus Hordeum, 2nd edn. Rome: International Plant Genetic Resources Institute.
White PJ, Broadley MR. 2001. Chloride in soils and its uptake and movement within the plant: a review. Annals of Botany 88, 967–988.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  A. I. Malik, J. P. English, and T. D. Colmer Tolerance of Hordeum marinum accessions to O2 deficiency, salinity and these stresses combined Ann. Bot., January 1, 2009; 103(2): 237 - 248. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. A. Cuin, S. A. Betts, R. Chalmandrier, and S. Shabala A root's ability to retain K+ correlates with salt tolerance in wheat J. Exp. Bot., July 1, 2008; 59(10): 2697 - 2706. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S Islam, A. Malik, A. Islam, and T. Colmer Salt tolerance in a Hordeum marinum-Triticum aestivum amphiploid, and its parents J. Exp. Bot., March 1, 2007; 58(5): 1219 - 1229. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Munns, R. A. James, and A. Lauchli Approaches to increasing the salt tolerance of wheat and other cereals J. Exp. Bot., March 1, 2006; 57(5): 1025 - 1043. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. D. Colmer, T. J. Flowers, and R. Munns Use of wild relatives to improve salt tolerance in wheat J. Exp. Bot., March 1, 2006; 57(5): 1059 - 1078. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||