Salt-sensitive Genotype Research Articles

Interaction of Salinity and Cadmium Stresses on Antioxidant Enzymes, Sodium, and Cadmium Accumulation in Four Barley Genotypes

ABSTRACT A hydroponic experiment was carried out utilizing four barley genotypes with differing salt tolerances to investigate the influence of salinity (NaCl) and cadmium (Cd) on the activities of antioxidant enzymes, sodium (Na) and Cd concentrations, and accumulation in plants. The activities of the two antioxidant enzymes, superoxide dismutase (SOD) and peroxidase (POD), were significantly increased when plants were exposed to both Na and Cd stresses for all genotypes, relative to the control. The increased enzymatic activity was more predominant with a prolonged time of stress exposure. The combined stress (NaCl+Cd) led to a further increase in POD activity, but had little effect on SOD activity. Two salt-tolerant genotypes, ‘Gebeina’ and ‘Zhou 1,’ showed a more rapid increase of POD and SOD activities than the two salt-sensitive genotypes, ‘Newgoutei’ and ‘Quzhou’ in response to the combined stress treatment. Additions of NaCl to the Cd-containing medium caused a significant reduction in both Cd concentration and accumulation. The extent of the reduction in Cd concentration was also dependent on genotypes. The salt-tolerant genotypes had lower Na concentrations than sensitive genotypes, and the effect of Cd stress on Na concentration and accumulation varied with genotypes. It may be concluded that a significant interaction exists between Na and Cd in their influence on antioxidant enzyme activity and the accumulation of each element in the plant.

Effect of NaCl salinity in the genotypic variation of cowpea ( Vigna unguiculata) during early vegetative growth

Twenty-five genotypes of cowpea ( Vigna unguiculata L. Walp.) were tested for salt-tolerance at the vegetative growth stage in pot in the greenhouse experiments at salinity levels of 0, 85, and 170 mM NaCl. Plant survival was the main criterion for classifying genotypes. Other criteria included the ion concentration (Na + and Cl −) in root and shoot and biomass accumulation. Four local accessions (‘Paceño’, ‘Tardón’, ‘Sonorense’, and ‘Cuarenteño’), three accessions from California (‘CB46’, ‘CB27’, and ‘CB3’), and one accession from the International Institute of Tropical Agriculture (IITA) (‘IT82D-889’) survived at concentrations of both 85 and 170 mM NaCl and were classified as salt-tolerant, while ‘IT96D-666’, ‘IT89KD-288’, and ‘IT93K-734’ from IITA were classified as salt-sensitive. One local accession (‘Sesenteño’), three accessions from IITA (‘PEPH-V Wes-85’, ‘IT86D-719’, and ‘IT95K-1090-12’), and one accession from California (‘CB5’) were classified as moderately salt-tolerant. Eight accessions from IITA (‘IT96D-733’, ‘IT90K-277-2’, ‘IT91K-93-10’, ‘IT91K-118-20’, ‘IT90K-284-2’, ‘IT95K-1088-4’, ‘IT89KD-391’, and ‘IT94K-437-1’) and one from California (‘CB88’) were classified as moderately salt-sensitive. Biomass was affected by both 85 and 170 mM NaCl in all groups of genotypes, however, salt-tolerant and moderately salt-tolerant genotypes showed higher biomass than genotypes classified as moderately salt-sensitive and salt-sensitive. In all genotypes Cl − concentration was higher in shoots than roots and increased as salinity increased. Similarly Na + concentration increased with increasing salinity. However, in salt-tolerant and moderately salt-tolerant genotypes, Na + concentration was more in roots than shoots, while in moderately salt-sensitive and salt-sensitive genotypes, Na + was higher in shoots than roots.

Antioxidant-enzymatic system of two sorghum genotypes differing in salt tolerance

Two forage sorghum genotypes were studied: CSF18 (salt-sensitive) and CSF20 (salt-tolerant). Shoot growth reduction as a result of salt stress was stronger in the salt sensitive genotype compared to the salt tolerant one. When the two genotypes were subjected to salt stress (75 mM NaCl) no significant change in lipid peroxidation was observed. However, salt stress induced increases in superoxide dismutase and catalase activities in both genotypes. These salt-induced increases were higher in the salt-tolerant genotype. Peroxidase activity was differentially affected by salt stress in the two genotypes. The activities of these peroxidases were decreased by salt stress in the salt-sensitive genotype and increased in the salt-tolerant genotype. In addition, the activity ratio between the superoxide dismutase and the H2O2-scavenging enzymes was higher in the salt-sensitive genotype. The results obtained support the hypothesis that the higher efficiency of the antioxidant-enzymatic system of the CSF20 genotype could be considered as one of the factors responsible for its tolerance to salt stress. Therefore, it is suggested that the ratio between superoxide dismutase and H2O2-scavenging enzyme activities could be used as a working hypothesis for a biochemical marker for salt tolerance in sorghum.

Comparative Transcriptional Profiling of Two Contrasting Rice Genotypes under Salinity Stress during the Vegetative Growth Stage

Rice (Oryza sativa), a salt-sensitive species, has considerable genetic variation for salt tolerance within the cultivated gene pool. Two indica rice genotypes, FL478, a recombinant inbred line derived from a population developed for salinity tolerance studies, and IR29, the sensitive parent of the population, were selected for this study. We used the Affymetrix rice genome array containing 55,515 probe sets to explore the transcriptome of the salt-tolerant and salt-sensitive genotypes under control and salinity-stressed conditions during vegetative growth. Response of the sensitive genotype IR29 is characterized by induction of a relatively large number of probe sets compared to tolerant FL478. Salinity stress induced a number of genes involved in the flavonoid biosynthesis pathway in IR29 but not in FL478. Cell wall-related genes were responsive in both genotypes, suggesting cell wall restructuring is a general adaptive mechanism during salinity stress, although the two genotypes also had some differences. Additionally, the expression of genes mapping to the Saltol region of chromosome 1 were examined in both genotypes. Single-feature polymorphism analysis of expression data revealed that IR29 was the source of the Saltol region in FL478, contrary to expectation. This study provides a genome-wide transcriptional analysis of two well-characterized, genetically related rice genotypes differing in salinity tolerance during a gradually imposed salinity stress under greenhouse conditions.

The expression of the endogenous vacuolar Na +/H + antiporters in roots and shoots correlates positively with the salt resistance of wheat ( Triticum aestivum L.)

Among the most common effects of salinity is the growth inhibition by Na + toxicity. Vacuolar Na +/H + antiporters have been suggested to be involved in sequestering Na + into vacuoles, thus preventing toxic effects of Na + in the cytoplasm. This study reports how the expression of endogenous vacuolar Na +/H + antiporters relates to the salt resistance of two wheat ( Triticum aestivum L.) genotypes that differ in Na + translocation from root to the shoot and Na + accumulation in the young and old leaves. The genotype SARC-1 having the lowest root-to-shoot Na + translocation was the most salt-resistant in terms of absolute and relative shoot fresh weight production. However, compared to the salt-sensitive wheat genotype 7-Cerros, the salt-resistant genotype SARC-1 showed a significantly higher Na + concentration in young leaves, a similar Na + concentration in medium leaves and a significantly lower Na + concentration in the old leaves. The expression of endogenous vacuolar Na +/H + antiporters in roots and shoots was significantly higher in the salt-resistant genotype SARC-1 than in the salt-sensitive genotype 7-Cerros. However, within a genotype there was little difference in the expression of vacuolar Na +/H + antiporters between shoots and roots, and between cortical and stelar root parts. It is suggested that the higher expression of endogenous vacuolar Na +/H + antiporters in roots and shoots of the salt-resistant wheat genotype SARC-1 facilitated Na + exclusion from the cytoplasm of its shoot cells and improved its salt resistance.

Effect of salt stress on antioxidative enzymes and lipid peroxidation in leaves and roots of salt-tolerant and salt-sensitive maize genotypes

The effects of salt stress on the activity of antioxidative enzymes and lipid peroxidation were studied in leaves and roots of two maize genotypes, BR5033 (salt-tolerant) and BR5011 (salt-sensitive), grown under control (nutrient solution) or salt stress (nutrient solution containing 100 mM NaCl) conditions. Leaves and roots of control and salt-stressed plants were harvested at various times starting 1 day prior to initiating the salt treatment. In leaves of salt-stressed plants, superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) activities increased with time when compared to the controls. The increase in enzyme activities was more pronounced in the salt-tolerant than in the salt-sensitive genotype. Salt stress had no significant effect on catalase (CAT) activity in the salt-tolerant, but it was reduced significantly in the salt-sensitive genotype. In salt-stressed roots of the salt-tolerant genotype, SOD and CAT activities decreased and APX, GPX and GR activities remained unchanged in comparison with the control. In roots of the salt-sensitive genotype, salinity reduced the activity of all studied enzymes. The data show that CAT and GPX enzymes had the greatest H 2O 2 scavenger activity in both leaves and roots. Moreover, CAT, APX and GPX activities in conjunction with SOD seem to play an essential protective role in the scavenging processes. Lipid peroxidation was enhanced only in salt-stressed leaves of the salt-sensitive genotype. These results indicate that oxidative stress may play an important role in salt-stressed maize plants and that the greater protection of BR5033 leaves and roots from salt-induced oxidative damage results, at least in part, through the maintenance and/or increase of the activity of antioxidant enzymes.

Growth, ion content, gas exchange, and water relations of wheat genotypes differing in salt tolerances

Although the mechanisms of salt tolerance in plants have received much attention for many years, genotypic differences influencing salt tolerance still remain uncertain. To investigate the key physiological factors associated with genotypic differences in salt tolerance of wheat and their relationship to salt stress, 13 wheat genotypes from Egypt, Australia, India, and Germany, that differ in their salt tolerances, were grown in a greenhouse in soils of 4 different salinity levels (control, 50, 100, and 150 mm NaCl). Relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), photosynthesis, chlorophyll content (SPAD value), and leaf water relations were measured at Days 45 and 60 after sowing. Mineral nutrient content in leaves and stems was determined at Day 45 and final harvest. Salinity reduced RGR, NAR, photosynthetic rate, stomatal conductance, water and osmotic potentials, and K+ and Ca2+ content in stems and leaves at all times, whereas it increased leaf respiration, and Na+ and Cl– content in leaves and stems. LAR was not affected by salinity and the effect of salinity on SPAD value was genotype-dependent. Growth of salt-tolerant genotypes (Sakha 8, Sakha 93, and Kharchia) was affected by salinity primarily due to a decline in photosynthetic capacity rather than a reduction in leaf area, whereas NAR was the more important factor in determining RGR of moderately tolerant and salt-sensitive genotypes. We conclude that Na+ and Cl– exclusion did not always reflect the salt tolerance, whereas K+ in the leaves and Ca2+ in the leaves and stems were closely associated with genotypic differences in salt tolerance among the 13 genotypes even at Day 45. Calcium content showed a greater difference in salt tolerance among the genotypes than did K+ content. The genotypic variation in salt tolerance was also observed for the parameters involved in photosynthesis, and water and osmotic potentials, but not for turgor pressure.

Evaluation of salt-tolerant genotypes of durum wheat derived from in vitro and field experiments

The performance of selected salt-tolerant genotypes of durum wheat [ Triticum turgidum L. subsp. durum (Desf.) Husn.], derived from field and in vitro assessment methods, was evaluated under greenhouse and field conditions. Eight durum wheat genotypes comprising three salt-tolerant genotypes and one salt-sensitive genotype selected from each of the methods were used. This study was conducted under both saline and non-saline field conditions as well as under greenhouse condition with salinized solution culture at 0 mM (control), 75 and 150 mM NaCl (concentrations) using supplemental Ca 2+. Days to heading, days to maturity, plant height, number of grains per spike, grain weight per spike, 1000 grain weight, number of spikes per m 2, grain yield and harvest index were recorded in the field experiments. Plant dry weight, Na +, K + and Ca 2+ accumulated in the hydroponically grown seedlings were measured 20 days after salinity treatments. In spite of the smaller range of genotypes used by the in vitro screening method, tolerant genotypes screened by the in vitro method (ITGs) performed comparably with those of the field-derived tolerant genotypes (FTGs) for grain yield under saline field conditions. Field salinity significantly reduced ( P < 0.01) means of all traits averaged on eight tested genotypes. In vitro salt-tolerant genotypes Dipper-6 and Prion-1 produced the highest dry weight and K +/Na + ratio under salt stress conditions (150 mM NaCl) in the greenhouse. Although dry matter correlated with the grain yield ( R 2 = 0.37), the regression coefficient was higher for shoot K +/Na + ratio ( R 2 = 0.44). Dipper-6 (ITG) and Prion-1 (ITG) genotypes have been ranked superior while Massara-1 (ISG) was inferior for salt tolerance in the regression analysis. However, based on grain yield reduction Ajaia/Hora/Jro/3/Gan (FTG) and PI40100 (ITG) were the most tolerant having 58% and 60% reduction, respectively.

Changes in growth and in solute concentrations in sorghum leaves and roots during salt stress recovery

Seedlings of two sorghum genotypes [ Sorghum bicolor (L.) Moench], one salt tolerant (CSF 20) and another salt sensitive (CSF 18) were exposed to 0 (control) and 100 mM NaCl (salt stress) in nutrient solution for seven days and, then, transferred to a new nutrient solution with no added NaCl for an additional period of five days (salt recovery). Plants were collected at the 7th (salt stressed) and 12th days (salt recovered) and relative growth rate (RGR) and organic and inorganic solutes in leaves and roots were determined. Salinity reduced RGR and increased Na +, Cl −, soluble carbohydrates and proline concentrations, and Na +/K + and Na +/Ca 2+ ratios, especially in the leaves of the salt sensitive genotype. During salt stress recovery, RGR of roots was lower in previously stressed seedlings, but shoot growth did not differ between these seedlings and control unstressed ones, in both genotypes. Salt recovered seedlings showed decrease in leaf Na + plus Cl − concentrations and in Na +/Ca 2+ ratio, and in root Na +/K + ratio. The reductions in organic solutes concentrations were quite small, especially in the older leaves. A lower toxic ion accumulation during salt stress was related to salt tolerance and to seedling growth during salt recovery phase. On the contrary, higher leaf organic solute accumulation during salt stress was not related nor to salt tolerance nor to seedling recovery after salt stress relief. So, the high capacity of sorghum seedlings to recover after salt stress relief appears to be related to an adequate partition of carbon between shoots and roots and to changes in absorption, transport and re-translocation of salts.

Influência do cálcio sobre o crescimento e solutos em plântulas de sorgo estressadas com cloreto de sódio

O aumento da concentração de Ca no ambiente radicular tem sido indicado para reduzir os efeitos deletérios da salinidade sobre o crescimento das plantas. Neste trabalho, plântulas de dois genótipos de sorgo forrageiro [Sorghum bicolor (L.) Moench], um tolerante (CSF 20) e outro sensível (CSF 18) à salinidade, foram expostas a duas concentrações de Na+ (0 e 75 mmol L-1) e duas de Ca²+ (0,65 e 2,6 mmol L-1), em solução nutritiva, em arranjo fatorial 2 x 2 x 2. Após sete dias de tratamento, foram determinados a produção de matéria seca e os teores de Cl-, Na+, K+, Ca²+ e de prolina em folhas e raízes. O estresse salino reduziu a produção de matéria seca nas duas partes das plântulas dos dois genótipos, principalmente do sensível, enquanto o aumento na concentração de Ca²+ no meio de cultivo amenizou parcialmente este efeito, principalmente na parte aérea do genótipo tolerante. O estresse salino também acarretou aumento nos teores de Na+ e de Cl- e redução nos teores de K+ nas duas partes das plântulas dos dois genótipos, especialmente do sensível. Adicionalmente, observou-se redução nos teores de Ca²+, bem como aumento nos teores de prolina, mas apenas nas folhas. O aumento na concentração de Ca²+ amenizou estes efeitos, reduzindo os teores de Na+ e Cl- e aumentando os teores de K+, principalmente nas folhas do genótipo tolerante. Este genótipo apresentou uma relação Na+/K+ bem inferior à observada no genótipo sensível, diferença esta que se acentuou ainda mais com o aumento da concentração de Ca²+ na solução nutritiva. O aumento na concentração de Ca²+ no meio nutritivo resultou em aumento nos teores de Ca²+ em folhas e raízes dos dois genótipos, porém as plântulas estressadas não foram capazes de manter as mesmas concentrações desse íon observadas nas plântulas-controle. O Ca²+ não teve qualquer efeito significativo sobre o acúmulo de prolina nas plântulas, submetidas ou não a estresse salino.

Cellular basis of salinity tolerance in plants

Glycophytes and halophytes are believed to have salt tolerance mechanisms that occur at the cellular level. One facet of the cellular mechanisms concerns the elements of the protoplasm. Variations in the response of plasma membrane permeability in salt sensitive and tolerant genotypes to salinity are explained by differences in composition and/or structure of the plasma membrane. Changes in plasma membrane lipid composition are evident upon salt exposure. Changes in protein–lipid interactions may also be involved in plasma membrane permeability variations. Agents that accumulate under salinity and have membrane protective function mitigate cellular alterations brought about by salinity-induced plasma membrane disruption. It is obvious that salt adaptation mechanisms depend on preservation of plasma membrane integrity under salt stress. Cytoplasmic viscosity responds differently to salt imposition in genotypes contrasting in salt tolerance, reflecting differences in cytoplasm structure and composition. Results also support a cytoplasmic basis for salt tolerance. Data indicate absence of association of osmotic adjustment and adaptation to salinity. More information is needed to interpret the response of cytoplasmic streaming to salinity. Assays of protoplasmic qualities, such as cell membrane permeability and cytoplasmic viscosity, will provide an easy and fast test for screening relatively large numbers of cultivars for salt tolerance.

Osmotic adjustment in roots and leaves of two sorghum genotypes under NaCl stress

Seedlings of two sorghum genotypes [Sorghum bicolor (L.) Moench], one salt tolerant (CSF 20) and the other salt sensitive (CSF 18) were grown in nutrient solution containing 0, 50 and 100 mmol.L-1 NaCl for seven days and the osmotic potential (Ys) and the contribution of organic and inorganic solutes to the Ys were determined in the leaves and roots. Salinity reduced the Ys of the cellular sap of leaves and roots in both genotypes, mainly in the salt sensitive one. The higher decrease in the Ys in the salt sensitive genotype was mostly due to higher accumulation of Na+ and Cl- that probably exceeded the amount needed for the osmotic adjustment. Among the inorganic solutes, K+ contributed the most to the Ys in control unstressed seedlings, but its contribution decreased as salt stress increased, especially in the salt sensitive genotype. Soluble carbohydrates and amino acids were the organic solutes that contributed the most to the leaf and root Ys, respectively. No statistically significant difference in these organic solute contributions to the leaf Ys between genotypes was observed. Their contributions to the root Ys, however, were higher in the salt tolerant genotype, especially at higher NaCl concentration. Proline contribution to leaf and root Ys was quite small in both genotypes and its accumulation was not related to salt tolerance. Our results suggest that the salt tolerant genotype was able to maintain a more adequate osmotic pool in the leaves and roots under salt stress than the salt sensitive genotype.

Interaction of NaCl and Cd stress on compartmentation pattern of cations, antioxidant enzymes and proteins in leaves of two wheat genotypes differing in salt tolerance

Physiological mechanisms of salinity–Cd interactions were investigated in inter- and intracellular leaf compartments of salt-tolerant wheat × Lophopyrum elongatum (Host) A. Love (syn. Agropyron elongatum) amphiploid and its salt-sensitive wheat parent (Triticum aestivum L. cv Chinese Spring). In comparison with the intracellular fluid, only very low Na+ concentrations (up to about 4 mM) were found in the intercellular leaf compartment of wheat after a 75 mM supply of NaCl. NaCl salinity led to a higher Cd concentration in leaves of the salt-sensitive genotype. Cd in the intercellular leaf compartment was not detectable. Higher K+ concentrations in the intercellular leaf compartment of the salt-sensitive genotype suggest a higher plasma membrane permeability caused by NaCl + Cd stress. Ascorbate peroxidase (APX) activity was increased in leaves of the salt-sensitive genotype under the combined NaCl and Cd stress. The highest non-specific peroxidase activities were detected under the combined stresses. It is suggested that NaCl and Cd stress in combination enhance the production of oxygen radicals and H2O2, especially in leaves of the salt-sensitive genotype. As a consequence, disturbed membrane function may cause elevated Cd concentrations in the intracellular leaf compartment under salinity. Cd did not change protein concentration and pattern in leaves. The protein content in inter-and intracellular leaf compartments of both genotypes was increased under salinity. A different protein pattern was obtained in inter- and intracellular leaf compartments. Thus, several physiological interactions between NaCl stress and Cd were found in the two wheat genotypes.

Osmotic Stress and Ion-Specific Effects on Xylem Abscisic Acid and the Relevance to Salinity Tolerance in Poplar

We designed two experiments to investigate the osmotic stress and ion-specific effects on xylem abscisic acid (ABA) and the relevance to salinity tolerance in one-year-old seedlings of Populus euphratica Oliv. (a salt-resistant genotype) and one-year-old rooted cuttings of P. 'popularis 35-44' (P. popularis) (a salt-sensitive genotype). Net photosynthetic rates (Pn) and unit transpiration rates (TRN) of the two genotypes were significantly decreased upon osmotic shock caused by PEG 6000 (osmotic potential = -0.24 MPa) or iso-NaCl (50 mM). Shoot xylem ABA concentrations in both genotypes increased rapidly after the onset of PEG stress, resulting from a decreased water flow. NaCl-treated trees of P. euphratica maintained considerably greater concentrations of ABA than PEG-treated plants in a longer term, whereas salinized P. popularis exhibited a transient accumulation of ABA in the shoot. TRN was greatly enhanced in both genotypes when pressure (0.24 MPa) was applied to counteract the osmotic suction of 50 mM NaCl. Pressurizing of root systems diluted solutes in the root xylem, but the dilution effect was more pronounced in P. popularis. Root xylem ABA concentrations in P. euphratica steadily increased with salt stress although pressurization lowered its levels. In contrast, there were no observed changes in ABA response to salinity in pressured P. popularis. Therefore, we concluded that the salt-tolerant P. euphratica had a greater capacity to synthesize ABA under saline conditions, which may partially result from specific salt effects. In addition, P. euphratica exhibited a higher capacity for salt (Na+ and Cl-) transport control under salt stress, compared with P. popularis. The possible association between ABA and salt transport limitation, and the relevance to salinity tolerance were discussed.

Sodium and chloride distribution in roots and transport in three poplar genotypes under increasing NaCl stress

We investigated the effects of increasing soil NaCl on growth, water flow, ion transport and intracellular compartmentation of Na + and Cl − in 1-year-old seedlings of Populus euphratica Oliv. and 1-year-old rooted cuttings of P.× euramericana cv. I-214 (cv. Italica) and P. ‘ popularis 35-44’ ( P. popularis). Relative growth rates of leaf area (RGR A) and shoot height (RGR H) of cv. Italica and P. popularis were severely restricted by increasing salinity, whereas in P. euphratica both were not significantly inhibited . Salinised trees of P. euphratica experienced 10% leaf area loss during a 30-day study, however, cv. Italica and P. popularis shed over 50% of their initial surface area. Leaf necrosis of the two salt-sensitive genotypes (cv. Italica and P. popularis) was attributed to excessive salt accumulation and reduced water loss. The rapid built-up of leaf salt in these two genotypes was mainly the result of high ion concentrations in the transpiration stream. An artificially generated lower shoot-to-root ratio, which was reached by removing approximately 50% of total leaf area from shoots of cv. Italica and P. popularis prior to the salt treatment did not enhance their salinity tolerance since root-to-shoot salt fluxes were largely independent of water flow. Compared with cv. Italica and P. popularis, P. euphratica maintained considerably higher unit leaf transpiration rates with lower salt concentrations in the transpiration stream during the period of salt stress. Therefore, salt tolerance of P. euphratica likely depends on its ability to restrict salt transport to leaves. X-ray microanalysis of root compartments showed that there was genotypic difference in the pattern of ion compartmentation. Cv. Italica exhibited a greater capacity to accumulate salt in cortical vacuoles compared with P. popularis, even though both were considered as salt-sensitive genotypes. P. euphratica was more effective than the other two genotypes to block apoplasmic ion transport and sequester Cl − in cortical vacuoles at high salinity. These limited ion loading into the xylem during radial transport, and thus contributed to the restriction of subsequent axial transport.

Reliable and easy screening technique for salt tolerance of citrus rootstocks under controlled environments

Three salt tolerance experiments using 5 common citrus rootstocks were carried out to find a reliable and easy screening technique for salt tolerance in breeding programs. The experiments were: (1) in vitro seed culture where salt tolerance was mainly evaluated as germination percentage, (2) hydroponic culture of 2-month-old seedlings where salt tolerance was mainly evaluated as survival percentage, and (3) hydroponic culture of satsuma-rootstock combinations where salt tolerance was evaluated by leaf and fruit characters. Treatments were: 4 mm K2CO3 and 0-100 mm NaCl in Expt 1; 3.5 mm K2CO3 and 0-50 mm NaCl, with and without K2CO3, in Expt�2; and 25 mm NaCl in Expt 3. Volkamer lemon was the most salt-sensitive genotype during seed germination (Expt�1), whereas Troyer citrange was the most sensitive when used as rootstock of satsuma (Expt 3). For seedling survival (Expt 2), the trifoliate orange variety Flying dragon showed the highest survival percentage, and chloride content of satsuma leaves and fruit juice were high on this rootstock under salinity (Expt 3). Alkalinity (pH = 8.5) greatly affected seedling survival of Cleopatra mandarin and Volkamer lemon (Expt 2), probably due to major disturbances in seedling nutrition. Analysis of trait values for the rootstocks in the different saline treatments in both the in vitro germination and the seedling survival experiments revealed some significant changes compared with control conditions. Most of these changes were not consistent between genotypes, except for chloride concentration in both shoot ([Cl]s) and root ([Cl]r). The ordering of genotypes for salt tolerance found in the literature, which corresponds to the ordering as chloride excluders in our satsuma Expt 3, agrees with the inverse ordering of genotypes regarding the increment of both [Cl]s and the ratio [Cl]s/[Cl]r from control to low salinity, but does not agree with salt tolerance measured as a percentage of germination or seedling survival. The increments of both [Cl]s and the ratio [Cl]s/[Cl]r from control to low salinity are suggested as criteria for early selection of salt-tolerant citrus rootstocks. Three salt tolerance mechanisms have been observed: chloride exclusion, water saving, and accumulation of soluble solids. They all seem to be presented by Cleopatra mandarin when used as rootstock, supporting its utilisation as donor of salt tolerance in breeding programs of citrus rootstocks.

NaCl pre-treatment at the seedling stage enhances fruit yield of tomato plants irrigated with salt water

Although salt-adaptation seems to be a widespread property of plants, the adaptive response has been rarely differentiated to the tolerance response. We report on the adaptive response of tomato plants to growing under saline conditions following a 15 day pre-treatment with a lower NaCl concentration (half) than that used during the plant growth. After 20 days of salt treatment (100 mM NaCl), the biomass of the adapted plants increased significantly with respect to that of the unadapted plants when the pre-treatment was applied to five leaf seedlings, but not at the two leaf stage. The long-term adaptive response was determined in two tomato genotypes with different tolerance to moderate salt levels. At 70 mM NaCl, the adapted-plants of the more salt-sensitive genotype produced up to 29% more fruit yield than did the unadapted plants. However, no positive effect was observed to long-term in the adapted-plants of the more salt-tolerant genotype, which suggests that the stress level necessary to trigger the adaptive response is related to the tolerance degree of genotype. The physiological response of the plants showing a positive response to the adaptation was also modified to long-term. Thus, K+ concentrations increased in the young leaves of the adapted plants, with respect to unadapted plants, and moreover these differences increased with the salinization period. These results indicate that the changes in growth and physiological responses induced by NaCl pre-treatment at the seedling stage are maintained throughout plant life cycle and this is, therefore, an interesting strategy for increasing the salt tolerance in tomato plants.

NaCl Effects on Root Plasma Membrane ATPase of Salt Tolerant Wheat

Wheat seedlings of a salt tolerant cultivar were grown hydroponically in presence and absence of 100 mM NaCl. Roots were harvested, and the plasma membrane (PM) fraction was purified. PM ATPase required a divalent cations for activity (Mg > Mn > Ca > Co > Zn > Ni > Cu), and it was further stimulated by monovalent cations (K > Rb > NH4 > Li > choline > Cs). The pH optima were 6.0 and 5.6 in absence and presence of 25 mM KCl, respectively. The enzyme was sensitive to vanadate and DCCD but insensitive to azide, oligomycine and nitrate. The enzyme displayed a high preference for ATP but was also able to hydrolyze other nucleotide tri- and diphosphates. The enzyme activity showed a simple Michaelis-Menten kinetics for the substrate Mg2+-ATP in both control and salt exposed roots. The polypeptide patterns of control and salt stressed PM fractions, detected by SDS-PAGE, were very similar. NaCl substantially reduced the PM ATPase specific activity, whereas it had little effect on the apparent Km for Mg2+-ATP. Since the root PM ATPase of salt sensitive and resistant genotypes responded similarly to salinity stress, it seems unlikely that the mechanism of salt tolerance in wheat is primarily based on differences in PM ATPase characteristics.

Root Tip Meristematic Cell and Leaf Chloroplast Structure in Three Barley (H. vulgare L.) Genotypes Exposed to Salinity Stress.

The effect of salinity on the ultrastructure of the chloroplast in the leaf and meristematic cells in the root tips was investigated in three barley genotypes, California Mariout, a salt-tolerant genotype, and two salt-sensitive genotypes, Teo and ICARDA 17. Salinity induced clear changes in the ultrastructure of the chloroplast. The most notable change was disorientated lamellar system with the grana and intergrana lamellae becoming swollen. The chloroplasts of California Mariout were less affected by salinity than those of ICARDA 17. Meristematic cells in the root tips exhibited various degrees of disruption in internal structure : vesiculated plasmalemma, accumulation of lipid droplets, vacuolation of cytoplasm and swelling to a complete damage of mitochondria were observed in the salinity treated plants.

AFLP variation in wild barley (Hordeum spontaneum C. Koch) with reference to salt tolerance and associated ecogeography

Thirty-nine genotypes of Hordeum spontaneum were selected from three geographically separated areas (southwestern, northern, and southeastern) of the Fertile Crescent. The lines were subject to AFLP (amplified fragment length polymorphism) analysis from which a similarity matrix was produced. A dendrogram of the data showed, with two exceptions, that the genotypes grouped together according to area of origin. This was confirmed by principal coordinate analysis in which the first principal coordinate separated the genotypes of the southwestern area from the other two areas, which in turn could be separated by the second principal coordinate. While genotypes from the same site of origin can exhibit very similar AFLP profiles, sharp genetic differences were detected between genotypes separated by relatively short distances. Thirty of the 39 genotypes were subjected to hydroculture salt tolerance tests. These were analysed for shoot Na+ content and carbon isotope composition (&delta;13C) after 4 weeks of treatment (100 mol&#x2219;m&minus;3 NaCl). Shoot Na+ content and &delta;13C were highly correlated. Twelve AFLP markers were found to be associated with both shoot Na+ content and shoot &delta;13C and were also associated with site of origin ecogeographic data, particularly longitude. The most salt tolerant genotype came from Ilam in the southeastern area and the most salt sensitive genotype originated in the southwestern area. The 12 markers were partitioned into groups that showed significant associations within groups but no significant association between groups. In a multiple regression analysis, three AFLP markers, from separate groups, accounted for more than 60% of the variation for shoot Na+ content and &delta;13C. The results demonstrate the effectiveness of AFLP fingerprinting in genetic studies of complex traits at the wild species and (or) population level.