Salt-sensitive Cv Research Articles

GhCLC5/16 genes participate in the regulation of Cl−-salinity tolerance in seedlings of different upland cotton cultivars

For plants or crops exposed to salinity stress, chloride channels (CLCs) play crucial functions in the regulation of anion (such as Cl− and NO3−) absorption, transport and distribution or anion homeostasis. In this study, how the physiological functions and molecular mechanisms of GhCLC5/16 genes affect Cl− -salinity tolerance in two upland cotton cultivars (the salt-tolerant cv. Lu7619 and the salt-sensitive cv. Xin51) was investigated using transformations of the yeast Δgef1 mutant, soybean hairy-root, Arabidopsis atclc-b mutant, and virus-induced gene silencing (VIGS) cotton plants. The results showed that, the target GhCLC5/16 genes, with the higher NaCl-induced upregulation of expression in the roots of Lu7619 plants, could complement the Cl−-sensitive phenotype of the yeast Δgef1 mutant. Under NaCl stress, compared to empty vector (EV) plants, GhCLC5/16-overexpressed soybean hairy-root composite plants (hrGhCLC5/16-OE) displayed enhanced NaCl tolerance with superior growth, lower relative electrolytic leakage (REL) values and malondialdehyde (MDA) contents in roots and leaves. Compared to the atclc-b mutant, atclc-b-GhCLC5 and atclc-b-GhCLC16 Arabidopsis seedlings displayed improved NaCl tolerance with less reduced root length, higher leaf chlorophyll content, lower shoot MDA content and REL values. GhCLC5/16-VIGS cotton plants displayed mitigated salt damage with significantly higher plant height and fresh weight (FW) than that of EV plants. The enhanced NaCl tolerance or mitigated salt damage of these plants, even with the salt-tolerant cv. Lu7619 (characterized by high GhCLC5/16 expression in the roots, whole plants, or GhCLC5/16-silencing in the leaves), occurs because the plants can accumulate more Cl− in the roots under NaCl stress, reduce the transport and accumulation of Cl− to shoots (especially the leaves), simultaneously enhance the NO3− content in the shoots/leaves, and thus significantly decrease the Cl−/NO3− ratio in the shoots/leaves. Therefore, GhCLC5/16 genes may be crucial members of the GhCLC family that contribute to the varied tolerance to Cl−-salinity observed in different cotton cultivars. The results may provide new perspectives and valuable candidate gene resources for molecular breeding of chloride-salinity tolerance in cotton and other crops.

Physiological and Biochemical Parameters of Salinity Resistance of Three Durum Wheat Genotypes.

The area of farming lands affected by increasing soil salinity is growing significantly worldwide. For this reason, breeding works are conducted to improve the salinity tolerance of important crop species. The goal of the present study was to indicate physiological or biochemical parameters characterizing three durum wheat accessions with various tolerance to salinity. The study was carried out on germinating seeds and mature plants of a Polish SMH87 line, an Australian cultivar ‘Tamaroi’ (salt-sensitive), and the BC5Nax2 line (salt-tolerant) exposed to 0–150 mM NaCl. Germination parameters, electrolyte leakage (EL), and salt susceptibility index were determined in the germinating caryopses, whereas photosynthetic parameters, carbohydrate and phenolic content, antioxidant activity as well as yield were measured in fully developed plants. The parameters that most differentiated the examined accessions in the germination phase were the percentage of germinating seeds (PGS) and germination vigor (Vi). In the fully developed plants, parameters included whether the plants had the maximum efficiency of the water-splitting reaction on the donor side of photosystem II (PSII)–Fv/F0, energy dissipation from PSII–DIo/CSm, and the content of photosynthetic pigments and hydrogen peroxide, which differentiated studied genotypes in terms of salinity tolerance degree. Salinity has a negative impact on grain yield by reducing the number of seeds per spike and the mass of one thousand seeds (MTS), which can be used as the most suitable parameter for determining tolerance to salinity stress. The most salt-tolerant BC5Nax2 line was characterized by the highest PGS, and Vi for NaCl concentration of 100–150 mM, content of chlorophyll a, b, carotenoids, and also MTS at all applied salt concentrations as compared with the other accessions. The most salt-sensitive cv. ‘Tamaroi’ demonstrated higher H2O2 concentration which proves considerable oxidative damage caused by salinity stress. Mentioned parameters can be helpful for breeders in the selection of genotypes the most resistant to this stress.

Silicate Inhibits the Cytosolic Influx of Chloride in Protoplasts of Wheat and Affects the Chloride Transporters, TaCLC1 and TaNPF2.4/2.5.

Chloride is an essential nutrient for plants, but high concentrations can be harmful. Silicon ameliorates both abiotic and biotic stresses in plants, but it is unknown if it can prevent cellular increase of chloride. Therefore, we investigated the influx of Cl− ions in two wheat cultivars different in salt sensitivity, by epifluorescence microscopy and a highly Cl−-sensitive dye, MQAE, N-[ethoxycarbonylmethyl]-6-methoxy-quinolinium bromide, in absence and presence of potassium silicate, K2SiO3. The Cl−-influx was higher in the salt-sensitive cv. Vinjett, than in the salt-tolerant cv. S-24, and silicate pre-treatment of protoplasts inhibited the Cl−-influx in both cultivars, but more in the sensitive cv. Vinjett. To investigate if the Cl−-transporters TaCLC1 and TaNPF2.4/2.5 are affected by silicate, expression analyses by RT-qPCR were undertaken of TaCLC1 and TaNPF 2.4/2.5 transcripts in the absence and presence of 100 mM NaCl, with and without the presence of K2SiO3. The results show that both transporter genes were expressed in roots and shoots of wheat seedlings, but their expressions were differently affected by silicate. The TaNPF2.4/2.5 expression in leaves was markedly depressed by silicate. These findings demonstrate that less chloride accumulates in the cytosol of leaf mesophyll by Si treatment and increases salt tolerance.

Cadmium accumulation in the grain of durum wheat is associated with salinity resistance degree

A serious problem in durum wheat cultivation is its genetic capacity to accumulate cadmium (Cd) in the grain. The aim of the study was to verify if the degree of durum wheat resistance to NaCl salinity is related to its tolerance to Cd contamination, and to search for physiological markers of Cd accumulation in the grain. The experiment involved a salt sensitive cv. Tamaroi and a salt resistant line BC<sub>5</sub>Nax<sub>2</sub>, as well as a moderately salt tolerant line SMH87. The plants grew in the soil supplemented with 3 mg or 5 mg Cd/kg dry weight. The plant response to Cd was evaluated based on chlorophyll fluorescence (ChlF) and Cd content in the grains. Toxic effects of both Cd levels on photosynthetic performance index were the strongest in salt sensitive cv. Tamaroi, which showed the highest Cd content in the seeds. We therefore assumed that tolerance to salinity and Cd has a common physiological background, and that ChlF parameters may be used as the markers of Cd tolerance.

Supplemental potassium mediates antioxidant metabolism, physiological processes, and osmoregulation to confer salt stress tolerance in cabbage (Brassica oleracea L.)

Soil salinity is one of the severe threats of climate change that inflicts heavy losses to vegetable production. Potassium (K) has been considered essential approach against abiotic stresses in food crops, however, understanding of K regulated mechanisms for inducing tolerance to NaCl stress in cabbage (Brassica oleracea L.) plants is, still elusive. Here, we report the supplemental K effects on antioxidant defense system and physiological processes that may influence the cabbage production under saline conditions. Initially, cabbage varieties (‘Stone Head’, ‘Golden Acre’, ‘9j-940’, ‘Beauty Ball’, ‘Green Ball’, ‘Green Rise’, ‘Marco F-1’) were tested under NaCl stress (50, 100, 150, and 200 mM) for their higher growth, vigor index and mineral contents. The identified cabbage var. salt-tolerant, cv. Beauty Ball (BB) and salt-sensitive cv. Green Ball (GB) were further exposed to foliar K (5 and 10 mM solutions of KNO3) under the same NaCl regimes. NaCl stress markedly inhibited photosynthetic efficiency, water status and chlorophyll pigments, thereby, resulted in reduced dry biomass of both varieties. Nevertheless, exogenous K spray at 10 mM caused positive gain in leaf water relations, chlorophyll contents in both cabbage varieties. The ameliorative impacts of K were more pronounced in salt-tolerant cv. BB as compared to salt-sensitive cv. GB in terms of higher accumulation of total soluble proteins, total free amino acids, proline contents, upregulated antioxidant activities and enhanced gas exchange characteristics. Hence, improvement in growth and K+/Na+ ratio of cabbage plants by foliar K application (10 mM) were related to up-regulation of physiological and biochemical mechanisms under saline conditions.

Exogenously applied zinc and copper mitigate salinity effect in maize (Zea mays L.) by improving key physiological and biochemical attributes

Zinc or copper deficiency and salinity are known soil problems and often occur simultaneously in agriculture soils. Plants undergo various changes in physiological and biochemical processes to respond to high salt in the growing medium. There is lack of information on the relation of exogenous application of Zn and Cu with important salinity tolerance mechanisms in plants. Therefore, the present study was conducted to determine the effect of foliar Zn and Cu on two maize cultivars (salt-tolerant cv. Yousafwala Hybrid and salt-sensitive cv. Hybrid 1898). Salinity caused a significant reduction in water and turgor potentials, stomatal conductance, and transpiration and photosynthetic rate, while increase in glycine betaine, proline, total soluble sugars, and total free amino acids was evident in plants under saline regimes. Furthermore, there was significant decline in P, N, Ca, K, Mn, Fe, Zn, and Cu and increase in Na and Cl contents in plants fed with NaCl salinity. Nitrate reductase activity was lower in salt-stressed plants. However, foliar application of Zn and Cu circumvented salinity effect on water relations, photosynthesis, and nutrition and this was attributed to the better antioxidant system and enhanced accumulation of glycine betaine, proline, total free amino acids, and sugars. The results of the present study suggested that Zn application was superior to Cu for mediating plant defense responses under salinity.

Salt response of photosynthetic electron transport system in wheat cultivars with contrasting tolerance

Soil salinity significantly decreases the photosynthetic efficiency and plant growth in wheat (Triticum aestivum L.). However, sensitivity of the photosynthetic electron transport system of wheat in relation with salt stress is unclear. Two wheat cultivars with contrasting salt tolerance were exposed to soil salinity, and the physiological responses and performance of photosynthetic electron system were investigated. The depressed photosynthetic carbon assimilation was mainly caused by stomatal closure and lower photosynthetic electron transport efficiency. Under salt stress, the salt-resistant cv. YN19 had higher efficiency in photosynthetic electron transport, hence maintaining higher photosynthetic rate under salt stress, compared with the salt-sensitive cv. JM22. In addition, the parameters derived from fast chlorophyll a fluorescence induction curve, i.e. the quantum yield for electron transport (φEo) and the probability that an electron moves futher than QA (ψEo), can be used as indicators for rapid screening of wheat cultivars tolerant to soil salinity.

Synergistic effects of drought and ascorbic acid on growth, mineral nutrients and oxidative defense system in canola (Brassica napus L.) plants

A study was conducted to find out the role of ascorbic acid (AsA) in modulating growth and different physio-biochemical attributes of canola plants under well-watered as well as water-deficit conditions. Drought stress imposed on 60 % field capacity significantly decreased the shoot and root fresh and dry weights, leaf chlorophyll contents, shoot and root P, root K+, and activity of CAT enzyme, while increased chlorophyll a/b contents, MDA, NPQ, leaf total phenolics, free proline and GB contents in both canola cultivars. Foliar-applied varying levels (50, 100 and 150 mg L−1) of AsA enhanced shoot and root fresh and root dry weights, qN, NPQ, shoot and root P, AsA as well as the activity of POD enzyme particularly under drought stress conditions. Of both canola cultivars, cv. Dunkeld was higher in shoot fresh weights, ETR and F v /F m, MDA, proline and GB contents, and POD activity, however, cv. Cyclone in total phenolics and qN under well-watered and water-deficit conditions. Overall, the foliar-applied AsA had a positive effect, though not marked, on salt sensitive cv. Cyclone in terms of improved growth and other attributes, whereas exogenously applied AsA had a non-significant effect on relatively salt tolerant cv. Dunkeld.

Expression and functional analysis of putative vacuolar Ca2+-transporters (CAXs and ACAs) in roots of salt tolerant and sensitive rice cultivars

Vacuolar Ca2+-transporters could play an important role for salt tolerance in rice (Oryza sativa L.) root. Here, we compared the expression profiles of putative vacuolar cation/H+ exchanger (CAX) and calmodulin-regulated autoinhibited Ca2+-ATPase (ACA) in rice roots of salt tolerant cv. Pokkali and salt sensitive cv. IR29. In addition to five putative vacuolar CAX genes in the rice genome, a new CAX gene (OsCAX4) has been annotated. In the present study, we isolated the OsCAX4 gene and showed that its encoded protein possesses a unique transmembrane structure and is potentially involved in transporting not only Ca2+ but also Mn2+ and Cu2+. These six OsCAX genes differed in their mRNA expression pattern in roots of tolerant versus sensitive rice cultivars exposed to salt stress. For example, OsCAX4 showed abundant expression in IR29 (sensitive) upon prolonged salt stress. The mRNA expression profile of four putative vacuolar Ca2+-ATPases (OsACA4-7) was also examined. Under control conditions, the mRNA levels of OsACA4, OsACA5, and OsACA7 were relatively high and similar among IR29 and Pokkali. Upon salt stress, only OsACA4 showed first a decrease in its expression in Pokkali (tolerant), followed by a significant increase. Based on these results, a role of vacuolar Ca2+ transporter for salt tolerance in rice root was discussed.

Influence of foliar-applied triacontanol on growth, gas exchange characteristics, and chlorophyll fluorescence at different growth stages in wheat under saline conditions

A greenhouse experiment was conducted to examine the effect of foliar application of triacontanol (TRIA) on two cultivars (cv. S-24 and MH-97) of wheat (Triticum aestivum L.) at different growth stages. Plants were grown in full strength Hoagland’s nutrient solution under salt stress (150 mM NaCl) or control (0 mM NaCl) conditions. Three TRIA concentrations (0, 10, and 20 μM) were sprayed over leaves at three different growth stages, i.e. vegetative (V), boot (B), and vegetative + boot (VB) stages (two sprays on same plants, i.e., the first at 30-d-old plants and the second 78-d-old plants). Salt stress decreased significantly growth, net photosynthetic rate (P N), transpiration rate (E), chlorophyll contents (Chl a and b), and electron transport rate (ETR), while membrane permeability increased in both wheat cultivars. Stomatal conductance (g s) decreased only in salt-sensitive cv. MH-97 under saline conditions. Foliar application of TRIA at different growth stages enhanced significantly the growth, P N, g s, Chl a and b contents, and ETR, while membrane permeability was reduced in both cultivars under salt stress. Of various growth stages, foliar-applied TRIA was comparatively more effective when it was applied at V and VB stages. Overall, 10 μM TRIA concentration was the most efficient in reducing negative effects of salinity stress in both wheat cultivars. The cv. S-24 showed the better growth and ETR, while cv. MH-97 exhibited higher nonphotochemical quenching.

QTLs mapping of physiological traits related to salt tolerance in young rice seedlings

Oryza sativa L. F2 population and F2:3 derived from a cross between salt tolerance cv. Tarommahali and salt sensitive cv. Khazar were used in this study. A linkage map based on F2 population was constructed (74 SSR markers on 192 individuals), which covered a total of 1231.50 cM with an average two locus interval of 19.83 cM. Two QTLs related to Na+/K+ ratio were found on chromosome 3 and 6. qDM-3 and qDM-8 (for dry mass of shoot) are major QTLs with very large effects explained 20.90 and 17.72 % of the total phenotypic variance, respectively. Major locus for DM (qDM-3) was bracketed by RM1022 - RM6283 spread over 13.6 cM on chromosome 3. Major part of the variability for standard tolerance ranking (STR) was explained by the qSTR-6 flanked by RM3727 - RM340 on chromosome 6, which exhibited phenotypic variance of 17.25 % and peak likelihood ratio (LR) of 17.51. The length of this QTL is 8.8 cM and identification of any tightly linked markers in this region will serve as a candidate gene for fine-mapping. qSTR-3 overlapped with qNA-3 and qNAK-3. The qSTR-3 may contain a new major gene for salt stress tolerance at seedling stage in rice. Major QTLs identified in this paper, after fine-mapping, could be used for marker assisted selection.

Effect of salt stress on antioxidant defense systems, lipid peroxidation, and chlorophyll content in green bean

Salt stress-induced changes in antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR), total chlorophyll content, and lipid peroxidation measured as malondialdehyde (MDA) content, in leaves of a green bean genotype Gevas sirsk 57 (GS57) and cv. Fransiz 4F-89 differing in salt tolerance were investigated. Plants were subjected to three salt treatments (0, 50, and 100 mM NaCl) under controlled climatic conditions for 7 days. The salt-sensitive cv. 4F-89 exhibited a decrease in GR activity at all salt treatments, but the salt-tolerant genotype GS57 showed only a slight decrease in GR under 50 mM salt treatment and an increase under 100 mM salt treatment. CAT and APX activities increased with increasing salt stress in both varieties. CAT and APX activities were higher in the salt-tolerant GS57 than salt-ensitive cv. 4F-89. The two varieties showed an increase in MDA content with an increase in salinity, but the increase in sensitive cv. 4F-89 under salt stress was higher than that in salt-tolerant GS57 genotype. The increasing NaCl concentration caused a reduction in the chlorophyll content in cv. 4F-89 but not in GS57.

Sodium Chloride-Induced Changes in Mineral Nutrients and Proline Accumulation in Indica Rice Cultivars Differing in Salt Tolerance

ABSTRACT The effect of increasing sodium chloride (NaCl; 0 to 300 mM) stress was investigated on plant growth, mineral nutrients, and proline accumulation in two indica rice cultivars differing in salt tolerance. The shoots and roots of ‘Karjat-3’ (salt sensitive cv.) showed greater reduction in fresh weight, dry weight, and water content under increasing salinity stress when compared to ‘Panvel-3’ (salt tolerant cv.). The magnitude of chloride (Cl) accumulation with increasing salinity varied between cultivars, with lesser accumulation in ‘Panvel-3’, whereas, calcium (Ca) content was more in ‘Panvel-3’ than ‘Karjat-3’ at all salinity levels. Increase in shoot-sodium (Na) did not show notable variation between cultivars under salinity stress; however, Na accumulation was notably lower in roots of ‘Panvel-3’ than ‘Karjat-3’. Under increasing salinity stress, ‘Panvel-3’ maintained significantly lower sodium/potassium, sodium/calcium and sodium/nitrogen ratios than ‘Karjat-3’, both in shoots and roots, with more differential response in roots. Regardless of treatment, proline concentration was considerably higher in ‘Panvel-3’ than in ‘Karjat-3’. The salt tolerance of cv. ‘Panvel-3’ was positively correlated with better growth, higher proline accumulation and enhanced uptakes of beneficial minerals such as potassium (K) and Ca.

Expressions of OsHKT1, OsHKT2, and OsVHA are differentially regulated under NaCl stress in salt-sensitive and salt-tolerant rice (Oryza sativa L.) cultivars

Under NaCl-dominated salt stress, the key to plant survival is maintaining a low cytosolic Na(+) level or Na(+)/K(+) ratio. The OsHKT1, OsHKT2, and OsVHA transporter genes might play important roles in maintaining cytosolic Na(+) homeostasis in rice (Oryza sativa L. indica cvs Pokkali and BRRI Dhan29). Upon NaCl stress, the OsHKT1 transcript was significantly down-regulated in salt-tolerant cv. Pokkali, but not in salt-sensitive cv. BRRI Dhan29. NaCl stress induced the expression of OsHKT2 and OsVHA in both Pokkali and BRRI Dhan29. In cv. Pokkali, OsHKT2 and OsVHA transcripts were induced immediately after NaCl stress. However, in cv. BRRI Dhan29, the induction of OsHKT2 was quite low and of OsVHA was low and delayed, compared with that in cv. Pokkali. OsHKT2 and OsVHA induction mostly occurred in the phloem, in the transition from phloem to mesophyll cells, and in the mesophyll cells of the leaves. The vacuolar area in cv. Pokkali did not change under either short- (5-10 min) or long-term (24 h) salt stress, although it significantly increased 24 h after the stress in cv. BRRI Dhan29. When expressional constructs of VHA-c and VHA-a with YFP and CFP were introduced into isolated protoplasts of cvs Pokkali and BRRI Dhan29, the fluorescence resonance energy transfer (FRET) efficiency between VHA-c and VHA-a upon salt stress decreased slightly in cv. Pokkali, but increased significantly in cv. BRRI Dhan29. The results suggest that the salt-tolerant cv. Pokkali regulates the expression of OsHKT1, OsHKT2, and OsVHA differently from how the salt-sensitive cv. BRRI Dhan29 does. Together, these proteins might confer salt tolerance in Pokkali by maintaining a low cytosolic Na(+) level and a correct ratio of cytosolic Na(+)/K(+).

Mechanisms of salt tolerance and interactive effects of Azospirillum brasilense inoculation on maize cultivars grown under salt stress conditions

The present work has been performed to study the growth and metabolic activities of two maize cultivars (cv. 323 and cv. 324) which are shown to have different tolerances to salt stress and to determine the effects of inoculation with Azospirillum spp. Along with identifying the mechanisms of maize salt tolerance and the role of Azospirillum (growth promoting rhizobacteria) in elevating salinity stress conditions is examined Maize cv. 323 was the most sensitive to salinity, while cultivar 324 was the most resistant of the 12 maize cultivars tested. Cultivars differences were apparent with certain growth criteria as well as related metabolic activities. The lack of a negative response to increasing NaCl concentration for water content, dry matter yield and leaf area of cv. 324 up to a concentration of − 0.6 MPa indicated salt tolerance. While for cv. 323 there was a marked inhibitory effect of salinity on growth. In the tolerant cv. 324, soluble and total saccharides, soluble protein in shoots and total protein in roots increased with salinity stress. The sensitivity of cv. 323 however was associated with depletion in saccharides and proteins. Proline accumulation was higher and detected earlier at a lower salinity concentration in the salt sensitive cv. 323 comapred to the salt tolerant cv. 324. When salt stressed maize was inoculated with Azospirillum, proline concentration declined significantly. The present study showed, in general, that the concentration of most amino acid increased on exposure to NaCl as well as when inoculated with Azospirillum. The relatively high salt tolerance of cv. 324, compared with cv. 323 was associated with a significantly high K+/Na+ ratio. Azospirillum inoculation markedly altered the selectivity of Na+, K+ and Ca++ especially in the salt sensitive cultivar cv. 323. Azospirillum restricted Na+ uptake and enhanced the uptake of K+ and Ca++ in cv. 323. A sharp reduction in the activity of nitrate reductase and nitrogenase in shoots and roots of both cultivars was induced by salinity stress. This reduction in NR and NA activity was highly significant at all salinity concentrations. Azospirillum inoculation stimulated NR and nitrogenase activity in both shoots and roots of both cultivars. The differential effect of Azospirillum inoculation on maize cv. 323 and cv. 324 illustrates the different sensitivity of these two cultivars to stress, but still does not provide any clues as to the key events leading to this difference.

Carbohydrate and proline contents in leaves, roots, and apices of salt-tolerant and salt-sensitive wheat cultivars

Intra-specific variations in nonstructural carbohydrates and free proline were determined in leaves, apices, roots, and maturing seeds of two salt-tolerant cultivars (CR and Kharchia-65) and one salt-sensitive cv. Ghods of spring wheat (Triticum aestivum L.) grown in sand culture at various levels of salinity (0, 100, 200, and 300 mM NaCl and CaCl2 at 5 : 1 molar ratio) under controlled environmental conditions. The levels of leaf, apex, and root ethanol-soluble carbohydrates, fructans, starch, and proline increased in line with elevating level of salinity in all three cultivars under investigation. The contents of proline, soluble and insoluble carbohydrates in the apex increased to levels exceeding those in the leaves and roots. Soluble carbohydrate content of salt-sensitive cv. Ghods was higher in the leaves, apices, and roots and lower in the maturing seeds than in the other cultivars at all levels of salinity except at 300 mM. The results show considerable variation in the amount of soluble, insoluble sugars, and proline among plant tissues and wheat genotypes in response to salinity. Higher soluble carbohydrates and fructan in leaves, roots and maturing seeds of stressed plants indicate that their accumulation may help plant to tolerate salinity. Salt-sensitive cv. Ghods accumulated less soluble sugars in the maturing seeds and higher soluble sugars in the apices, which might be used as an indicator in screening wheat genotypes for salinity tolerance.

SALT TOLERANCE IN TWO SOYBEAN CULTIVARS

Experiments were conducted in an environmentally controlled growth chamber to evaluate the role of the root system in the salt tolerance of two soybean (Glycine max(L.) Merr.) cultivars, Tachiyutaka and Dare, that differ in salt tolerance. Young plants were submitted to 0 (control), 40, 80, and 120 mM NaCl treatments for 3, 23, and 30 days in three experiments, respectively. The most significant differences between the two cultivars were obtained in 40 mM NaCl. Under this condition, compared with salt sensitive cv. Tachiyutaka, tolerant cv. Dare showed a higher relative shoot and root growth (Dare: 70 and 63%, Tachiyutaka: 42 and 42%, respectively), water extraction ability (Dare: 0.18 g cm−2 d−1 for transpiration and 0.98 g m−1 d−1 for water uptake, Tachiyutaka: 0.13 g cm−2 d−1 and 0.81 g m−1 d−1 respectively), root pressure (Dare: 5.68 mg g−1 for root exudate, Tachiyutaka: 0.32 mg g−1), better root osmotic adjustment (Dare: −0.61 MPa for osmotic potential, Tachiyutaka: −0.59 MPa), and less sodium (Na+) accumulation in plant tissue (Dare: 0.1, 0.4, and 9.2 mg g−1 in leaf, stem, and root, respectively, Tachiyutaka: 1.4, 3.5, and 11.6 mg g−1). The difference in salt tolerance between the two cultivars is attributed to the root system. The salt tolerance of cv. Dare is associated with high water uptake, and Na+ and chloride (Cl−) exclusion of the roots.

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO2 assimilation rate (P N), stomatal conductance (g s), and transpiration rate (E) declined, and intercellular CO2 concentration (C i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P N and g s coupled with a better C i and water use efficiency (WUE) than the sensitive cultivar.

Changes in Soluble Proteins in Spring Wheat Stressed with Sodium Chloride

Two newly developed salt-tolerant genotypes of spring wheat, S24 and S36 and their salt-tolerant parents, LU26S (from Pakistan) and Kharchia (from India) along with a salt-sensitive cv. Potohar were grown in full strength Hoagland's nutrient solution with 0 or 125 mM NaCl. At the onset of the booting stage third leaf from top was sampled for protein analysis. Total soluble protein content increased due to salt treatment in all cultivars/lines but this increase was more marked in salt-sensitive cv. Potohar and low in salt-tolerant S24 as compared with the other lines. Patterns of labelled polypeptides in all cultivars/lines were identical; the differences were only quantitative (for instance, 29 kD and 48 kD polypeptides were reduced significantly due to NaCl treatment only in the cv. Potohar).

Root elongation in saline solution related to calcium binding to root cell plasma membranes

To gain a better understanding of the relations between root elongation and the amount of Ca2+ bound to the plasma membrane (PM), melon plants were grown in aerated solutions containing different concentrations of CaCl2 with various concentrations of NaCl or mannitol. With increasing external concentrations of NaCl or mannitol, root elongation was suppressed. Addition of CaCl2 to the external medium alleviated the inhibition of root elongation by high concentrations of Na+, but not of mannitol. Root elongation in media containing high concentrations of NaCl was correlated with the computed amount of Ca2+ bound to the PM. A model describing relative root elongation (RRL) under salt stress was developed. This model takes into account the osmotic potential in the growing solution (based on the mannitol experiments) and the computed amount of Ca2+ bound to the PM. Calcium binding was calculated by applying a Gouy-Chapman-Stern sorption model using the same parameters deduced from studies on PM vesicles. This model combines electrostatic theory with competitive binding at the PM surface. The model for RRL allowed the computation of a critical value for the fraction of negative sites binding Ca2+ on the PM needed for nearly optimal (95%) root elongation. Any decrease below this critical value decreased the RRL. Root elongation of Honey Dew (salt-resistant cv.) was greater than that of Eshkolit Ha'Amaqim (salt-sensitive cv.) under NaCl stress. Nearly optimal root growth for Honey Dew and Eshkolit Ha'Amaqim occurred when 40% and 51% of total membrane charged sites were bound by Ca2+, respectively. The effect of osmotic potential on the suppression of root elongation was the same for the two cultivars. To our knowledge, this report provides the first fully quantitative estimates of PM-bound Ca2+ relative to salt toxicity.