EFFECTS OF SALINITY ON ACCUMULATION OF MINERAL NUTRIENTS IN WHEAT GROWN WITH NITRATE–NITROGEN OR MIXED AMMONIUM:NITRATE–NITROGEN

ABSTRACT

Two cultivars of wheat (Triticum aestivum cvs. Fresco and Hussar) were grown in hydroponic culture with nitrogen (N) supplied either as nitrate or equimolar ammonium and nitrate, and with a range of concentrations of NaCl from 0 to 100 mM. Plant growth was stimulated by low concentrations of NaCl and was depressed by high concentrations of NaCl. Growth was higher with mixed N nutrition than with nitrate supplied alone at all rates of NaCl supply. Shoot:root ratio was also depressed by salinity. Concentrations of potassium (K) decreased with salinity and were generally higher with mixed N supply, whereas concentrations of Na were higher with salinity and lower with mixed N supply. There were strong positive linear relationships between total plant dry mass and the concentrations of copper (Cu) in the roots and strong negative linear relationships between total plant dry mass and the concentrations of manganese (Mn) in both shoots and roots and zinc (Zn) in the shoots. The concentrations of Cu in the roots were higher with mixed N supply, lower with high salinity, and the concentrations of Mn in both shoots and roots were lower with mixed N supply and generally higher with high salinity. Tissue concentrations of these ions appear to be major determinants of wheat growth in saline environments.     

EFFECTS OF SOIL SALINITY IN THE GROWTH OF AMBROSIA ARTEMISIIFOLIA BIOTYPES COLLECTED FROM ROADSIDE AND AGRICULTURAL FIELD

Morphological differences were observed between roadside (R) and agricultural field (F) biotypes of Ambrosia artemisiifolia, in which R-type seedlings were shorter and produced larger and heavier seeds under greenhouse grown conditions. Previous findings indicated that A. artemisiifolia R-types exhibited greater salt tolerance with respect to germination. However, the impact of biotype and salt tolerance on morphological variation has not been investigated in A. artemisiifolia plants. After performing replicated greenhouse experiments with both biotypes, it was shown that salinity level was a critical factor influencing both seedling and mature plant size and this response was dependent upon biotype. The R-type exhibited slight but significant increases in growth at low/mild salinity levels (50–100 mM) compared with non-saline conditions, while the F-type exhibited significantly reduced growth at the low/mild salinity levels. The reductions in growth of F-type plants in low/mild salinity were similar to those reductions of R-types observed in non-saline conditions. As both biotypes produced seeds at low/mild salinity levels, we conclude that low/mild salinity affects A. artemisiifolia plant size and overall growth rate, and secondly, certain F-type plants may acclimate to the roadside environment over time by reducing their size while producing larger seed under saline conditions. It is possible that this species may exhibit changes in morphology after several generations of exposure to saline roadside conditions. Toxicity due to salt treatment at high salinity (400 mM) was observed in both biotypes, whereas the R-type was more tolerant to both low and high salinity levels with respect to seed germination. Differential A. artemisiifolia growth responses which occur from seed germination to plant maturity may be partially attributed to its ability to tolerate saline soil conditions both under greenhouse and field conditions. This ability to tolerate saline conditions may be especially important in early spring when roadside soils experience increased salinity, caused by de-icing salt treatments applied during the winter season.     

Effect of salt stress on tomato plant and the role of calcium

Abstract

Salinity is one of the serious abiotic stresses that has adverse effects on plant growth. The aim of this study was to investigate the effect of sodium chloride (NaCl) on germination and growth parameters of tomato plant as well as the role of Ca²⁺as an ameliorating agent. 100?mM NaCl and two concentrations of calcium (5 and 10?mM) were applied to tomato seeds and seedlings. This study was carried out in a Completely Randomized Design (CRD) with a total of six treatments each comprising of three replicates. The application of 100?mM of NaCl delayed the germination time by 27.6%, reduced the seedling length and seedling vigor by 24.33% and germination stress tolerance by 27.6% as compared to control. Salinity also reduced the plant growth (root and shoot length, root fresh and dry weight, shoot fresh and dry weight, membrane stability, relative water content and leaf area), whereas the application of calcium mitigated the negative effects of salinity on germination and growth to a greater extent. With increased calcium concentration, growth and germination increased significantly both alone and in the salt-affected plant. 10?mM calcium showed best results and enhanced the promptness index by 20.7%, seedling length and vigor by 15.1% and GSI by 20.7%. It also improved root fresh and dry weight, shoot fresh and dry weight, relative water content and leaf area. Similarly, 5?mM calcium also increased plant height and membrane stability index. The present study suggests that application of Ca²⁺ enhanced the growth of tomato plant under saline conditions.     

Induced Salinity and Supplementary Phosphorus on Growth and Mineral Content of Frijolillo

Abstract

A greenhouse pot experiment was carried out using pumice material to investigate the response of frijolillo [Rhynchosia minima (L.) DC] grown at high salinity to supplementary P (P). Plants were tested during a period from germination to vegetative growth stage. Four levels of sodium chloride (NaCl; 0, 25, 50, and 100 mM) combined with two levels of P (4 and 8 meq L^?1) were tested in a factorial arrangement with four replications. This cultivar was tolerant to salinity stress up to 50 mM of NaCl and its growth was not affected. However, with high salinity (100 mM of NaCl), growth of both stem and root was reduced. Concentration of potassium (K) and P was affected adversely. The increment of P in the saline solution results in a greatest accumulation of biomass and in a better response to the osmotic adjustment of this wild specie. The amount of NaCl was correlated negatively with the amount of K and calcium (Ca) and positively correlated with P and magnesium (Mg).     

Effects of Sodium Chloride and Mineral Nutrients on Initial Stages of Development of Sunflower Life

Abstract

The effects of three levels of salinity [0, 50, and 100 mM of sodium chloride (NaCl)] and the addition of potassium, calcium, nitrogen, phosphorus, iron, manganese, and boron (K, Ca, N, P, Fe, Mn, and B) on seed germination and survival of Helianthus annuus L. plants grown in an inert medium were studied. Increasing levels of salinity significantly decreased germination percentage. The presence of NaCl affected seedling survival rather than germination. Nitrogen addition damaged seedling growth, especially in high saline conditions. Addition of some nutrients may alleviate the effects induced by NaCl. Calcium additions to the culture medium significantly improved germination percentage and seedling survival, which markedly decreased after addition of K and B under saline conditions. Iron addition, especially in the ferrous form, counteracted the effects of salinity on seed germination and seedling survival. Phosphorus addition showed detrimental effects on germination and especially in seedling survival; however, it benefited the surviving seedling's growth.     

Interactive Effect of Moisture Levels and Salinity Levels of Soil on the Growth and Ion Relations of Halophyte

Abstract

A pot culture experiment with four levels of soil moisture (40, 55, 70, and 85% of field capacity) and five levels of sodium chloride (NaCl) concentration (0, 50, 100, 150, and 200 mM) in soil was conducted to examine the interactive effect of soil moisture and NaCl on the growth of halophyte Suaeda salsa. Results showed that growth was largest at 55% of field capacity, in the range of 50–100 mM NaCl. However, at 85% of field capacity, it can grow better at higher salinity levels; and at 40% of field capacity, the growth of S. salsa was increased greatly by moderate salinity. Contents of sodium (Na) and chloride (Cl) in plant tissues increased with the decrease of moisture levels of soil. Potassium (K) concentrations were also increased at low soil moisture. Drought tolerance was increased by moderate NaCl concentrations. It is thus considered that some amounts of Na and Cl are required to absorb water in this plant.     

Salinity Effects on Yield and Yield Components of Contrasting Naked Oat Genotypes

ABSTRACT

Global crop production systems are challenged by the increasing areas of saline soil in arid and semi-arid regions. Two naked oat (Avena sativa L.) lines (‘VAO-7’ and ‘VAO-24’) with distinct seedling tolerance to salinity were subjected to six levels of salt concentrations in a controlled greenhouse, and the response of yield and yield components to salinity stress was determined. The salt treatments 50, 100, 150, 200, and 250 mM sodium chloride (NaCl) (corresponding to EC: 3.42, 6.74, 9.66, 12.40, 15.04 dS m^?1) imposed through modified Hoagland solution. Plain Hoagland was used as control. Complete nutrient elements were provided during the entire growth period. At maturity, the number of tillers with emerged heads was counted; the plant was then harvested and separated into shoots, seeds, and roots. Both plant height and days to maturity were shortened with increasing salt stress. Among the yield components, spikelet, tiller number, and grain dry weight per plant were significantly reduced by increasing salt concentration. Number of spikelets and grain weight per plant were the most salt-sensitive yield components. Thousand grain weight also varied as salinity stress increased. Harvest index remained relatively unchanged until the salinity reached 150 mM and higher. Our data indicate that grain yield reduction in oat due to salinity stress is associated with reduced number of grains per plant and mean grain weight.     

Effect of exogenous application of salicylic acid on salt-stressed sorghum growth and nutrient contents

This study was conducted to investigate the effect of salinity and foliar application of salicylic acid (SA) on sorghum biomass and nutrient contents. Treatments were comprised of salinity levels (0 and 100?mM NaCl) and SA concentrations (0.3, 0.7, 1.1 and 1.5?mM). Salinity increased sodium (Na), chlorine (Cl) and copper (Cu) but decreased nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulfur (S), iron (Fe), zinc (Zn) and manganese (Mn) contents and the root and shoot dry matter. Fe and Zn were the most affected nutrients by salinity. However, SA reduced Na and Cl but increased plant dry matter and nutrient content. SA had greater positive effects on root than on shoot dry matter. Maximum increases through SA were achieved in N, K, Fe, Mn, Cu, and shoot weight under salt stress but in Zn and root weight under non-saline condition. In most cases 1.1?mM was the most effective SA concentration in reducing the negative effects of salinity.     

Genotype-Dependent Differential Responses of Three Forage Species to Calcium Supplement in Saline Conditions

Salt toxicity comprises of osmotic and ionic components both of which can severely affect root and shoot growth. In many crop species, supplemental calcium (Ca) reduces the inhibition of growth typical of exposure to salt stress. The objective of this study was to compare whole plant growth and physiological responses to interactive effect of salinity and Ca level on three forage species [African millet (AM), tall wheat grass (TW), and perennial ryegrass (PR)] differing in tolerance to sodium chloride (NaCl) salinity. Plants were grown under glasshouse condition and supplied with nutrient solution containing 0, 100, and 250 mM NaCl supplemented with 0.5, 5, or 10 mM calcium chloride (CaCl₂). Plant growth, ionic concentration, water relations, and solute (proline and glycinebetaine) concentrations of the plants were determined two weeks after the salinity treatments. At 100 mM NaCl, there was a moderate reduction in dry matter (DM) production of all three species. A drastic decrease in DM occurred at 250 mM NaCl. Supplemental Ca reduced the adverse effects of salinity on all three species. The TW showed higher shoot and root growth in 100 and 250 mM NaCl than AM and PR. It also showed the highest DM at 5 and 10 mM Ca supplement. The shoot and root DM of TW increased by about 45 and 15%, respectively compared to the control. Chemical analysis indicated that in TW, Ca restricted both uptake and transport of sodium (Na) from root to shoot. It also increased Ca and potassium (K) concentrations in both organs. The transport of K and Ca from root to shoot of AM and PR were decreased by NaCl, but were restored with increasing Ca in the medium. The opposite occurred for Na. In PR, more K uptake was observed in shoot at 250 mM NaCl with 10 mM Ca supplement. The sap osmotic potential (Ψ_S) was the highest in TW at 10 mM Ca in the presence of 250 mM NaCl. Contribution of various solutes to the difference in Ψ_S among the species from the control and 250 mM salt treatment differed greatly. Supplemental Ca induced decline in the leaf Ψ_S of TW which was predominately due to K, glycinebetaine, Na and proline accumulation. Addition of 10 mM Ca to the growth medium maintained a low Na and a high K level. Accumulation of glycinebetaine and proline in leaf contributed the NaCl tolerance of TW. The presented results suggest that supplement Ca, not only improved ionic relations but also induced plant ability in production of compatible solutes (glycinebetaine and proline) and osmotic adjustment. Accordingly, genotype dependent capacity could be found using supplemental Ca.     

Interactive effects of salinity and iron deficiency on different rice genotypes

Salinity adversely affects plant growth, photosynthesis, and availability of nutrients including iron. Rice (Oryza sativa L.) is susceptible to soil salinity and highly prone to iron (Fe) deficiency due to lower release of Fe‐chelating compounds under saline conditions. In order to investigate the effects of salinity and low iron supply on growth, photosynthesis, and ionic composition of five rice genotypes (KS‐282, Basmati Pak, Shaheen Basmati, KSK‐434 and 99417), a solution culture experiment was conducted with four treatments (control, 50 mM NaCl, Fe‐deficient, and 50 mM NaCl + Fe‐deficient). Salinity and Fe deficiency reduced shoot and root growth, photosynthetic and transpiration rates, chlorophyll concentration, and stomatal conductance. The reduction in all these parameters was more in the interactive treatment of salinity and low Fe supply. Moreover, a significant increase in shoot and root Na⁺ with corresponding decrease in K⁺ and Fe concentrations was also observed in the combined salinity and Fe‐deficiency treatment. Among the tested genotypes, Basmati Pak was the most sensitive genotype both under salt stress and Fe deficiency. The genotype KS‐282 performed better than other genotypes under salinity stress alone, whereas Shaheen Basmati was the best genotype under Fe deficiency in terms of all the studied parameters.     

Evaluation of Salt Tolerance and Its Relationship with Carbon Isotope Discrimination and Physiological Parameters of Barley Genotypes

Soil management through the cultivation of salt-tolerant plants is a practical approach to combat soil salinization. In this study, salt tolerance of 35 barley (Hordeum vulgare L.) genotypes was tested at four salinity levels (0, 100, 200, and 300 mM NaCl in Hoagland nutrient solution) at two growth stages (germination and vegetative). The relationship between salinity tolerance and carbon isotope discrimination (CID) was also accessed. Results of the study carried out under laboratory conditions showed that a negative linear relationship was observed between salt concentration and germination as well as other growth parameters. Some genotypes showed good salt tolerance at germination but failed to survive at seedling stage. However, five genotypes, namely, Jau-83, Pk-30109, Pk-30118, 57/2D, and Akermanns Bavaria showed better tolerance to salinity (200 mM) both at germination and at vegetative growth stage. The salt tolerance of these barley genotypes was significantly correlated with minimum decrease in K⁺:Na⁺ ratio in plant tissue with increase in the root zone salinity. However, the case was reversed in sensitive genotypes. CID was decreased linearly with increase in root zone salinity. However, salt-tolerant genotypes maintained their turgor by osmotic adjustment and by minimum increase in diffusive resistance and showed minimum reduction in CID (Δ) with gradual increase in rooting medium salt concentration. Results suggested that the tolerant genotypes make osmotic adjustments by selective uptake of K⁺ and by maintaining a higher K⁺:Na⁺ ratio in leaves. Moreover, CID technique can also be good criteria for screening of salt-tolerant germplasm.     

Ameliorative Effect of Hydro Gel Substrate on Growth,Inorganic Ions,Proline, and Nitrate Contents of Bean under Salinity Stress

The effect of varying hydrogel (0, 0.5, and 1.0% w/w) supply on some agro-physiological properties, such as dry matter, nutrient contents, chlorophyll contents, proline content, and ionic balance of bean plants in different salt sources and stress due to doses were investigated. Plants were treated with eight salt sources [sodium chloride (NaCl), sodium sulfate (Na₂SO₄), calcium chloride (CaCl₂), calcium sulfate (CaSO₄), potassium chloride (KCl), potassium sulfate (K₂SO₄), magnesium chloride (MgCl₂), magnesium sulfate (MgSO₄)] and four concentrations (0, 30, 60, and 120 mM doses) for 60 days in a growth media. Salt type, doses, and hydrogel (HG) affected the soil electrical conductivity. Soil salinity affected the parameters considered, and changed the nutrient balance of plants. High salt concentration caused substantial reduction in plant growth. Different salt concentrations negatively affected plant dry weight. The highest decrease of plant root dry weight was obtained with NaCl application followed by Na₂SO₄, CaCl₂, CaSO_4, MgCl₂, MgSO₄, KCl, and K₂SO₄, and similarly NaCl, Na₂SO₄, CaCl₂, CaSO_4, KCl, K₂SO₄, MgCl₂, and MgSO₄ in root dry weight. Total chlorophyll and nitrate contents of plants decreased with increasing salt doses, and the lowest value was obtained for NaCl application. Proline contents of plants were increased with increasing salt doses, and the highest value was obtained with the NaCl application. The effects of salt concentrations in nitrogen (N), potassium (K), and phosphorus (P) content of plants were significant. The presence of salt in the growth medium induced an important decrease the macro nutrient of the root and shoot part of plant such as N, P, K, calcium (Ca), and magnesium (Mg) content, but the N and P content of root and shoot part of the plant were increased with increasing of the HG application doses. The highest N and P increases were obtained with the 1.0 HG application for all salt types for both the root and shoots of plants. The HG added to saline soil significantly improved the variables affected by high salinity and also increased plant N and P, reduced soil electricity conductivity, nitrate, proline, and electrolyte leakage of plants, enhanced plant root and shoot dry weight by allowing nutrients and water to release to the plant as needed. The results suggested that HG has great potential for use in alleviating salinity stress on plant growth and growth parameters in saline soils of arid and semi-arid areas. This HG appears to be highly effective for use as a soil conditioner in vegetable growing, to improve crop tolerance and growth in saline conditions. It is intended to confirm the results of these studies by field trials.     

Nitrogen and NaCl salinity effects on the growth and nutrient acquisition of the grasses Aeluropus littoralis,Catapodium rigidum,and Brachypodium distachyum

Salinity and low nitrogen availability are important growth‐limiting factors for most plants. Our objective was to assess the influence of nitrogen (N) and salt levels on the growth and mineral nutrition of three forage grasses of varying salt resistance which are widely found in Tunisian salt lands, Aeluropus littoralis, Catapodium rigidum, and Brachypodium distachyum. Their response to salt and N interaction has not been studied and further investigations are necessary. Twenty day–old plantlets were hydroponically cultivated in Hewitt's nutrient solution. Half the plants were then exposed to 100 mM NaCl and the other half to no NaCl, and N was supplied at 0.5 or 5.0 mM N as NH₄NO₃. Plants were harvested after 60 d growth. Saline treatment (100 mM NaCl) decreased growth of B. distachyum (a relatively salt‐sensitive plant), but no significant effect was noted for A. littoralis (a relatively salt‐resistant plant) in both low– and high–N availability treatments. However, the effect of 100 mM NaCl on growth of C. rigidum (a moderately salt‐resistant plant) depended on N level. Increasing N availability and NaCl did not influence phosphate, sulfate, calcium, and magnesium concentrations in both A. littoralis and C. rigidum, but increased N supply reduced shoot sodium and chloride (Cl^–) accumulation. Potassium acquisition in A. littoralis and C. rigidum plants was severely depressed by increasing N availability under saline and nonsaline conditions, respectively. In these species, the increase of nitrate accumulation via N was attenuated by salinity. In contrast, total N content and allocation toward shoots were enhanced in these conditions, especially in A. littoralis, the most resistant species. It appears that increasing N availability at moderate salt levels has a beneficial effect on growth of species with high and moderate salt resistance, but not on species with low resistance to salinity.     

Seed Treatment to Overcome Salt and Drought Stresses During Germination in Safflower (Carthamus tinctorius L.)

Although safflower is drought and salt tolerant, it is susceptible to drought and salinity at the germination and seedling stages. Priming techniques have been used to overcome salinity and drought tolerance at germination stage. Osmopriming potassium nitrate (KNO₃) and hydropriming were used to determine drought [by polyethylene glycol (PEG)-6000 at water potentials of 0, ?0.3 and ?0.6 MPa] and salt electrical conductivity (EC) (values of the sodium chloride (NaCl) solutions were 0, 6 and 12 ds.m^?1) tolerance of primed seeds of safflower. Germination index, shoot/root ration, germination uniformity, days to 50% germination (D50) and abnormal germination percentage were measured. Treatment 0f seeds with hydropriming increased germination index, shoot/root ration and germination uniformity, while decrease days to 50% germination under salt and water stress. Seed treated with KNO₃ reduced abnormal germination percentage in salt stress. KNO₃ improved germination uniformity and germination index of the low water potentials. As salinity increased, germination index and shoot/root ration were decreased, while germination uniformity, days to 50% germination and abnormal germination percentage were increased. Hydropriming enhanced germination under both salt and drought stresses and non-stress conditions. Therefore, hydropriming could be used to improved seed performance of safflower under saline and drought stress. This treatment dose not needs expensive chemicals or sophisticated equipment.     

Inducing Salt Tolerance in Wheat by Exogenously Applied Ascorbic Acid through Different Modes

ABSTRACT

In order to assess whether exogenous application of ascorbic acid (AsA) through different ways could alleviate the adverse effects of salt-induced adverse effects on two wheat cultivars differing in salinity tolerance, plants of a salt tolerant (‘S-24’) and a moderately salt sensitive (‘MH-97’) cultivar were grown at 0 or 120 mM sodium chloride (NaCl). Ascorbic acid (100 mg L^?1) was applied through the rooting medium, or as seed soaking or as foliar spray to non-stressed and salt stressed plants of wheat. Salt stress-induced reduction in growth was ameliorated by exogenous application of ascorbic acid through different ways. However, root applied AsA caused more growth enhancement under saline conditions. Leaf ascorbic acid, catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities were also maximal in salt stressed plants of both cultivars treated with AsA through the rooting medium. Furthermore, leaf ascorbic acid, CAT, POD, and SOD activities were higher in salt stressed plants of ‘S-24’ than those of ‘MH-97’. Root applied AsA caused more enhancements in photosynthetic rate. Root applied AsA caused more reduction in leaf sodium (Na⁺) compared with AsA applied as a seed soaking or foliar spray. Overall, AsA-induced growth improvement in these two wheat cultivars under saline conditions was cultivar specific and seemed to be associated with higher endogenous AsA, which triggered the antioxidant system and enhanced photosynthetic capacity.     

Involvement of nitrogen in salt resistance of Atriplex portulacoides is supported by split‐root experiment data and exogenous application of N‐rich compounds

Using a split‐root system, we aimed to identify the limiting factors for the growth of the halophyte Atriplex portulacoides L. under extreme salinity (800 mM NaCl) conditions. One half of the root system was immersed in complete nutrient solution at 0 or 800 mM NaCl and the other half was immersed in NaCl‐free medium, containing all nutrients or deprived of potassium (K⁺) or calcium (Ca²⁺) or nitrogen (N). Data indicate that at high salinity levels A. portulacoides growth is limited by the restrictions imposed by NaCl on N uptake. Next, the alleviation of the adverse impact by salt stress (800 mM NaCl) on plant growth was investigated through urea (U) and/or thiourea (TU) external addition through foliar application. Whether separately or supplied together, both components mitigated the negative impact of salinity on the plant growth by significantly improving the photosynthetic activity parameters [CO₂ assimilation rate, stomatal conductance and maximum quantum efficiency of PSII photochemistry (F_v/F_m)], as well as shoot N concentration and the photosynthetic nitrogen‐use efficiency (PNUE). A concomitant increase of protein and free amino acid concentrations was also observed. As a whole, the present study highlights the significance of N in A. portulacoides response to high salinity and suggests that combined application of U and TU could promote the growth of this halophyte potentially useful for saline soil reclamation and revegetation purposes.     

Enhancing of symbiotic efficiency and salinity tolerance of chickpea by phosphorus supply

This study aims to highlight the beneficial effect of the phosphorus on enhancing of growth plant, the efficiency of use rhizobial symbiosis and ionic partition in chickpea grown under salt stress. Exposure of plants to salt stress (0, 150 mM of NaCl) caused ionic imbalance, which resulted in increased Na⁺ and P and reduced K⁺ contents in the leaves and root. Indeed, stressed plants showed decrease of plant growth and phosphorus use efficiency. The efficiency use of rhizobial symbiosis was also affected by salinity. However, addition of two different level of phosphorus (37 and 55 mM) to saline soil increased significantly availability of P in plant organs. Specially, the (150 mM NaCl?×?37 mM P) mixture increased (33%) phosphorus use efficiency, induced better nodulation and increased plant biomass which results in the high efficiency in use of the rhizobial symbiosis. Our findings suggest that the combination of low level of P to saline soil presumably improved the tolerance of chickpea plant to salinity.

Abbreviations: phosphorus (P); phosphorus use efficiency (PUE); biological nitrogen fixation (BNF); plant dry weight (PDW); yeast extract mannitol (YEM); efficiency in use of the rhizobial symbiosis (EURS); shoot dry weight (SDW); symbiotic nitrogen fixation (SNF).     

Effect of Foliar Salicylic Acid Applications on Growth,Chlorophyll, and Mineral Content of Cucumber Grown Under Salt Stress

The objective of this study was to determine the effect of foliar salicylic acid (SA) applications on growth, chlorophyll, and mineral content of cucumber grown under salt stress. The study was conducted in pot experiments under greenhouse conditions. Cucumber seedlings were treated with foliar SA applications at different concentrations (0.0, 0.25, 0.50, and 1.00 mM). Salinity treatments were established by adding 0, 60, and 120 mM of sodium chloride (NaCl) to a base complete nutrient solution. The SA was applied with spraying two times as before and after transplanting. Salt stress negatively affected the growth, chlorophyll content and mineral uptake of cucumber plants. However, foliar applications of SA resulted in greater shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight as well as higher plants under salt stress. Shoot diameter and leaf number per plant increased with SA treatments under salt stress. The greatest chlorophyll content was obtained with 1.00 mM SA treatment in both saline and non-saline conditions. Leaf water relative content (LWRC) reduced in response to salt stress while SA raised LWRC of salt stressed cucumber plants. Salinity treatments induced significant increases in electrolyte leakage. Plants treated with foliar SA had lower values of electrolyte leakage than non-treated ones. In regard to nutrient content, it can be interfered that foliar SA applications increased almost all nutrient content in leaves and roots of cucumber plants under salt stress. Generally, the greatest values were obtained from 1.00 mM SA application. Based on these findings, the SA treatments may help alleviate the negative effect of salinity on the growth of cucumber.     

Salinity and Temperature Effects on Seed Germination of Milk Thistle

Abstract

Milk thistle [Silybum marianum (L.) Gaertn] is an annual plant belonging to the Asteraceae family whose ripe seeds contain flavonoid substances, which are important in the modern pharmaceutical industry. Seed germination is a major factor limiting the establishment of plants under saline conditions. The effect of salinity and temperatures on germination and seedling establishment was studied in two genotypes of milk thistle, an Iranian wild type and German (Royston) type in the laboratory and in the field. Experiments were done with seven salt concentrations [0.1 (control), 1, 3, 6, 9, 12, and 15 dS/m] and three temperatures (15, 25, and 35°C). There were three replications for each treatment, and the experiment was run three times. The results showed that the percentage of germination and the number of normal seedlings at different salt treatment at 15°C were higher than at 25 or 35°C. The mean time to 50% germination was least at this temperature for both genotypes. Results suggested all germination indices and seedling emergence (50%) were achieved at levels up to 9 dS/m salinity at 15°C. Also, seeds at a salinity of 9–15 dS/m will germinate and up to 25% of the control nonstress treatment could emerge at the low temperature of 15°C.     

RESPONSES OF SOME ENZYMES AND KEY GROWTH PARAMETERS OF SALT-STRESSED MAIZE PLANTS TO FOLIAR AND SEED APPLICATIONS OF KINETIN AND INDOLE ACETIC ACID

The study examined the effects of kinetin (KIN) and indoleacetic acid (IAA) applied as seed treatment or sprayed on leaves of salinity stressed plants. Five -week old maize (Zea mays L. cv. ‘DK 647 F1’) plants were grown in pots containing peat and perlite in 1:1 (v/v) mixture. Different treatments used were: 1) control (nutrient solution alone), 2) salt stress [100 mM sodium chloride (NaCl)], 3) 100 mM NaCl and 1 mM kinetin (KIN), 4) 100 mM NaCl and 2 mM KIN, 5) 100 mM NaCl and 1 mM indole acetic acid (IAA), 6) 100 mM NaCl and 2 mM IAA, 7) 100 mM NaCl and 25 mg L^?1 KIN and 8) 100 mM NaCl and 25 mg L^?1 IAA. In treatments 7 and 8 application was to the seeds, for treatments 3-6 it was applied to foliage. The seeds were soaked in KIN or IAA solution for 12 h. Salt stress reduced the total dry matter, chlorophyll content, and relative water content (RWC), but increased proline accumulation, activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7), catalase (CAT; EC. 1.11.1.6) and polyphenol oxidase (PPO; 1.10.3.1) and electrolyte leakage. Both foliar applications of KIN and IAA treatments overcame to variable extents the adverse effects of NaCl stress on the above mentioned physiological parameters. However, seed treatments with KIN or IAA did not improve salinity tolerance in maize plants. Furthermore, foliar application or seed treatments with KIN and IAA reduced the activities of antioxidant enzymes in the salt stressed-plants. Salt stress lowered some macronutrient concentrations [calcium (Ca) and potassium (K) in leaves and roots, phosphorus (P) in roots] but foliar application of both KIN and IAA increased Ca in both leaves and roots and P in leaves. Foliar application of IAA increased K concentrations in leaves of the salt-stressed plants. Foliar application of KIN and IAA, especially at 2 mM concentration, counteracted some of the adverse effects of NaCl salinity by causing the accumulation of proline and essential inorganic nutrients as well as by maintaining membrane permeability.