RESPONSE OF SALT STRESSED STRAWBERRY PLANTS TO FOLIAR SALICYLIC ACID PRE-TREATMENTS

Salinity has deleterious effects on plant growth and development through membrane stability, photosynthetic activity, protein content, and ionic composition; however, salicylic acid (SA) could restore these properties in plants. The objective of this study was to determine the ameliorative effects of SA as foliar pre-treatments on membrane permeability, proline and protein contents, chlorophyll a, b and total chlorophyll and ionic composition of strawberry cv. ‘Camarosa’ under saline conditions. Membrane permeability and proline content significantly increased and protein and chlorophyll contents significantly decreased by 6 mS cm^?1 application without SA treatment compared with the control (2 mS cm^?1) treatment. Membrane permeability decreased from 6.9 in 0 mM SA treatment to 5.2 by application of 1.0 mM SA under saline conditions and same to the control (5.2). Compared with 0 mM SA treatment, the average increases of proline and protein contents were 66.7% in 0.25 mM SA treatment and 62.2% in 0.1 mM SA treatment in 6 mS cm^?1 level, respectively. Chlorophyll b and total chlorophyll significantly increased by 0.25 mM SA treatments under saline conditions. The lowest and the highest chlorophyll b and total chlorophyll were obtained from 0 mM SA treatment (19.6 and 44.5 mg L^?1) and 0.25 mM SA treatment (28.6 and 52.9 mg L^?1) in 6 mS cm^?1 salinity level. Ionic compositions of leaves were significantly affected by salinity and SA treatments. Nitrogen in 1.0 mM SA treatment and P contents of leaves in 0.1 mM SA treatment significantly increased but Na and Cl contents of leaves significantly decreased by SA treatments in 6 mS cm^?1 salinity level. The results of this study were clearly indicated that the SA application on strawberry plants could ameliorate the deleterious effect of salt stress on membrane permeability, proline, protein, and chlorophyll contents. Therefore, SA treatment could offer an economic and simple application to salinity stress.     

Effectiveness of salicylic acid in mitigating salt-induced adverse effects on different physio-biochemical attributes in sweet basil (Ocimum basilicum L.)

The objective of this study was to determine the effects of foliar salicylic acid (SA) on salt tolerance of sweet basil seedlings by examining growth, photosynthetic activity, total osmoregulators, and mineral content under salinity. Salinity treatments were established by adding 0, 60, and 120 mM sodium chloride (NaCl) to a base nutrient solution. The addition of 60 and 120 mM NaCl inhibited the growth, photosynthetic activity, and nutrient uptake of sweet basil seedlings, and increased the electrolyte leakage and the plant contents of proline and Na. Sweet basil seedlings were treated with foliar SA application at different concentrations (0.0, 0.50, and 1.00 mM). Foliar applications of SA led to an increase in the growth, chlorophyll content, and gas exchange attributes. With regard to nutrient content, it can be inferred that foliar SA applications increased almost all nutrient content in leaves of sweet basil plants under salt stress. Generally, the greatest values were obtained from 1.00 mM SA application.     

Barley growth,yield, antioxidant enzymes,and ion accumulation affected by PGRs under salinity stress conditions

Application of plant growth regulator (PGR) may alleviate some negative effects of environmental stresses such as salinity. A controlled environment experiment was conducted to study barley (Hordeum vulgare L. cv. Reyhane) growth, yield, antioxidant enzymes and ions accumulation affected by PGRs under salinity stress conditions at Shiraz University during 2012. The treatments were PGRs at four levels—water (as control), cycocel (CCC, 19 mM), salicylic acid (SA, 1 mM), and jasmonic acid (JA, 0.5 mM)—and four salinity levels—no stress (0.67 dS m^?1, as control), 5, 10, and 15 dS m^?1, which were arranged in a factorial experiment based on completely randomized design with four replicates. The results showed that salinity stress significantly decreased plant height, peduncle length, leaf area, ear length, grain number, dry weight, grain yield, harvest index, potassium (K⁺) accumulation, and potassium/sodium (K⁺/Na⁺) concentration ratio, which were closely associated with stress severity. However, PGRs compensated some of these negative effects, so that SA foliar application had the most ameliorative effect. Salt stress also increased Na⁺ accumulation as well as the activity of peroxidase, catalase, and superoxide dismutase (SOD). Since ion discrimination and enhanced antioxidant enzymes are associated with salt tolerance, in this experiment PGRs application might have enhanced K⁺ accumulation and antioxidant enzyme activity. The activity of SOD and K⁺/Na⁺ ratio were found to be useful in salt tolerance manipulation in barley plants.     

Silicon Ameliorates the Adverse Effects of Salinity on Turfgrass Growth and Development

An experiment was conducted to assess the effect of foliar application of potassium silicate on Cynodon dactylon [L.] Pers., Festuca arundinacea Schreb. and Lolium perenne L. With increased salinity level, chlorophyll content and relative water content (RWC) in these three turfgrasses were reduced significantly when compared with the untreated control. Supplementary silicon (Si) ameliorated the adverse effects of salinity on chlorophyll content. Silicon treatments decreased proline at all salinity levels. Moreover, addition of Si increased shoot length and shoot number in all turfgrasses. Sodium (Na) concentration was increased in both leaves and roots of turfgrasses at high salinity level; however, Si treatment significantly reduced Na concentration in all of them. Silicon increased Potassium concentration in shoots and roots (though not significantly) in most cases. It can be concluded that Si alleviated the adverse effects of salt stress in all turfgrasses.     

Effect of salinity and nitrogen on growth,sodium, potassium accumulation,and osmotic adjustment of halophyte Suaeda aegyptiaca (Hasselq.) Zoh

Suaeda aegyptiaca is an important native annual halophyte in salt-affected soils around coastal areas of the Persian Gulf. In order to study the effects of different levels of saturation paste soil salinity (10, 20, 40, 60, and 80 dS m^?1) and nitrogen supply (25, 50, and 75 mg kg^?1 N as urea) on growth and physiological characteristic of S. aegyptiaca, a greenhouse factorial experiment in completely randomized design was conducted with three replications. Salinity treatments were established after early growth of plants and nitrogen was applied in two steps. Results showed that increasing salinity up to 20 dS m^?1 led to increase in dry weight (DW) of plants and this decreased by increasing salinity. Also, DW of plants was significantly increased by application of 75 mg kg^?1 nitrogen. Increasing salinity significantly decreased plant height, chlorophyll index, and total nitrogen content; while proline content and total soluble solids (TSS) were significantly increased. The electrolyte leakage (EL) and sodium concentration were increased under salinity stress. However, further increase in salinity decreased these two parameters. By increasing the nitrogen levels, relative water content (RWC), chlorophyll index, proline, and total nitrogen contents were increased, whereas EL was decreased.     

The effect of zeolite,selenium and silicon on qualitative and quantitative traits of onion grown under salinity conditions

Considering the importance of onion and its cultivation in saline soils, a two-year experiment was carried out to investigate the effects of soil applied zeolite and foliar application of selenium (Se) and silicon (Si) on onion yield, qualitative traits and physiological attributes, under salinity stress. An experiment was performed at three-way factorial design with three replications as follows: zeolite at three levels (0, 4 and 8 ton ha-1), Se at three levels (0, 0.5 and 1 kg ha-1) and Si at three levels (0, 200 and 400 kg ha-1). The results indicated that the effect of year was significant on all studied traits except for soluble solids, bulb nitrogen, leaf sodium and potassium, chlorophyll content and peroxidase activity. Number of small-sized bulbs decreased with increasing zeolite, Se and Si application. Dry matter, soluble solids, nitrogen content, nitrate concentration as well as protein content significantly increased due to zeolite, Se and Si application. Leaf sodium content and enzyme activity decreased due to zeolite, Se and Si application. Overall, 8 ton ha-1 zeolite along with 1 kg ha-1 Se and 400 kg ha-1 Si caused the maximum onion yield and qualitative and physiologic traits including soluble solids, potassium, protein, chlorophyll and photosynthesis .     

EFFECTS OF PHYTOHORMONES ON PROLINE CONTENT AND ANTIOXIDANT ENZYMES OF VARIOUS WHEAT CULTIVARS UNDER SALINITY STRESS

Salinity stress is one of the important agricultural problems in the world. A factorial experiment based on completely randomized design with four replications was conducted to evaluate the effects of phytohormones (gibberellic acid and abscisic acid) on the activity of antioxidant enzymes (peroxidase, superoxide dismutase and catalase), rubisco activity and content, and proline in three wheat cultivars (Gascogen, Zagros, and Kuhdasht) under control and salinity stress (3.5 and 7 dS m^?1). The results showed that salinity stress (3.5 and 7 dS m^?1) decreased the activity of catalase, rubisco, carboxylase, but increased peroxidase, superoxide dismutase activity and proline content. Gibberellic acid caused 58.03% increased in rubisco carboxylase activity in Zagros at 7 dS m^?1 in comparison with abscisic acid under salinity stress compared with the control plants in Kuhdasht. Activity of superoxide dismutase in Kuhdasht cultivar at 7 dS m^?1 salinity level showed 76.43% increased in Gascogen under salinity stress compared with the control plants with gibberellic acid application. The highest proline content as an osmolyte was found in Zagros at 7 dS m^?1 salinity level with abscisic acid (194 μmol g^?1 DM) application. Peroxidase activity increased 83.31% and catalase activity decreased 61.27% compared with the control plants in Zagros. Gibberellic acid application significantly prevented reduction in rubisco content under salinity stress. In conclusion, increased in peroxidase and superoxide dismutase activity and proline content decreased the adverse effects of salinity stress on studied cultivars. Also, the foliage spray of gibberellic acid enhanced and improved the growth condition. In this experiment, Zagros cultivar showed more tolerance to salinity stress than the other two cultivars.     

Effects of Nitrogen Application on Chlorophyll Content,Water Relations,and Yield of Maize Hybrids under Saline Conditions

An experiment was conducted to assess whether accumulation of photosynthetic pigments, proline, and maintenance of water relation attributes relate to the yield of maize hybrids differing in salt tolerance. Two maize hybrids, Pioneer32B33 and Dekalb979, were grown at three salinity levels under four nitrogen treatments. The experiment was laid out in a three-factor randomized complete block design and there were three replications of each treatment. Salt stress significantly decreased leaf chlorophyll a and a/b contents, whereas chlorophyll b and total chlorophyll were slightly increased. Under salinity stress, relative water content decreased, and water potential and osmotic potential become more negative. As a result, turgor potential also decreased. Nitrogen application improved all the chlorophyll pigments, water-related attributes, and yield components. However, chlorophyll a/b ratio was decreased. Overall, because of the differential response of maize hybrids to salt stress in terms of their performance in photosynthetic pigments, water relations, and yield, it can be concluded that hybrid Pioneer32B33 might perform better, if grown under salinity regime and sufficient nitrogen was applied in the growth medium.     

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.     

Effect of salinity and arbuscular mycorrhizal fungi on growth and some physiological parameters of Citrus jambheri

Arbuscular mycorrhizal (AM) fungi alleviate the unfavorable effects of salinity stress on plant growth. A pot study was conducted to determine the effects of AM fungi and salt on growth and some physiological parameters of Citrus jambheri rootstock. Four levels of salinity (2, 4, 6, and 8 dS m^?1 as NaCl) and three mycorrhizal treatments (Glomus etunicatum, Glomus intraradices and non-mycorrhizal (NM) control) were used. As salinity increased, all measured characteristics of plants after 4.5-month growth except Na uptake, proline content, and electrolyte leakage decreased. Shoot dry weight and K uptake were significantly higher in G. intraradices-colonized seedlings than NM controls at all salinity levels. Root dry weight and shoot P uptake were significantly higher in G. etunicatum-colonized seedlings than NM controls at all salinity levels. G. intraradices-colonized seedlings had significantly higher proline content than NM controls and G. etunicatum-colonized seedlings at salinity levels of 4, 6 and 8 dS m^?1. The electrolyte leakage percentage was significantly lower in G. intraradices-colonized seedlings than NM controls at all salinity levels. The data demonstrated that mycorrhizal citrus seedlings exhibited greater tolerance to salt stress than NM seedlings and the enhanced proline content seems to be one of the mechanisms involved.     

Exogenous applications of salicylic acid affect quality and yield of strawberry grown under antifrost heated greenhouse conditions

Abiotic stress is becoming more prevalent as the intensity of agriculture and the demand for farmable land are ever increasing. Besides drought and salinity stress, chilling or freezing stress is one of the most important limiting factors of crop production all around the world. Salicylic acid (SA) is a common plant‐produced signal molecule that is responsible for inducing resistance to a number of biotic and abiotic stresses. This study was conducted to determine the effect of foliar SA applications on fruit‐quality characteristics and yield of strawberry under antifrost heated greenhouse conditions in two successive experiments. Spraying of 1 mM SA (1 mM) was done once (SA1), twice (SA2), three times (SA3), or four times (SA4) during the vegetation period with 7 d intervals. Concentrations of chlorophyll and minerals were measured in leaves, and vitamin C (ascorbic acid), total soluble solids (TSS), titratable acidity (TA), and color (a*) in fruits. Fruit weight, early yield, and total yield were also determined. Foliar applications of SA positively affected TSS and ascorbic acid (AA) content of strawberry fruits. Salicylic acid treatments had no effect on TA of strawberry fruits. SA4 treatment gave the greatest a* in fruit and chlorophyll‐concentration values in the leaves. It was shown that SA treatments increased the content of all nutrients in the leaves of strawberry plants, and greater values often were obtained from SA3 and SA4 treatments. The early yield and total yield of strawberry were significantly affected by SA applications, among which SA3 and SA4 resulted in the highest early and total yields. The present study suggests that SA3 and SA4 treatments can ameliorate the deleterious effects of low temperatures on strawberry plants and that SA application may offer an economical and simple method for low‐temperature protection.     

Influence of Salicylic Acid and Jasmonic Acid on Wheat Under Drought Stress

Salicylic acid and jasmonic acid play an important role in plants coping with abiotic stresses. An experiment was conducted to examine the effect of salicylic acid and jasmonic acid on wheat under drought. Seeds were primed with jasmonic acid (100µM) and salicylic acid (10 Mm). Water stress was applied by withholding water and each treatment was replicated three times with a factorial block design. Application of Salicylic acid and Jasmonic acid mitigated drought effects in wheat. Results revealed that 100µM Jasmonic acid was more effective than 10 mM SA. Drought decreased germination by 26%, whereas application of Jasmonic acid and Salicylic acid ameliorated stress with the increase of germination by 27% and 21%, respectively. An increase in the shoot length of 23% and 20% was observed with Jasmonic acid and Salicylic acid, under drought conditions. The increase in water potential was 60% and 47% with JA and SA while the increase in proline and soluble sugar was 14% and 25% respectively. The application of Jasmonic acid and Salicylic acid has a potential to enhance the growth of wheat plants under drought.     

Physiological and biochemical responses of Melissa officinalis L. to nickel stress and the protective role of salicylic acid

The present study investigated the mediatory effects of salicylic acid (SA) in alleviating nickel (Ni) toxicity in Melissa officinalis L. One-month-old plants were exposed to different levels of Ni and SA concentrations in sand culture under greenhouse conditions. Excess Ni significantly inhibited the growth indices and dramatically increased accumulation of Ni in the leaves and roots. Exogenously SA applications (1.0 mM) led to a substantial improvement in the shoot and root fresh and dry weights. Foliar application of SA mitigated the deleterious effects of Ni and decreased its transport to the shoots. The results showed a significant loss in chlorophylls and carotenoids contents only at 500 µM of Ni. The impact of SA was not significant in terms of chlorophyll contents, while carotenoid contents of the Ni-stressed plants were significantly affected by SA. Exposure to Ni did not modify proline accumulation. Hydrogen peroxide accumulation was observed under Ni stress, while lipid peroxidation significantly decreased at the same conditions. Application of SA caused a significant decrease in electrolyte leakage of Ni-stressed plants. Due to the high potential for Ni accumulation in the roots and translocation factor values lower than 1, M. officinalis could be introduced as an excluder medicinal plant.     

Effects of biofertilizers and cycocel on some physiological and biochemical traits of wheat (Triticum aestivum L.) under salinity stress

In order to study the effects of biofertilizers and cycocel on some physiological and biochemical characteristics of wheat (Triticum aestivum L.) under salinity condition, a factorial experiment was conducted based on randomized complete block design with three replications under greenhouse condition in 2015. Treatments were included salinity in four levels [no salt (control or S₀), salinity 30 (S₁), 60 (S₂) and 90 (S₃) mM NaCl equivalent of 2.76, 5.53 and 8.3 dS m^?1, respectively], four biofertilizers levels [no biofertilizer (F₀), seed inoculation by Azotobacter chrocoocum strain 5 (F₁), Pseudomonas putida strain 186 (F₂), both inoculation Azotobacter + Pseudomonas (F₃)] and three cycocel levels [without cycocel as control (C₀), application of 600 (C₁) and 1000 (C₂) mg L^?1]. Results showed that salinity severe stress (90 mM) decreased chlorophyll content, relative water content (RWC), total chlorophyll, photochemical efficiency of PSII and yield of wheat. Whereas, soluble sugars and proline content, electrical conductivity (EC), the activity of catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) enzymes were increased. Similar results were observed in CAT, POD and PPO activities due to inoculation by biofertilizers and cycocel. Salinity at 30 mM increased the photochemical efficiency of PSII and chlorophyll content in plants grown under biofertilizer and cycocel treatment but with increasing salinity up to 90 mM mentioned parameters were decreased. The highest proline and soluble carbohydrate at all salinity levels were observed in plants treated in the highest cycocel level and Azotobacter+ Pseudomonas application. Generally, it was concluded that biofertilizers and cycocel can be used as a proper tool for increasing wheat yield under salinity condition.     

Influence of Zeolite,Selenium and Silicon upon Some Agronomic and Physiologic Characteristics of Canola Grown under Salinity

The effect of soil applied zeolite, foliar application of selenium and silicon on the agronomic and physiologic traits of canola grown under salt stress conditions was investigated in two-year field experiment during 2012 and 2013. The experimental design was randomized complete blocks, arranged in factorial with 27 treatments forming combinations of zeolite (0, 5 and 10 ton ha^?1), selenium (0, 2 and 4 g liter^?1) and silicon (0, 2 and 4 g liter^?1) and three replicates. The results indicated that zeolite improved plant growth in terms of plant height and increased yield and yield components of canola. In addition, biological yield, harvest index and oil percentage increased due to zeolite application. Zeolite could decrease respiration, malondialdehyde and proline in salt-stressed plants. Soluble sugars and potassium content increased in response to zeolite application while sodium content significantly decreased. Selenium led to an increase in plant height, silique number, seed number in silique, biological yield, harvest index and oil percentage, while respiration, malondialdehyde, proline and sodium decreased on account of selenium application. Similarly, silicon had a significant effect on growth and agronomic traits and increased them. Silicon promoted chlorophyll synthesis while preventing malondialdehyde, proline and sodium accumulation in plant tissues. Catalase and superoxide dismutase activities were suppressed by using silicon on plants. Interaction between zeolite and selenium was significant on leaf relative water content, photosynthesis, chlorophyll content and activity of antioxidant enzymes. In addition, seed weight, seed yield, photosynthesis and soluble sugar content were affected by selenium and silicon application.     

Effects of Silicon Application on Wheat Growth and Some Physiological Characteristics under Different Levels and Sources of Salinity

We investigated the effects of silicon (Si) and the levels and sources of salinity on the growth and some physiological properties of wheat (Triticum aestivum cv. Chamran) in a sandy loam soil under greenhouse conditions. Treatments comprised four Si levels (8, 50, 100 and 150 mg kg^?1 soil), four salinity levels (0.46, 4, 8 and 12 dS m^?1) and two salinity sources (sodium chloride (NaCl) and four-salt combination). Salts combination included NaCl, sodium sulfate (Na₂SO₄), calcium chloride (CaCl₂) and magnesium sulfate (MgSO₄) at a molar ratio of 4:2:2:1. The experiment was arranged as a completely randomized design in a factorial manner, with three replications. Increasing salinity level resulted in a significant decrease in shoot dry weight, chlorophyll content and catalase (CAT) activity, and it caused a marked increase in proline and glycine betaine (GB) concentrations and superoxide dismutase (SOD) enzyme activity. The stimulating effect on GB accumulation and SOD activity was more intense in NaCl-treated plants. However, the source of salinity had no significant effect on shoot dry weight, chlorophyll and proline concentrations, and CAT activity. Si application enhanced all the above-mentioned parameters, except for proline. The suppressing effect of salinity on shoot dry weight, chlorophyll concentration and CAT activity was alleviated by Si supplementation. The stimulating effects of Si fertilization on shoot dry weight and chlorophyll concentration became more pronounced at higher salinity levels. It could be concluded that a decrease in soil osmotic potential, nutrient imbalance and increasing reactive oxygen species (ROS) in salt-treated plants caused growth suppression, while Si supply decreased the deleterious effects of excess salt on wheat growth. Consequently, it appears that when wheat plants are to be grown in salt-affected soils, it is highly recommended to supply them with adequate available silicon (Si).     

Effect of potassium sulfate on the physiological characteristics of canola cultivars in late season drought stress conditions

Abstract

In order to reduce the damage caused by the late-season drought stress of canola, a factorial split-plot experiment was performed based on the randomized complete blocks design with three replications in Karaj, Iran. The treatments were Potassium sulfate in two levels, including application and non-application of potassium sulfate, irrigation at three levels including normal irrigation (control), restricted irrigation from the flowering and pod formation stage, as factorial were in main plots and winter canola cultivars including Opera, L72, KR1, GKH3705, GKH0224 were in subplots. The simple effect of irrigation and potassium sulfate on all of the studied traits and the simple effect of cultivar on all traits except chlorophyll b were significant. The interaction effect of irrigation?×?cultivar on soluble carbohydrate, stomatal resistance, proline content, chlorophyll a and total chlorophyll content was significant. The interaction effect of irrigation?×?potassium sulfate on the amount of soluble carbohydrates, stomatal resistance and proline content of leaves was significant. In irrigation interruption from the pod formation stage, the promising line of L72, and in irrigation interruption from the flowering stage, the Neptune cultivar exhibited the most positive effect of potassium application on the studied traits. As a result, the application of potassium sulfate in addition to the L72 and Neptune cultivars is recommended in areas similar to the tested area encountering the late-season drought stress.     

Drought and Salt Stress Mitigation by Seed Priming with KNO3 and Urea in Various Maize Hybrids: An Experimental Approach Based on Enhancing Antioxidant Responses

Priming offers an effective means for counteracting different stresses induced oxidative injury and raising seed performance in many crop species. The present study was carried out to investigate the ability of potassium nitrate (KNO₃) and urea to promote the tolerance of different maize hybrids to drought and salt stresses to identify some biochemical parameters associated with KNO₃ and urea induced resistance in maize seedlings. An experiment was conducted in a controlled environment of the laboratory at the college of agriculture, Shiraz University, Shiraz Iran, during 2010. The first factor was stress type and intensity at five levels; moderate drought, severe drought, moderate salt, severe salt, and control (without stress). Seed priming was the second factor; water as control, KNO₃, and urea, and maize hybrids, including Maxima, SC704, Zola, and 304 were the third factor. Results indicated that the highest chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (Ch T) contents, and carotenoids (Car) were found in no stress treatments and the most proline, protein contents, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities in severe drought treatment. Also, results revealed that generally, drought and salinity stresses decreased the amount of Ch a and the lowest Ch a was recorded for severe salinity stress (4.29 mg g^?1). Stresses caused decrease in Ch b, but the effect of sever salinity level was higher than the others. Priming of KNO₃ had significantly higher proline content than water and urea priming. The SC704 and 304 hybrids showed higher proline content than the other ones. Finally, the maize seed KNO₃ and urea priming lead to high activities of antioxidant defensive enzymes and increase the tolerance level to abiotic stresses such as salt and drought.     

PHYSIOLOGICAL RESPONSE OF SPRING DURUM WHEAT GENOTYPES TO SALINITY

Soil salinity is a serious threat in many parts of Iran, which negatively affects plant production. In order to investigate response of durum wheat to salinity, two genotypes, ‘Turkey 506’ (salt tolerant) and ‘Egypt 557’ (salt sensitive), were grown in hydroponic conditions, exposed to various salt levels (0, 50, 100, 150 and 200 mmol NaCl) in a split split plot based on randomized complete block design with three replications of each treatment. Salinity stress decreased relative water content (RWC), potassium content, potassium/sodium ratio, chlorophyll a (chla), chlorophyll b (chlb), and total chlorophyll contents, efficiency of photosystem II (F_v/F_m) and membrane stability index (MSI), and increased sodium, proline and soluble sugars concentrations and ratio of chla/chlb in both genotypes. The decrease in RWC, chla, chlb, F_v/F_m, and MSI were significantly higher in ‘Egypt 557’ than ‘Turkey 506’. ‘Turkey 506’ showed higher content of potassium, potassium/sodium ratio, proline, and soluble sugar concentrations as well as lower sodium content as compared with ‘Egypt 557’. The salinity tolerance of ‘Turkey 506’ is associated with higher RWC, potassium content, osmolyte concentrations, chlorophyll contents, F_v/F_m ratio, and maybe more vacuole sequestration of sodium.     

COMPARISON OF OSMOTIC REGULATION IN DEHYDRATION- AND SALINITY-STRESSED SUNFLOWER SEEDLINGS

Plant dry matter accumulation rate (DMAR), relative water content (RWC), electrolyte leakage percentage (ELP), chlorophyll content, osmotic adjustment ability (OAA), and osmotica accumulation in leaves of sunflower (Helianthus annuus L.) seedlings under different levels of dehydration and salinity stress induced by iso-osmotic PEG (polyethylene glycol) or sodium chloride (NaCl) were evaluated. Plants were subjected to four stress treatments for 10 days: ?0.44 MPa PEG6000, ?0.44 MPa NaCl, ?0.88 MPa PEG6000, ?0.88 MPa NaCl. Results showed that PEG and NaCl treatments decreased the plant's DMAR and RWC, and NaCl treatments had more severe inhibitory effect on the plants than PEG treatments. Leaf ELP in sunflower seedlings increased after NaCl and PEG treatments. However, leaf ELP under salt stress was higher than that under dehydration stress (PEG treatment). All stress treatments increased OAA in plant leaves. Leaf OAA was enhanced significantly as PEG concentration increases, while leaf OAA was less enhanced at higher concentration of NaCl. OAA of sunflower leaves under dehydration stress was due to an increase in potassium (K⁺), calcium (Ca²⁺), amino acid, organic acid, magnesium (Mg²⁺), and proline content. OAA of sunflower leaves under moderate salt stress was owing to an increase in K⁺, chlorine (Cl^?), amino acid, organic acid, sodium (Na⁺), and proline content, and was mainly due to an accumulation of K⁺, Cl^?, Na⁺, and proline under severe salt stress.