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.     

Protective role of proline against salt stress is partially related to the improvement of water status and peroxidase enzyme activity in cucumber

Abstract

A salt-sensitive cucumber cultivar “Jinchun No. 2” (Cucumis sativus L.) was used to investigate the role of proline in alleviating salt stress in cucumber. Proline was applied twice (day 0 and day 4 after salt treatment) as a foliar spray, with a volume of 25?mL per plant at each time. Plant dry weight, leaf relative water content, proline, malondialdehyde (MDA), Na⁺, K⁺ and Cl^? contents, as well as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities in the plants were determined at day 8 after salt treatment. The results showed that 100?mmol?L^–1 NaCl stress significantly decreased plant dry weight, leaf relative water and K⁺ contents, and increased leaf MDA, Na⁺ and Cl^? contents and SOD, POD, CAT and APX activities. However, leaf proline accumulation was not affected by salinity. The exogenous application of proline significantly alleviated the growth inhibition of plants induced by NaCl, and was accompanied by higher leaf relative water content and POD activity, higher proline and Cl^? contents, and lower MDA content and SOD activity. However, there was no significant difference in Na⁺ and K⁺ contents or in CAT and APX activities between proline-treated and untreated plants under salt stress. Taken together, these results suggested that the foliar application of proline was an effective way to improve the salt tolerance of cucumber. The enhanced salt tolerance could be partially attributed to the improved water status and peroxidase enzyme activity in the leaf.     

Nitrate Reduction and Nutrient Accumulation in Wheat Grown in Soil Salinized with Four Different Salts

ABSTRACT

The effect of salinization of soil with Na₂SO₄, CaCl₂, MgCl₂, and NaCl (70:35:10:23) on the biochemical characteristics of three wheat (Triticum aestivum L.) cultivars (‘LU-26S,’ ‘Sarsabaz’ and ‘Pasban-90’) was investigated under natural environmental conditions. Twenty-day-old seedlings of all three cultivars were subjected to three salinity treatments: 1.3 (control), 5.0, and 10 dSm^?1 for the entire life period of plants. After 120 d of seed sowing, plant biomass production decreased by 49% and 65%, respectively, in response to 5 and 10 dSm^?1 salinity levels. Addition of salts to growth medium also had a significant adverse effect on plant height. Increasing salinity treatments caused a great reduction in nitrate reductase activity (NRA) of the leaf. The inhibitory effect of salinity on nitrate reduction rate was more pronounced at the reproductive stage than at the vegetative stage of plant growth. Wheat cultivars ‘LU-26S’ and ‘Sarsabaz’ showed less reduction in NRA due to salinity compared with ‘Pasban-90.’ Ascending salinity levels significantly reduced potassium (K⁺) and calcium (Ca²⁺) accumulation in shoots, while the concentration of sodium (Na⁺) was increased. Salts of growth medium increased the shoot nitrogen (N) concentration, whereas phosphorous (P) concentration of shoots was significantly reduced due to salinity. Wheat cultivars ‘LU-26S’ and ‘Sarsabaz’ proved to be the salt-tolerant ones, producing greater biomass, showing less reduction in NRA, maintaining low sodium (Na⁺), and accumulating more K⁺ and Ca²⁺ in response to salinity. These two cultivars also showed less reduction in shoot K⁺/Na⁺ and Ca⁺/Na⁺ ratios than in ‘Pasban-90,’ particularly at the 10 dSm^?1 salinity level.     

Effects of 5‐aminolevulinic acid on water uptake,ionic toxicity,and antioxidant capacity of Swiss chard (Beta vulgaris L.) under sodic‐alkaline conditions

Sodic‐alkalinity may be more deleterious to plant growth than salinity. The objectives of this study were to determine whether 5‐aminolevulinic acid (ALA: an essential precursor for chlorophyll biosynthesis) foliar application could improve the sodic‐alkaline resistance of Swiss chard (Beta vulgaris L. subsp. cicla ) by regulating water uptake, ionic homeostasis, photosynthetic capacity, and antioxidant metabolism. Eight‐week‐old uniform plants were grown in nutrient medium without and with a sodic‐alkaline regime generated by a mixture of NaHCO₃ and Na₂CO₃ (NaHCO₃ : Na₂CO₃ = 9:1 molar ratio) for 12 d, and leaves were sprayed daily with water or ALA. The Na⁺ and ALA concentrations were gradually increased to 60 mM and 120 μM, respectively. ALA foliar application alleviated the physiological damage from sodic‐alkalinity, as reflected by the increases in plant dry weight, relative growth rate, chlorophyll, Mg²⁺ concentration, and the decrease in Na⁺ concentration. However, ALA foliar application did not change the water uptake capacity or the concentration of K⁺, Fe³⁺, and endogenous ALA in leaf tissues under sodic‐alkaline conditions. ALA foliar application effectively mitigated damage from sodic‐alkalinity because of the increased activity of antioxidant enzymes (catalase and guaiacol peroxidase), particularly superoxide dismutase activity, which was maintained at the same level as for control plants. These results suggest that ALA foliar application alleviated sodic‐alkaline stress mainly owing to its antioxidant capacity, and superoxide dismutase has the main responsibility for reducing oxidative stress in Swiss chard.     

Comparative Effect of Nitrogen Forms on Nitrogen Uptake and Cotton Growth Under Salinity Stress

The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na⁺), ammonium (NH₄⁺), and nitrate (NO₃^?) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO₃-N were greater than those treated with NH₄-N with or without salinity stress. Under salinity stress, the Na⁺ content of seedlings treated with NO₃-N was lower than that in seedlings treated with NH₄-N owing to higher root Na⁺ efflux. A lower net NO₃^? efflux was observed in roots of nitrate-fed plants relative to the net NH₄⁺ efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in different tissues, especially in leaves, thereby enhancing photosynthesis in nitrate-fed plants under salinity stress. Nitrate-N is superior to ammonium-N based on nitrogen uptake and cotton growth under salinity stress.     

Drought and salinity: A comparison of their effects on mineral nutrition of plants

The increasing frequency of dry periods in many regions of the world and the problems associated with salinity in irrigated areas frequently result in the consecutive occurrence of drought and salinity on cultivated land. Currently, 50% of all irrigation schemes are affected by salinity. Nutrient disturbances under both drought and salinity reduce plant growth by affecting the availability, transport, and partitioning of nutrients. However, drought and salinity can differentially affect the mineral nutrition of plants. Salinity may cause nutrient deficiencies or imbalances, due to the competition of Na⁺ and Cl^– with nutrients such as K⁺, Ca²⁺, and NO . Drought, on the other hand, can affect nutrient uptake and impair acropetal translocation of some nutrients. Despite contradictory reports on the effects of nutrient supply on plant growth under saline or drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and when the drought or salt stress is severe. A better understanding of the role of mineral nutrients in plant resistance to drought and salinity will contribute to an improved fertilizer management in arid and semi‐arid areas and in regions suffering from temporary drought. This paper reviews the current state of knowledge on plant nutrition under drought and salinity conditions. Specific topics include: (1) the effects of drought and salt stress on nutrient availability, uptake, transport, and accumulation in plants, (2) the interactions between nutrient supply and drought‐ or salt‐stress response, and (3) means to increase nutrient availability under drought and salinity by breeding and molecular approaches.     

Effects of foliar selenium application on some physiological and phytochemical parameters of Vitis vinifera L. cv. Sultana under salt stress

Abstract

In this research the effect of foliar application of selenium (Se) at four levels (Na₂OSe₄; 0, 5, 10 and 20?mg L^?1) was evaluated on some phytochemical characteristics of Sultana grapevine under different salinity levels (NaCl; 0 or 75?mM). The vines were fed twice a week with Hoagland nutrient solution and Se was foliar applied twice with 24 intervals. During growing period, plant height, leaf number and leaf area were recorded. Moreover, at the end of experiment, mature leaves from middle nods of canes were used for measurement of some phytochemical indices. According to results, Se application had a positive effect on plant height, leaf numbers, leaf area and photosynthetic pigments content especially at 5?mg L^?1 and to some extent 10?mg L^?1 Se levels. Under salinity stress, foliar application of Se at 5?mg L^?1 considerably decreased vines leaves electrolyte leakage and lipid peroxidation values compared to non se-treated plants under salinity stress condition. Selenium had an additive effect on salinity stress (75?mM NaCl) induced accumulation of total phenol, total flavonoid, soluble sugars and proline content in leave of vines. Moreover, the interaction of salinity and Se at 5 and 10?mg L^?1 improved leaves antioxidant enzymes activities in Sultana grapevine. Likewise, foliar application of Se improved leaf mineral content in 75?mM NaCl -treated vines. Totally, foliar application of selenium (Se at 5 or 10?mg L^?1) increased salt tolerance through improvement in nutritional balance and by enzymatic and non-enzymatic antioxidant capacity in grapevine leaves.     

Effects of foliar application of methanol on some physiological characteristics of Lavandula stoechas L. under NaCl salinity conditions

In order to study the effects of foliar applications of methanol (0, 15, and 30%) and NaCl salinity (0, 50, and 100?mM) on some physiological characteristics of Lavandula stoechas L. plants, a pot experiment was carried out at the Research Greenhouse of Azarbaijan Shahid Madani University. Physiological characteristics (stem and leaf dry weights, total phenolic and flavonoids compounds, chlorophyll a and K⁺ contents, and K⁺/Na⁺ ratio) were significantly affected by the interaction effects of Methanol foliar application and salinity levels. The highest K⁺ content, K⁺/Na⁺ ratio, chl a and stem dry weight, belonged to NaCl 0?×?Methanol 30% and NaCl 50?×?Methanol 30%. For the leaves’ dry weight, the greatest data were recorded for NaCl 0?×?Methanol 30% and NaCl 0?×?methanol 15%. Methanol spray promoted the total phenolic content, especially at NaCl 50?×?methanol 30% and NaCl 100?×?methanol 15% and 30% and flavonoid content at NaCl 50?×?methanol 30%. Anthocyanin content, essential oil percent, and flower dry weight were affected by NaCl salinity levels, and the highest amount of anthocyanin was recorded for the control treatment. The highest data for Essential oil was attained by the NaCl 0 and 50?mM. The Na⁺ content was affected by methanol foliar application and the highest amount was obtained in the control treatment. Both foliar application levels and salinity levels influenced the flower dry weight. The highest amount of the flower dry weight was recorded at 30% methanol spray level and 0?mM NaCl treatments. The results reveal that methanol application had significant effects on the physiological characteristics of Lavandula plants growing under salinity stress condition.     

Potassium–sodium interactions in soil and plant under saline‐sodic conditions

About 7% of the total land around the globe is salt‐affected causing a great loss to agriculture. Salt stress refers to the excessive amount of soluble salts in the root zone which induce osmotic stress and ion toxicity in the growing plant. Among toxic ions, sodium (Na⁺) has the most adverse effects on plant growth by its detrimental influence on plant metabolism in inhibiting enzyme activities. An optimal potassium (K⁺) : Na⁺ ratio is vital to activate enzymatic reactions in the cytoplasm necessary for maintenance of plant growth and yield development. Although most soils have adequate amounts of K⁺, in many soils available K⁺ has become insufficient because of large amounts of K⁺ removal by high‐yielding crops. This problem is exacerbated under sodic or saline‐sodic soil conditions as a consequence of K⁺‐Na⁺ antagonism. Here K⁺ uptake by plants is severely affected by the presence of Na⁺ in the nutrient medium. Due to its similar physicochemical properties, Na⁺ competes with K⁺ in plant uptake specifically through high‐affinity potassium transporters (HKTs) and nonselective cation channels (NSCCs). Membrane depolarization caused by Na⁺ makes it difficult for K⁺ to be taken up by K⁺ inward‐rectifying channels (KIRs) and increases K⁺ leakage from the cell by activating potassium outward‐rectifying channels (KORs). Minimizing Na⁺ uptake and preventing K⁺ losses from the cell may help to maintain a K⁺ : Na⁺ ratio optimum for plant metabolism in the cytoplasm under salt‐stress conditions. It would seem a reasonable assumption therefore that an increase in the concentration of K⁺ in salt‐affected soils may support enhanced K⁺ uptake and reduce Na⁺ influx via HKTs and NCCSs. Although very useful information is available regarding K⁺‐Na⁺ homeostasis indicating their antagonistic effect in plants, current knowledge in applied research is still inadequate to recommend application of potassium fertilizers to alleviate Na⁺ stress in plants under sodic and saline‐sodic conditions. Nevertheless some encouraging results regarding alleviation of Na⁺ stress by potassium fertilization provide the motivation for conducting further studies to improve our understanding and perspectives for potassium fertilization in sodic and saline‐sodic environments.     

Growth response and ion homeostasis in two bermudagrass (Cynodon dactylon) cultivars differing in salinity tolerance under salinity stress

Bermudagrass (Cynodon dactylon) is a salinity-tolerant turfgrass that has good use potential in the saline-alkali lands of warm regions. However, the systematic Na⁺ and K⁺ regulation mechanisms under salinity stress remain unclear at the whole plant level. Two bermudagrass cultivars differing in salinity tolerance were exposed to 0, 50, 100, 200, or 300 mM NaCl in a hydroponic system. Growth, absorption, transportation, and secretion of Na⁺ and K⁺, and gas exchange parameters were determined in both cultivars. K⁺ contents were decreased and Na⁺ contents and Na⁺/K⁺ ratios were increased in both bermudagrasses with increased salinity; however, lower Na⁺ content and Na⁺/K⁺ ratio and more stable K⁺ content were found in the leaves of the salinity-tolerant ‘Yangjiang’ than the salinity-sensitive ‘Nanjing’. Higher Na⁺ contents in root cortical cells were found than in the stele cells of ‘Yangjiang’, but the opposite was observed in ‘Nanjing’. Lower Na⁺ contents and higher K⁺ contents were found in vessels for ‘Yangjiang’ than for ‘Nanjing’. Salinity stress increased the selective transport of K⁺ over Na⁺ from roots to leaves and the Na⁺-selective secretion via salt glands, which were stronger in ‘Yangjiang’ than ‘Nanjing’. Net photosynthetic rate and stomatal conductance decreased in the two bermudagrasses with increased salinity; however, they were more stable in ‘Yangjiang’. The results suggested that bermudagrass could reduce Na⁺ accumulation and maintain K⁺ stability in leaves under salinity stress by restricting Na⁺ into vessels in roots, selectively transporting K⁺ over Na⁺ from roots to leaves, selectively secreting Na⁺ via leaf salt glands, and maintaining suitable stomatal conductance.     

Zinc Sulfate Foliar Application Effects on Some Physiological Characteristics and Phenolic and Essential Oil Contents of Lavandula stoechas L. Under Sodium Chloride (NaCl) Salinity Conditions

Lavandula stoechas L. plant is a perennial evergreen used as a fragrant ornamental and medicinal plant. In order to study the effect of foliar spray of zinc sulfate (ZnSO₄) (0, 1000, and 2000 mgL^?1) and sodium chloride (NaCl) salinity (0, 75, and 150 mM) on some physiological characteristics of Lavandula stoechas L. plants, a pot experiment was carried out at the Research Greenhouse of Azarbaijan Shahid Madani University, Iran. Physiological characteristics [root and leaf dry weights, total soluble solids (TSSs), total anthocyanins, chlorophyll b, Zn²⁺, potassium (K⁺) contents, and K⁺/Na⁺ ratio] were significantly affected by the interaction effects of ZnSO₄ foliar application and salinity levels. The highest root dry weight, chlorophyll b, anthocyanin, and Zn contents as well as TSS were found in the plants with NaCl₀ × ZnSO_{4 2000} mgL^?1. For Na⁺, the greatest value was recorded with NaCl ₁₅₀ × ZnSO₄₀. The highest K⁺/Na⁺ ratio was found in the control plants. Foliar application of ZnSO₄ promoted the total phenolic content, especially at 2000 mgL^–1. The highest amounts of flower dry weights were recorded at NaCl₀. Chlorophyll a, total flavonoids, stem dry weight, and essential oil content were affected with ZnSO₄ treatment and salinity levels. The highest values for the essential oil content, chlorophyll a content, and stem dry weight were attained by the nonsaline treatment. Both foliar application levels positively influenced the essential oil and flavonoid contents of the plants. The results reveal that zinc application had marked effects on the physiological characteristics of Lavandula stoechas L. plants growing under salinity stress conditions.     

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.     

WHEAT GENOTYPES DIFFERED SIGNIFICANTLY IN THEIR RESPONSE TO SILICON NUTRITION UNDER SALINITY STRESS

We studied the growth and ionic composition of five wheat genotypes (Inqlab-91, Uqab 2002, SARC-1, SARC-3, and SARC-5) grown under salinity stress to applied silicon. Plants were grown with three levels of salinity [0, 60, and 120 mM sodium chloride (NaCl)] in the presence of 0, 2, and 4 mM Si in nutrient solution for 40 days. Salinity stress significantly decreased shoot and root biomass in plants with varying degrees. Genotype SARC-3 exhibited higher salt tolerance than other genotypes. Silicon (Si) application significantly (P < 0.05) increased plant biomass at both control as well as under saline conditions. Genotypes differed significantly for their response to applied Si in terms of biomass production. Silicon application significantly (P < 0.01) increased potassium (K⁺) concentration in shoots. Enhanced salinity tolerance in wheat by Si application was attributed to increased K⁺ uptake thereby increasing K⁺/sodium (Na⁺) ratio and lower Na⁺ translocation towards shoot.     

Effect of salinity on growth,photosynthesis and mineral composition in leguminous plant Alhagi pseudoalhagi (Bieb.)

Leguminous plant Alhagi pseudoalhagi was subjected to 0 (control), 50, 100, and 200 mM NaCI treatments during a 30 d period to examine the mechanism of tolerance to salinity. Plant dry weight, net CO₂ assimilation rate, leaf stomatal conductance, intercellular CO₂ concentration, and solute concentration in leaves, stems, and roots were determined. Total plant weight in the 50 mM treatment was 170% of that of the control after 10 d of treatment. Total plant weight was lower in the 100 and 200 mM treatments than in the control. The leaf CO₂ assimilation rate was approximately 150% of that of the control in the 50 mM treatment, but was not affected significantly by 100 mM of NaCI, while it was reduced to about 60% of that the control in the 200 mM treatment. Similarly stomatal conductance was consistent with the CO₂ assimilation rate regardless of the treatments. Intercellular CO₂ concentration was lower in the NaCI-treated plants than in the control. Changes in CO₂ assimilation rate due to salinity stress could be mainly associated with stomatal conductance and the carboxylation activity. Although the leaf Na⁺ concentration increased to 900 mmol kg^-1 dry weight in the 200 mM treatment compared to 20 mmol kg^-1 in the control, the plants did not die and continued to grow at such a high leaf Na⁺ concentration. Uptake and transportation rates of Na+, Ca²⁺, Mg²⁺, and K⁺, and the accumulation of N were promoted by 50 mM NaCI. Na⁺ uptake rate continued to increase in response to external NaCI concentration. However, the uptake and transportation rates of Ca²⁺, Mg²⁺, and K⁺ behaved differently under 100 and 200 mM salt stress. The results suggest that A. pseudoalhagi is markedly tolerant to salinity due mainly to its photosynthetic activity rather than to other physiological characteristics.     

EFFECT OF SALINITY AND EXOGENOUSLY APPLIED POLYAMINES ON GROWTH AND ION RELATIONS IN SPINACH

ABSTRACT

It has been suggested that polyamines are involved in many growth and development processes in plants and may serve as growth regulators. These nitrogenous compounds have been shown to be involved in cell division, nucleic acid and proteins synthesis, and normal senescence. It is thought by some that polyamines may be involved in the plant's mechanistic response to stress. More importantly, some reports indicate that exogenously applied polyamines can overcome the growth reduction brought about by salinity stress. In this report, growth studies were performed on to examine the effect of exogenously applied putrescine, spermidine, and spermine on the alleviation of salinity stress. Spinacia oleracea, L. cv. Space was chosen since much of our understanding of the sugar metabolism needed for growth has been derived from this plant. Polyamines were applied in a manner used in earlier reports, i.e., foliar spray. The effect of salinity and polyamines on leaf number, leaf area, fresh and dry weight was observed. Our analysis showed that putrescine and spermine had no significant effect on plant growth throughout the range of salinities studied (2 to 11.7?dS?m^?1). Spermidine slightly decreased growth. Further studies on ion uptake indicated that none of the polyamines tested had a significant effect on plant ion content. While we failed to document any growth response to putrescine or spermine treatment, we did find a significant reduction of growth as salinity increased in the irrigation water. Further analysis of the ion data indicated that K⁺:Na⁺ selectivity significantly increased with increasing salinity. This preferential increased influx of K⁺ ions may be an important mechanism by which spinach maintains low Na⁺ tissue levels relative to external concentrations. Additionally, Ca²⁺:Na⁺ selectivity as measured by the Gapon constant, K _g , greatly increased. Conversely, Ca²⁺:Mg²⁺ selectivity decreased resulting in an increase in Mg²⁺ tissue concentrations. Our results are discussed in terms of possible salt tolerance mechanisms in spinach as they relate to the preferential uptake of specific nutrient ions from saline irrigation waters.     

Effect of potassium on uptake and translocation of sodium and potassium in Chinese cabbage under NaCl stress

To investigate the influence of potassium (K⁺) on the salinity tolerance of Chinese cabbage (Brassica pekinensis Rupr.) seedlings, the plants were cultured at three K⁺ levels (0, 5, or 10?mM), under normal (0?mM NaCl) and high-salt (100?mM NaCl) conditions. The results indicated that the dry weight of Chinese cabbage increased with the application of K⁺ under salt stress. Addition of K⁺ increased K⁺ concentrations and suppressed sodium (Na⁺) concentration, which eventually increased the K⁺/Na⁺ ratios in roots or shoots. Application of K⁺ enhanced the uptake of K⁺ and suppressed the uptake of Na⁺. Moreover, the ratios of shoot-K⁺/root-K⁺ increased considerably, but the ratios of shoot-Na⁺/root-Na⁺ decreased in response to K⁺ application. It was concluded that the application of K⁺ could enhance the salt stress tolerance in Chinese cabbage because more K⁺ than Na⁺ was absorbed and translocated from roots to shoots.     

Comparative growth and physiological responses of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance to salinity and cyclic drought stress

Two cultivars of wheat (Triticum aestivum L.) with differential salinity tolerance were compared by evaluating the growth attributes, pigment composition and accumulation of Na⁺, K⁺, Zn²⁺, Fe ²⁺, Mn ²⁺ and proline. Wheat cultivars Al-Moiaya (AM) (salt tolerant) and Habbe-Druma (HD) (salt sensitive) were subjected to four levels of salinity (1.21 dS m^?1, 4.4 dS m^?1, 8.8 dS m^?1 and 13.2 dS m^?1) in factorial combinations with three drought stress (FC 30%, FC 60% and FC 90%) treatments in a randomized complete block design. Plant dry weight, leaf area ratio (LAR), soluble protein and total chlorophyll (Chl) content were higher in AM than HD. Salt-tolerant AM maintains a higher K⁺/ Na⁺ ratio and thereby is able to grow better than the salt-sensitive HD under both the stresses. The lower foliar Na⁺ in AM resulted in retention of higher Chl content, reflected in the strong positive correlations between plant ion status and Chl contents (Na⁺-Chl r² = 0.83; Chl- Fe²⁺ r² = 0.76; Zn²⁺ r² = 0.93 and Mn²⁺ r² = 0.88). In conclusion, our results suggested that the K⁺/Na⁺ ratio, exclusion of Na⁺ and ion homeostasis play much more important roles in the tolerance to salinity and drought stress than the compatible osmolyte, proline.     

Silicon and Potassium Nutrition Enhances Salt Adaptation Capability of Sunflower by Improving Plant Water Status and Membrane Stability

The relationships between salinity and mineral nutrition are extremely complex and may change depending on many factors in soil-plant system. We investigated the contribution of silicon (Si at 50 mg kg^?1 soil) and potassium (K at 40 and 60 mg K₂O kg^?1 soil) to improve salt tolerance in sunflower grown with 100 mM sodium chloride (NaCl). The experimental design was factorial based on a completely randomized design with five replications. Added NaCl increased sodium ion (Na⁺) accumulation by 966 percent in shoots and 1200 percent in roots but reduced shoot potassium ion (K⁺) concentration by 49 percent, root K⁺ 51 percent, and shoot K⁺/Na⁺ ratio 95 percent. However, Si and K application effectively reduced Na⁺ accumulation and increased K⁺ concentration and K⁺:Na⁺ ratio, with a significant improvement in plant growth and yield. Among all treatments, greater alleviative effects of Si and K were observed for 50 mg Si + 60 mg K₂O kg^?1 soil, which decreased shoot Na⁺ concentration by 67 percent, root Na⁺ 18 percent, and shoot Na⁺/root Na⁺ ratio 60 percent and increased shoot K⁺ by 198 percent, shoot K⁺/Na⁺ ratio 812 percent, membrane stability index (MSI) 35 percent, relative water content (RWC) 26 percent, and seed weight head^?1 86 percent compared to salt-stressed plants without supplemental Si and K. Most of the plant growth parameters were negatively correlated with Na⁺ accumulation but positively correlated with K⁺ and K⁺/Na⁺ ratio. This study suggests that Si and K mediated reduction in Na⁺ accumulation, and increase in K⁺ concentration, K⁺/Na⁺ ratio, RWC, and MSI are the main factors contributing to improved adaptation capability of sunflower to NaCl stress.     

Differences in Physiological Traits Among Salt‐Stressed Barley Genotypes

Abstract

The effect of salinity on some physiological parameters in 16 barley genotypes with different salt tolerance was investigated. The results showed 50 mM NaCl treatment increased Na⁺/K⁺ ratio, malondialdehyde (MDA) and proline contents, and decreased cell membrane stability index (CMSI) and fresh shoot biomass (FSB) of all tested genotypes. Salt stress also resulted in a decreased chlorophyll (Chl) content and net photosynthesis (Pn) for most genotypes. Under higher salt stress (300 mM NaCl), the marked increase for Na⁺/K⁺, MDA, and proline content, and decrease for other parameters were found for all genotypes. The affected extent of these parameters by salt stress varied with genotypes. Proline accumulation in barley was associated with injured extent under salt stress, indicating it is not a defensive reaction to the stress. K⁺ uptake was less affected, whereas Na⁺ accumulation in plants was enhanced under high salt stress. The correlation analysis showed that MDA and proline content, Na⁺ concentration and Na⁺/K⁺ were negatively correlated with FSB, whereas other parameters examined in the study were positively correlated with FSB.     

Consequences of sodium exclusion for the osmotic potential in the rhizosphere – Comparison of two maize cultivars differing in Na+ uptake

According to the biphasic model of growth response to salinity, growth is first reduced by a decrease in the soil osmotic potential (Ψ_o), i.e., growth reduction is an effect of salt outside rather than inside the plant, and genotypes differing in salt resistance respond identically in this first phase. However, if genotypes differ in Na⁺ uptake as it has been described for the two maize cultivars Pioneer 3906 and Across 8023, this should result in differences in Na⁺ concentrations in the rhizosphere soil solution and thus in the concentration of salt outside the plant. It was the aim of the present investigation to test this hypothesis and to investigate the effect of such potential differences in soil Ψ_o caused by Na⁺ exclusion on plant water relations. Sodium exclusion at the root surface of intact plants growing in soil was investigated by sampling soil solution from the rhizosphere of two maize cultivars (Across 8023, Pioneer 3906). Plants were grown in a model system, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 μm mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). Across 8023 accumulated higher amounts of sodium in the shoot compared to the excluder (Pioneer 3906). The lower Na⁺ uptake in the excluder was partly compensated by higher K⁺ uptake. Pioneer 3906 not only excluded sodium from the shoot but also restricted sodium uptake more efficiently from roots relative to Across 8023. This was reflected by higher Na⁺ concentrations in the rhizosphere soil solution of the excluder 34 days after planting (DAP). The difference in Na⁺ concentration in rhizosphere soil solution between cultivars was neither due to differences in transpiration and thus in mass flow, nor due to differences in actual soil water content. As the lower Na⁺ uptake of the excluder (Pioneer 3906) was only partly compensated by increased uptake of K⁺, soil Ψ_o in the rhizosphere of the excluder was more negative compared to Across 8023. However, no significant negative effect of decreased soil Ψ_o on plant water relations (transpiration rate, leaf Ψ_o, leaf water potential, leaf area) could be detected. This may be explained by the fact that significant differences in soil Ψ_o between the two cultivars occurred only towards the end of the experiment (27 DAP, 34 DAP).