Role of Nitrogen and Gibberellin (GA3) in the Regulation of Enzyme Activities and in Osmoprotectant Accumulation in Brassica juncea L. under Salt Stress

Salt stress alters a wide array of plant metabolic mechanisms. Different strategies of the application of nutrients and phytohormones are required to overcome the adverse effects of salt stress. The main objective of the present study was to determine if added nitrogen (N) and gibberellin (GA₃) in growth medium could alleviate the adverse effects of salt stress on plant metabolism. Two‐week‐old plants were fed with: (i) 0 mm NaCl + 0 mg N kg^?1 sand + 0 m GA₃ (control), (ii) 100 mm NaCl + 0 mg N kg^?1 sand + 0 m GA₃, (iii) 0 mm NaCl + 40 mg N kg^?1 sand + 0 m GA₃, (iv) 0 mm NaCl + 0 mg N kg^?1 sand + 10^?5 m GA₃, (v) 100 mm NaCl + 40 mg N kg^?1 sand + 0 m GA₃, (vi) 100 mm NaCl + 0 mg N kg^?1 sand + 10^?5 m GA₃, (vii) 100 mm NaCl + 40 mg N kg^?1 sand + 10^?5 m GA₃. Growth and physio‐biochemical attributes i.e. shoot length, leaf area, fresh weight, dry weight, net photosynthetic rate, stomatal conductance, malondialdehyde concentration, electrolyte leakage, total chlorophyll concentration, nitrate reductase and carbonic anhydrase activities, proline and glycinebetaine concentration, leaf – N, potassium (K) and sodium (Na) concentration and K/Na ratio were affected by NaCl treatment. But application of N or GA₃ alone as well as in combination proved beneficial in alleviating the adverse effects of salt stress on these growth and physio‐biochemical parameters. However, N applied with GA₃ proved more effective than N and GA₃ applied alone. The results revealed that combined application of N and GA₃ may ameliorate most of the attributes and prove to be a physiological remedy to increase the tolerance against the ill effects of salt stress in Brassica.     

Differences in Ion Accumulation and Salt Tolerance among Glycine Accessions

Salinity reduces crop yield by limiting water uptake and causing ion‐specific stress. Soybean [Glycine max (L.) Merr.] is sensitive to soil salinity. However, there is variability among soybean genotypes and wild relatives for salt tolerance, suggesting that genetic improvement may be possible. The objective of this study was to identify differences in salt tolerance based on ion accumulation in leaves, stems and roots among accessions of four Glycine species. Four NaCl treatments, 0, 50, 75 and 100 mm , were imposed on G. max, G. soja, G. tomentella and G. argyrea accessions with different levels of salinity tolerance. Tolerant genotypes had less leaf scorch and a greater capacity to prevent Na⁺ and Cl^? transport from soil solution to stems and leaves than sensitive genotypes. Magnitude of leaf injury per unit increase in leaf Na⁺ or Cl^? concentrations was lower in tolerant than in susceptible accessions. Also, plant injury was associated more with Na⁺ rather than with Cl^? concentration in leaves. Salt‐tolerant accessions had greater leaf chlorophyll‐meter readings than sensitive genotypes at all NaCl concentrations. Glycine argyrea and G. tomentella accessions possessed higher salt tolerance than G. soja and G. max genotypes.     

Interaction of Phosphate and Salinity on the Growth and Yield of Rice (Oryza sativa L.)

The role of phosphorus application on growth and yield of rice under saline conditions was studied in a set of two experiments, one in nutrient and the other in soil culture. In experiment 1, the effect of inorganic phosphate (P_i) on the growth and ionic relations of four rice cultivars, varying in salt tolerance and phosphorus use efficiency, grown in nutrient solution with and without 50 mol m^?3 NaCl was measured in a 2 week trial. The growth of all rice cultivars was affected to different degrees due to external P, in the presence of salt. External P, concentration up to 100 μM in the presence of NaCl caused stimulation of all growth parameters (shoot, root, tillering capacity), above this concentration P, had an inhibitory effect. Salt-induced P toxicity was exhibited at a much lower P, concentration (10 μM) by the salt sensitive cultivar. Increasing the supply of phosphorus (from 1 to 100 μM P_i) to the saline medium tended to decrease the concentrations of Na¹ and CI in all cultivars except IR 1561. Shoot concentrations of these saline ions were much lower in the salt tolerant and moderately salt tolerant rice cultivars. Shoot P and Zn concentrations showed an increasing trend in the presence of external P, and salt in the rooting nr -idium but most strikingly P: Zn ratio was lower in salt tolerant and moderately salt tolerant cultivars. Significantly higher concentrations of Na⁺, P and CI, and lower concentrations of Zn, were determined in the shoots of salt sensitive cultivars when exposed to salt stress in the presence of P_i Results were confirmed in naturally salt-affected soils of two different types (saline-sodic and saline) where paddy yield of NIAB 6 (salt tolerant) and IR 1561 (salt sensitive) showed improvement through moderate phosphorus supply (18 kg P ha^?1).     

Differential Cl−/Salt Tolerance and NaCl‐Induced Alternations of Tissue and Cellular Ion Fluxes in Glycine max,Glycine soja and their Hybrid Seedlings

The salt‐sensitive Glycine max N23674 cultivar, the salt‐born Glycine soja BB52 population, and their hybrid 4076 strain (F₅) selected for salt tolerance generation by generation were used as the experimental materials in this study. First, the effects of NaCl stress on seed germination, tissue damage, and time‐course ionic absorption and transportation were compared. When qualitatively compared with seed germination appearance in culture dishes, and tissue damages on roots or leaves of seedlings, or quantitatively compared with the relative salt injury rate, the inhibition on N23674 was all the most remarkable. After the exposure of 140 mm NaCl for 1 h, 4 h, 8 h, 12 h, 2 days and 4 days, the content of Cl^? gradually increased in the roots and leaves of seedlings of BB52, 4076 and 23674. Interestingly, the extents of the Cl^? rise in roots of the three experimental soybean materials were BB52 > 4076 > N23674, whereas those in leaves were just on the contrary. Secondly, by using the scanning ion‐selective electrode technique (SIET), fluxes of Na⁺ and Cl^? in roots and protoplasts isolated from roots and leaves were also investigated among the three experimental soybean materials. After 140 mm NaCl stress for 2, 4 and 6 days, and when compared with N23674, slighter net Cl^? influxes were observed in root tissue and protoplasts of roots and leaves of BB52 and 4076 seedlings, especially at the cellular protoplast level. The results indicate that with regard to the ionic effect of NaCl stress, Cl^? was the main determinant salt ion for salt tolerance in G. soja, G. max and their hybrid, and the difference in their Cl^?/salt tolerance is mainly attributed to the capacity of Cl^? restriction to the plant above‐ground parts such as leaves.     

Effect of Salinity Stress on Growth and Nutrient Composition of Three Soybean (Glycine max L. Merrill) Cultivars

Soil salinity is a major limitation to legume production in many areas of the world. The salinity sensitivity of soybean was studied to determine the effect of salinity on seed germination, shoot and root dry weights, and leaf mineral contents. Three soybean cultivars, Lee, Coquitt, and Clark 63, were planted in soils of different salinity levels. The electrical conductivity (EC) of the soils used in this experiment was 0.5 dS m^?1. The soil salinity treatments were 0.5, 2.5 4.5, 6.5 and 8.5 dS m^?1. Saline drainage water from a drainage canal with an EC of 15 dS m^?1 was used to treat the soil samples in order to obtain the desired salinity levels. Germination percentages were recorded 10 days after planting. Shoot and root dry weights of 45‐day‐old plants were measured. Nutrient concentrations for Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^? were determined. Germination percentages were significantly reduced with increasing salinity levels. The cultivar Lee was less affected by salinity stress than Coquitt and Clark 63. At 8.5 dS m^?1 a significant reduction in plant height was found in all three cultivars. However, Lee plants were taller than plants of the other two cultivars. Salinity stress induced a significant increase in leaf sodium (Na⁺) and chloride (Cl^?) in all cultivars. However, the cultivar Lee maintained lower Na⁺ and Cl⁺ concentrations, a higher potassium (K⁺) concentration and a higher K⁺/Na⁺ ratio at higher salinity levels than Coquitt and Clark 63. Saline stress reduced the accumulation of K⁺, calcium (Ca²⁺) and magnesium (Mg²⁺) in the leaves of the cultivars studied. This study suggests that Lee is the most tolerant cultivar, and that there is a relationship between the salt tolerance of the cultivar and macronutrient accumulation in the leaves.     

Salt‐Induced Regulation of Some Key Antioxidant Enzymes and Physio‐Biochemical Phenomena in Five Diverse Cultivars of Turnip (Brassica rapa L.)

A greenhouse experiment was carried out to examine the differential morpho‐physiological responses of five cultivars of turnip (Brassica rapa L.) to salt stress. Five diverse cultivars of turnip (shaljum desi surakh, shaljum purple top, shaljum golden bal, neela shaljum, and peela shaljum) were subjected for 6 weeks to varying levels of NaCl, i.e. 0, 80 and 160 mm in Hoagland’s nutrient solution in sand culture. Imposition of varying levels of salt substantially decreased shoot and root fresh and dry weights, chlorophyll contents, leaf osmotic potential, relative water contents, different gas exchange attributes, total phenolics, malondialdehyde, activities of superoxide dismutase, peroxidase catalase, and leaf and root K⁺ levels while enhanced the proline contents, membrane permeability, level of H₂O₂, leaf and root Na⁺ and Cl^? and leaf Ca²⁺ in all turnip cultivars under study. Of all cultivars, peela shaljum and neela shaljum were consistently higher in their growth than the other turnip cultivars at all salt concentrations of the growth medium. Photosynthetic capacity (A) and stomatal conductance (g_s) were higher in high biomass‐producing cultivars, i.e. peela shaljum and neela shaljum, which provide to be potential selection criteria of salt tolerance in turnip. However, the regulation of antioxidant system was cultivar‐specific under saline conditions.     

Growth‐Related Changes in Subcellular Ion Patterns in Maize Leaves (Zea mays L.) under Salt Stress

Na⁺ accumulation in the leaf apoplast has been suggested to lead to dehydration, later wilting and finally, the death of the affected leaves. Our aim has been to evaluate whether the reduction in the plant growth of sensitive maize in response to salinity is correlated with higher amounts of Na⁺ and Cl^? concentrations in the leaf apoplast. Subcellular ion patterns in intact leaves were investigated by using deionised water infiltration. We found an increase in soluble Na⁺ and Cl^? concentrations of about 16‐ and 4‐fold, respectively, compared with the control. These concentrations characterized the apoplasts of expanding leaves that had entirely developed under salinity. Interestingly, the K⁺ concentration was significantly reduced by 64 % compared with its control in the symplast under salinity. Our finding of a significantly decreased Ca²⁺ concentration in shoots suggested a possible association of Ca²⁺ concentration with the reduction in leaf expansion under salinity. As the absolute increase in the apoplastic Na⁺ concentration during salt treatment was much lower compared with the increase in the symplastic Na⁺ concentration, salt treatment in maize appears not to result in osmotic stress imposed by a high apoplastic Na⁺ concentration as has been suggested for other plant species (Oertli hypothesis).     

Influence of Calcium Silicate on Growth, Physiological Parameters and Mineral Nutrition in Two Legume Species Under Salt Stress

Cowpea and kidney bean plants were grown in a hydroponic system, and the effect of calcium silicate supplied to the nutrient solution under salt stress was investigated. The plants were subjected to four different treatments: (1) nutrient solution alone (C), (2) nutrient solution + 40 mmol l⁻¹ NaCl (NaCl), (3) nutrient solution + 40 mmol l⁻¹ NaCl + 0.5 mmol l⁻¹ CaSiO₃ (NaCl + Si₁) and (4) nutrient solution + 40 mmol l⁻¹ NaCl+1 mmol l⁻¹ CaSiO₃ (NaCl + Si₂). The results showed that, in both species, salinity reduced all growth variables but silicate supplementation however partly overcame this growth reduction. Addition of silicate in NaCl‐stressed plants maintained membrane permeability. Net photosynthesis, chlorophyll content, stomatal conductance and transpiration were higher in plants under control treatment, and the inclusion of silicate in the nutrient solution resulted in a slight increase in these plant parameters. Intercellular CO₂ was slightly higher in plants under silicate treatment than in plants under control or NaCl treatment. Calcium concentration in shoots and roots in both species was slightly higher in the treatments where silicate was added. Potassium concentration for salt treatment was reduced in shoot and root of both species in the absence of silicate. Sodium and chloride concentration in shoots and roots in both species were slightly higher in the presence of NaCl and were slightly reduced in the plants under silicate treatments. The results suggest that, in hydroponically grown plants, the inclusion of silicate in the nutrient solution is beneficial because it improves growth, physiological parameters and may contribute to a more balanced nutrition by enhancing nutrient uptake under NaCl‐stressed conditions. Added calcium silicate may ameliorate the parameters affected by high salinity, may reduce sodium and chloride, and can slightly increase calcium and potassium concentrations in shoots and roots of salt‐stressed cowpea and kidney bean.     

The Key Physiological Response to Alkali Stress by the Alkali‐Resistant Halophyte Puccinellia tenuiflora is the Accumulation of Large Quantities of Organic Acids and into the Rhyzosphere

Eight‐week‐old seedlings of Puccinellia tenuiflora were stressed by exposure to 1 : 1 molar ratio mixtures either of the two neutral salts NaCl and Na₂SO₄ or of the two alkali salts, NaHCO₃ and Na₂CO₃. To identify the physiological mechanisms involved in this plant’s resistance to alkali stress, the relative growth rates, the quantities and compositions of organic acids accumulated and secreted through the roots into the rhyzosphere, the concentrations of inorganic ions, proline and other solutes accumulating in the shoots were measured. The results show that the organic acid constituents in the shoots and roots were much the same. These were predominantly malic acid, oxalic acid, citric acid and succinic acid. The total concentration of organic acids in the shoots increased strongly with increasing alkali stress. However, these either did not increase or they decreased slightly with increasing salt stress. Of the four organic acids, the concentration difference between salt‐ and alkali‐stressed plants was most striking for citric acid. This became the dominant organic acid component under alkali stress. Results show that proline is the main organic osmolyte, whereas the contribution of betaine to osmotic adjustment is insignificant under either salt or alkali stress. The main organic acid accumulated was not only an important organic osmotic regulator, but also an important negative charge contributor, playing important roles in ionic balance and pH adjustment. The concentrations of Na⁺, K⁺, Cl^? and of organic acid were 80.7% of all solutes under salt stress. The concentrations of Na⁺, K⁺, Cl^? and of organic acid were 85.4% of all solutes under alkali stresses. The ionic balance was disrupted by the strong increase in Na⁺ content under alkali stress. This perhaps explains why large amounts of the organic acids were accumulated. The organic acid concentration in the roots was lower than in the shoots. The roots secreted citric acid into the rhyzosphere only under alkali stress, secretion of the other organic acids was not detected. Therefore, citric acid secreted from the roots probably plays an important role in pH adjustment in the rhyzosphere of P. tenuiflora.     

Physiological processes associated with salinity tolerance in an alfalfa half‐sib family

We previously reported an alfalfa half‐sib family, HS‐B, with improved salt tolerance, compared to parental plants, P‐B. In this study, we conducted additional experiments to address potential physiological mechanisms that may contribute to salt tolerance in HS‐B. Vegetatively propagated HS‐B and P‐B plants were treated with a nutrient solution (control) or a nutrient solution containing NaCl (EC = 12 dS/m). Shoots and roots were harvested at various time points after treatment for quantification of proline, soluble sugar, and H₂O₂ using spectrophotometers. Subcellular localization and quantification of Na in roots were conducted using a Na⁺‐specific dye under a confocal microscope. HS‐B produced 86 and 89% greater shoot and root dry biomass, respectively, compared to parental plants, P‐B, under salinity in the greenhouse. Under saline conditions the HS‐B shoots accumulated 115% and roots 55% more soluble sugars than P‐B counterparts. The non‐saline HS‐B shoots, however, showed 72% less soluble sugars than the non‐saline P‐B plants. Under saline conditions HS‐B accumulated 39% less proline in shoots, while roots accumulated 56% more proline, compared to their P‐B parents. HS‐B plants also showed a greater reduction of stomatal conductance under mild saline stress. HS‐B shoots and roots contained 3–4 times less reactive oxygen species (H₂O₂) after salt treatment compared to P‐B plants. Sodium localization and distribution analysis using Na⁺‐specific dye revealed HS‐B plants accumulated 88% and 48% less Na⁺ in stele and xylem vessels compared to P‐B. The study provides insights into the potential mechanisms that may contribute to salt tolerance in HS‐B: maintaining RWC by accumulating soluble sugars while reducing transpiration, maintaining healthy status by reducing oxidative stresses, and preventing salt toxicity by reducing accumulation of Na⁺ inside root cells and xylem.     

Salt (NaCl)‐Induced Modulation in some Key Physio‐Biochemical Attributes in Okra (Abelmoschus esculentus L.)

Salt (NaCl)‐induced regulation of some key physio‐biochemical characteristics in two okra (Abelmoschus esculentus L.) cultivars (Nirali and Posa Sawni) was examined under greenhouse conditions. Plants of both cultivars were subjected for 30 days to sand culture salinized with four salt levels [0 (control), 50, 100 and 150 mm NaCl] in Hoagland’s nutrient solution. Salt stress significantly reduced the shoot and root fresh weights, transpiration rate, chlorophyll b content, net CO₂ assimilation (A), transpiration rate (E), while enhanced leaf and root Na⁺ and Cl^– concentrations in both cultivars. In contrast, chlorophyll a content, stomatal conductance (g_s), leaf internal CO₂ (C_i), C_i/C_a ratio, water‐use efficiency (A/E) and fluorescence characteristics such as photochemical quenching (qP), non‐photochemical quenching (NPQ), efficiency of PS‐II (F_v/F_m), proline contents, and leaf and root K⁺, Ca^{2 +} and N contents remained almost unaffected in both lines due to salt stress. The efficiency of PSII (F_v/F_m), A, chlorophyll b, root fresh weight and root N were higher in relatively salt tolerant cv. Nirali, whereas leaf Na⁺ and root Cl^– were higher in cv. Posa Sawni. The relatively more reduction in growth in the cv. Posa Sawni was found to be associated with higher accumulation of Na⁺ in its leaves and Cl^– in roots.     

Copper‐Induced Oxidative Stress and Responses of the Antioxidant System in Roots of Medicago sativa

The effects of various copper (Cu) concentrations on the antioxidative system in the roots of Medicago sativa were explored. The results indicated that the Cu content of the roots reached a value of 854 μg g^?1 DW at 10 μm Cu and a value of 4415 μg g^?1 DW at 100 μm Cu, suggesting that M. sativa has better ability to tolerate and accumulate Cu than other Cu‐bioaccumulators, and is a potential plant for phytoremediation. Treatment with Cu resulted in a significant increment in the levels of H₂O₂, O₂˙^? and OH˙. The reduced form of ascorbate and glutathione reached a peak at 30 μm Cu, and was followed by a sharp depletion to a lower level than that of the control. In contrast, the levels of the oxidised forms of ascorbate and glutathione showed a progressive increment with increasing Cu concentrations, suggesting that the antioxidant system was unable to cope with Cu stress at higher Cu levels. Under the Cu concentrations tested, the activity of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) increased at lower Cu concentrations, and then decreased, reaching a maximum at 30 μm of Cu for APX and GR, at 10 μm for CAT, whereas the activities of guaiacol peroxidase (POD, EC 1.11.1.7) were gradually increased with increasing Cu concentrations. PAGE analysis of superoxide dismutase (SOD, EC 1.1.5.1.1) revealed that one band is a Mn‐SOD and five bands are identified as Cu, Zn‐SOD, whereas Fe‐SOD isoforms were not found in the roots of alfalfa. Cu at 10–100 μm increased the intensity of constitutive isozymes of CAT, APX and POD, whereas it decreased the intensity of isozymes of glucose‐6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49) significantly. The activities of lipoxygenases (LOX, EC 1.13.11.12) were gradually augmented with increasing Cu concentrations, demonstrating that LOXs are probably involved in production of lipid hydroperoxides and superoxide anion. There was a continuous and pronounced enhancement in the activity of esterase (EST, EC 3.1.1.1) in roots treated with 10–30 Cu μm , whereas EST activity in roots exposed to above 30 μm Cu declined, suggesting that EST plays a protective role under lower Cu concentrations stress.     

Salt Stress Delayed Flowering and Reduced Reproductive Success of Chickpea (Cicer arietinum L.), A Response Associated with Na+ Accumulation in Leaves

Salinity is known to reduce chickpea yields in several regions of the world. Although ion toxicity associated with salinity leads to yield reductions in a number of other crops, its role in reducing yields in chickpea growing in saline soils is unclear. The purpose of this study was to (i) identify the phenological and yield parameters associated with salt stress tolerance and sensitivity in chickpea and (ii) identify any pattern of tissue ion accumulation that could relate to salt tolerance of chickpea exposed to saline soil in an outdoor pot experiment. Fourteen genotypes of chickpea (Cicer arietinum L.) were used to study yield parameters, of which eight were selected for ion analysis after being grown in soil treated with 0 and 80 mm NaCl. Salinity delayed flowering and the delay was greater in sensitive than tolerant genotypes under salt stress. Filled pod and seed numbers, but not seed size, were associated with seed yield in saline conditions, suggesting that salinity impaired reproductive success more in sensitive than tolerant lines. Of the various tissues measured for concentrations of Cl^?, Na⁺ and K⁺, higher seed yields in saline conditions were positively correlated with higher K⁺ concentration in seeds at the mid‐filling stage (R² = 0.55), a higher K⁺/Na⁺ ratio in the laminae of fully expanded young leaves (R² = 0.50), a lower Na⁺ concentration in old green leaves (R² = 0.50) and a higher Cl^? concentration in mature seeds. The delay in flowering was associated with higher concentrations of Na⁺ in the laminae of fully expanded young leaves (R² = 0.61) and old green leaves (R² = 0.51). We conclude that although none of the ions appeared to have any toxic effect, Na⁺ accumulation in leaves was associated with delayed flowering that in turn could have played a role in the lower reproductive success in the sensitive lines.     

Root Nitrogen Remobilization and Ion Status of Two Alfalfa (Medicago sativa L.) Cultivars in Response to Salinity Stress

In a pot experiment the responses of two alfalfa cultivars differing in salt tolerance were evaluated in terms of root nitrogen remobilization rates (RNRR) and their relationship with the ionic status of the plants. A split‐plot design with factorial treatments in three replications was used. Three levels of salinity stress with electrical conductivities (EC_s) of 1.2, 7 and 12 ds m^?1 were established in irrigation water by using tap water with and without NaCl. The average data taken from plant materials at three defoliations were used for statistical analysis. Each time, plant materials were harvested at the 10 % flowering stage and then 10 days later. From the results observed, it was found that alfalfa shoot growth is highly dependent on RNRR under salinity stress. However, the total N reserves within the roots do not appear to be a limiting factor. The high positive correlation coefficient between shoot K⁺/Na⁺ and RNRR (r = 0.77; P = 0.01) indicates that lower demands for N because of diminished metabolic activities within the shoot sink may have reduced the rates of root N utilization. Unlike in some other species, the shoot K⁺ concentration and contents of alfalfa plants were significantly reduced by increasing salt stress. However, a relatively suitable K⁺/Na⁺ ratio of 7.1 is maintained in the shoots at the second level of salinity, as lowering the rates of salt induced an increase in Na⁺ uptake (Na exclusion). The salt tolerance recognized in the Bami cultivar may be attributed to the 339 % increase in its selectivity rates of K⁺ over Na⁺ in ion transport from the soil to the shoots, as the shoot Na⁺ content did not increase with increasing salt levels.     

盐胁迫条件下外源Ca2+对蚕豆气孔运动及质膜K+通道的调控

研究了Ca²⁺ 对NaCl胁迫下蚕豆气孔运动及质膜K+通道的影响。结果表明,100 mmol L^-1 NaCl可明显诱导气孔开放,该现象可被10 mmol L^-1 CaCl₂ 显著抑制。为探讨盐胁迫下Ca²⁺对K⁺和Na⁺跨膜运输的调控机制,我们利用膜片钳技术记录全细胞K⁺ 电流发现,在100 mmol L^-1 NaCl胁迫下,加入10 mmol L^-1 CaCl₂胞外处理,显著抑制质膜K+内向及外向通道电流,这种抑制可被1 mmol L^-1 La³⁺ (Ca²⁺通道抑制剂)缓解。非盐胁迫下,10 mmol L^-1 CaCl₂ 胞外处理也能显著抑制质膜内向K⁺通道,但明显激活其外向通道,加入1 mmol L^-1 La³⁺并不能被缓解。用H₂O₂专一的荧光探针二氯荧光素二乙酸酯(H2DCF-DA)单细胞分析保卫细胞内H₂O₂含量变化显示,在100 mmol L^-1 NaCl盐胁迫下,10 mmol L^-1 CaCl₂ 处理明显诱导H₂O₂在保卫细胞中积累;100 mmol L^-1 NaCl和10 mmol L^-1 CaCl₂单独处理并不能诱导H₂O₂积累。推测Ca²⁺在盐胁迫下可能先诱导H₂O₂在胞内积累,进而激活质膜Ca²⁺通道,迅速提高胞内Ca²⁺浓度以抑制Na⁺通过质膜K⁺通道跨膜内流,同时调节Na⁺外流,两种效应共同作用促使气孔关闭,减少盐胁迫下水分的过度散失。上述结果将为Ca²⁺调控作物抗盐机制研究提供新的思路。     

Salt Tolerance is Associated with Differences in Ion Accumulation,Biomass Allocation and Photosynthesis in Cowpea Cultivars

Cowpea is widely cultivated in arid and semi‐arid regions of the world where salinity is a major environmental stress that limits crop productivity. The effects of moderate salinity on growth and photosynthesis were examined during the vegetative phase of two cowpea cultivars previously classified as salt‐tolerant (Pitiúba) and salt‐sensitive (TVu). Two salt treatments (0 and 75 mm NaCl) were applied to 10‐day‐old plants grown in nutrient solution for 24 days. Salt stress caused decreases (59 % in Pitiúba and 72 % in TVu) in biomass accumulation at the end of the experiment. Photosynthetic rates per unit leaf mass, but not per unit leaf area, were remarkably impaired, particularly in TVu. This response was unlikely to have resulted from stomatal or photochemical constraints. Differences in salt tolerance between cultivars were unrelated to (i) variant patterns of Cl^? and K⁺ tissue concentration, (ii) contrasting leaf water relations, or (iii) changes in relative growth rate and net assimilation rate. The relative advantage of Pitiúba over TVu under salt stress was primarily associated with (i) restricted Na⁺ accumulation in leaves paralleling an absolute increase in Na⁺ concentration in roots at early stages of salt treatment and (ii) improved leaf area (resulting from a larger leaf area ratio coupled with a larger leaf mass fraction and larger specific leaf area) and photosynthetic rates per unit leaf mass. Overall, these responses would allow greater whole‐plant carbon gain, thus contributing to a better agronomic performance of salt‐tolerant cowpea cultivars in salinity‐prone regions.     

Salinity Effects on the Growth and Ion Contents of Some Chickpea (Cicer arietinum L.) and Lentil (Lens culinaris Medic.) Varieties

The effect of salinity on seed germination, plant yield parameters, and plant Na, Cl and K concentrations of chickpea and lentil varieties was studied. Results showed that in both crops percentage emergence was significantly reduced by increasing NaCl levels (0–8dSm^?1). From the plant growth studies it was found that differences existed among chickpea and lentil varieties in their response to NaCl application. In chickpea, the variety Mariye showed the comparatively lowest germination percentage and the lowest seedling shoot dry weight in response to salinity and was also among the two varieties which had the lowest relative plant height, shoot and root dry weight and grain yield at maturity. Similarly, variety DZ-10-16-2, which was the second best in germination percentage and the highest in terms of seedling shoot dry weight, also had the highest relative plant height, shoot and root dry weights, and grain yield at maturity. In lentil, however, such relationships were less pronounced. Chloride concentration (mg g^?1) in the plant parts at salt levels other than the control was about 2–5 times that of Na. K concentration in the plants was significantly reduced by increasing NaCl levels. Chickpea was generally more sensitive to NaCl salinity than lentil. While no seeds were produced at salinity levels beyond 2dSm^?1 in chickpea (no seeds were produced at this salt level in the most sensitive variety, Mariye), most lentil varieties could produce some seeds up to the highest level of NaCl application. Overall, varieties R-186 (lentil) and Mariye (chickpea) were the most sensitive of all varieties. On the other hand, lentil variety NEL-2704 and chickpea variety DZ-10-16-2 gave comparatively higher mean relative shoot and root dry weights, and grain yield, thus showing some degree of superiority over the others. The observed variations among the varieties may be useful indications for screening varieties of both crops for salt tolerance.     

Variation in Salinity Tolerance in Sunflower (Helianthus annum L.)

Forty-five accessions of sunflower collected from different countries were screened for salinity tolerance after 2 weeks growth in sand culture salinized with 150 meq l^?1 of NaCl₂+ CaCl₂ (1:1 ratio equivalent wt. basis) in half strength Hoagland's nutrient solution. The results for plant biomass of 45 accessions show that there was considerable variation in salinity tolerance. In a further greenhouse experiment, the salinity tolerance of three tolerant (HO-1, Predovik, Euroflor) and two sensitive (SMH-24, 9UO-985) lines (selected on the basis of their performance in the seedling experiment) was assessed at the adult stage to evaluate the consistency of salinity tolerance at different growth stages. All three salt tolerant accessions produced significantly greater plant biomass, seed yield and seed oil content than the salt sensitive accessions. The tolerant accessions accumulated less Cl^? and more K⁺ in the leaves under saline conditions compared with the salt sensitive accessions. The salt tolerant accessions also maintained relatively high leaf K:Na ratio and K⁺ versus Na⁺ selectivity. Although statistically nonsignificant, all three tolerant accessions had greater soluble carbohydrates, soluble proteins, total free amino acids and proline in the leaves than the sensitive accessions. A field trial conducted in a salt-affected field confirmed the greenhouse results of the selected accessions. This study shows that salinity tolerance of sunflower does not vary with stage of plant cycle, so selection for increased salt tolerance can be carried out at the initial growth stage. Secondly, it is found that there is great variation of salt tolerance in sunflower. Low uptake of Cl^?, high uptake of K⁺, and maintenance of high K:Na ratios and K⁺ versus Na⁺ selectivity in the leaves and possibly the accumulation of organic osmotica such as soluble carbohydrates, soluble proteins, proline and free amino acids seem to be the important components of salt tolerance in sunflower.     

冠菌素对棉花幼苗盐害的缓解效应

 以转基因抗虫棉(Gossypium hirsutum L.)中棉所45为材料,通过水培试验研究了冠菌素对盐胁迫下棉花萌发出苗和幼苗生长的影响。结果表明,盐胁迫严重抑制棉花种子萌发和幼苗生长,且对地上部的抑制程度大于对根系的抑制。盐胁迫对棉花萌发出苗和幼苗生长的抑制程度能被0.01 μmol·L^-1 的冠菌素缓解。苗期盐胁迫21 d内,冠菌素处理的棉花根、茎和叶的生物积累量较未施加冠菌素的盐处理增加1倍;活体组织化学原位检测结果显示,低浓度冠菌素处理降低盐胁迫诱导的主根H₂O₂含量。上述研究结果说明低浓度的冠菌素能提高棉花萌发出苗和苗期的耐盐性。     

Boron Induced Oxidative Stress,Antioxidant Defence Response and Changes in Artemisinin Content in Artemisia annua L.

Boron is an essential plant micronutrient and the range between deficient and toxic levels of boron is narrow for most of the plants. Like other elements, boron becomes toxic to growth at high concentrations. High boron concentrations in soil reduce crop productivity in many areas of the world. The effect of increasing levels of boron (0, 0.50, 1.00, 1.50, 2.00 mm ) on oxidative stress, antioxidant defence response and changes in artemisinin content in Artemisia annua were investigated in the present study. Boron toxicity reduced the growth parameters viz. stem height, fresh weight and dry weight. Treatments induced oxidative stress resulting in lower net photosynthetic rate, stomatal conductance, internal CO₂ and total chlorophyll content. The increased activities of antioxidant enzymes like CAT, POX and SOD were also noted in response to increasing levels of boron stress. However, H₂O₂ and artemisinin content were found to be high up to 1.00 mm concentration of boron compared to control, and on applying higher doses, further reduced contents were obtained. Thus, the results suggest that a mild stress of boron can be utilized for enhanced artemisinin production.