Combined effects of salinity and phosphorus availability on growth,gas exchange,and nutrient status of Catapodium rigidum

The combined effects of NaCl-salinity and phosphorus deficiency on biomass production, nutritional status, and photosynthetic activity were studied in Catapodium rigidum: an annual Poacea with fodder potential. Plants were grown in hydroponic conditions for 55 days under two phosphorus (P) supply: 5 (low) or 180?µmol KH₂PO₄ (sufficient), in the absence or presence of 100?mM NaCl. Obtained results demonstrated that both salinity and P deficiency treatments applied separately reduced substantially plant growth and CO₂ assimilation rate with a more marked impact of salt stress. Salinity has no substantial effect on both shoot P concentrations and phosphorus acquisition efficiency independently of P availability. The highest decrease in plant growth (?91%) was observed in plants simultaneously submitted to both stresses suggesting an additive effect of the two stresses and that P deficiency increased the susceptibility of C. rigidum to salinity. This may be linked to a significant decrease in potassium acquisition (?95%), K/Na selectivity ratio (?73%), stomatal conductance (?66%), CO₂ assimilation rate (?64%), and shoot water content (66%). Furthermore, plants cultivated under combined salinity and sufficient P supply displayed higher stomatal conductance, CO₂ assimilation rate, K/Na selectivity ratio, and plant growth than plants cultivated under combined effects of salinity and P deficiency. These results suggest that adding P to saline soils could be an alternative for alleviating the negative effects of salinity and may ameliorate salinity tolerance.     

Effects of spermidine and salinity stress on growth and biochemical response of paraquat‐susceptibe and ‐resistant goosegrass (Eleusine indica L.)

This study aimed to investigate the interaction effect of spermidine (Spd) and salinity stress on growth, photosynthetic rate, antioxidant system and free polyamines (PAs) contents of goosegrass (Eleusine indica L.) seedlings. E. indica was raised in a growth chamber under normal and toxic salt stress (100 mM of NaCl) and sprayed with 0 and 1.00 mM of Spd. The degree of growth inhibition caused by salt stress was lower in a paraquat‐resistant (R) biotype compared to a paraquat‐susceptible (S) biotype. Salt stress significantly elevated the accumulation of malondialdehyde, electrolyte leakage and proline and resulted in the degradation of chlorophyll; reduction in chlorophyll fluorescence; and a decrease in photosynthetic rate, relative water content and biomass. Spd‐treated plants maintained higher activities of antioxidant enzymes (catalase, superoxide dismutase and peroxidase), a greater rate of photosynthesis and lower osmotic pressure than untreated plants in the S biotype. Endogenous Spd content was reduced significantly in response to salt stress in both biotypes, but free PAs content in the S biotype was remarkably enhanced with exogenous Spd application under normal or salinity stress conditions. The result indicated that the S biotype was more sensitive to salinity than the R biotype; meanwhile, exogenous Spd maybe play an important role in protecting S biotype plants from salt stress.     

Effect of Azospirillum and Azotobacter Species on the Performance of Cherry Tomato under Different Salinity Levels

Abiotic stress has a negative impact on plant physiology, influencing the overall growth and development of plant crops. Saline stress is one of the most serious environmental issues limiting crop plant production. Biofertilizers are reparative elements used in soil to increase tolerance to salinity and drought stress. We investigated the effect of salinity stress on qualitative and quantitative characteristics of cherry tomato plants (Lycopersicon esculentum cerasiforme) with biofertilizer application 0, 15 and 30 days after transplanting in this study. After different days of transplantation, different levels of salinity (0, 50, 100, and 150?mM) were used with biofertilizer (Azospirillum sp. and Azotobacter sp.) application (0, 15 and 30 days). The salinity (150?mM NaCl) significantly affected the studied variables, which were recorded with minimum levels of leaf area (52.42?cm²), root length (6.54?cm), fresh root weight (13.64?g), yield (6.52 tons/ha), leaf chlorophyll content (36.11?mg/m²) and maximum levels of total soluble solids (TSS, 8.87 °Brix). Control samples had higher leaf area (58.35?cm²), root length (15.23?cm), fresh root weight (17.86?g), yield (9.39 tons/ha), leaf chlorophyll content (44.09?mg/m²), and lower TSS (7.93 °Brix). Plants that received biofertilizer (15 days after transplanting) had higher plant height (73.41?cm), stem diameter (0.74?cm), leaf area (61.16?cm²), root length (15.35?cm), fresh root weight (18.38?g), root dry matter (60.41%), yield (10.43?t/ha), leaf chlorophyll content (42.55?mg/m²), fruit dry matter content (10.12?g), pH 4.52, and TSS (9.30 °Brix). The minimum plant height (51.33?cm), stem diameter (0.55?cm), leaf area (49.60?cm²), root length (7.04?cm), fresh root weight (12.76?g), root dry matter (42.16?g), yield (5.15 tons/ha), leaf chlorophyll content (35.18?mg/m²), fruit dry matter content (6.59?g), pH 4.27 and TSS (7.55 °Brix) were recorded in plants with no application of biofertilizer. The present study revealed that most growth and quality variables were negatively affected by salinity except for TSS, which showed positive effect with application of 150?mM of NaCl. Biofertilizer application at 15 days significantly influences the quantitative and qualitative attributes of cherry tomato under different levels of salinity.

     

Effects of salt treatment on growth,lipid membrane peroxidation,polyphenol content,and antioxidant activities in leaves of Sesuvium portulacastrum L.

Changes in growth, leaf contents of proline, oxidative stress-related parameters, and phenolic compounds, and antioxidant activities were investigated in the halophyte species Sesuvium portulacastrum L. under saline conditions. Rooted cuttings were individually cultivated in sandy soil. After five weeks of pre-treatment, seedlings were submitted during one month to different salt concentrations ranging from 0 to 800?mM NaCl. The plant growth was significantly improved by salt at 200–600?mM concentration. This trend was associated with (i) the stimulation of photosynthetic activity, (ii) the protection of membrane integrity (leaf MDA content 50% lower than the control), and (iii) higher total antioxidant activity, especially at 400?mM NaCl. At this salt concentration plants accumulated high contents of proline, polyphenols, antocyanins, and carotenoids. These compounds could be implied in the protection of the photosynthetic system and in the improvement of growth. Exposure to 800?mM NaCl impaired significantly photosynthesis, proline, polyphenol, antocyanin, and carotenoid accumulation. Yet, the strong antiradical activity (DPPH) observed at this extreme salinity might partly explain the plant survival. S. portulacastrum could be used in the rehabilitation and the stabilisation of saline or saline arid land. Additionally, under saline conditions, S. portulacastrum accumulate a large amount of proline and exhibits important antioxidant potentialities.     

Differences in physiological responses to NaCl between salt-tolerant Sesbania rostrata Brem. & Oberm. and non-tolerant Phaseolus vulgaris L.

Sesbania rostrata ( S. rostrata) Brem. & Oberm., a member of the Fabaceae family, has been used as a promising halophytic plant to ameliorate soil salinity in north-east Thailand. To obtain information regarding the mechanism of salt tolerance, the physiological responses of S. rostrata to NaCl was compared with those of the salt-susceptible species, kidney bean ( Phaseolus vulgaris L. cv. Meal). Seedlings were grown hydroponically with 0, 50, 100 and 150 m m NaCl for 10 days and their effects on growth, chlorophyll content, fluorescence yield ( F _v/ F _m), inorganic elements and amino acid content were determined. The results showed that tolerance to NaCl was clearly different between the two plants. At the highest concentration (150 m m ), the dry weight of S. rostrata was more than 50% greater than the control, whereas the kidney bean could not survive. Chlorophyll a content drastically reduced only in the kidney bean. The F _v/ F _m of S. rostrata did not change with increasing concentrations of NaCl, but that of kidney bean decreased. Greater percentages (≥80%) of absorbed Na⁺ and Cl^– were translocated and accumulated in the shoots of S. rostrata , but remained largely in the roots of kidney bean. The enhancement of contents of amino acids, including proline, with increasing NaCl was observed in both species. These results strongly suggest that the salt tolerance of S. rostrata is associated with the ability of the plant to translocate and sequester Na⁺ and Cl^– in the shoot cells.     

Response of<Emphasis Type="Italic">Tetranychus cinnabarinus</Emphasis> feeding on NaCl-stressed strawberry plants

The development and reproductive rates ofTetranychus cinnabarinus Boisduval (Acari: Tetranychidae), the carmine spider mite, were studied on two strawberry cultivars (Fragaria ×ananassa Duch.; ‘Camarosa’ and ‘Sweet Charlie’) at three NaCl concentrations, 1760, 2400 and 3040 mgl ⁻¹, and control. The effects of NaCl application on the contents of plant nutrients, chlorophyll, proline, peroxidase activity (POX) and proteins were assessed. On Camarosa,T. cinnabarinus had a faster development rate with applications of NaCl than without, except for female development at the highest salinity level. The total development time of females increased with the NaCl concentration, whereas total development time of males decreased. The oviposition period and female longevity on Camarosa was significantly longer in the control than with NaCl, whereas daily and total fecundity were significantly higher at all NaCl concentrations than in the control, except for total fecundity at the lowest salinity level. The total development time, oviposition period, female longevity, daily and total fecundity on Sweet Charlie did not differ significantly between NaCl salinity levels and the control. The intrinsic rate of natural increase (r _m ) on Camarosa and Sweet Charlie were significantly higher with NaCl than in the control. However, the contents of Na, Cl, P, chlorophyll, proline, POX and protein in the two strawberry cultivars changed depending on NaCl concentration. On the other hand, the K and N contents were not affected significantly by NaCl salinity. http://www.phytoparasitica.org posting Nov. 19, 2006.     

Mitigation of Salt Stress Negative Effects on Sweet Pepper Using Arbuscular Mycorrhizal Fungi (AMF), <Emphasis Type="Italic">Bacillus megaterium</Emphasis> and Brassinosteroids (BRs)

A study was conducted at the experimental farm of Faculty of Agriculture, Ain Shams University, Cairo, Egypt, during two successive summer seasons (2014 and 2015) to investigate the effects of arbuscular mycorrhizal fungi (Glomus irradicans 10% w/w), Bacillus megaterium (10?ml/pot) and brassinosteroids (24-EBL, C₂₈H₄₈O_6; 2?µM) on growth, nutrient absorption, chlorophyll, proline content, antioxidant enzymes activity and fruit yield of sweet pepper plants (Capsicum annuum L.) cv. Marconi. Plants were grown under three levels of salinity (0, 25 and 50?mM). The obtained results showed that plants grown under non-saline water (0?mM NaCl), with or without treatments, significantly gave the most vigorous vegetative growth and had the highest fruit yield compared with those grown under salt stress conditions. All anti-salinity treatments (Mycorrhiza, Bacillus and Brassinosteroids) improved growth when compared with untreated plants (control). Plants inoculated with mycorrhiza or treated with brassinosteroids showed better vegetative growth and shoot biomass (total fresh and dry weight per plant), chlorophyll a and b concentrations, antioxidant content expressed as total soluble phenols and proline concentrations at all studied salinity levels followed by plants inoculated with Bacillus megaterium compared with control plants which showed severe growth retardant especially under higher salt concentration (50?mM). Carotenoids concentration increased proportionally with the increase of salinity concentration. The maximum leaf relative water content (LRWC) and lowest values of membrane permeability (MP) were significantly observed with mychorhiza inoculated plants and brassinosteroid application respectively, followed by Bacillus inoculated plants. Antioxidant enzyme activity were highest in plants irrigated with moderate saline water (25?mM) than plants under high salinity irrigation water (50?mM) except polyphenol oxidase (PPO) as compared with unstressed plants (0?mM). Mycorrhizal inoculated plants accumulated higher K and lower Na and Cl followed by plants treated with brassinosteroids and then plants inoculated with Bacillus megaterium. Anti-salinity treatments positively enhanced fruit yield of sweet pepper plants under all salinity stress levels and the highest fruit yield were significantly observed with brassinosteroid application followed by mychorhiza inoculated plants and then Bacillus inoculated plants.     

Growth and leaf chemistry of Atriplex species from Northern Mexico as affected by salt stress

Atriplex species are tolerant to salinity and water stress and thus they are suitable for restoration of many degraded ecosystems. In addition, many Atriplex species offer good value as forages. We compared growth and leaf chemistry of Atriplex canescens, a well-known halophyte, and A. acanthocarpa, a poorly-studied species, as affected by salinity in a greenhouse study. Seeds and soil were collected in northern Mexico, the native range of these species. Plants were grown in pots containing native soil and irrigated with NaCl solutions of 0, 50, and 100 mM. Shoot growth of A. canescens declined 37% as NaCl treatments increased from 0 to 100 mM while shoot growth of A acanthocarpa was not significantly affected by salinity. The high salt tolerance of A. acanthocarpa was linked to a high accumulation of leaf sodium (Na) (7- to 13-fold higher than A. canescens). A. acanthocarpa had also higher growth rate than A. canescenes, making the former species a good candidate for cultivation, especially under saline conditions. Tissue concentration of potassium (K) in both species was minimally affected by the salinity treatments. Leaf nitrogen (N) concentration increased as plants faced higher salinity treatments, especially in A. canescens. The high salt tolerance and higher Na accumulation of A. acanthocarpa make this species an attractive choice for reclamation of saline areas. We suggest A. acanthocarpa should be explored as viable forage for cultivation and for reclamation of degraded areas just as A. canescens has been throughout the world.     

Ascorbic Acid Enhances Growth and Yield of Sweet Peppers (Capsicum annum) by Mitigating Salinity Stress

Salinity is a crucial problem which has affected crop productivity globally. Ascorbic acid is considered helpful against abiotic stresses due to its powerful antioxidant potential. In the pot experiment, salinity stress (0, 35, 70, and 105?mM) was applied to sweet peppers in split doses after 20 days of transplantation. To mitigate the adverse effects of salinity, ascorbic acid (0, 0.40, 0.80, and 1.20?mM) was applied as foliar spray after a 6-day interval during vegetative growth. Sweet pepper plants sprayed with distilled water (control) recorded maximum plant height (cm), leaf area (cm²), number of branches, stem diameter (mm), number of fruit plant^?1, fruit diameter (cm), yield plant^?1 (g), and chlorophyll content (mg 100?g^?1), while the maximum polyphenol oxidase (PPO) activity (unit mg protein^?1 min^?1) and ascorbate peroxidase (APX) activity (unit mg protein^?1 min^?1) were recorded in plants treated with 70?mM NaCl application. Salinity stress beyond 70?mM significantly reduced all the studied parameters. An ascorbic acid concentration of 1.20?mM significantly mitigated the negative effects of salt stress and recorded maximum plant height (cm), number of leaves plant^?1, leaf area (cm²), number of branches plant^?1, stem diameter (mm), number of fruit plant^?1, fruit diameter (cm), yield plant^?1 (g), chlorophyll content (mg 100?g^?1), PPO activity (unit mg protein^?1 min^?1), and APX activity (unit mg protein^?1 min^?1). Hence, a 1.20?mM concentration of foliar ascorbic acid could be used in saline conditions up to 70?mM of sodium chloride (NaCl) for better growth, productivity, and enzymatic activity of sweet peppers.

     

Impact of Exogenous Application of Salicylic Acid on Growth,Water Status And Antioxidant Enzyme Activity of Strawberry Plants (Fragaria vesca L.) Under Salt Stress Conditions

Irrigation with saline water can act as an alternate water resource and thus plays an important role in saving freshwater resources as well as promoting agriculture. Furthermore, salinity stress is considered one of the major abiotic stress factors, which strongly reduces crop productivity. In this context, the present work was conducted to examine the effect of exogenous salicylic acid (SA) application on salt stress tolerance of strawberry plants. For this purpose, strawberry plants (Fragaria vesca L.), three months old, were treated with three SA concentrations (0?mM, 0.25?mM and 0.5?mM), then subjected to 80?mM NaCl or not. After five weeks of treatment, growth responses, water status, photochemical efficiency and oxidative stress indicators were measured. The obtained results showed that irrigation with saline water negatively affected the growth parameters, the leaf water potential (LWP), the relative water content (RWC), the stomatal conductance (gs) and photochemical efficiency (Fv/Fm). While, the total protein content, the electrolyte leakage (EL), the malondialdehyde (MDA) and the hydrogen peroxide (H₂O₂) contents were increased in stressed plants compared to unstressed ones. Salt stress also leads to the activation of the antioxidant enzymes. However, the exogenous application of SA under salt stress conditions reduced the H₂O₂ accumulation, the electrolyte leakage and the MDA content. It has also improved the growth parameters, the LWP, the RWC, the gs, the Fv/Fm, the protein content and the antioxidant enzyme activities (POD, CAT and SOD) in the treated plants compared to those without SA application. Therefore, the beneficial effect of 0.25?mM SA on Fragaria vesca L. salinity tolerance may provide some practical basis for strawberry cultivation under saline conditions.

     

Exogenously applied hexaconazole ameliorates salinity stress by inducing an antioxidant defense system in Brassica napus L. plants

The ability of hexaconazole (HEX) to ameliorate salinity stress was studied in canola plants (Brassica napus L.). Canola seedlings were subjected to sodium chloride (NaCl) treatment. A treatment with 200 mM NaCl reduced growth parameters, chlorophyll content and protein content as well as increased the proline (Pro) content in canola plants. In addition, NaCl stress increased the endogenous, nonenzymatic antioxidants and the activity of antioxidant enzymes, such as peroxidase (POX; EC 1.11.1.7), superoxide dismutase (SOD; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6). When these plants were treated with a combination of NaCl and 50 mg L⁻¹ HEX, the inhibitory effects of NaCl stress were decreased by increasing the root growth, shoot growth, dry weight (DW), chlorophyll content, protein content and antioxidant enzyme activity by ameliorating the salinity injury. These results suggested that HEX has an important role in the enhancement of plant antioxidant systems and resistance to salinity in canola plants.     

Growth,physiological status,and yield of salt-stressed wheat (Triticum aestivum L.) plants affected by biofertilizer and cycocel applications

This factorial study was conducted based on randomized complete block design with three replications in a greenhouse during spring 2015 to investigate changes in dry matter mobilization, grain filling period, and some physiological characteristics of wheat. Treatments were four salt levels [0 (S₁), 30 (S₂), 60 (S₃), and 90 (S₄) mM sodium chloride (NaCl) equivalent to 2.76, 5.53, and 8.3 dS m^?1, respectively], four biofertilizers levels [(no biofertilizer (F₀), seed inoculation by Azotobacter chroococcum Beijerinck strain 5 (F₁), Pseudomonas putida (Trevisan) Migula 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)]. Salinity stress increased leaf electrical conductivity and decreased chlorophyll index, quantum yield, relative water content, and stomata conductance. However, the application of cycocel and biofertilizer reduced the negative impacts at each level of salinity tested. When treated with cycocel, salt stressed plants demonstrated a significant decrease in stomata conductance compared to the salt-treated plants with no cycocel. The results revealed that the maximum shoot and stem dry matter mobilization (0.89 and 0.67?g, respectively) and contribution of stem reserves to grain yield (38.01%) were observed in salinity severe stress (90?mM) and no cycocel application. The application of Azotobacter?+?Pseudomonas had the greatest grain filling rate (0.002?g day^?1) without salinity stress. The greatest grain filling period (43.26 days) was achieved by the highest cycocel level without salinity stress. The application of biofertilizer and cycocel as F₃C₂ had 24.7% more grain yield in comparison to the controls.     

外源NO对NaCl胁迫下玉米幼苗生长和渗透调节能力的影响

采用水培法,研究了50、100、200μmol·L~(-1)外源一氧化氮(NO)供体硝普钠(SNP)对盐胁迫下玉米幼苗生长和渗透调节能力的影响。结果表明,外施NO可明显缓解Na Cl胁迫对玉米幼苗生长的抑制作用,与不施SNP的处理相比,100μmol·L~(-1)SNP处理全株干重的增加幅度达到19%。外施NO降低盐胁迫下玉米幼苗叶片及根系中可溶性糖和可溶性蛋白的含量,其中叶片中可溶性糖和可溶性蛋白分别降低19.9%和7.9%,根系中可溶性糖和可溶性蛋白含量分别降低9.6%和9%。外源一氧化氮(NO)使盐胁迫下玉米幼苗根系、生长叶和成熟叶叶鞘的Na~+含量分别降低38.4%、5.1%和17.2%;同时,增加根系和成熟叶叶鞘中K~+、Ca~(2+)、Mg~(2+)含量,降低玉米幼苗各器官内的Na~+/K~+、Na~+/Ca~(2+)比值,维持盐胁迫下玉米幼苗中的离子平衡,但对成熟叶片中离子含量的影响不大。研究认为,外源NO可维持盐胁迫下玉米幼苗的碳氮代谢平衡,改善玉米幼苗离子的吸收与分配,缓解Na Cl胁迫对玉米幼苗带来的伤害,其中以100μmol·L~(-1)的SNP处理效果最明显。     

盐胁迫条件下骆驼刺与绿豆光合日变化特征及午休现象的成因

为了研究盐生豆科植物骆驼刺与盐敏感植物绿豆在盐胁迫下光合日变化与光合“午休”现象的成因,在网室培养,并用0 mmol•L^-1(对照)、50 mmol•L^-1、100mmol•L^-1、200 mmol•L^-1 NaCl处理2周,测定光合作用日变化、叶绿素含量和Rubisco大亚基基因的表达等参数。结果表明：未经盐处理时,骆驼刺和绿豆光合日变化均呈单峰型;经盐处理后,两者光合日变化响应有明显差异。骆驼刺50～200 mmol•L^-1NaCl处理后,其净光合速率（Pn）均比未处理(对照)上升速率快,而其他处理峰值与对照之间没有显著差异;绿豆对照光合速率的上升则比盐处理的快,盐处理光合速率峰值低于对照。骆驼刺50 mmol•L^-1、100 mmol•L^-1和绿豆50 mmol•L^-1处理Pn没有出现“午休”现象,而骆驼刺200 mmol•L^-1处理与绿豆100 mmol•L^-1处理出现“午休”现象。骆驼刺在重度盐胁迫下,由于气孔导度（Gs）下降而引起轻微的“午休”现象,而盐处理绿豆中Rubisco被抑制,对Pn 午休的贡献比其Gs的贡献更为显著。在绿豆中大亚基基因（rbcL）的表达量随着盐胁迫的提高而下降。骆驼刺中rbcL的表达在50 mmol•L^-1和100 mmol•L^-1处理下有所增加,而在200 mmol•L^-1处理显著降低。绿豆和骆驼刺的总叶绿素含量及其Chl a/b比值的动态变化表明,绿豆PSI复合体下降速率较PSII快;与此相反,骆驼刺盐处理后PSI复合体浓度的增加却比PSII复合体快。     

霸王树的抗盐性研究

鉴于在干旱区农业中利用盐水资源的需求,我们对霸王树在水培生长中的抗盐性进行了研究。NaCl浓度范围为5(对照)至200molm~(-3)。结果表明,叶状枝的生长对盐敏感,在盐浓度为50molm~(-3)时,生长量为对照的60%。根茎比仅在浓度为200molm~(-3)时才显著降低。对其它不同指标也进行了研究,例如水分含量、Na、K及Cl含量、渗透压和CO_2吸收等。这些指标中,叶状枝水分含量和CO_2吸收的降低均与叶状枝生长降低相联系。含盐量增高使叶状枝渗透压增加,这同组织脱水有关。我们认为霸王树在盐水胁迫下不产生渗透压的调节作用。     

盐碱胁迫对盐生植物种子萌发的影响

采用不同浓度的NaCl(中性盐)和Na2CO3(碱性盐)胁迫三种盐生植物盐地碱蓬、碱蓬和盐爪爪正在萌发的种子,以研究不同类型盐对种子萌发特性的影响.结果表明,随着两种盐浓度的升高,种子萌发率下降,萌发率与盐浓度间呈现显著的负相关关系;盐地碱蓬、碱蓬和盐爪爪种子萌发率与NaCl胁迫相关系数分别为0.9206、0.8989和0.8956,与Na2CO3胁迫相关系数分别为0.9148、0.7193和0.6327;蒸馏水中三种盐生植物种子萌发率最高,Na2CO3对种子萌发的抑制作用强于NaCl.     

Exogenous Silicon Protects <Emphasis Type="Italic">Brassica napus</Emphasis> Plants from Salinity-Induced Oxidative Stress Through the Modulation of AsA-GSH Pathway,Thiol-Dependent Antioxidant Enzymes and Glyoxalase Systems

Although silicon (Si) has showed its potential role in mitigating abiotic stress-induced damages in many plant species its role in coordinated induction of antioxidant defense is yet to be elucidated. Therefore, we studied rapeseed (Brassica napus) seedlings applied with exogenous Si for changes occurring in antioxidant defense and glyoxalase systems. Seedlings (12-day-old) grown semi-hydroponically were exposed to Si (silicon dioxide, SiO₂; 1?mM) solely and in combination with NaCl (100 and 200?mM) for 48?h. Salinity created oxidative damage by increasing H₂O₂ and malondialdehyde (MDA) contents resulting in disruption of antioxidant defense system and in arousing methylglyoxal (MG) toxicity by the down-regulation of glyoxalase enzyme activities. Exogenous Si treatment showed reduction of both H₂O₂ and MDA contents and up-regulation of antioxidant components including the activities of related enzymes (APX, MDHAR, DHAR, GR, GST, GPX and CAT) and the contents of AsA and GSH. Enhanced activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) detoxified the toxic MG. Thus, this study clearly indicates that Si improved plant tolerance to salinity stress through enhancement of both antioxidant defense and glyoxalase systems that led to reduced oxidative damage and MG toxicity.     

Effects of sodium on nitrate uptake and osmotic adjustment of Suaeda physophora

Na+ ions play an important role in the growth of halophyte. The effect of Na+ ions on nitrate uptake and osmotic adjustment in the euhalophyte Suaeda physophora was investigated under glasshouse conditions. Seedlings were exposed to 1 mmol/L NaCl (control),300 mmol/L NaCl,150 mmol/L NaCl plus 150 mmol/L KCl or 300 mmol/L KCl treatments for 24 d. Dry weight was not affected greatly by different salt treatments,but water content and succulence in leaves of S. physophora were significantly increased at 300 mmol/L NaCl and 150 mmol/L NaCl plus 150 mmol/L KCl treatments. The concentrations of Na+ and NO3’ in leaves of S. physophora were the highest at 150 mmol/L NaCl plus 150 mmol/L KCl,but lowest at 300 mmol/L KCl treatment. Moreover,the increase of NO3’ concentration did not result in the decrease of Cl-concentration at 150 mmol/L NaCl plus 150 mmol/L KCl treatments. The estimated contribution of NO3’ to osmotic potential (CNO3) in leaves of S. physophora was 9.8% at 150 mmol/L NaCl plus 150 mmol/L KCl,and CNa and CCl were 31.0% and 23.3%,respectively. However,CNO3,CNa and CCl were respectively 1.6%,7.9% and 11.9% at 300 mmol/L KCl treatment. It is concluded that Na+ stimulates NO3’ absorption and the stimulation is independent on the internal or the external Cl-concentration in the euhalophyte S. physo-phora. These characteristics may explain the high levels of N in leaves of saline desert plants in arid ecosystem.     

Growth,Fiber and Nitrogen Content in Sisal Plants (<Emphasis Type="Italic">Furcraea</Emphasis> sp) Under NaCl Salinity

Soil contains water and nutrients necessary for the development of cultivated plants and serves as a substrate and support in terrestrial ecosystems. For reasons inherent to the nature of soil, salt content can considerably limit the growth of plants. With the implementation of salinity-tolerant crops, saline soils can be transformed into productive and sustainable areas. In Tunja, Colombia, a trial was developed to quantify the changes in growth, water intake, fiber, nitrogen and chlorophyll content in Furcraea hexapetala plants exposed to NaCl saline conditions. Plantlets obtained from bulbs were grown in an aerated nutrient solution under greenhouse conditions. Measurements of 30, 60 or 90?mmol NaCl was added to the nutrient solution and control plants were left without addition of salt. As a consequence of salinity, leaf area, leaf area ratio, water uptake, absolute growth rate, relative growth rate, fiber content, dry matter, chlorophyll and nitrogen content in leaves were reduced. The accumulation of dry matter in leaves, stem and roots was especially affected when the plants were exposed to 90?mmol of NaCl. Accumulated dry matter increased in the stems, but reduced in the leaves. These results suggest that plants of Furcraea hexapetala can tolerate up to 60?mmol of NaCl (4.9?dS?m^?1) without substantially affecting the parameters that determine the growth or the fiber content in the leaves.