Role of Arbuscular Mycorrhizal (AM) Fungi on Growth, Cadmium Uptake, Osmolyte, and Phytochelatin Synthesis in Cajanus cajan (L.) Millsp. Under NaCl and Cd Stresses

Application of phosphatic (P) fertilizers and biosolids is known to enhance cadmium (Cd) contamination in saline soils. Increased concentration of dissolved chloride (Cl^?) in soil solution significantly influences Cd bioavailability in P fertilizer- or biosolid-amended soils. Arbuscular mycorrhizal (AM) fungi have an ability to protect plants against salinity and heavy metals by mediating interactions between toxic ions and plant roots. The effects of Glomus mosseae (AM) and NaCl and Cd stresses on Cd uptake and osmolyte and phytochelatin (PCs) synthesis in Cajanus cajan (L.) Millsp. (pigeonpea) were studied under greenhouse conditions. Two genotypes [Sel 85?N (tolerant) and ICP 13997 (sensitive)] were subjected to NaCl (4 and 6?dS?m^?1) and Cd (CdCl₂, 25 and 50?mg?kg^?1 dry soil) treatments. NaCl and Cd applied individually as well as in combination caused dramatic reductions in plant biomass and induced membrane peroxidation, ionic perturbations, and metabolite synthesis in both genotypes, although Sel 85?N was less affected than ICP 13997. Cadmium uptake was enhanced when NaCl was added along with Cd. The protection of growth in Sel 85?N was associated with restricted accumulation of Na⁺, Cl^?, and Cd²⁺ and higher concentrations of stress metabolites (sugars, proteins, free amino acids, proline, glycine betaine). Cd led to a significant increase in biothiols (NP-SH) and glutathione (GSH), with a larger pool of NP-SH which strongly induced accumulation of phytochelatins, whereas no significant effects in their concentrations were detectable under NaCl stress. The interactive effects of NaCl and Cd on all parameters were larger than those of individual treatments. Fungal inoculations improved plant growth and reduced accumulation of toxic ions. Higher stress metabolite synthesis and PCs observed in AM plants of Sel 85?N indicated the role of an efficient AM symbiosis capable of attenuating NaCl and Cd stresses.     

Effect of NaCl on growth and Cd accumulation of halophyte Spartina alterniflora under CdCl2 stress

A study quantifying the effect of NaCl on growth and Cd accumulation of Spartina alterniflora subjected to Cd stress was conducted. Seedlings were cultivated in the presence of 1 or 3 mM Cd alone, or combined with NaCl (50 or 100 mM). The results showed that NaCl magnified the phytotoxicity of moderate Cd stress (1 mM Cd) on plants due to reduced levels of plant biomass, plant height, and chlorophyll a + b, while no synergistic effects were recorded under severe Cd stress (3 mM Cd). Proline and Ca^2 + accumulated along with additional NaCl under moderate Cd stress, instead of reduced or unchanged levels under severe Cd stress owing to different adoption strategies caused by NaCl under different Cd stresses. NaCl reduced the oxidative stress in Cd-treated plants through increasing levels of antioxidative enzymes (catalase (CAT) and peroxidase (POD)) under moderate Cd stress. With NaCl addition, Cd^2 + contents in S. alterniflora increased and reduced under moderate and severe Cd stress, respectively. However, total Cd^2 + amounts increased with increasing NaCl concentration due to biological dilution. NaCl improved the increase of Cd^2 + translocation factor (TF) under moderate Cd stress, indicating that NaCl might improve Cd^2 + uptake and translocation from roots to shoots, and enhance the phytoextraction of S. alterniflora on Cd; while phytostabilization of Cd under severe Cd stress may be possible due to the reduced TF. Thus, NaCl alleviated phytotoxicity caused by Cd stress through improved management of osmotic solutes and oxidative status, and affected Cd accumulations in S. alterniflora differently under moderate and severe Cd stresses.     

NaCl differently interferes with Cd and Zn toxicities in the wetland halophyte species Kosteletzkya virginica (L.) Presl.

Hydroponic experiments were carried out using seedlings of the wetland halophyte species Kosteletzkya virginica (L.) Presl. exposed to 10???M Cd or 100???M Zn in the absence or presence of 50?mM NaCl. Interaction between salinity and heavy metals was analysed in relation to plant growth, water status and tissue ion contents (Na, K and Ca). Results showed a strong inhibition effect of Cd on leaf emergence, lateral branch development and leaf expansion. Heavy metals induced a significant decrease in plant dry weight, water content, osmotic potential (?? _S) and leaf water potential (?? _w). Cadmium and Zn accumulated to higher extent in the roots than in the shoots. Cadmium increased the leaf K concentration while Zn had an opposite effect. Salinity strongly reduced Cd uptake and translocation from roots to shoots: it mitigated the Cd impact on lateral branch emergence but had no effects on plant dry weight and water status. Cadmium drastically reduced Na translocation in salt-treated plants while Zn increased it. It is concluded that complex interactions exist between heavy metals and monovalent cations in salt conditions and that Cd and Zn display contrasting behaviour in this respect. Stress-induced modification of ion content did not fully explain growth inhibition in Kosteletzkya virginica.     

Antioxidant enzyme activities and hormonal status in response to Cd stress in the wetland halophyte Kosteletzkya virginica under saline conditions

Salt marshes constitute major sinks for heavy metal accumulation but the precise impact of salinity on heavy metal toxicity for halophyte plant species remains largely unknown. Young seedlings of Kosteletzkya virginica were exposed during 3 weeks in nutrient solution to Cd 5 µM in the presence or absence of 50 mM NaCl. Cadmium (Cd) reduced growth and shoot water content and had major detrimental effect on maximum quantum efficiency (F_v/F_m), effective quantum yield of photosystem II (Y(II)) and electron transport rates (ETRs). Cd induced an oxidative stress in relation to an increase in O₂^?? and H₂O₂ concentration and lead to a decrease in endogenous glutathione (GSH) and α‐tocopherol in the leaves. Cd not only increased leaf zeatin and zeatin riboside concentration but also increased the senescing compounds 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and abscisic acid (ABA). Salinity reduced Cd accumulation already after 1 week of stress but was unable to restore shoot growth and thus did not induce any dilution effect. Salinity delayed the Cd‐induced leaf senescence: NaCl reduced the deleterious impact of Cd on photosynthesis apparatus through an improvement of F_v/F_m, Y(II) and ETR. Salt reduced oxidative stress in Cd‐treated plants through an increase in GSH, α‐tocopherol and ascorbic acid synthesis and an increase in glutathione reductase (EC 1.6.4.2) activity. Additional salt reduced ACC and ABA accumulation in Cd+NaCl‐treated leaves comparing to Cd alone. It is concluded that salinity affords efficient protection against Cd to the halophyte species K. virginica, in relation to an improved management of oxidative stress and hormonal status.     

Interaction of NaCl and Cd stress on compartmentation pattern of cations,antioxidant enzymes and proteins in leaves of two wheat genotypes differing in salt tolerance

Physiological mechanisms of salinity–Cd interactions were investigated in inter- and intracellular leaf compartments of salt-tolerant wheat × Lophopyrum elongatum (Host) A. Löve (syn. Agropyron elongatum) amphiploid and its salt-sensitive wheat parent (Triticum aestivum L. cv Chinese Spring). In comparison with the intracellular fluid, only very low Na⁺ concentrations (up to about 4 mM) were found in the intercellular leaf compartment of wheat after a 75 mM supply of NaCl. NaCl salinity led to a higher Cd concentration in leaves of the salt-sensitive genotype. Cd in the intercellular leaf compartment was not detectable. Higher K⁺ concentrations in the intercellular leaf compartment of the salt-sensitive genotype suggest a higher plasma membrane permeability caused by NaCl + Cd stress. Ascorbate peroxidase (APX) activity was increased in leaves of the salt-sensitive genotype under the combined NaCl and Cd stress. The highest non-specific peroxidase activities were detected under the combined stresses. It is suggested that NaCl and Cd stress in combination enhance the production of oxygen radicals and H₂O₂, especially in leaves of the salt-sensitive genotype. As a consequence, disturbed membrane function may cause elevated Cd concentrations in the intracellular leaf compartment under salinity. Cd did not change protein concentration and pattern in leaves. The protein content in inter-and intracellular leaf compartments of both genotypes was increased under salinity. A different protein pattern was obtained in inter- and intracellular leaf compartments. Thus, several physiological interactions between NaCl stress and Cd were found in the two wheat genotypes.     

Influence of aqueous leaf extract of common lambsquarters and NaCl salinity on the germination, growth, and nutrient content of wheat

Aqueous leaf extract of common lambsquarters (Chenopodium album L.) was evaluated alone or in combination with NaCl salinity for its influence on germination, seedling growth and contents of Na, K, and Ca by shoots and roots of wheat. The leaf extract and NaCl alone or in combination did not have any significant effect on germination, but the shoot and root lengths of seedlings and their dry weight decreased significantly by the treatments. Root growth was affected more than the shoot. The combination of leaf extract and NaCl drastically reduced the growth more than the separate effects of these stress treatments. The incorporation of leaf extract in the growth media decreased the content of Na by shoot, whereas the contents of K and Ca increased. NaCl treatments in combination with leaf extract increased the content of Na. Similar increases were observed for K and Ca in shoot, while these nutrients were increased in roots compared to control.     

Effective Phytoextraction of Cadmium (Cd) with Increasing Concentration of Total Phenolics and Free Proline in Cannabis sativa (L) Plant Under Various Treatments of Fertilizers,Plant Growth Regulators and Sodium Salt

The comparative effect of fertilizers (NPK), plant growth regulators (GA₃, IAA, Zeatin) and sodium chloride (NaCl) on Cd phytoaccumulation, proline and phenolics production in Cannabis sativa was evaluated. Proline and phenolices were correlated with Cd contents in plant. Cd significantly reduced the plant growth. Fertilizers application (in combination) most significantly increased the growth (19 cm root and 47 cm shoot) on Cd contaminated soil. All treatments increased the Cd contents in plant tissues. This increase was highly significant in fertilizers treated plants (1101, 121 and 544 ppm in roots, stem and leaves respectively). Significantly positive correlation was found between Cd concentration and dry biomass of root (R² = 0.7511) and leaves (R² = 0.5524). All treatments significantly increased the proline and total phenolics and maximum was recorded in NaCl treated plants followed by fertilizers. Proline was higher in roots while phenolics in leaves. The correlation between proline and phenolics was positive in leaf (R² = 0.8439) and root (R² = 0.5191). Proline and phenolics showed positive correlation with Cd concentration in plant. Conclusively, fertilizers in combination seem to be the better option for Cd phytoextraction. Further investigation is suggested to study the role of phenolics and proline in Cd phytoextraction.     

Soil cadmium toxicity and nitrogen deposition differently affect growth and physiology in <Emphasis Type="Italic">Toxicodendron vernicifluum</Emphasis> seedlings

To ultimately determine whether different levels of soil nitrogen (N) deposition can modify the detrimental effects of cadmium (Cd), the seedlings of Toxicodendron vernicifluum (Strokes) F. A. Barkley were exposed to soil Cd stress (0, 5 and 15 mg kg^?1 dry soil), N deposition (0, 13 and 40 mg kg^?1 dry soil) and their combinations. Soil Cd stress caused damage in plant growth, photosynthesis and other physiological indexes, and in the ultrastructure of mesophyll cells. The effects of N deposition on growth, lipid peroxidation and enzyme activities depended on the relative amounts of N supplied. The combination of low N deposition and Cd stress was positive to plant growth, photosynthesis and enzyme activities, and it caused lower levels of Cd accumulation and lipid peroxidation compared with the effect of Cd stress alone. The combination of high N deposition and Cd stress led to a higher Cd accumulation and lipid peroxidation, and to lower enzyme activities, as compared with the effect of Cd stress alone. T. vernicifluum was found to be sensitive to soil Cd stress. Soil Cd had detrimental effects on T. vernicifluum seedlings, but the tolerance of T. vernicifluum to Cd increased under low N deposition.     

Combined effects of NaCl and Cd2+ stress on the photosynthetic apparatus of Thellungiella salsuginea

Plants show complex responses to abiotic stress while, the effect of the stress combinations can be different to those seen when each stress is applied individually. Here, we report on the effects of salt and/or cadmium on photosynthetic apparatus of Thellungiella salsuginea. Our results showed a considerable reduction of plant growth with some symptoms of toxicity, especially with cadmium treatment. The structural integrity of both photosystems (PSI and PSII) was mostly maintained under salt stress. Cadmium induced a considerable decrease of both PSI and PSII quantum yields and the electron transport rate ETR(I) and ETR(II) paralleled by an increase of non-photochemical quenching (NPQ). In addition, cadmium alone affects the rate of primary photochemistry by an increase of fluorescence at O-J phase and also the photo-electrochemical quenching at J-I phase. A positive L-band appeared with (Cd) treatment as an indicator of lower PSII connectivity, and a positive K-band reflecting the imbalance in number of electrons at donor and acceptor side. In continuity to our previous studies which showed that NaCl supply reduced Cd²⁺ uptake and limited its accumulation in shoot of divers halophyte species, here as a consequence, we demonstrated the NaCl-induced enhancement effect of Cd²⁺ toxicity on the PSII activity by maintaining the photosynthetic electron transport chain as evidenced by the differences in ψ_O, φ_Eo, ABS/RC and TR₀/RC and by improvement of performance index PI_(ABS), especially after short time of treatment. A significant decrease of LHCII, D1 and CP47 amounts was detected under (Cd) treatment. However, NaCl supply alleviates the Cd²⁺ effect on protein abundance including LHCII and PSII core complex (D1 and CP47).     

High salinity helps the halophyte <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis> in defense against Cd toxicity by maintaining redox balance and photosynthesis

Main conclusion

NaCl alleviates Cd toxicity in Sesvium portulacastrum by maintaining plant water status and redox balance, protecting chloroplasts structure and inducing some potential Cd ²⁺ chelators as GSH and proline. It has been demonstrated that NaCl alleviates Cd-induced growth inhibition in the halophyte Sesuvium portulacastrum. However, the processes that mediate this effect are still unclear. In this work we combined physiological, biochemical and ultrastructural studies to highlight the effects of salt on the redox balance and photosynthesis in Cd-stressed plants. Seedlings were exposed to different Cd concentrations (0, 25 and 50 µM Cd) combined with low (0.09 mM) (LS), or high (200 mM) NaCl (HS) in hydroponic culture. Plant–water relations, photosynthesis rate, leaf gas exchange, chlorophyll fluorescence, chloroplast ultrastructure, and proline and glutathione concentrations were analyzed after 1 month of treatment. In addition, the endogenous levels of stress-related hormones were determined in plants subjected to 25 µM Cd combined with both NaCl concentrations. In plants with low salt supply (LS), Cd reduced growth, induced plant dehydration, disrupted chloroplast structure and functioning, decreased net CO₂ assimilation rate (A) and transpiration rate (E), inhibited the maximum potential quantum efficiency (Fv/Fm) and the quantum yield efficiency (Φ _PSII) of PSII, and enhanced the non-photochemical quenching (NPQ). The addition of 200 mM NaCl (HS) to the Cd-containing medium culture significantly mitigated Cd phytotoxicity. Hence, even at similar internal Cd concentrations, HS-Cd plants were less affected by Cd than LS-Cd ones. Hence, 200 mM NaCl significantly alleviates Cd-induced toxicity symptoms, growth inhibition, and photosynthesis disturbances. The cell ultrastructure was better preserved in HS-Cd plants but affected in LS-Cd plants. The HS-Cd plants showed also higher concentrations of reduced glutathione (GSH), proline and jasmonic acid (JA) than the LS-Cd plants. However, under LS-Cd conditions, plants maintained higher concentration of salicylic acid (SA) and abscisic acid (ABA) than the HS-Cd ones. We conclude that in S. portulacastrum alleviation of Cd toxicity by NaCl is related to the modification of GSH and proline contents as well as stress hormone levels thus protecting redox balance and photosynthesis.

     

Arbuscular mycorrhizal fungi and potassium bicarbonate enhance the foliar content of the vinblastine alkaloid in Catharanthus roseus

Vinca (Catharanthus roseus (L.) G. Don.) is an important medicinal plant species from which antineoplastic alkaloids such as vinblastine are extracted. However, neither abiotic stress nor inoculation of arbuscular mycorrhizal fungi (AMF) has been evaluated on the accumulation of vinca alkaloids under controlled conditions. This study evaluated the effects of AMF and/or abiotic stress induced by the application of potassium bicarbonate (KHCO₃) and/or sodium chloride (NaCl) on plant growth, and on total content of phenolic compounds (TCPC), total antioxidant activity (TAOX), and total content of vinblastine alkaloid in leaves of vinca. TCPC, TAOX, and vinblastine were measured via spectrophotometric methods. After 75 days under greenhouse conditions, either the AMF inoculation without abiotic stress or the application of KHCO₃ (2.5 and 7.5 mM) resulted in significantly (P?≤?0.001) enhanced plant growth, TCPC, TAOX, and total content of vinblastine. The application of NaCl significantly diminished plant growth, but did not stimulate the content of vinblastine. The combined application of NaCl and KHCO₃ significantly decreased AMF-colonization in roots. The sole inoculation of AMF or the single application of 7.5 mM KHCO₃ induced the accumulation of vinblastine in leaves of vinca.     

Interactive effects of cadmium and carbon nanotubes on the growth and metal accumulation in a halophyte Spartina alterniflora (Poaceae)

A study quantifying the interactive effects of cadmium (Cd) and carbon nanotubes (CNTs) on plant growth and Cd accumulation of pot-cultured Spartina alterniflora was conducted. The experiment consisted of two Cd levels (50, 200 mg kg^?1) as well as two CNTs levels (800, 2,400 mg kg^?1). As expected, CNTs alleviated higher Cd stress (200 mg kg^?1) due to restored shoot growth reduction, retrieved water content and resumed plant height. Furthermore, CNTs mitigated the deleterious effects of Cd stress through improving K⁺ and Ca²⁺ contents, while reducing Na⁺/K⁺ and Na⁺/Ca²⁺ ratios, regardless of the level of Cd stress. The proline contents in combined Cd and CNTs treatments were lower than Cd alone, suggesting that CNTs could reduce production of organic solutes under Cd stress. The results also showed higher Cd accumulation in roots than shoots, and both were improved by CNTs, except inhibition in roots under higher Cd stress (200 mg kg^?1). It appears that CNTs may not significantly affect negative Cd effects on growth of S. alterniflora, but improve total Cd accumulation under lower Cd stress (50 mg kg^?1). However, under higher Cd stress (200 mg kg^?1), CNTs restored the reduced plant growth, improved and reduced Cd accumulation in shoots and roots, respectively. Therefore, the effects of CNTs on plant growth and Cd accumulation are different, and levels of Cd stress should be considered when evaluating the combined application of CNTs and S. alterniflora on phytoremediation of Cd pollution.     

Effect of NaCl stress on dihaploid tobacco lines tolerant to Potato virus Y

Salinity is an important abiotic factor that limits plant growth and development. The influence of salt stress induced by sodium chloride on plant growth, proline content, level of lipid peroxidation and activities of antioxidative enzymes was studied in F1 hybrid DH10 and four dihaploid lines (207B, 238C, 239K, 244B) of tobacco (Nicotiana tabacum L.). Dihaploids were obtained from anther-derived haploids of hybrid DH10 and were previously proved to be tolerant to Potato virus Y (PVY). In our study, plants were grown in vitro and exposed to NaCl (100 and 200 mM) for 33 days. All dihaploids and hybrid DH10 showed reduced growth after NaCl treatment. They accumulated significant amounts of sodium and proline in response to salt stress as have already been observed in tobacco and other plant species. In tobacco exposed to NaCl the lipid peroxidation level did not increase and activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate peroxidase and catalase (CAT) mostly did not change significantly. The exception was line 239K where salt induced higher activities of SOD, CAT and POD. Two (238C and 244B) out of four dihaploids appeared more susceptible to salt stress as they showed weak growth in correlation with high proline and sodium content. Therefore, it seems that salt tolerance is not associated with tolerance to PVY. Variations in malondialdehyde and proline content as well as in enzymes activities observed among tobacco lines imply that dihaploids have different genetic properties which might result in different sensitivity to NaCl.     

Nitric oxide (NO) counteracts cadmium induced cytotoxic processes mediated by reactive oxygen species (ROS) in Brassica juncea: cross-talk between ROS, NO and antioxidant responses

Research on NO in plants has achieved huge attention in recent years mainly due to its function in plant growth and development under biotic and abiotic stresses. In the present study, we investigated Cd induced NO generation and its relationship to ROS and antioxidant regulation in Brassica juncea. Cd accumulated rapidly in roots and caused oxidative stress as indicated by increased level of lipid peroxidation and H₂O₂ thus, inhibiting the overall plant growth. It significantly decreased the root length, leaf water content and photosynthetic pigments. A rapid induction in intracellular NO was observed at initial exposures and low concentrations of Cd. A 2.74-fold increase in intracellular NO was recorded in roots treated with 25 μM Cd than control. NO effects on Malondialdehyde (MDA) content and on antioxidant system was investigated by using sodium nitroprusside (SNP), a NO donor and a scavenger, [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] (cPTIO). Roots pretreated with 5 mM SNP for 6 h when exposed to 25 μM Cd for 24 h reduced the level of proline, non-protein thiols, SOD, APX and CAT in comparison to only Cd treatments. However, this effect was almost blocked by 100 μM cPTIO pretreatment to roots for 1 h. This ameliorating effect of NO was specific because cPTIO completely reversed the effect in the presence of Cd. Thus, the present study report that NO strongly counteracts Cd induced ROS mediated cytotoxicity in B. juncea by controlling antioxidant metabolism as the related studies are not well reported in this species.     

Mechanism of cadmium tolerance in Salicornia europaea at optimum levels of NaCl

• Many saline-alkali soils around the world are polluted by the heavy metal Cd, restricting the development of agriculture and ecology in those regions. The halophyte Salicornia europaea L. is capable of growing healthily in Cd-contaminated saline-alkali soil, suggesting that the species is tolerant to stress caused by both salt and heavy metals. In this study, the mechanism of Cd tolerance in this species was explored under 200 mM NaCl.
• Flame spectrophotometric assays for ions content and spectrophotometric for organic soluble substances, antioxidant enzyme activity, phytochelatins (PCs) content and phytochelatin synthase (PCS) activity, the photosynthetic parameters by portable photosynthesis measurement system, genes expression by qRT-PCR analysis were carried out.
• Cd treatment significantly decreased the dry weight, photosynthetic rate, K⁺, Zn²⁺, and Fe^2+/3+ content, while significantly increasing Na⁺ and Cd⁺, soluble organic matter, and reactive oxygen species (ROS) levels. Compared with Cd treatment at 0 mM NaCl, Cd treatment at 200 mM NaCl significantly increased dry weight and photosynthetic rate while significantly decreasing ROS content through increased antioxidant enzyme activity. When exposed to Cd stress, treatment with 200 mM NaCl significantly increased PCs content and PCS activity and up-regulated the expression of the phytochelatin synthase genes CDA1 and PCS1 were, thereby increasing resistance to Cd.
• NaCl treatment increases the tolerance of S. europaea to the heavy metal Cd by growing rapidly, reducing the quantity of Cd²⁺ from entering the plant shoots, increasing the levels of PCs that chelate Cd²⁺, thereby reducing its toxicity.

     

Morpho-physiological variations in response to NaCl stress during vegetative and reproductive development of rice

The complex nature of plant resistance to adverse environmental conditions, such as salinity and drought requires a better understanding of the stress-induced changes that may be involved in tolerance mechanisms. Here we investigate stress-related morpho-physiological effects during vegetative and reproductive growth in two Japonica rice cultivars (Bomba and Bahia) exposed to a range of NaCl concentrations from the seedling stage. The stress-related detrimental effects were observed either earlier or to a higher extent in cv. Bomba than in Bahia. Damages to the photosynthetic apparatus were related to loss of chlorophyll (Chl) and to a decrease of the maximum potential efficiency of PSII (F _v /F _m), affecting negatively net CO₂ assimilation rate (P _N). Stress-related leaf anatomical alterations were analysed during the vegetative and reproductive stages. The size of bulliform cells as well as dimensions related to the vascular system increased under mild stress but decreased in the longer term or under higher stress level. The pattern of the anatomical alterations observed at the reproductive stage under 20 mM NaCl was reflected in poor panicle development and yield loss, with effects more pronounced in cv. Bomba than in Bahia. In summary, our results show that some physiological and, particularly, leaf anatomical responses induced by NaCl stress are distinctive indicators of sensitivity to salt stress in rice cultivars.     

Effect of water stress and NaCl triggered changes on yield,physiology, biochemistry of broad bean (Vicia faba) plants and on quality of harvested pods

Salinity and drought are the most important abiotic stresses affecting crop yield. Broad bean was chosen as model plant for assessing the impact of salt stress and its interaction with drought in the field experiments. The factors examined in the experiments were the two irrigation rates (normal watering — NW with 3 L plant^?1 and drought — D) and three salinity rates imposed by foliar application (0, 50, 100 mg L^?1 NaCl). Highest NaCl level with normal water irrigation caused maximum reduction in plant height and production, which it was due to photosynthetic disturbances. Salt injuries were alleviated by increasing water stress. The control plants exposed to NaCl lost their ability over water control. The increased malondialdehyde (MDA) and H₂O₂ indicate the prevalence of oxidative stress due to salinity. The levels of proline and carbohydrates were higher under salinity alone than under simultaneous exposure to drought and NaCl. The protein concentration of immature and mature broad bean pods was more inhibited more by NaCl supply than by drought alone. The combination of drought and NaCl resulted in a significant increase in proteins, glucose, fructose and sucrose content. Overall, the ameliorative effect of drought under NaCl supply was quantified.     

茶多酚对盐胁迫下小麦幼苗叶片生理特性的影响

以春小麦"陇春30号"为实验材料,主要研究了150 mmol/L NaCl和不同浓度(25 mg/L和100 mg/L)茶多酚(tea polyphenols, TP)单独或复合处理对小麦幼苗叶片叶绿素含量、叶绿素荧光参数及过氧化氢(H_2O_2)产生等生理特性的影响。结果表明:(1)150 mmol/L NaCl单独处理导致小麦幼苗叶片叶绿素含量及光适应下实际光量子产量[actual light quantum yield,Y(II)]、光化学淬灭(photochemical quenching, qP)、光合电子传递效率(photosynthetic electron transfer efficiency, ETR)均降低,非光化学淬灭(non-photochemical quenching, NPQ)增大;TP单独处理不影响这些指标。(2)盐胁迫诱导细胞壁过氧化物酶(cell wall-peroxidase, cw-POD)、二胺氧化酶(diamine oxidase, DAO)和多胺氧化酶(polyamine oxidase, PAO)活性显著增高;低浓度TP使cw-POD活性显著增大,而DAO和PAO活性无显著变化;不同的是,高浓度TP不影响cw-POD活性,却使DAO和PAO活性显著减小。(3)与NaCl单独处理相比,TP的添加导致NaCl处理下小麦幼苗叶片叶绿素含量增加,最大光化学效率(maximal photochemical efficiency,F_v/F_m)和ETR值增大,而NPQ值、H_2O_2含量及cw-POD、DAO和PAO三种酶活性均降低。总之,TP有效地缓解了盐胁迫诱导的小麦幼苗叶绿素含量的减少及对PS II光合电子传递效率和光化学反应速率的抑制,增强了植物的光合能力,与此同时降低了cw-POD、DAO和PAO活性,减少了H_2O_2的产生,从而缓解盐胁迫对小麦幼苗造成的伤害,提高小麦幼苗对盐环境的耐受性。     

Effects of NaCl stress on the growth and photosynthetic characteristics of Ulmus pumila L. seedlings in sand culture

The effects of NaCl stress on the growth and photosynthetic characters of Ulmus pumila L. seedlings were investigated under sand culture condition. With increasing NaCl concentration, main stem height, branch number, leaf number, and leaf area declined, while Na⁺ content and the Na⁺/K⁺ ratio in both expanded and expanding leaves increased. Na⁺ content was significantly higher in expanded leaves than in those just expanding. Chlorophyll (Chl) a and Chl b contents declined as NaCl concentration increased. The net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, and transpiration rate also declined, but stomatal limitation value increased as NaCl concentration increased. Both the maximal quantum yield of PSII photochemistry and the effective quantum yield of PSII photochemistry declined as NaCl concentration rose. These results suggest that the accumulation of Na⁺ in already expanded leaves might reduce damage to the expanding leaves and help U. pumila endure high salinity. The reduced photosynthesis in response to salt stress was mainly caused by stomatal limitation.     

Growth,photosynthesis and ion balance of sesame (Sesamum indicum L.) genotypes in response to NaCl concentration in hydroponic solutions

A hydroponic, greenhouse experiment was conducted to assess the effects of NaCl on growth, gas-exchange parameters, chlorophyll (Chl) content, and ion distribution in seven sesame (Sesamum indicum L.) genotypes (Ardestan, Varamin, Naz-Takshakhe, Naz-Chandshakhe, Oltan, Yekta, Darab). The plants were grown in 4-L containers and subjected to varying levels of salinity (0, 30, and 60 mM NaCl). After 42 days, salt treatments induced decreases of plant fresh and dry mass, total leaf area, and plant height in all genotypes. Increasing NaCl concentration caused significant, genotypedependent decrease in the net photosynthetic rate, stomatal conductance, Chl content, and maximum quantum efficiency of photosystem II, while it increased the intercellular CO₂ concentration. Based on the dry matter accumulation under salinity, the genotypes were categorized in two groups, i.e., salt-tolerant and salt-sensitive. The impact of salt on plant ion concentrations differed significantly among the sesame genotypes and between both two groups. The plant Na⁺ concentrations were significantly lower in Ardestan, Darab, and Varamin genotypes than those found in the remaining genotypes. The highest plant K⁺ and Ca²⁺ concentrations together with the lowest Na⁺/K⁺ and Na⁺/Ca²⁺ ratios were observed in Ardestan, Varamin, and Darab genotypes. Our results indicated the presence of differences in salt response among seven sesame genotypes. It suggested that growth and photosynthesis could depend on ion concentrations and ratios in sesame.