Salt stress effects on the photosynthetic electron transport chain in two chickpea lines differing in their salt stress tolerance

The main objective of this study was to evaluate the effects of salt stress on the photosynthetic electron transport chain using two chickpea lines (Cicer arietinum L.) differing in their salt stress tolerance at the germination stage (AKN 87 and AKN 290). Two weeks after sowing, seedlings were exposed to salt stress for 2 weeks and irrigated with 200 ml of 200 mM NaCl every 2 days. The polyphasic OJIP fluorescence transient and the 820-nm transmission kinetics (photosystem I) were used to evaluate the effects of salt stress on the functionality of the photosynthetic electron transport chain. It was observed that a signature for salt stress was a combination of a higher J step (V_J), a smaller IP amplitude, and little or no effect on the primary quantum yield of PSII (φ_Po). We observed for AKN 290 a shorter leaf life cycle, which may represent a mechanism to cope with salt stress. For severely salt-stressed leaves, an inhibition of electron flow between the PQ pool and P700 was found. The data also suggest that the properties of electron flow beyond PSI are affected by salt stress.     

Responses of antioxidant gene, protein and enzymes to salinity stress in two genotypes of perennial ryegrass (Lolium perenne) differing in salt tolerance

Salinity could damage cellular membranes through overproduction of reactive oxygen species (ROS), while antioxidant capacities play a vital role in protecting plants from salinity caused oxidative damages. The objective of this study was to investigate the toxic effect of salt on the antioxidant enzyme activities, isoforms and gene expressions in perennial ryegrass (Lolium perenne L.). Salt-tolerant ‘Quickstart II’ and salt-sensitive ‘DP1′ were subjected to 0 and 250 mM NaCl for 12 d. Salt stress increased the content of lipid peroxidation (MDA), electrolyte leakage (EL) and hydrogen peroxide (H₂O₂), to a greater extent in salt-sensitive genotype. Salt-stressed plant leaves exhibited a greater activity of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11) at 4 d after treatment (DAT), but a lower level of enzyme activity at 8 and 12 d, when compared to the control. Catalase (CAT, EC 1.11.1.6) activity was greater at 4 DAT and thereafter decreased in salt tolerant genotype relative to the control, whereas lower than the control during whole experiment period for salt-sensitive genotype. There were different patterns of five isoforms of SOD, POD and two isoforms of APX between two genotypes. Antioxidant gene expression was positively related to isoenzymatic and total enzymatic activities during 12-d salt-treated leaves of two genotypes, with a relatively higher level in salt-tolerant genotype. Thus, salt tolerance could be related to the constitutive/induced antioxidant gene, leading to more efficient enzyme stimulation and protection in perennial ryegrass.     

Antioxidant defense system and cadmium uptake in barley genotypes differing in cadmium tolerance

Using two barley (Hordeum vulgare) cultivars (cvs. Tokak and Hamidiye) nutrient solution experiments were conducted in order to study the genotypic variation in tolerance to Cd toxicity based on (i) development of leaf symptoms, (ii) decreases in dry matter production, (iii) Cd concentration and (iv) changes in antioxidative defense system in leaves (i.e., superoxide dismutase, ascorbate peroxidase, glutathione reductase, catalase, ascorbic acid and non-protein SH-groups). Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 15, 30, 60 and 120 micromol/L Cd) for different time periods. Of the barley cultivars Hamidiye was particularly sensitive to Cd as judged by the severity and earlier development of Cd toxicity symptoms on leaves. Within 48 h of Cd application Hamidiye rapidly developed severe leaf Cd toxicity symptoms whereas in Tokak the leaf symptoms appeared only slightly. Hamidiye also tended to show more decrease in growth caused by Cd supply when compared to Tokak. The differences in sensitivity to Cd between Tokak and Hamidiye were not related to Cd concentrations in roots and shoots or Cd accumulation per plant. With the exception of catalase, activities of the enzymes involved in detoxification of reactive oxygen species (ROS) were markedly enhanced in Hamidiye by increasing Cd supply. By contrast, in Tokak there was either only a slight increase or no change in the activities of the antioxidative enzymes. Similarly, levels of ascorbic acid and especially non-protein SH-groups were increased in Hamidiye by Cd supply, but not affected in Tokak. The results indicate the existence of a large genotypic variation between barley cultivars for Cd tolerance. The differential Cd tolerance found in the barley cultivars was not related to uptake or accumulation of Cd in plants, indicating importance of internal mechanisms in expression of differential Cd tolerance in barley. As a response to increasing Cd supply particular increases in antioxidative mechanisms in the Cd-sensitive barley cultivar Hamidiye suggest that the high Cd sensitivity of Hamidiye is related to enhanced production and oxidative damage of ROS.     

Effect of NaCl salinity on photosynthetic rate,transpiration rate,and oxidative stress tolerance in contrasting wheat genotypes

Wheat (Triticum aestivum L.) genotypes K-65 (salt tolerant) and HD 2329 (salt sensitive) were grown in pots under natural conditions and irrigated with NaCl solutions of electrical conductivity (ECe) 4.0, 6.0, and 8.0 dS m⁻¹. Control plants were irrigated without saline water. Observations were made on the top most fully expanded leaf at tillering, anthesis, and grain filling stages. The net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were reduced with the addition of NaCl. The reduction was higher in HD 2329 than in K-65. Salinity enhanced leaf to air temperature gradient (ΔT) in both the genotypes. NaCl increased the activities of superoxide dismutase (SOD) and peroxidase (POX); the percent increment was higher in K-65. The sodium and potassium contents were higher in the roots and leaves of K-65 over HD 2329. Thus at cellular level K-65 has imparted salt tolerance by manipulating P _N, E, g _s, and K accumulation in leaves along with overproduction of antioxidative enzyme activities (SOD and POX).     

The response of Mo-hydroxylases and abscisic acid to salinity in wheat genotypes with differing salt tolerances

The differential responses of the wheat cultivars Shi4185 and Yumai47 to salinity were studied. The higher sensitivity of Yumai47 to salinity was linked to a greater growth reduction under salt stress, compared to more salt-tolerant Shi4185. Salinity increased the Na⁺, proline and superoxide anion radical (O₂ ^?) contents in both cultivars. Leaf Na⁺ content increased less in the more salt-tolerant cultivar Shi4185 than salt-sensitive Yumai47. The proline content increased more significantly in Shi4185 than Yumai47; on the contrary, superoxide anion radical content increased less in Shi4185 than Yumai47. This data indicated that wheat salinity tolerance can be increased by controlling Na⁺ transport from the root to shoot, associated with higher osmotic adjustment capability and antioxidant activity. Although salinity increased aldehyde oxidase (AO) activity and abscisic acid (ABA) content in the leaves and roots of both cultivars following the addition of NaCl to the growth medium, AO and ABA increased more in the salt-sensitive cultivar Yumai47 than the more salt-tolerant cultivar Shi4185. Xanthine dehydrogenase (XDH) activity in the leaves of both cultivars increased with increasing concentrations of NaCl; however, leaf XDH activity increased more significantly in Yumai47 than Shi4185. Root XDH activity in Shi4185 decreased with increasing NaCl concentrations, whereas salinity induced an increased root XDH activity in Yumai47. The involvement of AO and XDH enzymatic activities and altered ABA content in the response mechanisms of wheat to salinity are discussed herein.     

The ionic effects of NaCl on physiology and gene expression in rice genotypes differing in salt tolerance

The effects of ionic stress on the physiology and gene expression of two rice genotypes (IR4630 and IR15324) that differ in salt tolerance, were investigated by evaluating changes in the biomass, Na⁺ and K⁺ concentrations and applying the cDNA-AFLP technique to highlight changes in gene expression. Over 8 days of salinisation, the effect of NaCl on the reduction of biomass (dry weight) was apparent from 24 h after salinisation (the first time point), indicating that the consequences of the build up of Na⁺ (and Cl^-) in the leaves of both lines was rapid. Furthermore, root growth of IR15324 was much more sensitive to salt than that of IR4630 (the reduction in root dry weight compared to non-salinised plants was three times greater in IR15324 than IR4630). The two rice lines also differed in their Na⁺ accumulation in saline conditions, a difference that was more marked in the shoots, particularly at the final harvest, than in the roots. Under salt stress, the K⁺ content (µmol/shoot) increased over four successive harvests (24, 48, 96, 192 h) in both lines, but was always greater in IR4630 than in IR15324: differences in Na⁺/K⁺ ratio appear to be an important determinant of salt tolerance in rice. To separate osmotic from ionic effects of salt, mannitol was applied as a non-ionic osmoticum at an osmotic potential estimated to be equivalent to 50 mM NaCl. Messenger RNA was sampled at 0.5, 6, 24, 48 and 192 hours after salinisation. Several products (AFLP-bands) were detected, which were upregulated in the response to ionic effects of salt in the tolerant line (IR4630) and not expressed in the sensitive line (IR15324). Bioinformatic analysis indicated three of these AFLP-bands have a high-degree of sequence similarity with the genes encoding a proline rich protein, senescence associated protein and heat-shock protein. The data are novel in that they differentially highlight changes induced by the ionic rather than osmotic effects of salt and in a tolerant rather than a sensitive genotype. The possible roles of the products of these genes are discussed.     

Sucrolytic activities during fruit development of Lycopersicon genotypes differing in tolerance to salinity

The different growth responses under control and moderate salinity (70 mM NaCl) in relation to the carbon partitioning and sucrose metabolism in developing tomato fruits [20 days after anthesis (DAA), start of ripening and ripe stages] were studied in the cultivated tomato Lycopersicon esculentum Mill (cv. H-324-1), in the wild relative species L. cheesmanii (ac. LA-530) (hexose-accumulators), L. chmielewskii (ac. LA-1028) (sucrose-accumulator) and in two interspecific F1 hybrids (hexose-accumulators) (F1-530: H-324-1 x A-530, F1-1028: H-324-1 x A-1028). The higher salt-tolerance of the wild species and hybrids with respect to the domestic tomatoes was also observed at the fruit level because these genotypes were less affected in the assimilation of dry weight (DW) under salinity. With the exception of the wild tomatoes, the sink strength, evaluated as the dry matter accumulation rate (mg DW day-1) and the sink activity, evaluated as a relative growth rate (mg DW mg-1 day-1), were reduced during the early fruit growing period (20 DAA-start ripening). However, a total recovery of growth was registered in the salinized hybrid fruits during the late growing period (start of ripening-ripe fruits). The early reduction in sink activity in the hybrid and domestic fruits was related to a sucrose accumulation and a decrease in the total sucrolytic activity at 20 DAA, especially the cytoplasmic sucrolytic activities sucrose synthase (EC 2.4.1.13) and neutral invertase (EC 3.2.1.26). The further recovery in sink strength of the hybrid fruits was related to the maintenance of the insoluble acid invertase (EC 3.2.1.25) and the induction of the cytoplasmic sucrolytic activities, namely at the start of ripening stage, demonstrating the existence of an inverse relationship between these activities, which suggests a regulatory mechanism in order to maintain the sink capacity. The roles of different enzymes in the control of assimilate import under salinity in relation to the sucrose transport and possible regulatory mechanisms are discussed.     

The proteome response of salt-resistant and salt-sensitive barley genotypes to long-term salinity stress

Responses of plants to salinity stress and the development of salt tolerance are extremely complex. Proteomics is a powerful technique to identify proteins associated with a particular environmental or developmental signal. We employed a proteomic approach to further understand the mechanism of plant responses to salinity in a salt-tolerant (Afzal) and a salt-sensitive (Line 527) genotype of barley. At the 4-leaf stage, plants were exposed to 0 (control) or 300 mM NaCl. Salt treatment was maintained for 3 weeks. Total proteins of leaf 4 were extracted and separated by two-dimensional gel electrophoresis. More than 500 protein spots were reproducibly detected. Of these, 44 spots showed significant changes to salt treatment compared to the control: 43 spots were upregulated and 1 spot was downregulated. Using MALDI-TOF-TOF MS, we identified 44 cellular proteins have been identified, which represented 18 different proteins and were classified into seven categories and a group with unknown biological function. These proteins were involved in various many cellular functions. Up regulation of proteins which involved in reactive oxygen species scavenging, signal transduction, protein processing and cell wall may increase plant adaptation to salt stress. The upregulation of the three of four antioxidant proteins (thioredoxin, methionine sulfoxide reductase and dehydroascorbate reductase) in susceptible genotype Line 527 suggesting a different tolerance mechanism (such as tissue tolerance) to tolerate a salinity condition in comparison with the salt sensitive genotype.     

Differences in physiological and biochemical characteristics in response to single and combined drought and salinity stresses between wheat genotypes differing in salt tolerance

The combined drought and salinity stresses pose a serious challenge for crop production, but the physiological mechanisms behind the stresses responses in wheat remains poorly understood. Greenhouse pot experiment was performed to study differences in genotype response to the single and combined (D + S) stresses of drought (4% soil moisture, D) and salinity (100 mM NaCl, S) using two wheat genotypes: Jimai22 (salt tolerant) and Yangmai20 (salt‐sensitive). Results showed that salinity, drought and/or D + S severely reduces plant growth, biomass and net photosynthetic rate, with a greater effect observed in Yangmai20 than Jimai22. A notable improvement in water use efficiency (WUE) by 239, 77 and 103% under drought, salinity and D + S, respectively, was observed in Jimai22. Moreover, Jimai22 recorded higher root K⁺ concentration in drought and salinity stressed condition and shoot K⁺ under salinity alone than that of Yangmai20. Jimai22 showed lower increase in malondialdehyde (MDA) accumulation, but higher activities of superoxide dismutase (SOD, EC 1.15.1.1) and guaicol peroxidase (POD, EC 1.11.1.7), under single and combined stresses, and catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) under single stress. Our results suggest that high tolerance of Jimai22 in both drought and D + S stresses is closely associated with larger root length, higher Fv/Fm and less MDA contents and improved capacity of SOD and POD. Moreover, under drought Jimai22 tolerance is firmly related to higher root K⁺ concentration level and low level of Na⁺, high‐net photosynthetic rate and WUE as well as increased CAT and APX activities to scavenge reactive oxygen species.     

Influence of waterlogging on some anti-oxidative enzymatic activities of two barley genotypes differing in anoxia tolerance

The experiment was conducted to investigate the formation of oxidative stress and the development of anti-oxidative enzymes in two barley genotypes differing in anoxia tolerance. Waterlogging led to significant reduction in root and shoot weight, green leaf area and tillers per plant, but tolerant Xiumai 3 was much less reduced than sensitive Gerdner. Malondialdehyde (MDA) content, an indicator of membrane lipid peroxidation, significantly increased in Gerdner when the plants were subjected to waterlogging, but remained little changed in Xiumai 3. Superoxide dismutase (SOD) activity was increased with waterlogging treatment and the sensitive cultivar had higher activity than the tolerant one during the experimental duration. At early stage of waterlogging treatment, both peroxidase (POD) and catalase (CAT) activities significantly increased in Xuimai 3, while obviously decreased in Gerdner. Moreover, both cultivars showed substantial increase in both POD and CAT with the progress of waterlogging exposure. Glutathione reductase (GR) activity was increased in both tolerant- and sensitive cultivars under waterlogging. It may be assumed from the current results that SOD activity appears to be not a constraining factor limiting the scavenging of ROS, and it is the change of POD and CAT activity under waterlogging that determine the status of oxidative stress. The difference between genotypes in waterlogging tolerance could be distinguished from the changed patterns of these enzymatic activities.     

The influence of salt stress on ABA and auxin concentrations in two maize cultivars differing in salt resistance

The plant hormones abscisic acid (ABA) and auxin (IAA, IBA) play important roles in plant responses to environmental stresses such as salinity. Recent breeding improvements in terms of salt resistance of maize have lead to a genotype with improved growth under saline conditions. By comparing this salt-resistant hybrid with a sensitive hybrid, it was possible to show differences in hormone concentrations in expanding leaves and roots. In response to salinity, the salt-resistant maize significantly increased IBA concentrations in growing leaves and maintained IAA concentration in roots. These hormonal adaptations may help to establish favorable conditions for growth-promoting agents such as β-expansins and maintain growth of resistant maize hybrids under salt stress. Moreover, ABA concentrations significantly increased in resistant maize leaves under salt stress, which may contribute to acidifying the apoplast, which in turn is a prerequisite for growth.     

Mechanisms of salt stress tolerance development in barley plants under the influence of 5-aminolevulinic acid

Growing barley (Hordeum vulgare L.) plants for 7 days on NaCl solutions (20–200 mM) decreased chlorophyll (Chl) a and b content with respect to that in untreated control plants. The content of free proline and the plant ability to synthesize 5-aminolevulinic acid (ALA) started to increase in parallel at salt concentrations of 20–50 mM. The maximum amount of ALA accumulated in plants grown at 100 mM NaCl was twofold higher than in control plants grown on fresh water. In this case the proline content increased 2.8-fold. On further increase in salt concentration, the rate of ALA accumulation decreased, approaching control values at 150 mM NaCl; even lower rates were observed at 200 mM NaCl. The reduced ability to synthesize ALA was accompanied by an increase in proline content. The albino tissue of plants treated at the seed stage with the antibiotic streptomycin lost its ability to synthesize ALA needed for Chl formation. The proline content in the albino tissue was tenfold higher than in control green plants and was 30-fold higher when the plants were grown on solutions with 100 mM NaCl. No effect of NaCl on ALA-dehydratase activity was noted. As NaCl concentration was raised, there occurred the decrease in magnesium chelatase activity, accumulation of reactive oxygen species (ROS), the increase in ascorbate peroxidase activity, and a slight decrease in lipid peroxidation level. Growing plants in the presence of 150 mM NaCl and 10 or 60 mg/l exogenous ALA led to the increase in proline content (by a factor of 1.8 and 4.2, respectively) and to the decrease in ROS content, in comparison with plants grown on salt solutions without ALA. Furthermore, in the presence of exogenous ALA, the parameters of seedling growth became similar to those of NaCl-untreated plants. The role of ALA in plants as an antistress agent is considered. ALA is supposed to confer tolerance to salt stress by taking part in Chl and heme biosynthesis and also through functioning as a plant growth regulator. A hypothesis is put forward that the impairment of ALA-synthesizing ability may redirect metabolic conversions of glutamic acid from Chl and heme synthesis to the proline synthesis pathway, which would stimulate proline biosynthesis and improve salt tolerance.     

Compatible solute accumulation and stress-mitigating effects in barley genotypes contrasting in their salt tolerance

The accumulation of compatible solutes is often regarded as a basic strategy for the protection and survival of plants under abiotic stress conditions, including both salinity and oxidative stress. In this work, a possible causal link between the ability of contrasting barley genotypes to accumulate/synthesize compatible solutes and their salinity stress tolerance was investigated. The impact of H(2)O(2) (one of the components of salt stress) on K(+) flux (a measure of stress 'severity') and the mitigating effects of glycine betaine and proline on NaCl-induced K(+) efflux were found to be significantly higher in salt-sensitive barley genotypes. At the same time, a 2-fold higher accumulation of leaf and root proline and leaf glycine betaine was found in salt-sensitive cultivars. The total amino acid content was also less affected by salinity in salt-tolerant cultivars. In these, potassium was found to be the main contributor to cytoplasmic osmolality, while in salt-sensitive genotypes, glycine betaine and proline contributed substantially to cell osmolality, compensating for reduced cytosolic K(+). Significant negative correlations (r= -0.89 and -0.94) were observed between Na(+)-induced K(+) efflux (an indicator of salt tolerance) and leaf glycine betaine and proline. These results indicate that hyperaccumulation of known major compatible solutes in barley does not appear to play a major role in salt-tolerance, but rather, may be a symptom of salt-susceptibility.     

Effect of salt stress on photosynthesis and physiological parameters of three contrasting barley genotypes

In order to understand the physiological traits important in conferring salt tolerance in three barley genotypes, this study was performed under field conditions with three water salinity levels (2, 10, and 18 dS m–1). High salinity decreased net photosynthetic rate, transpiration rate, and stomatal conductance, K⁺ concentration, K⁺:Na⁺ ratio, and grain yield, but increased electrolyte leakage and Na⁺ content. Under 10 and 18 dS m–1 salinity, Khatam (salt-tolerant) had the maximum stomatal conductance, K⁺, K⁺:Na⁺ ratio, and the grain yield, and a minimum Na⁺ content and electrolyte leakage, whereas Morocco (salt-sensitive) had the lowest net photosynthetic rate, stomatal conductance, K⁺ content, K⁺:Na⁺ ratio, and grain yield, and the highest Na⁺ content and electrolyte leakage. This study showed that tolerant genotypes of barley may avoid Na⁺ accumulation in aboveground parts, facilitating a higher photosynthetic rate and higher grain yield.     

Effects of salicylic acid and salinity on apoplastic antioxidant enzymes in two wheat cultivars differing in salt tolerance

The effects of salicylic acid (SA) and salinity on the activity of apoplastic antioxidant enzymes were studied in the leaves of two wheat (Triticum aestivam L.) cultivars: salt-tolerant (Gerek-79) and salt-sensitive (Bezostaya). The leaves of 10-d-old seedlings grown at nutrient solution with 0 (control), 250 or 500 mM NaCl were sprayed with 0.01 or 0.1 mM SA. Then, the activities of catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) were determined in the fresh leaves obtained from 15-d-old seedlings. The NaCl applications increased CAT and SOD activities in both cultivars, compared to those of untreated control plants. In addition, the NaCl increased POX activity in the salt-tolerant while decreased in the salt-sensitive cultivar. In control plants of the both cultivars, 0.1 mM SA increased CAT activity, while 0.01 mM SA slightly decreased it. SA treatments also stimulated SOD and POX activity in the salt-tolerant cultivar but significantly decreased POX activity and had no effect on SOD activity in the saltsensitive cultivar. Under salinity, the SA treatments significantly inhibited CAT activity, whereas increased POX activity. The increases in POX activity caused by SA were more pronounced in the salt-tolerant than in the salt-sensitive cultivar. SOD activity was increased by 0.01 mM SA in the salt-tolerant while increased by 0.1 mM SA treatment in the salt-sensitive cultivar.     

Proteomic analysis of salt stress and recovery in leaves of Vigna unguiculata cultivars differing in salt tolerance

Key message

Cowpea cultivars differing in salt tolerance reveal differences in protein profiles and adopt different strategies to overcome salt stress. Salt-tolerant cultivar shows induction of proteins related to photosynthesis and energy metabolism.

Abstract

Salinity is a major abiotic stress affecting plant cultivation and productivity. The objective of this study was to examine differential proteomic responses to salt stress in leaves of the cowpea cultivars Pitiúba (salt tolerant) and TVu 2331 (salt sensitive). Plants of both cultivars were subjected to salt stress (75 mM NaCl) followed by a recovery period of 5 days. Proteins extracted from leaves of both cultivars were analyzed by two-dimensional electrophoresis (2-DE) under salt stress and after recovery. In total, 22 proteins differentially regulated by both salt and recovery were identified by LC–ESI–MS/MS. Our current proteome data revealed that cowpea cultivars adopted different strategies to overcome salt stress. For the salt-tolerant cultivar (Pitiúba), increase in abundance of proteins involved in photosynthesis and energy metabolism, such as rubisco activase, ribulose-5-phosphate kinase (Ru5PK) (EC 2.7.1.19), glycine decarboxylase (EC 1.4.4.2) and oxygen-evolving enhancer (OEE) protein 2, was observed. However, these vital metabolic processes were more profoundly affected in salt-sensitive cultivar (TVu), as indicated by the down-regulation of OEE protein 1, Mn-stabilizing protein-II, carbonic anhydrase (EC 4.2.1.1) and Rubisco (EC 4.1.1.39), leading to energy reduction and a decline in plant growth. Other proteins differentially regulated in both cultivars corresponded to different physiological responses. Overall, our results provide information that could lead to a better understanding of the molecular basis of salt tolerance and sensitivity in cowpea plants.     

N-acetyl-cysteine alleviates Cd toxicity and reduces Cd uptake in the two barley genotypes differing in Cd tolerance

A hydroponic experiment was carried out to study the physiological mechanisms of N-acetyl cysteine (NAC) in mitigating cadmium (Cd) toxicity in two barley (Hordeum vulgare L.) genotypes, Dong 17 (Cd-sensitive) and Weisuobuzhi (Cd-tolerant). Addition of 200 μM NAC to a culture medium containing 5 μM Cd (Cd + NAC) markedly alleviated Cd-induced growth inhibition and toxicity, maintained root cell viability, and dramatically depressed O ₂ ^·? and ·OH, and malondialdehyde accumulation, significantly reduced Cd concentration in leaves and roots, especially in the sensitive genotype Dong 17. External NAC counteracted Cd-induced alterations of certain antioxidant enzymes, e.g., brought root superoxide dismutase and glutathione reductase, leaf/root peroxidase and glutathione peroxidase activities of the both genotypes down towards the control level, but elevated Cd-stress-depressed leaf catalase in Dong 17 and root ascorbate peroxidase activities in both genotypes. NAC counteracted Cd-induced alterations in amino acids and microelement contents. Furthermore, NAC significantly reduced Cd-induced damage to leaf/root ultrastructure, e.g. the shape of chloroplasts in plants treated with Cd + NAC was relatively normal with well-structured thylakoid membranes and parallel pattern of lamellae but less osmiophilic plastoglobuli compared with Cd alone treatment; nuclei of root cells were better formed and chromatin distributed more uniformly in both genotypes. These results suggested that under Cd stress, NAC may protects barley seedlings against Cd-induced damage by directly and indirectly scavenging reactive oxygen species and by maintaining stability and integrity of the subcellular structure.