Cadmium effects on growth and antioxidant enzymes activities in Miscanthus sinensis

Plants of Miscanthus sinensis (cv. Giganteus) were grown in hydroponics for three months in nutrient solution with 0, 2.2, 4.4 and 6.6 μM CdNO₃. Growth parameters, catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities were analysed in leaves and roots collected after 1-and 3-month exposure. Dry biomass of all miscanthus organs was affected by Cd concentration both after 1-and 3-month exposure. No visible symptoms of Cd toxicity were observed in shoots and rhizomes of plants grown in presence of Cd. In contrast, roots became shorter and thicker and the whole root system more dense and compact already after one month of treatment with 6.6 μM Cd. The lower Cd concentration increased the enzymes activities after 3 months in leaves and only after 1-month in roots, while a decrease in activity was observed at higher Cd concentrations.     

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.     

Silicon alleviates cadmium toxicity in peanut plants in relation to cadmium distribution and stimulation of antioxidative enzymes

Silicon (Si) is generally considered a beneficial element for the growth of higher plants, especially for those grown under stressed environments. Recently, the mitigating role of Si in cadmium (Cd) stress has received some attention. However, its mechanisms involved remain poorly understood. We studied the effects of Si on tissue and subcellular distribution of Cd, as well as the activities of major antioxidant enzymes (SOD, POD and CAT) with two contrasting peanut (Arachis hypogaea L.) cultivars (Luhua 11 and Luzi 101) differing in their Cd tolerance. The results showed that Cd exposure alone depressed plant growth and caused oxidative stress for both cultivars, and this toxicity was more obvious in Cd-sensitive cultivar (Luhua 11) than in Cd-tolerant cultivar (Luzi 101). Si supply significantly alleviated the toxicity of Cd in peanut seedlings; this was correlated with a reduction of shoot Cd accumulation, an alteration of Cd subcellular distribution in leaves, and a stimulation of antioxidative enzymes. The mechanisms of Si amelioration of Cd stress were cultivar and tissue dependent. For Luhua 11, Si-mediated inhibition of Cd transport from roots to shoots, reduction of Cd content in cell organelle fractions of leaves, and enhancement of the SOD, POD and CAT activities in roots, might responsible for the role of Si in alleviating Cd toxicity. For Luzi 101, Si alleviation of Cd toxicity is mainly attributed to the decrease in Cd concentration in shoot and stimulation of antioxidants systems.     

Genotypic variation in safflower (Carthamus spp.) cadmium accumulation and tolerance affected by temperature and cadmium levels

Soil pollution is a world-wide problem, with heavy metals being a major part of the concern. To investigate the effect of temperature on cadmium (Cd) uptake and translocation, as well as Cd tolerance in wild and cultivated species of safflower, a hydroponic experiment was conducted under controlled conditions. The responses of four wild genotypes (Isfahan, Arak, Azari, and Shiraz) and four cultivated genotypes (AC-Sterling, 2811, Saffire, and C111) of safflower to nine levels of CdCl₂ (0, 0.5, 1, 5, 10, 20, 50, 100, and 500 μM) in solution were examined under two temperatures (18 and 23 °C). Cadmium sensitivity was determined using the Weibull model on the total dry weight of the plants. Cadmium uptake and translocation were analyzed on 1 μM Cd treated plants. Results revealed that safflower genotypes differed in terms of uptake, translocation, and tolerance to Cd, with AC-Sterling and Arak indicating the most and the least tolerance to Cd, respectively. Relative Cd uptake and Cd concentration in roots and shoots increased with an increase in temperature in all genotypes, with the exception of AC-Sterling. Net accumulation of Cd via root increased with an increase in temperature for the wild Azari and the cultivated 2811, Saffire, and C111, though it decreased for the rest of genotypes. Cadmium translocation to shoots significantly increased with increased temperature in all genotypes. Cadmium translocation from roots to shoots in cultivated genotypes was significantly greater than in wild genotypes. Root Cd concentration in wild genotypes was significantly greater than in cultivated genotypes. It seems that wild and cultivated species of safflower differ in their response to Cd. Furthermore, temperature may affect the plant's tolerance to Cd, probably through accompanying changes in Cd uptake and translocation from root to shoot.     

Antioxidative responses of wheat treated with realistic concentration of cadmium

Two cvs. of wheat differently sensitive to many stress factors (cv. Ofanto less sensitive than cv. Adamello) were grown in a controlled environment with cadmium near threshold concentrations supplying the metal at equal-effect concentrations. Cd excess determined in both cvs. a reduction in water and turgor potential but a maintenance of relative water content. Cv Ofanto showed a higher capacity of Cd exclusion from roots but a higher translocation to shoots in comparison with cv. Adamello. Notwithstanding the higher metal concentration in leaves of cv. Ofanto, K⁺ leakage was more pronounced in Adamello suggesting that mechanisms of Cd detoxification and tolerance such as vacuolar compartmentalisation were activated in the first one. In Adamello plants, ethylene rose at the lowest metal concentration and the activation in roots of the antioxidative enzymes catalase, ascorbate peroxidase and guaiacol peroxidase came into play whereas in Ofanto ethylene and catalase did not change. Following cadmium treatment, superoxide dismutase activity was reduced or remained at the control value in roots and in leaves. For both cultivars ascorbate peroxidase, syringaldazine peroxidase and guaiacol peroxidase activities were always higher in roots than in leaves. These activities were induced by Cd in Ofanto leaves, whereas in Adamello leaves they remained at control levels or increased somewhat at the highest metal concentration. Cadmium changed the peroxidase isozyme pattern in both cultivars. Cv. Ofanto showed, as for other stress such as drought, salinity, nickel and copper, a co-tolerance towards Cd. Analogies in the response to other metals such as copper could be found in activation of catalase at the lower metal concentration in cv. Adamello and in the induction of ascorbate peroxidase in leaves of cv. Ofanto.     

Cadmium-induced changes in antioxidant enzyme activities in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. cv. Dongjin)

We studied how the relationship between cadmium (Cd) toxicity and oxidative stress influenced the growth, photosynthetic efficiency, lipid peroxidation, and activity of ntioxidative enzymes in the roots and leaves of rice(Oryza sativa L Dongjin). Plants were exposed to Cd for 21 d. Both seedling growth and photosynthetic efficiency decreased gradually with increasing cadmium concentrations. Lipid peroxidation increased slowly in both roots and leaves, causing oxidative stress. However, each tissue type responded differently to Cd concentrations with regard to the induction/ inhibition of antioxidative enzymes. The activity of Superoxide dismutase (SOD) increased in both roots and leaves. Ascorbate peroxidase (APX) activity increased in leaves treated with up to 0.25 μM Cd, then decreased gradually at higher concentrations. In contrast, APX activity in roots increased and remained constant between 0.25 and 25 μM Cd. Enhanced peroxidase (POD) activity was recorded for treatments with up to 25/M Cd, gradually decreasing at higher concentrations in the leaves but remaining unchanged in the roots. Catalase (CAT) activity increased in the roots, but decreased in the leaves, whereas the activity of glutathione reductase (GR) was enhanced in both roots and leaves, where it remained elevated at higher Cd concentrations. These results suggest that rice seedlings tend to cope with free radicals generated by Cd through coordinated, enhanced activities of the antioxidative enzymes involved in detoxification.     

Physiological Responses and Tolerance Mechanisms to Cadmium in Conyza canadensis

Experiments were conducted to examine the effects of different concentrations of Cd on the performance of the Cd accumulator Conyza canadensis. Cd accumulation in roots and leaves (roots > leaves) increased with increasing Cd concentration in soil. High Cd concentration inhibited plant growth, increased the membrane permeability of leaves, and caused a significant decline in plant height and chlorophyll [chlorophyll (Chl) a, Chl b, and total Chl] content. Leaf ultrastructural analysis of spongy mesophyllic cells revealed that excessive Cd concentrations cause adverse effects on the chloroplast and mitochondrion ultrastructures of C. canadensis. However, the activities of antioxidant enzymes, such as superoxide dismutase, catalase, peroxidase, total non-protein SH compounds, glutathione, and phytochelatin (PC) concentrations, showed an overall increase. Specifically, the increase in enzyme activities demonstrated that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Cd in C. canadensis. Furthermore, results demonstrate that PC synthesis in plant cells is related to Cd concentration and that PC production levels in plants are related to the toxic effects caused by soil Cd level. These findings demonstrate the roles played by these compounds in supporting Cd tolerance in C. canadensis.     

Cadmium toxicity affects chlorophyll a and b content,antioxidant enzyme activities and mineral nutrient accumulation in strawberry

Background

Cadmium (Cd) is well known as one of the most toxic metals affecting the environment and can severely restrict plant growth and development. In this study, Cd toxicities were studied in strawberry cv. Camarosa using pot experiment. Chlorophyll and malondialdehyde (MDA) contents, catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) activities and mineral nutrient concentrations were investigated in both roots and leaves of strawberry plant after exposure Cd.

Results

Cd content in both roots and leaves was increased with the application of increasing concentrations of Cd. We found higher Cd concentration in roots rather than in leaves. Chlorophyll a and b was decreased in leaves but MDA significantly increased under increased Cd concentration treatments in both roots and leaves. SOD and CAT activities was also increased with the increase Cd concentrations. K, Mn and Mg concentrations were found higher in leaves than roots under Cd stress. In general, increased Cd treatments increased K, Mg, Fe, Ca, Cu and Zn concentration in both roots and leaves. Excessive Cd treatments reduced chlorophyll contents, increased antioxidant enzyme activities and changes in plant nutrition concentrations in both roots and leaves.

Conclusion

The results presented in this work suggested that Cd treatments have negative effect on chlorophyll content and nearly decreased 30% of plant growth in strawberry. Strawberry roots accumulated higher Cd than leaves. We found that MDA and antioxidant enzyme (CAT, SOD and APX) contents may have considered a good indicator in determining Cd tolerance in strawberry plant.     

Characteristics of cadmium accumulation and tolerance in <Emphasis Type="Italic">Rorippa globosa</Emphasis> (Turcz.) Thell., a species with some characteristics of cadmium hyperaccumulation

Characteristics of cadmium (Cd) accumulation and tolerance in Rorippa globosa (Turcz.) Thell., a species with some characteristics of cadmium hyperaccumulation were further investigated and compared with a closely related species, Rorippa islandica. The results showed that there was no phytotoxicity for R. globosa leaves or reduction in biomass when treated with 25 μg Cd g⁻¹, although the concentration of Cd accumulated in the leaves was up to 218.9 μg Cd g⁻¹ dry weight (DW). On the contrary, Cd toxicity was observed in R. islandica leaves by way of determining changes in fresh weight (FW), malondialdehyde (MDA) level and chlorophyll content while treated with 25 μg Cd g⁻¹ DW. R. globosa had stronger self-protection ability than R. islandica to adapt to oxidative stress caused by Cd. Application of Cd significantly increased the activity of superoxide dismutase (SOD) in leaves, the activity of peroxidase (POD) in roots, and the activity of catalase (CAT) in leaves and roots of R. globosa. By contrast, in R. islandica, the activity of antioxidant enzymes was inhibited or unchanged by various Cd treatments. However, R. globosa leaves had higher activity of antioxidant enzymes such as SOD and POD than that of R. islandica. The antioxidative defense systems in R. globosa might play an important role in Cd tolerance. The Cd treatments significantly induced the synthesis of phytochelatins (PCs) in the two species. Leaf PCs and Cd accumulation by R. globosa were much greater than those by R. islandica, but root PCs and Cd accumulation by R. islandica were much greater than those by R. globosa, suggesting that PCs in leaves may be a biomarker of Cd hyperaccumulation, and the synthesis of PCs may be related to an increase in the uptake of Cd ions into the cytoplasm, not the primary mechanism for Cd tolerance.     

Effects of cadmium on antioxidant enzyme and photosynthetic activities in leaves of two maize cultivars

Effects of cadmium (Cd(2+)) on photosynthetic and antioxidant activities of maize (Zea mays L.) cultivars (3223 and 32D99) were investigated. Fourteen-day-old cultivar seedlings were exposed to different Cd concentrations [0, 0.3, 0.6 and 0.9mM Cd(NO(3))(2).4H(2)O] for 8 days. The results of chlorophyll fluorescence indicated that different levels of Cd affected photochemical efficiency in 3223 much more than that in 32D99. In parallel, the level of Cd at 0.9mM caused oxidative damage but did not indicate cessation of PSII activity of the cultivars; plant death was not observed at highly toxic Cd levels. Additionally, the increase in Cd concentration caused loss of chlorophylls and carotenoid and membrane damage in both cultivars, but greater membrane damage was observed in 3223 than in 32D99. Depending on Cd accumulation, a significant reduction in dry biomass was observed in both cultivars at all Cd concentrations. The accumulation of Cd was higher in roots than in leaves for both cultivars. Nevertheless, cultivar 3223 transferred more Cd from roots to leaves than did 32D99. On the other hand, our results suggest that there were similar responses in SOD, APX and GR activities with increasing Cd concentrations for both cultivars. However, POD activity significantly increased at highly toxic Cd levels in 32D99. This result may be regarded as an indication of better tolerance of the Z. mays L. cultivar 32D99 to Cd contamination.     

Distribution and phytotoxicity of cadmium in tomato seedlings

Thirty-day-old seedlings of tomato (Lycopersicon esculentum cv. Kwangsoo) were treated with various cadmium (Cd) concentrations (0, 10, 50, 100, and 500 μM) for up to 20 days, and the detailed distribution of absorbed Cd and its phytotoxicity in different plant parts (root, stem, and leaves) were investigated. The accumulation of Cd in plants increased with external Cd concentrations and Cd was strongly retained by roots, with less than 30% of the absorbed Cd being transported to shoots. Among the leaves, the lower positioned older leaves accumulated more Cd than the younger leaves. Furthermore, Cd-exposure not only reduced the dry weight and length of both shoot and root, chlorophyll levels in leaves, and levels of photosynthesis, but also enhanced the concentration of malondialdehyde (a lipid peroxidation product) in all plant parts. Our results indicate that the physiological impairment of tomato seedlings exposed to toxic levels of Cd may be related to the internal distribution of absorbed Cd, prolonged exposure, and oxidative stress in different plant parts.     

Accumulation and translocation of Cd metal and the Cd-induced production of glutathione and phytochelatins in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

Translocation of cadmium (Cd) in the tissues of Vicia faba, the water content in biomass, the biomass production, and the glutathione and phytochelatin tissue concentrations were studied and correlated with the plant sensitivity and/or tolerance to Cd. The total concentrations of Cd were determined by inductively coupled plasma/mass spectrometry (ICP-MS), the concentrations of glutathione (GSH) and phytochelatins 2 and 3 (PC2 and PC3) were determined by on-line high performance liquid chromatography/electrospray-ionization tandem mass spectrometry (HPLC–ESI–MS–MS) in the roots and leaves of the sensitive and the tolerant cultivars of V. faba grown in Cd containing nutrient solutions (NS, 0–100 μmol l⁻¹ Cd²⁺). Both the cultivars of V. faba accumulate a major portion of Cd in the roots and only a minor part of ca. 4% in the leaves. The differences between the cultivars concerning Cd accumulation in leaves were apparent from higher Cd concentrations in NS and the Cd amount in the sensitive cultivar was approximately twice as high. In the roots, the differences between the cultivars in the Cd accumulation were only statistically significant with the highest Cd concentrations in NS, with the tolerant cultivar accumulating about 16% more of Cd compared to the sensitive one. The biomass production of the sensitive cultivar decreased approximately twice as fast with increasing Cd concentration in NS. The biomass water content decreased with increasing Cd concentration in NS in both the cultivars. In general, the GSH concentration did not linearly correlate with Cd accumulation, except for the roots of the sensitive cultivar where it was independent, and was higher in the sensitive cultivar than in the tolerant one in both the leaves and roots. The GSH concentration in leaves was approximately one order of magnitude higher than that in the roots for both the cultivars. The relationships between the PC and Cd concentrations in tissues were found nonlinear. At lower Cd accumulation levels, the PC concentrations followed an increase in the Cd accumulation in both the roots and leaves, whereas at higher Cd accumulations the relations differed between roots and leaves. In the roots, the PC concentrations decreased with increasing Cd accumulation, whereas the PC concentration in the leaves followed the decrease in the Cd accumulation.     

Role of abscisic acid in cadmium tolerance of rice (Oryza sativa L.) seedlings

Changes in abscisic acid (ABA) contents in Cd-treated rice (Oryza sativa L.) seedlings of two cultivars were investigated. On treatment with CdCl2, the ABA content rapidly increased in the leaves and roots of Cd-tolerant cultivar (cv. Tainung 67, TNG67) but not in the Cd-sensitive cultivar (cv. Taichung Native 1, TN1). The reduction of transpiration rate of TN1 caused by Cd was less than that of TNG67. Exogenous application of ABA reduced transpiration rate, decreased Cd content, and enhanced Cd tolerance of TN1 seedlings. Exogenous application of the ABA biosynthesis inhibitor, fluridone, reduced ABA accumulation, increased transpiration rate and Cd content, and decreased Cd tolerance of TNG67 seedlings. Fluridone effect on Cd toxicity of TNG67 seedlings was reversed by the application of ABA. The roles of endogenous ABA in Cd tolerance of rice seedlings are discussed and suggested.     

Comparative lipid peroxidation,antioxidant defense systems and proline content in roots of two rice cultivars differing in salt tolerance

The changes in the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), peroxidase (POX: EC 1.11.1.7), ascorbate peroxidase (APOX: EC 1.11.1.11) and glutathione reductase (GR: EC 1.6.4.2), free proline content, and the rate of lipid peroxidation level in terms of malondialdehyde (MDA) in roots of two rice cultivars (cvs.) differing in salt tolerance were investigated. Plants were subjected to three salt treatments, 0, 60, and 120 mol m⁻³ NaCl for 7 days. The results showed that activated oxygen species may play a role in cellular toxicity of NaCl and indicated differences in activation of antioxidant defense systems between the two cvs. The roots of both cultivars showed a decrease in GR activity with increase in salinity. CAT and APOX activities increased with increasing salt stress in roots of salt-tolerant cultivar Pokkali but decreased and showed no change, respectively, in roots of IR-28 cultivar. POX activity decreased with increasing NaCl concentrations in salt-tolerant Pokkali but increased in IR-28. SOD activity showed no change in roots of both cultivars under increasing salinity. MDA level in the roots increased under salt stress in sensitive IR-28 but showed no change in Pokkali. IR-28 produced higher amount of proline under salt stress than in Pokkali. Increasing NaCl concentration caused a reduction in root fresh weight of Pokkali and root dry weight of IR-28. The results indicate that improved tolerance to salt stress in root tissues of rice plants may be accomplished by increased capacity of antioxidative system.     

Antioxidant defense system in leaves of Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassica juncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.     

Genotype-Dependent Effect of Exogenous Nitric Oxide on Cd-induced Changes in Antioxidative Metabolism, Ultrastructure, and Photosynthetic Performance in Barley Seedlings (Hordeum vulgare)

A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O₂^•−, H₂O₂, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P _n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD) and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover, Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced damage to leaf/root ultrastructure, and increased chlorophyll content and P _n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments. Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular structure.     

Lead-induced oxidative stress and role of antioxidant defense in wheat ( Triticum aestivum L.)

The aim of this study was to investigate soil lead pollution on biochemical properties and gene expression pattern of antioxidant enzymes in three wheat cultivars (Morvarid, Gonbad and Tirgan) at flag leaf sheath swollen stage. Lead (Pb(NO3)2) was used at four different concentrations (0, 15, 30 and 45 mg/kg of soil). The leaf and roots samples were taken at late-booting stage (Zadoks code, GS: 45). The results showed that lead heavy metal toxicity increased the expression of some genes and the activity of key enzymes of the antioxidant defense system in wheat. Moreover, the cell oxidation levels (MDA, LOX) enhanced under lead stress conditions. The relative gene expression and activity of antioxidant enzymes (CAT, SOD, GPX and APX) increased significantly in the both leaves and root tissues under lead stress conditions. The level of gene expression and enzymatic activity were higher in the root than the leaf tissue. There was no significant difference among cultivars in each of lead concentrations but Morvarid and Tirgan cultivars had more tolerance to toxic concentrations of lead when compared to Gonbad cultivar.     

Short-term cold stress in two cultivars of <Emphasis Type="Italic">Digitaria eriantha</Emphasis>: effects on stress-related hormones and antioxidant defense system

The two cultivars of Digitaria eriantha: cv. Sudafricana (a cold-sensitive cultivar) and cv. Mejorada INTA (a cold-resistant cultivar) were exposed to low temperature and compared in terms of the involvement of abscisic acid (ABA) and catabolites, jasmonates, and antioxidant defense in cold tolerance. Cold stress caused a greater ABA increase in cv. Mejorada INTA than in cv. Sudafricana. In both cultivars abscisic acid glucose ester and dihydrophaseic acid were the most abundant catabolites. Cold treatment decreased JA in leaves of both cultivars. In cv. Sudafricana, 12-hydroxyjasmonate (12-OH-JA) decreased and 12-oxo-phytodienoic acid increased. In regard to antioxidant defense, both cultivars increased the non-protein thiols in response to cold stress. However, reduced glutathione (GSH) level was higher in leaves of cv. Mejorada INTA than cv. Sudafricana. Cold-treated leaves of cv. Sudafricana increased thiobarbituric acid-reactive substances (TBARS), but cv. Mejorada INTA leaves showed no such increase. Superoxide dismutase activity decreased and ascorbate peroxidase activity increased in cold-treated leaves of cv. Sudafricana. No significant change of these enzymes was observed for cv. Mejorada INTA. The cold tolerance of cv. Mejorada INTA could be related to JA, 12-OH-JA and GSH high basal contents, ABA increase, and TBARS stability after cold treatment.