Antioxidant defense mechanisms in response to cadmium treatments in two safflower cultivars

By using two safflower (Carthamus tinctorius L.) cultivars, Arak2811 and Goldasht, the experiments were conducted in order to study (i) the genotypic variation in cadmium (Cd) tolerance, (ii) Cd concentrations in plants, and (iii) changes in the antioxidant defense systems in leaves, including antioxidant enzymes and nonenzymatic antioxidants. Plants were grown under controlled environmental conditions and subjected to Cd treatments (0, 25, 50, 75, and 100 μM Cd) for different time periods. Cd concentrations and cultivar-dependent response to Cd were assessed. Of the two cultivars, Goldasht showed a greater sensitivity to Cd toxicity as judged from the severity of Cd toxicity symptoms on leaves, much stronger enhancement in the MDA level, and decreases in dry matter production. Increasing Cd supply markedly reduced the shoot and root dry weights in both cultivars, but at the higher Cd concentrations and longer exposure durations, this decrease was more marked in cv. Goldasht. Plants accumulated substantial amount of Cd, especially in the roots, the highest being in the roots of cv. Arak2811 at 100 μM Cd after 4 days. Cd-induced oxidative stress as was indicated by the increase in lipid peroxidation with the increase in metal concentration and exposure duration. Under different Cd stress levels, activities of antioxidant enzymes differed in the two cultivars. The results indicated that Cd tolerance of cv. Arak2811 was related to the retention of Cd in the roots and avoiding the toxic effect by activation of the antioxidant system.     

不同镉水平下大麦幼苗生长和镉及养分吸收的品种间差异

利用水培试验研究了不同Cd水平下大麦幼苗的Cd和几种矿质元素吸收、积累、生长和生物学产量的品种间差异 .结果表明 ,1μmol·L-1Cd处理显著降低麦苗株高、绿叶数、叶绿素计读数、地上部和根系干重 ,显著抑制植株对Zn、Mn、Cu的吸收和累积 ;品种之间存在着显著差异 ,无芒六棱受抑制最为严重 ,米麦 114和浙农 1号表现出相对较强的抗性 .麦苗Cd含量和累积量品种之间也有显著差异 ,浙农 1号的Cd含量最高 ,米麦 114最低 .相关分析表明 ,麦苗生物学产量与地上部Cd含量、累积量及根系Cd含量呈显著负相关 ,其中与地上部Cd含量的相关性最强 ,与根系Cd累积量无显著相关 .     

Genotypic variation of the response to cadmium toxicity in Pisum sativum L

This work evaluates the (cor-)relations between selected biochemical responses to toxic Cd and the degree of Cd sensitivity in a set of pea genotypes. Ten genotypes were analysed that differ in their growth response to Cd when expressed as root or shoot tolerance indices (TIs). Concentrations of non-protein thiols (NPTs) and malondialdehyde (MDA), activity of chitinase, peroxidase (POX), and catalase significantly increased in all pea genotypes treated with Cd. Cd-sensitivity of genotypes was correlated with relative increases in MDA concentration as well as activities of chitinase and POX, suggesting similar Cd stress effects. Activities of ascorbate peroxidase (APX) decreased, but concentrations of glutathione (GSH) increased in the less Cd-sensitive genotypes. Differences in root and leaf contents of Cd revealed no correlation with TI, metabolic parameters, and enzyme activities in Cd-treated plants, respectively, except that shoot Cd concentration positively correlated with shoot chitinase activity. Toxic Cd levels inhibited uptake of nutrient elements such as P, K, S, Ca, Zn, Mn, and B by plants in an organ- and genotype-specific manner. Cd-sensitivity was significantly correlated with decreased root Zn concentrations. The results show both similarities, as well as distinct features, in Cd toxicity expression in genotypes of one species, suggesting that independent and multi-factorial reactions modulate Cd sensitivity on the low-tolerance level of plants. The study illustrates the biochemical basis of earlier detected genotypic variation in Cd response.     

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.     

Apoplastic peroxidases and ascorbate are involved in manganese toxicity and tolerance of Vigna unguiculata

Excessive manganese (Mn) supply induced the formation of brown spots on leaves as typical Mn toxicity symptoms in cowpea ( Vigna unguiculata L. Walp.) grown in hydroponics. Differences in Mn resistance between cv. TVu 91 (Mn-sensitive) and cv. TVu 1987 (Mn-tolerant) expressed in the density of brown spots in older leaves were due to higher Mn tissue tolerance. Apoplastic water-soluble peroxidase (POD) in the apoplastic washing fluid (AWF) was enhanced by increasing Mn leaf content and generally significantly higher in leaves of cv. TVu 91 than in cv. TVu 1987. Electrophoresis of AWF revealed the presence of several water-soluble POD isoenzymes. At toxic Mn supply, the activities of these and additional POD isoenzymes increased more in the Mn-sensitive cultivar. Levels of ascorbic acid in the apoplast and cytoplasm of the Mn-sensitive cv. TVu 91 decreased with increasing leaf Mn contents, whereas Mn-tolerant cv. TVu 1987 was not affected. Mn treatment lead to a stimulation of the enzymes of the ascorbic acid regeneration system (monodehydroascorbic acid reductase and glutathione reductase) in both cultivars, but the activation of glutathione reductase was clearly more enhanced in the Mn-tolerant cultivar TVu 1987. The results provide circumstantial evidence that apoplastic ascorbate and peroxidases are involved in the expression of Mn toxicity and genotypic Mn tolerance.     

Responses of two kidney bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis>) cultivars to the combined stress of sulfur deficiency and cadmium toxicity

Plants suffer from combined stress of sulfur deficiency and cadmium toxicity in some agricultural lands. However, little is known about the reaction in plants, such as responses in antioxidant enzymes and non-protein thiol compounds, to such combined stress. Therefore, in this study, four treatments, S-sufficiency (T_S?Cd), S-deficiency (T_?S?Cd), Cd stress (T_S+Cd) and combined stress of S-deficiency and Cd stress (T_?S+Cd), were set up to investigate (1) the effects of sulfur deficiency or sulfur sufficiency on Cd toxicity to kidney bean cultivar seedlings and the related mechanisms, and (2) the responses of two kidney bean cultivars to combined stress of S-deficiency and Cd-tolerance. The results showed significant increases in hydrogen peroxide (H₂O₂) and malondialdehyde contents and significant increases in antioxidant enzyme (superoxide dismutase, catalase, peroxidase, and glutathione S-transferase) activities and non-protein thiol compounds (non-protein thiols, reduced glutathione, phytochelatins) synthesis in the plants in T_S+Cd and T_?S+Cd. On the tissue level, higher proportion of Cd was found to be immobilized/deposited in roots, while on the sub-cell level, higher proportion of Cd was located in cell walls and vacuole fractions with lower in cell organelles. Taken together, the results indicated that Cd detoxification was achieved by the two kidney bean cultivars through antioxidant enzyme activation, non-protein thiol compound synthesis and sub-cellular compartmentalization. In addition, the results indicated that sufficient S supply helped to relieve Cd toxicity, which is of special significance for remediation or utilization of Cd-contaminated soils as S is a plant essential nutrient.     

Protective role of salicylic acid applied before cold stress on antioxidative system and protein patterns in barley apoplast

This study was carried out to better understand the role of salicylic acid (SA) applied before cold stress in the cold tolerance mechanism. Two barley (Hordeum vulgare) cultivars, cold-sensitive (Akhisar) and cold-tolerant (Tokak), were used and 0.1 mM SA was applied to 7-d-old barley seedlings growing under control conditions (20/18 °C). The seedlings were transferred to cold chamber (7/5 °C) at the age 14, 21, and 28 d. After three days, the leaves were harvested to determine the activities of apoplastic antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) and ice nucleation activity and electrophoretic patterns of apoplastic proteins. Cold treatment decreased the activities of all enzymes in cold-sensitive cultivar, however, it increased CAT and POX activities in cold-tolerant cultivar. Exogenous SA increased enzyme activities in both cultivars. Ice nucleation activity increased by cold treatment, especially in 17-d-old seedlings in both cultivars. In addition, SA treatment increased ice nucleation activity in all examined samplings in both cultivars. SA treatment caused accumulation or de novo synthesis of some apoplastic proteins. The results of the present study show that exogenous SA can improve cold tolerance by regulating the activities of apoplastic antioxidative enzymes, ice nucleation activity, and the patterns of apoplastic proteins.     

Cadmium-induced oxalate secretion from root apex is associated with cadmium exclusion and resistance in Lycopersicon esulentum

The mechanisms of heavy metal resistance in plants can be classified into internal tolerance and exclusion mechanisms, but exclusion of heavy metals with the help of organic acids secretion has not been well documented. Here we demonstrated the contribution of oxalate secretion to cadmium (Cd) exclusion and resistance in tomato. Different Cd resistance between two tomato cultivars was evaluated by relative root elongation (RRE) and Cd accumulation. Cultivar 'Micro-Tom' showed better growth and lower Cd content in roots than 'Hezuo903' at different Cd concentrations not only in short-term hydroponic experiment but also in long-term hydroponic and soil experiments, indicating that the genotypic difference in Cd resistance is related to the exclusion of Cd from roots. 'Micro-Tom' had greater ability to secrete oxalate, suggesting that oxalate secretion might contribute to Cd resistance. Cd-induced secretion of oxalate was localized to root apex at which the majority of Cd accumulated. Phenylglyoxal, an anion-channel inhibitor, effectively blocked Cd-induced oxalate secretion and aggravated Cd toxicity while exogenous oxalate supply ameliorated Cd toxicity efficiently. These results indicated that the oxalate secreted from the root apex helps to exclude Cd from entering tomato roots, thus contributes to Cd resistance in the Cd-resistant tomato cultivar.     

Effects of cadmium stress upon activities of antioxidative enzymes, photosynthetic rate, and production of phytochelatins in leaves and chloroplasts of wheat cultivars differing in yield potential

We tested the mode of action of Cd on photosynthesis and activities of ATP-sulfurylase (ATP-S), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), and on contents of phytochelatins (PCs) and glutathione (GSH) in two cultivars of wheat (Triticum aestivum L.) PBW-343 and WH-542 differing in yield potential. Cd treatment increased Cd content and photosynthetic activity in PBW-343 more than in WH-542. The activities of APX, GR, ATP-S, and synthesis of PCs and GSH were also increased by Cd, but the CAT and SOD activities were inhibited in both the cultivars. The efficient functioning of antioxidative enzymes, production of PCs and GSH, helped in counteracting the effects of Cd namely in PBW-343, protected photosynthetic ability, and increased the tolerance to Cd.     

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.     

Elucidating Cd-mediated distinct rhizospheric and in planta ionomic and physio-biochemical responses of two contrasting Zea mays L. cultivars

Cadmium (Cd) in soil–plant system can abridge plant growth by initiating alterations in root zones. Hydroponics and rhizoboxes are useful techniques to monitor plant responses against various natural and/or induced metal stresses. However, soil based studies are considered more appropriate in order to devise efficient food safety and remediation strategies. The present research evaluated the Cd-mediated variations in elemental dynamics of rhizospheric soil together with in planta ionomics and morpho-physio-biochemical traits of two differentially Cd responsive maize cultivars. Cd-sensitive (31P41) and Cd-tolerant (3062) cultivars were grown in pots filled with 0, 20, 40, 60 and 80 µg/kg CdCl₂ supplemented soil. The results depicted that the maize cultivars significantly influenced the elemental dynamics of rhizosphere as well as in planta mineral accumulation under applied Cd stress. The uptake and translocation of N, P, K, Ca, Mg, Zn and Fe from rhizosphere and root cell sap was significantly higher in Cd stressed cv. 3062 as compared to cv. 31P41. In sensitive cultivar (31P41), Cd toxicity resulted in significantly prominent reduction of biomass, leaf area, chlorophyll, carotenoids, protein contents as well as catalase activity in comparison to tolerant one (3062). Analysis of tolerance indexes (TIs) validated that cv. 3062 exhibited advantageous growth and efficient Cd tolerance due to elevated proline, phenolics and activity of antioxidative machinery as compared to cv. 31P41. The cv. 3062 exhibited 54% and 37% less Cd bio-concentration (BCF) and translocation factors (TF), respectively in comparison to cv. 31P41 under highest Cd stress regime. Lower BCF and TF designated a higher Cd stabilization by tolerant cultivar (3062) in rhizospheric zone and its potential use in future remediation plans.     

Cadmium tolerance and antioxidative defenses in hairy roots of the cadmium hyperaccumulator,Thlaspi caerulescens

Plant species capable of hyperaccumulating heavy metals are of considerable interest for phytoremediation and phytomining. This work aims to identify the role of antioxidative metabolism in heavy metal tolerance in the Cd hyperaccumulator, Thlaspi caerulescens. Hairy roots of T. caerulescens and the non-hyperaccumulator, Nicotiana tabacum (tobacco), were used to test the effects of high Cd environments. In the absence of Cd, endogenous activities of catalase were two to three orders of magnitude higher in T. caerulescens than in N. tabacum. T. caerulescens roots also contained significantly higher endogenous superoxide dismutase activity and glutathione concentrations. Exposure to 20 ppm (178 microM) Cd prevented growth of N. tabacum roots and increased hydrogen peroxide (H(2)O(2)) levels by a factor of five relative to cultures without Cd. In contrast, growth was maintained in T. caerulescens, and H(2)O(2) concentrations were controlled to low, nontoxic levels in association with a strong catalase induction response. Treatment of roots with the glutathione synthesis inhibitor, buthionine sulfoximine (BSO), exacerbated H(2)O(2) accumulation in Cd-treated N. tabacum, but had a relatively minor effect on H(2)O(2) levels and did not reduce Cd tolerance in T. caerulescens. Lipid peroxidation was increased by Cd treatment in both the hyperaccumulator and non-hyperaccumulator roots. This work demonstrates that metal-induced oxidative stress occurs in hyperaccumulator tissues even though growth is unaffected by the presence of heavy metals. It also suggests that superior antioxidative defenses, particularly catalase activity, may play an important role in the hyperaccumulator phenotype of T. caerulescens.     

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.     

Antioxidative enzymes in cultivars of pepper plants with different sensitivity to cadmium

The effect of growing five different cultivars of pepper plants (Capsicum annuum L.) with CdCl₂ concentrations ranging from 0.125 to 0.5 mM on different physiological parameters, and antioxidative enzyme activities of leaves was studied. On the basis of growth parameters, pepper plants were relatively tolerant to cadmium, although metal concentrations higher than 0.125 mM produced a significant inhibition of growth, net photosynthesis, and water use efficiency. Different sensitivities to Cd⁺⁺ ions were observed among cultivars, Abdera being the most resistant to cadmium stress, while Mondo and Herminio were the most sensitive cultivars. Cadmium concentrations of 0.5 mM produced an increase in the activity of glutathione reductase, and guaiacol peroxidase in most cultivars, while catalase and superoxide dismutase (SOD) were slightly depressed. The analysis of the SOD activity pattern by native-PAGE showed the presence in most cultivars of four SODs which were identified as Mn–SOD, Fe–SOD, CuZn–SOD I and CuZn–SOD II. However, the two CuZn–SODs were absent in the Cd-sensitive cv. Herminio. The growth of pepper plants with 0.5 mM cadmium inhibited the activity of CuZn–SODs in all cultivars, while the activity of Mn- and Fe–SOD was enhanced. The activity of NADPH-dehydrogenases (glucose-6-P-dehydrogenase, 6-phosphogluconate dehydrogenase, NADP–isocitrate dehydrogenase and malic enzyme) showed a Cd-dependent enhancement in most cultivars, the highest increase being observed in the tolerant cv. Abdera. These results suggest that in pepper plants the tolerance to Cd toxicity is more dependent on the availability of NADPH than on its antioxidant capacity.     

An investigation of boron toxicity in barley using metabolomics

Boron (B) is an essential micronutrient that affects plant growth at either deficient or toxic concentrations in soil. The aim of this work was to investigate the adaptation of barley (Hordeum vulgare) plants to toxic B levels and to increase our understanding of B toxicity tolerance mechanisms. We used a metabolomics approach to compare metabolite profiles in root and leaf tissues of an intolerant, commercial cultivar (cv Clipper) and a B-tolerant Algerian landrace (cv Sahara). After exposure to elevated B (200 and 1,000 microM), the number and amplitude of metabolite changes in roots was greater in Clipper than in Sahara. In contrast, leaf metabolites of both cultivars only responded following 1,000 microM treatment, at which B toxicity symptoms (necrosis) were visible. In addition, metabolite levels were dramatically altered in the tips of leaves of the sensitive cultivar Clipper after growth in 1,000 microM B compared to those of Sahara. This correlates with a gradual accumulation of B from leaf base to tip in B-intolerant cultivars. Overall, there were always greater differences between tissue types (roots and leaves) than between the two cultivars. This work has provided insights into metabolic differences of two genetically distinct barley cultivars and information about how they respond metabolically to increasing B levels.     

Different mechanisms for metal-induced adaptation to cadmium in the human lung cell lines A549 and H441

Sensitivity to Cd and Zn as well as the capacity to develop tolerance were characterized in human lung cells A549 and H441. In the A549 cells, a 2-fold lower LC₅₀ was obtained for Cd compared to Zn, whereas H441 cells were similarly sensitive to both metals. H441 cells were twice as resistant to Cd as the A549 cells. Higher HSP70, but not metallothionein (MT) or glutathione (GSH) levels, could contribute to this better resistance. A 1.5- and 2-fold increase in the LC₅₀ for Cd was obtained in the A549 cells pre-exposed to non-cytotoxic concentrations of Cd (20 μM) or Zn (40 μM) for 24 h. On the other hand, only Zn increased H441 cells’ resistance to Cd. Maximum Zn- and Cd-induced tolerances were reached as early as 3 and 12 h, respectively. Increases in MT-IIa and HSP70 messenger RNA levels were higher in A549 cells, but cycloheximide eliminated the induction of tolerance only in the H441 cells. Protein synthesis is a prerequisite for metal-induced tolerance to Cd in the H441 cells but not the A549 cells. Results obtained with l-buthionine sulfoximine revealed that GSH synthesis is not responsible for the acquired tolerance in both cell lines. However, GSH plays a critical role against Cd toxicity, and pro-oxidant conditions sensitized cells to Cd with different impacts on the metal-induced mechanisms of acquired tolerance. GSH and catalase both provide antioxidative protection, but only the stress related to low GSH content, not that resulting from catalase inhibition, may be alleviated with Zn.     

Effects of mercury and cadmium on the activities of antioxidative enzymes in the seedlings ofPhaseolus aureus

Phaseolus aureus Roxb. was exposed to HgCl₂ and Cd(NO₃)₂ either at the germination stage in concentration 0.5, 5 and 25 μM for 48 and 96 h, or at the seedling stage (5^th day of germination) in concentration 0.5, 5 and 20 μM for 6, 24 and 48 h. The germination and the growth of roots (germination stage treatment) were less in Hg than in Cd treatment. The seedlings (seedling stage treatment) were, however, more susceptible to Cd than Hg. Both root and leaf tissues of the plant treated at the germination stage showed enhanced lipid peroxidation and activities of the antioxidative enzymes (catalase, guaiacol peroxidase and ascorbate peroxidase), except the catalase in leaf in 25 μM Cd treatment. At seedling stage the content of malondialdehyde increased significantly only in the leaf tissue, during 6 h exposure. The activities of all the enzymes exhibited an increasing trend in both the tissue of the seedlings, particularly the leaf, at least after 24 and 48 h, except the catalase whose activity declined in response to Cd. Active involvement of the guaiacol and ascorbate peroxidases, rather than catalase, in scavenging cellular H₂O₂ was indicated. It was concluded that the two metals had little primary damaging effect on membranes.     

Comparative study of four rice cultivars with different levels of cadmium tolerance

Cadmium (Cd) has been identified as a significant pollutant due to its high solubility in water and soil and high toxicity to plants and animals. Rice, as one of the most important food crops, is grown in soils with variable levels of Cd and therefore, is important to discriminate the Cd tolerance of different rice cultivars to determine their suitability for cultivation in Cd-contaminated soils. This study investigates the primary mechanisms employed by four rice cultivars in attaining Cd tolerance. HA63 cultivar reduces Cd uptake by increasing Fe absorption through activation of phytosiderophores. T3028 cultivar accumulates the highest level of Cd in leaves while also activating its reactive oxygen species (ROS) scavenging system, including antioxidant enzymes and phytochelatins. In some rice cultivars (such as HA63), a cyanide-resistant respiration mechanism, important in Cd detoxification, was also promoted under the Cd stress. In conclusion, different rice cultivars may adopt different biochemical strategies and respond with different efficiency to Cd stress.     

Functional associations between the metabolome and manganese tolerance in Vigna unguiculata

Genotypic- and silicon (Si)-mediated differences in manganese (Mn) tolerance of cowpea (Vigna unguiculata) arise from a combination of symplastic and apoplastic traits. A detailed metabolomic inspection could help to identify functional associations between genotype- and Si-mediated Mn tolerance and metabolism. Two cowpea genotypes differing in Mn tolerance (TVu 91, Mn sensitive; TVu 1987, Mn tolerant) were subjected to differential Mn and Si treatments. Gas chromatography-mass spectrometry (GC-MS)-based metabolite profiling of leaf material was performed. Detailed evaluation of the response of metabolites was combined with gene expression and physiological analyses. After 2 d of 50 μM Mn supply TVu 91 expressed toxicity symptoms first in the form of brown spots on the second oldest trifoliate leaves. Silicon treatment suppressed symptom development in TVu 91. Despite higher concentrations of Mn in leaves of TVu 1987 compared with TVu 91, the tolerant genotype did not show symptoms. From sample cluster formation as identified by independent component analysis (ICA) of metabolite profiles it is concluded that genotypic differences accounted for the highest impact on variation in metabolite pools, followed by Mn and Si treatments in one of two experiments. Analysis of individual metabolites corroborated a comparable minor role for Mn and Si treatments in the modulation of individual metabolites. Mapping individual metabolites differing significantly between genotypes onto biosynthetic pathways and gene expression studies on the corresponding pathways suggest that genotypic Mn tolerance is a consequence of differences (i) in the apoplastic binding capacity; (ii) in the capability to maintain a high antioxidative state; and (iii) in the activity of shikimate and phenylpropanoid metabolism.