Role of salicylic acid in alleviating oxidative damage in rice roots (Oryza sativa) subjected to cadmium stress

Time-dependent changes in enzymatic and non-enzymatic antioxidants, and lipid peroxidation were investigated in roots of rice (Oryza sativa) grown hydroponically with Cd, with or without pretreatment of salicylic acid (SA). Exposure to 50 microM Cd significantly decreased root growth, and activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), but increased the concentrations of H(2)O(2), malondialdehyde (MDA), ascorbic acid (AsA), glutathione (GSH) and non-protein thiols (NPT). However, pretreatment with 10 microM SA enhanced the activities of antioxidant enzymes and the concentrations of non-enzymatic antioxidants, but lowered the concentrations of H(2)O(2) and MDA in the Cd-stressed rice compared with the Cd treatment alone. Pretreatment with SA alleviated the Cd-induced inhibition of root growth. The results showed that pretreatment with SA enhanced the antioxidant defense activities in Cd-stressed rice, thus alleviating Cd-induced oxidative damage and enhancing Cd tolerance. The possible mechanism of SA-induced H(2)O(2) signaling in mediating Cd tolerance was discussed.     

Effects of Cd2+ on K+, Ca2+ and N uptake in two halophytes Sesuvium portulacastrum and Mesembryanthemum crystallinum: consequences on growth

One of the limits of Cd2+-phytoextraction is the high toxicity of this metal to plants. Growth restriction, chlorosis and necrosis are usually accompanied with a large disturbance of the uptake of essential elements. This work aims to study the effects of cadmium (Cd2+) on potassium (K+), calcium (Ca2+) and nitrogen (N) acquisition, and their consequences on growth in two halophytes species: Sesuvium portulacastrum and Mesembryanthemum crystallinum. Seedlings were grown for 30 days in split-root conditions. One half of the root system was immersed in complete nutrient solution (Basal medium (B)) supplemented with 100 microM Cd2+, and the other half was immersed in a Cd2+-free medium, containing all nutrients (B/Cd plants) or deprived of potassium ((B-K)/Cd) or calcium ((B-Ca)/Cd) or nitrogen ((B-N)/Cd). Using this approach, we demonstrated that K+ and Ca2+ uptake was impaired in roots exposed to Cd2+. Concerning N, we noticed no indication of uptake inhibition by Cd2+. However, restriction of K+ uptake by roots was compensated by an increase in the K+-use efficiency, so that growth was not inhibited. Calcium uptake was strongly limited by Cd2. This inhibition was accompanied by a reduction in growth of ((B-Ca)/Cd) plants. Thus, we conclude that Cd2+ limits growth of both halophytes through restriction imposed on Ca2+ uptake. We suggest that the increase of Ca2+ availability in soils could improve the growth of both species in the presence of Cd2+. This would be essential for improving their utility for extraction of this metal by from salty contaminated soils.     

Effect of cadmium on free amino acid, glutathione and ascorbic acid concentrations in two barley genotypes (Hordeum vulgare L.) differing in cadmium tolerance

Hydroponic experiment was carried out to study the effect of three Cd levels on glutathione (GSH), free amino acids (FAA), and ascorbic acid (ASA) concentration in the different tissues of 2 barley cultivars with different Cd tolerance. Cadmium concentration in both roots and shoots increased with external Cd level, while biomass and ASA concentration declined, and Wumaoliuling, a Cd-sensitive genotype was more affected than ZAU 3, a Cd-tolerant genotype. The effect of Cd on GSH concentration was dose- and time-dependent. In the 5 d exposure, root GSH concentration increased in 0.5 microM Cd treatment compared with control, but decreased significantly in 5 microM Cd treatment, irrespective of genotypes. However, in the 10 d exposure, GSH concentration in all plant tissues decreased with increasing Cd levels in the culture medium, and Wumaoliuling was much more affected than ZAU 3. Cadmium treatment greatly altered FAA concentration and composition in plants. The effect of Cd on glutathione (Glu) concentration in roots varied with genotypes. ZAU 3 showed a steady increase in root Glu concentration in both 0.5 and 5 microM Cd treatments, while Wumaoliuling was decreased by 38.0% in 5 microM Cd treatment, compared with the control. The results indicate that GSH and ASA are attributed to Cd tolerance in barley plants, and the relative less reduction in GSH concentration in ZAU 3 under Cd stress relative to the control may account for its higher Cd tolerance.     

Calcium protects roots of Sedum alfredii H. against cadmium-induced oxidative stress

Sedum alfredii is a well-known Cd (cadmium) hyperaccumulator native to China. The impacts of exogenous Ca on Cd-induced oxidative stress and antioxidant systems in roots of S. alfredii were investigated by using cellular and biochemical approaches. Supplementation of the medium with higher Ca levels resulted in alleviated growth inhibition and decreased Cd concentration, as well as increased Ca concentration in roots. Cadmium induced lipid peroxidation and loss of plasma membrane integrity, reactive oxygen species overproduction, as well as ultrastructural changes of root cells were largely reversed by Ca supplementation in the medium. Calcium application significantly altered the Cd effects on antioxidant enzymes and non-enzyme antioxidants (non-protein thiols), and significantly increased glutathione (GSH) biosynthesis. The results suggest that Ca is able to protect the roots of S. alfredii against Cd toxicity by restoration of Cd-displaced Ca, alleviation of the metal induced oxidative stress, as well as promotion of GSH biosynthesis.     

Growth and photosynthetic responses of the bloom-forming cyanobacterium Microcystis aeruginosa to elevated levels of cadmium

Effects of cadmium (Cd) on the growth and photosynthesis of the bloom-forming cyanobacterium Microcystis aeruginosa Kütz 854 were investigated. The growth was markedly inhibited when it was treated with 4 microM Cd. However, the biomass production was almost not influenced after a prolonged exposure at Cd concentrations < or = 2 microM. Chlorophyll content was more sensitive to Cd toxicity than phycobiliproteins at 0.5 microM Cd. However, the decrease of phycobiliproteins was larger than chlorophyll at the highest Cd concentration. A significant increase of F(v)/F(m) value was observed at Cd concentrations < or = 2 microM. On the other hand, when cells were treated with 4 microM Cd, F(v)/F(m) was significantly increased after 12 h of treatment but decreased after 48 h. The true photosynthesis was decreased with the increase of Cd concentration at 2 h. However, we noticed a recovery when the treatment was prolonged. After 48 h of exposure at the highest Cd concentration, photosynthetic oxygen evolution was markedly inhibited but dark respiration increased by 67%. Cellular Cd contents were augmented with the increase of Cd concentration. To our knowledge, we have demonstrated for the first time that the inhibitory site of Cd in M. aeruginosa is not located at the PSII or PSI level, but is probably situated on the ferredoxin/NADP(+)-oxidoreductase enzyme at the terminal of whole electron transport chain. We noticed also an increase of PSI activity, which is probably linked to the enhancement of cyclic electron transport around PSI. We can conclude that the increase of cyclic electron transport and dark respiration activities, and the decrease of phycobiliproteins might be adaptive mechanisms of M. aeruginosa 854 under high Cd conditions.     

Cadmium accumulation and its influence on lipid peroxidation and antioxidative system in an aquatic plant, Bacopa monnieri L

Bacopa monnieri L. plants exposed to 10, 50, 100 and 200 microM cadmium (Cd) for 48, 96 and 144 h were analysed with reference to the accumulation of metal and its influence on various enzymatic and non-enzymatic antioxidants, thiobarbituric acid reactive substances (TBARS), photosynthetic pigments and protein content. The accumulation of Cd was found to be increased in a concentration and duration dependent manner with more Cd being accumulated in the root. TBARS content of the treated roots and leaves increased with increase in Cd concentration and exposure periods, indicating the occurrence of oxidative stress. Induction in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) was recorded in metal treated roots and leaves of B. monnieri. In contrast, a significant reduction in catalase activity in Cd treated B. monnieri was observed. An increase was also noted in the levels of cysteine and non-protein thiol contents of the roots of B. monnieri followed by a decline. However, in leaves, cysteine and non-protein thiol contents were found to be enhanced at all the Cd concentrations and exposure periods. A significant reduction in the level of ascorbic acid was observed in a concentration and duration dependent manner. The total chlorophyll and protein content of B. monnieri decreased with increase in Cd concentration at all the exposure periods. Results suggest that toxic concentrations of Cd caused oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, B. monnieri is able to combat metal induced oxidative injury involving a mechanism of activation of various enzymatic and non-enzymatic antioxidants.     

Effects of cadmium on glutathione synthesis in hepatopancreas of freshwater crab, Sinopotamon yangtsekiense

Cadmium (Cd) is one of the most deleterious heavy metals in aquatic systems that could promote oxidative damage. To explore the effects of Cd exposure of a freshwater crab (Sinopotamon yangtsekiense) on hepatopancreatic glutathione (GSH) synthesis, crabs were exposed to the reagent with a dose range of 7.25-116.00 mg L(-1) for 48 h. The concentrations of GSH, oxidized glutathione (GSSG), NADPH and NADP(+), as well as the activities of enzymes involved in GSH synthesis, i.e. glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), gamma-glutamylcysteine synthetase (gamma-GCS) were determined. Progressive depletion of cellular GSH content was observed with the increasing of Cd concentrations, while the level of GSSG remained constant. In response to Cd exposure, crabs showed significant induction of G6PD and NADPH, however, only up to moderate exposures. GR activity remained at a steady level at all exposure concentrations. The activity of gamma-GCS was significantly positively correlated with the Cd concentration. These results suggested that GSH synthesis could be activated against reactive oxygen species induced by lower Cd exposure; under the higher Cd exposure conditions, an inhibition of NADPH-dependant redox cycling and de novo GSH synthesis led to significant decrease in GSH content.     

Biochemical responses of the mycorrhizae in Pinus massoniana to combined effects of Al, Ca and low pH

Biochemical responses of Pinus massoniana, with and without the inoculation mycorrhizal fungus Pisolithus tinctorius at the root, to artificial acid rain (pH 2.0) and various Ca/Al ratios were investigated. Some enzymes associated with the nutritive metabolism, such as acid phosphatase, alkaline phosphatase, nitrate reductase, mannitol dehydrogenase and trehalase, in the roots, stems and leaves of plant were obviously inhibited by the artificial acid rain and Al. After treatment with pH 2.0 + Ca/Al (0/1 or 1/10) artificial acid rain, the protein content in the organs was decreased. However, the activities of superoxide dismutase (SOD) and peroxidase (POD) and glutathione (GSH) concentrations were induced. It demonstrated that acid rain and Al could induce oxygen radicals in plant. Compared with the treatments with lower pH or Al, respectively, the combination of lower pH and Al concentration was more toxic to P. massoniana. Al toxicity could be ameliorated by the addition of Ca and the amelioration was the most when the ratio was 1/1 among the various Ca/Al ratio. Infection with mycorrhizal fungus P. tinctorius at the root of P. massoniana increased the ability of the plant to resist the toxicity of artificial acid rain and Al stress.     

The role of bacteria in the heavy metals removal and growth of Sedum alfredii Hance in an aqueous medium

This study was the first attempt to examine the possible role of the naturally occurring rhizospheric bacteria in heavy metal removal by Sedum alfredii Hance, a terrestrial Zn/Cd hyperaccumuluator, from Zn, Cd, Cu and Pb contaminated water using antibiotic ampicillin. Moreover, the toxicity symptom in plants under heavy metal stress expressed as total chlorophyll, chlorophyll a and b content, growth inhibition, root length, and N, P contents were studied, and the possible relationship among them were also discussed. These results indicate that rhizospheric bacteria may play an important role in the uptake of N and P by S. alfredii, and consequently result in the increase of Chlorophyll content in the leaves and plant biomass due to improved photosynthesis. At the same time, root length significantly decreased under the treatment with ampicillin, which suggested that rhizospheric bacteria appeared to protect the roots against heavy metal toxicity. The Pb, Zn, Cu and Cd concentrations in the roots, stems and leaves of S. alfredii were much higher than those exposed to ampicillin. Accordingly, metal concentrations in the contaminated water without ampicillin treatment were lower than those treated with ampicillin. These results suggest that the rhizospheric bacteria may be useful in plant tolerance to heavy metal toxicity, and also accelerate the metal removal from contaminated water.     

Chromium (VI) accumulation reduces chlorophyll biosynthesis, nitrate reductase activity and protein content in Nymphaea alba L

Plants of Nymphaea alba L. grown at various levels of chromium (VI) ranging from 1 to 200 microM accumulated chromium in concentration and duration-dependent manner. At all Cr levels, chromium accumulation by various plant tissues followed the order roots > leaves > rhizomes. Approximately 93% of total chromium present in the medium was accumulated by plants at lowest conentration (1 microM) used in the experiment. Chromium-induced toxicity appears at 1 microM chromium resulting in the build-up of delta-aminolevulinic acid (ALA) and reduced activities of delta-aminolevulinic acid dehydratase (ALAD) and nitrate reductase (NR), total chlorophyll (Chl) and protein contents. Ch1a was more sensitive than Ch1b to chromium toxicity. It could be inferred that chromium toxicity is not located at the level of ALA synthesis, but, probably at the ALAD activity which was more severely affected during chlorophyll biosynthesis. Finally, impaired chlorophyll biosynthesis resulted in reduced total chlorophyll content.     

Arsenic accumulation and physiological attributes of spinach in the presence of amendments: an implication to reduce health risk

The current study examined the effect of calcium (Ca) and ethylenediaminetetraacetic acid (EDTA) on arsenic (As) uptake and toxicity to spinach (Spinacia oleracea) as well as assessed the potential human health risks. Spinach seedlings were exposed to three levels of As (25, 125, and 250 μM) alone or together with three levels of EDTA (25, 125, and 250 μM) and Ca (1, 5, and 10 mM). The effect of EDTA and Ca was assessed in terms of As contents in roots and shoots, hydrogen peroxide production, chlorophyll contents, and lipid peroxidation. The accumulation and toxicity of As to spinach plants increased with increasing As levels in nutrient solution. Exposure to As resulted in lipid peroxidation and reduced chlorophyll contents. The highest level of As alone (250 μM) showed highest human health risk (hazard quotient of 7.09 at As-250). Addition of EDTA enhanced As accumulation by spinach, while reduced As toxicity to spinach, as well as human health risk (hazard quotient of 4.01 at As-250). Similarly, Ca significantly reduced As toxicity to spinach and the human health risks (hazard quotient of 3.79 at As-250) by reducing its accumulation in spinach. Higher levels of Ca were more effective in reducing As uptake and toxicity as well as enhancing chlorophyll contents.     

Aseptic hydroponics to assess rhamnolipid-Cd and rhamnolipid-Zn bioavailability for sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis>): a phytoextraction mechanism study

The availability of cadmium (Cd) and zinc (Zn) to sunflower (Helianthus annuus) was investigated in rhamnolipid- and ethylenediaminetetraacetic acid (EDTA)-buffered solutions in order to evaluate the influence of aqueous speciation of the metals on their uptake by the plant, in relation to predictions of uptake by the free ion activity model (FIAM). Free metal ion activity was estimated using the chemical equilibrium program MINTEQ or measured by Donnan dialysis. The uptake of Cd followed the FIAM for the EDTA-buffered solution at EDTA concentrations below 0.4 μM; for the rhamnolipid-buffered solution, the uptake of both metals in roots was not markedly affected by increasing rhamnolipid concentrations in solution. This suggests rhamnolipid enhanced metal accumulation in plant roots (per unit free metal in solution) possibly through formation and uptake of lipophilic complexes. The addition of normal Ca concentrations (low millimetre range) to the rhamnolipid uptake solutions reduced Cd accumulation in shoots by inhibiting Cd translocation, whereas it significantly increased Zn accumulation in shoots. This study confirms that although rhamnolipid could enhance accumulation of Cd in plants roots at low Ca supply, it is not suitable for Cd phytoextraction in contaminated soil environments where Ca concentrations in soil solution are orders of magnitude greater than those of Cd.     

Toxicity and bioaccumulation of thallium in Hyalella azteca, with comparison to other metals and prediction of environmental impact

Thallium (Tl) is an extremely toxic but little studied metal. For Hyalella azteca exposed in Lake Ontario water, a 25% reduction in survival (the LC25) occurred at about 48 nmol litre(-1) after 4 weeks. Body concentrations of Tl, which were proportional to water concentrations, averaged 290 nmol g(-1) dry mass at the LC25. Growth was reduced at slightly lower concentrations. Concentrations affecting reproduction were variable at < 50% of the LC25. On a water-concentration basis Tl was more toxic than Ni, Cu or Zn, but less toxic than Cd or Hg to Hyalella; toxicity to Pb was similar. On a body-concentration basis, the toxicities of Tl, Cd, Hg and Pb were all similar. Unlike Cd, Tl toxicity and uptake was affected by K concentrations in the water, and not by Ca, Mg, Na or other ions. Toxicity was proportional to uptake, and body concentrations were better predictors of toxicity than water concentrations in media with varying K concentrations. Preliminary measurements of Tl and Cd uptake by Hyalella from Hamilton Harbour and Lake Ontario sediments suggested that total bioavailable metal concentrations were greater in deep-water sediments from Lake Ontario than in sediments from the harbour. The ratio of bioavailable metal to the toxic threshold was slightly higher for Cd than for Tl, but well below 1 for both metals.     

The response of Lemna trisulca L. to cadmium

Lemna trisulca was grown, using aseptic culture techniques in a filter-sterilized medium, a portion of which was replaced regularly during experiments. L. trisulca responded to the addition of 0.64 microM Cd with a reduction in multiplication rate (MR) 2 +/- 1 days after exposure. The internal Cd content reached 1000 +/- 140 microg Cd/g (dry wt) within 2 days exposure to 0.64 microM Cd. The final yield was reduced by an average of c.8% for each day of exposure to 0.64 microM Cd in a 14 day experiment. This implies that an equilibration period should be used for short-term bioassay tests before the effect of a toxicant is determined. Pretreating L. trisulca with 0.08 or 0.32 microM Cd for 6 weeks had no significant effect on MR or Cd uptake when plants were subsequently exposed to a range of Cd concentrations or grown in a control medium. This suggests that L. trisulca does not become acclimated to elevated Cd concentrations. The MR of L. trisulca fluctuated over a period of almost 600 days and the doubling time ranged from 1.6 to 2.4 days. This produced more than a fivefold difference in final yield in experiments of 14 days duration. The reduction in MR in response to 0.32 microM Cd during this same 600 days period averaged 24% with a coefficient of variation of 38%, and varied with the MR of control cultures. Fluctuations in the intrinsic growth rate and the effect of a toxicant on L. trisulca could potentially confound the assessment of toxicity and must be carefully considered when designing test protocols for aquatic plants.     

Antioxidative response to Cd in a newly discovered cadmium hyperaccumulator, Arabis paniculata F

A hydroponic experiment was carried out to study the effect of cadmium (Cd) on growth, Cd accumulation, lipid peroxidation, reactive oxygen species (ROS) content and antioxidative enzymes in leaves and roots of Arabis paniculata F., a new Cd hyperaccumuator found in China. The results showed that 22-89 microM Cd in solution enhanced the growth of A. paniculata after three weeks, with 21-27% biomass increase compared to the control. Cd concentrations in shoots and roots increased with increasing Cd supply levels, and reached a maximum of 1662 and 8670 mg kg(-1) Cd dry weight at 178 microM Cd treatment, respectively. In roots, 22-89 microM Cd reduced the content of malondialdehyde (MDA), superoxide (O(2)(-1)) and H(2)O(2) as well as the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR). In leaves, the contents of MDA, O(2)(-1) and H(2)O(2) remained unaffected by 22-89 microM Cd, while 178 microM Cd treatment significantly increased the MDA content, 69.5% higher than that of the control; generally, the activities of SOD, catalase (CAT), GPX and APX showed an increasing pattern with increasing Cd supply levels. Our present work concluded that A. paniculata has a great capability of Cd tolerance and accumulation. Moderate Cd treatment (22-89 microM Cd) alleviated the oxidative stress in roots, while higher level of Cd addition (178 microM) could cause an increasing generation of ROS, which was effectively scavenged by the antioxidative system.     

The role of citric acid in cadmium and nickel uptake and translocation, in Halimione portulacoides

Some plants have high ability to absorb heavy metals in high concentrations. In this study, Halimione portulacoides was tested in conjunction with citric acid, in order to evaluate the possible use of this plant in phytoremediation processes in salt marshes. Two different concentrations of chelator were used combined with two heavy metal concentrations. When 25microM of citric acid was applied, Cd uptake and translocation was enhanced while for Ni these processes were almost inhibited. Increasing citric acid concentration to 50microM, Ni absorption decreased by the roots while for Cd there was still an increase in root uptake. Analysing translocation with this concentration of chelator, a decreased metal content in the upper organs for both metals was observed. While for Cd an optimal concentration of 25microM of citric acid was observed for phytoremediative processes, for nickel neither concentrations of chelator showed advantages for application in this remediative method.     

5-Aminolevulinic acid ameliorates cadmium-induced morphological, biochemical, and ultrastructural changes in seedlings of oilseed rape

Due to its prolific growth, oilseed rape (Brassica napus L.) can be grown successfully for phytoremediation of cadmium (Cd)-contaminated soils. Nowadays, use of plant growth regulators against heavy metals stress is one of the major objectives of researchers. The present study evaluates the ameliorate effects of 5-aminolevulinic acid (ALA, 0, 0.4, 2, and 10 mg/l) on the growth of oilseed rape (B. napus L. cv. ZS 758) seedlings under Cd stress (0, 100, and 500 μM). Results have shown that Cd stress hampered the seedling growth by decreasing the radical and hypocotyls length, shoot and root biomass, chlorophyll content, and antioxidants enzymes. On the other hand, Cd stress increased the level of malondialdehyde (MDA) and production of H₂O₂ and accumulation of Cd in the shoots. The microscopic study of leaf mesophyll cells showed that toxicity of Cd totally destroyed the whole cell structure, and accumulation of Cd also appeared in micrographs. Application of ALA at lower dosage (2 mg/l) enhanced the seedling growth and biomass. The results showed that 2 mg/l ALA significantly improved chlorophyll content under Cd stress and decreased the level of Cd contents in shoots. Application of ALA reduced the MDA and H₂O₂ levels in the cotyledons. The antioxidants enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase, and superoxide dismutase) enhanced their activities significantly with the application of 2 mg/l ALA under Cd stress. This study also indicated that higher dosage of ALA (10 mg/l) imposed the negative effect on the growth of oilseed rape. Microscopic study showed that application of ALA alleviated the toxic effects of Cd in the mesophyll cell and improved the cell structure. Use of 2 mg/l ALA under 500 μM Cd was found to be more effective, and under this dosage, cell structure was clear, with obvious cell wall and cell membrane as well as a big nucleus, which was found with well-developed two or more nucleoli. Chloroplast was almost round in shape and contained thylakoids membranes and grana, but starch grains were not found in chloroplast comparatively to other treatments. On the basis of our results, we can conclude that ALA has a promotive effect which could improve plant survival under Cd stress.     

Genotypic differences in effects of cadmium exposure on plant growth and contents of cadmium and elements in 14 cultivars of bai cai

Fourteen cultivars of bai cai (Brassica campestris L. ssp. chinensis var. communis) were grown in the nutrient solutions containing 0-0.5 microg mL(-1) of cadmium (Cd) to investigate genotypic differences in the effects of Cd exposure on the plant growth and uptake and distribution of Cd in bai cai plants. The Cd exposure significantly reduced the dry and fresh weights of roots and shoots, the dry weight ratio of shoot/root (S/R), total biomass, and chlorophyll content (SPAD value). Cd concentrations in bai cai ranged from 13.3 to 74.9 microg g(-1) DW in shoots and from 163.1 to 574.7 microg g(-1) DW in roots under Cd exposure, respectively. The considerable genotypic differences of Cd concentrations and accumulations in both shoots and roots were observed among 14 bai cai cultivars. Moreover, Cd mainly accumulated in the roots. Cd also caused the changes of uptake and distribution of nutrients in bai cai and under the influence of cadmium, the concentration of potassium (K) decreased in shoot and increased in root. However, the concentrations of magnesium (Mg), phosphorus (P), manganese (Mn), boron (B), and iron (Fe) increased in shoots and decreased in roots. In addition, Cd exposure resulted in an increase in calcium (Ca), sulphur (S), and zinc (Zn) concentrations in both shoots and roots but had no significant effects on the whole uptake of the examined mineral nutrients except for S.     

Calcium invigorates the cadmium-stressed <Emphasis Type="Italic">Brassica napus</Emphasis> L. plants by strengthening their photosynthetic system

Introduction  

Cadmium (Cd) in plants interrupts numerous metabolic processes and reduces the water and nutrient uptake that cause chlorosis, growth retardation, and ultimately plant death. Response of Brassica napus L. to calcium (Ca) enrichment in growth medium for reducing Cd toxicity stress by strengthening the photosynthesis organelles and their functionality was explored in this study.     

Impact of spiked concentrations of Cd,Pb, As and Zn in growth medium on elemental uptake of Nasturtium officinale (Watercress)

This study is aimed at investigating the impact of water quality on the uptake and distribution of three non-essential and toxic elements, namely, As, Cd and Pb in the watercress plant to assess for metal toxicity. The plant was hydroponically cultivated under greenhouse conditions, with the growth medium being spiked with varying concentrations of As, Cd and Pb. Plants that were harvested weekly for elemental analysis showed physiological and morphological symptoms of toxicity on exposure to high concentrations of Cd and Pb. Plants exposed to high concentrations of As did not survive and the threshold for As uptake in watercress was established at 5 ppm. Translocation factors were low in all cases as the toxic elements accumulated more in the roots of the plant than the edible leaves. The impact of Zn on the uptake of toxic elements was also evaluated and Zn was found to have an antagonistic effect on uptake of both Cd and Pb with no notable effect on uptake of As. The findings indicate that phytotoxicity or death of the watercress plant would prevent it from being a route of human exposure to high concentrations of As, Cd and Pb in the environment.