Effects Of Heavy Metal Stress Research Articles

Salt and heavy metal stress responses and metal uptake potentials of some leafy vegetables

AbstractAbiotic stress conditions caused by increasing anthropogenic activities over the years necessitate using marginal waters in agricultural irrigation and pose a risk to public health by causing salt stress and heavy metal pollution in the soil. The study exposed rocket (Eruca sativa L.), cress (Lepidium sativum L.), and parsley (Petroselinum crispum Mill.) plants to heavy metals (Zn, Cu, Ni, Pb, Cd, and Cr at rates of 300, 140, 75, 300, 3, and 100 mg kg−1, respectively) and salt stress (3, 6, and 9 dS m−1). Both stress conditions affected plant growth negatively. Biomass losses reaching 88% occurred in the rocket, which was determined to be more sensitive to salt stress than heavy metal stress. In parsley, on the other hand, it was determined that the above‐ground organs were more affected by salt stress, but the negative effect of heavy metal stress on the roots was higher than salt stress. In cress, the cultivars produced different responses to stress factors. The Zeybek cultivar was more affected by salt stress, and Bahargülü was more affected by heavy metal stress. In general, an increase in macro‐ and micronutrients was found under stress conditions. In addition, it was determined that the plants were hyper‐accumulative in terms of lead absorption and were sorted as cress > parsley > rocket in terms of metal uptake. According to these findings, these plants should be grown taking into account the lead values in the soil, and consumers should be aware that they are a group of vegetables that accumulate lead.

Plant Growth-Promoting Bacteria (PGPB): A Potent Source of Heavy Metal Stress Management in Plants

Heavy metals or metalloids are toxic elements found throughout the crust of the earth’s surface. The gradual increase of heavy metal concentration in soil and water due to some natural and anthropogenic activities like application of agrochemicals, waste disposal, industrial activities, mining, smelting, lead-based paints, etc cause stress to the local vegetation. Soil microorganisms play a critical part in the remediation of heavy metal contaminated soil and thereby exert direct or indirect promotion to plant growth. Plant growth-promoting bacteria (PGPB), specially the Plant growth-promoting rhizobacteria (PGPR), are a natural, sustainable, and eco-friendly solution for mitigating stress challenges. They can boost plant growth by alleviating heavy metal toxicity through various mechanisms such as metal sequestration, metal immobilization, and production of metal chelating compounds, which reduce metal toxicity and enhance plant growth. This review summarizes the effect of heavy metal stress on plants, the response of plants to heavy metal stress, mechanisms involved in metal stress tolerance by soil bacteria, and their application in managing heavy metal stress in plants.

Determination of the Effects of Heavy Metal Stress on Plant Development and Physiology in Feed Soybean (Glycine Max L.)

This study was carried out to determine the tolerance level of cadmium and lead applications at different concentrations on physiological and morphological parameters in soybean (Glycine max L.) The experiment was carried out in Atatürk University Plant Production Application and Research Center greenhouses. Yeşilsoy variety of feed soybean (Glycine max L.) was used as plant material. Plant growth (seedling height, stem diameter, fresh and dry weight, etc.), physiological properties (tissue proportional water content, tissue electrical conductivity) and biochemical parameters (chlorophyll amount, superoxide distumase (SOD), catalase (CAT), heavy metal applications) peroxidase (POD) enzyme activities, etc.) were investigated. All treatments had negative effects on all parameters compared to the control group. Growth retardation was experienced at the highest concentrations applied, but plant deaths were not observed. Although it is known that cadmium metal is more toxic than lead metal, the wet weight values of the plants to which the highest dose of both metals were applied were included in the same statistical group.

Copper nanoparticles alleviate cadmium stress in Solanum melongena through endogenous melatonin and regulation of some physiochemical attributes

Different chemicals and substances are often used to increase plant growth and production, and their efficacy is impacted by things like concentration and growth stage. This study aimed to investigate the impact of cadmium (Cd) stress on Solanum melongena L. and evaluate the potential alleviating effects of Cu-nanoparticles. The findings revealed that low concentrations of Cu-nanoparticles effectively protected S. melongena. from the adverse effects of heavy metal stress. Cu-nanoparticles exhibited a crucial role in plant physiology by stimulating enzyme activity and defense mechanisms. Furthermore, moderate concentrations of Cu-nanoparticles were observed to promote plant growth and increase chlorophyll content. Additionally, the treatments with low concentrations of Cu-nanoparticles resulted in reduced oxidative stress, as evidenced by decreased levels of hydrogen peroxide and malondialdehyde (MDA) content. Moreover, the application of Cu-nanoparticles positively influenced total soluble protein levels and relative water content. Furthermore, the Cu-nanoparticles treatment effectively alleviated Cd-induced oxidative stress and increased the concentration of melatonin. Antioxidant accumulation exhibited an increase under various treatments, with the moderate concentration of Cu-nanoparticles showing the most favorable impact. In conclusion, the moderate concentration of Cu-nanoparticles demonstrated promising effects in mitigating Cd-induced stress and optimizing the growth and physiology of S. melongena plants.

Characterizing of heavy metal accumulation, translocation and yield response traits of Chenopodiumquinoa

Heavy metal contamination in soil is a major environmental threat that reduces crop productivity. Quinoa as a phytoremediation potential is a viable option to mitigate the effect of heavy metal stress. This study aimed to investigate the phytoremediation characteristics of four quinoa lines when exposed to soil contaminated with heavy metal. Four quinoa lines (A1, A2, A7, and A9) were allowed to grow in three fields (control (UAF), Chakera farm (UAF), and Chakera village) under RCBD split plot arrangement with three replication. Maximum seed yield (4100 kg ha−1) was obtained by A7 which was statistically similar to the A2 line (3648 kg ha−1) obtained from Chakera Farm (UAF) having sewage water application. While low yield was obtained from A9 (1482 kg ha−1) in normal soil (control). Both A7 and A2 lines exhibited higher biomass and seed yield at three fields. Both fields having sewage water application resulted in higher growth and superb seed yield of quinoa lines as compared to the control. Quinoa lines (A2 and A7) attained (51 and 43%) high seed yield at Chakera farm (UAF) having sewage water application in comparison to control having normal irrigation. Seed quality was substantially affected by heavy metal concentration in both contaminated fields. Metals concentration determined in seed samples of A7 was high as compared to A2. Hence A2 may be said a nutritionally superior quinoa line as metal levels were within the permissible level set by FAO/WHO.

Investigating the efficacy of tartaric acid and zinc-mediated endogenous melatonin induction for mitigating arsenic stress in Tagetes patula L.

In order to enhance plant growth and productivity, various chemicals and substances are commonly employed, wherein their effectiveness is influenced by factors such as concentration and growth stage. This study aimed to investigate the impact of arsenic stress on Tagetes patula L. and evaluate the potential alleviating effects of zinc (Zn) and tartaric acid. The findings revealed that low concentrations of Zn and tartaric acid effectively protected Tagetes patula L. from the adverse effects of heavy metal stress. Zinc exhibited a crucial role in plant physiology by stimulating enzyme activity and defense mechanisms. Furthermore, moderate concentrations of Zn and tartaric acid were observed to promote plant growth and increase chlorophyll content. Notably, the combined application of Zn and tartaric acid exhibited the most significant improvements in plant morphology and chlorophyll levels. Additionally, the treatments with low concentrations of Zn and tartaric acid resulted in reduced oxidative stress, as evidenced by decreased levels of hydrogen peroxide and malondialdehyde (MDA) content. Moreover, the application of zinc and tartaric acid positively influenced total soluble protein levels and relative water content. The combined treatment also enhanced the activities of antioxidant enzymes, thereby mitigating oxidative damage induced by arsenic stress. Furthermore, the synergistic effect of the Zn and tartaric acid treatment effectively alleviated arsenic-induced oxidative stress and increased the concentration of melatonin. Proline accumulation exhibited an increase under various treatments, with the combination of Zn and tartaric acid showing the most favorable impact. The resting membrane potential (RMP) of the plants was influenced by different treatments, with consistent effects observed in the combined Zn and tartaric acid treatment. Additionally, the combination of targeted amendments (TA) and Zn treatments proved beneficial in reducing soil pollution indicators. In conclusion, the synergistic application of Zn and tartaric acid demonstrated promising effects in mitigating arsenic-induced stress and optimizing the growth and physiology of Tagetes patula plants.

Study on Rice Phenological Differences under Heavy Metal Stress by Using Multi-source Remote Sensing Time-Series Images

Heavy metal pollution is surveyed rapidly and accurately, which is of great significance for soil pollution control. heavy metal pollution on farmland results in phenological changes, and we can use remote sensing technology to observe these changes. In the paper, Normalized Difference Vegetation Index (NDVI) time-series is built based on multi-source remote sensing images. Savitzky-Golay filter (S-G filter) was applied for denoising and reconstructing the time series. NDVI time series were used to calculate phenological indicators. Five phenological indicators were selected, which include seasonal amplitude, growth rate, seasonal length, seasonal integral and base level, to study on effect of heavy metal stress on rice phenology. The results showed that differences in phenological indexes at different levels of heavy metal stress as well as the phenological indicators under the stressed condition were generally lower than those under mild and moderate stress. From the findings, it can be concluded that the superiority of remote sensing phenological information in the monitoring of heavy metal stress in rice, and a new method for distinguishing heavy metal stress in rice will be provided.

Effect of Heavy Metal Stress on Phenolic Compounds Accumulation in Winter Wheat Plants.

Heavy metal stress can lead to many adverse effects that inhibit cellular processes at various levels of metabolism, causing a decrease in plant productivity. In response to environmental stressors, phenolic compounds fulfill significant molecular and biochemical functions in plants. Increasing the biosynthesis of phenolic compounds in plants subjected to heavy metal stress helps protect plants from oxidative stress. A pot experiment was carried out to determine the effect of the accumulation of copper (Cu) and lead (Pb) salts at concentrations of 200, 500, and 1000 ppm on seed germination, the activity of enzymes in the phenylalanine ammonia-lyase pathway (PAL) and tyrosine ammonia-lyase (TAL), along with the total phenol and flavonoid contents in seedlings of hybrid Triticum aestivum L. (winter wheat) cultivars. The accumulation of heavy metals, especially Cu, had a negative impact on the seed germination process. The cultivar "Hyacinth" reacted most strongly to heavy metal stress, which was confirmed by obtaining the lowest values of the germination parameters. Heavy metal stress caused an increase in the activity of PAL and TAL enzymes and an increase in the accumulation of phenolic compounds. Under the influence of Cu, the highest activity was shown in cv. "Hyvento" (especially at 200 ppm) and, due to the accumulation of Pb, in cv. "Hyacinth" (1000 ppm) and cv. "Hyking" (200 ppm). The cultivar "Hyking" had the highest content of phenolic compounds, which did not increase with the application of higher concentrations of metals. In other cultivars, the highest content of total phenols and flavonoids was usually observed at the lowest concentration (200 ppm) of the tested heavy metals, Cu and Pb.

Effects of Heavy Metal Stress on Physiology, Hydraulics, and Anatomy of Three Desert Plants in the Jinchang Mining Area, China.

The physiological mechanisms and phytoremediation effects of three kinds of native quinoa in a desert mining area were studied. We used two different types of local soils (native soil and tailing soil) to analyze the changes in the heavy metal content, leaf physiology, photosynthetic parameters, stem hydraulics, and anatomical characteristics of potted quinoa. The results show that the chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate of Kochia scoparia were decreased, but intercellular CO2 concentration (Ci) was increased under heavy metal stress, and the net photosynthetic rate (Pn) was decreased due to non-stomatal limitation. The gas exchange of Chenopodium glaucum and Atriplex centralasiatica showed a decrease in Pn, stomatal conductance (Gs), and transpiration rate (E) due to stomatal limitation. The three species showed a similar change in heavy metal content; they all showed elevated hydraulic parameters, decreased vessel density, and significantly thickened vessel walls under heavy metal stress. Physiological indicators such as proline content and activity of superoxide dismutase (SOD) and peroxidase (POD) increased, but the content of malondialdehyde (MDA) and glutathione (GSH), as well as catalase (CAT) activity, decreased in these three plants. Therefore, it can be concluded that these three species of quinoa, possibly the most dominant 30 desert plants in the region, showed a good adaptability and accumulation capacity under the pressure of heavy metal stress, and these plants can be good candidates for tailings remediation in the Jinchang desert mining area.

New Evidence of Semi-Mangrove Plant Barringtonia racemosa in Soil Clean-Up: Tolerance and Absorption of Lead and Cadmium.

Mangrove plants play an important role in the remediation of heavy-metal-contaminated estuarine and coastal areas; Barringtonia racemosa is a typical semi-mangrove plant. However, the effect of heavy metal stress on this plant has not been explored. In this study, tolerance characteristics and the accumulation profile of cadmium (Cd) and lead (Pb) in B. racemosa were evaluated. The results indicated that B. racemosa exhibited a high tolerance in single Cd/Pb and Cd + Pb stress, with a significant increase in biomass yield in all treatment groups, a significant increase in plant height, leaf area, chlorophyll and carotenoid content in most treatment groups and without significant reduction of SOD, POD, MDA, proline content, Chl a, Chl b, Chl a + b, Car, ratio of Chl a:b and ratio of Car:Chl (a + b). Cd and Pb mainly accumulated in the root (≥93.43%) and the content of Cd and Pb in B. racemosa was root > stem > leaf. Pb showed antagonistic effects on the Cd accumulation in the roots and Cd showed antagonistic or synergistic effects on the Pb accumulation in the roots, which depended on the concentration of Cd and Pb. There was a significant synergistic effect of Cd and Pb enrichment under a low Cd and Pb concentration treatment. Thus, phytoremediation could potentially use B. racemosa for Cd and Pb.

Mechanism of Lead-zinc Enrichment and Resistance of Spent Mushroom Compost to Lead-Zinc Slag in Koelreuteria paniculata

Phytoremediation is an ecological technique for tailing area restoration; adding substrate modifiers can reduce the stress of heavy metals on plants and enhance the restoration efficiency. The woody plant Koelreuteria paniculata was used as a test plant and potted in 100% tailings (S), 90% tailings+5% mushroom residue (SMC)+5% CaCO3 (MS), and natural red soil (RS). The effects of physiological responses and tolerance enrichment effects on Pb and Zn tolerance in K. paniculata under different treatments were investigated to compare the growth morphology, microscopic morphological changes, and microbial diversity changes in each substrate of K. paniculata seedlings. The results showed that compared with the control group S, the MS treatment group could significantly improve the structure and fertility of the tailing substrates; significantly enhance the relevant physiological indicators such as biomass, plant height, and chlorophyll content of K. paniculate; and increase the accumulated heavy metal content in K. paniculata. In the treatment group, the overall physiological indexes of MS compared to RS biomass and plant height were promoted, and the total root length increased up to 69.3%, whereas the average root diameter of RS in the treatment group decreased 118.7% compared to that in the control group S. The MS treatment group showed a 266.67% increase in Pb and Zn residue state, a significant decrease in the weak acid extractable state and oxide-bound state compared to that in the control group S. The heavy metals were less active for plant migration. Furthermore, most of the heavy metals were trapped in the roots of K. paniculata, and the changes in its root conformation indicated its strong adaptability in the face of high Pb stress. Transmission electron microscopy (TEM) analysis showed that the higher concentration of heavy metals in the S control damaged the cell wall structure and caused toxic effects on plant cells. The addition of the modifier effectively alleviated the effects of heavy metal stress on various tissues of K. paniculata, affected the structure of microbial communities, significantly increased microbial richness and diversity, and enhanced the adaptability of K. paniculata to heavy metals and phytoremediation ability.

Heavy Metal Toxicity in Plants: An Overview on Tolerance Mechanisms and Management Strategies

Heavy metals are one of the factors that pollute the environment and significantly affect soil fertility, plant physiology, development, and productivity. The tolerance of plants to toxicity depends on the species and tissue, element type, and duration of exposure to stress. Some special signal molecules such as nitric oxide (NO), hydrogen peroxide (H2O2), beneficial ions, hyperaccumulating plants, stress hormones, nanoparticles, organic compounds, and microbial applications can be recommended to alleviate the stress effects caused by toxic heavy metals in plants. Induction of other promising techniques like seed priming, active involvement of plant growth regulator, use of osmoprotectants, successful plant microbes’ crosstalk and recent utilization of nanoparticles are worth using strategies in mitigation of heavy metal stress in plants. These practices effectively regulate the activities of antioxidant enzymes for the alleviation of stress in plants, creditably improving the plant tolerance via preserving cell homeostasis and amending the adversative effects of heavy metal stress in plants. These inventive strategies offer an enriched understanding of how to boost crop productivity under heavy metal stress in order to decrease the risk to global food security.

Literature Review on the Effects of Heavy Metal Stress and Alleviating Possibilities through Exogenously Applied Agents in Alfalfa (Medicago sativa L.).

Heavy metals (HMs) are among the most important toxic agents since they reach the soil through various routes and accumulate in the food chain. Therefore, HMs induce problems in soil integrity and in plant, animal, and human health. Alfalfa (Medicago sativa L.) is a significant crop worldwide, utilized in animal production. Furthermore, because of its nitrogen-absorbing ability via symbiotic strains of bacteria, it increases soil productivity. However, there are relatively few studies investigating the effects of HMs and their alleviation possibilities on alfalfa plants. Therefore, the goal of this review is to clarify the current state of research into HM-induced alterations in alfalfa and to determine the extent to which externally applied microorganisms and chemical compounds can mitigate the negative effects. The aim is to indicate areas of development towards further understanding of HM detoxification in alfalfa and to identify future research directions.

Alleviation of Cadmium and Nickel Toxicity and Phyto-Stimulation of Tomato Plant L. by Endophytic Micrococcus luteus and Enterobacter cloacae.

Cadmium (Cd) and nickel (Ni) are two of the most toxic metals, wreaking havoc on human health and agricultural output. Furthermore, high levels of Cd and Ni in the soil environment, particularly in the root zone, may slow plant development, resulting in lower plant biomass. On the other hand, endophytic bacteria offer great promise for reducing Cd and Ni. Moreover, they boost plants’ resistance to heavy metal stress. Different bacterium strains were isolated from tomato roots. These isolates were identified as Micrococcus luteus and Enterobacter cloacae using 16SrDNA and were utilized to investigate their involvement in mitigating the detrimental effects of heavy metal stress. The two bacterial strains can solubilize phosphorus and create phytohormones as well as siderophores. Therefore, the objective of this study was to see how endophytic bacteria (Micrococcus luteus and Enterobacter cloacae) affected the mitigation of stress from Cd and Ni in tomato plants grown in 50 μM Cd or Ni-contaminated soil. According to the findings, Cd and Ni considerably lowered growth, biomass, chlorophyll (Chl) content, and photosynthetic properties. Furthermore, the content of proline, phenol, malondialdehyde (MDA), H2O2, OH, O2, the antioxidant defense system, and heavy metal (HM) contents were significantly raised under HM-stress conditions. However, endophytic bacteria greatly improved the resistance of tomato plants to HM stress by boosting enzymatic antioxidant defenses (i.e., catalase, peroxidase, superoxide dismutase, glutathione reductase, ascorbate peroxidase, lipoxygenase activity, and nitrate reductase), antioxidant, non-enzymatic defenses, and osmolyte substances such as proline, mineral content, and specific regulatory defense genes. Moreover, the plants treated had a higher value for bioconcentration factor (BCF) and translocation factor (TF) due to more extensive loss of Cd and Ni content from the soil. To summarize, the promotion of endophytic bacterium-induced HM resistance in tomato plants is essentially dependent on the influence of endophytic bacteria on antioxidant capacity and osmoregulation.

Microbial community succession in soils under long-term heavy metal stress from community diversity-structure to KEGG function pathways

Currently, understanding the structure and function of the microbial community is the key step in artificially constructing microbial communities to control soil heavy metal pollution. Abundant/rare microbial communities play different roles in different levels of concentrations. However, the correlation between heavy metals and rare/abundant subgroups is poorly understood. In this study, we used a metagenomics approach to comprehensively investigate the evolutionary changes in microbial diversity, structure, and function under different heavy metal concentration stress in soils surrounding gold tailings. The results show that the main pollutants were Pb, As, and Zn. Indigenous microorganisms have different responses to heavy metal concentrations. Bacteria are the main components of indigenous microorganisms, mainly including Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria. With the increase of heavy metal pollution, the relative abundance of Proteobacteria increased, and that of Actinobacteria decreased. Archaea was significantly inhibited by heavy metal stress and was more sensitive to heavy metal concentration. The response of fungi to heavy metal concentration was not obvious. The results of KEGG pathways showed that carbon fixation was inhibited with increasing heavy metal concentrations, while nitrogen metabolism was in contrast. Abundant subcommunity had a greater correlation mainly with metal resistance mechanisms, and rare subcommunity plays a key role for soil nutrient cycling such as N, S cycling in soils contaminated. Overall, this study provides a comprehensive analysis of the effects of heavy metal stress at different concentrations on microorganisms in farmland around gold tailings and reveals the relationship between heavy metals on KEGG pathways.

Micronutrient seed priming: new insights in ameliorating heavy metal stress.

Plants need to survive with changing environmental conditions, be it different accessibility to water or nutrients, or attack by insects or pathogens. Few of these changes, especially heavy metal stress, can become more stressful and needed strong countermeasures to ensure survival of plants. Priming, a pre-sowing hydration treatment, involves pre-exposure of plants to an eliciting component which enhance the plant's tolerance to later stress events. By considering the role of micronutrients in aiding plants to cope up under adverse conditions, this review addresses various aspects of micronutrient seed priming in attenuating heavy metal stress. Priming using micronutrients is an adaptive strategy that boosts the defensive capacity of the plant by accumulating several active or inactive signaling proteins, which hold considerable importance in signal amplification against the triggered stimulus. Priming induced 'defence memory' persists in both present generation and its progeny. Therefore, it is considered a promising approach by seed technologist for commercial seed lots to enhance the vigour in terms of seed germination potential, productivity and strengthening resistance response against metalloid stress. The present review provides an overview regarding the potency of priming with micronutrient to ameliorate harmful effects of heavy metal stress, possible mechanism how attenuation is accomplished, role of priming in enhancing crop productivity and inducing defence memory against the metalloid stress stimulus.

Effects of cadmium on oxidative stress and cell apoptosis in Drosophila melanogaster larvae

With the increase of human activities, cadmium (Cd) pollution has become a global environmental problem affecting biological metabolism in ecosystem. Cd has a very long half-life in humans and is excreted slowly in organs, which poses a serious threat to human health. In order to better understand the toxicity effects of cadmium, third instar larvae of Drosophila melanogaster (Canton-S strain) were exposed to different concentrations (1.125 mg/kg, 2.25 mg/kg, 4.5 mg/kg, and 9 mg/kg) of cadmium. Trypan blue staining showed that intestinal cell damage of Drosophila larvae increased and the comet assay indicated significantly more DNA damage in larvae exposed to high Cd concentrations. The nitroblue tetrazolium (NBT) experiments proved that content of reactive oxygen species (ROS) increased, which indicated Cd exposure could induce oxidative stress. In addition, the expression of mitochondrial adenine nucleotide transferase coding gene (sesB and Ant2) and apoptosis related genes (Debcl, hid, rpr, p53, Sce and Diap1) changed, which may lead to increased apoptosis. These findings confirmed the toxicity effects on oxidative stress and cell apoptosis in Drosophila larvae after early cadmium exposure, providing insights into understanding the effects of heavy metal stress in animal development.

تاثیر قارچ Piriformospora indica بر صفات مورفوفیزیولوژیک گیاه تربچه (Raphanus raphanistrum L.) در شرایط تنش فلزات سنگین

AbstractBackground and Objective: Piriformospora indica is an endophytic fungus, which transfers several benefits to hosts including enhance plant growth and induce tolerance to abiotic stress as heavy metals stress. The aim of this study was to investigate the effect of P. indica on some morphophysiological parameters of radish (Raphanus sativus) under normal conditions and heavy metal stress. Materials and Methods: This experiment was conducted as a factorial experiment in a completely randomized design with three replications in the greenhouse of Agricultural Faculty of Malayer University. The experimental factors included four heavy metals (zinc, nickel, lead and control) and three fungal inoculums (inoculated with spores and mycelium and non-inoculated). Shoot dry weight, relative water content, photosynthetic pigments, electrolyte leakage, total soluble carbohydrate, protein and proline contents were investigated parameters. Results: The results showed that the heavy metal stress significantly decreased dry weight, RWC, chlorophyll, total soluble carbohydrate, protein and proline contents; whereas inoculation with fungual spore and mycelium affected parameters such as proline, total soluble carbohydrate and protein and mitigated the adverse effect of heavy metal stress. Heavy metal stress with increasing electrolyte leakage causes membrane instability, whereas inoculation with P. indica especially spore decreased lipid peroxidation. Conclusion: Using biotic methods can play an important role in counteracting with toxic effect of heavy metals. Based on these results and because P. indica can be propagated axenically on various medium, it can be concluded that this endophytic fungus serves as a promising approach to clean soil contaminated with heavy metal ions.

PGPR-Mediated Plant Growth Attributes and Metal Extraction Ability of Sesbania sesban L. in Industrially Contaminated Soils

The release of harmful wastes via different industrial activities is the main cause of heavy metal toxicity. The present study was conducted to assess the effects of heavy metal stress on the plant growth traits, antioxidant enzyme activities, chlorophyll content and proline content of Sesbania sesban with/without the inoculation of heavy-metal-tolerant Bacillus gibsonii and B. xiamenensis. Both PGP strains showed prominent ACC-deaminase, indole acetic acid, exopolysaccharides production and tolerance at different heavy metal concentrations (50–1000 mg/L). Further, in a pot experiment, S. sesban seeds were grown in contaminated and noncontaminated soils. After harvesting, plants were used for the further analysis of growth parameters. The experiment comprised of six different treatments. The effects of heavy metal stress and bacterial inoculation on the plant root length; shoot length; fresh and dry weight; photosynthetic pigments; proline content; antioxidant activity; and absorption of metals were observed at the end of the experiment. The results revealed that industrially contaminated soils distinctly reduced the growth of plants. However, both PGPR strains enhanced the root length up to 105% and 80%. The shoot length was increased by 133% and 75%, and the fresh weight was increased by 121% and 129%. The proline content and antioxidant enzymes posed dual effects on the plants growing in industrially contaminated soil, allowing them to cope with the metal stress, which enhanced the plant growth. The proline content was increased up to 190% and 179% by the inoculation of bacterial strains. Antioxidant enzymes, such as SOD, increased to about 216% and 245%, while POD increased up to 48% and 49%, respectively. The results clearly show that the utilized PGPR strains might be strong candidates to assist S. sesban growth under heavy metal stress conditions. We highly suggest these PGPR strains for further implementation in field experiments.

Ecophysiological differences between five mangrove seedlings under heavy metal stress

It was studied for the effects of heavy metal stress on the antioxidant activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and lipid peroxidation (MDA) in the leaves of five mangrove plants. The results showed the protein concentrations were significantly higher in B. gymnorrhiza (7.55 mg prot /mL: Cu2+), K. obovata (11.21 mg prot/mL: Cd2+) and R. stylosa (12.51 mg prot/mL: Cd2+) (p < 0.05). Comparably, MDA contents were remarkably high in A. marina than other species under the same conditions (p < 0.05). The SOD, POD and CAT were observed to be significantly high in A. marina, A. corniculatum and B. gymnorrhiza under the same heavy metal treatment (p < 0.05). The PCA revealed that POD, SOD and MDA of five mangrove species were the major indices for response to heavy metal. And A. marina was more tolerant to heavy metal stress than others.