Bioaccumulation and Physiological Response of Five Willows to Toxic Levels of Cadmium and Zinc

We evaluated the phytoremediation potential of Salix spp. exposed to high cadmium (Cd) and zinc (Zn) concentrations to select feasible plant materials for restoration and revegetation of mining soil contaminated by heavy metals on the basis of their Cd and Zn accumulation, Cd-Zn interaction on bioaccumulation, and the changes of photosynthetic parameters. The Cd and Zn concentrations were in the order of root > leaf > stem, regardless of the species. In the combined Cd and Zn treatment, the leaf and stem Cd concentration in all species were higher relative to Cd-alone treatment. In contrast, the Zn concentration in plant tissues when exposed to the combined Cd + Zn treatment decreased relative to the Zn-alone treatment. The translocation factor (TF) of Cd and Zn from root to leaf was generally higher compared to TF from root to stem than those in the single treatment. The Cd + Zn treatments resulted in enhanced translocation of Cd from root to aboveground tissue (synergistic), while the same treatment suppressed the Zn translocation from root to leaf and stem (antagonistic). The reduction of photosynthetic parameters in Zn alone and Cd + Zn treatments was generally higher than that of Cd-alone treatment. Among the different species, S. caprea and P. alba×glandulosa have the lowest photosynthetic reduction relative to the control. Overall, S. caprea could be a potential candidate for phytoremediation of Cd- and Zn-contaminated sites.     

Piriformospora indica?rescues growth diminution of rice seedlings during high salt stress

Piriformospora indica association has been reported to increase biotic as well as abiotic stress tolerance of its host plants. We analyzed the beneficial effect of P. indica association on rice seedlings during high salt stress conditions (200 and 300 mM NaCl). The growth parameters of rice seedlings such as root and shoot lengths or fresh and dry weights were found to be enhanced in P. indica-inoculated rice seedlings as compared with non-inoculated control seedlings, irrespective of whether they are exposed to salt stress or not. However, salt-stressed seedlings performed much better in the presence of the fungus compared with non-inoculated control seedlings. The photosynthetic pigment content [chlorophyll (Chl) a, Chl b, and carotenoids] was significantly higher in P. indica-inoculated rice seedlings under high salt stress conditions as compared with salt-treated non-inoculated rice seedlings, in which these pigments were found to be decreased. Proline accumulation was also observed during P. indica colonization, which may help the inoculated plants to become salt tolerant. Taken together, P. indica rescues growth diminution of rice seedlings under salt stress.     

Chromate resistantBacillus cereus augments sunflower growth by reducing toxicity of Cr (VI)

Impact of four chromium resistant bacterial strains (S3, S4, S6, and S7) was studied on the different growth parameters of sunflower (Helianthus annuus var SF-187) in chromium free or under chromium stress. Strains used exhibited very high-level resistance to chromate (up to 50 mg ml^-1 on nutrient agar and 1-2 mg ml^-1 in minimal medium). Application of Cr(VI) salt adversely affected the seed germination, root and shoot length, and fresh weight of seedlings. Bacterial inoculations improved the growth parameters. The effects of Cr(VI) on the different biochemical parameters were also very severe but seedlings inoculated with bacteria showed much improvements as compared to non-inoculated controls. Uptake of Cr(VI) was higher than Cr(III) by the seedlings. Inoculated seedlings contained less chromium than non-inoculated seedlings. Much improvement in the internal region of root and shoot was observed in inoculated plants especially in guard cells.     

Long-term effects of exogenous silicon on cadmium translocation and toxicity in rice (Oryza sativa L.)

Most nutrient solution studies on the interactions between silicon (Si) and cadmium (Cd) are short term. Here we reported a long-term experiment in which rice (Oryza sativa L.) was cultured for 105 days and harvested at four different growth stages to measure biomass accumulation and Cd uptake and distribution in shoots and roots. Exogenous Si increased shoot biomass by 61–238% and root biomass by 48–173% when the culture solution was free of Cd. When 2 μmol L^?1 Cd was added, Si supply increased shoot and root biomass by 125–171% and by 100–106% compared to the zero-Si treatment. Increasing the Cd concentration to 4 μmol L^?1 decreased the beneficial effects of Si on root and shoot biomass. Silicon supply decreased shoot Cd concentrations by 30–50% and Cd distribution ratio in shoot by 25.3–46%, compared to the treatment without Si supply. Additionally, lower Si supply or more serious Cd stress would lead to roots with bigger biomass and higher Si concentration. Energy-dispersive X-ray microanalysis showed that both Si and Cd accumulated synchronously in the border and middle of phytoliths of the shoots. We conclude that Si enhances plant growth and decreases Cd accumulation in shoots and thereby helps to lower the potential risks of food contamination.     

Root foraging for zinc and cadmium requirement in the Zn/Cd hyperaccumulator plant Sedum alfredii

Positive root response to metals may enhance metal accumulation for greater requirement in hyperaccumulators. The effects of spatially heterogeneous Zn/Cd addition on root allocation, metal accumulation, and growth of the Zn/Cd hyperaccumulator Sedum alfredii were assessed in a pot experiment. Young shoots of S. alfredii were grown with or without supplied Zn/Cd. Two concentrations were used of each metal, and each metal concentration had one homogeneous and two heterogeneous treatments. Growth increased by 1.6–3.2 times with the increasing overall dose of Zn/Cd addition, and shoot biomass was positively correlated with shoot Zn/Cd concentration (P?<?0.001). In all heterogeneous treatments, the plants consistently allocated approximately 90% of root biomass to the metal-enriched patches, and shoot Zn/Cd contents were greater than or similar to those in the homogeneous treatment at each metal concentration. Plants in the control treatment showed symptoms of Zn deficiency, although their shoots had Zn concentrations 100-fold higher than the critical deficiency value for most plants. We conclude that S. alfredii has evolved root foraging mechanisms associated with its greater requirements for Zn/Cd. These results could have important implications both for phytoremediation and for investigation of positive role of Cd in higher plants.     

Interactions between root and shoot competition among four plant species in an alpine meadow on the Tibetan Plateau

At low altitudes, the interactions between root and shoot competition on plant growth have been extensively studied, and such interaction effects were found to be positive, negative, or neutral. However, little is known about such effects at high altitudes where the environmental conditions are harsher than those at low altitudes. We carried out a field experiment in an alpine meadow in the northeast Tibetan Plateau to test the hypothesis that a negative interaction between root and shoot competition exists for alpine plant species. Root and shoot competition were experimentally manipulated in the four grass species (Kobresia humilis, Saussurea superba, Stipa aliena and Elymus nutans). We found that K. humilis and S. aliena grew better without competition, whereas S. superba grew better with shoot competition and E. nutans grew better with root competition. The interactions between root and shoot competition were negative in K. humilis, positive in S. superba, but neutral in S. aliena and E. nutans, suggesting that the interaction effects are species-specific. This study also suggested that alpine plants may trade off both plant–plant interactions and competition shift between root and shoot to adapt to stressful environments.     

Effects of bacterial single inoculation and co-inoculation on growth and phytohormone production of sunflower seedlings under water stress

The purpose of the study was to measure shoot and root dry matter (DM) and production of auxins, salicylic acid, abscisic acid, and jasmonic acid in sunflower (Helianthus annuus L.) seedlings cultivated under water stress and singly inoculated or co-inoculated with Achromobacter xylosoxidans (SF2) and Bacillus pumilus (SF3 and SF4) bacterial strains. Shoot DM was higher in non-stressed seedlings than in stressed seedlings for all inoculation treatments. Water stress resulted in decreased relative water content and reduction of shoot DM. Root DM was higher in stressed seedlings than in non-stressed seedlings. Salicylic acid was the most abundant phytohormone in shoots of stressed, singly inoculated and co-inoculated seedlings. High salicylic acid content in stressed seedlings suggests that this hormone plays a key role in abiotic stress. Abscisic acid was higher in stressed and co-inoculated seedlings than in non-stressed seedlings but was lower than that of salicylic acid. Auxin profile was similar to that of abscisic acid in co-inoculated seedlings. Shoot jasmonic acid content was increased in stressed seedlings co-inoculated with SF2/SF3 or SF2/SF4. Shoot hormonal profiles were different from those of root, suggesting a differential effect of bacterial inoculation on these plant organs. Our findings will be useful in future strategies to mitigate drought effects on crop plants through bacterial inoculation treatments.     

Bioaccumulation and translocation of heavy metals by Plantago major L. grown in contaminated soils under the effect of traffic pollution

The present study was performed at a heavy-traffic affected soil to examine the efficacy of bioaccumulation and translocation potentials of heavy metals by the naturally growing weed Plantago major. Heavy metals were analyzed in soil as well as in plant below- and above-ground parts along different distances from a heavy-traffic highway. All the investigated soil heavy metals, except Cd, varied significantly, while pH and E.C had no significant difference, with increasing distance from the highway. Likewise, there was a significant decrease of heavy metals in plant below- and aboveground parts. In addition, no significant difference between most soil and root heavy metals at 20 and 100 m as well as those at 500 and 750 m distance from the highway. The bioaccumulation factor (BF) of all heavy metals, except Cd and Sr, were less than unity at most distances. However, Cd showed relative BF decline with the distance in contrast to Sr, which increases as distance from the highway increases. On the other hand, the translocation factors (TF) of Cd, Co, Cu, Pb and Zn were higher at the distances far from the highway, while that of Fe, Cr and Sr were higher near the highway. Furthermore, the enrichment factor (EF) showed small variations, among the investigated heavy metals, with varying distances from the pollution source. It was found that soil Fe, Al, Cr, Ni, Sr, V and Zn had significant positive correlation with all investigated heavy metals in P. major roots. The higher TFs of Cd, Fe and Pb in P. major shoots makes it suitable for phytoextraction from soil, while the lower ratios of Al, Mn, V, Co, Ni, Cr, Zn, Cu and Sr make it suitable for their phytostabilization. Therefore, this plant can be used as a bioindicator and biomonitor for traffic related heavy metals.     

Bioaccumulation of Trace Elements in Trophic Levels of Wetland Plants and Waterfowl Birds

Present study investigates relationships between total and bioaccessibility of trace elements (Cd, Co, Cr, Cu, Mn, NI, Pb, V, and Zn) concentrations in sediment and their bioaccumulation in species in Shadegan wetland in southwest of Iran. Bioavailability factor (BAF) and translocation factor (TF) were calculated in plants and trophic transfer factor (TTF) was determined in bird species. For this purpose, sampling of sediments, aquatic plants including Phragmites australis, Typha australis, Scripus maritimus and two bird species encircling Porphyrio porphyrio and globally threatened Marmaronetta angustirostris were carried out during winter 2009. Result of chemical analysis show that bioaccessibility concentrations of Mn (8.31 mg/kg), V (1.33 mg/kg), and Pb (1.03 mg/kg) are higher than other metals. The uptake trend of trace elements in plant decreases as root > stem > leaf. Accumulation levels of trace elements in different tissues of P. porphyrio and M. angustirostris are almost identical and considerable. Accumulation and toxicity of Cd in birds is more than plants. In addition, BAF of V, Pb, and Cr indicates high accumulation by plants and great pollution rate in the area of study. In S. maritimus TF for Mn, Cu, Pb, and V are high whereas in T. australis, Cu and Pb posses the highest TF. Also Cr, Co, Mn, Ni, and Zn have higher TF from stem to leaf than root to stem in P. australis. Finally, TTFs were compared in various bird species.     

Hyperaccumulation of cadmium in Matricaria chamomilla: a never-ending story?

Chamomile (Matricaria chamomilla L.) is a widely used medicinal plant but may also accumulate metals including cadmium. Because recent paper (Masarovi?ová et al. 2010 Acta Physiol Plant 32:823–829) contradicts previous results of our research group and suggested Cd “hyper/accumulation” in chamomile, present study examined Cd uptake in a long-term experiment (7 weeks) using low Cd concentration (1.5 μM). Besides, typical Cd hyperaccumulator Thlaspi caerulescens and Ni hyperaccumulator Thlaspi goesingense were also cultured under identical conditions. Data obtained indicate that shoot Cd content and bioaccumulation factor (BAF) in chamomile was ca. 5–10 times lower than that in Thlaspi. In this view, chamomile is not a hyperaccumulator species. Comparison of shoot Cd content, BAF and translocation factor (TF) in selected crops is also provided.     

Salicylic acid-mediated alleviation of cadmium toxicity in hemp plants in relation to cadmium uptake,photosynthesis, and antioxidant enzymes

To assess the role of salicylic acid (SA) in alleviating cadmium (Cd) toxicity in hemp (Cannabis sativa L.) plants, the growth parameters, Cd accumulation, photosynthetic performance and activities of major antioxidant enzymes were investigated in hemp seedlings treated with 500 μM SA, under 0, 25, 50, and 100 mg Cd kg⁻¹ sands (DW) conditions, respectively. Cd exposure resulted in a small reduction in biomass (12.0–26.9% for root, and 8.7–29.4% for shoot, respectively), indicating hemp plants have innate capacity to tolerant Cd stress. This was illustrated by little inhibition in photosynthetic performance, unchanged malondialdehyde content, and enhancement of superoxide dismutase (SOD) and peroxidases (POD) activities in hemp plants. Cd content in root is 25.0–29.5 times’ higher than that in shoot, suggesting the plant can be classified as a Cd excluder. It is concluded that SA pretreatment counteracted the Cd-induced inhibition in plant growth. The beneficial effects of SA in alleviating Cd toxicity can be attributed to the SA-induced reduction of Cd uptake, improvement of photosynthetic capacity, and enhancement of SOD and POD activities.     

Endophytic fungus Serendipita indica increased nutrition absorption and biomass accumulation in Cunninghamia lanceolata seedlings under low phosphate

Cunninghamia lanceolata is important forest tree species in southern China, and its successive plantations resulted in degradation of soil fertility in pure stands, causing decline in forest productivity. How to improve productivity in C. lanceolata pure stands is a tough task. Usage of mycorrhizal fungi might be a plausible access to the task. The objective is to study the possibility of the endophytic fungus Serendipita indica (named formerly as Piriformospora indica) in culture of C. lanceolata. Seeds were sowed in plastic pots with river sand. When seedlings had two true leaves, hyphae suspension solution of S. indica was added to near the roots of seedlings in each plastic pot. Such pots with seedlings were placed in a greenhouse and normal management was carried out for the seedlings. Symbiosis effects on root development, nutrition uptake and allocation, and biomass accumulation of C. lanceolata seedlings under low phosphate were investigated. The results showed that S. indica could symbiose with C. lanceolata. The symbiosis did not result in significant changes in root system architecture under low phosphate, but significantly increased nitrogen and phosphorus levels in leaves under low phosphate. Although the symbiosis did not significantly increased nitrogen allocation in leaves under low phosphate, it significantly increased phosphorus allocation in leaves. The interaction between S. indica and C. lanceolata resulted in increase in total biomass under low phosphate and changes in biomass allocation between shoots and roots. The results suggested that S. indica helps host plants to absorb more nutrients under low phosphate and to allocate more nitrogen and phosphate to leaves, promoting plant growth; the fungus might be used in pure stands of C. lanceolata because of its large-scaled axenic culture.     

Photosynthetic pigments content, <Emphasis Type="Italic">δ</Emphasis>-aminolevulinic acid dehydratase and acid phosphatase activities and mineral nutrients concentration in cadmium-exposed <Emphasis Type="Italic">Cucumis sativus</Emphasis> L.

In this study, the effects of cadmium chloride (CdCl₂) on plant growth, histology of roots, photosynthetic pigments content, δ-aminolevulinic acid dehydratase (ALA-D; E.C. 4.2.1.24) and acid phosphatase activities (AP; E.C. 3.1.3.2), soluble phosphorus (Pi) measurement and mineral nutrients content in cucumber seedlings (Cucumis sativus L.) were investigated. Cucumber seedlings were grown in vitro in an agar-solidified substrate containing four CdCl₂ treatments (0, 100, 400, and 1000 μM) for ten days. Cd was readily absorbed by seedlings and its content was greater in the roots than in the shoot. Cd reduced shoot and root length, and fresh and dry biomass of seedlings. Inhibition of root cell elongation in Cd-treated seedlings was observed by the increase of the mean radial size of cells belonging to three zones of the root tip. The highest level of Cd reduced in a similar manner chlorophyll a, chlorophyll b and total chlorophyll contents. Increasing concentrations of Cd resulted in a linear decrease in carotenoids levels of cotyledons. Interestingly, the ALA-D activity in cotyledons was inhibited only at the highest level of Cd. Root and shoot AP activities were, respectively, activated and inhibited at all CdCl₂ concentrations. Root Pi concentration was increased in all Cd treatments and it was not altered in the shoot tissues. Moreover, in general, the nutrient contents were increased in the root and decreased in the shoot. Therefore, we suggest that Cd affects negatively growth, photosynthetic pigments, ALA-D and AP activities and partition of mineral nutrients in cucumber seedlings.     

Multi-Wall Carbon Nanotubes Effects on Plant Seedlings Growth and Cadmium/Lead Uptake In Vitro

The effects of multi-wall carbon nanotubes (MWCNTs) on plant growth and Cd/Pb accumulation was investigated on seedlings of three plant species including Brassica napus L., Helianthus annus L. and Cannabis sativa L. The experiment consisted of MWCNTs on three concentration levels (0, 10, 50 mg/L) and 200 μM CdCl₂ or 500 μM Pb(NO₃)₂. MWCNTs application effectively improved root and shoot growth inhibited by Cd and Pb salts. In B. napus, total chlorophyll (Chl) content increased by both MWCNTs 10 and 50 mg/L exposure under cadmium or lead stress. MWCNT 10 mg/L mitigated the deleterious effects of Cd ions on total chlorophyll content of H. annus and C. sativa. Wherease higher concentration of MWCNTs decreased Chl content under either Cd or Pb treatments on sunflower seedlings. MWCNT10 effectivly raised cadmium accumulation in seedlings of all three species. MWCNT10 and 50 mg/L also caused higher Pb accumulation in canola and cannabis seedlings, respectively. Based on the results, it seems that the effects of MWCNTs on growth parameters and heavy metal accumulation in plant seedlings is strongly depends on heavy metal type, MWCNTs concentration and plant species.     

Response of sunflower (Helianthus annuus L) genotypes to PEG-mediated water stress

Drought tolerance of two sunflower (Helianthus annuus L.) genotypes, cultivated cultivar 1114 and interspecific line H. annuus × H. mollis, was studied under laboratory conditions using PEG-6000. Four levels of osmotic stress (?0.4, ?0.6, ?0.8 and ?1.0 MPa) were created and performances were monitored against a control. Physiological and biochemical stress determining parameters such as malondialdechyde (MDA), proline content, and hydrogen peroxide (H₂O₂) were compared between seedlings of both genotypes. The results indicated that both genotypes have similar responses at four osmotic potentials for all traits studied. All seedling growth parameters such as germination percentage, root length, shoot length, root and shoot dry weight decreased with increasing osmotic stress. MDA, proline, and H₂O₂ were found to be increased at different osmotic gradients in comparison to control. Cultivar 1114 was less affected than the interspecific line under these stress conditions. The data observed in the experiments revealed that perennial wild H. mollis can hardly be considered to be an excellent candidate of drought tolerance genes.     

Non-invasive microelectrode cadmium flux measurements reveal the spatial characteristics and real-time kinetics of cadmium transport in hyperaccumulator and nonhyperaccumulator ecotypes of Sedum alfredii

This study aims to determine the spatial characteristics and real-time kinetics of cadmium transport in hyperaccumulator (HE) and non hyperaccumulator (NHE) ecotypes of Sedum alfredii using a non-invasive Cd-selective microelectrode. Compared with the NHE S. alfredii, the HE S. alfredii showed a higher Cd influx in the root apical region and root hair cells, as well as a significantly higher Cd efflux in the leaf petiole after root pre-treatment with cadmium chloride (CdCl₂). Thus, HE S. alfredii has a higher capability for the translocation of absorbed Cd to the shoot. Moreover, the mesophyll tissues, isolated mesophyll protoplasts, and intact vacuoles from HE S. alfredii exhibited an instantaneous influx of Cd in response to CdCl₂ treatment with mean rates that are markedly higher than those from NHE S. alfredii. Therefore, the hyper-accumulating trait of HE S. alfredii is characterized by the rapid Cd uptake in specific root regions, including the apical region and root hair cells, as well as by the rapid root-to-shoot translocation and the highly efficient Cd-permeable transport system in the plasma membrane and mesophyll cell tonoplast. We suggest that the non-invasive Cd-selective microelectrode is an excellent method with a high degree of spatial resolution for the study of Cd transport at the tissue, cellular, and sub-cellular levels in plants.     

Cadmium accumulation and tolerance of Lagerstroemia indica and Lagerstroemia fauriei (Lythraceae) seedlings for phytoremediation applications

Contamination by heavy metals is one of the most serious environmental problems generated from human activities. Because phytoremediation utilizes plants to uptake contaminants, it could potentially be used to remediate metal-contaminated areas. A pot culture experiment with four levels of cadmium (Cd) (0, 20, 40, and 80 mg of Cd/kg dry soil) was conducted to investigate Cd accumulation and tolerance of roots, shoots, and leaves of Lagerstroemia indica and Lagerstroemia fauriei as well as their potential for phytoremediation. Experimental results indicated that Cd inhibited seedling growth only at the higher Cd exposure concentration (40 and 80 mg/kg). The tolerance index revealed that on average L. indica is more tolerant of Cd than L. fauriei. Moreover, plants in the experiment accumulated Cd differentially. In comparisons between L. indica and L. fauriei, the leaves of the former had higher concentrations of Cd, while the roots of latter had higher concentrations of Cd. Furthermore, the roots, shoots, and leaves had very high bioaccumulation factors that markedly exceeded 1.0 (exceptional only in shoots of 80 mg/kg for L. fauriei), indicating that the seedlings extracted Cd from the soil. The leaves' translocation factor of L. indica was greater than 1.0, being significantly higher than that of L. fauriei. Chlorophyll a, Chlorophyll b and total declined in both species significantly as Cd concentrations exceeded 40 mg/kg in the soil. In contrast, lipid peroxidation and proline content was found to increase with increasing Cd concentration. From the assessments of biomass production, Cd tolerance and uptake L. indica and L. fauriei could stand as excellent species for remediating Cd-contaminated soils.     

Cadmium accumulation and its effects on physiological and biochemical characters of summer savory (Satureja hortensis L.).

Abstract

The objective of this study was to determine the effects of cadmium (Cd) toxicity on accumulation, growth, physiological responses, and biochemical characters in summer savory (Satureja hortensis L.). Plants were subjected to different levels of Cd concentrations including 0 (control), 2.5, 5, and 15?mg L^?1 in the growing medium. Cd exposure led to a significant increase in root and shoot Cd content. Calculation of bioaccumulation factor, translocation factor, and transfer coefficient revealed that Cd mostly accumulated in roots of S. hortensis and root to shoot transport was effectively restricted. Cd toxicity negatively affected plant growth and significantly reduced chlorophyll content. Contrarily, proline, soluble and reducing carbohydrates, anthocyanin content, and the activity of antioxidant enzymes significantly increased as a result of Cd exposure. Cd application led to a significant increase in essential oil content of S. hortensis. GC-MS analysis revealed that percentage main constitute of S. hortensi, carvacrol, which determines the quality of oil increased under the highest Cd treatment. Based on our findings, S. hortensis can be considered an invaluable alternative crop for mildly Cd-contaminated soils. Besides, due to the high potential of Cd accumulation in the root, S. hortensis may offer a feasible tool for phytostabilization purposes.     

Water relations and drought tolerance of young African tamarind (Tamarindus indica L.) trees

Tamarindus indica L. is an important multipurpose tree, indigenous to Africa, now introduced worldwide and known for its drought tolerance. The effects of drought on tamarinds, especially at seedling stage, are hardly investigated. However, this information is important for its conservation and domestication. In a growth chamber experiment we investigated the water relations of African tamarind seedlings under short-term soil drought stress. Initially tamarind seedlings can be considered as drought-tolerant at the expense of internal water storage reserves as they keep on transpiring (sap flow) and growing (diameter fluctuations). They finally spent 20% of their stem and root water storage reserves and experienced stem water potentials near − 3 MPa. Therefore, they can be classified as anisohydric. Their risk-taking behavior led to a high rate of seedling mortality (50%) because of whole plant hydraulic failure. They were not hydraulically efficient and they possessed low water storage capacity in stem and root (45%) due to high tissue density. When re-irrigated, remaining seedlings recovered slowly as a consequence of non-stomatal limitations and partial shoot dieback. Although tamarind seedlings show traits related to drought tolerance, we suggest that the species contains some water saving mechanisms. Contrasts with the co-occurring water-conserving tree species baobab (Adansonia digitata L.) are also discussed.