Hyperaccumulators are ideal plant species used for phytoremediation of soils contaminated by heavy metals. A full understanding of metal tolerance mechanisms of hyperaccumulators will facilitate ...enhancing their phytoremediation efficiency. However, how Cd affects N metabolism and which role plays the response of N metabolism to Cd toxicity in the tolerance of hyperaccumulators are still unknown. To clarify these questions, this study investigated the effects of various soil Cd levels on the concentrations of N forms and the activity of key enzymes involved in N metabolism in leaves of the Cd hyperaccumulator,
Solanum nigrum L. The results showed that its growth and all N metabolism indicators were normal at low Cd exposure (≤12
mg
kg
−1). At 24
mg
Cd
kg
−1 soil, nitrate assimilation indicators (nitrate concentration and activity of nitrate reductase) were reduced significantly, whereas most ammonia assimilation indicators (ammonium concentration and activity of glutamine synthetase) remained normal. However, when exposed to a higher Cd level (48
mg
kg
−1), growth and most N metabolism indicators were reduced significantly. Therefore, N metabolism in leaves of
S. nigrum could be tolerant of Cd toxicity to a certain extent (soil Cd concentration ≤12
mg
kg
−1), and this might be involved in the Cd-tolerance of this Cd-hyperaccumulator.
All plants in nature harbor a diverse community of endophytic bacteria which can positively affect host plant growth. Changes in plant growth frequently reflect alterations in phytohormone ...homoeostasis by plant-growth-promoting (PGP) rhizobacteria which can decrease ethylene (ET) levels enzymatically by 1-aminocyclopropane-1-carboxylate (ACC) deaminase or produce indole acetic acid (IAA). Whether these common PGP mechanisms work similarly for different plant species has not been rigorously tested.
We isolated bacterial endophytes from field-grown Solanum nigrum; characterized PGP traits (ACC deaminase activity, IAA production, phosphate solubilization and seedling colonization); and determined their effects on their host, S. nigrum, as well as on another Solanaceous native plant, Nicotiana attenuata. In S. nigrum, a majority of isolates that promoted root growth were associated with ACC deaminase activity and IAA production. However, in N. attenuata, IAA but not ACC deaminase activity was associated with root growth. Inoculating N. attenuata and S. nigrum with known PGP bacteria from a culture collection (DSMZ) reinforced the conclusion that the PGP effects are not highly conserved.
We conclude that natural endophytic bacteria with PGP traits do not have general and predictable effects on the growth and fitness of all host plants, although the underlying mechanisms are conserved.
Remediation of plant–microorganism–chelates synergy has been proposed as an effective remediation method for enhancing the removal efficiency of heavy metal. Manipulation of the antioxidative system ...increases plant tolerance, thereby potentially enhancing the uptake capacity to heavy metal. In this study, we investigated the possibility of improving the phytoextraction of Cd and the antioxidative defense of
Solanum nigrum L. by application of a new isolated strain (
Paecilomyces lilacinus NH1) (PLNH1) and citric acid (CA). The results showed that application of CA or PLNH1 significantly promoted
S. nigrum's growth under Cd stress, but the synergistic effect of CA and PLNH1 on
S. nigrum's growth was more obvious. The coexistence of CA and PLNH1 could enhance about 30% of Cd accumulation in different organs of
S. nigrum compared to the treatment without the addition of CA and PLNH1, whereas single CA or PLNH1 added treatment only enhanced about 10–15% of Cd accumulation in different organs of
S. nigrum. The antioxidative defense in
S. nigrum under Cd stress was significantly improved as result of application of CA and PLNH1. The responses of antioxidative enzymes to Cd stress significantly decreased following application of CA and PLNH1, and the oxidative stress experienced by the plant due to Cd in the soil was significantly alleviated.
► Endophyte LRE07 was inoculated into plant to improve Cd phytoremediation efficiency. ► Endophyte inoculation enhanced growth and total Cd-uptake of host plant. ► The beneficial effect of endophyte ...was more obvious at 10μM Cd. ► Possible mechanisms are enhancement of nutrition uptake and enzymes activities.
The aim of this work was to evaluate effects of endophytic bacterium inoculation on plant growth and assess the possible mechanism of endophyte in heavy metal phytoremediation. Seeds of Solanum nigrum L. were inoculated with endophyte Serratia nematodiphila LRE07 and were subjected to Cd in the growing medium. Cd produced a significant inhibition on plant growth and a reduction in the content of photosynthetic pigments. The inoculation of endophytic bacterium alleviated the Cd-induced changes, resulting in more biomass production and higher photosynthetic pigments content of leaves compared with non-symbiotic ones. The beneficial effect was more obvious at relatively low Cd concentration (10μM). Based on the alteration of nutrient uptake and activated oxygen metabolism in infected plants, the possible mechanisms of endophytic bacterium in Cd phytotoxicity reduction can be concluded as uptake enhancement of essential mineral nutrition and improvement in the antioxidative enzymes activities in infected plant.
Traditional metal chelators, such as ethylenediaminetetraacetic acid (EDTA), have been gradually replaced due to their poor biodegradability in soil and high risk of heavy metal leaching into ...groundwater, which pose high environmental risks to the health of humans and animals. In this study, a liquid amino acid fertilizer (LAAF, waste proteins from hydrolysates of animal carcasses) and polyaspartate (PASP) were used as additives to enhance the phytoextraction of cadmium (Cd) and lead (Pb) from contaminated soil. We conducted pot experiments to investigate the phytoextraction capacity of Solanum nigrum, a Cd accumulator, grown on soil highly contaminated with Cd and Pb in the absence (as controls) or presence of PASP and LAAF. Both PASP and LAAF significantly improved plant growth, Cd accumulation, and total Cd and Pb content in S. nigrum shoots and roots. PASP and LAAF application promoted Cd translocation from roots to shoots in S. nigrum and Cd bio-accessibility in rhizosphere soils, but this was not the case for Pb. Both PASP and LAAF increased Cd and Pb phytoextraction by S. nigrum plants, and Cd phytoextraction was more effective in LAAF-assisted S. nigrum than in PASP-assisted S. nigrum. These findings demonstrate that the low cost and ecofriendly features of recycled waste proteins make them good candidates for chelant-enhanced phytoextraction from heavy metal-contaminated soils.
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•PASP or LAAF significantly enhanced the growth of S. nigrum.•PASP or LAAF significantly improved Cd concentration, total Cd and Pb amounts in S. nigrum.•PASP or LAAF elevated Cd translocation from roots to shoots in S. nigrum.•PASP or LAAF increased available Cd while decreased available Pb.•LAAF is more effective than PASP on Cd phytoextraction.
Electrokinetics is a new attempt of strengthening hyperaccumulator Solanum nigrum L. Cd extraction. The effects of different electric fields and electrodes on S. nigrum accumulating Cd among of four ...electric field conditions (1 V cm−1) and two electrodes were determined. The results showed that the AC electric field significantly stimulated (p < 0.05) the growth of S. nigrum, and the biomass increased nearly by 40% compared with the control, while the DC electric field (including the switching polarity) had no significant effect. Electric field significantly increased (p < 0.05) Cd concentration in S. nigrum and the highest one was recorded for the DC electric field with switching polarity. S. nigrum Cd accumulation (ug pot−1) was the highest under the AC electric field, which was nearly 70% higher compared to the control. The innovation found was that the role of biomass enhancement for S. nigrum accumulating Cd (ug pot−1) was the first and increased Cd concentration was secondary under AC electrical field, which might be relative with S. nigrum is a weed species. Basically, there was no significant difference between the graphite and stainless steel electrode, but under AC electric field conditions, Cd accumulation of S. nigrum was significantly higher (p < 0.05) than stainless steel electrode, which is worthy of further revelation besides of statistic factor. In general, the accumulation (ug pot−1) of Cd by S. nigrum was the highest under the AC electric field, which was a very important reference for the electrokinetic conditions to be used in the practice of phytoremediation.
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•Appropriate electric field increased the concentration of extractable Cd in soil.•AC electric field improved the growth and Cd accumulation of Solanum nigrum L.•The effects of stainless steel electrode and graphite electrode on S. nigrum accumulating Cd were basically same.
A microcosm experiment with artificially contaminated soils was conducted in a greenhouse to evaluate the effect of gibberellic acid 3 (GA3) on phytoremediation efficiency of Solanum nigrum L. The ...GA3 was applied at three different concentrations (10, 100, 1000 mg L⁻¹) to S. nigrum. Results indicated that GA3 can significantly (p < 0.05) increase the biomass of S. nigrum by 56 % at 1000 mg L⁻¹. Concurrently, GA3 application increased Cd concentrations in the shoot of S. nigrum by 16 %. The combined effects resulted in an increase in the amount of Cd extracted by a single plant by up to 124 %. Therefore, it is possible to use GA3 to promote the Cd phytoremediation efficiency of S. nigrum.
In the current experiment, influence of NPK composition on the Cd contaminated soil-plant (Solanum nigrum L.) system as well as the phytoremediation efficiency were comprehensively studied. The ...composition of NPK was optimized for a sustainable phytoremediation and simultaneous agronomic technique in Cd-contaminated soil by orthogonal (L14) experiment, aimed to achieve plant productivity and maximum phytoremediation potential enhancement. Results showed that different treatments of NPK composition enhanced soil properties including saccharase, urease, catalase and acid phosphatase activities as compared to the control treatment, however, soil pH was slightly decreased by 3.64%~6.67% with different composition of NPK treatments. Plant biomass and Cd concentration in the aboveground part (stem and leaves) of S. nigrum were significantly (P < 0.05) enhanced by 14.19%~48.97% and 38.50%~127.15% as compared to control plants with the addition of NPK fertilizers having different composition. Meanwhile, with the application of NPK fertilizer root/shoot Cd ratio and translocation factor (TF) was significantly decreased, however, bioconcentration factor (BCF) was increased as compared to control. Additionally, different composition of NPK fertilizers significantly increased photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids) and soluble protein in comparison to control. The activities of antioxidant enzymes in S. nigrum including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) were increased, while malonaldehyde (MDA) and proline contents were decreased. Principal component analysis (PCA) showed that N3P2K2 treatment had the highest comprehensive score amongst other studied treatments of NPK composition, owing to its optimal composition for the investigated soil-S. nigrum system. Moreover, it was found that optimal composition (N3P2K2) of fertilizer resulted in increase of the plant resistance to Cd and the efficiency of phytoextraction. Therefore, it is suggested to all the small-holder famers and scientific community that precise composition of NPK fertilizer should be utilized according to soil properties, environmental conditions and plant requirements under Cd-stress condition in order to achieve maximum biomass, Cd uptake efficiency as well phytoremediation potential in moderately Cd contaminated soil.
•Holistic NPK composition based sustainable phytomanagement strategy proposed.•A correlation was found among soil properties and plant growth under Cd stress.•NPK fertilization influenced plant growth via improving soil nutrient quality.•Optimal NPK (N3P2K2) composition improved Cd phytoremediation efficiency.•Optimal NPK composition was suggested for remediation moderately Cd contaminated soil.
Cadmium (Cd) triggers molecular alterations in plants, perturbs metabolites and damages plant growth. Therefore, understanding the molecular mechanism underlying the Cd tolerance in plants is ...necessary for assessing the persistent environmental impact of Cd. In this study, Solanum nigrum was selected as the test plant to investigate changes in biomass, Cd translocation, cell ultrastructure, metabolites and genes under hydroponic conditions. The results showed that the plant biomass was significantly decreased under Cd stress, and the plant has a stronger Cd transport capability. Transmission electron microscopy revealed that increased Cd concentration gradually damaged the plant organs (roots, stems and leaves) cell ultrastructure, as evidenced by swollen chloroplasts and deformed cell walls. Additionally, metabolomics analyses revealed that Cd stress mainly affected seven metabolism pathways, including 19 differentially expressed metabolites (DEMs). Moreover, 3908 common differentially expressed genes (DEGs, 1049 upregulated and 2859 downregulated) were identified via RNA-seq among five Cd treatments. Meanwhile, conjoint analysis found several DEGs and DEMs, including laccase, peroxidase, D-fructose, and cellobiose etc., are associated with cell wall biosynthesis, implying the cell wall biosynthesis pathway plays a critical role in Cd detoxification. Our comprehensive investigation using multiple approaches provides a molecular-scale perspective on plant response to Cd stress.
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•Cadmium (Cd) accumulation damages the cell ultrastructure of plant tissues.•The cell walls and vacuoles play a vital role in detoxification of Cd.•Cd phytotoxicity has an adverse effect on the metabolome and transcriptome.•Cd significantly interferes with the cell wall synthesis and metabolism pathway.•Induction of cell wall biosynthesis pathway may associate with Cd concentrations.
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