Crystallization of poorly crystalline minerals generally remobilizes the adsorbed heavy metals. In contrast, we find that the conversion of poorly crystalline layered δ-MnO2 to crystalline 2 × 2 tunneled α-MnO2 significantly increases both the amount and stability of Pb2+ immobilization. The varied characterization analyses reveal that Pb2+ first exchanges surface K+ associated with δ-MnO2 and is then sequestered into α-MnO2 2 × 2 tunnels via oriented attachment along the (001) plane. Without the crystallization process, Pb2+ cannot substitute for tunnel K+ in α-MnO2 and can only weakly bind to the external (310) surface. Stability comparisons across outer-surface adsorption, wall substitution, and tunnel incorporation indicate that only tunnel-resident metals achieve strongly enhanced and persistent Pb sequestration. This study not only challenges the conventional understanding that mineral crystallization and layer-to-tunnel transformation lead to the release of adsorbed heavy metals but also suggests a potential strategy for selective metal trapping in engineered remediation materials and environmental matrices.

Excessive cadmium (Cd) accumulation in rice poses significant risks to public health. Wild rice as the ancestor of cultivated rice is regarded as a treasure trove of rice germplasm resources. Two wild rice Oryza officinalis Wall. and Oryza rufipogon Griff. were used as test materials to understand the response of morphological traits and anatomy structure of wild rice roots to Cd treatments (0, 1, 5, 15, and 30 mg·kg− 1). The results showed that the RRS (ratio of root biomass to shoot biomass) of O. officinalis and O. rufipogon under 30 mg·kg− 1 Cd treatments both reached the highest, while the root surface area and root volume decreased. The SRL (ratio of total root length to total biomass) and SRV (ratio of total root volume to total biomass) under 30 mg·kg− 1 Cd treatment was the lowest. The exodermis cells of wild rice under 30 mg·kg− 1 Cd treatment were large and loosely arranged with some cortical thin-walled cells to be collapsed. The casparian strips and suberin layer were more deepening staining and thicker with root porosity decreased and electron-dense, particle-like structures observed under Cd treatment in root cells. The thickness of the exodermis cells of O. officinalis under 30 mg·kg− 1 Cd treatment increased by 45.6

The membrane transporters of plants are important for the transport and distribution of heavy metals, which is the basis for accumulation of heavy metals in hyperaccumulators. Pot and hydroponic experiments were conducted in order to understand effects of Cd dose (0, 10, 20 mg·kg−1) on the transport pathway of Cd in hyperaccumulator Arabis alpina, the concentrations of transporter CAX (cation/H+ reverse transporter) and HMA (heavy metal ATPase), and the response of Cd distribution to the inhibitors DNP (2,4-dinitrophenol), which is oxidative phosphorylation uncoupling agent and reduce HMA activity. The results showed that the concentrations of transporter CAX and HMA in roots under 20 mg∙kg−1 Cd treatment decreased by 31

Cadmium and arsenic co-contamination found in mining actions indicates major effluence in adjacent farmland soils, disturbing the plant physiology and soil’s microbial community. Phosphorus (P) plays a vital role in reducing soil contamination from Cd and As bioavailability and uptake by plants. However, the right P sources for remediation approaches are critical and still require further research in Cd- and As-contaminated soil. This study aimed to explore the effects of different phosphorus fertilizer sources on Lolium perenne growth and its physiological and rhizosphere microbial diversity under combined contamination with Cd and As. Pot experiments were performed with seven treatments including SSP (single super phosphate), DAP (diammonium phosphate), MAP (monoammonium phosphate), CaP (calcium phosphate), HighCaP (high calcium phosphate), RP (rock phosphate), and no phosphorus fertilizer application (CK) with five replications in the RCB design. The SSP treatment showed the greatest plant height (15.7 cm), hay yield (3567.6 kg·ha−1), and enhanced antioxidant defense activities. It also achieved the highest phosphorus accumulation rate (0.63 g·kg−1) with reduced Cd and As uptake. In addition, SSP promoted higher non-protein sulfhydryl (NPT) and phytochelatin synthetase (PCs) contents along with γ-glutamylcysteine synthetase (γ-ECS) activity, and enriched the rhizosphere microbial community, where the Sphingomonas abundance was 7.08% higher than for other treatments. Therefore, this result indicates that SSP can improve the yield and physiology in L. perenne, as well as soil the rhizosphere microbial community structure, while reducing Cd and As accumulation in plants under Cd and As stress.

Cadmium (Cd) is a hazardous element that limits plant growth and productivity. To assess the role of phosphorus nutrition in mitigating Cd stress, a pot experiment was conducted using six different phosphorus rates (0, 40, 80, 160, 240, 300 mg kg(-1) P2O5) under Cd concentration stress (0, 2, 20 mg kg(-1) Cd2+). The highest Alfalfa growth (56.79 cm), hay yield (2165.61 kg ha(-1)), and nutritional quality as relative feed value (245.63), soluble sugar content (4.13 mg kg(-1)), crude protein content (31.19%) showed significant responses at 160 mg kg(-1) phosphorus application rate under Cd stress at 2 mg kg(-1). Cd content in both the shoots and roots decreased by 41.7% and 39.2%. The order of the Cd content in subcellular components was cell wall > cytoplasm > mitochondria > chloroplast. Enzyme activities of peroxidase (POD), superoxide dismutase (SOD), and ascorbic acid (AsA) content showed a trend of first increasing and then decreasing. Malonaldehyde (MDA), phytochelatins (PCs), non- protein sulfhydryl (NPT), and catalase (CAT) activities significantly increased, while the content of glutathione (GSH) was significantly reduced. These results indicate that 160 mg kg(-1) phosphorus fertilizer application can improve Alfalfa's tolerance to Cd, thereby alleviating Cd toxicity and enabling high-quality alfalfa forage production.

The distribution, accumulation, and toxicological effects of two perennial ryegrass (Lolium perenne L.) varieties under combined cadmium (Cd)-arsenic (As) stress are worth exploring. Two varieties, ʻNicaraguaʼ (high-Cd/As-accumulating, DPB) and ʻVenusʼ (low-Cd/As-accumulating, WNS), were selected as experimental materials for pot trials. Subcellular fractionation, ultrastructural changes, and key transporter proteins cation exchanger (CAX), heavy metal ATPase (HMA), natural resistance-associated macrophage protein (NRAMP), and phosphate transporter (PHT) were analyzed under combined Cd-As stress. (1) The translocation factors of perennial ryegrass for Cd and As were < 1. Cd and As were mainly distributed in the cell wall and the soluble fractions. The total percentage of Cd and As in the cell wall and the soluble fractions of DPB variety was 92.53 and 91.29

Magnesium oxide nanomaterials (nano-MgO) have many advantages, such as environmentally benign, high thermal stability, no need of illumination, broad-spectrum antibacterial activity and more. However, its low activity has restricted the application in environmental purification and antibacterial disinfection. Herein, the equal volume impregnation-air calcination method was first used in the synthesis of nano-MgO and a series of nano-MgO with varying amounts of Li doping were prepared to enhance their antibacterial properties. Li doping leads to the distortion of MgO lattice structure and the presence of oxygen vacancies, enhancing oxygen absorption and alkalinity. This enhancement effectively promotes the formation of reactive oxygen species (ROS) and maintains its high chemical reactivity. The Li doped nano-MgO at 100 mu g mL-1 showed a significant improvement in antibacterial activity, achieving the antibacterial ratio of 99.6% against Escherichia coli (E. coli). Moreover, the contribution of alkalinity, ROS, physical morphology effect, and dissolved ions (Mg2+ and Li+) to the antibacterial ability was further discussed. Especially, the results of dialysis tube test indirectly indicated that ROS played the crucial role in enhancing the antibacterial performance of nano-MgO. This study lays an essential foundation for further investigation into the antibacterial performance and mechanism of nano-MgO.

Microplastics coexist with cadmium in agricultural soils, and their complex effects on crop growth and cadmium accumulation have garnered increasing attention. Pot experiments were conducted to elucidate the response mechanisms of rhizosphere microorganisms and root metabolites of Panax notoginseng (Burk.) F. H. Chen to polyethylene microplastics (PE-MPs) at concentrations of 0.1 %, 1 %, and 2 %, as well as cadmium (Cd) at levels of 0.6 mg kg-1 and 6.0 mg kg-1. The results indicated that: (1) The biomass of shoots and roots under the treatment of 0.1 % PE-MPs combined with 0.6 mg kg-1 Cd increased by 18.1 % and 137.5 %, respectively, compared to the treatment with only 0.6 mg kg-1 Cd; conversely, biomass decreased under the treatment of 0.1 % PE-MPs combined with 6 mg kg-1 Cd. (2) The root diameter increased with increase of PE-MPs treatment concentrations. (3) Under 2 % PE-MPs + 0.6 mg kg-1 Cd treatment, the Cd content in fibrous roots was 1.89 times of that under 0.6 mg kg-1 Cd treatment. The migration was inhibited from fibrous roots to main root or from main root to shoot under 2 % PE + Cd treatment. (4) The presence of PE-MPs influenced secondary metabolite pathways including pantothenate biosynthesis, phenylpropanoid biosynthesis, flavonoid biosynthesis along with sulfur relay systems, while up-regulating ABC transporters based on KEGG analysis. (5) Under 2 % PE-MPs + Cd treatment, the relative abundances of rhizosphere microorganism Candidatur koribacter, Bradyrhizobium, Ktedonosporobacter, Pedosphaera, Novosplingobium and Chthoniobacter at the genus level and Ktedonosporobacter rubrisoli, Chthoniobacter flavus, Silvibacterium bohemicum, Novosplingobium flavum and Fimbriilglobus ruber at the species level increased compared to 1 % PE-MPs + Cd treatment. There was negative correlated between the relative abundance of Ohtaekwangia koreensis and Cd accumulation in fibrous roots. In general, the biomass and accumulation of Cd in roots of P. notoginseng under the combined microplastics and Cd stress depended on the concentrations of PE-MPs, and the roots developed resistance by synthesizing secondary metabolites and recruiting Ohtaekwangia koreensis in the rhizosphere.

The ecological and health risks posed by heavy metals transport via runoff and sediment from lead-zinc mine wastelands have attracted increasing attention. While straw checkerboard barriers (SCBs) are known to mitigate soil erosion, their combined effect with artificial plant communities on controlling heavy metals migration from such sites remains unclear. To evaluate the effectiveness of straw checkerboard barriers (SCBs) and artificial plant communities in mitigating soil erosion and controlling heavy metals diffusion in lead-zinc mine wastelands, a field runoff plot experiment was conducted. Three artificial plant community patterns (grass, shrub-grass, tree-shrub-grass) were established on the wasteland, and SCBs were integrated into each plant community patterns (grass + SCBs, shrub-grass + SCBs, tree-shrub-grass + SCBs). Surface runoff, sediment yield, and heavy metals outputs (Cd, Pb, As) were monitored to investigate synergistic effects. Results demonstrated that artificial plant communities reduced the cumulative runoff by 23.18 % similar to 40.11 % and sediment yield by 49.55 % similar to 75.78 % compared to the control plot across six rainfall events. Integrating SCBs further decreased runoff by 17.20 % similar to 25.10 % and sediment yield by 39.22 % similar to 46.30 % within the same plant community. Soil quality improved markedly after plant community establishment, with significant increases in total nitrogen, total phosphorus, total potassium, organic matter, and soil moisture content. Vegetation coverage and soil moisture also increased when SCBs were constructed within plant communities. With increasing plant diversity, cumulative losses of Cd, Pb, and As, primarily in the particulate form, decreased significantly. SCBs further improved the ability of plant communities to stabilize heavy metals, reducing Cd by 9.36 % similar to 19.27 %, Pb by 11.99 % similar to 17.11 %, and As by 7.45 % similar to 35.66 %. Key factors influencing Cd, Pb, and As outputs included soil erosion, vegetation coverage, plant community pattern, and the presence of SCBs. Sediment yield was strongly correlated with heavy metals loss and was the best predictor for particulate Cd output (R-2 = 0.979). In conclusion, SCBs integration improves artificial plant communities' control of surface runoff, sediment yield, and heavy metals diffusion in abandoned lead-zinc mine sites, which creates favorable conditions for ecological restoration and long-term stabilization.

δMnO2 is an important component of environmental minerals and is among the strongest sorbents and oxidants. The crystalline morphology of δ-MnO2 is one of the key factors affecting its reactivity. In this work, δ-MnO2 was initially synthesized and placed in an acidic environment to react with Mn2+ and undergo a crystalline transformation. During the transformation of crystalline δ-MnO2, kinetic sampling was conducted, followed by analyses of the structures and morphologies of the samples. The results showed that at pH 2.5 and 4, δ-MnO2 nanoflakes spontaneously self-assembled into nanoribbons via edge-to-edge assembly in the initial stage. Subsequently, these nanoribbons attached to each other to form primary nanorods through a face-to-face assembly along the c-axis. These primary nanorods then assembled along the (001) planes and lateral surfaces, achieving further growth and thickening. Since a lower pH is more favorable for the formation of vacancies in δ-MnO2, δ-MnO2 can rapidly adsorb Mn2+ directly onto the vacancies to form tunnel walls. At the same time, the rapid formation of the tunnel walls leads to a quick establishment of hydrogen bonding between adjacent nanoribbons, enabling the assembly of these nanoribbons into primary nanorods. Therefore, in a solution with the same concentration of Mn2+, the structure transformation and morphology evolution of δ-MnO2 to α-MnO2 occur faster at pH 2.5 than at pH 4. These findings provide insights into the mechanism for crystal growth from layer-based to tunnel-based nanorods and methods for efficient and controlled syntheses of nanomaterials.

Plants endogenous hormones play an important role in resistance to soil lead (Pb) contamination. In order to explore the response of plant hormones to Pb stress, pot experiment was conducted to analysis the hormones contents, related gene expressions and Pb accumulation of Arabis alpina under Pb treatment and transporter (CAX(cation exchangers), HMA(heavy metal ATPase) and ABC(ATP-binding cassette transporter)) activities under foliage spraying auxin (IAA). The results showed that contents of total Pb and soluble components Pb (vacuoles) in roots and leaves of Arabis alpina increased with increase of Pb treatment concentrations. Compering to 100 mg·kg-1 Pb2+ treatment, Pb contents in soluble components of roots and leaves under 300 mg·kg-1 Pb2+ treatment increased by 896.3% and 238.8%, respectively. The contents of endogenous hormones in leaves and roots increased under Pb treatment concentrations. Comparing to control (0 mg·kg-1 Pb2+ treatment), contents of auxin in roots and leaves under 100 mg∙kg-1 Pb treatment increased by 176.19% and 585.29%, respectively. Auxin contents in xylem saps under 100 and 300 mg∙kg-1 Pb treatments increased by 283.14% and 100.30%, respectively. Gene expression related to auxin transport was up-adjusted. The expressions of three gene related to auxin-repressed 12.5 kDa protein and auxin-responsive GH3 family were down-adjusted. Under foliage spraying IAA, Pb contents in leaves increased by 29.81% and Pb content in symplast sap was higher than that with non spraying IAA treatment. The activities of CAX and HMA in roots of A. alpina increased by 9.62% and 8.79% with foliage spraying IAA treatment, while activity of ABC decreased by 21.94%. In general, contents of auxin and related genes expressions of A. alpina increased under Pb treatment, which enhanced activities of CAX and HMA resulting in Pb translocation through symplast pathway.

The mining of metal minerals generates considerable mining wasteland areas, which are characterized by poor soil properties that hinder plant growth. In this study, a field plot experiment was carried out in the mining wasteland of the Lanping lead–zinc mine in Yunnan Province to study the effects of applying three organic materials—biochar (B), organic fertilizer (OF), and sludge (S)—at concentrations of 1% (mass fraction), on promoting the soil of mining wasteland and the growth of two plant varieties (Huolieniao and Yingshanhong). The results showed that the amount of available nutrients in the surface soil of a mining wasteland could be considerably increased by S and OF compared to the control check (CK). In the rhizosphere soils of two Rhododendron simsii varieties, the application of S increased the available phosphorus (P) content by 66.4% to 108.8% and the alkali-hydrolyzed nitrogen (N) content by 61.7% to 295.5%. However, the contents of available cadmium (Cd) and available lead (Pb) were reduced by 17.1% to 32.0% and 14.8% to 19.0%, respectively. Moreover, three organic materials increased the photosynthetic rate and biomass of two R. simsii varieties. Specifically, OF and S were found to significantly increase the biomass of R. simsii. Organic materials have direct impacts on the increased plant height and biomass of R. simsii. Additionally, organic materials indirectly contribute to the growth of R. simsii by reducing the content of available Cd and available Pb in rhizosphere soil while increasing the content of available nutrients according to the structural equation model (SEM). Overall, S can stabilize Cd and Pb, increase soil nutrient contents, and promote the growth of R. simsii effectively, and has great potential in the vegetation reconstruction of mining wasteland.

To investigate the characteristics of Cd transport and distribution in the wild rice roots, Oryza rufupogon Griff. and Oryza officinalis Wall. were used at research materials. Pot experiment was conducted to study the effects of different concentrations of Cd (0, 1, 5, 15 and 30 mg center dot kg(-1)) treatments on the root pectin content, root pectin methyl esterase(PME) activity, Cation/proton exchanger(CAX), heavy metal ATPase(HMA) and ATP-binding cassette protein(ABC) activities of wild rice. The difference in Cd flow rate of wild rice root was investigated through non-invasive micro-test technique (NMT). The results showed that the Cd in roots tended to increase with the increase of Cd treatment concentrations. Compared to the CK treatment (0 mg center dot kg(-1) Cd), the root pectin content of O. rufupogon and O. officinalis under 30 mg center dot kg(-1) Cd stress were significantly increased by 126.73 % and 109.69 %, respectively. The distribution of Cd contents in wild rice roots were all greater than those in shoots. Under Cd stress, the translocation factor of O. rufupogon (0.46-1.44) were all higher than those of O. officinalis (0.15-0.37). The Cd transport capacity in O. rufupogon was more stronger than in O. officinalis. The Cd content in the xylem sap of O. officinalis was lower than that of O. rufupogon. Compared to the CK, CAX and ABC activities in O. officinalis root under 30 mg center dot kg(-1) Cd treatment were significantly increased by 11.03 % and 2.37 %, respectively. HMA activity in O. rufupogon root was significantly increased by 4.95 %. Cd flow rate in the root xylem of O. officinalis was higher than that of O. rufupogon. In root cells, the subcellular distribution of Cd contents showed cell wall > soluble components> organelles. With the Cd treatment concentrations increased, the percentage of Cd content in the soluble fractions of the root cells of wild rice showed an increasing. In general, the result showed that O. officinalis immobilized more Cd in the roots by influencing the pectin methyl esterification reaction through PME activity. Under high Cd stress, Cd was immobilized in root cell vacuoles of O. officinalis by enhancing roots CAX and ABC activities, whereas HMA activities were enhanced of O. rufupogon to reduce the damage caused by Cd.

Variations in the cadmium (Cd) accumulation and root characteristics of different genotypes of rice during three developmental periods of dry cultivation were investigated in pot experiments in which two levels of Cd were added to the soil (0 and 10 mg kg−1). The results show that the Cd concentration in each organ of the different rice genotypes decreased in both the order of roots > shoots > grains and during the three developmental periods in the order of the maturity stage > booting stage > tillering stage. The lowest bioaccumulation factor (BCF) and translocation factor (TF) were found in Yunjing37 (YJ37) under Cd stress. At maturity, Cd stress inhibited the root length of Dianheyou34 (DHY34) the most and that of Dianheyou 918 (DHY918) the least, also affecting the root volume of DHY34 and Dianheyou615 (DHY615) the most and that of YJ37 and Yiyou 673 (YY673) the least; the inhibition rates were 41.80, 5.09, 40.95, and 10.51%, respectively. The exodermis showed the greatest thickening in YY673 and the lowest thickening in DHY615, while the endodermis showed the opposite result. The rates of change were 16.48, 2.45, 5.10, and 8.49%, respectively. The stele diameter of DHY615 decreased the most, and that of YY673 decreased the least, while the secondary xylem area showed the opposite result; the rates of change were −21.50, −14.29, −5.86, and −26.35%, respectively. Under Cd stress treatment at maturity, iron plaque was extracted using the dithionite–citrate–bicarbonate (DCB) method. The concentration of iron (DCB-Fe) was highest in YJ37, and the concentration of cadmium (DCB-Cd) was lowest in DHY34. YJ37 was screened as a low Cd-accumulating variety. The concentration of available Cd in the rhizosphere soil, iron plaque, root morphology, and anatomy affect Cd accumulation in rice with genotypic differences. Our screening of Cd-accumulating rice varieties provides a basis for the dry cultivation of rice in areas with high background values of Cd in order to avoid the health risks of Cd intake.

Widespread lead (Pb) contamination of agricultural soils is a global issue stemming from human activities. The remediation of Pb-contaminated soils used for agricultural purposes is critically important to safeguard food crop safety. Despite the modulating effects of sulfur (S) on plant responses to toxic heavy metals, the ecological, physiological, and molecular mechanisms driving such modulation in the Pb hyperaccumulator Arabis alpina L. remain unclear. Here, we investigated the effects of five S concentrations (0, 50, 100, 150, and 200 mg kg−1) on A. alpina grown in Pb-contaminated soil from a lead-zinc mining area. Under S50 (i.e., 50 mg kg−1) and S100 treatments, the Pb concentration in both shoots and roots of A. alpina significantly decreased compared to the control (S0). Specifically, the S50 treatment significantly enhanced Pb accumulation, plant biomass, and plant height, indicating that low S applications facilitate Pb accumulation from the soil and alleviate Pb toxicity. Additionally, S50, S100, and S150 treatments significantly improved photosynthetic rate, stomatal conductance, and intercellular CO2 concentration in A. alpina. Transcriptomic analysis showed that S50 and S100 treatments increased the expression of the LHCA, LHCB, psa, and psb genes, which had a significant impact on photosynthetic efficiency. S50 and S100 boosted glutathione (GSH) levels in A. alpina roots, and the increased expression of GST gene enhanced tolerance to environmental stress. In summary, these results suggest that an appropriate supply of S (S50 and S100) not only alleviates Pb toxicity by enhancing plant biomass, height, photosynthetic features, and sulfur metabolites but also stimulates Pb accumulation in the hyperaccumulator A. alpina. Our study elucidated the specific concentrations of sulfur that optimally enhance both Pb accumulation and stress tolerance in the hyperaccumulator A. alpina, providing novel insights into the practical application of sulfur in phytoremediation strategies and advancing our understanding of the underlying molecular mechanisms.

The effect of UV-B radiation exposure on transgenerational plasticity, the phenomenon whereby the parental environment influences both the parent’s and the offspring’s phenotype, is poorly understood. To investigate the impact of exposing successive generations of rice plants to UV-B radiation on seed morphology and proanthocyanidin content, the local traditional rice variety ‘Baijiaolaojing’ was planted on terraces in Yuanyang county and subjected to enhanced UV-B radiation treatments. The radiation intensity that caused the maximum phenotypic plasticity (7.5 kJ·m−2) was selected for further study, and the rice crops were cultivated for four successive generations. The results show that in the same generation, enhanced UV-B radiation resulted in significant decreases in grain length, grain width, spike weight, and thousand-grain weight, as well as significant increases in empty grain percentage and proanthocyanidin content, compared with crops grown under natural light conditions. Proanthocyanidin content increased as the number of generations of rice exposed to radiation increased, but in generation G3, it decreased, along with the empty grain ratio. At the same time, biomass, tiller number, and thousand-grain weight increased, and rice growth returned to control levels. When the offspring’s radiation memory and growth environment did not match, rice growth was negatively affected, and seed proanthocyanidin content was increased to maintain seed activity. The correlation analysis results show that phenylalanine ammonialyase (PAL), cinnamate-4-hydroxylase (C4H), dihydroflavonol 4-reductase (DFR), and 4-coumarate:CoA ligase (4CL) enzyme activity positively influenced proanthocyanidin content. Overall, UV-B radiation affected transgenerational plasticity in seed morphology and proanthocyanidin content, showing that rice was able to adapt to this stressor if previous generations had been continuously exposed to treatment.

In order to study the effects of oxalic acids on plant growth and Pb accumulation in different parts of the plants of intercropping Arabis alpina and Zea mays, pot experiment was conducted to investigate the changes of oxalic acid contents of the plants and Pb accumulation through exogenous oxalic acid addition (0, 5, 25 and 50 mmol kg-1). The results showed the root biomass of intercropped A. alpina and total biomass of Z. mays increased by 3.22 folds and 2.97 folds with 5 mmol kg-1 oxalic acid treatment. The oxalic acid contents of shoots and root secretions decreased by 86.5% and 44.3%, respectively. The BCF (bio-accumulation factor) and TF (translocation factor) of intercropping A. alpina reduced under 25 - 50 mmol kg-1 oxalic acid treatments. There were relationships between exogenous oxalic acid treatment concentrations and oxalic acid contents of A. alpina shoots, Z. mays root secretions. The Pb contents of shoots of A. alpina and Z. mays were related to exogenous oxalic acid additions and oxalic acid contents of shoots. In general, 5 mmol kg-1 oxalic acid treatment, that can improve plant growth of intercropped A. alpina and Z. mays, which Pb translocation and accumulation of A. alpina were promoted, whereas Pb accumulation of A. alpina was inhibited with 25 - 50 mmol kg-1 concentrations addition. This study will provide a basis for promoting the application of phytoremediation techniques and efficient crop production in heavy metal contaminated areas.

Lead (Pb) pollution in soil affects growth of plants. Plants' endogenous hormones play an important role in resistance to Pb of plant. In order to explore the hormone-based mechanisms of Pb accumulationin in hyperaccumulator Arabis alpina, a pot experiment was conducted to analyze the contents of endogenous hormones (auxin, gibberellin, abscisic acid, and cytokinin) and related genes expressions, and Pb contents of A. alpina, as well as the transporter (cation exchangers (CAX), heavy metal ATPases (HMA), and ATP-binding cassette (ABC)) concentrations under foliar spraying of indoleacetic acid (IAA). The results showed that the soluble components (vacuoles) Pb contents under 300 mg kg-1 Pb2+ treatment in shoots and roots increased by 238.8% and 896.3%, respectively, compared to 100 mg kg-1 Pb2+ treatment. The content of endogenous hormones in leaves and roots increased under increasing Pb-treatment concentrations. Compared with the control (0 mg kg-1 Pb2+ treatment), the content of auxin in roots and leaves under the 100 mg kg-1 Pb treatment increased by 176.2% and 585.3%, respectively. The auxin content in xylem saps under the 100 and 300 mg kg-1 Pb treatments increased by 283.1% and 100.3%, respectively. The gene expression related to auxin transport was up-regulated. The expression of three genes related to the auxin-repressed 12.5 kDa protein and the auxin-responsive GH3 (Gretchen Hagen 3) family were down-regulated. Under foliar spraying of IAA, the Pb content in leaves increased by 29.81%, and the Pb content in the symplast sap was higher than that without IAA spraying treatment. The concentrations of CAX and HMA in the roots of A. alpina increased by 9.6% and 8.8%, respectively, with foliar spraying treatment with IAA, while the ABC concentration decreased by 21.9%. In general, the transport and accumulation of Pb is related to the IAA content and the gene expression of AaGDCST, a signal transducer for inducing increased concentrations of the transporter CAX and HMA in the roots of A. alpina. Pb transport via the symplast pathway under IAA application. Regarding the Pb hyperaccumulation of A. alpina, gene AaGDCST has the potential to be utilized as a candidate gene.

Wild rice is a natural gene pool for modern cultivated rice germplasm resources. In the long process of independent evolution, wild rice has developed an extremely rich genetic diversity through natural selection in a variety of adverse environments. Wild rice is belonging to grade II of national protect plant in China and rarity. Field surveys were conducted to collect samples of seven Oryza granulata Balli., three Oryza rufupogon Griff. and three Oryza officinalis Wall. plants and relative native habitat soils from different sites in Yunnan province, China. The physical and chemical properties of soil, heavy metal (Hg, Cr, Ni, Sn, Cu, Zn, Cd, Pb) contents of soil and plants, morphological and anatomical structural characteristics of wild rice roots were analyzed. The results showed that soil pH was predominantly acidic. The soil total nitrogen, total phosphorus, available potassium, available nitrogen of O. officinalis were all at low levels. Soil heavy metal contents (Hg, Cr, Ni, Cu, Zn, Sn and Pb) were below the standard values, except for the soil Cd contents of O. granulata, which reached the level of moderate to light contamination (>0.3 mg & sdot;g(- 1), GB 15618-2018). O. granulata had the largest thickness of endodermis, exodermis and thick-walled tissues and the the biggest areas of stele and vessel. O. officinalis had the most developed root system which had the highest area of diameter and cross-sectional in root. Compared to the other wild rice, Cd contents in roots and shoot of O. granulata were the highest. The bio-accumulation factor (BCF) of Cd was all higher than 1 in O. granulata and translocation coefficient(TC) of six heavy metals (Hg, Cr, Ni, Cu, Si and Pb) was the largest, which was higher than 1. The BCF of four heavy metal (Cr, Zn, Cd and Si) in O. rufupogon and O. officinalis was higher than 1 and TC of three heavy metals (Hg, Cr and Zn) was higher than 1. In conclusion, O. granulata increased the thickness of endodermis, exodermis and thick-walled tissues to adapt the stress of soil Cd. O. rufupogon increased total root length to get more nutrition and O. officinalis increased diameter and cross-sectional area of root to adapt submerged environment.