Silicon combined with foliar melatonin for reducing the absorption and translocation of Cd and As by Oryza sativa L. in two contaminated soils.

Potentially toxic elements (PTE) toxicity has serious effects for human health. Si has been tested to investigate their ability to mitigate Cd and As contamination of rice. In this study, the combined effect of Si and melatonin (MT) on Cd and As uptake and transport in rice plants is tested in two contaminated soils via controlled pot experiments. Results showed that a combined Si and MT treatment (Si + MT) was more effective at reducing Cd and As uptake and transport than Si alone. The treatment had the strongest effect on Cd concentrations in rice grains from high-polluted soil (HP) when treated at the flowering stage (81.8% reduction) and from low-polluted soil (LP) at the tillering stage (TS, 64.9%). The greatest reduction of grain As was found when treated at TS in both soils, by 58.2% and 39.2% in HP and LP soil, respectively. The significant upregulation of CAT, SOD, and POD activities, and downregulation of MDA by Si + MT was more effective than that of Si alone; Si + MT significantly decreased expressions of Nramp1, HMA2, and IRT2 in roots in both soils, and also Nramp5, HMA3, and IRT1 in LP soil, which might result in Si+MT effect on Cd and As accumulation. However, Si + MT had little effect on the amino acid content of grains compared to Si alone. Overall, the combination of Si and MT was substantially more effective at reducing Cd and As uptake and transport than Si alone, especially in HP soil. This effect might result from the regulation of antioxidant potential and gene expression relating Cd uptake and transport.

Effect of nitrogen fertilizer and/or rice straw amendment on methanogenic archaeal communities and methane production from a rice paddy soil.

Nitrogen fertilization and returning straw to paddy soil are important factors that regulate CH4 production. To evaluate the effect of rice straw and/or nitrate amendment on methanogens, a paddy soil was anaerobically incubated for 40 days. The results indicated that while straw addition increased CH4 production and the abundances of mcrA genes and their transcripts, nitrate amendment showed inhibitory effects on them. The terminal restriction fragment length polymorphism (T-RFLP) analysis based on mcrA gene revealed that straw addition obviously changed methanogenic community structure. Based on mcrA gene level, straw-alone addition stimulated Methanosarcinaceaes at the early stage of incubation (first 11 days), but nitrate showed inhibitory effect. The relative abundance of Methanobacteriaceae was also stimulated by straw addition during the first 11 days. Furthermore, Methanosaetaceae were enriched by nitrate-alone addition after 11 days, while Methanocellaceae were enriched by nitrate addition especially within the first 5 days. The transcriptional methanogenic community indicated more dynamic and complicated responses to straw and/or nitrate addition. Based on mcrA transcript level, nitrate addition alone resulted in the increase of Methanocellaceae and the shift from Methanosarcinaceae to Methanosaetaceae during the first 5 days of incubation. Straw treatments increased the relative abundance of Methanobacteriaceae after 11 days. These results demonstrate that nitrate addition influences methanogens which are transcriptionally and functionally active and can alleviate CH4 production associated with straw amendment in paddy soil incubations, presumably through competition for common substrates between nitrate-utilizing organisms and methanogens.

Lead toxicity thresholds in 17 Chinese soils based on substrate-induced nitrification assay.

The influence of soil properties on toxicity threshold values for Pb toward soil microbial processes is poorly recognized. The impact of leaching on the Pb threshold has not been assessed systematically. Lead toxicity was screened in 17 Chinese soils using a substrate-induced nitrification (SIN) assay under both leached and unleached conditions. The effective concentration of added Pb causing 50% inhibition (EC50) ranged from 185 to >2515mg/kg soil for leached soil and 130 to >2490mg/kg soil for unleached soil. These results represented >13- and >19-fold variations among leached and unleached soils, respectively. Leaching significantly reduced Pb toxicity for 70% of both alkaline and acidic soils tested, with an average leaching factor of 3.0. Soil pH and CEC were the two most useful predictors of Pb toxicity in soils, explaining over 90% of variance in the unleached EC50 value. The relationships established in the present study predicted Pb toxicity within a factor of two of measured values. These relationships between Pb toxicity and soil properties could be used to establish site-specific guidance on Pb toxicity thresholds.

Nano zero-valent iron and melatonin synergistically alters uptake and translocation of Cd and As in soil-rice system and mechanism in soil chemistry and microbiology.

Nanoscale zero-valent iron (Fe) is a promising nanomaterial for remediating heavy metal-contaminated soils. Melatonin (MT) is essential to alleviate environmental stress in plants. However, the conjunction effects of Fe and MT (FeMT) on rice Cd, As accumulation and the mechanism of soil chemical and microbial factors interaction are unclear. Here, a pot experiment was conducted to evaluated the effects of the FeMT for rice Cd, As accumulation and underlying mechanisms. The findings showed that FeMT significantly reduced grains Cd by 92%-87% and As by over 90%, whereas improving grains Fe by over 213%. Soil available-Cd and iron plaques-Cd (extracted by dithionite-citrate-bicarbonate solution, DCB-Cd) significantly regulated roots Cd, thus affected Cd transport to grains. Soil pH significantly affected soil As and DCB-As, which further influenced roots As uptake and the transport to shoots and grains. The interactions between the soil bacterial community and soil Fe, available Fe, and DCB-Fe together affected root Fe absorption and transportation in rice. FeMT significantly influenced rhizosphere soil bacterial α- and ß-diversity. Firmicutes as the dominant phylum exhibited a significant positive response to FeMT measure, and acted a key role in reducing soil Cd and As availability mainly by improving iron-manganese plaques. The increase of soil pH caused by FeMT was beneficial only for Actinobacteriota growth, which reduced Cd, As availability probably through complexation and adsorption. FeMT also showed greater potential in reducing human health and ecological risks by rice consumption and straw returning. These results showed the important role of both soil chemical and microbial factors in FeMT-mediated rice Cd, As reduction efficiency. This study opens a novel strategy for safe rice production and improvement of rice iron nutrition level in heavy-metals polluted soil, but also provides new insights into the intricate regulatory relationships among soil biochemistry, toxic elements, microorganism, and plants.

Iron-lanthanum supported on graphite sheets for As(III) removal from aqueous solution: kinetics, thermodynamic and ecotoxicity assessment.

Graphene-based material is widely used to remove arsenic from water due to its layered structure with high surface area. Here, we have successfully synthesized Fe-La bimetallic modified graphite sheet materials to more efficiently remove As(III) from aqueous solution. The results showed that Fe-La-graphite sheets (FL-graphite sheets) have a larger specific surface area (194.28 m2·g-1) than graphite sheets (2.80 m2·g-1). The adsorption capacity of FL-graphite sheets for As(III) was 51.69 mg·g-1, which was higher than that of graphite sheets (21.91 mg·g-1), La-graphite sheets (26.06 mg·g-1), and Fe-graphite sheets (40.26 mg·g-1). The FL-graphite sheets conformed to the Freundlich and Dubinin-Radushkevich isotherm, and the maximum adsorption capacity was 53.62 mg·g-1. The removal process obeys intra-particle diffusion and pore diffusion for As(III). The results of batch adsorption experiments and characterization analyses demonstrated that oxidation, ligand exchange, and inner sphere complexation mechanisms involved in the adsorption of FL-graphite sheets to As(III) in comparison with graphite sheets. In addition, electrostatic attraction mechanism was found vital in the adsorption. Ecotoxicity assessment revealed that FL-graphite sheets have little influence on rice germination and growth, but reduced the toxicity of As(III) to rice. Therefore, the FL-graphite sheets have good practical application value in purifying As(III) polluted water with litter ecotoxicity.

Metabolic regulation mechanism of melatonin for reducing cadmium accumulation and improving quality in rice.

Melatonin acts as a potential regulator of cadmium (Cd) tolerance in rice. However, its practical value in rice production remains unclear. To validate the hypothesis that melatonin affects Cd accumulation and rice quality, a series of experiments were conducted. The results showed that exogenous melatonin application was associated with reduced Cd accumulation (23-43%) in brown rice. Fourier transform infrared spectroscopy (FTIR) analysis showed that exogenous melatonin affected the rice protein secondary structure and starch short-range structure. Metabolomics based on LC-MS/MS revealed that exogenous melatonin altered the brown rice metabolic profile, decreased fatty acid metabolite content, but increased amino acid metabolite, citric acid, melatonin biosynthetic metabolite, and plant hormone contents. These findings indicate that exogenous melatonin can effectively reduced Cd accumulation and improve rice quality through metabolic network regulation, serving as an effective treatment for rice cultivated in Cd-contaminated soil.

Molecular mechanisms of growth promotion and selenium enrichment in tomato plants by novel selenium-doped carbon quantum dots.

Selenium (Se)-doped nanoparticles as novel Se fertilizers have a promising potential in the agricultural application. Here, the effects of two novel Se-doped carbon quantum dots (Se-CQDs1 and Se-CQDs2, prepared using co-cracking and adsorption-reduction methods, respectively) on the growth and Se enrichment of tomato plants were studied, where the promoting molecular mechanisms were explored in terms of the related genes expression and soil microbial composition. The results indicated that the soil application of 2.5 mg kg-1 Se-CQDs1 more significantly increased the root growth, plant biomass, and fruit yield than that of Se-CQDs2 and Na2SeO3 treatments (control). Specifically, Se-CQDs1 treatment was more effective to up-regulate the expressions of aquaporin gene (i.e., PIP) and growth hormone synthesis gene (i.e., NIT) than Se-CQDs1 and Na2SeO3 treatments. The expressions of Se methyltransferase gene (smt) and methionine methyltransferase gene (mmt) induced by Se-CQDs1 were 1.45 and 1.18 times higher than that by Se-CQDs2 as well as 1.82 and 2.17 times higher than that by Na2SeO3. Also, Se-CQDs1 more greatly increased the diversity and relative abundance of soil bacterial communities, especially the Actinobacteria phylum, which was beneficial to increase plant growth-promoting substances. These outstanding promoting effects of Se-CQDs1 were mainly ascribed to its higher hydrophilicity and content of the stable doped-Se. The overall results demonstrated that Se-CQDs would be a promising candidate for nano-fertilizer to increase crop growth and development (e.g., tomato plants), where the synthesis modes of Se-CQDs play a critical role in regulating the utilization efficiency of Se.

Exogenous plant hormones alleviate As stress by regulating antioxidant defense system in Oryza sativa L.

Plant hormones play essential roles in plant growth regulation and resistance to environmental pressure. A hydroponic experiment was conducted using Zhongjiazao 17 rice to explore the effects of exogenous plant hormones on antioxidant response and As accumulation in rice under As stress. Melatonin (MT), 2,4-epibrassinolide (EBL), and jasmonic acid (JA) reduced the As content in seedlings significantly by 13.4% (MT)-32.5% (EBL) under 5 µM As stress. Three hormones increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, and glutathione (GSH) content significantly (2.2%-82.9%) in 5 µM As stress condition, whereas the levels of H2O2 and malondialdehyde (MDA) were reduced significantly (32.3%-78.1%). Plant hormone addition reduced the As content in seedlings significantly by 18.2% (JA)-33.3% (MT) under 25 µM As stress. SOD, POD, and CAT activities and GSH content in seedlings increased significantly (5.6-90.4%) with three hormones addition in 25 µM As stress, whereas the levels of H2O2, O2˙¯, and MDA reduced significantly (20.9-73.0%). Staining with 2',7'-dichlorodihydrofluorescein diacetate and nitroblue tetrazolium showed that green fluorescence and blue spots decreased gradually in hormone-treated seedlings, further confirming that the exogenous addition of hormones weakened the oxidative stress of As to seedlings. Oxidative damage by As stress was reduced more by EBL than by the other hormones MT or JA. Totally, exogenous plant hormone can alleviate As stress in rice by activating enzyme activity of antioxidant defense system and scavenging reactive oxygen species, thus reducing oxidative damage and As accumulation in rice seedlings.

Melatonin alleviates arsenite toxicity by decreasing the arsenic accumulation in cell protoplasts and increasing the antioxidant capacity in rice.

Arsenic (As) is a common environmental pollutant that seriously interferes with the normal growth of organisms. There is an urgent need to take environment-safe and efficient strategies to mitigate As toxicity. Melatonin (MT) is a pleiotropic molecule that regulates plant growth and organ development and alleviates heavy metal stresses. The experiment aims to explore the mechanism of MT in reducing arsenite toxicity by hydroponic rice seedlings. The results showed that MT application reduced the As content in rice roots and shoots by 26.4% and 37.5%, respectively, and mainly decreased As content in the soluble fractions of the rice root cell. MT application also increased the As content of chelated-soluble pectin and alkali-soluble pectin in the cell wall by 14.7% and 74.4%, respectively. It promoted the generation of the functional group of the root cell walls by the FTIR analysis, indicating that MT may promote the fixation of As on the cell wall. Meanwhile, MT contributed to scavenging excess H2O2, reducing MDA content, and maintaining normal morphology of root cells by stimulating SOD, POD and CAT activities and increasing the level of GSH. The research deepens our understanding of how MT participates in maintaining redox homeostasis in rice cells, reducing As toxicity, and decreasing As concentration in rice seedlings, thereby providing more possibilities for reducing As accumulation in rice.

Melatonin Alleviates Antimony Toxicity by Regulating the Antioxidant Response and Reducing Antimony Accumulation in Oryza sativa L.

Antimony (Sb) is a hazardous metal element that is potentially toxic and carcinogenic. Melatonin (MT) is an indole compound with antioxidant properties that plays an essential role in plant growth and alleviates heavy metal stresses. Nevertheless, little is known about the effects and mechanisms of exogenous MT action on rice under Sb stress. The aim of this experiment was to explore the mechanism of MT reducing Sb toxicity in rice via hydroponics. The results showed that Sb stress significantly inhibited the growth of rice, including biomass, root parameters, and root viability. Exogenous MT obviously alleviated the inhibition of Sb stress on seedling growth and increased biomass, root parameters, and root viability by 15-55%. MT significantly reduced the total Sb content in rice and the subcellular Sb contents in roots by nearly 20-40% and 12.3-54.2% under Sb stress, respectively. MT significantly decreased the contents of malondialdehyde (MDA, by nearly 50%), ROS (H2O2 and O2·-, by nearly 20-30%), and RNS (NO and ONOO-) in roots under Sb stress, thus reducing oxidative stress and cell membrane damage. Furthermore, MT reversed Sb-induced phytotoxicity by increasing the activities of antioxidant enzymes (SOD, POD, CAT, and APX) by nearly 15% to 50% and by regulating the AsA-GSH cycle. In conclusion, this study demonstrates the potential of MT to maintain redox homeostasis and reduce Sb toxicity in rice cells, decreasing the content of Sb in rice and thereby alleviating the inhibition of Sb on rice growth. The results provided a feasible strategy for mitigating Sb toxicity in rice.

[Effects of Exogenous Melatonin Treatment on the Growth and Antioxidant System of Rice Seedlings Under Antimony Stress].

To investigate the effect of exogenous application of melatonin (MT) on rice seedlings under antimony (Sb) stress, hydroponic experiments were carried out with rice seedlings (Huarun No.2). The fluorescent probe localization technology was used to locate the reactive oxygen species (ROS) in the root tips of rice seedlings, and the root viability, malondialdehyde (MDA) content, ROS (H2O2 and O2-·) content, antioxidant enzyme (SOD, POD, CAT, and APX) activities, and antioxidant (GSH, GSSG, AsA, and DHA) contents in the roots of rice seedlings were analyzed. The results showed that exogenous addition of MT could alleviate the adverse effects of Sb stress on the growth and increase the biomass of rice seedlings. Compared with the Sb treatment, the application of 100 µmol·L-1 MT increased rice root viability and total root length by 44.1% and 34.7% and reduced the content of MDA, H2O2, and O2-· by 30.0%, 32.7%, and 40.5%, respectively. Further, the MT treatment increased the activities of POD and CAT by 54.1% and 21.8%, respectively, and also regulated the AsA-GSH cycle. This research indicated that exogenous application of 100 µmol·L-1MT can promote the growth and antioxidant ability of rice seedlings and alleviate the damage of lipid peroxidation by Sb stress, thus improving the resistance of rice seedlings under Sb stress.

Effects of optimized water management on the uptake and translocation of cadmium and arsenic in Oryza sativa L. in two contaminated soils.

Water management has opposite effects on the bioavailability of Cd and As in soil. In order to identify the most efficient water management strategy for reducing Cd and As accumulations and amino acid (AA) synthesis in rice in two soils with different Cd and As contents, a pot experiments were conducted in greenhouse. A treatment consisting of 5 days of flooding followed by 3 days of drainage (F5D3, repeated every 8 days) was identified as the most effective treatment for simultaneously decreasing Cd and As in grains, with reductions of grain Cd and As contents of more than 80.0% and 73.1%, respectively, compared with either a drained treatment or a flooded treatment alone; this is probably related to the high efficiency of the F5D3 treatment in reducing dissolved Cd and As according to its minimum "trade-off value" (an index for evaluating the degree of trade-off between soil solution As and Cd concentrations in water management condition), due to the variations in grain Cd and As contents which were significantly correlated with the variations in soil solution Cd (R2=0.98) and As (R2=0.92, P=0.0001) concentrations. Additionally, grain Cd content was also significantly related to the organs Cd contents (especially root Cd content, R2=0.99) and the root-to-shoot Cd translocation factors (R2=0.99), whereas grain As content was significantly related to soil Eh (R2=-0.82, P=0.003) and pH (R2=0.88, P=0.0008). The AA contents in organs under the F5D3 treatment were lower than those under the flooded and drained treatments. These results indicated that the F5D3 treatment was the most effective water management strategy for simultaneously reducing grain Cd and As contents and AA synthesis in rice, which was probably due to there being no need for rice to synthesize abundant AAs to chelate metal ions.

Long-term enclosure at heavy grazing grassland affects soil nitrification via ammonia-oxidizing bacteria in Inner Mongolia.

Enclosure and grazing can significantly change the turnover of nitrogen in grassland soil. Changes of soil nitrogen mineralization and ammonium-oxidizing microorganisms caused by enclosure in different grazing intensities (about 30 years of grazing history) grassland, however, has rarely been reported. We selected the grassland sites with high and medium grazing intensity (HG and MG, 4 and 2 sheep ha-1, respectively) and had them enclosed (45 × 55 m) in 2005 while outside the enclosure was continuously grazed year-round. A two factorial study was designed: grazing intensity (MG and HG sites) and enclosure (fence and non-fence). Nitrogen mineralization was detected through a laboratory incubation experiment. The abundance and community structure of soil ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were analyzed using quantitative PCR (q-PCR), terminal-restriction fragment length polymorphism (T-RFLP), cloning, and sequencing. Results showed that compared with MG site, at HG site the AOB abundance and community structure of AOB changed significantly while the AOA abundance and community structure did not change obviously. Enclosure significantly decreased the cumulative mineralized N, N mineralization rate, the abundance of AOB and the AOB community structure at the HG site, while at MG site, enclosure did not change these parameters. Potential nitrification rate (PNR) was positively correlated with the abundance of AOA and AOB at the MG and HG sites, respectively. The abundance of AOA was significantly correlated with soil pH; however, AOB abundance was significantly correlated with soil available N, total N, C/N ratio, pH, etc. The phylogenetic analysis showed that Nitrososphaeraceae and Nitrosomonadaceae were the dominant AOA and AOB, respectively. Totally, the responses of AOB and AOA mainly were associated to changes in soil physicochemical properties caused by different intensity grazing; AOB and AOA may be the dominant functional players in ammonia oxidation processes at HG and MG site, respectively.

A novel mechanism study of microplastic and As co-contamination on indica rice (Oryza sativa L.).

Although the compound pollution of microplastics and arsenic (As) in paddy soil can affect the growth and quality of rice, relevant research on this phenomenon was limited. Therefore, we combined a pot experiment with computational chemistry to explore the effects and mechanism of polystyrene (PSMP) and polytetrafluoroethylene (PTFE) microplastics on As bioavailability. PSMP and PTFE interacted with rice root exudates through van der Waals forces, approached the rice root system, inhibited root activity, reduced the relative abundance of Geobacteria and Anaeromyxobacter, and consequently reduced the iron plaques on the root surfaces. Consequently, As uptake by the rice was inhibited. PSMP and PTFE reduced the hemoglobin content by directly destroying its tertiary structure, thereby retarding rice growth. In contrast, As increased the hemoglobin content by inducing reactive oxygen species in rice. Under the influence of PSMP, PTFE, and As, the activities of soluble starch synthase and pyrophosphorylase in rice grains were inhibited, and starch accumulation decreased. Thus, PSMP, PTFE, and As reduced rice biomass and yield owing to their physiological toxicity and adverse impacts on root activity. Grain yields in soil with an As content of 86.3 mg·kg-1, 0.5% small particle-sized PSMP, and 0.5% small particle-sized PTFE decreased by 30.7%, 20.6%, and 19.4%, respectively, compared to the control. This study determined the comprehensive mechanism through which PSMP and PTFE affect As bioavailability, which is critical for managing rice biomass and low yields in As and microplastic co-contaminated soil.

[Effects of Exogenous Jasmonic Acid on Arsenic Accumulation and Response to Stress in Roots of Rice Seedlings].

Arsenic (As) pollution has a toxic effect on crop growth, leading to reduced crop quality and yield. Therefore, it is urgent to explore safe and effective strategies to reduce its toxicity. In this experiment, hydroponics, fluorescent probe locating technology, differential centrifugation, and Fourier infrared spectroscopy (FTIR) analysis were used to research the effect of exogenous jasmonic acid (JA) on the accumulation and stress resistance of rice seedlings. The results showed that JA application reduced the As content in the roots and shoots of rice by 31.4% and 51.4%, respectively, and significantly reduced As content in the cell wall and soluble fractions of rice roots. JA changed the distribution ratio of As in the subcellular components. The distribution ratio of As in the cell wall increased by 16.4%, and the distribution ratio of soluble fractions decreased by 17.3%. JA enhanced the fixation of As by the cell wall and reduced the As content in the soluble fraction. Furthermore, JA increased the levels of SOD, CAT, GSH, and PEPC in root cells and reduced the contents of H2O2 and MDA, indicating that JA reduced lipid peroxidation damage, regulated carbon and nitrogen metabolism, and alleviated As toxicity. This research provides a new approach for the prevention and control of rice As pollution.

Jasmonic acid alleviates cadmium toxicity through regulating the antioxidant response and enhancing the chelation of cadmium in rice (Oryza sativa L.).

Cadmium (Cd) is a potentially hazardous element with substantial biological toxicity, adversely affecting plant growth and physiological metabolism. Therefore, it is necessary to explore practical and environment-friendly approaches to reduce toxicity. Jasmonic acid (JA) is an endogenous growth regulator which helps plants defend against biological and abiotic stresses. To determine how JA help relieve Cd toxicity in rice, both laboratory and field experiments were implemented. In the seedling stage, the role of JA in mediating rice Cd tolerance was investigated via a fluorescent probe in vivo localization, Fourier Transform Infrared Spectroscopy (FTIR), and colorimetry. At the mature growth stage of rice, field experiments were implemented to research the effects of JA on the Cd uptake and translocation in rice. In the seedling stage of rice, we found that JA application increased the cell wall compartmentalization of Cd by promoting the Cd combination on chelated-soluble pectin of rice roots and inhibited Cd movement into protoplasts, thereby reducing the Cd content in the roots by 30.5% and in the shoots by 53.3%, respectively. Application of JA reduced H2O2 content and helped relieve Cd-induced peroxidation damage of membrane lipid by increasing the level of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), but had no significant effect on the superoxide dismutase (SOD) activity. Additionally, field experiments showed that foliar spraying of JA inhibited rice Cd transport from the stalk and root to the grain and reduced Cd concentration in grain by 29.7% in the high-Cd fields and 28.0% in the low-Cd fields. These results improve our understanding of how JA contributes to resistance against Cd toxicity in rice plants and reduces the accumulation of Cd in rice kernels.

[Effect of Chelating Agents and Organic Acids on Remediation of Cadmium and Arsenic Complex Contaminated Soil Using Xanthium sibiricum].

In order to improve the phytoextraction efficiency of Xanthium sibiricum on farmland soil that had been contaminated by Cd and As, this study explored the effects of chelating agents and organic acids (EDTA, SAP, CA, and MA) on the extraction of Cd and As heavy metals using X. sibiricum. The results showed that the four different chelating agents and organic acids had little effect on the biomass of the roots, stems, and leaves of X. sibiricum. However, they had different effects on the concentrations and accumulation of Cd and As in various organs of X. sibiricum. Compared with the those in the CK treatment, EDTA, SAP, CA, and MA significantly increased the Cd concentrations in the leaves of X. sibiricum by 44.1%, 32.4%, 41.2%, and 38.2% and the As concentrations in the roots of X. sibiricum by 89.6%, 7.4%, 94.8%, and 61.5%, respectively. The four treatments (EDTA, SAP, CA, and MA) improved the total Cd accumulation of X. sibiricum, with increasing ranges, respectively, of 70.2%, 29.4%, 28.9%, and 33.1%, and the As accumulation increased by 67.0%, 19.6%, 81.9%, and 40.8%, respectively, compared with that of the CK treatment. The four chelating agents and organic acids had different effects on the Cd and As bioconcentration factor and transfer factor of various organs of X. sibiricum. Treatments with EDTA, SAP, CA, and MA resulted in a decrease of 32.7%-38.2% in soil Cd concentrations and a decrease of 14.6%-20.5% in soil As concentrations. These four chelating agents can be used for enhancing the efficiency of extraction Cd and As heavy metals by X. sibiricum.

Combined effect of iron and zinc on micronutrient levels in wheat (Triticum aestivum L.).

A nutrient solution experiment was conducted to investigate the effect of Fe and Zn supply on Fe, Zn, Cu, and Mn concentrations in wheat plants. The experiment used a factorial combination of two Fe levels (0 and 5 mg l(-1)) and three Zn levels (0, 0.1 and 10 mg I(-1)). The supply of Fe (5 mg l(-1)) and Zn (0.1 mg l(-1)) increased plant dry weight and leaf chlorophyll content compared to the Fe or Zn deficient (0 mg 11) treatments. However, excess Zn supply (10 mg l(-1)) reduced plant dry weights and leaf chlorophyll content. Iron supply (5 mg l(-1)) reduced wheat Zn concentrations by 49%, Cu concentrations by 34%, and Mn by 56% respectively. Zinc supply (10 mg l(-1)) reduced wheat Fe concentrations by an average of 8%, but had no significant effect on Cu and Mn concentrations. Stepwise regression analyses indicated that Zn, Cu, and Mn concentrations were negatively correlated with root- and leaf-Fe concentrations, but positively correlated with stem-Fe concentrations. Leaf-Mn concentrations were negatively correlated with root-, stem- and leaf-Zn concentrations.

[Effects of Different Exogenous Plant Hormones on the Antioxidant System and Cd Absorption and Accumulation of Rice Seedlings Under Cd Stress].

In order to explore the effects of the exogenous addition of plant hormones on the antioxidant system and Cd absorption and accumulation of rice seedlings under Cd stress, the transportation and accumulation of Cd was reduced in plants to alleviate the stress of Cd on the rice. With the rice seedlings of Zhongjiazao 17 as the research object, a hydroponic experiment was carried out with three Cd concentration treatments (0, 5, and 25 µmol·L-1), and four exogenous plant hormone treatments:no plant hormones, 100 µmol·L-1 melatonin (MT), 0.2 µmol·L-1 2,4-epibrassinolide (EBL), and 0.2 µmol·L-1 jasmonic acid (JA), for a total of 12 treatments, each treatment repeated three times. The contents of Cd in the rice seedlings were analyzed, as well as the content of MDA, POD, CAT, and reduced GSH in the shoots and roots of the rice seedlings. The results indicated that under the stress of 5 µmol·L-1 and 25 µmol·L-1 Cd, the addition of MT, EBL, and JA significantly reduced the MDA content of the shoots by 11%-24%, and the roots and shoots were healthy. On the contrary, the addition of the three exogenous substances all caused an increase in the MDA content in the root system, but the effects of MT and EBL were obvious. Under the 5 µmol·L-1 Cd stress, compared with CK, the MDA contents increased by 45.5% and 20.0% respectively; under 25 µmol·L-1 Cd stress, they increased by 46.2% and 19.8%. The exogenous addition of plant hormones can significantly increase the activity of POD and CAT in the shoots and underground parts of the rice seedlings and reduce the contents of GSH and Cd. Under the 5 µmol·L-1 Cd stress, the Cd content in the shoots of rice plants decreased by 39.4%, 40.1%, and 51.6%, the roots were reduced by 38.9%, 40.2%, and 7.0%. Under the 25 µmol·L-1 Cd stress, the aboveground Cd content was reduced by 18.9%, 14.5%, and 35.6%, and the roots were reduced by 85.3%, 81.1%, and 56.5%. By exogenously adding low-concentration plant hormones MT, EBL, and JA, the stress of Cd on the rice can be alleviated, and the toxic effect of Cd on rice can be reduced.

[Effects of Exogenous Spermidine on Seed Germination and As Uptake and Accumulation of Rice Under As5+ Stress].

As pollution in farmland has a toxic effect on the growth of crops, which reduces their yield and quality. The effects of exogenous spermidine (Spd) on rice seed germination and seedling growth under As5+ stress were studied. The results showed that exogenous Spd could promote the germination of rice seeds under As5+ stress, improve the germination potential and germination rate of seeds, and promote the growth of seedling roots. The addition of Spd could increase the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) of rice seedlings and roots under As5+ stress, and reduce the content of malondialdehyde (MDA) in rice buds and roots. When As5+ concentration was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, MDA content in rice roots was decreased by 12.3% and 31.3% and CAT activity of rice shoots was increased by 105.1% and 101.4%, and CAT activity of rice roots was increased by 29.9% and 57.1%, respectively. The addition of Spd also affected the uptake and accumulation of As in rice. When the concentration of As5+ was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, the concentration of As in rice shoots decreased by 69.4% and 75.1%, and As concentration in rice roots decreased by 7.6% and 24.4%, respectively. Spd could therefore effectively alleviate the toxic effect of As5+ on rice.