Graphitic carbon nitride alleviates cadmium toxicity to soybeans through nitrogen supply.

Graphitic carbon nitride (g-C3N4) is a promising candidate for heavy metal remediation, primarily composed of carbon (C) and nitrogen (N). It has been demonstrated that g-C3N4 adjusts rhizosphere physicochemical conditions, especially N conditions, alleviating the absorption and accumulation of Cadmium (Cd) by soybeans. However, the mechanisms by which g-C3N4 induces N alterations to mitigates plant uptake of Cd remain unclear. This study investigated the impact of g-C3N4-mediated changes in N conditions on the accumulation of Cd by soybeans using pot experiments. It also explored the microbiological mechanisms underlying alterations in soybean rhizospheric N cycling induced by g-C3N4. It was found that g-C3N4 significantly increased N content in the soybean rhizosphere (p < 0.05), particularly in terms of available nitrogen (AN) of nitrate and ammonium. Plants absorbed more ammonium nitrogen (NH4⁺-N), the content of which in the roots showed a significant negative correlation with Cd concentration in plant (p < 0.05). Additionally, g-C3N4 significantly affected rhizospheric functional genes associated with N cycling (p < 0.05) by increasing the ratio of the N-fixation functional gene nifH and decreasing the ratios of functional genes amoA and nxrA involved in nitrification. This enhances soybean's N-fixing potential and suppresses denitrification potential in the rhizosphere, preserving NH4⁺-N. Niastella, Flavisolibacter, Opitutus and Pirellula may play a crucial role in the N fixation and preservation process. In summary, the utilization of g-C3N4 offers a novel approach to ensure safe crop production in Cd-contaminated soils. The results of this study provide valuable data and a theoretical foundation for the remediation of Cd polluted soils.

Graphitic carbon nitride nanosheets mitigate cadmium toxicity in Glycine max L. by promoting cadmium retention in root and improving photosynthetic performance.

Cadmium (Cd) pollution poses a serious threat to plant growth and yield. Nanomaterials have shown great application potential for alleviation of Cd toxicity to plants. In this study, we applied graphitic carbon nitride nanosheets (g-C3N4 NSs) for alleviation of Cd-toxicity to soybean (Glycine max L.). The g-C3N4 NSs supplementation significantly improved plant growth and reduced oxidative damage in the Cd-toxicated soybean seedlings through hydroponic culture. Particularly, the g-C3N4 NSs dynamically regulated the root cell wall (RCW) components by increasing pectin content and modifying its demethylation via enhancing pectin methylesterase (PME) activity, therefore greatly enhanced stronger RCW-Cd retention (up to 82.8%) and reduced Cd migration to the shoot. Additionally, the g-C3N4 NSs reversed the Cd-induced chlorosis, increased photosynthetic efficiency because of enhancement in Fv/Fm ration, Y(II) and sugars content. These results provide new insights into the alleviation of Cd toxicity to plants by g-C3N4 NSs, and shed light on the application of low-cost and environmental-friendly carbon-based NMs for alleviating heavy metal toxicity to plants.

A promising product: Abscisic acid-producing bacterial agents for restricting cadmium enrichment in field vegetable crops.

Soil heavy metal contamination and its enrichment in the edible parts of crops have gained global concern. In this study, a compound bacterial agent possessing the ability to produce the plant hormone, abscisic acid (ABA), was applied to contaminated farmland in Hunan province. Its application reduced the concentration of Cd in radish, cabbage, mustard, and lettuce by 15-144%. Accordingly, the Cd contents in these vegetables were found to be below the maximum limits set by GB 2762-2017. Meanwhile, bacteria agents also led to a significant increase in crops yield by 45-82%. Furthermore, the nutritional indices, including soluble sugar and soluble protein increased by 18-66%, as well as the antioxidant indices, including total phenolic, ascorbate content, and DPPH capacity, enhanced by 12-76%, 10-49% and 50-140%, respectively. In conclusion, the use of ABA-producing bacteria is anticipated to be a novel approach for the safe use of soil with moderate and low pollution.

Graphitic carbon nitride alleviates cadmium toxicity to microbial communities in soybean rhizosphere.

Cadmium (Cd) contamination has led to various harmful impacts on soil microbial ecosystem, agricultural crops, and thus human health. Nanomaterials are promising candidates for reducing the accumulation of heavy metals in plants. In this study, graphitic carbon nitride (g-C3N4), a two-dimensional polymeric nanomaterial, was applied for ameliorating Cd phytotoxicity to soybean (Glycine max (L.) Merr.). Its impacts on rhizosphere variables, microorganisms, and metabolism were examined. It was found that g-C3N4 increased carbon/nitrogen/phosphorus (C/N/P) content, especially when N contents were averagely 4.2 times higher in the g-C3N4-treated groups. g-C3N4 significantly induced alterations in microbial community structures (P < 0.05). The abundance of the probiotics class Nitrososphaeria was enriched (on average 70% higher in the g-C3N4-treated groups) as was Actinobacteria (226% higher in the g-C3N4 group than in the CK group). At the genus level, g-C3N4 recruited more Bradyrhizobium (122% higher) in the Cd + g-C3N4 group than in the Cd group and more Sphingomonas (on average 24% higher) in the g-C3N4-treated groups. The changes of microbial clusters demonstrated the potential of g-C3N4 to shape microbial functions, promote plant growth, and enhance Cd resistance, despite observing less pronounced modifications in microbial communities in Cd-contaminated soil compared to Cd-free soil. Moreover, abundance of functional genes related to C/N/P transformation was more significantly promoted by g-C3N4 in Cd-contaminated soil (increased by 146%) than in Cd-free one (increased by 32.8%). Therefore, g-C3N4 facilitated enhanced microbial survival and adaptation through the amplification of functional genes. These results validated the alleviation of g-C3N4 on the microbial communities in the soybean rhizosphere and shed a new light on the application of environmental-friendly nanomaterials for secure production of the crop under soil Cd exposure.

Using brefeldin A to disrupt cell wall polysaccharide components in rice and nitric oxide to modify cell wall structure to change aluminum tolerance.

The components and structure of cell wall are closely correlated with aluminum (Al) toxicity and tolerance for plants. However, the cell wall assembly and function construction in response to Al is not known. Brefeldin A (BFA), a macrolide, is used to disrupt cell wall polysaccharide components, and nitric oxide (NO), a signal molecule, is used to modify the cell wall structure. Pretreatment with BFA accelerated Al accumulation in root tips and Al-induced inhibition of root growth of two rice genotypes of Nipponbare and Zhefu 802, and significantly decreased the cell wall polysaccharide content including pectin, hemicellulose 1, and hemicellulose 2, indicating that BFA inhibits the biosynthesis of components in the cell wall and makes the root cell wall lose the ability to resist Al. The addition of NO donor (SNP) significantly alleviated the toxic effects of Al on root growth, Al accumulation, and oxidative damage, and decreased the content of pectin polysaccharide and functional groups of hydroxyl, carboxyl, and amino in the cell wall via FTIR analysis, while had no significant effect on hemicellulose 1 and hemicellulose 2 content compared with Al treatment. Furthermore, NO didn't change the inhibition effect of BFA-induced cell wall polysaccharide biosynthesis and root growth. Taken together, BFA disrupts the integrity of cell wall and NO modifies partial cell wall composition and their functional groups, which change the Al tolerance in rice.

Nitric oxide reduces the aluminum-binding capacity in rice root tips by regulating the cell wall composition and enhancing antioxidant enzymes.

Plant cell wall, the first interface or barrier for toxic ions entering into protoplast, suffers from risk. Nitric oxide (NO) plays an important role in plant growth and responses to abiotic stresses, however, it is not clear whether NO is connected with the response of cell wall to aluminum (Al) tolerance in rice (Oryza sativa L.). In this study, we found that the application of 50 µM Al induces nitrate reductase (NR) activity and endogenous NO production, but not nitric oxide synthase (NOS) activity in two rice genotypes. Pretreatment with 100 µM NO donor (sodium nitroprusside, SNP) reduced Al-induced inhibition of root elongation by 32.3% and 91.7%, and Al accumulation in root-tip by 38.4% and 44.3% in Nipponbare and Zhefu802, respectively. The addition of SNP significantly decreased Al-induced accumulation of pectin, hemicellulose 1 and hemicellulose 2 by 43.1%, 13.1% and 19.2% in Zhefu802 and by 16.9%, 13.4% and 14.0% in Nipponbare, compared with roots treated with Al alone, as well as pectin methylesterase (PME) activity. Therefore, the content of Al absorbed in cell walls was decreased, indicating that the Al-induced structure damage to cell walls was alleviated. Furthermore, the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) treated by Al were all increased by SNP pretreatment, and the lipid peroxidation and damage to plasma membrane of root tips detected with Schiff's reagent and Evans blue reduced. In contrast, the effect was abolished when NO scavenger (cPTIO), and NR inhibitor (NaN3), were added. These results indicated that by regulating the Al-binding capacity to cell walls and lipid peroxidation, the structure of cell walls can be stabilized and that Al toxicity in rice can be alleviated with increased NO.

[Effects of IAA on physiological response to aluminum stress and DNA damage of Trichosanthes kirilowii.] / å²å“šä¹™é ¸å¯¹é“èƒè¿«ä¸‹æ æ¥¼ç”Ÿç†å“åº”åŠDNA损伤的缓解作用.

To investigate the physiological response of IAA (indoleacetic acid) to Trichosanthes kirilowii under aluminum stress and the mitigation of DNA damage, the effects of IAA (0, 10, 25, 50, 75 µmol·L-1 denoted by I0, I10, I25, I50 and I75, respectively) on antioxidant enzyme activity, malondialdehyde (MDA), photosynthetic characteristics, root activity, chlorophyll content and DNA damage of two varieties of T. kirilowii under 300 and 800 µmol·L-1 aluminum environment (denoted by Al300 and Al800, respectively) were examined in hydroponic culture experiments with Hebei Anguo (aluminium tolerant variety) and Zhejiang Puyang Trichosanthes kirilowii (aluminum sensitive variety). The results showed that the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), photosynthesis ability, and root activity of both varieties were inhibited to different degrees by aluminum stress, MDA content was significantly increased, and DNA damage was aggravated. The maximum increase of SOD, CAT and POD activities in Anguo and Puyang T. kirilowii under aluminum stress by IAA application were 15.0%, 31.2%, 72.3% and 13.8%, 26.9%, 26.4%, respectively, chlorophyll content increased by 49.9% and 17.9%, MDA accumulation decreased by 39.2% and 22.4% and fluorescence parameters were significantly improved. The treatment of 25 µmol·L-1 IAA significantly increased root activity by 159.1% and 90.9%, while 50 µmol·L-1 IAA effectively slowed the DNA tailing phenomenon in roots, with the product (OTM) value of tail DNA percentage content and tail moment being decreased by 27.6%. 10-50 µmol·L-1 IAA could effectively improve the physiological activity of T. kirilowii under aluminum stress and slow the degree of DNA damage. The tolerance of Anguo variety to aluminum stress was stronger than that of Puyang variety.

Immobilization of aluminum with mucilage secreted by root cap and root border cells is related to aluminum resistance in Glycine max L.

The root cap and root border cells (RBCs) of most plant species produced pectinaceous mucilage, which can bind metal cations. In order to evaluate the potential role of root mucilage on aluminum (Al) resistance, two soybean cultivars differing in Al resistance were aeroponic cultured, the effects of Al on root mucilage secretion, root growth, contents of mucilage-bound Al and root tip Al, and the capability of mucilage to bind Al were investigated. Increasing Al concentration and exposure time significantly enhanced mucilage excretion from both root caps and RBCs, decreased RBCs viability and relative root elongation except roots exposed to 400 µM Al for 48 h in Al-resistant cultivar. Removal of root mucilage from root tips resulted in a more severe inhibition of root elongation. Of the total Al accumulated in root, mucilage accounted 48-72 and 12-27 %, while root tip accounted 22-52 and 73-88 % in Al-resistant and Al-sensitive cultivars, respectively. A (27)Al nuclear magnetic resonance spectrum of the Al-adsorbed mucilage showed Al tightly bound to mucilage. Higher capacity to exclude Al in Al-resistant soybean cultivar is related to the immobilization and detoxification of Al by the mucilage secreted from root cap and RBCs.

Response and tolerance of root border cells to aluminum toxicity in soybean seedlings.

Root border cells (RBCs) and their secreted mucilage are suggested to participate in the resistance against toxic metal cations, including aluminum (Al), in the rhizosphere. However, the mechanisms by which the individual cell populations respond to Al and their role in Al resistance still remain unclear. In this research, the response and tolerance of RBCs to Al toxicity were investigated in the root tips of two soybean cultivars [Zhechun No. 2 (Al-tolerant cultivar) and Huachun No. 18 (Al-sensitive cultivar)]. Al inhibited root elongation and increased pectin methylesterase (PME) activity in the root tip. Removal of RBCs from the root tips resulted in a more severe inhibition of root elongation, especially in Huachun No. 18. Increasing Al levels and treatment time decreased the relative percent viability of RBCs in situ and in vitro in both soybean cultivars. Al application significantly increased mucilage layer thickness around the detached RBCs of both cultivars. Additionally, a significantly higher relative percent cell viability of attached and detached RBCs and thicker mucilage layers were observed in Zhechun No. 2. The higher viability of attached and detached RBCs, as well as the thickening of the mucilage layer in separated RBCs, suggest that RBCs play an important role in protecting root apices from Al toxicity.

Developmental characteristics and aluminum resistance of root border cells in rice seedlings.

The developmental characteristics of root border cells (RBCs) and their role in protection of root apices of rice seedling from Al toxicity were evaluated in two rice (Oryza sativa L.) cultivars differing in Al tolerance. Root elongation and RBCs viability were used as indicators for Al effects. The formation of RBCs and the emergence of the root tip occurred almost simultaneously. Treatment of the root with Al inhibited root elongation and increased Al accumulation in the root tips. Physical removal of RBCs from root tips resulted in a more severe inhibition of root elongation and a higher Al accumulation in the root tips. These effects were more pronounced in the Al-sensitive rice cultivar (II You 6216) than that in the Al-tolerant rice cultivar (II You 838). The relative viability of attached and detached RBCs decreased with increasing Al concentrations. Al also induced a thicker mucilage layer surrounding attached RBCs of both cultivars, and detached RBCs did not. Maintaining the abundant live RBCs encapsulated root tip and enhancing their mucilage secretion, appear to be important in alleviating Al toxicity and in allowing exclusion of Al from the rice root apex.

[Analysis and comparison of trace elements of herba euphorbiae humifusae in different periods by microwave digestion-atomic absorption spectroscopy].

Herba euphorbiae humifusae is the dried whole plant of Euphorbia humi fusa Willd. that belongs to euphorbiaceae. In the present paper, the microwave digestion procedure was used to digest herba euphorbiae humifusae collected in different periods, and then flame atomic absorption spectrometry (FAAS) was used to determine the contents of eight kinds of trace elements of herba euphorbiae humifusae in different periods, and the change in the contents of trace elements at different times was studied and analysed. The results showed that of all the trace elements of herba euphorbiae humifusae in different periods, element Fe was the highest in June, element K was in August at the highest level, element Mn reached the highest content in September, elements Na and Ca were dividedly at the highest content in October and November, and in December the highest content elements were Zn, Cu and Mg. In one word, the change of Na and Ca was jumping, while the change of Cu and Zn was comparatively mild. The results provide scientific basis for the time of collection of herba euphorbiae humifusae.

Developmental characteristics and response to iron toxicity of root border cells in rice seedlings.

To investigate the Fe2+ effects on root tips in rice plant, experiments were carried out using border cells in vitro. The border cells were pre-planted in aeroponic culture and detached from root tips. Most border cells have a long elliptical shape. The number and the viability of border cells in situ reached the maxima of 1600 and 97.5%, respectively, at 20-25 mm root length. This mortality was more pronounced at the first 1-12 h exposure to 250 mg/L Fe2+ than at the last 12-36 h. After 36 h, the cell viability exposed to 250 mg/L Fe2+ decreased to nought, whereas it was 46.5% at 0 mg/L Fe2+. Increased Fe2+ dosage stimulated the death of detached border cells from rice cultivars. After 4 h Fe2+ treatment, the cell viabilities were > or =80% at 0 and 50 mg/L Fe2+ treatment and were <62% at 150, 250 and 350 mg/L Fe2+ treatment; The viability of border cells decreased by 10% when the Fe2+ concentration increased by 100 mg/L. After 24 h Fe2+ treatment, the viabilities of border cells at all the Fe2+ levels were <65%; The viability of border cells decreased by 20% when the Fe2+ concentration increased by 100 mg/L. The decreased viabilities of border cells indicated that Fe2+ dosage and treatment time would cause deadly effect on the border cells. The increased cell death could protect the root tips from toxic harm. Therefore, it may protect root from the damage caused by harmful iron toxicity.