Soil application of graphitic carbon nitride nanosheets alleviate cadmium toxicity by altering subcellular distribution, chemical forms of cadmium and improving nitrogen availability in soybean (Glycine max L.).

Cadmium (Cd)-contamination impairs biological nitrogen fixation in legumes (BNF), threatening global food security. Innovative strategies to enhance BNF and improve plant resistance to Cd are therefore crucial. This study investigates the effects of graphitic carbon nitride nanosheets (g-C3N4 NSs) on soybean (Glycine max L.) in Cd contaminated soil, focusing on Cd distribution, chemical forms and nitrogen (N) fixation. Soybean plants were treated with 100 mg kg-1 g-C3N4 NSs, with or without 10 mg kg-1 Cd for 4 weeks. Soil addition of g-C3N4 NSs alleviated Cd toxicity and promote soybean growth via scavenging Cd-mediated oxidative stress and improving photosynthesis. Compared to Cd treatment, g-C3N4 NSs increased shoot and root dry weights under Cd toxicity by 49.5% and 63.4%, respectively. g-C3N4 NSs lowered Cd content by 35.7%-54.1%, redistributed Cd subcellularly by increasing its proportion in the cell wall and decreasing it in soluble fractions and organelles, and converted Cd from high-toxicity to low-toxicity forms. Additionally, g-C3N4 NSs improved the soil N cycle, stimulated nodulation, and increased the N-fixing capacity of nodules, thus increasing N content in shoots and roots by 12.4% and 43.2%, respectively. Mechanistic analysis revealed that g-C3N4 NSs mitigated Cd-induced loss of endogenous nitric oxide in nodules, restoring nodule development. This study highlights the potential of g-C3N4 NSs for remediating Cd-contaminated soil, reducing Cd accumulation, and enhancing plant growth and N fixation, offering new insights into the use of carbon nanomaterials for soil improvement and legume productivity under metal(loid)s stress.

Effects of zeolite imidazole frameworks on rice seedlings (Oryza sativa L.): Phytotoxicity, transformation, and bioaccumulation.

Zeolite imidazole frameworks (ZIFs), a class of the metal organic framework, have been extensively studied in environmental applications. However, their environmental fate and potential ecological impact on plants remain unknown. Here, we investigated the phytotoxicity, transformation, and bioaccumulation processes of two typical ZIFs (ZIF-8 and ZIF-67) in rice (Oryza sativa L.) under hydroponic conditions. ZIF-8 and ZIF-67 in the concentration of 50 mg/L decreased root and shoot dry weight maximally by 55.2% and 27.5%, 53.5% and 37.5%, respectively. The scanning electron microscopy (SEM) imaging combined with X-ray diffraction (XRD) patterns revealed that ZIFs on the root surface gradually collapsed and transformed into nanosheets with increasing cultivation time. The fluorescein isothiocyanate (FITC) labeled ZIFs were applied to trace the uptake and translocation of ZIFs in rice. The results demonstrated that the transformed ZIFs were mainly distributed in the intercellular spaces of rice root, while they cannot be transported to culms and leaves. Even so, the Co and Zn contents of rice roots and shoots in the ZIFs treated groups were increased by 1145% and 1259%, 145% and 259%, respectively, compared with the control groups. These findings suggested that the phytotoxicity of ZIFs are primarily attributed to the transformed ZIFs and to a less extent, the metal ions and their ligands, and they were internalized by rice root and increased the Co and Zn contents of shoots. This study reported the transformation of ZIFs and their biological effectiveness in rice, highlighting the potential environmental hazards and risks of ZIFs to crop plants.

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.

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.

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.

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.

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.

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.