Transcriptome and metabolome analysis reveal key genes and metabolic pathway responses in Leersia hexandra Swartz under Cr and Ni co-stress.

Phytoremediation, an eco-friendly approach for mitigating heavy metal contamination, is reliant on hyperaccumulators. This study focused on Leersia hexandra Swart, a known chromium (Cr) hyperaccumulator with demonstrated tolerance to multiple heavy metals. Our objective was to investigate its response to simultaneous Cr and nickel (Ni) stress over 12 days. Results from physiological experiments demonstrated a significant increase in the activities of antioxidant enzymes (APX, SOD, CAT) and glutathione (GSH) content under Cr and Ni stress, indicating enhanced antioxidant mechanisms. Transcriptome analysis revealed that stress resulted in the differential expression of 27 genes associated with antioxidant activity and metal binding, including APX, SOD, CAT, GSH, metallothionein (MT), and nicotinamide (NA). Among them, twenty differentially expressed genes (DEGs) related to GSH metabolic cycle were identified. Notably, GSTU6, GND1, and PGD were the top three related genes, showing upregulation with fold changes of 4.57, 6.07, and 3.76, respectively, indicating their crucial role in metal tolerance. The expression of selected DEGs was validated by quantitative real-time PCR, confirming the reliability of RNA-Seq data. Metabolomic analysis revealed changes in 1121 metabolites, with amino acids, flavonoids, and carbohydrates being the most affected. Furthermore, glucosinolate biosynthesis and amino acid biosynthesis pathways were represented in the KEGG pathway of differentially expressed metabolites (DEMs). This study provides insights into the tolerance mechanisms of L. hexandra under the co-stress of Cr and Ni, offering a new perspective for enhancing its remediation performance.

Mn Pretreatment Improves the Physiological Resistance and Root Exudation of Celosia argentea Linn. to Cadmium Stress.

Phytoextraction using Celosia argentea Linn. by Mn pretreatment can potentially decontaminate Cd-contaminated soils. However, the mechanism that accelerates the Cd bioaccumulation is still unknown. In order to study the effect and mechanism of Mn pretreatment on Cd bioaccumulation in C. argentea, the hydroponic experiments were set to determine the chlorophyll content, antioxidant enzyme activity, malondialdehyde content, and root exudation of C. argentea. The results indicated that after seven days of Mn pretreatment, both the biomass and Cd concentrations in plants increased compared to the control group. One of the mechanisms for this was the improvement in the physiological resistance of C. argentea following pretreatment with Mn. Compared with Cd stress alone, Mn pretreatment increased photosynthesis and reduced membrane lipid peroxidation. Meanwhile, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were significantly reduced in leaves of C. argentea after Mn pretreatment through the reduction in the production of reactive oxygen species. In addition, Mn promoted the exudation of organic acids in the roots of C. argentea. The contents of citric and malic acids increased by 55.3% and 26.4%, respectively, which may be another important reason for Mn pretreatment increasing Cd bioaccumulation in C. argentea. Therefore, the present work shows that the pretreatment of seedlings with Mn can provide a meaningful strategy to improve the remediation efficiency of Cd-contaminated soils by C. argentea.

Preparation and Characterization of Fe-Mn Binary Oxide/Mulberry Stem Biochar Composite Adsorbent and Adsorption of Cr(VI) from Aqueous Solution.

This study details the preparation of Fe-Mn binary oxide/mulberry stem biochar composite adsorbent (FM-MBC) from mulberry stems via the multiple activation by potassium permanganate, ferrous chloride, triethylenetetramine, and epichlorohydrin. The characteristics of FM-MBC had been characterized by SEM-EDS, BET, FT-IR, XRD, and XPS, and static adsorption batch experiments such as pH, adsorption time, were carried out to study the mechanism of Cr(VI) adsorption on FM-MBC and the impact factors. The results indicated that in contrast with the mulberry stem biochar (MBC), the FM-MBC has more porous on surface with a BET surface area of 74.73 m2/g, and the surface loaded with α-Fe2O3 and amorphization of MnO2 particles. Besides, carboxylic acid, hydroxyl, and carbonyls functional groups were also formed on the FM-MBC surface. At the optimal pH 2.0, the maximum adsorption capacity for Cr(VI) was calculated from the Langmuir model of 28.31, 31.02, and 37.14 mg/g at 25, 35, and 45 °C, respectively. The aromatic groups, carboxyls, and the hydroxyl groups were the mainly functional groups in the adsorption of Cr(VI). The mechanism of the adsorption process of FM-MBC for Cr(VI) mainly involves electrostatic interaction, surface adsorption of Cr(VI) on FM-MBC, and ion exchange.