Nitrate-induced AHb1 expression aggravates Cd toxicity in plants

Exploring the phytotoxicity mechanisms of PET nanoplastics and 6:2 FTSA in water hyacinth under individual and combined exposure scenarios

Due to its similarity in hydrophobic properties to perfluorooctanesulfonic acid (PFOS), 6:2 fluorotelomer sulfonic acid (6:2 FTSA) has emerged as a key substitute for PFOS. Its presence in aquatic environments, along with the coexistence of polyethylene terephthalate (PET), may impact the growth of aquatic plants and ecosystem stability. This study explored the changes in antioxidant defense, photosynthetic system, and metabolic responses of water hyacinths (Eichhornia crassipes) under individual and combined exposure conditions. The results indicated that water hyacinth efficiently accumulated 6:2 FTSA, with notably higher accumulation levels in leaves compared to roots, leading to a more pronounced stress response in leaves. The contents of nitrate, nitrite, ammonium, and the activities of nitrogen assimilation enzymes in leaves increased significantly, which in turn boosted the levels of reactive oxygen species (ROS) scavengers such as glutamic acid and glutathione, as well as antioxidant defense enzymes. Meanwhile, leaf photosynthesis was significantly suppressed due to the resource reallocation. This was corroborated by disruptions in the chloroplast thylakoid structure and alterations in chlorophyll fluorescence parameters. Metabolomics analysis further revealed that the contents of monosaccharides and organic acids decreased markedly, whereas amino acid levels increased significantly, suggesting that water hyacinths prioritized antioxidant defense mechanisms at the expense of growth. Additionally, we observed that the phytotoxic effects of 6:2 FTSA were exacerbated in the presence of PET nanoplastics, with the aforementioned indicators exhibiting synergistic effects. This study provides phenotypic, physiological, metabolic, and transcriptional insights into the toxic effects of the coexistence of PET nanoplastics and 6:2 FTSA on water hyacinths, offering toxicological data (e.g., oxidative stress markers and gene expression profiles) for assessing the environmental risks associated with emerging contaminants and proposing management strategies.

Role of SbNRT1.1B in cadmium accumulation is attributed to nitrate uptake and glutathione-dependent phytochelatins biosynthesis

Phytoremediation of cadmium (Cd)-polluted soil by using sweet sorghum displays a tremendous potential as it is a fast-growing, high biomass and Cd tolerant energy plant. Previous study has demonstrated SbNRT1.1B expression change is in accordance with enhanced Cd accumulation by external nitrate supply in sweet sorghum. Nevertheless, underlying mechanism of SbNRT1.1B response to Cd stress is still elusive. SbNRT1.1B exhibited a positive response to Cd stress in sweet sorghum. Overexpressing SbNRT1.1B increased primary root length, shoot fresh weight, nitrate and chlorophyll concentrations compared with Col-0 under Cd stress, while complementary SbNRT1.1B rescued these decreased values in mutant chl1-5. Cd concentrations in overexpressing SbNRT1.1B, complementary SbNRT1.1B and Col-0 lines were 3.2-4.1, 2.5-3.1 and 1.2-2.1 folds of that in chl1-5. Consistent with Cd concentrations, non-protein thiol (NPT), reduced glutathione (GSH) and phytochelatins (PCs) concentrations as well as the related genes expression levels showed the same trends under Cd stress. GSH biosynthesis inhibitor failed to reverse the patterns of GSH-dependent PCs concentrations changes in different lines, suggesting that SbNRT1.1B plays an upstream role in GSH-dependent PCs biosynthesis under Cd treatment. Altogether, SbNRT1.1B enhances nitrate concentrations contributing to increased chlorophyll concentrations and GSH-dependent PCs metabolites biosynthesis, thereby improving growth and Cd concentrations in plants.

Mechanisms of Cadmium stress response in watermelon: Insights from physiological, transcriptomic, and metabolic analyses

Cadmium (Cd) contamination of soil may lead to Cd stress for plants, which significantly hinders plant growth and development, posing a risk to human health through the consumption of Cd-contaminated foods. Watermelon (Citrullus lanatus), a widely consumed fruit, is particularly affected by Cd stress globally, yet the mechanisms underlying its response are not well understood. Here, we subjected watermelon seedlings to simulated Cd stress treatment and explored the physiological, transcriptomic, and metabolic response. Our findings revealed that Cd stress treatment led to increased accumulation of reactive oxygen species (ROS) in watermelon leaves. Transcriptome sequencing unveiled a multitude of osmotic and oxidative stress-responsive genes, including peroxidase (POD), MYB, voltage-dependent anion channel (SLAC1), and ABC transporter. KEGG enrichment analysis highlighted the predominant enrichment of Cd stress-responsive genes in pathways such as glutathione (GSH) metabolism, MAPK signaling, and biosynthesis of secondary metabolites. Within the GSH metabolism pathway, several glutathione S-transferase (GST) genes were up-regulated, alongside phytochelatin synthetase (PCS) genes involved in phytochelatin synthesis. In the MAPK signaling pathway, genes associated with ABA and ethylene signal transduction showed up-regulation following Cd stress. Metabolomic analysis demonstrated that Cd stress enhanced the production of amino acids, phenolamines, and esters. Overall, our study elucidates that watermelon responds to Cd stress by activating its antioxidant system, GSH metabolism pathway, MAPK signal pathway, and biosynthesis of key metabolites. These findings offer valuable insights for the remediation of heavy metal pollution in soil affecting plant life.

Co-mutation of OsLPR1/3/4/5 provides a promising strategy to minimize Cd contamination in rice grains

Minimizing cadmium (Cd) contamination in rice grains is crucial for ensuring food security and promoting sustainable agriculture. Utilizing genetic modification to generate rice varieties with low Cd accumulation is a promising strategy due to its cost-effectiveness and operational simplicity. Our study demonstrated that the CRISPR-Cas9-mediated quadruple mutation of the multicopper oxidase genes OsLPR1/3/4/5 in the japonica rice cultivar Tongjing 981 had little effect on yields. However, a notable increase was observed in the cell wall functional groups that bind with Cd. As a result, the quadruple mutation of OsLPR1/3/4/5 enhanced Cd sequestration within the cell wall while reducing Cd concentrations in both xylem and phloem sap, thereby inhibiting Cd transport from roots to shoots. Consequently, Cd concentrations in brown rice and husk in oslpr1/3/4/5 quadruple mutants (qm) decreased by 52% and 55%, respectively, compared to the wild-type. These findings illustrate that the quadruple mutation of OsLPR1/3/4/5 is an effective method for minimizing Cd contamination in rice grains without compromising yields. Therefore, the quadruple mutation of OsLPR1/3/4/5 via biotechnological pathways may represent a valuable strategy for the generation of new rice varieties with low Cd accumulation.

ABA-importing transporter (AIT1) synergies enhances exogenous ABA minimize heavy metals accumulations in Arabidopsis

Exogenous abscisic acid (ABA) presents a novel approach to mitigate heavy metal (HM) accumulation in plants, yet its efficacy against multiple HMs and potential enhancement methods remain underexplored. In this study, we demonstrated that the exogenous ABA application simultaneously decreased Zn, Cd and Ni accumulation by 22-25 %, 27-39 % and 60-62 %, respectively, in wild-type (WT) Arabidopsis. Conversely, ABA reduced Pb in shoots but increased its root concentration. ABA application also modulated the expression of HM uptake genes, inhibiting IRT1, NRAMP1, NRAMP4, and HMA3, and increasing ZIP1 and ZIP4 expressions. Further analysis revealed that overexpressing the ABA-importing transporter (AIT1) in plants intensified the reduction of Cd, Zn, and Ni, compared to WT. However, the inhibitory effect of exogenous ABA on Pb accumulation was mitigated in shoots with higher AIT1 expression. Furthermore, HMs-induced growth inhibition and the damage to photosynthesis were also alleviated with ABA treatment. Conclusively, AIT1's synergistic effect with ABA effectively reduces Cd, Zn and Ni accumulation, offering a synergistic approach to mitigate HM stress in plants.

NRT1.2 overexpression enhances the synergistic interplay between ABA-generating bacteria and biochars in reducing heavy metal accumulation in pak choi

The agricultural sector faces severe challenges owing to heavy metal (HM) contamination of farmlands, requiring urgent preventive measures. To address this, we investigated the impact of the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium producing abscisic acid (ABA), and biochar to minimize HM accumulation in pak choi, using three distinct expression levels of the ABA transporter NRT1.2 in pak choi and three different types of contaminated soils as experimental materials. The results revealed that pak choi with low, medium, and high NRT1.2 expression intensity, when subjected to bacterial strain-biochar treatment, exhibited an increasing trend in ABA content compared to the control. Correspondingly, the aboveground HM content decreased by 1-49 %, 22-52 %, and 15-96 %, whereas the fresh weight increased by 12-38 %, 88-126 %, and 152-340 %, respectively, showing a significant correlation with NRT1.2 expression. Pearson correlation analysis demonstrated that NRT1.2 expression intensity was inversely associated with the combined treatment's reduction in HM accumulation and positively correlated with the promotional effect. Simultaneously, soil discrepancies significantly affected the combined treatment, which was likely associated with variations in the active forms of HM in each soil. Consequently, when employing ABA-producing bacteria for mitigating crop HM accumulation, selecting plants with higher relative NRT1.2 expression intensity, combined with biochar, is recommended.

ABA-metabolizing bacteria and rhamnolipids as valuable allies for enhancing phytoremediation efficiency in heavy metal-contaminated soils

Microbial-assisted phytoremediation has great potential to improve the efficiency of phytoremediation in heavy metal (HM)-contaminated soils. In this study, the synergistic effects of rhamnolipids and the abscisic acid (ABA)-metabolizing bacterium Rhodococcus qingshengii on the phytoremediation efficiency of Indian mustard (Brassica juncea) in HM-contaminated soils were investigated. The Cd, Zn, and Pb contents in plants treated with a combination of rhamnolipids and R. qingshengii were 48.4-77.1 %, 14.6-40.4 %, and 16.1-20.0 % higher, respectively, than in those treated with R. qingshengii alone, and 42.8-59.2 %, 13.1-48.2 %, and 7.3-67.5 % higher, respectively, than in those treated with rhamnolipids alone. In addition, the bioconcentration factors of each metal were improved, and the biomass further increased by 36.6-65.7 % compared to that of single treatments. Pearson's correlation analysis showed that rhamnolipids and R. qingshengii enhanced the accumulation of HMs in B. juncea by activating the available forms of HMs in the soil and regulating the ABA and indole-3-acetic acid in plants, respectively. The structural equation model indicated that R. qingshengii had a larger path coefficient than rhamnolipids in terms of HM content and plant biomass, suggesting that R. qingshengii may have a greater contribution to promoting the extraction of HMs from the soil under synergistic conditions. In conclusion, the combination of rhamnolipids and R. qingshengii has great potential to enhance the phytoremediation efficiency of hyperaccumulating plants in HM-contaminated soils.