Analysis of anatomical changes and cadmium distribution in Aegiceras corniculatum (L.) Blanco roots under cadmium stress

Root radial apoplastic transport contributes to shoot cadmium accumulation in a high cadmium-accumulating rice line

Radial transport of cadmium (Cd) in roots governs the amount of Cd loaded into xylem vessels, where Cd ions are translocated upward into shoots, while the mechanism of differential Cd radial transport between the high Cd-accumulating rice line Lu527-8 and the normal rice line Lu527-4 remains ambiguous. A higher Cd distribution in cross sections and root apoplast and higher bypass flow of Cd were found in Lu527-8, explaining a greater Cd translocation through the apoplastic pathway. The lower relative area of the epidermis and the constant relative area of the cortex in Lu527-8 opened-up root radial transport for Cd. Deposition of apoplastic barriers (Casparian strips and suberin lamellae) was stimulated by Cd, which effectively prevented Cd from entering the stele through the apoplastic pathway. In Lu527-8, apoplastic barriers were further from the root apex with lower expression of genes responsible for biosynthesis of Casparian strips and suberin lamellae, enhancing radial transport of Cd. Our data revealed that the higher radial apoplastic transport of Cd played an integral role in Cd translocation, contributed to a better understanding of the mechanism involved in high Cd accumulation in Lu527-8 and helped achieve the practical application of phytoextraction.

Root cell wall remodeling: A way for exopolysaccharides to mitigate cadmium toxicity in rice seedling

Exopolysaccharides (EPS) are macromolecules with environment beneficial properties. Currently, numerous studies focus on the absorption of heavy metals by EPS, but less attention has been paid to the effects of EPS on the plants. This study explored the effects of EPS from Lactobacillus plantarum LPC-1 on the structure and function of cell walls in rice seedling roots under cadmium (Cd) stress. The results showed that EPS could regulate the remodeling process of the cell walls of rice roots. EPS affects the synthesis efficiency and the content of the substances that made up the cell wall, and thus plays an essential role in limiting the uptake and transport of Cd in rice root. Furthermore, EPS could induce plant resistance to heavy metals by regulating the lignin biosynthesis pathway in rice roots. Finally, the cell wall remodeling induced by EPS likely contributes to plant stress responses by activating the reactive oxygen species (ROS) signaling.

New Evidence of Semi-Mangrove Plant Barringtonia racemosa in Soil Clean-Up: Tolerance and Absorption of Lead and Cadmium

Mangrove plants play an important role in the remediation of heavy-metal-contaminated estuarine and coastal areas; Barringtonia racemosa is a typical semi-mangrove plant. However, the effect of heavy metal stress on this plant has not been explored. In this study, tolerance characteristics and the accumulation profile of cadmium (Cd) and lead (Pb) in B. racemosa were evaluated. The results indicated that B. racemosa exhibited a high tolerance in single Cd/Pb and Cd + Pb stress, with a significant increase in biomass yield in all treatment groups, a significant increase in plant height, leaf area, chlorophyll and carotenoid content in most treatment groups and without significant reduction of SOD, POD, MDA, proline content, Chl a, Chl b, Chl a + b, Car, ratio of Chl a:b and ratio of Car:Chl (a + b). Cd and Pb mainly accumulated in the root (≥93.43%) and the content of Cd and Pb in B. racemosa was root > stem > leaf. Pb showed antagonistic effects on the Cd accumulation in the roots and Cd showed antagonistic or synergistic effects on the Pb accumulation in the roots, which depended on the concentration of Cd and Pb. There was a significant synergistic effect of Cd and Pb enrichment under a low Cd and Pb concentration treatment. Thus, phytoremediation could potentially use B. racemosa for Cd and Pb.

Proteomic analysis reveals molecular mechanism of Cd2+ tolerance in the leaves of halophyte Halogeton glomeratus

Halogeton glomeratus (H. glomeratus) is categorized as a halophyte, it can potentially endure not only salt but also heavy metals. The aim of this work was to study the molecular mechanisms underlying the Cd²⁺ tolerance of halophyte H. glomeratus seedlings. For that we used a combination of physiological characteristics and data-independent acquisition-based proteomic approaches. The results revealed that the significant changes of physiological characteristics of H. glomeratus occurred under approximately 0.4 mM Cd²⁺ condition and that Cd²⁺ accumulated in Cd²⁺-treated seedling roots, stems and leaves. At the early stage of Cd²⁺ stress, numerous differentially abundant proteins related to "phosphoenolpyruvate carboxylase", "transmembrane transporters", and "vacuolar protein sorting-associated protein" took important roles in the response of H. glomeratus to Cd²⁺ stress. At the later stage of Cd²⁺ stress, some differentially abundant proteins involved in "alcohol-forming fatty acyl-CoA reductase", "glutathione transferase", and "abscisic acid receptor" were considered to regulate the adaptation of H. glomeratus exposed to Cd²⁺ stress. Finally, we found various detoxification-related differentially abundant proteins related to Cd²⁺ stress. These biological processes and regulators synergistically regulated the Cd²⁺ tolerance of H. glomeratus. SIGNIFICANCE: The halophyte, H.glomeratus, has a strong tolerance to salinity, also survives in the heavy metal stress. At present, there are few reports on the comprehensive characterization and identification of Cd²⁺ response and adaption related regulators in H.glomeratus. This research focuses on the molecular mechanisms of H. glomeratus tolerance to Cd²⁺ stress at proteome levels to uncover the novel insight of the Cd²⁺-related biological processes and potential candidates involved in the response and adaption mechanism. The results will help elucidate the genetic basis of this species' tolerance to Cd²⁺ stress and develop application prospect of wild genetic resources to heavy metal phytoremediation.

Performance of tidal and non-tidal mangrove constructed wetlands in treating maricultural wastewater

This study aims to evaluate the removal efficiency of nitrogen and phosphorus in the tidal and non-tidal constructed wetlands with typical mangrove (Aegiceras corniculatum) as a wetland plant model to treat simulated marine wastewater. The results showed that the average removals of NO₂^--N, NO₃^--N, NH₄⁺-N, TN and TP were 88.4, 80.5, 81.4, 79.7 and 40.8%, respectively, in the non-tidal subsurface flow (HF) mangrove wetland, and 65.3, 61.3, 90.6, 60.1 and 19.2% in the tidal (TF) mangrove wetland, and 11.4, 64.6, 68.7, 56.6 and 16.3% in the non-tidal free water surface (FWS) mangrove wetland, respectively. Moreover, it was observed that the composition of microbial communities in the HF mangrove wetland was beneficial to the nitrogen cycle and has more quantitative associations of N-metabolism genes. The results indicated that non-tidal HF mangrove wetland has a stable and an effective capacity for potential treatment of marine wastewater compared with the non-tidal FWS mangrove wetland and tidal TF mangrove wetland.

Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

Cadmium (Cd) is a major environmental contaminant due to its widespread industrial use. Cd contamination of soil and water is rather classical but has emerged as a recent problem. Cd toxicity causes a range of damages to plants ranging from germination to yield suppression. Plant physiological functions, i.e., water interactions, essential mineral uptake, and photosynthesis, are also harmed by Cd. Plants have also shown metabolic changes because of Cd exposure either as direct impact on enzymes or other metabolites, or because of its propensity to produce reactive oxygen species, which can induce oxidative stress. In recent years, there has been increased interest in the potential of plants with ability to accumulate or stabilize Cd compounds for bioremediation of Cd pollution. Here, we critically review the chemistry of Cd and its dynamics in soil and the rhizosphere, toxic effects on plant growth, and yield formation. To conserve the environment and resources, chemical/biological remediation processes for Cd and their efficacy have been summarized in this review. Modulation of plant growth regulators such as cytokinins, ethylene, gibberellins, auxins, abscisic acid, polyamines, jasmonic acid, brassinosteroids, and nitric oxide has been highlighted. Development of plant genotypes with restricted Cd uptake and reduced accumulation in edible portions by conventional and marker-assisted breeding are also presented. In this regard, use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics to enhance the adverse impacts of Cd in plants may be quite helpful. The review's results should aid in the development of novel and suitable solutions for limiting Cd bioavailability and toxicity, as well as the long-term management of Cd-polluted soils, therefore reducing environmental and human health hazards.

Root anatomy, growth, and development of Typha domingensis Pers. (Typhaceae) and their relationship with cadmium absorption, accumulation, and tolerance

Typha domingensis Pers. is a plant that grows in marshy environments, where cadmium (Cd) accumulates. The root is the first organ that comes into contact with the metal. The aim of this study was to evaluate the effect of Cd on the roots of T. domingensis. The experiment was conducted in a greenhouse using different Cd concentrations: (1) 0 µM (control), (2) 10 µM, and (3) 50 µM, with 10 replicates for 90 days. The plants were placed in plastic containers containing 5 L of nutrient solution modified with the different Cd concentrations. At the end of the experiment, the roots were measured, sampled, fixed, and subjected to usual plant microtechniques. The slides were observed and photographed under light microscopy and analyzed in ImageJ software. To measure Cd absorption, atomic-absorption spectrometry was used. The data were subjected to analysis of variance and comparison of means by the Scott-Knott test at P < 0.05. When exposed to 50 µM of Cd, the roots accumulated 99.35% of the Cd. At this concentration, there was a reduction in the exodermis but there was an increase in the diameter of the cortical cells and in the proportion of aerenchyma in the cortex. There was an increase in the root cap, which guaranteed the protection of the primary meristems. Therefore, T. domingensis adjusts its root anatomy improving the Cd tolerance and shows potential for phytoremediation purposes.

Phytoextraction and Antioxidant Defense of Mangrove Seedling (Kandelia obovata) to Inorganic Arsenate Exposure

Increasing arsenic (As) pollution is posing potential endangerment to mangrove wetland ecosystems. Mangrove phytoextraction, translocation, and responses to As exposure must be urgently addressed. In this study, the growth and physiological response of Kandelia obovata seedlings were examined after addition of 25−200 mg kg−1 As under sediment culture conditions. Results showed that the seedling morphological variations were not significant below 100 mg kg−1 compared to the control group, indicating superoxide dismutase, peroxidase, and catalase synergetic interaction to resist the As exposure. High As concentrations (150–200 mg kg−1) inhibited the seedling growth accompanied by a significant increase in malondialdehyde content and decrease in activities of antioxidant enzymes. Toxicity symptoms and mortality appeared in 200 mg kg−1 As, presumably because the plant reached the limit of As tolerance. Besides, As accumulated mainly in roots, accounting for 87.04–97.85% of the total As, and the bioaccumulation factor (BCF) was >100%. However, the BCF and translocation factor (TF) in stems and leaves were below unity, illustrating a weak capacity of transferring As to aerial parts of the seedlings. Overall, K. obovata is a potential remediated species in polluted coastal wetlands due to high phytoextraction capacity and high tolerance to As exposure.

Increased fluctuation of sulfur alleviates cadmium toxicity and exacerbates the expansion of Spartina alterniflora in coastal wetlands

Evidence suggests that the invasion of Spartina alterniflora (S. alterniflora) poses potentially serious risks to the stability of coastal wetlands, an ecosystem that is extremely vulnerable to both biological and non-biological threats. However, the effects and mechanisms of sulfur (S) in mediating the growth and expansion of S. alterniflora are poorly understood, particularly when sediments are contaminated with cadmium (Cd). A 6-month greenhouse study was conducted to evaluate the mediating effect of S on Cd tolerance and growth of S. alterniflora. Treatments consisted of a factorial combination of three S rates (applied as Na₂SO₄; 0, 500, 1000 mg kg^-1 dry weight (DW), as S₀, S₅₀₀, and S₁₀₀₀) and four Cd rates (applied as CdCl₂; 0, 1, 2, 4 mg kg^-1 DW, as Cd₀, Cd₁, Cd₂, and Cd₄). Results showed that although the exogenous S supply obviously increased Cd accumulation in roots (up to 71.22 ± 6.43 mg kg^-1 DW) due to the decrease of Fe concentration in iron plaque (down to 4.02 ± 1.18 mg g^-1 DW), biomass reduction and oxidative stress in plant tissues were significantly alleviated. The addition of S significantly up-regulated the concentration of compounds related to Cd tolerance, including proline and glutathione. Therefore, the translocation of Cd was restricted, and plant growth was not impacted. The present study demonstrated that the exogenous sulfur supply could promote the growth of S. alterniflora and enhance its tolerance to Cd. Therefore, under the effects of S. alterniflora, the increased fluctuations of S pool caused by the release and deposition of S might further exacerbate S. alterniflora expansion in Cd contaminated coastal wetlands.

Evaluation of heavy metals effects on morpho-anatomical alterations of wheat (Triticum aestivum L.) seedlings

The present study aimed to evaluate the effects of Cd and Cr as separate and in combinations in hydroponically grown seedlings of FA-08 and SH-13 cultivars of wheat (Triticum aestivum L.). The concentrations of heavy metals were higher in the root as compared to shoot and were more pronounced in SH-13 than FA-08 cultivar. The decrease in the seedling length and biomass was observed when the metals were applied in combined form (Cd-Cr 80-120, Cd-Cr 100-120, Cr-Cd 140-80, and Cr-Cd 140-100). There were more declines in root length in the cultivar SH-13 as compared to the shoot length, as the concentration of HMs increased. The root at level Cr-140 and shoot at level Cd-100 showed more reduction in SH-13 than FA-08. The high concentration of Cd and Cr affected the root epidermis, the cortical cells, and the xylem vessel. The size and number of stomata, length of long cells and short cells, and trichome were reduced at the concentration Cd-100 and Cr-140. The present study showed that the higher concentration of Cd and Cr affects the morpho-anatomical features of both selected wheat cultivar moderately.