Cadmium tolerance and detoxification in Myriophyllum aquaticum: physiological responses, chemical forms, and subcellular distribution

Subcellular distribution, chemical forms of cadmium and rhizosphere microbial community in the process of cadmium hyperaccumulation in duckweed

Duckweed is a newly reported Cd hyperaccumulator that grow rapidly; however, little is known about its tolerance and detoxification mechanisms. In this study, we investigated the tissue, subcellular, and chemical form distribution of the Cd in duckweed and studied the influences of Cd on duckweed growth, ultrastructure, and rhizosphere microbial community. The results showed that Cd could negatively affect the growth of duckweed and shorten the root length. More Cd accumulated in the roots than in the leaves, and Cd was transferred from the roots to the leaves with time. During 12-24 h, Cd mainly existed in the cell wall fraction (2.05 %-95.52 %) and the organelle fraction (5.03 %-97.80 %), followed the soluble fraction (0.14 %-16.98 %). Over time, the proportion of Cd in the organelles increased (46.64 %-92.83 %), exceeding that in the cell wall (6.79 %-66.23 %), which indicated that duckweed detoxification mechanism may be related to the retention of cell wall and vacuole. The main chemical form of Cd was the NaCl-extracted state (30.15 %-88.66 %), which was integrated with pectate and protein. With increasing stress concentration and time, the proportion of the HCl-extracted state and HAc-extracted state increased, and they were low-toxic Cd oxalate and Cd phosphate, respectively. Cd damaged the ultrastructure of cells such as chloroplasts and mitochondria and inhibited the diversity of microbial communities in the duckweed rhizosphere; however, the dominant populations that could tolerate heavy metals increased. It was speculated that duckweed distributed Cd in a less toxic chemical form in a less active location, mainly through retention in the root cell wall and sequestration in the leaf vacuoles, and is dynamically adjusted. The rhizosphere microbial communities tolerate heavy metals may also be one of the mechanisms by which duckweed can tolerate Cd. This study revealed the mechanism of duckweed tolerance and detoxification of Cd at the molecular level and provides a theoretical basis for further development of duckweed.

Molecular insights into lignin biosynthesis on cadmium tolerance: Morphology, transcriptome and proteome profiling in Salix matsudana

Soil pollution caused by cadmium (Cd) is a serious concern. Phytoremediation is a popular technology in the remediation of Cd-contaminated soil. Salix matsudana var. matsudana f. umbraculifera Rehd. has been characterized as a high Cd-accumulating and tolerant willow (HCW). Here, transcriptome and proteome profiling, along with morphology analyses were performed to explore molecular cross-talk involved in Cd tolerance. Our results showed that 73%- 83% of the Cd in roots accumulated in the cell walls and root xylem cell walls were significantly thickened. From transcriptome and proteome analysis, a total of 153 up-regulated differentially-expressed genes and 655 up-regulated differentially-expressed proteins were found in common between two comparison groups (1 d and 4 d vs. respective control). Furthermore, phenylpropanoid biosynthesis was identified as a key pathway in response to Cd stress. In this pathway, lignin biosynthesis genes or proteins were significantly up-regulated, and lignin content increased significantly in roots under Cd stress. Two Cd-induced genes cinnamoyl-CoA reductase 1 (SmCCR1) and cinnamyl alcohol dehydrogenase 7 (SmCAD7) from HCW increased the lignin content and enhanced Cd tolerance in transgenic poplar calli. These results lay the foundation for further clarifying the molecular mechanisms of Cd tolerance in woody plants.

A novel phytoremediation technology for polluted cadmium soil: Salix integra treated with spermidine and activated carbon

A variety of plants have been used as phytoremediation materials to remove Cd from polluted soil. However, the disadvantages of using plants for decontamination include low biomass, low uptake, and inefficiency. We conducted experiments to determine the effects of spermidine and activated carbon treatments of Salix integra on Cd removal. The results showed that exogenous spermidine and activated carbon increased plant growth and root development compared with the CK. The increased dry mass (39.65-92.95%) with the combined spermidine and activated carbon treatments was higher than that with either single treatment (14.79-62.80%). The root length, surface area, root volume, and root diameter with the combined spermidine and activated carbon treatments (53.51-189.35%, 113.08-207.62%, 111.71-499.27%, and 32.51-106.62%, respectively) were higher than those of the lone application treatments (19.35-132.23%, 52.33-111.57%, 35.08-297.07%, and 24.22-81.38%, respectively). In addition, spermidine and activated carbon application reduced the toxicity of Cd to S. integra by improving the antioxidant capacity, thereby increasing the accumulation of Cd. The application of spermidine and activated carbon also changed the distribution of Cd in each part of S. integra. There was increased accumulation of Cd in the shoots and better absorption by the S. integra shoots, thereby improving their Cd remediation efficiency. The combined 0.8 mM spermidine and 0.5 g kg^-1 activated carbon were most effective on removing Cd from the soil. The Cd removal efficiency was 78.11-120.86% higher than that of the CK. Our results may provide foundational information for understanding the mechanisms for the sustainable remediation of Cd-contaminated soil using a combination of spermidine and activated carbon.

Research on the Mechanisms of Plant Enrichment and Detoxification of Cadmium

The heavy metal cadmium (Cd), as one of the major environmentally toxic pollutants, has serious impacts on the growth, development, and physiological functions of plants and animals, leading to deterioration of environmental quality and threats to human health. Research on how plants absorb and transport Cd, as well as its enrichment and detoxification mechanisms, is of great significance to the development of phytoremediation technologies for ecological and environmental management. This article summarises the research progress on the enrichment of heavy metal cadmium in plants in recent years, including the uptake, transport, and accumulation of Cd in plants. The role of plant roots, compartmentalisation, chelation, antioxidation, stress, and osmotic adjustment in the process of plant Cd enrichment are discussed. Finally, problems are proposed to provide a more comprehensive theoretical basis for the further application of phytoremediation technology in the field of heavy metal pollution.

Lemna minor, a hyperaccumulator shows elevated levels of Cd accumulation and genomic template stability in binary application of Cd and Ni: a physiological and genetic approach

In this study, to determine whether having potential to be used as hyperaccumulator for Cd and Ni, numerous experiments were designed for conducting assessments for physiological and genotoxic changes along with defining possible alterations on mineral nutrient status of Lemna minor L. by applying Cd-Ni binary treatments (0, 100, 200 and 400 µM). Our study revealed that there were increases in the concentrations of B, Cr, Fe, K, Mg, and Mn whereas decreases were noticed in the concentrations of Na and Zn and the levels of Ca were inversely proportional to Cd-Ni applications showing tendency to increase at the low concentration and to decrease at the high concentration. Randomly Amplified Polymorphic DNA (RAPD) and Inter Simple Sequence Repeat (ISSR) analyses revealed that rather than band losses and new band formations, mostly intensity changes in the band profiles, and low polymorphism and high genomic template stability (GTS) were observed. Although, to date, L. minor was defined as an efficient hyperaccumulator/potential accumulator or competent phytoremedial agent by researchers. Our research revealed that L. minor showing high accumulation capability for Cd and having low polymorphism rate and high genomic template stability is a versatile hyperaccumulator, especially for Cd; therefore, highly recommended by us for decontamination of water polluted with Cd. NOVELTY STATEMENTMany studies have been focused on the effects of individual metal ions. However, heavy metal contaminants usually exist as their mixtures in natural aquatic environments. Especially, Cd and Ni coexist in industrial wastes.In this study, the accumulation properties of Lemna minor for both Cd and Ni were investigated and the effects of Cd and Ni on the bioaccumulation of B, Ca, Cu, Fe, Mg, K, Mn, Na, Pb and Zn in L. minor were also determined. This study furthermore aimed to assess the genotoxic effects of Cd and Ni found in being extended concentrations on DNA using the Randomly Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) method.