Effects of cadmium on transcription, physiology, and ultrastructure of two tobacco cultivars

Variety-dependent responses of common tobacco with differential cadmium resistance: Cadmium uptake and distribution, antioxidative activity, and gene expression

Cadmium (Cd), which accumulates in tobacco leaves, enters the human body through inhalation of smoke, causing harmful effects on health. Therefore, identifying the pivotal factors that govern the absorption and resistance of Cd in tobacco is crucial for mitigating the harmful impact of Cd. In the present study, four different Cd-sensitive varieties, namely, ZhongChuan208 (ZC) with resistance, ZhongYan100 (ZY), K326 with moderate resistance, and YunYan87 (YY) with sensitivity, were cultivated in hydroponic with different Cd concentrations (20 µM, 40 µM, 60 µM and 80 µM). The results indicated that plant growth was significantly decreased by Cd. Irrespective of the Cd concentration, ZC exhibited the highest biomass, while YY had the lowest biomass; ZY and K326 showed intermediate levels. Enzymatic (APX, CAT, POD) and nonenzymatic antioxidant (Pro, GSH) systems showed notable variations among varieties. The multifactor analysis suggested that the ZC and ZY varieties, with higher levels of Pro and GSH content, contribute to a decrease in the levels of MDA and ROS. Among all the Cd concentrations, ZC exhibited the lowest Cd accumulation, while YY showed the highest. Additionally, there were significant differences observed in Cd distribution and translocation factors among the four different varieties. In terms of Cd distribution, cell wall Cd accounted for the highest proportion of total Cd, and organelles had the lowest proportion. Among the varieties, ZC showed lower Cd levels in the cell wall, soluble fraction, and organelles. Conversely, YY exhibited the highest Cd accumulation in all tissues; K326 and ZY had intermediate levels. Translocation factors (TF) varied among the varieties under Cd stress, with ZC and ZY showing lower TF compared to YY and K326. This phenomenon mainly attributed to regulation of the NtNramp3 and NtNramp5 genes, which are responsible for the absorption and transport of Cd. This study provides a theoretical foundation for the selection and breeding of tobacco varieties that are resistant to or accumulate less Cd.

Kitchen compost-derived humic acid application promotes ryegrass growth and enhances the accumulation of Cd: An analysis of the soil microenvironment and rhizosphere functional microbes

Phytoremediation is an environmentally friendly and safe approach for remediating environments contaminated with heavy metals. Humic acid (HA) has high biological activity and can effectively complex with heavy metals. However, whether HA affects available Cd storage and the Cd accumulation ability of plants by altering the soil microenvironment and the distribution of special functional microorganisms remains unclear. Here, we investigated the effects of applying kitchen compost-derived HA on the growth and Cd enrichment capacity of ryegrass (Lolium perenne L.). Additionally, the key role of HA in regulating the structure of rhizosphere soil bacterial communities was identified. HA promoted the growth of perennial ryegrass and biomass accumulation and enhanced the Cd enrichment capacity of ryegrass. The positive effect of HA on the soil microenvironment and rhizosphere bacterial community was the main factor promoting the growth of ryegrass, and this was confirmed by the significant positive correlation between the ryegrass growth index and the content of SOM, AP, AK, and AN, as well as the abundance of rhizosphere growth-promoting bacteria such as Pseudomonas, Steroidobacter, Phenylobacterium, and Caulobacter. HA passivated Cd and inhibited the translocation capacity of ryegrass. The auxiliary effect of resistant bacteria on plants drove the absorption of Cd by ryegrass. In addition, HA enhanced the remediation of Cd-contaminated soil by ryegrass under different Cd levels, which indicated that kitchen compost-derived HA could be widely used for the phytoremediation of Cd-contaminated soil. Generally, our findings will aid the development of improved approaches for the use of kitchen compost-derived HA for the remediation of Cd-contaminated soil.

Comparative transcriptome analysis and Arabidopsis thaliana overexpression reveal key genes associated with cadmium transport and distribution in root of two Capsicum annuum cultivars

The molecular mechanisms underlying high and low cadmium (Cd) accumulation in hot pepper cultivars remain unclear. In this study, comparative transcriptome analysis of root between high-Cd (J) and low-Cd (Z) cultivars was conducted under hydroponic cultivation with 0 and 0.4 mg/L Cd, respectively. The results showed that J enhanced the root uptake of Cd by elevating the expression of Nramp5 and counteracting Cd toxicity by increasing the expression of genes, such as NIR1, GLN1, and IAA9. Z reduced Cd accumulation by enhancing the cell wall lignin synthesis genes PAL, COMT, 4CL, LAC, and POD and the Cd transporters ABC, MTP1, and DTX1. Elevated expression of genes related to sulfur metabolism was observed in Z, potentially contributing to its ability to detoxify Cd. To investigate the function of CaCOMT1, an Arabidopsis thaliana overexpression line (OE-CaCOMT1) was constructed. The results revealed that OE-CaCOMT1 drastically increased the lignin content by 38-42% and reduced the translocation of Cd to the aboveground parts by 32%. This study provides comprehensive insights into the mechanisms underlying Cd accumulation in hot pepper cultivars using transcriptome analysis. Moreover, this study elucidates the critical function of CaCOMT1, providing a theoretical foundation for the production of low-Cd vegetables for food safety.

NRAMP6c plays a key role in plant cadmium accumulation and resistance in tobacco (Nicotiana tabacum L.)

Tobacco plants (Nicotiana tabacum L.) exhibit considerable potential for phytoremediation of soil cadmium (Cd) pollutants, owing to their substantial biomass and efficient metal accumulation capabilities. The reduction of Cd accumulation in tobacco holds promise for minimizing Cd intake in individuals exposed to cigar smoking. NRAMP transporters are pivotal in the processes of Cd accumulation and resistance in plants; however, limited research has explored the functions of NRAMPs in tobacco plants. In this investigation, we focused on NtNRAMP6c, one of the three homologs of NRAMP6 in tobacco. We observed a robust induction of NtNRAMP6c expression in response to both Cd toxicity and iron (Fe) deficiency, with the highest expression levels detected in the roots. Subsequent subcellular localization and heterologous expression analyses disclosed that NtNRAMP6c functions as a plasma membrane-localized Cd transporter. Moreover, its overexpression significantly heightened the sensitivity of yeast cells to Cd toxicity. Through CRISPR-Cas9-mediated knockout of NtNRAMP6c, we achieved a reduction in Cd accumulation and an enhancement in Cd resistance in tobacco plants. Comparative transcriptomic analysis unveiled substantial alterations in the transcriptional profiles of genes associated with metal ion transport, photosynthesis, and macromolecule catabolism upon NtNRAMP6c knockout. Furthermore, our study employed plant metabolomics and rhizosphere metagenomics to demonstrate that NtNRAMP6c knockout led to changes in phytohormone homeostasis, as well as shifts in the composition and abundance of microbial communities. These findings bear significant biological implications for the utilization of tobacco in phytoremediation strategies targeting Cd pollutants in contaminated soils, and concurrently, in mitigating Cd accumulation in tobacco production destined for cigar consumption.

Differential responses of chili varieties grown under cadmium stress

Heavy metal cadmium (Cd) naturally occurs in soil and is a hazardous trace contaminant for humans, animals, and plants. The main sources of Cd pollution in soil include overuse of phosphatic fertilizers, manure, sewage sludge, and aerial deposition. That's why an experiment was conducted to analyze the effect of Cd toxicity in Capsicum annuum L. by selecting its seven varieties: Hybrid, Desi, Sathra, G-916, BR-763, BG-912, and F1-9226. Cadmium was spiked in soil with four levels, i.e., (0, 3, 4, and 5 mg Cd kg- 1 of soil) for a week for homogeneous dispersion of heavy metal. Chili seeds were sown in compost-filled loamy soil, and 25-day-old seedlings were transplanted into Cd-spiked soil. Cadmium increasing concentration in soil decreased chili growth characteristics, total soluble sugars, total proteins, and amino acids. On the other hand, the activities of antioxidant enzymes were increased with the increasing concentration of Cd in almost all the varieties. Treatment 5 mg Cd/kg application caused - 197.39%, -138.78%, -60.77%, -17.84%, -16.34%, -11.82% and - 10.37% decrease of carotenoids level in chili V2 (Desi) followed by V4 (G-916), V1 (Hy7brid), V7 (F1-9226), V6 (BG-912), V5 (BR-763) and V3 (Sathra) as compared to their controls. The maximum flavonoids among varieties were in V5 (BR-763), followed by V6 (BG-912), V7 (F1-9226), V3 (Sathra) and V1 (Hybrid). Flavonoids content was decreased with - 37.63% (Sathra), -34.78% (Hybrid), -33.85% (G-916), -31.96% (F1-9226), -31.44% (Desi), -30.58% (BR-763), -22.88% (BG-912) as compared to their control at 5 mg Cd/kg soil stress. The maximum decrease in POD, SOD, and CAT was - 31.81%, -25.98%, -16.39% in chili variety V7 (F1-9226) at 5 mg Cd/kg stress compared to its control. At the same time, maximum APX content decrease was - 82.91%, followed by -80.16%, -65.19%, -40.31%, -30.14%, -10.34% and - 6.45% in V4 (G-916), V2 (Desi), V3 (Sathra), V6 (BG-912), V1 (Hybrid), V7 (F1-9226) and V5 (BR-763) at 5 mg Cd/kg treatment as compared to control chili plants. The highest CAT was found in 5 chili varieties except Desi and G-916. Desi and G-916 varieties. V5 (BR-763) and V6 (BG-912) were susceptible, while V1 (Hybrid), V3 (Sathra), and V7 (F1-9226) were with intermediate growth attributes against Cd stress. Our results suggest that Desi and G-916 chili varieties are Cd tolerant and can be grown on a large scale to mitigate Cd stress naturally.

Mercapto-based palygorskite modified soil micro-biology and reduced the uptake of heavy metals by Salvia miltiorrhiza in cadmium and lead co-contaminated soil

Salvia miltiorrhiza is an important traditional Chinese medicinal and edible plant that can easily accumulate excessive cadmium (Cd) and lead (Pb) from contaminated soils. The soil contaminated with heavy metals severely threatened the quality of S. miltiorrhiza products. In this study, we investigated the effects of mercapto-based palygorskite (MPAL), a new passivation amendment, on restraining the uptake of Cd and Pb by S. miltiorrhiza, and the impact on soil micro-ecology. Results showed that the application of MPAL prominently enhanced the biomass and antioxidant enzyme activities of S. miltiorrhiza. With the treatment of 4% MPAL, the Cd and Pb contents in the roots were significantly decreased by 81.42% and 69.09%, respectively. The active ingredients of S. miltiorrhiza, including Danshensu, Cryptotanshinone, Tanshinone I and Tanshinone II were remarkedly increased by 1899.46%, 5838.64%, 54.23% and 200.78%, respectively. In addition, MPAL decreased the bio-availability of Cd and Pb by speciation transformation, which simultaneously boosted the activities of cellulase and sucrase. The application of MPAL also improved the bacterial community composition. These findings revealed that the application of MPAL regulated the soil micro-ecology, positively modified the growth and obstructed the Cd and Pb accumulation in S. miltiorrhiza.

Physiological and Cellular Ultrastructural Responses of Sesuvium portulacastrum under Cd Stress Grown Hydroponically

This study aimed to investigate the physiological and cellular mechanisms of Sesuvium portulacastrum under heavy metal stress to evaluate possible tolerance and adaptation mechanisms in a metal-polluted environment. The physiological and cellular ultrastructural responses of S. portulacastrum were studied hydroponically under exposure to a range of cadmium (Cd) concentrations (50 µM to 600 µM) for 28 days. The activity of antioxidant enzymes like catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), changes in chlorophyll, and cellular ultrastructural content were examined. There was no significant difference in chlorophyll content in the leaf under the stress of 300 μM, but 400 μM and 600 μM Cd stress showed significantly decreased chlorophyll content. The SOD activity indicates an increase under the Cd stress of 100 μM for leaves, 300 μM for stems, and 50 μM for roots; after that, the SOD activity gradually decreased with increasing Cd concentrations. But POD activity was considerably increased with increasing Cd stress. CAT activity showed a gradual increase in concentrations until 300 μM of Cd stress and then decreased sharply in roots, stems, and leaf tissues. Cd stress had a considerable impact on the structure of the roots, stems, and leaves cells, such as distorted and thinner cell walls and the deformation of chloroplasts, mitochondria, and other organelles. Therefore, the increased number of nucleolus in the cell nucleus suggests that cells may be able to maintain their protein synthesis in a stressful environment. This study concludes that SOD is the dominant antioxidant enzyme activity during low Cd toxicity (<100 μM), while POD is the dominant enzyme activity during higher Cd toxicity (>100 μM).

Hydrogel-potassium humate composite alleviates cadmium toxicity of tobacco by regulating Cd bioavailability

Cadmium (Cd) removal from soil to reduce Cd accumulation in plants is essential for agroecology, food safety, and human health. Cd enters plants from soil and affects plant growth and development. Hydrogels can easily combine with Cd, thereby altering its bioavailability in soil. However, few studies have evaluated the effects of hydrogel on the complex phytotoxicity caused by Cd uptake in plants and the microbial community structure. Herein, a new poly (acrylic acid)-grafted starch and potassium humate composite (S/K/AA) hydrogel was added to soil to evaluate its impact on tobacco growth and the soil microenvironment. The results indicate that the addition of S/K/AA hydrogel can significantly improve the biomass, chlorophyll (Chl) content, and photosynthetic capacity of tobacco plants during Cd stress conditions, and decrease Cd concentration, probably by affecting Cd absorption through the expression of Cd absorption transporters (e.g., NRAMP5, NRAMP3, and IRT1). Moreover, the application of S/K/AA hydrogel not only reduced the accumulation of reactive oxygen species (ROS), but also reduced the antioxidant activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), suggesting that S/K/AA hydrogel alleviates Cd toxicity via a non-antioxidant pathway. Notably, we further analyzed the effectiveness of the hydrogel on microbial communities in Cd-contaminated soil and found that it increased the Cd-tolerant microbial community (Arthrobacter, Massilia, Streptomyces), enhancing the remediation ability of Cd-contaminated soil and helping tobacco plants to alleviate Cd toxicity. Overall, our study provides primary insights into how S/K/AA hydrogel affects Cd bioavailability and alleviates Cd toxicity in plants.

Low pe+pH inhibits Cd transfer from paddy soil to rice tissues driven by S addition

Both soil irrigation and sulfur (S) are associated with the precipitation of cadmium (Cd)-sulfide in paddy soil, their interaction affecting on Cd solubility and extractability is still unknown. This study primarily discusses the effect of exogenous S addition on the bioavailability of Cd in paddy soil under unsteady pe + pH conditions. The experiment was treated with three different water strategies: continuous dryness (CD), continuous flooding (CF), and alternating dry-wet cycles for one cycle (DW). These strategies were combined with three different S concentrations. The results indicate that the CF treatment, particularly when combined with S addition, had the most significant effect on reducing pe + pH and Cd bioavailability in the soil. The reduction of pe + pH from 10.2 to 5.5 resulted in a decrease in soil Cd availability by 58.3%, and Cd accumulation in rice grain by 52.8%, compared to the other treatments. While it was more conducive to the formation of iron plaque on the root surface in DW treatment with S addition at rice maturing stage and enhanced the gathering of Fe/S/Cd. Structural equation model (SEM) analysis further confirmed a significant negative correlation (r = -0.916) between the abundance of soil Fer-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB) like Desulfuromonas, Pseudomonas, Geobacter, and the Cd content in rice grains. This study provides a basic mechanistic understanding of how soil redox status (pe + pH), S addition, and FeRB/SRB interacted with Cd transfer in paddy soil-rice tissues.

Physiological dynamics as indicators of plant response to manganese binary effect

Introduction

Heavy metals negatively affect plant physiology. However, plants can reduce their toxicity through physiological responses. Broussonetia papyrifera is a suitable candidate tree for carrying out the phytoremediation of manganese (Mn)-contaminated soil.

Methods

Considering that Mn stress typically exerts a binary effect on plants, to reveal the dynamic characteristics of the physiological indexes of B. papyrifera to Mn stress, we conducted pot experiments with six different Mn concentrations (0, 0.25, 0.5, 1, 2, and 5 mmol/L) for 60 days. In addition to the chlorophyll content, malondialdehyde (MDA), proline (PRO), soluble sugar, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the absorption and transfer characteristics of Mn, and root structure were also measured.

Results

Phytoremedial potential parameters such as the bioconcentration factor (BCF) and translocation factor (TF) displayed an increasing trend with the increase of Mn concentration. At lower Mn concentrations (<0.5 mmol/L), the TF value was <1 but crossed 1 when the Mn concentration exceeded 100 mmol/L. The Mn distribution in various tissues was in the following order: leaf > stem > root. The root structure analysis revealed that low-level concentrations of Mn (1 mmol/L) promoted root development. Mn concentration and stress duration had significant effects on all measured physiological indexes, and except soluble sugar, Mn concentration and stress time displayed a significant interaction on the physiological indexes.

Discussion

Our study demonstrates that the physiological indexes of B. papyrifera display dynamic characteristics under Mn stress. Thus, during the monitoring process of Mn stress, it appears to be necessary to appropriately select sampling parts according to Mn concentration.