Physiological and proteomic analyses reveal the effects of exogenous nitrogen in diminishing Cd detoxification in Acacia auriculiformis

Energy metabolism, antioxidant defense system, metal transport, and ion homeostasis are key contributors to Cd tolerance in SSSL derived from wild rice

Cadmium (Cd) toxicity poses major challenges to rice cultivation, affecting plant growth and development. Wild rice and nanoparticles offer promising strategies to enhance Cd tolerance, yet little is known about their combined effects. This study evaluates the single segment substitution line (SG004) from Oryza glumaepatula (wild rice) and its response to Cd stress compared to cultivated rice (HJX74). Both genotypes were also treated with calcium oxide nanoparticles (np-CaO). Results showed that Cd exposure disrupts reactive oxygen species (ROS) metabolism in both lines, such as malondialdehyde (MDA) increases by 57 % in HJX74 compared to SG004. Moreover, SG004 exhibited a 26 % reduction in shoot length compared to 41 % in HJX74 and a 42 % decline in chlorophyll ab content versus 53 % in HJX74. Antioxidant activity such as glutathione (GSH) decreased 25 % more in HJX74 than SG004 under Cd toxicity. Additionally, SG004 had lower Cd accumulation in roots (70 %) and shoots (85 %) than HJX74, indicating its enhanced tolerance to Cd toxicity. The root cell cytology reveals several deformations in different organelles of HJX74 but less in SG004. RNAseq analysis identifies key pathways, including energy metabolism, antioxidant defense, metal transport, and ion homeostasis, which may be critical for SG004 enhanced tolerance. Notably, two distinct metallothionein-like genes (BGIOSGA019338, BGIOSGA035982), a peroxidase (BGIOSGA019133), ammonium (BGIOSGA008640, BGIOSGA008641, and potassium transporters (BGIOSGA030867), NRAMP1 (BGIOSGA025476), and an aluminum-activated malate transporter (BGIOSGA014531), showed differential expressions in SG004 under Cd stress. Genes within the substituted fragment, including those for peroxidase 25 (BGIOSGA002866), metallothionein (BGIOSGA002389), and reductase (BGIOSGA002387), are also upregulated in SG004, reinforcing the role of antioxidant and ion homeostasis pathways. The utilization of np-CaO alleviates Cd-induced stress in both genotypes, hence reinforcing the application of wild rice and nanoparticles to improve Cd tolerance.

Lead accumulation and concomitant reactive oxygen species (ROS) scavenging in Robinia pseudoacacia are dependent on nitrogen nutrition

Heavy metal pollution combined with nitrogen (N) limitation is a major factor preventing revegetation of contaminated land. Woody N2-fixing legumes are a natural choice for phytoremediation. However, the physiological responses of woody legumes to lead (Pb) with low N exposure are currently unknown. In the present study, a common Robinia cultivar from Northeast China, inoculated and non-inoculated with rhizobia, was exposed to -Pb or + Pb at moderate (norN) or low N application (lowN). Our results showed that without inoculation, independent of N application, Pb taken up by the roots was allocated to the shoot and inhibited photosynthesis and biomass production. In non-inoculated Robinia, Pb-mediated oxidative stress resulted in reduced H2O2 scavenging as indicated by increased ascorbate peroxidase (APX) activity in the leaves and proline contents in the roots, independent of N application. Combined lowN∗Pb exposure significantly increased malondialdehyde (MDA) contents in roots and leaves and enhanced APX and dehydroascorbate reductase activities in leaves compared to individual Pb exposure. Rhizobia inoculation raised the abundance of nodules and promoted Pb uptake by roots. Under Pb exposure, inoculation with rhizobia reduced MDA contents, increased proline contents in leaves and roots and enhanced activity of nitrate reductase in the leaves, independent of N application. Under Pb exposure, nitrogenase activity of inoculated Robinia under low- and norN application were similar indicating that enhanced of N2-fixation at lowN was counteracted by Pb exposure. These results show that inoculation of Robinia with rhizobia can alleviate Pb toxicity at combined lowN and Pb exposure by reducing oxidative stress.

How plants respond to heavy metal contamination: a narrative review of proteomic studies and phytoremediation applications

MAIN CONCLUSION

Heavy metal pollution caused by human activities is a serious threat to the environment and human health. Plants have evolved sophisticated defence systems to deal with heavy metal stress, with proteins and enzymes serving as critical intercepting agents for heavy metal toxicity reduction. Proteomics continues to be effective in identifying markers associated with stress response and metabolic processes. This review explores the complex interactions between heavy metal pollution and plant physiology, with an emphasis on proteomic and biotechnological perspectives. Over the last century, accelerated industrialization, agriculture activities, energy production, and urbanization have established a constant need for natural resources, resulting in environmental degradation. The widespread buildup of heavy metals in ecosystems as a result of human activity is especially concerning. Although some heavy metals are required by organisms in trace amounts, high concentrations pose serious risks to the ecosystem and human health. As immobile organisms, plants are directly exposed to heavy metal contamination, prompting the development of robust defence mechanisms. Proteomics has been used to understand how plants react to heavy metal stress. The development of proteomic techniques offers promising opportunities to improve plant tolerance to toxicity from heavy metals. Additionally, there is substantial scope for phytoremediation, a sustainable method that uses plants to extract, sequester, or eliminate contaminants in the context of changes in protein expression and total protein behaviour. Changes in proteins and enzymatic activities have been highlighted to illuminate the complex effects of heavy metal pollution on plant metabolism, and how proteomic research has revealed the plant's ability to mitigate heavy metal toxicity by intercepting vital nutrients, organic substances, and/or microorganisms.

Synergistic interactions of assorted ameliorating agents to enhance the potential of heavy metal phytoremediation

Pollution by toxic heavy metals creates a significant impact on the biotic community of the ecosystem. Nowadays, a solution to this problem is an eco-friendly approach like phytoremediation, in which plants are used to ameliorate heavy metals. In addition, various amendments are used to enhance the potential of heavy metal phytoremediation. Symbiotic microorganisms such as phosphate-solubilizing bacteria (PSB), endophytes, mycorrhiza and plant growth-promoting rhizobacteria (PGPR) play a significant role in the improvement of heavy metal phytoremediation potential along with promoting the growth of plants that are grown in contaminated environments. Various chemical chelators (Indole 3-acetic acid, ethylene diamine tetra acetic acid, ethylene glycol tetra acetic acid, ethylenediamine-N, N-disuccinic acid and nitrilotri-acetic acid) and their combined action with other agents also contribute to heavy metal phytoremediation enhancement. With modern techniques, transgenic plants and microorganisms are developed to open up an alternative strategy for phytoremediation. Genomics, proteomics, transcriptomics and metabolomics are widely used novel approaches to develop competent phytoremediators. This review accounts for the synergistic interactions of the ameliorating agent's role in enhancing heavy metal phytoremediation, intending to highlight the importance of these various approaches in reducing heavy metal pollution.

Comprehensive mechanisms of heavy metal toxicity in plants, detoxification, and remediation

Natural and anthropogenic causes are continually growing sources of metals in the ecosystem; hence, heavy metal (HM) accumulation has become a primary environmental concern. HM contamination poses a serious threat to plants. A major focus of global research has been to develop cost-effective and proficient phytoremediation technologies to rehabilitate HM-contaminated soil. In this regard, there is a need for insights into the mechanisms associated with the accumulation and tolerance of HMs in plants. It has been recently suggested that plant root architecture has a critical role in the processes that determine sensitivity or tolerance to HMs stress. Several plant species, including those from aquatic habitats, are considered good hyperaccumulators for HM cleanup. Several transporters, such as the ABC transporter family, NRAMP, HMA, and metal tolerance proteins, are involved in the metal acquisition mechanisms. Omics tools have shown that HM stress regulates several genes, stress metabolites or small molecules, microRNAs, and phytohormones to promote tolerance to HM stress and for efficient regulation of metabolic pathways for survival. This review presents a mechanistic view of HM uptake, translocation, and detoxification. Sustainable plant-based solutions may provide essential and economical means of mitigating HM toxicity.

Nitrate enhances cadmium accumulation through modulating sulfur metabolism in sweet sorghum

Sweet sorghum deploys tremendous potential for phytoremediation of cadmium (Cd)-polluted soils. Nitrate increases Cd accumulation in sweet sorghum, but the mechanism underlying this is still elusive. Sulfur-containing metabolites have been corroborated to play important roles in Cd tolerance in plants. Thus, whether sulfur metabolism contributed to nitrate-increased Cd accumulation in sweet sorghum was investigated in the present study. Two-way ANOVA analysis showed that most sulfur-containing metabolites concentrations and relevant enzymes activities were regulated by nitrate, Cd and interplay of nitrate and Cd. By using grey correlation analysis and Pearson correlation coefficient, Cd accumulation in shoots as affected by nitrate was also mainly ascribed to sulfur metabolism. ATP sulfurylase (ATPS) activities and non-protein thiol (NPT) concentrations in leaves were the two prominent factors that positively correlated with Cd accumulation in shoots. Excess nitrate elevated ATPS activities in leaves which contributed to increased NPT and phytochelatins (PCs) concentrations in leaves. Nitrate enhanced Cd accumulation in shoots of sweet sorghum under a low level of Cd treatment. Intriguingly, Cd accumulation in shoots of sweet sorghum was similar between a low level and a high level of Cd treatment. Principal Components Analysis (PCA) based on 34 parameters failed to separate the low Cd treatment from the high Cd treatment either, suggesting sweet sorghum is exclusively suitable for phytoremediation of slight Cd-polluted arable lands. Taken together, enhanced Cd accumulation in shoots of sweet sorghum by excess nitrate application is closely correlated with sulfur metabolism containing elevated ATPS activities, NPT and PCs concentrations in leaves.

Enhanced cadmium phytoremediation capacity of poplar is associated with increased biomass and Cd accumulation under nitrogen deposition conditions

Nitrogen (N) deposition plays a significant role in soil cadmium (Cd) phytoremediation, and poplar has been considered for the remediation of contaminated soil because of its enormous biomass and strong Cd resistance. To reveal the underlying physiological and root phenotypic mechanisms of N deposition affecting Cd phytoextraction in poplar, we assessed root phenotypic characteristics, Cd absorption and translocation, chlorophyll fluorescence performance, and antioxidant enzyme activities of a clone of Populus deltoides × P. nigra through combined greenhouse Cd and N experiments. Our results showed that Cd significantly changed the root phenotype by reducing root length, tip number, and diameter. Cd also caused the peroxidation of lipids, damaged the photosystem II (PSII) reaction centre, and reduced photosynthetic capacity, resulting in a decrease in biomass accumulation in poplar. The N60 (60 kg N·ha^-1·yr^-1) and N90 (90 kg N·ha^-1·yr^-1) treatments promoted the net photosynthetic rate of poplar by increasing the activity of antioxidant enzymes and proline content and repairing the PSII reaction centre, thus increasing the biomass accumulation of poplar exposed to Cd stress. Simultaneously, the N60 and N90 treatments might have increased Cd uptake from the soil by upregulating total root length, root tips, and fine root length. Cd mainly accumulated in roots and stems but not in leaves. The N30 (30 kg N·ha^-1·yr^-1) treatment had no obvious effects on these parameters compared with the single Cd treatment. Consequently, our study suggested that adequate N can improve biomass and Cd accumulation to enhance the phytoremediation capacity of poplar for Cd, which might be related to the improvement of leaf physiological defence and the change in root phenotypic characteristics.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Effects of lime and oxalic acid on antioxidant enzymes and active components of Panax notoginseng under cadmium stress

Cadmium (Cd) pollution poses potential safety risks for Panax notoginseng cultivation, a medicinal plant in Yunnan. Under exogenous Cd stress, field experiments were conducted to understand the effects of lime (0, 750, 2250 and 3750 kg hm⁻²) applied and oxalic acid (0, 0.1 and 0.2 mol L⁻¹) leaves sprayed on Cd accumulation, antioxidant system and medicinal components of P. notoginseng. The results showed that Lime and foliar spray of oxalic acid were able to elevate Ca²⁺ and alleviate Cd²⁺ toxicity in P. notoginseng under Cd stress. The addition of lime and oxalic acid increased the activities of antioxidant enzymes and alters osmoregulator metabolism. The most significant increase in CAT activities increased by 2.77 folds. And the highest increase of SOD activities was 1.78 folds under the application of oxalic acid. While MDA content decreased by 58.38%. There were very significant correlation with soluble sugar, free amino acid, proline and soluble protein. Lime and oxalic acid were able to increase calcium ions (Ca²⁺), decrease Cd content and improve the stress resistance of P. notoginseng, while increasing the production of total saponins and flavonoids. Cd content were the lowest, 68.57% lower than controls, and met the standard value (Cd ≤ 0.5 mg kg⁻¹, GB/T 19086-2008). The proportion of SPN was 7.73%, which reached the highest level of all treatments, the flavonoids content increased significantly by 21.74%, which reached the medicinal standard value and optimal yield.

Enhancement of Photosynthetic Capacity in Spongy Mesophyll Cells in White Leaves of Actinidia kolomikta

Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (F _v/F _m) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas F _v/F _m and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.