Comparative Study of Growth, Cadmium Accumulation and Tolerance of Three Chickpea (Cicer arietinum L.) Cultivars

Synergistic effects of PGPRs and fertilizer amendments on improving the yield and productivity of Canola (Brassica napus L.)

BACKGROUND

Organic fertilizers are safer and more eco-friendly than chemical fertilizers; hence, organic fertilizers can be used to support sustainable farming. The effects of PGPRs are manifold in agriculture, especially in monoculture crops, where the soil needs to be modified to increase germination, yield, and disease resistance. The objective of this study was to assess the effects of PGPRs combined with fertilizer on the yield and productivity of canola. Canola was chosen for its global importance as an oilseed crop and its responsiveness to soil amendments, making it ideal for evaluating the synergistic effects of PGPRs and fertilizers on yield and soil health.

METHODOLOGY

This research, which was carried out over two years, was aimed at establishing the effectiveness of PGPRs together with organic and inorganic fertilizers on canola yields and was performed with a two-factorial RCBD design under field conditions. We applied Azotobacter salinestris and Bacillus subtilis with biochar, compost, animal manure, poultry manure, and NPK fertilizer. Insect pest management and other agronomic practices were carried out to maintain the experiment.

RESULTS

Canola yield and agronomic traits were enhanced by the combination of Bacillus subtilis with the fully recommended N: P:K ratio (140:55:40 kg/ha). Additionally, the application of Bacillus subtilis with biochar at 2 tons/ha improved the yield and quality of canola, as well as the structure and nutrient regulation of the soil.

CONCLUSION

In light of these results, we recommend the application of Bacillus subtilis to canola seeds along with either 2 t/ha biochar or the entire recommended dose of N: P:K (140:55:40 kg/ha). These strategies are sustainable and help producers and the environment increase the productivity of canola. Combining PGPRs with fertilizers for canola enhances nutrient efficiency, promotes sustainable growth, and boosts stress resilience, addressing agricultural and environmental challenges.

CLINICAL TRIAL NUMBER

Not Applicable.

Enhancing cadmium stress resilience in chickpea (Cicer arietinum L.) via exogenous melatonin application

Chickpea (Cicer arietinum L.) productivity is hindered by biotic and abiotic stresses, particularly heavy metal toxicity. The pot experiment was carried out at the botanical garden of The Islamia University of Bahawalpur, Bahawalpur-Pakistan. The experimental treatments comprised of following details: T0 = Control + 0 µM MT, T1 = Control + 15 µM MT, T2= Control + 30 µM MT, T3 = 100 µM Cd + 0 µM MT, T4 = 100 µM Cd + 15 µM MT and T5 = 100 µM Cd + 30 µM MT. A completely randomized design (CRD) with three replicates was used. Cd stress significantly reduced shoot fresh (51.3%) and dry weight (50.4%), total chlorophyll (53.6%), and shoot Ca2+ (56.6%). However, it increased proline (38.3%), total phenolics (74.2%), glycine betaine (46.4%), TSS (67.7%), TSP (50%), SOD (49.5%), POD (107%), and CAT (74.2%). Conversely, 30 µM MT improved shoot fresh (78.5%) and dry weight (76%), total chlorophyll (47%), SOD (26.5%), POD (35.8%), CAT (27.8%), proline (19%), TSS (24.5%), TSP (25.8%), and shoot Ca2+ (56.6%). Results indicated that MT enhanced photosynthetic pigments and antioxidant activities, maintained ion homeostasis, and reduces reactive oxygen species. Desi variety performed better than Kabuli, and 30 µM MT application effectively mitigated Cd toxicity.

Comprehensive Physio-Biochemical Evaluation Reveals Promising Genotypes and Mechanisms for Cadmium Tolerance in Tibetan Hull-Less Barley

Cadmium (Cd) toxicity in agricultural soil is increasing globally and significantly impacts crop production and food safety. Tibetan hull-less barley (Hordeum vulgare L. var. nudum), an important staple food and economic crop, exhibits high genetic diversity and is uniquely adapted to the harsh conditions of the Qinghai-Tibet Plateau. This study utilized hydroponic experiments to evaluate the genotypic differences in Cd tolerance among 71 Tibetan hull-less barley genotypes. Physiological assessments revealed significant reductions in various growth parameters under Cd stress compared to normal conditions: soil-plant analysis development (SPAD) value, shoot height, root length, shoot and root fresh weight, shoot and root dry weight, of 11.74%, 39.69%, 48.09%, 52.88%, 58.39%, 40.59%, and 40.52%, respectively. Principal component analysis (PCA) revealed key traits contributing to Cd stress responses, explaining 76.81% and 46.56% of the variance in the preliminary and secondary selection. The genotypes exhibited varying degrees of Cd tolerance, with X178, X192, X215, X140, and X162 showing high tolerance, while X38 was the most sensitive based on the integrated score and PCA results. Validation experiments confirmed X178 as the most tolerant genotype and X38 as the most sensitive, with observed variations in morphological, physiological, and biochemical parameters, as well as mineral nutrient responses to Cd stress. Cd-tolerant genotypes exhibited higher chlorophyll content, net photosynthesis rates, and effective photochemical capacity of photosystem II, along with an increased Cd translocation rate and reduced oxidative stress. This was accompanied by elevated activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), indicating a robust stress response mechanism. These findings could facilitate the development of high-tolerance cultivars, with X178 as a promising candidate for further research and cultivation in Cd-contaminated soils.

Exogenously Applied Triacontanol Mitigates Cadmium Toxicity in Vigna radiata L. by Optimizing Growth, Nutritional Orchestration, and Metal Accumulation

Cadmium (Cd) is one of the foremost phytotoxic elements. Its proportion in agricultural soil is increasing critically due to anthropogenic activities. Cd stress is a major crop production threat affecting food security globally. Triacontanol (TRIA) is a phytohormone that promotes growth, development, and metabolic processes in plants. The current study explicates the mitigation of Cd toxicity in Vigna radiata L. (mung bean) seedlings through the application of TRIA by a seed priming technique under Cd stress. The role of TRIA in improving metabolic processes to promote Vigna radiata (mung bean, green gram) vegetative growth and performance under both stressed and unstressed conditions was examined during this study. To accomplish this, three doses of TRIA (10, 20, and 30 µmol L-1) were used to pretreat V. radiata seeds before they were allowed to grow for 40 days in soil contaminated with 20 mg kg-1 Cd. Cd stress lowered seed germination, morphological growth, and biomass in V. radiata plants. The maximum root and shoot lengths, fresh and dry weights of roots, and shoot and seed germination rates were recorded for TRIA2 compared with those of TRIA1 and TRIA3 under Cd stress. In Cd-stressed V. radiata plants, TRIA2 increased the content of chlorophyll a (2.1-fold) and b (3.1-fold), carotenoid (4.3-fold), total chlorophyll (3.1-fold), and gas exchange attributes, such as the photosynthetic rate (2.9-fold), stomatal conductance (6.0-fold), and transpiration rate (3.5-fold), compared with those in plants treated with only Cd. TRIA seed priming increased nutrient uptake (K1+, Na1+, Mg2+, and Zn2+), total phenolic content, total soluble protein content, and DPPH (2,2-diphenyl-1-picrylhydrazyl) activity. Additionally, TRIA2 significantly reduced the quantity of Cd in the plants (3.0-fold) and increased the metal tolerance index (6.6-fold) in plants contrasted with those in the Cd-treated plants. However, TRIA2 promoted plant growth and biomass production by lowering Cd-induced stress through modifying the plant antioxidant machinery and reducing oxidative stress. The improved yield characteristics of V. radiata seedlings treated with TRIA suggest that exogenous TRIA may be used to increase plant tolerance to Cd stress.

Genome-wide analysis of miR172-mediated response to heavy metal stress in chickpea (Cicer arietinum L.): physiological, biochemical, and molecular insights

BACKGROUND

Chickpea (Cicer arietinum L.), a critical diploid legume in the Fabaceae family, is a rich source of protein, vitamins, and minerals. However, heavy metal toxicity severely affects its growth, yield, and quality. MicroRNAs (miRNAs) play a crucial role in regulating plant responses to both abiotic and biotic stress, including heavy metal exposure, by suppressing the expression of target genes. Plants respond to heavy metal stress through miRNA-mediated regulatory mechanisms at multiple physiological, biochemical, and molecular levels. Although the Fabaceae family is well represented in miRNA studies, chickpeas have been notably underrepresented. This study aimed to investigate the effects of heavy metal-induced stress, particularly from 100 µM concentrations of cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), and 30 µM arsenic (As), on two chickpea varieties: ILC 482 (sensitive) and Azkan (tolerant). The assessment focused on physiological, biochemical, and molecular parameters. Furthermore, a systematic characterization of the miR172 gene family in the chickpea genome was conducted to better understand the plant's molecular response to heavy metal stress.

RESULTS

Variance analysis indicated significant effects of genotype (G), treatment (T), and genotype-by-treatment (GxT) interactions on plant growth, physiological, and biochemical parameters. Heavy metal stress negatively impacted plant growth in chickpea genotypes ILC 482 and Azkan. A reduction in chlorophyll content and relative leaf water content was observed, along with increased cell membrane damage. In ILC 482, the highest hydrogen peroxide (H₂O₂) levels in shoot tissue were recorded under As, Cd, and Ni treatments, while in Azkan, peak levels were observed with Pb treatment. Malondialdehyde (MDA) levels in root tissue were highest in ILC 482 under Cd and Ni exposure and in Azkan under As, Cr, and Cd treatments. Antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), were significantly elevated under heavy metal stress in both genotypes. Gene expression analysis revealed upregulation of essential antioxidant enzyme genes, such as SOD, CAT, and APX, with APX showing notable increases in both shoot and root tissues compared to the control. Additionally, seven miR172 genes (miR172a, miR172b, miR172c, miR172d, miR172e, miR172f, and miR172g) were identified in the chickpea genome, distributed across five chromosomes. All genes exhibited conserved hairpin structures essential for miRNA functionality. Phylogenetic analysis grouped these miR172 genes into three clades, suggesting strong evolutionary conservation with other plant species. The expression analysis of miR172 and its target genes under heavy metal stress showed varied expression patterns, indicating their role in enhancing heavy metal tolerance in chickpea.

CONCLUSIONS

Heavy metal stress significantly impaired plant growth and physiological and biochemical parameters in chickpea genotypes, except for cell membrane damage. The findings underscore the critical role of miR172 and its target genes in modulating chickpea's response to heavy metal stress. These insights provide a foundational understanding for developing stress-tolerant chickpea varieties through miRNA-based genetic engineering approaches.

Hormetic responses to cadmium exposure in wheat seedlings: insights into morphological, physiological, and biochemical adaptations

Cadmium is commonly recognized as toxic to plant growth, low-level Cd has promoting effects on growth performance, which is so-called hormesis. Although Cd toxicity in wheat has been widely investigated, knowledge of growth response to a broad range of Cd concentrations, especially extremely low concentrations, is still unknown. In this study, the morphological, physiological, and biochemical performance of wheat seedlings to a wide range of Cd concentrations (0-100 µΜ) were explored. Low Cd treatment (0.1-0.5 µM) improved wheat biomass and root development by enhancing the photosynthetic system and antioxidant system ability. Photosynthetic rate (Pn) was improved by 5.72% under lower Cd treatment (1 µΜ), but inhibited by 6.05-49.85% from 5 to 100 µΜ. Excessive Cd accumulation induced oxidative injury manifesting higher MDA content, resulting in lower photosynthetic efficiency, stunted growth, and reduction of biomass. Further, the contents of ascorbate, glutathione, non-protein thiols, and phytochelatins were improved under 5-100 µΜ Cd treatment. The ascorbate peroxidase activity in the leaf showed a hormetic dose-response characteristic. Correlation analysis and partial least squares (PLS) results indicated that antioxidant enzymes and metabolites were closely correlated with Cd tolerance and accumulation. The results of the element network, correlation analysis, and PLS showed a crucial role for exogenous Cd levels in K, Fe, Cu, and Mn uptake and accumulation. These results provided a deeper understanding of the hormetic effect of Cd in wheat, which would be beneficial for improving the quality of hazard and risk assessments.

How does silicon alleviate Cd-induced phytotoxicity in barley, Hordeum vulgare L.?

Toxic heavy metal accumulation in edible plants has become a problem worth worrying about for human health. Cadmium is one of the most toxic metals presenting high bioavailability in the environment. The main route of transfer of Cd to humans is the consumption of contaminated food which suggests that reducing of Cd absorption by plants could reduce this risk. In this context, it was suggested that silicon supply would be able to limit the transfer of Cd to the plants. Thus, this work evaluated the effects of 0.5 mM Si on Cd absorption and accumulation in barley (Hordeum vulgare L.). Plants were grown hydroponically for 21 days in the presence of 0 and 15 μM Cd2+ combined or not with 0.5 mM Si. Analyses were related to growth and photosynthesis parameters, Cd accumulation in organs and Cd subcellular distribution in the shoots. Results showed that, under Cd alone, plants showed severe toxicity symptoms as chlorosis and necrosis and produced significantly less biomass as compared to control. 0.5 mM Si in the medium culture significantly reduced Cd-induced toxicity by mitigating symptoms and restoring growth, photosynthesis, and nutrition. Si also induced a significant reduction of Cd concentration in plants and changed its sub-cellular compartmentalization by enhancing fixation to cell walls and reducing the Cd concentration in the cytoplasmic and organelles fractions. These data suggest that the application of Si could significantly increase Cd tolerance and reduce the risk of the Cd accumulation in edible plants.

Leveraging machine learning to unravel the impact of cadmium stress on goji berry micropropagation

This study investigates the influence of cadmium (Cd) stress on the micropropagation of Goji Berry (Lycium barbarum L.) across three distinct genotypes (ERU, NQ1, NQ7), employing an array of machine learning (ML) algorithms, including Multilayer Perceptron (MLP), Support Vector Machines (SVM), Random Forest (RF), Gaussian Process (GP), and Extreme Gradient Boosting (XGBoost). The primary motivation is to elucidate genotype-specific responses to Cd stress, which poses significant challenges to agricultural productivity and food safety due to its toxicity. By analyzing the impacts of varying Cd concentrations on plant growth parameters such as proliferation, shoot and root lengths, and root numbers, we aim to develop predictive models that can optimize plant growth under adverse conditions. The ML models revealed complex relationships between Cd exposure and plant physiological changes, with MLP and RF models showing remarkable prediction accuracy (R2 values up to 0.98). Our findings contribute to understanding plant responses to heavy metal stress and offer practical applications in mitigating such stress in plants, demonstrating the potential of ML approaches in advancing plant tissue culture research and sustainable agricultural practices.

The effect of sulphur supplementation on cadmium phytotoxicity in wheat and lettuce: changes in physiochemical properties of roots and accumulation of phytochelatins

Intensive sulphur fertilisation has been reported to improve the nutrient balance and growth of Cd-exposed plants, but the reasons of this phenomenon and the role of sulphur compounds in the resistance to cadmium are unclear. We investigated sulphur supplementation-induced changes in the surface properties of roots and the level of thiol peptides (PCs) in Cd-stressed Triticum aestivum L. (monocots clade) and Lactuca sativa L. (dicots clade) grown in nutrient solution. The combination of three sulphur (2 mM S-basic level, 6 or 9 mM S-elevated levels) and four cadmium (0, 0.0002, 0.02 or 0.04 mM Cd) concentrations was used. The physicochemical parameters of the roots were determined based on the apparent surface area (Sr), total variable surface charge (Q), cation exchange capacity (CEC) and surface charge density (SCD). In Cd-exposed plants supplied with sulphur, a different character and trend in the physicochemical changes (adsorption and ion exchange) of roots were noted. At the increased sulphur levels, as a rule, the Sr, CEC, Q and SCD values clearly increased in the lettuce but decreased in the wheat in the entire range of the Cd concentrations, except the enhanced Sr of wheat supplied with 6 mM S together with elevated (0.0002 mM) and unchanged (0.02, 0.04 mM Cd) value of this parameter at 9 mM S. This indicates a clade-specific and/or species-specific plant reaction. The 6 mM S appears to be more effective than 9 mM S in alleviation of the cadmium's toxic effects on roots. It was found that at 0.02 and 0.04 mM Cd, the use of 6 mM S limits the Cd accumulation in the roots of both species in comparison with the basic S fertilisation. Moreover, PC accumulation was much more efficient in wheat than in lettuce, and intensive sulphur nutrition generally induced biosynthesis of these chelating compounds. Physicochemical parameters together with quantitative and qualitative assessment of thiol peptides can be important indicators of the efficiency of root system functioning under cadmium stress. The differences between the species and the multidirectional character of the changes are a result of the involvement of a number of multi-level mechanisms engaged in the defence against metal toxicity.

Enhanced wedelolactone content in in vitro-raised genetically uniform Wedelia chinensis under the influence of CuSO4

In the present study, we addressed the imperative for potent anticancer agents through Wedelia chinensis, a medicinal plant abundant in the robust antihepatotoxic and antitumor compound wedelolactone. Hindrances in conventional propagation methods due to cross-pollination and habitat degradation prompted us to pioneer in vitro rapid multiplication using plant tissue culture. Optimal outcomes were attained employing Murashige and Skoog (MS) medium supplemented with Indole-3-butyric acid (IBA) (0.5 mg/L) and Kinetin (KN) (5.0 mg/L), yielding 97.67% shoot regeneration and 81.67% rooting from nodal explants. Transplanted plantlets exhibited a 92% survival rate. We established a wedelolactone extraction protocol using toluene:ethyl acetate:formic acid (5:4:1) for High-performance thin-layer chromatography (HPTLC) analysis, trailblazing wedelolactone quantification and 2C DNA analysis in W. chinensis via flow cytometry. Experiments under heavy metal stress with CuSO4 unveiled physiological responses, with peak wedelolactone content [193.90 μg/g dry weight (dw)] in vitro at 75 μM CuSO4, surpassing in vivo levels (89.95 μg/g dw) by 116%. By pioneering successful in vitro rapid multiplication and enhanced wedelolactone content, we bridge a critical gap in the conservation and production of this medicinal plant. Our findings not only offer a sustainable means of propagation but also present a viable strategy for elevating the yield of potent bioactive molecules like wedelolactone, holding immense promise for the development of novel therapeutic interventions and addressing the pressing healthcare challenges of our time.

Assessing lead and cadmium tolerance of Chenopodium ambrosioides during micropropagation: an in-depth qualitative and quantitative analysis

The tolerance of Chenopodium ambrosioides to some heavy metals under in vitro environment was thoroughly investigated. A micropropagation protocol was developed to facilitate the mass production of plants and to identify metals-tolerant species for potential use in the restoration of polluted areas. Nodal explants exhibited callus formation when treated with N6-benzyladenin (BA) (1.5 mg/l) and a combination of BA/α-naphthalene acetic acid (NAA) at concentrations of 1.5/1.0 mg/l on the Murashige and Skoog (MS) medium. The optimal shoot formation was achieved with the callus grown on a medium enriched with 1.5/1.0 mg/l BA/NAA, resulting in an impressive number (21.89) and length (11.79 cm) of shoots. The in vitro shoots were rooted using NAA (1.0 and 1.5 mg/l) and were acclimatized in pots with 71% survival rate. After standardizing micropropagation protocol, the in vitro shoots were subjected to various doses of lead nitrate (Pb(NO3)2 and cadmium chloride (CdCl2). Pb(NO3)2 and CdCl2 in the media let to a reduction in shoot multiplication, decreasing from 18.73 in the control group to 11.31 for Pb(NO3)2 and 13.89 for CdCl2 containing medium. However, Pb(NO3)2 and CdCl2 promoted shoot length from 5.61 in the control to 9.86 on Pb(NO3)2 and 12.51 on CdCl2 containing medium. In the case of Pb(NO3)2 treated shoots, the growth tolerance index (GTI) ranged from117.64% to 194.11%, whereas for CdCl2 treated shoots, the GTI ranged from 188.23% to 264.70%. Shoots treated with high level of Pb(NO3)2induced reddish-purple shoots, while a low level of Pb(NO3)2 induced shoots displayed both green and reddish-purple colors in the same explants. In CdCl2 treated culture, the toxic effects were narrow leaf lamina, elongated petiole and a dark reddish purple coloration. These findings highlight the remarkable potential of C. ambrosioides to maintain growth and organogenesis even in the presence Pb(NO3)2 and CdCl2 on the MS medium, indicating a high degree of metal tolerance.

Metal tolerance and Cd phytoremoval ability in Pisum sativum grown in spiked nutrient solution

In the presented study, the effects of cadmium (Cd) stress and silicon (Si) supplementation on the pea plant (Pisum sativum L.) were investigated. The tendency to accumulate cadmium in the relevant morphological parts of the plant (roots and shoots respectively)-bioaccumulation, the transfer of this element in the plant (translocation) and the physiological parameters of the plant through indicators of oxidative stress were determined. Model studies were carried out at pH values 6.0 and 5.0 plant growth conditions in the hydroponic cultivation. It was shown that Cd accumulates mostly in plant roots at both pH levels. However, the Cd content is higher in the plants grown at lower pH. The Cd translocation factor was below 1.0, which indicates that the pea is an excluder plant. The contamination of the plant growth environment with Cd causes the increased antioxidant stress by the growing parameters of the total phenolic content (TPC), polyphenol oxidase activity (PPO), the malondialdehyde (MDA) and lipid peroxidation (LP). The results obtained showed that the supplementation with Si reduces these parameters, thus lowering the oxidative stress of the plant. Moreover, supplementation with Si leads to a lower content of Cd in the roots and reduces bioaccumulation of Cd in shoots and roots of pea plants.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

A meta-analysis on the heavy metal uptake in Amaranthus species

Metals can accumulate in different parts of plant species in high concentrations, which gives the basis for the plant-based technology called phytoremediation. Among annual species, Amaranthus is a well-studied, potential metal accumulator genus; however, some conflicts are found among published results. Thus, we studied the metal (Cd, Cu, Fe, Ni, Pb, and Zn) accumulation potential of Amaranthus plant parts (root, stem, and leaf) by meta-analysis, furthermore, by calculation of bioaccumulation factor (BAF) values. After the extensive literature search and the calculation of relative interaction intensity (RII) values, we found significant accumulation for each metal by Amaranthus individuals growing on contaminated soils compared to plants collected from uncontaminated ones. Differences among plant parts were significant for Cu and Fe, minor for Ni, Pb, and Zn, and negligible for Cd. The BAF values indicated high accumulation in the leaf, moderate in root and stem for Cd, moderate in each plant part for Pb, and very low in each plant part for Fe, Ni, and Zn. We highlight that Amaranthus species are good prospects for metal phytoremediation projects, although, due to specific plant part-metal patterns, special attention should be paid to the harvesting practice.

How heavy metal stress affects the growth and development of pulse crops: insights into germination and physiological processes

The current work is an extensive review addressing the effects of heavy metals in major pulse crops such as Chickpea (Cicer arietinum L.), Pea (Pisum sativum L.), Pigeonpea (Cajanus cajan L.), Mung bean (Vigna radiata L.), Black gram (Vigna mungo L.) and Lentil (Lens culinaris Medik.). Pulses are important contributors to the global food supply in the world, due to their vast beneficial properties in providing protein, nutritional value and health benefits to the human population. Several studies have reported that heavy metals are injurious to plants causing inhibition in plant germination, a decrease in the root and shoot length, reduction in respiration rate and photosynthesis. Properly disposing of heavy metal wastes has become an increasingly difficult task to solve in developed countries. Heavy metals pose one of the substantial constraints to pulse crops growth and productivity even at low concentrations. This article attempts to present the morphological, biochemical and various physiological changes induced on the pulse crops grown under various heavy metal stress such as As, Cd, Cr, Cu, Pb, and Ni.

Plant Metabolomics: An Overview of the Role of Primary and Secondary Metabolites against Different Environmental Stress Factors

Several environmental stresses, including biotic and abiotic factors, adversely affect the growth and development of crops, thereby lowering their yield. However, abiotic factors, e.g., drought, salinity, cold, heat, ultraviolet radiations (UVr), reactive oxygen species (ROS), trace metals (TM), and soil pH, are extremely destructive and decrease crop yield worldwide. It is expected that more than 50% of crop production losses are due to abiotic stresses. Moreover, these factors are responsible for physiological and biochemical changes in plants. The response of different plant species to such stresses is a complex phenomenon with individual features for several species. In addition, it has been shown that abiotic factors stimulate multi-gene responses by making modifications in the accumulation of the primary and secondary metabolites. Metabolomics is a promising way to interpret biotic and abiotic stress tolerance in plants. The study of metabolic profiling revealed different types of metabolites, e.g., amino acids, carbohydrates, phenols, polyamines, terpenes, etc, which are accumulated in plants. Among all, primary metabolites, such as amino acids, carbohydrates, lipids polyamines, and glycine betaine, are considered the major contributing factors that work as osmolytes and osmoprotectants for plants from various environmental stress factors. In contrast, plant-derived secondary metabolites, e.g., phenolics, terpenoids, and nitrogen-containing compounds (alkaloids), have no direct role in the growth and development of plants. Nevertheless, such metabolites could play a significant role as a defense by protecting plants from biotic factors such as herbivores, insects, and pathogens. In addition, they can enhance the resistance against abiotic factors. Therefore, metabolomics practices are becoming essential and influential in plants by identifying different phytochemicals that are part of the acclimation responses to various stimuli. Hence, an accurate metabolome analysis is important to understand the basics of stress physiology and biochemistry. This review provides insight into the current information related to the impact of biotic and abiotic factors on variations of various sets of metabolite levels and explores how primary and secondary metabolites help plants in response to these stresses.

Rice Plants (Oryza sativa L.) under Cd Stress in Fe Deficiency Conditions

Due to the environment pollution by cadmium (Cd) near industrial metallurgic factories and the widespread use of phosphorus fertilizers, the problem of toxic Cd effect on plants is well discussed by many authors, but the phytotoxicity of Cd under iron (Fe) deficiency stress has not been sufficiently studied. The aim of the work was to study comprehensively the effect of Cd under Fe deficiency conditions on physiological, biochemical, and anatomical parameters of rice varieties, to identify varietal differences in plant response to the effect of double stress. Relative resistance and sensitivity to the joint effect of Cd and Fe deficiency stress rice varieties have been identified. Double stress decreased a linear growth and biomass accumulation of roots and shoots (by 36-50% and 33-46% and 32-56% and 32-48%, accordingly), content of photosynthetic pigments (Chla, Chlb, and carotenoids by 36-51%, 32-47%, and 64-78%, accordingly), and relative water content (by 18-26%). Proline content increased by 28-103% in all rice varieties, but to a lesser extent in sensitive varieties. The thickness of the lower and upper epidermis and the diameter of vascular bundles of leaves decreased by 18-50%, 46-60%, and 13-48%, accordingly. The thickness of the root endodermis and exodermis and diameter of the central cylinder mainly decreased. The thickness of the exodermis increased slightly by 7%, and the diameter of the central cylinder remained at the control level in resistant Madina variety while in sensitive Chapsari variety, these indicators decreased significantly by 50 and 45%, accordingly. Thus, the aggravation of adverse effect of Cd under Fe deficiency conditions and the varietal specificity of plants' response to double stress were shown. It creates the need for further study of these rice varieties using Fe to identify mechanisms for reducing the toxic effect of Cd on plants as well as the study of Fe and Cd transporter genes at the molecular level.

The Butterfly Effect: Mild Soil Pollution with Heavy Metals Elicits Major Biological Consequences in Cobalt-Sensitized Broad Bean Model Plants

Among the heavy metals (HMs), only cobalt induces a polymorphic response in Vicia faba plants, manifesting as chlorophyll morphoses and a ‘break-through’ effect resulting in the elevated accumulation of other HMs, which makes Co-pretreated broad bean plants an attractive model for investigating soil pollution by HMs. In this study, Co-sensitized V. faba plants were used to evaluate the long-term effect of residual industrial pollution by examining biochemical (H₂O₂, ascorbic acid, malondialdehyde, free proline, flavonoid, polyphenols, chlorophylls, carotenoids, superoxide dismutase) and molecular (conserved DNA-derived polymorphism and transcript-derived polymorphic fragments) markers after long-term exposure. HM-polluted soil induced a significantly higher frequency of chlorophyll morphoses and lower levels of nonenzymatic antioxidants in Co-pretreated V. faba plants. Both molecular markers effectively differentiated plants from polluted and control soils into distinct clusters, showing that HMs in mildly polluted soil are capable of inducing changes in DNA coding regions. These findings illustrate that strong background abiotic stressors (pretreatment with Co) can aid investigations of mild stressors (slight levels of soil pollution) by complementing each other in antioxidant content reduction and induction of DNA changes.

Growth tolerance, concentration, and uptake of heavy metals as ameliorated by silicon application in vegetables

Lead (Pb) and cadmium (Cd) are among the heavy metals with phytotoxic and toxic effects on vegetables resulting in a significant decrease in crop yields. On the contrary, silicon (Si) has beneficial effects in enhancing plants' tolerance to biotic and abiotic stresses such as that imposed by heavy metals. This study evaluated the effects of Pb and Cd on the growth, biomass, and ameliorative mechanism of Si on concentration and uptake by leafy vegetables: spinach, kale, and amaranth. The greenhouse experiment treatments were Pb, Pb + Si, Cd, Cd + Si, Si, and control. These were arranged as a split-plot in a complete randomized design (CRD): main plots constituted vegetable species and treatments as subplots. The field experiment was carried in the Kenyatta University Research Farm, and treatments included Si application and control, arranged in a randomized complete block design (RCBD). Cadmium application reduced root biomass by 53-70% while Pb reduced it by 54-61% when compared with control. Silicon fertilization enhanced biomass tolerance by three-folds' and significantly (p < 0.001) reduced concentration and uptake of Pb and Cd. Results indicated a strong negative correlation between Cd concentrations and growth parameters (r = 0.8). The study recommends Si application to enhance leafy vegetables' tolerance to Pb and Cd.

Differences in Cadmium Accumulation, Detoxification and Antioxidant Defenses between Contrasting Maize Cultivars Implicate a Role of Superoxide Dismutase in Cd Tolerance

Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, 12 Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and we determined their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd-tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. A principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd-tolerance, we studied the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT). Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology, antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd-tolerance.

Effect of Cadmium and Copper Exposure on Growth, Physio-Chemicals and Medicinal Properties of Cajanus cajan L. (Pigeon Pea)

Soil contamination with heavy metals is an emerging concern in the modern era, affecting all forms of life. Pigeon pea is a multi-use shrub with medicinal and nutritional values. On the basis of a randomized complete design, we investigated in the current project the combined cadmium (Cd) and copper (Cu) effect on plant growth and physio-chemical/medicinal properties of pigeon pea. Three-week-old seedlings were grown in combined Cd and Cu amended soil with increasing metal concentrations (control, 20 + 30 mg/kg, 40 + 60 mg/kg, and 60 + 90 mg/kg) for three months. At high-dose metal cumulative stress (60 + 90 mg/kg), plant shoot and root growth in terms of plant height as well as fresh and dry weight were significantly inhibited in association with decreased photosynthetic attributes (chlorophyll a and b contents, net photosynthesis, transpiration rate, stomatal conductance, intercellular CO₂ concentrations) and diminished nutrient contents. Cd and Cu at high amounts inflicted oxidative stresses as assessed in elevated lipid peroxidation (MDA), hydrogen peroxide (H₂O₂), and electrolyte leakage contents. Antioxidant enzyme activities, namely, those of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione peroxidase (GPX), were enhanced, along with proline content with increasing metal quantity. Phenolics and flavonoids exhibited a diverse response regarding metal concentration, and their biosynthesis was significantly suppressed at high Cd and Cu cumulative stress. The reduction in secondary metabolites may account for declined medicinal properties of pigeon pea as appraised in reduced antibacterial, 2, 2-diphenyl-1-picrylhydrazyl (DPPH), and ferric-reducing antioxidant potential (FRAP) activities. Our results clearly demonstrate that the exposure of pigeon pea to Cd- and Cu-contaminated soil might affect consumers due to the presence of metals and the negligible efficacy of the herbal products.

Jasmonic acid (JA) and gibberellic acid (GA3) mitigated Cd-toxicity in chickpea plants through restricted cd uptake and oxidative stress management

Cadmium stress is one of the chief environmental cues that can substantially reduce plant growth. In the present research, we studied the effect of jasmonic acid (JA) and gibberellic acid (GA₃) applied individually and/or in combination to chickpea (Cicer arietinum) plants exposed to 150 µM cadmium sulphate. Cadmium stress resulted in reduced plant growth and pigment contents. Moreover, chickpea plants under cadmium contamination displayed higher levels of electrolytic leakage, H₂O_2, and malonaldehyde, as well as lower relative water content. Plants primed with JA (1 nM) and those foliar-fed with GA₃ (10^-6 M) showed improved metal tolerance by reducing the accumulation of reactive oxygen species, malonaldehyde and electrolytic leakage, and increasing relative water content. . Osmoprotectants like proline and glycinebetaine increased under cadmium contamination. Additionally, the enzymatic activities and non-enzymatic antioxidant levels increased markedly under Cd stress, but application of JA as well as of GA₃ further improved these attributes. Enzymes pertaining to the ascorbate glutathione and glyoxylase systems increased significantly when the chickpea plants were exposed to Cd. However, JA and GA₃ applied singly or in combination showed improved enzymatic activities as well as nutrient uptake, whereas they reduced the metal accumulation in chickpea plants. Taken together, our findings demonstrated that JA and GA₃ are suitable agents for regulating Cd stress resistance in chickpea plants.

Lead contamination affects the primary productivity traits, biosynthesis of macromolecules and distribution of metal in durum wheat (Triticumdurum L.)

Lead (Pb) pollution emerged as an international issue particularly during second and third industrial revolution and is of serious global concern. Cereal crops have shown different capabilities, innate variability and mechanisms to cope with heavy metals present in their environment. Keeping in view the perspectives of food security and safety with increasing demand for Triticum durum L. it becomes imperative to appraise sustainability potential of the crop for Pb contaminated soils. The current study was conducted to test the hypothesis that T. durum germplasm holds genetic variability to evolve under Pb contamination through modulations of morpho-biochemical parameters of selective advantage. The performance of nine T. durum L. cultivars (CBD25, CBD46, CBD58, CBD59, CBD63, CBD66, CBD68, CBD69 and CBD82) was evaluated following exposure to varying Pb levels (control, 10, 20 and 40 mg kg-1) in soil. Growth, biosynthesis of macromolecules and metal distribution in plant parts were assessed using valid procedures and protocols. The cultivars exhibited a differential degree of tolerance to Pb and among the tested germplasm, CBD59 performed better followed by CBD63 and CBD66 for their primary productivity traits, biosynthesis of pigments and other macromolecules (amino acids, proteins and sugar) along with resilience for Pb uptake and its consequent bioaccumulation in grains. The traits used in the study served as strong predictors to provide superior/selective ability to survive under contaminated environment. The study signified that metal tolerance/sensitivity in the cultivars is independent of magnitude of metal stress, growth responses and Pb accumulation in plant parts hence varied in space and time. The existence of genetic variability, which is a pre-requisite for selection can definitely be of great advantage for future breeding projects to develop high yielding varieties/ cultivars of durum wheat with Pb free grains to assure food security and safety.

Alleviation of adverse effects of nickel on growth and concentration of copper and manganese in wheat through foliar application of ascorbic acid

We investigated the role of ascorbic acid (AsA) to alleviate nickel (Ni) induced adverse effects on growth and concentration of Ni, copper (Cu), and manganese (Mn) in hydroponically grown wheat varieties viz. Galaxy, Punjab-2011, and FSD-08. Plants were exposed to five levels of Ni viz. 0, 5, 10, 15, and 20 mg L^-1. After 1 week, AsA (1 mM) was sprayed onto the Ni-stressed plants. FSD-08 produced the maximum SDW with and without AsA compared to other varieties. FSD-08, Galaxy, and Punjab-2011 witnessed 2.61-, 2.83-, and 7.5-fold increases in SDW with AsA, respectively. Wheat plants contained the maximum Ni in shoots and roots with a Ni level of 20 mg L^-1 irrespective of varieties. Nickel in shoots decreased with AsA witnessing 13, 12, and 10% decrease in FSD-08, Punjab-2011, and Galaxy, respectively. Nickel in roots of FSD-08 decreased by 18% while increased by 3.34-fold and 3.50-fold in Galaxy and Punjab-2011, respectively with AsA. Nickel decreased Cu in shoot and Mn in shoot and root while Cu in roots of all wheat varieties increased. It was concluded that AsA improved the growth of Ni-stressed and FSD-08 performed better by maintaining good growth and less Ni in shoots compared to other varieties.

Effect of Cadmium Chloride and Cadmium Nitrate on Growth and Mineral Nutrient Content in the Root of Fava Bean (Vicia faba L.)

The present study aimed to analyze the differences in the tolerance of fava bean (Vicia faba cv. Aštar) roots to cadmium in nitrate-Cd(NO₃)₂-and chloride-CdCl₂-solutions. The physiological and biochemical parameters were assessed. The tested doses of Cd (50, 100, 150 and 300 mg/L) did not influence the germination of seeds. However, considerable growth inhibition and dehydration were observed after 96 h incubation. The thickness of roots and rupture of cell membranes increased along with the increasing concentration of the metal in the solution. At a Cd dose of 300 mg/L, irrespective of the solution used, increased nitrogen concentration and no change in sodium content were observed. The content of magnesium increased due to the dose of 100 mg/L (cadmium nitrate) and the content of calcium increased due to the dose of 300 mg/L (in either nitrate or chloride). The correlation analyses pointed to a possible effect of nitrates in the applied solutions on the accumulation of Cd and some minerals in the roots of the given variety of fava bean. This may be important for both research and agricultural practice. The identification of crops with high tolerance to cadmium, as well as knowledge about the mechanisms of ion interactions at the soil solution-plant level, is important in terms of such crops' use in the process of the remediation of cadmium-contaminated soils coupled with food production.

Ameliorative Effects of Exogenous Proline on Photosynthetic Attributes, Nutrients Uptake, and Oxidative Stresses under Cadmium in Pigeon Pea (Cajanus cajan L.)

Proline plays a significant role in the plant response to stress conditions. However, its role in alleviating metal-induced stresses remains elusive. We conducted an experiment to evaluate the ameliorative role of exogenous proline on cadmium-induced inhibitory effects in pigeon pea subjected to different Cd treatments (4 and 8 mg/mL). Cadmium treatments reduced photosynthetic attributes, decreased chlorophyll contents, disturbed nutrient uptake, and affected growth traits. The elevated activity of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), in association with relatively high contents of hydrogen peroxide, thiobarbituric acid reactive substances, electrolyte leakage, and endogenous proline, was measured. Exogenous proline application (3 and 6 mM) alleviated cadmium-induced oxidative damage. Exogenous proline increased antioxidant enzyme activities and improved photosynthetic attributes, nutrient uptake (Mg²⁺, Ca²⁺, K⁺), and growth parameters in cadmium-stressed pigeon pea plants. Our results reveal that proline supplementation can comprehensively alleviate the harmful effects of cadmium on pigeon pea plants.

Phytoremediation potential of Chromolaena odorata, Impatiens patula, and Gynura pseudochina grown in cadmium-polluted soils

To assess the cadmium (Cd) phytoremediation of three native plant species from Padeang zinc (Zn) mine area (Chromolaena odorata, Impatiens patula, and Gynura pseudochina), a hydroponic experiment was performed in nutrient solutions containing various concentrations of Cd (0, 5, 10, 20, and 50 mg L^-1) for 15 days. In the hydroponic experiment, C. odorata showed significantly higher total Cd content than those grown in 50 mg L^-1 Cd solutions. Only C. odorata and I. patula were chosen for the pot experiment. The plants were grown in spiked Cd-contaminated soils for 90 days, with different concentrations of Cd (0, 20, 40, 60, and 80 mg kg^-1). The results from the pot experiment revealed that both species accumulated more Cd in their root parts, with translocation factor values < 1. C. odorata exhibited the highest biomass production, relative growth rate, and Cd uptake or removal. The findings of the study clearly demonstrate the best uptake of C. odorata in Cd phytoremediation. Novelty statementEven though Chromolaena odorata, Impatiens patula, and Gynura pseudochina have been reported as a Cd accumulator but the assessment of these species by nutrient medium and the soil was not undertaken so far. The discovery of new Cd-accumulator plants has been hindered by the lack of efficient assessing. To assess the suitability of specific species of tropical plants that are able to uptake high amounts of Cd without risk of toxicity under conditions similar to the actual field study, is a novelty.