Essential and Beneficial Trace Elements in Plants, and Their Transport in Roots: a Review

The Interplay between Toxic and Essential Metals for Their Uptake and Translocation Is Likely Governed by DNA Methylation and Histone Deacetylation in Maize

The persistent nature of lead (Pb) and cadmium (Cd) in the environment severely affects plant growth and yield. Conversely, plants acquire zinc (Zn) from the soil for their vital physiological and biochemical functions. However, the interplay and coordination between essential and toxic metals for their uptake and translocation and the putative underlying epigenetic mechanisms have not yet been investigated in maize. Here, we report that the presence of Zn facilitates the accumulation and transport of Pb and Cd in the aerial parts of the maize plants. Moreover, the Zn, Pb, and Cd interplay specifically interferes with the uptake and translocation of other divalent metals, such as calcium and magnesium. Zn, Pb, and Cd, individually and in combinations, differentially regulate the expression of DNA methyltransferases, thus alter the DNA methylation levels at the promoter of Zinc-regulated transporters, Iron-regulated transporter-like Protein (ZIP) genes to regulate their expression. Furthermore, the expression of histone deacetylases (HDACs) varies greatly in response to individual and combined metals, and HDACs expression showed a negative correlation with ZIP transporters. Our study highlights the implication of DNA methylation and histone acetylation in regulating the metal stress tolerance dynamics through Zn transporters and warns against the excessive use of Zn fertilizers in metal contaminated soils.

Heavy Metal Levels and Mineral Nutrient Status in Different Parts of Various Medicinal Plants Collected from Eastern Mediterranean Region of Turkey

Medicinal plants have been used for treatment of many diseases since the ancient times with traditional knowledge being transferred from generation to generation. However, in recent years, many natural habitats have been contaminated due to increased anthropogenic activities. Plants which are exposed to heavy metal toxicity may experience several serious problems. Furthermore, the inclusion of these plants into the food chain poses a threat to human health as well. Additionally, presence of heavy metals directly effect mineral nutrition and consequently the food quality. The aim of this study herewith is to determine the heavy metal content and mineral nutrient status of some medicinal plants to have insight on their health repercussions on plants and humans. The concentrations of Al, B, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn in commonly used parts (root, rhizome, seed, resin, gall, fruit) especially for remedial purposes of 17 medicinal plants collected from Turkey were analyzed by ICP-OES. The measured values for concentrations from lowest to highest were (in mg kg^-1) 30.983-368.877 for Al, 13.845-186.015 for B, 1335.699-11213.951 for Ca, 0.016-0.653 for Cd, 0.379-30.708 for Cr, 23.838-90.444 for Cu, 78.960-1228.845 for Fe, 1035.948-6393.491 for K, 83.193-2252.031 for Mg, 12.111-362.570 for Mn, 278.464-1968.775 for Na, 1.945-35.732 for Ni, 0.796-17.162 for Pb and 166.910-395.252 for Zn. Overall, heavy metal concentrations in medicinal plants collected nearby industrial regions, mining and farming sites, were found to be in slightly higher levels. This shows us that it is of crucial importance that the areas where medicinal plants are collected are clean especially by means of heavy metals for the reason that these plants can cause more harm than the benefits they may provide if they are contaminated.

Impact of copper oxide nanoparticles on the germination, seedling growth, and physiological responses in Brassica pekinensis L

Wide application of nanoparticles causes considerable environmental, health, and safety problems. However, their potential impact and mechanisms on plant growth are not completely clear. In the present study, the effects of different concentration of copper oxide nanoparticles (nCuO) on seed germination and seedling growth, as well as physiological parameters of Brassica pekinensis L., were investigated. The seeds were exposed to 10-, 100-, and 1000-mg L-1 nCuO suspensions and 0.8-mg L-1 Cu2+ released from 1000-mg L-1 nCuO for 7 day. The results showed that nCuO did not affect the germination rate, germination potential, and germination index of B. pekinensis but significantly affected the vitality index. The growth of roots and shoots of B. pekinensis was promoted at 10-mg L-1 nCuO, while they were inhibited under 1000-mg L-1 nCuO and Cu2+ ion treatments, and roots suffered more damage than shoots. Cu content in shoots and roots of B. pekinensis increased with increasing concentrations of nCuO, which is significantly higher in roots as compared with shoots. Roots and shoots accumulated more Cu under nCuO treatments compared with Cu2+ ion treatment. nCuO treatments led to significant lignification in roots of B. pekinensis. Furthermore, nCuO increased in the contents of soluble sugar and protein in shoots, while nCuO at 1000 mg L-1 significantly inhibited the content of soluble protein in roots. In addition, concentration-dependent augmentation of lipid peroxidation, hydrogen peroxide and superoxide generation, and antioxidant enzyme activity were noticed in shoots and roots of B. pekinensis seedlings under nCuO and Cu2+ ion treatments. Altogether, the results strongly suggested that the phytotoxicity of nCuO in B. pekinensis was caused by both the nanoparticles itself and the released Cu2+ ions.

Potentially toxic elements (PTEs) in crops, soil, and water near Xiangtan manganese mine, China: potential risk to health in the foodchain

The pollution from large-scale manganese mining and associated industries in Xiangtan (south Central China) has created a significant burden on the local environment. The proximity of mining, and other industrial activity to the local population, is of concern and impact of past industrial on the food chain was evaluated by the assessment of common food groups (rice, soybean, and sweet potato), and the associated soil and water in the region. We focused on specific potentially toxic elements (PTEs): Mn, Pb, Cd, Cr, Cu, and Zn associated with industrial activity, identifying the distribution of pollution, the potential significance of total health index (THI) for local people and its spatial distribution. The study area showed severe contamination for Mn, followed by Cd and Pb, while other PTEs showed relatively light levels of pollution. When analyzing the impact on crops exceeding the tolerance limit, the dominant PTEs were Mn, Cd, and Pb, with lower significance for Zn, Cu, and Cr. The average THI value for adults is 4.63, while for children, is 5.17, greatly exceeding the recommended limit (HQ > 1), confirming a significant health risk. In the spatial distribution of the THI, the region shows strong association with the transport and industrial processing infrastructure. Long-term management needs to consider remediation aligned to specific industrial operations and enhance contamination control measures of ongoing activity.

The Role of Selenium Mineral Trace Element in Exercise: Antioxidant Defense System, Muscle Performance, Hormone Response, and Athletic Performance. A Systematic Review

Exercise overproduces oxygen reactive species (ROS) and eventually exceeds the body's antioxidant capacity to neutralize them. The ROS produce damaging effects on the cell membrane and contribute to skeletal muscle damage. Selenium (Se), a natural mineral trace element, is an essential component of selenoproteins that plays an important role in antioxidant defense. The activity of the enzyme glutathione peroxidase (GPx), a highly-efficient antioxidant enzyme, is closely dependent on the presence of Se. These properties of Se may be potentially applicable to improve athletic performance and training recovery. We systematically searched for published studies to evaluate the effectiveness of Se supplementation on antioxidant defense system, muscle performance, hormone response, and athletic performance among physically active individuals. We used the Preferred Reporting Elements for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and searched in SCOPUS, Web of Science (WOS), and PubMed databases to identify published studies until March 2020. The systematic review incorporated original studies with randomized controlled crossover or parallel design in which intake of Se administered once a day was compared with the same placebo conditions. No exclusions were applied for the type of physical exercise performed, the sex, nor the age of the participants. Among 150 articles identified in the search, 6 met the criteria and were included in the systematic review. The methodological quality of the studies was evaluated using the McMaster Critical Review Form. Oral Se supplementation with 180 µg/day or 240 µg/day (selenomethionine) and 200 µg/day (Sodium Selenite), significantly decreased lipid hydroperoxide levels and increased GPx in plasma, erythrocyte, and muscle. No significant effects were observed on athletic performance, testosterone hormone levels, creatine kinase activity, and exercise training-induced adaptations on oxidative enzyme activities or on muscle fiber type myosin heavy chain expression. In addition, Se supplementation showed to have a dampening effect on the mitochondria changes in chronic and acute exercise. In summary, the use of Se supplementation has no benefits on aerobic or anaerobic athletic performance but it may prevent Se deficiencies among athletes with high-intensity and high-volume training. Optimal Se plasma levels may be important to minimize chronic exercise-induced oxidative effects and modulate the exercise effect on mitochondrial changes.

Ethephon mitigates nickel stress by modulating antioxidant system, glyoxalase system and proline metabolism in Indian mustard

The role of ethylene (through application of ethephon) in the regulation of nickel (Ni) stress tolerance was investigated in this study. Ethephon at concentration of 200 µl l^-1 was applied to mustard (Brassica juncea) plants grown without and with 200 mg kg^-1 soil Ni to study the increased growth traits, biochemical attributes, photosynthetic efficiency, nutrients content, activities of antioxidants such as superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione peroxidase, glyoxalase systems and enhanced the proline metabolism. In the absence of ethephon, Ni increased oxidative stress with a concomitant decrease in photosynthesis, growth and nutrients content. However, application of ethephon positively increased growth traits, photosynthetic parameters, nutrients content and also elevated the generation of antioxidants enzymes and glyoxalase systems, proline production to combat oxidative stress. Plants water relations and cellular homeostasis were maintained through increased photosynthetic efficiency and proline production. This signifies the role of ethylene in mediating Ni tolerance via regulating proline production and photosynthetic capacity. Ethephon can be used as an exogenous supplement on plants to confer Ni tolerance. The results can be exploited to develop tolerance in plants via gene editing technology encoding enzymes responsible for proline synthesis, antioxidant defence, glyoxalase systems and photosynthetic effectiveness.

Selenium Biofortification Impacts the Nutritive Value, Polyphenolic Content, and Bioactive Constitution of Variable Microgreens Genotypes

Selenium (Se) is considered essential for human nutrition as it is involved in the metabolic pathway of selenoproteins and relevant biological functions. Microgreens, defined as tender immature greens, constitute an emerging functional food characterized by overall higher levels of phytonutrients than their mature counterparts. The nutraceutical value of microgreens can be further improved through Se biofortification, delivering Se-enriched foods and potentially an enhanced content of bioactive compounds. The current study defined the effect of sodium selenate applications at three concentrations (0, 8, and 16 μM Se) on the bioactive compounds and mineral content of coriander, green basil, purple basil, and tatsoi microgreens grown in soilless cultivation. Analytical emphasis was dedicated to the identification and quantification of polyphenols by UHPLC-Q-Orbitrap-HRMS, major carotenoids by HPLC-DAD, and macro micro-minerals by ICP-OES. Twenty-seven phenolic compounds were quantified, of which the most abundant were: Chlorogenic acid and rutin in coriander, caffeic acid hexoside and kaempferol-3-O(caffeoyl) sophoroside-7-O-glucoside in tatsoi, and cichoric acid and rosmarinic acid in both green and purple basil. In coriander and tatsoi microgreens, the application of 16 μM Se increased the total phenols content by 21% and 95%, respectively; moreover, it improved the yield by 44% and 18%, respectively. At the same Se dose, the bioactive value of coriander and tatsoi was enhanced by a significant increase in rutin (33%) and kaempferol-3-O(feruloyl)sophoroside-7-O-glucoside (157%), respectively, compared to the control. In green and purple basil microgreens, the 8 μM Se application enhanced the lutein concentration by 7% and 19%, respectively. The same application rate also increased the overall macroelements content by 35% and total polyphenols concentration by 32% but only in the green cultivar. The latter actually had a tripled chicoric acid content compared to the untreated control. All microgreen genotypes exhibited an increase in the Se content in response to the biofortification treatments, thereby satisfying the recommended daily allowance for Se (RDA-Se) from 20% to 133%. The optimal Se dose that guarantees the effectiveness of Se biofortification and improves the content of bioactive compounds was 16 μM in coriander and tatsoi, and 8 μM in green and purple basil.

Interactive effects of polyamines and arbuscular mycorrhiza in modulating plant biomass, N2 fixation, ureide, and trehalose metabolism in Cajanus cajan (L.) Millsp. genotypes under nickel stress

Nickel (Ni) is an essential micronutrient but considered toxic for plant growth when present in excess in the soil. Polyamines (PAs) and arbuscular mycorrhiza (AM) play key roles in alleviating metal toxicity in plants. Present study compared the roles of AM and PAs in improving rhizobial symbiosis, ureide, and trehalose (Tre) metabolism under Ni stress in Cajanus cajan (pigeon pea) genotypes (Pusa 2001, AL 201). The results documented significant negative impacts of Ni on plant biomass, especially roots, more in AL 201 than Pusa 2001. Symbiotic efficiency with Rhizobium and AM declined under Ni stress, resulting in reduced AM colonization, N₂ fixation, and ureide biosynthesis. This decline was proportionate to increased Ni uptake in roots and nodules. Put-reduced Ni uptake improved plant growth and functional efficiency of nodules and ureides synthesis, with higher positive effects than other PAs. However, AM inoculations were most effective in enhancing nodulation, nitrogen fixing potential, and Tre synthesis under Ni toxicity. Combined applications of AM with respective PAs, especially +Put+AM, were highly beneficial in alleviating Ni-induced nodule senescence by arresting leghemoglobin degradation and improving functional efficiency of nodules by boosting Tre metabolism, especially in Pusa 2001. The study suggested use of Put along with AM as a promising approach in imparting Ni tolerance to pigeon pea plants.

OsZIP1 functions as a metal efflux transporter limiting excess zinc, copper and cadmium accumulation in rice

BACKGROUND

Metal homeostasis is critical for plant growth, development and adaptation to environmental stresses and largely governed by a variety of metal transporters. The plant ZIP (Zn-regulated transporter, Iron-regulated transporter-like Protein) family proteins belong to the integral membrane transporters responsible for uptake and allocation of essential and non-essential metals. However, whether the ZIP family members mediate metal efflux and its regulatory mechanism remains unknown.

RESULTS

In this report, we provided evidence that OsZIP1 is a metal-detoxified transporter through preventing excess Zn, Cu and Cd accumulation in rice. OsZIP1 is abundantly expressed in roots throughout the life span and sufficiently induced by excess Zn, Cu and Cd but not by Mn and Fe at transcriptional and translational levels. Expression of OsZIP-GFP fusion in rice protoplasts and tobacco leaves shows that OsZIP1 resides in the endoplasmic reticulum (ER) and plasma membrane (PM). The yeast (Saccharomyces cerevisiae) complementation test shows that expression of OsZIP1 reduced Zn accumulation. Transgenic rice overexpressing OsZIP1 grew better under excess metal stress but accumulated less of the metals in plants. In contrast, both oszip1 mutant and RNA interference (RNAi) lines accumulated more metal in roots and contributed to metal sensitive phenotypes. These results suggest OsZIP1 is able to function as a metal exporter in rice when Zn, Cu and Cd are excess in environment. We further identified the DNA methylation of histone H3K9me2 of OsZIP1 and found that OsZIP1 locus, whose transcribed regions imbed a 242 bp sequence, is demethylated, suggesting that epigenetic modification is likely associated with OsZIP1 function under Cd stress.

CONCLUSION

OsZIP1 is a transporter that is required for detoxification of excess Zn, Cu and Cd in rice.

Application of modified receptor model for soil heavy metal sources apportionment: a case study of an industrial city, China

As we all know, geochemical data usually contain outliers and they are heterogeneous, which will severely affect the use of receptor models based on classical estimates. In this paper, an advanced modified RAPCS-RGWR (robust absolute principal component scores-robust geographically weighted regression) receptor model was introduced to analyze the pollution sources of eight heavy metals (Cd, Hg, As, Pb, Ni, Cu, Zn) in a city of southern China. The results showed that source identification and source apportionment are more consistent by this advanced model even though the soil types and farming patterns are diverse. Moreover, this model decreased the occurrence of negative values of the source contribution. For these reasons, the pollution sources were classified into five types by the new model in the study area: agricultural sources, industrial sources, traffic sources, comprehensive sources, and natural sources. (1) The contributions of agricultural sources to Cr and Ni were 243.36% and 242.61%, respectively; (2) the contribution of industrial sources to Cd was 79.25%; (3) the contribution of traffic sources to Cu was 100.31%; (4) the contributions of comprehensive sources to Hg, Pb, and Zn were 253.90%, 242.31%, and 93.32%, respectively; and (5) the contribution of natural sources to As was 208.21%. Overall, the RAPCS-RGWR receptor model improved the validity of the receptor models. It is of great realistic significance to understand and popularize the advanced model in soil source apportionment in agricultural land.

Heavy Metal Levels and Mineral Nutrient Status of Natural Walnut (Juglans regia L.) Populations in Kyrgyzstan: Nutritional Values of Kernels

In this study, mineral nutrient and heavy metal (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and Zn) contents of the walnut kernels and their co-located soil samples collected from the four different zones of natural walnut forests (Sary-Chelek, Arslanbap, and Kara-Alma in Jalal-Abad Region and Kara-Shoro in Osh Region) in Kyrgyzstan were investigated. The highest concentrations for all elements determined in the soil samples were observed in the Sary-Chelek zone whereas the Arslanbap zone was found to be having the lowest concentrations except Fe and Zn. The highest concentrations in the kernels of walnut samples were found to be in the Sary-Chelek zone for Ca, Fe, K, Mg, and Zn; in the Kara-Shoro zone for Cu; in the Arslanbap zone for Mn; and in the Kara-Alma zone for Na whereas the lowest concentrations were found to be in the Arslanbap zone for Ca, Fe, K, Mg, Na, and Zn and in the Sary-Chelek zone for Cu and Mn, respectively. Also, the levels of Al, Cd, Ni, and Pb in kernel samples could not be detected by ICP-OES because their levels were lower than the threshold detection point (10 μg.kg^-1). Additionally, our data indicated that the walnut kernels from Kyrgyzstan have higher values for RDA (recommended daily allowances) in comparison with the walnut kernels from other countries.

Arsenate phytoextraction abilities of one-year-old tree species and its effects on the nutritional element content in plant organs

The aim of the study was to evaluate the As phytoextraction potential of four tree species: Acer pseudoplatanus L., Betula pendula Roth., Quercus robur L., and Ulmus laevis Pall. in light of their prospective use in the phytoremediation of arsenate [As(V)] contaminated soils. The content of nutritional elements: B, Ca, K, Mg, Na, Si, P, and S was also analyzed. The trees were grown for 1 month in hydroponic cultures (Knop medium) supplemented with As(V), (1 mM). The results showed that the highest As accumulation efficiency was characterized by B. pendula (BCF = 0.87) and Q. robur (BCF = 0.5). Betula pendula accumulated about 80% of As in its roots (TF = 0.22) whereas Q. robur accumulated more than 60% of As in its shoots (TF = 1.60). The other tree species accumulated significantly lower amounts of As, more than 60% of which collected in their shoots. As(V) phytoextraction led to a significantly lower level of P and S in the roots of all tested tree species. Betula pendula seems promising for phytostabilisation and Q. robur for phytoextraction of As(V) from contaminated soils. The obtained results confirm the accumulation and translocation of As(V), as well as the acquisition of nutritional elements by the selected tree species.

Salicylic acid and jasmonic acid restrains nickel toxicity by ameliorating antioxidant defense system in shoots of metallicolous and non-metallicolous Alyssum inflatum Náyr. Populations

The presence of heavy metals in the soils is undoubtedly one of the prime abiotic stresses in the world. There are a considerable amount of plant yield losses because of heavy metal stress. The goal of this study was to assess the morphological, physiological and biochemical changes in Alyssum inflatum Nyár. populations upon exposure to different levels of nickel (Ni) (0, 100, 200, 400) μM, salicylic acid (SA) (0, 50, 200) μM and jasmonic acid (JA) (0, 5, 10) μM. Results showed that there were no considerable interpopulation differences, including the shoot Ni concentrations. Reversing the effects of Ni, SA and JA decreased due to Ni accumulation in both populations. By increasing the levels of Ni stress, the fresh weight (FW) of shoot decreased, whereas the application of SA + JA elevated the FW of the shoot in NM plants. Also, SA + JA mitigated Ni oxidative effects by reducing H₂O₂ concentration in both populations. The results revealed that the exposure of both M and NM plants to high Ni concentration increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities compared to control in both populations. Conversely, APX activity was inhibited in NM plants. Furthermore, SA and JA treatments reversed the detrimental effects of Ni on carotenoid content and reduced the content of proline in plants exposed to Ni stress. All the above suggests that SA and JA confer tolerance to Ni stress in two population of A. inflatum via several mechanisms.

Combating Micronutrient Deficiency and Enhancing Food Functional Quality Through Selenium Fortification of Select Lettuce Genotypes Grown in a Closed Soilless System

Selenium (Se) is an essential trace element for human nutrition and a key component of selenoproteins having fundamental biological and nutraceutical functions. We currently examined lettuce biofortification with Se in an open-gas-exchange growth chamber using closed soilless cultivation for delivering Se-rich food. Morphometric traits, minerals, phenolic acids, and carotenoids of two differently pigmented Salanova cultivars were evaluated in response to six Se concentrations (0-40 μM) delivered as sodium selenate in the nutrient solution. All treatments reduced green lettuce fresh yield slightly (9%), while a decrease in red lettuce was observed only at 32 and 40 μM Se (11 and 21% respectively). Leaf Se content increased in both cultivars, with the red accumulating 57% more Se than the green. At 16 μM Se all detected phenolic acids increased, moreover a substantial increase in anthocyanins (184%) was recorded in red Salanova. Selenium applications slightly reduced the carotenoids content of green Salanova, whereas in red Salanova treated with 32 μM Se violaxanthin + neoxanthin, lutein and β-cryptoxanthin spiked by 38.6, 27.4, and 23.1%, respectively. Lettuce constitutes an ideal target crop for selenium biofortification and closed soilless cultivation comprises an effective tool for producing Se-enriched foods of high nutraceutical value.

Assessment of trace metals contamination in surficial sediments along Lebanese Coastal Zone

A Characterization and assessment study was conducted for trace metals pollution in surface sediments at six sites including harbors, bays and river input along Lebanese coast (LCZ). A particular attention was given to Tripoli Port in order to identify the main sources of trace metals pollution inside this harbor. Total metals concentrations were compared with those reported for the shale. The results revealed that trace metals (Cd, Pb, Zn, and Cr) contamination was significantly localized at Beirut Port, which is classified as the most highly polluted site. At Tripoli Port site, metals contamination was classified as moderate; it is affected by shipping, ship maintenance activities and sewage outfall. According to the SQGs guideline, the biological adverse effect of Cd, Pb and Zn were expected to occur frequently at Beirut Port. The results obtained would be helpful in developing more effective harbor management strategies to control and monitor the metal discharges.