Interaction of heavy metals with the sulphur metabolism in angiosperms from an ecological point of view

Effects of metal amendment and metalloid supplementation on foliar defences are plant accession-specific in the hyperaccumulator Arabidopsis halleri

Soil pollution by metals and metalloids as a consequence of anthropogenic industrialisation exerts a seriously damaging impact on ecosystems. However, certain plant species, termed hyperaccumulators, are able to accumulate extraordinarily high concentrations of these metal(loid)s in their aboveground tissues. Such hyperaccumulation of metal(loid)s is known to act as a defence against various antagonists, such as herbivores and pathogens. We investigated the influences of metal(loid)s on potential defence traits, such as foliar elemental, organic and mechanical defences, in the hyperaccumulator plant species Arabidopsis halleri (Brassicaceae) by artificially amending the soil with common metallic pollutants, namely cadmium (Cd) and zinc (Zn). Additionally, unamended and metal-amended soils were supplemented with the metalloid silicon (Si) to study whether Si could alleviate metal excess. Individuals originating from one non-/low- and two moderately to highly metal-contaminated sites with different metal concentrations (hereafter called accessions) were grown for eight weeks in a full-factorial design under standardised conditions. There were significant interactive effects of metal amendment and Si supplementation on foliar concentrations of certain elements (Zn, Si, aluminium (Al), iron (Fe), potassium (K) and sulfur (S), but these were accession-specific. Profiles of glucosinolates, characteristic organic defences of Brassicaceae, were distinct among accessions, and the composition was affected by soil metal amendment. Moreover, plants grown on metal-amended soil contained lower concentrations of total glucosinolates in one of the accessions, which suggests a potential trade-off between inorganic defence acquisition and biosynthesis of organic defence. The density of foliar trichomes, as a proxy for the first layer of mechanical defence, was also influenced by metal amendment and/or Si supplementation in an accession-dependent manner. Our study highlights the importance of examining the effects of co-occurring metal(loid)s in soil on various foliar defence traits in different accessions of a hyperaccumulating species.

Cadmium and zinc accumulation and tolerance in two Egyptian cultivars (S53 and V120) of Helianthus annuus L. as potential phytoremediator

One of the most important oil crops in the world, sunflower (Helianthus annuus L.), is recognized to help in soil phytoremediation. Heavy metal (HM) contamination is one of the most abiotic challenges that may affect the growth and productivity of such an important crop plant. We studied the influence of HM-contaminated soils on metal homeostasis and the potential hypertolerance mechanisms in two sunflower Egyptian cultivars (V120 and S53). Both cultivars accumulated significantly higher cadmium concentrations in their roots compared to their shoots during Cd and Zn/Cd treatments. Higher root concentrations of 121 mg g-1 dry weight (DW) and 125 mg g-1 DW were measured in V120 plants compared to relatively lower values of 111 mg g-1 DW and 105 mg g-1 DW in the roots of S53 plants, respectively. Cadmium contamination significantly upregulated the expression of heavy metal ATPases (HaHMA4) in the shoots of V120 plants. On the other hand, their roots displayed a notable expression of HaHMA3. This study indicates that V120 plants accumulated and sequestered Cd in their roots. Therefore, it is advised to cultivate the V120 cultivar in areas contaminated with heavy metals as it is a promising Cd phytoremediator.

Decreased cadmium content in Solanum melongena induced by grafting was related to glucosinolates synthesis

Grafting is an effective horticultural method to reduce Cd accumulation in crops. However, the mechanism of grafting inducing the decrease in Cd content in scions remains unclear. This study evaluated the effect of grafting on fruit quality, yield, and Cd content of Solanum melongena, and explored the potential mechanism of grafting reducing Cd content in scions. In the low Cd-contaminated soil, compared with un-grafted (UG) and self-grafted plants (SG), the fruit yield of inter-grafted plants (EG) increased by 38 %, and the fruit quality was not markedly affected. In EG, the decrease in total S and Cd content was not related to organic acids and thiol compounds. The decrease in total S and Cd content in EG leaves and fruits was closely related to the synthesis and transportation of glucosinolates (GSL). The genes encoding GSL synthesis in leaves, such as basic helix-loop-helix, myelocytomatosis proteins, acetyl-CoA, cytochrome P450, and glutathione S-transferases, were significantly downregulated. In EG leaves, the contents of five of the eight amino acids involved in GSL synthesis decreased significantly (P < 0.05). Notably, total GSL in EG stems, leaves, and fruits had a significant linear correlation with total S and Cd. In summary, the decrease in total S and Cd content in scions caused by grafting is closely related to GSL. Our findings provide a theoretical basis for the safe use of Cd-contaminated soil, exploring the long-distance transport of Cd in plants and cultivating crops with low Cd accumulation.

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.

Unveiling the Dual Nature of Heavy Metals: Stressors and Promoters of Phenolic Compound Biosynthesis in Basilicum polystachyon (L.) Moench In Vitro

The global industrial revolution has led to a substantial rise in heavy metal levels in the environment, posing a serious threat to nature. Plants synthesize phenolic compounds under stressful conditions, which serve as protective agents against oxidative stress. Basilicum polystachyon (L.) Moench is an herbaceous plant of the Lamiaceae family. Some species within this family are recognized for their capacity to remediate sites contaminated with heavy metals. In this study, the effects of mercury (II) chloride and lead (II) nitrate on the in vitro propagation of B. polystachyon were investigated. Shoot tips from in vitro plantlets were cultured in Murashige and Skoog's (MS) media with heavy metals ranging from 1 to 200 µM to induce abiotic stress and enhance the accumulation of phenolic compounds. After three weeks, MS medium with 1 µM of lead (II) supported the highest shoot multiplication, and the maximum number of roots per explant was found in 100 µM of lead (II), whereas a higher concentration of heavy metals inhibited shoot multiplication and root development. The plantlets were hardened in a greenhouse with a 96% field survival rate. Flame atomic absorption spectroscopy (FAAS) was used to detect heavy metal contents in plant biomass. At both 200 µM and 50 µM concentrations, the greatest accumulation of mercury (II) was observed in the roots (16.94 ± 0.44 µg/g) and shoots (17.71 ± 0.66 µg/g), respectively. Similarly, lead (II) showed the highest accumulation in roots (17.10 ± 0.54 µg/g) and shoots (7.78 ± 0.26 µg/g) at 200 µM and 50 µM exposures, respectively. Reverse-phase high-performance liquid chromatography (RP-HPLC) identified and quantified various phenolic compounds in B. polystachyon leaves, including gallic acid, caffeic acid, vanillic acid, p-coumaric acid, ellagic acid, rosmarinic acid, and trans-cinnamic acid. These compounds were found in different forms, such as free, esterified, and glycosylated. Mercury (II)-exposed plants exhibited elevated levels of vanillic acid (1959.1 ± 3.66 µg/g DW), ellagic acid (213.55 ± 2.11 µg/g DW), and rosmarinic acid (187.72 ± 1.22 µg/g DW). Conversely, lead (II)-exposed plants accumulated higher levels of caffeic acid (42.53±0.61 µg/g DW) and p-coumaric acid (8.04 ± 0.31 µg/g DW). Trans-cinnamic acid was the predominant phenolic compound in control plants, with a concentration of 207.74 ± 1.45 µg/g DW. These results suggest that sublethal doses of heavy metals can act as abiotic elicitors, enhancing the production of phenolic compounds in B. polystachyon. The present work has the potential to open up new commercial opportunities in the pharmaceutical industry.

Molecular-Assisted Breeding of Cadmium Pollution-Safe Cultivars

Cadmium (Cd) contamination in edible agricultural products, especially in crops intended for consumption, has raised worldwide concerns regarding food safety. Breeding of Cd pollution-safe cultivars (Cd-PSCs) is an effective solution to preventing the entry of Cd into the food chain from contaminated agricultural soil. Molecular-assisted breeding methods, based on molecular mechanisms for cultivar-dependent Cd accumulation and bioinformatic tools, have been developed to accelerate and facilitate the breeding of Cd-PSCs. This review summarizes the recent progress in the research of the low Cd accumulation traits of Cd-PSCs in different crops. Furthermore, the application of molecular-assisted breeding methods, including transgenic approaches, genome editing, marker-assisted selection, whole genome-wide association analysis, and transcriptome, has been highlighted to outline the breeding of Cd-PSCs by identifying critical genes and molecular biomarkers. This review provides a comprehensive overview of the development of Cd-PSCs and the potential future for breeding Cd-PSC using modern molecular technologies.

Copper and zinc accumulation, distribution, and tolerance in Pistia stratiotes L.; revealing the role of root caps

Pollution by potentially toxic trace metals, such as copper or zinc, is global. Both Cu and Zn are essential microelements, which in higher concentrations become toxic. The aquatic plant Pistia stratiotes(L. has great potential for phytoremediation. Also, it has an unusually large and easily detachable root cap, which makes it a suitable model for studying the potential role of the root cap in metal uptake. Plant response to environmentally relevant concentrations of Cu (0.1, 0.3, and 1 μM) and Zn (0.3, 1, and 3 μM) was investigated with the aim of studying their interaction and distribution at the root tissue level as well as revealing their tolerance mechanisms. Changes in the root anatomy and plant ionome were determined using light and fluorescence microscopy, ICP-MS, and μXRF imaging. Alterations in photosynthetic activity caused by Cu or Zn excesses were monitored by direct imaging of fast chlorophyll fluorescence kinetics (OJIP). Fe and Mn were preferentially localized in the root cap, while Ca, Cu, Ni, and Zn were mainly in the root tip regardless of the Cu/Zn treatment. Translocation of Cu and Zn to the leaves increased with higher doses, however the translocation factor was the lowest in the highest treatments. Measurements of photosynthetic parameters showed a higher susceptibility of electron transport flux from QA to QB under increasing Cu than Zn supply. This, along with our findings regarding the root anatomy and the differences in Ca accumulation and distribution, led to the conclusion that P. stratiotes is more effective for Zn remediation than Cu.

Phytoremediation as an Effective Remedy for Removing Trace Elements from Ecosystems

The pollution of soil by trace elements is a global problem. Conventional methods of soil remediation are often inapplicable, so it is necessary to search intensively for innovative and environment-friendly techniques for cleaning up ecosystems, such as phytoremediation. Basic research methods, their strengths and weaknesses, and the effects of microorganisms on metallophytes and plant endophytes resistant to trace elements (TEs) were summarised and described in this manuscript. Prospectively, bio-combined phytoremediation with microorganisms appears to be an ideal, economically viable and environmentally sound solution. The novelty of the work is the description of the potential of "green roofs" to contribute to the capture and accumulation of many metal-bearing and suspended dust and other toxic compounds resulting from anthropopressure. Attention was drawn to the great potential of using phytoremediation on less contaminated soils located along traffic routes and urban parks and green spaces. It also focused on the supportive treatments for phytoremediation using genetic engineering, sorbents, phytohormones, microbiota, microalgae or nanoparticles and highlighted the important role of energy crops in phytoremediation. Perceptions of phytoremediation on different continents are also presented, and new international perspectives are presented. Further development of phytoremediation requires much more funding and increased interdisciplinary research in this direction.

Exogenous tryptophan application improves cadmium tolerance and inhibits cadmium upward transport in broccoli (Brassica oleracea var. italica)

Cadmium (Cd) pollution not only reduces crop yields, but also threatens human health and food safety. It is of great significance for agricultural production to improve plant Cd resistance and reduce Cd accumulation. In Arabidopsis, tryptophan (Trp) has been found to play a role in Cd resistance. However, studies on the role of exogenous Trp on Cd tolerance in crops are limited. Here, we report that exogenous Trp application can effectively alleviate biomass decline induced by Cd stress and inhibit Cd transport from roots to shoots in Brassica oleracea var. italica (broccoli). Compared to Cd stress alone, the fresh weight of shoots and roots of B. oleracea seedlings treated with Cd and Trp increased by 25 and 120%, respectively, and the Cd content in shoots decreased by 51.6%. In combination with physiological indices and transcriptome analysis, we preliminarily explored the mechanism of Trp alleviating Cd stress and affecting Cd transport. Trp inhibited Cd-induced indole-3-acetic acid (IAA) conjugation, thereby providing enough free IAA to sustain growth under Cd stress; Trp inhibited the indolic glucosinolate (IGS) biosynthesis induced by Cd. Considering that the synthesis of IGS consumes glutathione (GSH) as a sulfur donor, the inhibition of Trp in IGS synthesis may be conducive to maintaining a high GSH content to be against Cd stress. Consistent with this, we found that GSH content under Cd stress with Trp application was higher than that of Cd alone. In addition to alleviating the damage caused by Cd, Trp can also inhibit the upward transport of Cd from roots to shoots, possibly by repressing the expression of HMA4, which encodes a transporter responsible for the xylem loading and Cd upward transport.

Metabolomic and antioxidant enzyme activity changes in response to cadmium stress under boron application of wheat (Triticum aestivum)

Boron (B) has previously been shown to inhibit cadmium (Cd) uptake in wheat. Here, we investigated the physiological response of external B application (C for no B added, B for B added, B+Cd for B and Cd added, B/Cd for B 24 h pretreatment before Cd added, B and Cd were 46.2 μM and 5 μM, respectively) on wheat growth under Cd stress. The results showed that the wheat growth was significantly weaker under Cd treatment, while B application did not significantly improve the wheat growth under Cd stress. However, B application decreased Cd concentrations and malondialdehyde (MDA) concentrations of shoot and root. The key enzyme activities including superoxide dismutase (SOD) and peroxidase (POD) significantly increased under Cd treatments while decreased under B treatments. Further, a total of 198, 680 and 204 of the differential metabolites were isolated between B and C treatment, Cd and C treatment and B+Cd and Cd treatment, respectively. The metabolites with up-accumulation in B application (B+Cd) roots were mainly galactaric acid, citric acid, N6-galacturonyl-L-lysine, D-glucose, while the metabolites with down-accumulation were mainly threoninyl-tryptophan and C16 sphinganine. The differential metabolic pathways were mainly concentrated in linoleic acid metabolism, galactose metabolism, sphingolipid metabolism, glycolysis/gluconeogenesis, propanoate metabolism in diabetic complications between B+Cd treatment and B treatment. The results indicate that B alleviates Cd toxicity in winter wheat by inhibiting Cd uptake, increasing antioxidant enzyme activity and changing metabolites.

Arabidopsis root growth and development under metal exposure presented in an adverse outcome pathway framework

Due to human activities, soils become more and more polluted with metals, which imposes risks for human health and wildlife welfare. As most of the metals end up in the food chain through accumulation in plants, we need to establish science-based environmental criteria and risk management policies. To meet these necessities, a thorough understanding is required of how these metals accumulate in and affect plants. Many studies have been conducted towards this aim, but strikingly, only a few entries can be found in ecotoxicological databases, especially on Arabidopsis thaliana, which serves as a model species for plant (cell) physiology and genetic studies. As experimental conditions seem to vary considerably throughout literature, extrapolation or comparison of data is rather difficult or should be approached with caution. Furthermore, metal-polluted soils often contain more than one metal, yet limited studies investigated the impact of metal mixtures on plants. This review aims to compile all data concerning root system architecture under Cu, Cd and Zn stress, in single or multi-metal exposure in A. thaliana, and link it to metal-induced responses at different biological levels. Global incorporation into an adverse outcome pathway framework is presented.

Comparative responses of cadmium accumulation and subcellular distribution in wheat and rice supplied with selenite or selenate

Cadmium (Cd) contamination of crop plants has aroused a worldwide concern because of the threats posed to human health through accumulation in the food chains. Selenium (Se) can alleviate the Cd-induced phytotoxicity, but the relevant underlying mechanisms are not fully understood. Therefore, with wheat (Triticum aestivum L.) and rice (Oryza sativa L.) chosen as the target plants in this study, the effects of selenite or selenate on Cd accumulation and subcellular distribution were investigated through greenhouse hydroponic experiments; and simultaneously, the effects of pre-Se treatment with selenite or selenate on Cd accumulation and root-to-shoot translocation in the studied plants were also included. Results showed the addition of Se slightly changed the Cd content in plant roots in a time-dependent manner; however, with the obvious decreasing trend on the Cd transfer factor (TF), its content in plant shoots was significantly reduced by selenite or selenate in a plant species-dependent manner. At 48 h of exposure, the supplementation of selenite and selenate significantly decreased the Cd content by 40.4% and 38.0% in wheat shoots, and by 72.2% and 40.9% in rice shoots, respectively. Additionally, the order of Cd proportion distributed to the different subcellular fractions of plant tissues was as follows: cell wall > soluble cytosol > organelle, irrespective of the Se treatments or the plant species. However, selenate increased the Cd percentage in soluble cytosol of wheat shoots, while selenite increased that percentage in the cell wall of rice shoots; and the Cd proportion in soluble cytosol of the studied plant roots was significantly enhanced owing to selenite or selenate addition. Moreover, similar to the co-application, the pre-Se treatment with inorganic Se also reduced the Cd accumulation and translocation both in wheat and rice. Our results proved that the inorganic Se could decline the Cd accumulation and translocation in the crop plants, although selenite was found more effective than selenate regarding such effects.

Sulfur Deprivation Modulates Salicylic Acid Responses via Nonexpressor of Pathogenesis-Related Gene 1 in Arabidopsis thaliana

Mineral nutrients are essential for plant growth and reproduction, yet only a few studies connect the nutritional status to plant innate immunity. The backbone of plant defense response is mainly controlled by two major hormones: salicylic acid (SA) and jasmonic acid (JA). This study investigated changes in the macronutrient concentration (deficiency/excess of nitrogen, phosphorus, potassium, magnesium, and sulfur) on the expression of PR1, a well-characterized marker in the SA-pathway, and PDF1.2 and LOX2 for the JA-pathway, analyzing plants carrying the promoter of each gene fused to GUS as a reporter. After histochemical GUS assays, we determined that PR1 gene was strongly activated in response to sulfur (S) deficiency. Using RT-PCR, we observed that the induction of PR1 depended on the function of Non-expressor of Pathogenesis-Related gene 1 (NPR1) and SA accumulation, as PR1 was not expressed in npr1-1 mutant and NahG plants under S-deprived conditions. Plants treated with different S-concentrations showed that total S-deprivation was required to induce SA-mediated defense responses. Additionally, bioassays revealed that S-deprived plants, induced resistance to the hemibiotrophic pathogen Pseudomonas syringae pv. DC3000 and increase susceptibility to the necrotrophic Botrytis cinerea. In conclusion, we observed a relationship between S and SA/JA-dependent defense mechanisms in Arabidopsis.

Cadmium-Tolerant and -Sensitive Cultivars Identified by Screening of Medicago truncatula Germplasm Display Contrasting Responses to Cadmium Stress

Cadmium (Cd) pollution in soils is an increasing problem worldwide, and it affects crop production and safety. We identified Cd-tolerant and -sensitive cultivars by testing 258 accessions of Medicago truncatula at seedling stage, using the relative root growth (RRG) as an indicator of Cd tolerance. The factorial analysis (principal component analysis method) of the different growth parameters analyzed revealed a clear differentiation between accessions depending on the trait (tolerant or sensitive). We obtained a normalized index of Cd tolerance, which further supported the suitability of RRG to assess Cd tolerance at seedling stage. Cd and elements contents were analyzed, but no correlations with the tolerance trait were found. The responses to Cd stress of two accessions which had similar growth in the absence of Cd, different sensitivity to the metal but similar Cd accumulation capacity, were analyzed during germination, seedling stage, and in mature plants. The results showed that the Cd-tolerant accession (CdT) displayed a higher tolerance than the sensitive cultivar (CdS) in all the studied stages. The increased gene expression of the three main NADPH recycling enzymes in CdT might be key for this tolerance. In CdS, Cd stress produced strong expression of most of the genes that encode enzymes involved in glutathione and phytochelatin biosynthesis (MtCYS, MtγECS, and MtGSHS), as well as GR, but it was not enough to avoid a redox status imbalance and oxidative damages. Our results on gene expression, enzyme activity, antioxidant content, and lipid peroxidation indicate different strategies to cope with Cd stress between CdS and CdT, and provide new insights on Cd tolerance and Cd toxicity mechanisms in M. truncatula.

Zinc allocation to and within Arabidopsis halleri seeds: Different strategies of metal homeostasis in accessions under divergent selection pressure

Vegetative tissues of metal(loid)-hyperaccumulating plants are widely used to study plant metal homeostasis and adaptation to metalliferous soils, but little is known about these mechanisms in their seeds. We explored essential element allocation to Arabidopsis halleri seeds, a species that faces a particular trade-off between meeting nutrient requirements and minimizing toxicity risks.Combining advanced elemental mapping (micro-particle induced X-ray emission) with chemical analyses of plant and soil material, we investigated natural variation in Zn allocation to A. halleri seeds from non-metalliferous and metalliferous locations. We also assessed the tissue-level distribution and concentration of other nutrients to identify possible disorders in seed homeostasis.Unexpectedly, the highest Zn concentration was found in seeds of a non-metalliferous lowland location, whereas concentrations were relatively low in all other seed samples-including metallicolous ones. The abundance of other nutrients in seeds was unaffected by metalliferous site conditions.Our findings depict contrasting strategies of Zn allocation to A. halleri seeds: increased delivery at lowland non-metalliferous locations (a likely natural selection toward enhanced Zn-hyperaccumulation in vegetative tissues) versus limited translocation at metalliferous sites where external Zn concentrations are toxic for non-tolerant plants. Both strategies are worth exploring further to resolve metal homeostasis mechanisms and their effects on seed development and nutrition.

Evaluation of sulfur and foliar application of Zn and Fe on yield and biochemical factors of cumin (Cuminum cyminum L.) under irrigation regimes

Introduction: Cumin, due to its food and medicinal properties, is one of the important plant species in the world. Moreover, water and nutrition deficiencies are serious abiotic stress factors. So, this experiment was conducted with the aim of investigating the effects of sulfur and foliar application of Fe and Zn on yield and biochemical characteristics of cumin under irrigation regimes. Methods: The experiment was conducted as a split plot on the basis of a completely randomized block design during the 2016-2017 growing seasons with three replications. Experimental factors were arranged in irrigation regimes as main plots at three levels (I1: No stress (control), I2: irrigation based on 40% available water discharge, I3: 80% available water discharge) and foliar application of Zinc (Zn) and Iron (Fe) as subplots [F1: control (water-soluble), F2: Iron, F3: Zinc, F4: Zinc and Iron chelate] and sub-sub plots including sulfur fertilizer [S1: control (no use of sulfur), S2: sulfur fertilizer with Thiobacillus]. Results: Analyzed data showed that total phenol content and flavonoids were enhanced with the increase of drought intensity and the maximum amount was recorded under I3, while I3 caused a substantial reduction in grain yield. Flavonoid and grain yield significantly increased in F4. Total phenol content was the highest in F2 and F3 treatments. Application of sulfur fertilizer resulted in a significant increase in peroxidase, phenol and flavonoids. The highest amount of peroxidase was obtained in I3F4 and I3F3. The largest total soluble sugar (TSS) was resulted by I3S2 and the least by I1S1. Foliar application of Zn and Fe with sulfur fertilizer increased TSS. Conclusion: The present study suggests that foliar application of Fe and Zn and sulfur fertilizer can improve the injurious effects of water deficiency on cumin plant through alteration in yield and biochemical characteristics.

Micronutrient Status and Selected Physiological Parameters of Roots in Nickel-Exposed Sinapis alba L. Affected by Different Sulphur Levels

An efficient method of improving the micronutrient status of Ni-treated white mustard (Sinapis alba L.) using intensive S-SO₄ nutrition was developed. Twelve variants of Hoagland’s nutrient solution differing in the concentration of S-SO₄ (standard: 2 mM S, and elevated level: 6 or 9 mM S) and Ni (0, 0.0004, 0.04, or 0.08 mM Ni) were tested. The beneficial effect of intensive S nutrition on Ni-stressed plants was manifested by a significant rise in the content of Fe, Mn, and Zn, especially in the shoots. An increase was also found in the shoot B, Cu, and Mo content, whilst there were no changes in their root concentrations. Simultaneously, the shoot Cl concentrations dropped. The elevated level of S in the nutrient solution in general enhanced the translocation of Fe, Cu, Mo, and B in Ni-exposed plants. The beneficial effect of intensive S nutrition on the growth and micronutrient balance of Ni-exposed plants can be at least partially related to the positive changes in root surface properties, especially in cation exchange capacity (CEC). Meanwhile both reduced glutathione (GSH) and phytochelatins (PCs) probably do not significantly contribute to Ni resistance of white mustard under intensive S nutrition.

Molecular characterization and expression dynamics of MTP genes under various spatio-temporal stages and metal stress conditions in rice

Metal Tolerance Proteins (MTPs) are the class of membrane proteins involved in the transport of metals, mainly Zn, Mn, Fe, Cd, Co and Ni, and confer metal tolerance in plants. In the present study, a comprehensive molecular analysis of rice MTP genes was performed to understand the evolution, distribution and expression dynamics of MTP genes. Exploration of the whole genome re-sequencing information available for three thousand rice genotypes highlighted the evolution and allelic diversity of MTP genes. Based on the presence of non-synonymous single nucleotide polymorphism (SNP), MTP1, MTP6, MTP8 and MTP9 were found to be the most conserved genes. Furthermore, results showed localization of MTP1, MTP8.1 and MTP9, and MTP11, respectively with QTLs/m-QTLs for Zn and Cd accumulation, making these genes promising candidates to understand the QTL regulation. Expression profiling of the entire set of 10 MTP genes revealed root and shoot specific expressions of MTP9 and MTP8.1, respectively, under all tested vegetative stages. Expression of seed-specific MTPs increased as seed maturation progressed, which revealed their potential role in transporting metals during seed filling. Upon exposure to harmful heavy metals, expression of most MTP genes decreased in root and increased in shoot, suggests that different mechanisms are being employed by MTPs in different tissues. Contrastingly, only a few MTPs were found to be responsive to Fe and/or Zn starvation conditions. The extensive analysis of MTPs presented here will be helpful in identifying candidate MTP genes for crop biofortification and bioremediation purposes.

Sulfur nutrition level modifies the growth, micronutrient status, and cadmium distribution in cadmium-exposed spring wheat

The effect of S nutrition level (standard-2 and intensive-6 or 9 mmol S L-1) on the growth, micronutrient status, and Cd concentration of Cd-exposed (0, 0.0002, 0.02, and 0.04 mmol Cd L-1) Triticum aestivum L. 'Zebra' was examined. The hypothesis that Cd-induced micronutrient imbalance in this species is alleviated by enhanced S-sulfate (S-SO4) nutrition was tested. The intensive S nutrition, especially the dose of 6 mmol L-1, to some extent alleviated Cd-induced stress by improving the adverse changes in micronutrient status and increase of the biomass. The root and shoot Fe, Cu, Mn, and Zn concentrations of Cd-exposed wheat rose at 6 and remained unaltered at 9 mmol S L-1. Particularly noteworthy is the substantial increase of Fe bioconcentration found in Cd-stressed plants at 6 mmol S L-1. The root Cu concentration increased at 6 and decreased at 9 mmol S L-1, but did not change in shoots. Simultaneously, both the high S levels elevated the shoot Cl concentration but had no effect on the root Cl concentration. There were no substantial changes in the Mo concentration. The intensive S nutrition of the Cd-treated wheat did not affect the translocation factor (TF) of Fe and B. In turn, root-to-shoot translocation of Mo and Zn was enhanced at 6 and remained unchanged at 9 mmol S L-1. The changes in TF of Cl, Cu, and Mn varied greatly, depending on the S and Cd concentrations. Intensive S nutrition of Cd-stressed wheat, as a rule, dropped the root and increased the shoot Cd concentration as well as reduced Cd bioconcentration/bioaccumulation factor enhancing root-to-shoot Cd translocation.

Heme bioavailability and signaling in response to stress in yeast cells

Protoheme (hereafter referred to as heme) is an essential cellular cofactor and signaling molecule that is also potentially cytotoxic. To mitigate heme toxicity, heme synthesis and degradation are tightly coupled to heme utilization in order to limit the intracellular concentration of "free" heme. Such a model, however, would suggest that a readily accessible steady-state, bioavailable labile heme (LH) pool is not required for supporting heme-dependent processes. Using the yeast Saccharomyces cerevisiae as a model and fluorescent heme sensors, site-specific heme chelators, and molecular genetic approaches, we found here that 1) yeast cells preferentially use LH in heme-depleted conditions; 2) sequestration of cytosolic LH suppresses heme signaling; and 3) lead (Pb²⁺) stress contributes to a decrease in total heme, but an increase in LH, which correlates with increased heme signaling. We also observed that the proteasome is involved in the regulation of the LH pool and that loss of proteasomal activity sensitizes cells to Pb²⁺ effects on heme homeostasis. Overall, these findings suggest an important role for LH in supporting heme-dependent functions in yeast physiology.

Trace element phytoextraction from contaminated soil: a case study under Mediterranean climate

The current field study aims to assess the suitability of four different plant species (i.e. poplar, willow, hemp and alfalfa) to be used for trace element (TE) (i.e. Cd, Cu, Ni, Pb and Zn) phytoextraction under hot-arid Mediterranean climate conditions. Plants were grown for two consecutive years on a moderate TE contaminated soil, supplied with water and mineral nutrients. The growth and physiological parameters were assessed throughout the trial to compare the response of plants to the environmental pollution, and TE uptake rates were measured for aboveground plant tissues. The phytoextraction rate for each species was expressed as a function of aboveground biomass yield and the TE uptake and translocation within the plant. Alfalfa played a significant role in reducing extractable Ni (60.6%) and Zn (46%) in the soil, whereas hemp reduced 32% of extractable Cd and 46% of extractable Pb; poplar decreased extractable Cd (37%), Ni (49%), Pb (46%) and Zn (63%); and willow reduced the extractable Zn (73%) compared to the beginning of the trial. No change in total TE content was observed; however, poplar and willow were able to extract and accumulate the highest amount of Zn (3200 and 5200 g ha^-1 year^-1 respectively) and Cu (182 and 116 g ha^-1 year^-1), whereas hemp, with 36 g ha^-1 year^-1, showed the best phytoextraction potential for Pb. Overall, we found a positive correlation between the phytoextraction rate and biomass yield, extractable TE concentration and translocation factor (TF) and a negative relationship with Ca concentration in the soil.

Belowground stressors and long-term seagrass declines in a historically degraded seagrass ecosystem after improved water quality

Continued seagrass declines in ecosystems with improved water quality may be driven by sediment stressors. One of the most cited examples of a seagrass ecosystem with declines is Cockburn Sound, Western Australia, where 75% of seagrasses (2169 ha) were lost in the 1960s-1980s due to poor water quality. Water quality has subsequently improved in Cockburn Sound, yet shoot density declines continue in some areas. Here, we investigated if sediment stressors (sulfide intrusion and heavy metals) contributed to declining Posidonia sinuosa shoot densities in Cockburn Sound. Seagrass δ³⁴S were depleted at sites with a history of seagrass declines, indicating seagrasses at these sites were under sulfide stress. Heavy metals (Fe, Zn, Mn, Cr, Cu and Cd) in sediments and seagrasses did not show clear patterns with shoot density or biomass, and largely decreased from similar measurements in the late 1970s. However, seagrass cadmium concentrations were negatively correlated to seagrass biomass and shoot density. High cadmium concentrations interfere with sulfur metabolism in terrestrial plants, but impacts on seagrasses remain to be explored. Given that sulfide intrusion can prevent recolonization and drive seagrass declines, management plans in degraded seagrass ecosystems should include management of sediment stressors and water quality to provide comprehensive management.

Zn Speciation and Stable Isotope Fractionation in a Contaminated Urban Wetland Soil-Typha latifolia System

Wetlands play a key role in the immobilization of metallic contaminants. In this context the mechanisms of Zn sequestration and Zn transfer and storage in Typha latifolia L. colonizing a frequently flooded contaminated soil were studied. A combination of EXAFS spectroscopy, micro X-ray fluorescence (μXRF) and Zn isotope measurements was applied to soil, plant organs and decaying biomass. Zn was present in the soil as Zn-layered double hydroxide, as tetrahedral and octahedral sorbed Zn species, and as ZnS. Octahedral and tetrahedral Zn (attributed to symplastic Zn-organic acid and apoplasmic Zn-cell wall complexes, respectively) and Zn-thiol species were observed in the roots, rhizomes and stems. Iron plaque was present on the rhizomes and roots. Enrichment in light isotopes for Zn sorbed on the plaque relative to the soil (Δ⁶⁶Zn_plaque-soil = -0.3 to -0.1‰) suggested the dissolution of ZnS (enriched in light isotopes) in the rhizosphere with subsequent Zn²⁺ sorption on the root plaque. Furthermore, enrichment in light isotopes of stems relative to leaves (Δ⁶⁶Zn_stem-leaves = -0.2‰) suggested the remobilization of Zn via the phloem, from leaves back to the stems. Overall these data highlight the role of thiols in controlling Zn speciation during its transfer and storage in T. latifolia.

Root Fungal Endophytes Enhance Heavy-Metal Stress Tolerance of Clethra barbinervis Growing Naturally at Mining Sites via Growth Enhancement, Promotion of Nutrient Uptake and Decrease of Heavy-Metal Concentration

Clethra barbinervis Sieb. et Zucc. is a tree species that grows naturally at several mine sites and seems to be tolerant of high concentrations of heavy metals, such as Cu, Zn, and Pb. The purpose of this study is to clarify the mechanism(s) underlying this species' ability to tolerate the sites' severe heavy-metal pollution by considering C. barbinervis interaction with root fungal endophytes. We measured the heavy metal concentrations of root-zone soil, leaves, branches, and fine roots collected from mature C. barbinervis at Hitachi mine. We isolated fungal endophytes from surface-sterilized root segments, and we examined the growth, and heavy metal and nutrient absorption of C. barbinervis seedlings growing in sterilized mine soil with or without root fungal endophytes. Field analyses showed that C. barbinervis contained considerably high amounts of Cu, Zn, and Pb in fine roots and Zn in leaves. The fungi, Phialocephala fortinii, Rhizodermea veluwensis, and Rhizoscyphus sp. were frequently isolated as dominant fungal endophyte species. Inoculation of these root fungal endophytes to C. barbinervis seedlings growing in sterilized mine soil indicated that these fungi significantly enhanced the growth of C. barbinervis seedlings, increased K uptake in shoots and reduced the concentrations of Cu, Ni, Zn, Cd, and Pb in roots. Without root fungal endophytes, C. barbinervis could hardly grow under the heavy-metal contaminated condition, showing chlorosis, a symptom of heavy-metal toxicity. Our results indicate that the tree C. barbinervis can tolerate high heavy-metal concentrations due to the support of root fungal endophytes including P. fortinii, R. veluwensis, and Rhizoscyphus sp. via growth enhancement, K uptake promotion and decrease of heavy metal concentrations.

Heavy Metal Tolerance in Plants: Role of Transcriptomics, Proteomics, Metabolomics, and Ionomics

Heavy metal contamination of soil and water causing toxicity/stress has become one important constraint to crop productivity and quality. This situation has further worsened by the increasing population growth and inherent food demand. It has been reported in several studies that counterbalancing toxicity due to heavy metal requires complex mechanisms at molecular, biochemical, physiological, cellular, tissue, and whole plant level, which might manifest in terms of improved crop productivity. Recent advances in various disciplines of biological sciences such as metabolomics, transcriptomics, proteomics, etc., have assisted in the characterization of metabolites, transcription factors, and stress-inducible proteins involved in heavy metal tolerance, which in turn can be utilized for generating heavy metal-tolerant crops. This review summarizes various tolerance strategies of plants under heavy metal toxicity covering the role of metabolites (metabolomics), trace elements (ionomics), transcription factors (transcriptomics), various stress-inducible proteins (proteomics) as well as the role of plant hormones. We also provide a glance of some strategies adopted by metal-accumulating plants, also known as "metallophytes."

Impact of copper toxicity on stone-head cabbage (Brassica oleracea var. capitata) in hydroponics

Arable soils are frequently subjected to contamination with copper as the consequence of imbalanced fertilization with manure and organic fertilizers and/or extensive use of copper-containing fungicides. In the present study, the exposure of stone-head cabbage (Brassica oleracea var. capitata) to elevated Cu(2+) levels resulted in leaf chlorosis and lesser biomass yield at ≥2 µ M. Root nitrate content was not statistically affected by Cu(2+) levels, although it was substantially decreased at ≥5 µ M Cu(2+) in the shoot. The decrease in nitrate contents can be related to lower nitrate uptake rates because of growth inhibition by Cu-toxicity. Shoot sulfate content increased strongly at ≥2 µ M Cu(2+) indicating an increase in demand for sulfur under Cu stress. Furthermore, at ≥2 µM concentration, concentration of water-soluble non-protein thiol increased markedly in the roots and to a smaller level in the shoot. When exposed to elevated concentrations of Cu(2+) the improved sulfate and water-soluble non-protein thiols need further studies for the evaluation of their direct relation with the synthesis of metal-chelating compounds (i.e., phytochelatins).

Jacks of metal/metalloid chelation trade in plants-an overview

Varied environmental compartments including soils are being contaminated by a myriad toxic metal(loid)s (hereafter termed as "metal/s") mainly through anthropogenic activities. These metals may contaminate food chain and bring irreparable consequences in human. Plant-based approach (phytoremediation) stands second to none among bioremediation technologies meant for sustainable cleanup of soils/sites with metal-contamination. In turn, the capacity of plants to tolerate potential consequences caused by the extracted/accumulated metals decides the effectiveness and success of phytoremediation system. Chelation is among the potential mechanisms that largely govern metal-tolerance in plant cells by maintaining low concentrations of free metals in cytoplasm. Metal-chelation can be performed by compounds of both thiol origin (such as GSH, glutathione; PCs, phytochelatins; MTs, metallothioneins) and non-thiol origin (such as histidine, nicotianamine, organic acids). This paper presents an appraisal of recent reports on both thiol and non-thiol compounds in an effort to shed light on the significance of these compounds in plant-metal tolerance, as well as to provide scientific clues for the advancement of metal-phytoextraction strategies.

Identification and comparative analysis of the Tegillarca granosa haemocytes microRNA transcriptome in response to Cd using a deep sequencing approach

Background

MicroRNAs (miRNAs) are endogenous non-coding small RNAs (sRNAs) that can base pair with their target mRNAs, which represses their translation or induces their degradation in various biological processes. To identify miRNAs regulated by heavy metal stress, we constructed two sRNA libraries for the blood clam Tegillarca granosa: one for organisms exposed to toxic levels of cadmium (Cd) and one for a control group.

Results

Sequencing of the two libraries and subsequent analysis revealed 215 conserved and 39 new miRNAs. Most of the new miRNAs in T. granosa were up- or down-regulated in response to Cd exposure. There were significant differences in expression between the Cd and control groups for 16 miRNAs. Of these, five miRNAs were significantly up-regulated and 11 were significantly down-regulated in the Cd stress library. Potential targets were predicted for the 16 differential miRNAs in pre-miRNAs identified according to sequence homology. Some of the predicted miRNA targets are associated with regulation of the response to stress induced by heavy metals. Five differentially expressed miRNAs (Tgr-nmiR-8, Tgr-nmiR-21, Tgr-miR-2a, Tgr-miR-10a-5p, and Tgr-miR-184b) were validated by qRT-PCR.

Conclusion

Our study is the first large-scale identification of miRNAs in T. granosa haemocytes. Our findings suggest that some miRNAs and their target genes and pathways may play critical roles in the responses of this species to environmental heavy metal stresses.

Unexpected behavior of some nitric oxide modulators under cadmium excess in plant tissue

Various nitric oxide modulators (NO donors - SNP, GSNO, DEA NONOate and scavengers – PTIO, cPTIO) were tested to highlight the role of NO under Cd excess in various ontogenetic stages of chamomile (Matricaria chamomilla). Surprisingly, compared to Cd alone, SNP and PTIO elevated Cd uptake (confirmed also by PhenGreen staining) but depleted glutathione (partially ascorbic acid) and phytochelatins PC₂ and PC₃ in both older plants (cultured hydroponically) and seedlings (cultured in deionised water). Despite these anomalous impacts, fluorescence staining of NO and ROS confirmed predictable assumptions and revealed reciprocal changes (decrease in NO but increase in ROS after PTIO addition and the opposite after SNP application). Subsequent tests using alternative modulators and seedlings confirmed changes to NO and ROS after application of GSNO and DEA NONOate as mentioned above for SNP while cPTIO altered only NO level (depletion). On the contrary to SNP and PTIO, GSNO, DEA NONOate and cPTIO did not elevate Cd content and phytochelatins (PC₂, PC₃) were rather elevated. These data provide evidence that various NO modulators are useful in terms of NO and ROS manipulation but interactions with intact plants affect metal uptake and must therefore be used with caution. In this view, cPTIO and DEA NONOate revealed the less pronounced side impacts and are recommended as suitable NO scavenger/donor in plant physiological studies under Cd excess.

Early transcriptional responses to mercury: a role for ethylene in mercury-induced stress

Understanding the cellular mechanisms of plant tolerance to mercury (Hg) is important for developing phytoremediation strategies of Hg-contaminated soils. The early responses of alfalfa (Medicago sativa) seedlings to Hg were studied using transcriptomics analysis. A Medicago truncatula microarray was hybridized with high-quality root RNA from M. sativa treated with 3 μM Hg for 3, 6 and 24 h. The transcriptional pattern data were complementary to the measurements of root growth inhibition, lipid peroxidation, hydrogen peroxide (H2 O2 ) accumulation and NADPH-oxidase activity as stress indexes. Of 559 differentially expressed genes (DEGs), 91% were up-regulated. The majority of DEGs were shared between the 3 and 6 h (60%) time points, including the 'stress', 'secondary metabolism' and 'hormone metabolism' functional categories. Genes from ethylene metabolism and signalling were highly represented, suggesting that this phytohormone may be relevant for metal perception and homeostasis. Ethylene-insensitive alfalfa seedlings preincubated with the ethylene signalling inhibitor 1-methylcyclopronene and Arabidopsis thaliana ein2-5 mutants confirmed that ethylene participates in the early perception of Hg stress. It modulates root growth inhibition, NADPH-oxidase activity and Hg-induced apoplastic H2 O2 accumulation. Therefore, ethylene signalling attenuation could be useful in future phytotechnological applications to ameliorate stress symptoms in Hg-polluted plants.

Improving growth and productivity of Oleiferous Brassicas under changing environment: significance of nitrogen and sulphur nutrition, and underlying mechanisms

Mineral nutrients are the integral part of the agricultural systems. Among important plant nutrients, nitrogen (N) and sulphur (S) are known essential elements for growth, development, and various physiological functions in plants. Oleiferous brassicas (rapeseed and mustard) require higher amounts of S in addition to N for optimum growth and yield. Therefore, balancing S-N fertilization, optimization of nutrient replenishment, minimization of nutrient losses to the environment, and the concept of coordination in action between S and N could be a significant strategy for improvement of growth and productivity of oleiferous brassicas. Additionally, positive interaction between S and N has been reported to be beneficial for various aspects of oilseed brassicas. The current paper updates readers on the significance of N and S for the improvement of plant growth, development, and productivity in detail. In addition, S-N nutrition-mediated control of major plant antioxidant defense system components involved in the removal and/or metabolism of stress-induced/generated reactive oxygen species in plants (hence, the control of plant growth, development, and productivity) has been overviewed.

Molecular Mechanism of Heavy Metal Toxicity and Tolerance in Plants: Central Role of Glutathione in Detoxification of Reactive Oxygen Species and Methylglyoxal and in Heavy Metal Chelation

Heavy metal (HM) toxicity is one of the major abiotic stresses leading to hazardous effects in plants. A common consequence of HM toxicity is the excessive accumulation of reactive oxygen species (ROS) and methylglyoxal (MG), both of which can cause peroxidation of lipids, oxidation of protein, inactivation of enzymes, DNA damage and/or interact with other vital constituents of plant cells. Higher plants have evolved a sophisticated antioxidant defense system and a glyoxalase system to scavenge ROS and MG. In addition, HMs that enter the cell may be sequestered by amino acids, organic acids, glutathione (GSH), or by specific metal-binding ligands. Being a central molecule of both the antioxidant defense system and the glyoxalase system, GSH is involved in both direct and indirect control of ROS and MG and their reaction products in plant cells, thus protecting the plant from HM-induced oxidative damage. Recent plant molecular studies have shown that GSH by itself and its metabolizing enzymes—notably glutathione S-transferase, glutathione peroxidase, dehydroascorbate reductase, glutathione reductase, glyoxalase I and glyoxalase II—act additively and coordinately for efficient protection against ROS- and MG-induced damage in addition to detoxification, complexation, chelation and compartmentation of HMs. The aim of this review is to integrate a recent understanding of physiological and biochemical mechanisms of HM-induced plant stress response and tolerance based on the findings of current plant molecular biology research.

Cadmium toxicity in glutathione mutants of Escherichia coli

The higher affinity of Cd(2+) for sulfur compounds than for nitrogen and oxygen led to the theoretical consideration that cadmium toxicity should result mainly from the binding of Cd(2+) to sulfide, thiol groups, and sulfur-rich complex compounds rather than from Cd(2+) replacement of transition-metal cations from nitrogen- or oxygen-rich biological compounds. This hypothesis was tested by using Escherichia coli for a global transcriptome analysis of cells synthesizing glutathione (GSH; wild type), gamma-glutamylcysteine (DeltagshB mutant), or neither of the two cellular thiols (DeltagshA mutant). The resulting data, some of which were validated by quantitative reverse transcription-PCR, were sorted using the KEGG (Kyoto Encyclopedia of Genes and Genomes) orthology system, which groups genes hierarchically with respect to the cellular functions of their respective products. The main difference among the three strains concerned tryptophan biosynthesis, which was up-regulated in wild-type cells upon cadmium shock and strongly up-regulated in DeltagshA cells but repressed in DeltagshB cells containing gamma-glutamylcysteine instead of GSH. Overall, however, all three E. coli strains responded to cadmium shock similarly, with the up-regulation of genes involved in protein, disulfide bond, and oxidative damage repair; cysteine and iron-sulfur cluster biosynthesis; the production of proteins containing sensitive iron-sulfur clusters; the storage of iron; and the detoxification of Cd(2+) by efflux. General energy conservation pathways and iron uptake were down-regulated. These findings indicated that the toxic action of Cd(2+) indeed results from the binding of the metal cation to sulfur, lending support to the hypothesis tested.

Glutathione and transition-metal homeostasis in Escherichia coli

Glutathione (GSH) and its derivative phytochelatin are important binding factors in transition-metal homeostasis in many eukaryotes. Here, we demonstrate that GSH is also involved in chromate, Zn(II), Cd(II), and Cu(II) homeostasis and resistance in Escherichia coli. While the loss of the ability to synthesize GSH influenced metal tolerance in wild-type cells only slightly, GSH was important for residual metal resistance in cells without metal efflux systems. In mutant cells without the P-type ATPase ZntA, the additional deletion of the GSH biosynthesis system led to a strong decrease in resistance to Cd(II) and Zn(II). Likewise, in mutant cells without the P-type ATPase CopA, the removal of GSH led to a strong decrease of Cu(II) resistance. The precursor of GSH, gamma-glutamylcysteine (gammaEC), was not able to compensate for a lack of GSH. On the contrary, gammaEC-containing cells were less copper and cadmium tolerant than cells that contained neither gammaEC nor GSH. Thus, GSH may play an important role in trace-element metabolism not only in higher organisms but also in bacteria.