Zinc Stress Research Articles

Response of MaHMA2 gene expression and stress tolerance to zinc stress in mulberry (Morus alba L.)

HMA2 (heavy metal ATPase 2) plays a crucial role in extracellular and intracellular Zn2+ transport across biomembranes, maintaining ion homeostasis, and playing an important role in the normal physiological metabolism, growth, and development of plants. In our study, a novel HMA2 gene, named MaHMA2, was isolated and cloned from white mulberry (Morus alba L.). The gene sequence obtained was 1,342 bp long, with an open reading frame of 1,194 bp, encoding a protein of 397 amino acids, with a predicted molecular mass of 42.852 kD and an isoelectric point of 7.53. This protein belonged to the PIB-type ATPase transport protein family. We analyzed the expression of the MaHMA2 gene by quantitative real-time PCR. The results showed that the level of MaHMA2 gene expression decreased to a Zn concentration of 800 mg/kg. Malondialdehyde and proline levels increased and responded to increasing Zn when the MaHMA2 gene was silenced, whereas the activities of peroxidase and superoxide dismutase tended to increase in response to increasing Zn2+ ion stress concentrations but were lower in the gene-silenced plants. These findings suggested that the MaHMA2 gene played an active role in the tolerance response of mulberry to Zn stress.

Dysregulation of Streptococcus pneumoniae zinc homeostasis breaks ampicillin resistance in a pneumonia infection model.

SUMMARYStreptococcus pneumoniae is the primary cause of community-acquired bacterial pneumonia with rates of penicillin and multidrug-resistance exceeding 80% and 40%, respectively. The innate immune response generates a variety of antimicrobial agents to control infection, including zinc stress. Here, we characterize the impact of zinc intoxication on S. pneumoniae, observing disruptions in central carbon metabolism, lipid biogenesis, and peptidoglycan biosynthesis. Characterization of the pivotal peptidoglycan biosynthetic enzyme GlmU indicates a sensitivity to zinc inhibition. Disruption of the sole zinc efflux pathway, czcD, renders S. pneumoniae highly susceptible to β-lactam antibiotics. To dysregulate zinc homeostasis in the wild-type strain, we investigated the safe-for-human-use ionophore 5,7-dichloro-2-[(dimethylamino) methyl]quinolin-8-ol (PBT2). PBT2 rendered wild-type S. pneumoniae strains sensitive to a range of antibiotics. Using an invasive ampicillin-resistant strain, we demonstrate in a murine pneumonia infection model the efficacy of PBT2 + ampicillin treatment. These findings present a therapeutic modality to break antibiotic resistance in multidrug-resistant S. pneumoniae.

Fe and Zn stress induced gene expression analysis unraveled mechanisms of mineral homeostasis in common bean (Phaseolus vulgaris L.)

Iron (Fe) and zinc (Zn) stress significantly affects fundamental metabolic and physiological processes in plants that results in reduction of plant growth and development. In the present study, common bean variety; Shalimar French Bean-1 (SFB-1) was used as an experimental material. Four different MGRL media i.e. normal MGRL medium (Control), media without Fe (0-Fe), media without Zn (0-Zn) and media with excess Zn (300-Zn) were used for growing seeds of SFB-1 under in vitro condition for three weeks under optimum conditions. Three week old shoot and root tissues were harvested from the plants grown in these four different in vitro conditions and were, subjected to Fe and Zn estimation. Further, extraction of total RNA for differential gene expression of ten candidate genes selected based on our in silico investigation and their classification, phylogeny and expression pattern was unraveled. Expression analysis of three candidate genes (OPT3, NRAMP2 and NRAMP3) in roots revealed possible cross talk among Fe/Zn stress that was further confirmed by observing less accumulation of Fe in roots under both these conditions. However, we observed, higher accumulation of Fe in shoots under 0-Fe condition compared to control that suggests precise sensing for priority based compartmentalization and partitioning leading to higher accumulation of Fe in shoots. Furthermore, the expression analysis of IRT1, FRO1 and Ferritin 1 genes under Fe/Zn stress suggested their role in uptake/transport and signaling of Fe and Zn, whereas the expression of ZIP2, NRAMP1, HA2 and GLP1 genes were highly responsive to Zn in Phaseolus vulgaris. The identified genes highly responsive to Fe and Zn stress condition can be potential candidates for overcoming mineral stress in dicot crop plants.

Maize Genotypes With Different Zinc Efficiency in Response to Low Zinc Stress and Heterogeneous Zinc Supply.

All over the world, a common problem in the soil is the low content of available zinc (Zn), which is unevenly distributed and difficult to move. However, information on the foraging strategies of roots in response to heterogeneous Zn supply is still very limited. Few studies have analyzed the adaptability of maize inbred lines with different Zn efficiencies to different low Zn stress time lengths in maize. This study analyzed the effects of different time lengths of low Zn stress on various related traits in different inbred lines. In addition, morphological plasticity of roots and the response of Zn-related important gene iron-regulated transporter-like proteins (ZIPs) were studied via simulating the heterogeneity of Zn nutrition in the soil. In this report, when Zn deficiency stress duration was extended (from 14 to 21 days), under Zn-deficient supply (0.5 μM), Zn efficiency (ZE) based on shoot dry weight of Wu312 displayed no significant difference, and ZE for Ye478 was increased by 92.9%. Under longer-term Zn deficiency, shoot, and root dry weights of Ye478 were 6.5 and 2.1-fold higher than those of Wu312, respectively. Uneven Zn supply strongly inhibited the development of some root traits in the -Zn region. Difference in shoot dry weights between Wu312 and Ye478 was larger in T1 (1.97 times) than in T2 (1.53 times). Under heterogeneous condition of Zn supply, both the –Zn region and the +Zn region upregulated the expressions of ZmZIP3, ZmZIP4, ZmZIP5, ZmZIP7, and ZmZIP8 in the roots of two inbred lines. These results indicate that extended time length of low-Zn stress will enlarge the difference of multiple physiological traits, especially biomass, between Zn-sensitive and Zn-tolerant inbred lines. There were significant genotypic differences of root morphology in response to heterogeneous Zn supply. Compared with split-supply with +Zn/+Zn, the difference of above-ground biomass between Zn-sensitive and Zn-tolerant inbred lines under split-supply with –Zn/+Zn was higher. Under the condition of heterogeneous Zn supply, several ZmZIP genes may play important roles in tolerance to low Zn stress, which can provide a basis for further functional characterization.

Oxidative and anti-oxidative responses to metal toxicity in an extremophilic alga (Cyanidium caldarium) and a neutrophilic alga (Chlamydomonas reinhardtii)

ABSTRACT Redox metabolism is integral to the functioning of photosynthetic organisms. The highly oxidative reactive oxygen species (ROS) are products of cellular redox processes and can cause major cellular damage. ROS are also produced in the face of environmental and cellular stress, including metal-induced oxidative stress. The degree of ROS production and the subsequent anti-oxidative response will vary according to the tolerance level of the species and the degree and type of stress it experiences. The extremophilic alga Cyanidium caldarium and neutrophilic alga Chlamydomonas reinhardtii have contrasting Zn tolerances, with the EC50 of the extremophile 128 times higher than that of the neutrophile. We examined the oxidative stress responses of these algae to zinc stress, using ROS production to establish the metal-induced oxidative state of the organisms. The anti-oxidative responses measured included total free-sulphydryl groups and total protein content as well as a heat shock protein 70 (HSP70) response assay to explore the role the stress protein HSP70 might play in the contrasting metal tolerance mechanisms in these two species. Results showed that the oxidative response in Cy. caldarium was dose-dependent, while in Ch. reinhardtii the oxidative response was more dependent on the time of exposure to Zn. Cyanidium caldarium managed to regain its base level of protein (i.e. that seen in naïve cells) upon acclimation (long-term exposure) to sub-toxic Zn levels. On the other hand, Ch. reinhardtii showed reduced total protein content upon acclimation. This raises questions about the different roles that ROS signalling might play in metal stress tolerance.

Salicylic acid ameliorates zinc and chromium-induced stress responses in wheat seedlings: a biochemical and computational analysis

Salicylic acid ameliorates zinc and chromium-induced stress responses in wheat seedlings: a biochemical and computational analysis

Divalent nutrient cations: Friend and foe during zinc stress in rice.

Zn deficiency is the most common micronutrient deficit in rice but Zn is also a widespread industrial pollutant. Zn deficiency responses in rice are well documented, but comparative responses to Zn deficiency and excess have not been reported. Therefore, we compared the physiological, transcriptional and biochemical properties of rice subjected to Zn starvation or excess at early and later treatment stages. Both forms of Zn stress inhibited root and shoot growth. Gene ontology analysis of differentially expressed genes highlighted the overrepresentation of Zn transport and antioxidative defense for both Zn stresses, whereas diterpene biosynthesis was solely induced by excess Zn. Divalent cations (Fe, Cu, Ca, Mn and Mg) accumulated in Zn-deficient shoots but Mg and Mn were depleted in the Zn excess shoots, mirroring the gene expression of non-specific Zn transporters and chelators. Ascorbate peroxidase activity was induced after 14 days of Zn starvation, scavenging H2 O2 more effectively to prevent leaf chlorosis via the Fe-dependent Fenton reaction. Conversely, excess Zn triggered the expression of genes encoding Mg/Mn-binding proteins (OsCPS2/4 and OsKSL4/7) required for antimicrobial diterpenoid biosynthesis. Our study reveals the potential role of divalent cations in the shoot, driving the unique responses of rice to each form of Zn stress.

Genome-wide analysis of the lignin toolbox for morus and the roles of lignin related genes in response to zinc stress.

Mulberry (Morus, Moraceae) is an important economic plant with nutritional, medicinal, and ecological values. Lignin in mulberry can affect the quality of forage and the saccharification efficiency of mulberry twigs. The availability of the Morus notabilis genome makes it possible to perform a systematic analysis of the genes encoding the 11 protein families specific to the lignin branch of the phenylpropanoid pathway, providing the core genes for the lignin toolbox in mulberry. We performed genome-wide screening, which was combined with de novo transcriptome data for Morus notabilis and Morus alba variety Fengchi, to identify putative members of the lignin gene families followed by phylogenetic and expression profile analyses. We focused on bona fide clade genes and their response to zinc stress were further distinguished based on expression profiles using RNA-seq and RT-qPCR. We finally identified 31 bona fide genes in Morus notabilis and 25 bona fide genes in Fengchi. The putative function of these bona fide genes was proposed, and a lignin toolbox that comprised 19 genes in mulberry was provided, which will be convenient for researchers to explore and modify the monolignol biosynthesis pathway in mulberry. We also observed changes in the expression of some of these lignin biosynthetic genes in response to stress caused by excess zinc in Fengchi and proposed that the enhanced lignin biosynthesis in lignified organs and inhibition of lignin biosynthesis in leaf is an important response to zinc stress in mulberry.

Proteomic responses of the coccolithophore Emiliania huxleyi to zinc limitation and trace metal substitution.

Zinc concentrations in pelagic surface waters are within the range that limits growth in marine phytoplankton cultures. However, the influence of zinc on marine primary production and phytoplankton communities is not straightforward due to largely uncharacterized abilities for some phytoplankton to access zinc species that may not be universally bioavailable and substitute zinc with cobalt or cadmium. We used a quantitative proteomic approach to investigate these strategies and other responses to zinc limitation in the coccolithophore Emiliania huxleyi, a dominant species in low zinc waters. Zinc limitation resulted in the upregulation of metal transport proteins (ZIP, TroA-like) and COG0523 metallochaperones. Some proteins were uniquely sensitive to growth under replete zinc, substitution of zinc with cobalt, or enhancement of growth with cadmium, and may be useful as biomarkers of zinc stress or substitution in situ. Several proteins specifically upregulated under cobalt-supported or cadmium-enhanced growth appear to reflect stress responses, despite titration of these metals to optimal nutritive levels. Relief from zinc limitation by zinc or cadmium resulted in increased expression of a δ-carbonic anhydrase. Our inability to detect metal binding enzymes that are specifically induced under cobalt- or cadmium-supported growth suggests cambialism is important for zinc substitution in E. huxleyi.

Association of Zinc Deficiency with Development of CVD Events in Patients with CKD.

Deficiency of the micronutrient zinc is common in patients with chronic kidney disease (CKD). The aim of this review is to summarize evidence presented in literature for consolidation of current knowledge regarding zinc status in CKD patients, including those undergoing hemodialysis. Zinc deficiency is known to be associated with various risk factors for cardiovascular disease (CVD), such as increased blood pressure, dyslipidemia, type 2 diabetes mellitus, inflammation, and oxidative stress. Zinc may protect against phosphate-induced arterial calcification by suppressing activation of nuclear factor kappa light chain enhancer of activated B. Serum zinc levels have been shown to be positively correlated with T50 (shorter T50 indicates higher calcification propensity) in patients with type 2 diabetes mellitus as well as those with CKD. Additionally, higher intake of dietary zinc was associated with a lower risk of severe abdominal aortic calcification. In hemodialysis patients, the beneficial effects of zinc supplementation in relation to serum zinc and oxidative stress levels was demonstrated in a meta-analysis of 15 randomized controlled trials. Thus, evidence presented supports important roles of zinc regarding antioxidative stress and suppression of calcification and indicates that zinc intake/supplementation may help to ameliorate CVD risk factors in CKD patients.

Impact assessment of zinc stress on pigmented rice (Oryza sativa) cultivars in Northeast India

Heavy metal is a serious abiotic factor that affects the growth and production of rice. In view of important properties such as anti-oxidant, anti-diabetic, anti-cancer activities and anti-cancer activities of pigmented rice, two important local pigmented rice varieties - Chakhou (Manipur) and Kawnglawng (Mizoram) were selected for this study. This study was conducted during the month of March to October (2018 to 2020) at the Department of Botany, Mizoram University, Mizoram, India to investigate the effects of zinc stress on two pigmented and aromatic local rice cultivars Chakhou and Kawnglawng. The pigmented rice cultivars were analyzed for germination percentage, protein contents, chlorophyll a and chlorophyll b, antioxidant enzymes- catalase (CAT) and ascorbate peroxidase (APX) and genome template stability (GTS) under different zinc stress conditions. Zinc stress affected chlorophyll and protein contents while CAT and APX activities were increased significantly. PCR-based Random Amplified Polymorphic DNA (RAPD) technique was employed to investigate the genome stability of the rice cultivars against zinc stress. Genome template stability (GTS) was found to be high (>94%) in both the cultivars. Hence, these cultivars can be suggested as a source for future breeding programs against zinc stress.

Absorption and Aggregation Characteristics and Changes in the Reflectance Spectrum of an Arid Desert Plant under Gold, Copper, Zinc and Nickel Stress

Remote sensing phytochemistry has been proven by many studies to be an effective method for the detection of hidden minerals in vegetation-covered areas. In this study, we determined whether Seriphidium terrae-albae, a small shrub distributed widely in arid deserts, could be an effective sampling medium for application in remote sensing plant geochemistry. The absorption and aggregation characteristics and spectral changes in Seriphidium terrae-albae transplants at varying soil concentrations of copper (Cu), nickel (Ni), gold (Au), and zinc (Zn) were studied via simulation testing using artificial transplant cultivation. The results showed the following. (1) There exists a good logarithmic relationship between Cu and Zn contents in Seriphidium terrae-albae and the corresponding contents in soil, with coefficients of determination (R2) reaching as high as 0.936 for Cu and 0.9568 for Zn, while a linear relationship is observed between Au and Ni contents in the plant and the corresponding contents in soil, with R2 values as high as 0.9524 for Au and 0.9177 for Ni. (2) The accumulation of Cu and Ni in Seriphidium terrae-albae transplants grown in soil with high Cu and Ni contents is higher than in controls grown in normal soil, demonstrating the ability to clearly indicate abnormal Cu and Ni contents. (3) The ratio vegetation index based on the reflectance at 747 and 742 nm can be adopted to estimate Cu content in Seriphidium terrae-albae. These results suggest that Seriphidium terrae-albae exhibits great potential as an effective geochemical remote sensing plant sampling medium for concealed Cu deposits. This study provides proof of concept for the hyperspectral remote sensing technique in the exploration of hidden minerals in arid deserts, a quick measurement means of Cu content anomalies in the Seriphidium terrae-albae plant and a reference for the identification of prospective metallogenic areas, which could not only expand the existing prospecting space but could also improve the prospecting efficiency in arid deserts.

Effects of zinc toxicity on the nitrogen-fixing cyanobacterium Anabaena sphaerica-ultastructural, physiological and biochemical analyses.

The current study describes the mechanisms of zinc toxicity in the cyanobacterium Anabaena sphaerica after eight days treatment with 10 mg L-1 ZnCl2. The application of zinc not only showed elevated accumulation of the metal inside the cells but also exhibited devastating impacts on the cell numbers, morphology, and ultrastructure of A. sphaerica. The effects of zinc on the pigments contents, oxygen evolution rate, Fv/Fm, electron transport rate, and carbohydrate content were also evaluated in A. sphaerica. Moreover, zinc adversely affected nutrient uptake and the cellular energy budget in the test cyanobacterium which in turn hampered heterocyst development and nitrogen fixation. Alongside, the cyanobacterium experienced zinc-mediated non-competitive inhibition of glutamine synthetase activity, curtailed synthesis of amino acids and proteins. Furthermore, drastically reduced total lipid and increased unsaturated lipid contents were also the prominent characteristics of zinc stressed A. sphaerica. Most importantly, zinc stress caused severe damages to the protein, lipid, and DNA by triggering hydrogen peroxide generation and accumulation of oxidized glutathione. Therefore, excess zinc is highly toxic to the cyanobacterium A. sphaerica, and the mechanisms of its toxicity followed a cascade of events including oxidative stress mediated geopardisation of growth and ultrastructure, metabolic derangements, and macromolecular damages.

Functional characterization of two chalcone isomerase (CHI) revealing their responsibility for anthocyanins accumulation in mulberry

Mulberry (Morus sp., Moraceae) is an important economic crop plant and mulberry fruits are rich in anthocyanidins. Chalcone isomerase (CHI) catalyzes the conversion of chalcones to flavanones providing precursors for biosynthesis of anthocyanidins. In this study, bona fide CHIs were cloned and characterized from different Morus species with differently colored fruits (Morus multicaulis, Mm and Morus alba variety LvShenZi, LSZ). Enzymatic assay of MmCHI1 and MmCHI2 showed that they can utilize naringenin chalcone as substrate. The catalytic efficiency of MmCHI2 and LSZCHI2 are approximately 200 and 120-fold greater than that of MmCHI1 respectively. Phylogenetic analysis showed the two mulberry CHIs belonged to different sub-clade of Type I CHI1 named type IA (CHI2) and type IB (CHI1). Type IB CHIs are mulberry specific. MmCHI1 and MmCHI2 had similar expression profiles and showed preferred expression in fruits. In addition, both mulberry CHI1 and CHI2 played roles in the response to excess zinc stress and sclerotiniose pathogen infection. Both MmCHI1 and MmCHI2 expression levels showed positive close relationship with anthocyanins content during fruit ripening process. The co-expression of MmCHI1 and MmCHI2 was observed during fruit ripening process and in transgenic mulberry. VIGS (virus induced gene silence) targeting on MmCHI1 and MmCHI2 showed significant down-regulation of MmCHI2 instead of MmCHI1 would result in significant (about 50%) decrease in anthocyanins content. MmCHI2 is the dominant CHI for anthocyanins accumulation in mulberry. The results presented in this work provided insight on bona fide CHIs in mulberry and reveal their roles in anthocyanins accumulation.

Silicon distribution in leaves and roots of rice and maize in response to cadmium and zinc toxicity and the associated histological variations.

At present, the levels of cadmium (Cd) and zinc (Zn) in arable land are high and affect the growth and development of important food crops, including rice and maize. However, the application of silicon (Si) in contaminated areas increases the metal tolerance potential of these plants. This work aimed to study the variations in the distribution pattern of endogenous Si in various tissue regions in roots and leaves of rice and maize exposed to cadmium (Cd) and zinc (Zn) stresses. For these experiments, 45 day-old rice (var. Varsha) and maize (var. CoHM6) seedlings were treated with 1.95 g Zn and 0.45 g Cd kg-1 soil. Under Cd stress, the distribution of Si was high in the cortical region of the root, but under Zn stress, the highest Si deposition was found in the endodermis. In leaves, Si deposition was high in both the mesodermis and stelar regions of Cd-treated plants but more Si was deposited in the mesodermis tissue of Zn-treated plants. Heavy metal (Cd and Zn) accumulation and Si deposition showed a strong negative correlation in the roots of rice and maize plants. Complexation with metal ions and redistribution of Si were considered the major mechanisms in Si-mediated mitigation of Cd and Zn stress. Cd- and Zn-induced anatomical changes, such as endodermal thickening, deposits in the xylary elements and aerenchyma formation in the roots of rice and maize, were also associated with the Si distribution.

Study on the impacts of chemical and green synthesized (Leucas aspera and oxy-cyclodextrin complex) dietary zinc oxide nanoparticles in Nile tilapia (Oreochromis niloticus)

The present study was designed to evaluate the health effects of dietary nanozinc prepared by two methods: conventional chemical method and green method. The parameters evaluated were the extent of bioaccumulation, antioxidant status, histological, immunological changes and DNA damage in Nile tilapia fed nanozinc feed. Zinc oxide nanoparticles were first prepared by green and chemical methods. Before feed preparation, the in vitro antioxidant activity and antibacterial activity of both types of nanoparticle solutions were tested and the results revealed enhanced activities in green synthesized ZnO NP solution. After the acclimatization period, 420 Nile tilapias were distributed randomly into 21 glass tanks with 20 fish per tank in triplicates. Fish were fed control diet without any ZnO NP and (i) GT1—green synthesized ZnO NP diet at 100 mg/kg, (ii) CT1—chemically synthesized ZnO NP diet at 100 mg/kg, (iii) GT2—green synthesized ZnO NP diet at 200 mg/kg, (iv) CT2—chemically synthesized ZnO NP diet at 200 mg/kg, (v) GT3—green synthesized ZnO NP diet at 400 mg/kg and (vi) CT3—chemically synthesized ZnO NP diet at 400 mg/kg for 60 days. After 60 days, gill and liver samples were collected for analysing oxidative stress, histopathological alterations and bioaccumulation of zinc, whereas serum samples were collected for evaluating immune response. The results revealed that the GT3 diet significantly (P < 0.05) enhanced the level of antioxidant enzymes (CAT, SOD, GPx, GR and GSH) than dietary nanozinc prepared by the chemical method. Similarly, the innate immunological parameters were significantly (P < 0.05) augmented in fish fed GT3 diet. Comparative histological study of liver and gill tissues revealed normal architecture in the tissues of fish fed green synthesized NP–enriched feed, whereas the tissues of fish fed chemically synthesized NP feed exhibited histological alterations. Bioaccumulation of zinc was more in the liver followed by the muscle and least in the gills and DNA damage was more evident in fish fed chemically synthesized ZnO NP–enriched feed. In conclusion, the results suggest that the inclusion of 400 mg/kg GT3 diet in fish diet enhanced the level of antioxidant enzymes, boosted immune response and did not cause histological damage to organs, and therefore, GT3 nanofeed can be recommended for fish health improvement.

Ameliorative effect of indole-3-acetic acid- and siderophore-producing Leclercia adecarboxylata MO1 on cucumber plants under zinc stress

ABSTRACT This study investigated the plant growth-promoting effects of Leclercia adecarboxylata MO1 for Zn stress mitigation and plant growth improvement in Zn-contaminated soil. Results demonstrated that L. adecarboxylata MO1 produced siderophores that could solubilize Zn and silicate, had a tolerance to elevated levels of Zn supplementation (2 and 5 mM) in growth mediums, and produced significant amounts of indole-3-acetic acid (IAA). It was also found to promote plant growth under both control conditions and Zn toxicity (2 and 5 mM). Furthermore, L. adecarboxylata MO1 positively regulated physiochemical attributes by decreasing hydrogen peroxide (H2O2) and Zn uptake in both roots and shoots, improving antioxidant systems (e.g. catalase (CAT), peroxidase (POD), polyphenol peroxidase (PPO), superoxide anion (SOA), lipid peroxidation (MDA), and glutathione (GSH)), and reducing stress-responsive endogenous abscisic acid (ABA) and salicylic acid (SA) in plants grown under Zn toxicity of 2 and 5 mM, compared with non-inoculated plants.

Split-root investigation of the physiological response to heterogeneous elevated Zn exposure in poplar and willow

Essential and toxic ions are often heterogeneously distributed within a soil landscape. This fact may complicate phytoextraction efforts to remove toxic ions such as heavy metals from the soil as the roots of some plants instead may colonize more favorable microenvironments and avoid heavy metal accumulation. In this study a split-root hydroponic experiment was used to test whether root-level exposure to zinc (Zn) stress to none, half or all of the root systems of Populus deltoides Bart. ex Marshall x Populus nigra L. (poplar) and Salix matsudana L. (willow) plants alters root and shoot physiology. Cuttings of both species were split to create two root system halves that were exposed to either control (-Zn) or stress (+1 mM Zn) solutions for 42 days. Weekly measurements of gas exchange, photosystem fluorescence parameters and pigments showed that poplar was more sensitive to the half stress (-Zn/+Zn) treatment than willow, with lower gas exchange rates and total chlorophyll and carotenoid values relative to their respective controls (-Zn/-Zn). Half stress willow plants had increased root growth in the half without Zn, demonstrating a reallocation of carbon to compensate with no negative impact to shoot physiology as compared to poplar. Water consumption was also reduced in half stress willow but not in poplar, suggesting an increase in water-use efficiency in response to heterogeneous Zn exposure that was not derived from dramatic reductions in transpiration rate. These significant differences between these two species in response to patchy distribution of toxic Zn concentration may impact the efficiency of phytoremediation efforts and suggests additional criteria to consider in the pre-selection process.

Heavy metal resistance in Marinobacter adhaerens HP15 supports colonization of transparent exopolymer particles during its interaction with diatoms

Marine diatoms and heterotrophic bacteria play a crucial role in the oceanic carbon cycle as they form aggregates that sink and transport biomass down in the water column. Polysaccharides are a major component of these aggregates and can bind heavy metal cations. Therefore, both organism groups might also be important for the vertical or micro-scale distribution of heavy metals in the ocean. Our model organism for diatom-bacteria interactions, Marinobacter adhaerens HP15, possesses 2 operons coding for heavy metal efflux pumps of the czcCBA type that are responsible for zinc resistance in this bacterium. The goal of this study was to elucidate the role of zinc resistance in M. adhaerens HP15 during its interaction with the diatom Thalassiosira weissflogii. For this, an HP15 mutant deficient in both czcCBA gene clusters was used in diatom co-cultivation experiments with or without zinc stress. When zinc was added to the co-cultures, the release of Alcian Blue-stainable particles increased 10-fold compared to assays without zinc. Both M. adhaerens HP15 wild-type and ΔczcCBA.1/2 mutant colonized the aggregates, and the percentage of bacteria attaching to transparent exopolymer particles (TEP) increased significantly under zinc stress. In the assays with zinc, HP15 wild-type had a higher cell density inside the aggregates than the mutant, although the zinc concentrations inside TEP were comparable. As TEP can bind and thus enrich heavy metals, resistance against them may help M. adhaerens HP15 to colonize aggregates. These results suggest that heavy metal resistance can be beneficial for bacteria during TEP- and aggregate-associated lifestyles.

Humic acid effects on retrotransposon polymorphisms caused by zinc and iron in the maize (Zea mays L.) genome

Long terminal repeat (LTR) retrotransposons are important pathways to examine various genome reorganizations based on environmental factors. The maize genome is one of the best representative examples. The aim of this study was to examine humic acid (HA) protective effects on genomic template stability (GTS) and LTR retrotransposon polymorphisms in corn seeds subjected to zinc (Zn) and iron (Fe) stress. In this study, maize seedlings were exposed to three doses (20, 40, and 60 mM) of ZnSO4·7H2O and FeSO4 and their combinations at 1500 ppm (0.075 g) HA. Inter-retrotransposon amplified polymorphism and retrotransposon-microsatellite amplified polymorphism techniques were used for genetic analyses. Results indicated that in all doses used, Zn and Fe increased retrotransposon polymorphisms and decreased the percentage of GTS via DNA damage. However, treatment of HA together with Zn and Fe resulted in decreased DNA damage and retrotransposon polymorphisms and increased GTS. These observations suggest that HA can be applied to reduce toxic effects in agricultural areas polluted with heavy metals.