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The resistance of crops to herbicides can be due to target site based resistance or non-target site based resistance mechanisms or a combination of both. In non-target site resistance, the detoxification efficiency plays a major role by involvement of enzymes such as P450s, GTs, GSTs and ABC transporters. The resistance of the first commercial Clearfield sunflower hybrids ( Imisun trait) to herbicides of imidazolinone group is based on a combination of both types of resistance. The target site resistance consists of a mutation in Ahasl1 gene, encoding the synthesis of the AHAS enzyme. The non-target site resistance is supposed to be due to intensified herbicide disposal and is not fully understood. The objective of this study was to detect the fast response of the glutathione-mediated detoxification system in IMI-R and IMI-S sunflower hybrids to the herbicide imazamox and to study the possible participation of GSTs in the enhancement of the hybrids' tolerance. The obtained results allow to presume that GSTs are involved in imazamox detoxification in the sunflower Imisun trait and thus contributing to its non-target site resistance. [ABSTRACT FROM AUTHOR]

Accurate identification and quantification of allergens is key in healthcare, biotechnology and food quality and safety. Celery (Apium graveolens) is one of the most important elicitors of food allergic reactions in Europe. Currently, the golden standards to identify, quantify and discriminate celery in a biological sample are immunoassays and two-step molecular detection assays in which quantitative PCR (qPCR) is followed by a high-resolution melting analysis (HRM). In order to provide a DNA-based, rapid and simple detection method suitable for one-step quantification, a fiber optic PCR melting assay (FO-PCR-MA) was developed to determine different concentrations of celery DNA (1 pM-0.1 fM). The presented method is based on the hybridization and melting of DNA-coated gold nanoparticles to the FO sensor surface in the presence of the target gene (mannitol dehydrogenase, Mtd). The concept was not only able to reveal the presence of celery DNA, but also allowed for the cycle-to-cycle quantification of the target sequence through melting analysis. Furthermore, the developed bioassay was benchmarked against qPCR followed by HRM, showing excellent agreement (R2 = 0.96). In conclusion, this innovative and sensitive diagnostic test could further improve food quality control and thus have a large impact on allergen induced healthcare problems. [ABSTRACT FROM AUTHOR]

Background: MicroRNAs are important posttranscriptional regulators of gene expression playing a role in developmental processes as well as in stress responses, including metal stress responses. Despite the identification of several metal-responsive miRNAs, the regulation and the role of these miRNAs and their targets remain to be explored. In this study, miRNAs involved in the response to Cd and Cu excess in Arabidopsis thaliana are identified. In addition, the involvement of the transcription factor SPL7, namely the key regulator of Cu homeostasis, in these metal stress responses is demonstrated by the use of an spl7 knockout mutant. Furthermore, more insight is given in the Cd-induced Cu deficiency response through determining the effects of adding supplemental Cu to Cd-exposed plants. Results: Thirteen miRNAs were identified in response to Cu and Cd excess in A. thaliana. Several of these miRNAs (miR397a, miR398b/c and miR857) were oppositely affected under Cu and Cd exposure. The induced expression of these miRNAs after Cd exposure was totally abolished in the spl7 mutant (SQUAMOSA promoter binding protein like7), indicating a major role for SPL7 in the Cd response. Plants exposed to Cd showed a higher Cu content in the roots, whereas the Cu content in the leaves of the spl7 mutant was reduced. Furthermore, the Cd-induced Cu deficiency response disappeared when supplemental Cu was added. Conclusions: Copper- and Cd-responsive miRNAs were identified and several of them are SPL7-dependently regulated. SPL7 seems to be a shared component between both the Cu toxicity and the Cd toxicity response, yet oppositely regulated, that is inactivated after Cu exposure and activated after Cd exposure. Since SPL7 is the key regulator of Cu homeostasis, and Cd affects the Cu homeostasis, we hypothesize that SPL7 is activated in response to Cd possibly due to a Cd-induced Cu deficiency. Since adding additional Cu to Cd-exposed plants resulted in the disappearance of the Cu deficiency response, Cd possibly provokes Cu deficiency, thereby activating SPL7 and inducing subsequently the Cu deficiency response. [ABSTRACT FROM AUTHOR]

Plant survival under abiotic stress conditions requires morphological and physiological adaptations. Adverse soil conditions directly affect root development, although the underlying mechanisms remain largely to be discovered. Plant hormones regulate normal root growth and mediate root morphological responses to abiotic stress. Hormone synthesis, signal transduction, perception and cross-talk create a complex network in which metal stress can interfere, resulting in root growth alterations. We focus on Arabidopsis thaliana, for which gene networks in root development have been intensively studied, and supply essential terminology of anatomy and growth of roots. Knowledge of gene networks, mechanisms and interactions related to the role of plant hormones is reviewed. Most knowledge has been generated for auxin, the best-studied hormone with a pronounced primary role in root development. Furthermore, cytokinins, gibberellins, abscisic acid, ethylene, jasmonic acid, strigolactones, brassinosteroids and salicylic acid are discussed. Interactions between hormones that are of potential importance for root growth are described. This creates a framework that can be used for investigating the impact of abiotic stress factors on molecular mechanisms related to plant hormones, with the limited knowledge of the effects of the metals cadmium, copper and zinc on plant hormones and root development included as case example. [ABSTRACT FROM AUTHOR]

Background Anthropogenic activities cause metal pollution worldwide. Plants can absorb and accumulate these metals through their root system, inducing stress as a result of excess metal concentrations inside the plant. Ethylene is a regulator of multiple plant processes, and is affected by many biotic and abiotic stresses. Increased ethylene levels have been observed after exposure to excess metals but it remains unclear how the increased ethylene levels are achieved at the molecular level. In this study, the effects of cadmium (Cd) exposure on the production of ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and on the expression of the ACC Synthase (ACS) and ACC Oxidase (ACO) multigene families were investigated in Arabidopsis thaliana. Results Increased ethylene release after Cd exposure was directly measurable in a system using rockwool-cultivated plants; enhanced levels of the ethylene precursor ACC together with higher mRNA levels of ethylene responsive genes: ACO2, ETR2 and ERF1 also indicated increased ethylene production in hydroponic culture. Regarding underlying mechanisms, it was found that the transcript levels of ACO2 and ACO4, the most abundantly expressed members of the ACO multigene family, were increased upon Cd exposure. ACC synthesis is the rate-limiting step in ethylene biosynthesis, and transcript levels of both ACS2 and ACS6 showed the highest increase and became the most abundant isoforms after Cd exposure, suggesting their importance in the Cd-induced increase of ethylene production. Conclusions Cadmium induced the biosynthesis of ACC and ethylene in Arabidopsis thaliana plants mainly via the increased expression of ACS2 and ACS6. This was confirmed in the acs2- 1acs6-1 double knockout mutants, which showed a decreased ethylene production, positively affecting leaf biomass and resulting in a delayed induction of ethylene responsive gene expressions without significant differences in Cd contents between wild-type and mutant plants. [ABSTRACT FROM AUTHOR]

To date, almost no information is available in roots and shoots of the model plant Arabidopsis thaliana about the hierarchic relationship between metal accumulation, phytohormone levels, and glutathione/phytochelatin content, and how this relation affects root development. For this purpose, specific concentrations of cadmium, copper and zinc, alone or in triple combination, were supplied for 12 days to in vitro growing seedlings. The accumulation of these metals was measured in roots and shoots, and a significant competition in metal uptake was observed. Microscopic analyses revealed that root morphology was affected by metal exposure, and that the levels of trans‐zeatin riboside, dihydrozeatin riboside, indole‐3‐acetic acid and the auxin/cytokinin ratio varied accordingly. By contrast, under metal treatments, minor modifications in gibberellic acid and abscisic acid levels occurred. Real‐time polymerase chain reaction analysis of some genes involved in auxin and cytokinin synthesis (e.g. AtNIT in roots and AtIPT in shoots) showed on average a metal up‐regulated transcription. The production of thiol‐peptides was induced by all the metals, alone or in combination, and the expression of the genes involved in thiol‐peptide synthesis (AtGSH1, AtGSH2, AtPCS1 and AtPCS2) was not stimulated by the metals, suggesting a full post‐transcriptional control. Results show that the Cd/Cu/Zn‐induced changes in root morphology are caused by a hormonal unbalance, mainly governed by the auxin/cytokinin ratio. [ABSTRACT FROM AUTHOR]

The hypothesis that mitogen-activated protein kinase ( MAPK) signalling is important in plant defences against metal stress has become accepted in recent years. To test the role of oxidative signal-inducible kinase ( OXI1) in metal-induced oxidative signalling, the responses of oxi1 knockout lines to environmentally realistic cadmium ( Cd) and copper ( Cu) concentrations were compared with those of wild-type plants. A relationship between OXI1 and the activation of lipoxygenases and other initiators of oxylipin production was observed under these stress conditions, suggesting that lipoxygenase-1 may be a downstream component of OXI1 signalling. Metal-specific differences in OXI1 action were observed. For example, OXI1 was required for the up-regulation of antioxidative defences such as catalase in leaves and Fe-superoxide dismutase in roots, following exposure to Cu, processes that may involve the MEKK1- MKK2- WRKY25 cascade. Moreover, the induction of Cu/Zn superoxide dismutases in Cu-exposed leaves was regulated by OXI1 in a manner that involves fluctuations in the expression of miRNA398. These observations contrast markedly with the responses to Cd exposure, which also involves OXI1-independent pathways but rather involves changes in components mediating intracellular communication. [ABSTRACT FROM AUTHOR]

Arabidopsis thaliana L. is a model plant but little information is available about morphological root changes as part of a phytohormonal common response against both biotic and abiotic stressors. For this purpose, two-week-old Arabidopsis seedlings were treated with 10 µM CdSO4 or infected with CMV. After 12 days the entire aerial parts and the root system were analyzed, and the presence of CMV or the accumulation of Cd were detected. Microscopic analysis revealed that both CMV and Cd influenced root morphology by a marked development in the length of root hairs and an intense root branching if compared to controls. Among the three treatments, Cd-treated seedlings showed a shorter root axis length and doubled their lateral root diameter, while the lateral roots of CMV-infected seedlings were the longest. The root growth patterns were accompanied by significant changes in the levels of indole-3-acetic acid, trans-zeatin riboside, dihydrozeatin riboside, as a probable consequence of the regulation of some genes involved in their biosynthesis/degradation. The opposite role on root development played by the phythormones studied is discussed in detail. The results obtained could provide insights into novel strategies for plant defense against pathogens and plant protection against pollutants. [ABSTRACT FROM AUTHOR]

Worldwide, metals have been distributed to excessive levels in the environment due to industrial and agricultural activities. Plants growing on soils contaminated with excess levels of metals experience a disturbance of the cellular redox balance, which leads to an augmentation of reactive oxygen species (ROS). Even though the increased ROS levels can cause cellular damage, controlled levels play an important role in modulating signaling networks that control physiological processes and stress responses. Plants control ROS levels using their antioxidative defense system both under non-stress conditions, as well as under stress conditions such as exposure to excess metals. Ascorbate (AsA) is a well-known and important component of the plant's antioxidative system. As primary antioxidant, it can reduce ROS directly and indirectly via ascorbate peroxidase in the ascorbate-glutathione cycle. Furthermore, AsA fulfills an essential role in physiological processes, some of which are disturbed by excess metals. In this review, known direct effects of excess metals on AsA biosynthesis and functioning will be discussed, as well as the possible interference of metals with the role of AsA in physiological and biochemical processes. [ABSTRACT FROM AUTHOR]

Abstract: Lipoxygenases (LOXes, EC 1.13.11.12) are involved in growth, development and responses to stress. Earlier results suggested a role in stress generation, signalling and/or responses when Arabidopsis thaliana is exposed to cadmium (Cd), and expression of the cytosolic LOX1 was highly upregulated in the roots after Cd exposure. To investigate the involvement of LOX1 in early metal stress responses, three-week-old wild-type and lox1-1 mutant A. thaliana plants were acutely (24 h) exposed to realistic Cd concentrations (5 and 10 μM) and several oxidative stress and signalling related parameters were studied at transcriptional and biochemical levels. Transcription of several genes encoding ROS producing and scavenging enzymes failed to be induced up to wild-type levels after Cd exposure. Expression of 9-LOX enzymes was inhibited in lox1-1 mutant roots due to lack of functional LOX1 and downregulated LOX5 expression, and the lox1-1 mutation also interfered with the expression of genes involved in jasmonate biosynthesis. LOX1 and RBOHD may be involved in stress signalling from roots to shoots, as the induction of APX2 expression, which is dependent on RBOHD activity, was disrupted in lox1-1 while RBOHD failed to be upregulated. A different pattern of H2O2 production and ascorbate and glutathione levels in lox1-1 mutants after Cd exposure may have indirectly influenced gene expression patterns. Although indirect effects of the lox1-1 mutation on gene expression complicate the determination of exact sensing – signalling – response pathways, the results presented here outline a more refined LOX1 functioning in Cd-induced stress responses that could be used in studies determining the exact involvement of LOX1 in these pathways. [Copyright &y& Elsevier]

Abstract: Zinc (Zn) is an essential micronutrient for plants, but accumulation of excess Zn causes oxidative stress, even though the element is not redox-active. An oxidative stress signature, consisting of multiple oxidative stress related parameters, is indicative of disturbance of redox homeostasis and signaling, but has not been determined after exposure to excess Zn. To reveal general and Zn-specific effects, changes in oxidative stress related gene expression, enzyme activities and metabolites were determined after 24h exposure of Arabidopsis thaliana plants to a concentration range of 0, 100, 250 or 500μM excess ZnSO4, and the oxidative stress signature compared to the ones reported previously for cadmium or copper exposure in the same experimental system. Zn accumulated in both roots and leaves, which led to a disturbed redox homeostasis as evident from increased H2O2 levels and altered glutathione redox state. In roots, magnesium uptake was affected and glutathione levels decreased due to reduced glutathione reductase activity and increased phytochelatin production. In leaves, mRNA levels of all chloroplast-localized superoxide dismutases (SOD) were downregulated, indicating that the converse regulation by Cu availability of FeSOD (FSD) and Cu/ZnSOD genes (CSDs) was disturbed. Furthermore, an opposite stress-dependent transcriptional regulation of the different loci of a miRNA species was observed: excess Zn repressed primary transcripts of the MIR398a gene, but increased MIR398b and MIR398c transcription. Also, accumulation of mRNA was inhibited for CSD2, but stimulated for CSD1. MiR398 has been reported to downregulate CSD1 and CSD2 mRNA. Here, the opposite effect on CSD1 and CSD2 mRNA accumulation under Zn stress in the leaves could be explained if CSD1 in the leaves would be regulated exclusively by miR398a, and not by miR398b/c under these conditions. The results support the existence of Zn-specific signal transduction pathways influencing anti-oxidative responses and are useful as a starting point for genetic screens identifying upstream metal-specific sensing and signaling mechanisms. [Copyright &y& Elsevier]

In plants, microRNAs (miRNAs) control various biological processes by negatively regulating the expression of complementary target genes, either (1) post-transcriptionally by cleavage or translational inhibition of target mRNA, or (2) transcriptionally by methylation of target DNA. Besides their role in developmental processes, miRNAs are main players in stress responses, including metal stress responses. Exposure of plants to excess metal concentrations disturbs the cellular redox balance and enhances ROS accumulation, eventually leading to oxidative damage or signaling. Plants modify their gene expression by the activity of miRNAs in response to metal toxicity to regulate (1) complexation of excess metals, (2) defense against oxidative stress and (3) signal transduction for controlling various biological responses. This review focuses on the biogenesis, working mechanisms and functioning of miRNAs in plants. In a final part, our current knowledge on the regulatory roles of miRNAs in plant metal stress responses is highlighted, and whether stress-regulated miRNAs have specific roles or are secondary consequences is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Metals, like cadmium (Cd) and copper (Cu), have the ability to induce the production of reactive oxygen species (ROS) at the cellular level. It is widely known that these ROS can cause irreversible damage to cellular components, like DNA, proteins and lipids. On the other hand, ROS can also act as signaling molecules and in this way they play an essential role in many normal physiological processes, but also in defense responses against stress. ROS signaling in plants uses mitogen-activated protein kinase (MAPK) pathways leading to the transcriptional control of target genes involved in the scavenging or production of ROS. Here, oxidative signaling induced by exposure to excess Cd or Cu was investigated in relation to anti-oxidative defense responses to these metals. Three-week-old Arabidopsis thaliana plants were exposed to environmentally realistic concentrations of Cu and Cd and immediate responses were measured at the level of hydrogen peroxide (H2O2) content, lipid peroxidation and transcript levels of genes involved in ROS homeostasis and signaling. Our findings show immediate (after 2h exposure) effects in the roots following Cu exposure, whereas effects in the leaves were generally more delayed. Effects of Cd exposure in leaves and roots were observed only after 24h exposure. On one hand, exposure of roots to Cu leads via activation of NADPH oxidases and Fenton reactions to H2O2 production that can induce MAPK and oxylipin signaling to control the cellular redox status. On the other hand, conversion of H2O2 to the more damaging hydroxyl radical by Fenton and Haber–Weiss reactions can initiate lipid peroxidation leading to membrane damage. In roots exposed to elevated Cd concentrations only oxidative signaling was initiated, possibly via NADPH oxidase-mediated ROS production. In leaves, time-dependent activation of MAPK and oxylipin signaling was seen after exposure to both metals, Cu or Cd, independent of changes in H2O2 content. [Copyright &y& Elsevier]

Exposure of plants to toxic concentrations of metals leads to disruption of the cellular redox status followed by an accumulation of reactive oxygen species (ROS). ROS, like hydrogen peroxide, can act as signaling molecules in the cell and induce signaling via mitogen-activated protein kinase (MAPK) cascades. MAPK cascades are evolutionary conserved signal transduction modules, able to convert extracellular signals to appropriate cellular responses. In this review, our current understanding about MAPK signaling in plant metal stress is discussed. However, this knowledge is scarce compared to research into the role of MAPK signaling in the case of other abiotic and biotic stresses. ROS production is a common response induced by different stresses and undiscovered analogies may exist with metal stress. Therefore, further attention is given to MAPK signaling in other biotic and abiotic stresses and its interplay with other signaling pathways to create a framework in which the involvement of MAPK signaling in metal stress may be studied. [ABSTRACT FROM AUTHOR]

Since the industrial revolution, the production, and consequently the emission of metals, has increased exponentially, overwhelming the natural cycles of metals in many ecosystems. Metals display a diverse array of physico-chemical properties such as essential versus non-essential and redox-active versus non-redox-active. In general, all metals can lead to toxicity and oxidative stress when taken up in excessive amounts, imposing a serious threat to the environment and human health. In order to cope with different kinds of metals, plants possess defense strategies in which glutathione (GSH; γ-glu-cys-gly) plays a central role as chelating agent, antioxidant and signaling component. Therefore, this review highlights the role of GSH in: (1) metal homeostasis; (2) antioxidative defense; and (3) signal transduction under metal stress. The diverse functions of GSH originate from the sulfhydryl group in cysteine, enabling GSH to chelate metals and participate in redox cycling. [ABSTRACT FROM AUTHOR]

A general status of oxidative stress in plants caused by exposure to elevated metal concentrations in the environment coincides with a constraint on mitochondrial electron transport, which enhances ROS accumulation at the mitochondrial level. As mitochondria are suggested to be involved in redox signaling under environmental stress conditions, mitochondrial ROS can initiate a signaling cascade mediating the overall stress response, i.e., damage versus adaptation. This review highlights our current understanding of metal-induced responses in plants, with focus on the production and detoxification of mitochondrial ROS. In addition, the potential involvement of retrograde signaling in these processes will be discussed. [ABSTRACT FROM AUTHOR]

Abstract: The promoter regions of plant pararetroviruses direct transcription of the full-length viral genome into a pregenomic RNA that is an intermediate in the replication of the virus. It serves as template for reverse transcription and as polycistronic mRNA for translation to viral proteins. We have identified functional promoter elements in the intergenic region of the Cavendish isolate of Banana streak virus (BSV-Cav), a member of the genus Badnavirus. Potential binding sites for plant transcription factors were found both upstream and downstream of the transcription start site by homology search in the PLACE database of plant cis-acting elements. The functionality of these putative cis-acting elements was tested by constructing loss-of-function and “regain”-of-function mutant promoters whose activity was quantified in embryogenic sugarcane suspension cells. Four regions that are important for activity of the BSV-Cav promoter were identified: the region containing an as-1-like element, the region around -141 and down to -77, containing several putative transcription factor binding sites, the region including the CAAT-box, and the leader region. The results could help explain the high BSV-Cav promoter activity that was observed previously in transgenic sugarcane plants and give more insight into the plant cell-mediated replication of the viral genome in banana streak disease. [Copyright &y& Elsevier]

Abstract. The Green Fluorescent Protein (GFP) from Aequorea victoria has begun to be used as a reporter protein in plants. It is particularly useful as GFP fluorescence can be detected in a non-destructive manner, whereas detection of enzyme-based reporters often requires destruction of the plant tissue. The use of GFP as a reporter enables transgenic plant tissues to be screened in vivo at any growth stage. Quantification of GFP in transgenic plant extracts will increase the utility of GFP as a reporter protein. We report herein the quantification of a mGFP5-ER variant in tobacco leaf extracts by UV excitation and a sGFP(S65T) variant in sugarcane leaf and callus extracts by blue light excitation using the BioRad VersaFluor Trademark Fluorometer System or the Labsystems Fluoroskan Ascent FL equipped with a narrow band emission filter (510 +/- 5 nm). The GFP concentration in transgenic plant extracts was determined from a GFP-standard series prepared in untransformed plant extract with concentrations ranging from 0.1 to 4 Mu g/ml of purified rGFP. Levels of sgfp(S65T) expression, driven by the maize ubiquitin promoter, in sugarcane calli and leaves ranged up to 0.525 Mu g and 2.11 Mu g sGFP(S65T) per mg of extractable protein respectively. In tobacco leaves the expression of mgfp5-ER, driven by the cauliflower mosaic virus (CaMV) 35S promoter, ranged up to 7.05 Mu g mGFP5-ER per mg extractable protein. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) induces the generation of reactive oxygen species (ROS) and stimulates ethylene biosynthesis. The phytohormone ethylene is a regulator of many developmental and physiological plant processes as well as stress responses. Previous research indicated various links between ethylene signalling and oxidative stress. Our results support a correlation between the Cd-induced oxidative challenge and ethylene signalling in Arabidopsis thaliana leaves. The effects of 24 or 72 h exposure to 5 μM Cd on plant growth and several oxidative stress-related parameters were compared between wild-type (WT) and ethylene insensitive mutants ( etr1-1 , ein2-1 , ein3-1 ). Cadmium-induced responses observed in WT plants were mainly affected in etr1-1 and ein2-1 mutants, of which the growth was less inhibited by Cd exposure as compared to WT and ein3-1 mutants. Both etr1-1 and ein2-1 showed a delayed response in the glutathione (GSH) metabolism, including GSH levels and transcript levels of GSH synthesising and recycling enzymes. Furthermore, the expression of different oxidative stress marker genes was significantly lower in Cd-exposed ein2-1 mutants, evidencing that ethylene signalling is involved in early responses to Cd stress. A model for the cross-talk between ethylene signalling and oxidative stress is proposed. [ABSTRACT FROM AUTHOR]

The stress hormone ethylene is known to be crucial for the survival of adverse environmental stimuli. Cadmium (Cd), a toxic metal, increases ethylene biosynthesis through an upregulated expression of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) isozymes, ACS2 and ACS6. In this study, wild-type (WT) and acs2-1acs6-1 double KO-mutant Arabidopsis thaliana plants were exposed to moderate (5 μM) and more severe (10 μM) Cd stress. The short-term influence of the Cd-induced ethylene production on growth and different oxidative stress parameters, and the consequent long-term influence on plant acclimation were investigated. Short-term moderate Cd stress conditions elicited enhanced stress-related responses in WT plants compared to the acs2-1acs6-1 mutants. The fresh weight of acs2-1acs6-1 mutant leaves was higher compared to the WT after 72 h exposure to moderate Cd stress. The transcript levels of pro-oxidative and oxidative stress marker genes as well as the expression of GSH1 and GSH2 , the enzymes synthesising the antioxidative metabolite glutathione (GSH) were lower in the acs2-1acs6-1 mutant plants compared to the WT. This also resulted in a lower GSH content in the leaves of the acs2-1acs6-1 mutant plants. Severe stress apparently overwhelmed the stress signal sensing system of both genotypes, overruling most of these different responses. Long-term exposure to moderate and severe Cd stress inhibited root and leaf development as well as the reproductive capacity of WT and acs2-1acs6-1 mutant plants without inducing differences between both genotypes, suggesting ethylene independence. We can conclude that ethylene plays an important role in the early oxidative challenge induced by moderate Cd stress in A. thaliana . [ABSTRACT FROM AUTHOR]

Abstract: Plant growth and development can be highly restricted by environmental stressors such as cadmium (Cd) pollution. The mitochondrial non-phosphorylating alternative respiratory pathway, mediated by alternative oxidase (AOX), alternative NAD(P)H dehydrogenases (NDs) and uncoupling protein (UCP), was suggested to be crucial in the acclimation of plants to fluctuating environmental conditions. Therefore, we examined the effects of environmentally realistic Cd exposure (5 and 10μM) on the alternative respiratory chain in Arabidopsis thaliana using a kinetic exposure setup. We demonstrated that during exposure to Cd, Arabidopsis seedlings show a mitochondrial oxidative challenge to which they acutely respond by increasing the transcript level of several AOX, ND and UCP isoforms in both roots and leaves. In addition, AOX protein levels increased during acute Cd exposure (2 and 24h). Based on our data, we suggest the formation of a condensed non-phosphorylating electron transport chain (ETC) functioning through cytosolic NDs and AOX, with co-regulation of ND and AOX expression during Cd stress. Therefore, both enzymes might cooperate in the potential acclimation of Arabidopsis seedlings to environmentally realistic Cd exposure by modulating the extent of mitochondrial ROS production. [Copyright &y& Elsevier]

Summary: The physiological effects of Cd and Cu have been highlighted in several studies over the last years. At the cellular level, oxidative stress has been reported as a common mechanism in both stress situations. Nevertheless, because of differences in their redox-related properties, the origin of the stress and regulation of these effects can be very different. Our results show a specific Cd-related induction of NADPH oxidases, whereas both metals induced lipid peroxidation via the activation of lipoxygenases. With respect to the antioxidative defense system, metal-specific patterns of superoxide dismutases (SODs) were detected, whereas gene expression levels of the H2O2-quenching enzymes were equally induced by both metals. Because monometallic exposure is very unusual in real-world situations, the metal-specific effects were compared with the mechanisms induced when the plants are exposed to both metals simultaneously. Combined exposure to Cd and Cu enhanced some of the effects that were induced when only one metal was applied to the medium. Other specific monometallically induced effects, such as a copper zinc superoxide dismutase (CSD2) downregulation due to Cd, were also sustained in a multipollution context, irrespective of the other monometallic effects. Furthermore, specific multipollution effects were unravelled, as iron superoxide dismutase 1 (FSD1) upregulation in the leaves was significant only when both Cu and Cd were applied. Additional relationships between these treatments and the common and specific stress induction mechanisms are discussed. [Copyright &y& Elsevier]

The mitochondrial alternative oxidase (AOX) is suggested to modulate metabolic homeostasis and is activated at transcript and protein level in cadmium (Cd)-exposed Arabidopsis thaliana plants. In this study, the importance of AOX in the metabolic response to Cd stress was investigated. Primary metabolites were determined in roots and leaves of wild-type plants and aox1a knockout mutants exposed to sublethal Cd concentrations for 24 and 72 h. Additional parameters (gene expression, enzyme capacity) were included to support the results at the metabolic level. Whereas sugar and organic acid levels initially dropped in roots, the opposite was observed in leaves of both genotypes exposed to Cd. Regarding genotype-related differences in the leaves, our results strengthen the previously proposed link between AOX1a and ethylene. Furthermore, respiratory flux dependent on amino acid degradation could be related to AOX1a function in leaves of Cd-exposed plants. In roots, a relation between AOX1a and antioxidative defence – in particular glutathione (GSH) – is demonstrated during Cd exposure. In conclusion, A. thaliana plants show a tissue-specific response to sublethal Cd exposure, with a differential role for AOX1a in roots and leaves. [ABSTRACT FROM AUTHOR]

This study aims to uncover the spatiotemporal involvement of glutathione (GSH) in two major mechanisms of cadmium (Cd)-induced detoxification (i.e. chelation and antioxidative defence). A kinetic study was conducted on hydroponically grown Arabidopsis thaliana (L. Heyhn) to gain insight into the early events after exposure to Cd. Cadmium detoxification was investigated at different levels, including gene transcripts, enzyme activities and metabolite content. Data indicate a time-dependent response both within roots and between plant organs. Early on in roots, GSH was preferentially allocated to phytochelatin (PC) synthesis destined for Cd chelation. This led to decreased GSH levels, without alternative pathways activated to complement GSH's antioxidative functions. After one day however, multiple antioxidative pathways increased including superoxide dismutase (SOD), ascorbate (AsA) and catalase (CAT) to ensure efficient neutralization of Cd-induced reactive oxygen species (ROS). As a consequence of Cd retention and detoxification in roots, a delayed response occurred in leaves. Together with high leaf thiol contents and possibly signalling responses from the roots, the leaves were protected, allowing them sufficient time to activate their defence mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Plants exposed to cadmium (Cd) show morphological and physiological disorders. To increase our knowledge regarding Cd-induced signalling, most often the effects of acute exposure are investigated. However, this does not allow in-depth analysis of morphological effects. Therefore, we chronically exposed Arabidopsis thaliana plants to environmentally realistic Cd concentrations (5 or 10 μM) and, using a described phenotypic framework methodology, we determined the impact of Cd on the plant’s ability to complete its life cycle and produce germinative seeds. Visible Cd-induced morphological changes were observed within a short exposure period, with chlorotic and anthocyanous leaf colouring occurring dose-dependently. Although rosette growth was severely reduced in Cd-exposed plants, all plants were able to emerge inflorescences and produce siliques containing germinative seeds, thus confirming the non-lethality of the used Cd concentrations. Although the growth inhibition of Cd-exposed plants was dependent on the dose, both concentrations had similar effects on inflorescence height and silique counts. In conclusion, vegetative growth of plants chronically exposed to Cd is inhibited in a concentration-dependent manner. However, the effect on plant regeneration is clearly stress-determined but independent on the Cd concentration applied. In Arabidopsis thaliana, vegetative and reproductive growth are differentially influenced by Cd. [Copyright &y& Elsevier]

Abstract: The production of reactive oxygen species (ROS) and the induction of the antioxidative defense mechanism are very important in heavy metal toxicity. In this study, biological effects induced after uranium contamination were investigated for Arabidopsis thaliana. Three-week-old seedlings were exposed for 4days to 100μM U in an adjusted Hoagland solution. Uranium exposure caused a decreased growth of leaves (38%) and roots (70%) and a modified nutrient profile was observed. Investigation of lipid peroxidation products indicated a significant increase of membrane damage. Important ROS-producing and -scavenging enzymes were studied at transcriptional and protein level to investigate the importance of the ROS-signature in uranium toxicity. Elevated gene expression was observed for NADPH-oxidase, a ROS-producing enzyme. Changes in gene expression for different ROS-scavenging enzymes as Cu/ZnSOD, FeSOD and APX were also observed. Analysis of enzyme capacities showed little effects after uranium contamination. Higher ascorbate levels in uranium exposed leaves suggested an increase of antioxidative defense via the ascorbate-glutathione pathway after uranium exposure. Theoretical calculations indicated rapid formation of uranium-phosphate precipitates if normal phosphate concentrations are used. Precipitation tests recommend the use of 25μM P in combination with 100μM U to inhibit uranium precipitation. Because this combination was used for uranium toxicity investigation, the influence of this low phosphate concentration on plant growth and oxidative stress had to be evaluated. Minor differences between low phosphate (25μM P) and high phosphate (100μM P) treatments were observed justifying the use of the low phosphate concentration in combination with uranium. [Copyright &y& Elsevier]

Abstract: The early antioxidative defence mechanisms were studied in Arabidopsis thaliana by applying a range of realistic Cd concentrations. Our data suggest that a 24h exposure to 20μM CdSO4 is already too toxic to study moderate toxicity, whereas a highly coordinated oxidative stress-related defence response could be observed after Cd application of 5 and 10μM. Significant differences in transcript abundance of several genes involved in antioxidative defence were observed. The generation of superoxide seems the main cause of oxidative stress in the roots, whereas in the leaves hydrogen peroxide appears to be an important player. Furthermore, an increased transcript level of lipoxygenase, a potential inducer of oxidative stress, suggests a central role of this gene in causing the Cd-related redox imbalance. Our results show that Cd as a non-redox-active metal induces oxidative stress and indicate that the antioxidative defence system is moderated by the activation of different genes in different organs and cellular compartments. [Copyright &y& Elsevier]