Copper excess triggers phospholipase D activity in wheat roots

Influence of arsenic exposure on the daily changes of glycerophospholipid turnover and assessment of defence mechanisms in tobacco hairy roots

Arsenic (As) affects several key physiological and metabolic processes, resulting in reduced seed germination and plant growth. The aim of this work was to study the impact of arsenite (AsIII) treatment on the metabolism of glycerophospholipids (MGPLs), evaluating the turnover activity (TA) of major GPLs, the expression of genes involved in this metabolism and also related to stress response. Total antioxidant activity (TAA) under AsIII-induced stress was evaluated as well as the implication of the circadian clock (CC) on the parameters studied. For this purpose, tobacco (Nicotiana tabacum) hairy roots (HRs) synchronized with a 12/12 h light/dark photoperiod were used. The TA of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) showed a circadian behavior, especially under untreated conditions. However, the As treatment significantly modified the TA profiles of all analyzed GPLs, by inducing an opposite oscillation (PC and LysoPC) or increasing their TA (LysoPE and cardiolipin) during both the light and dark phase. Curiously, under As-treatment, the relative expression of key genes involved in the MGPLs (NtLPAT2 and NtCEK4) was increased and showed a circadian oscillation, while under control conditions, no significant changes were detected. NtPHT4;1 gene, involved in As-induced stress, showed a circadian expression profile, which was conserved under AsIII treatment but with an antiphase performance. Moreover, TAA was significantly affected in AsIII-treated HRs, mainly during the dark phase. Our results show that AsIII treatment affected the parameters studied and constitute valuable evidence to unravel the plant responses and the CC implication under AsIII-induced stress.

BcGR1.1, a Cytoplasmic Localized Glutathione Reductase, Enhanced Tolerance to Copper Stress in Arabidopsis thaliana

Copper is a mineral element, which is necessary for the normal growth and development of plants, but high levels of copper will seriously damage plants. Studies have shown that AtGR1 improves the tolerance of Arabidopsis to aluminum and cadmium stress. However, the role of GR in the copper stress response of plants is still unclear. Here, we identified four genes (named BcGR1.1, BcGR1.2, BcGR2.1 and BcGR2.2, respectively) encoding glutathione reductase (GR) in non-heading Chinese cabbage (Brassica campestris (syn. Brassica rapa) ssp. chinensis), which could be divided into two types based on the subcellular localization. Among them, BcGR1.1, which belonged to the cytoplasmic localization type, was significantly upregulated under copper stress. Compared to WT (the wild type), Arabidopsis thaliana heterologously overexpressed BcGR1.1 had longer roots, higher fresh weight, higher GSH levels and GSH/GSSG (oxidized form of GSH) ratio, and accumulated more superoxide dismutase and peroxidase under copper stress. However, in the AsA-GSH cycle under copper stress, the contents of AsA and AsA/DHA were significantly downregulated, and the contents of DHA and T-AsA (total AsA) were upregulated, in the BcGR1.1-overexpressing Arabidopsis. Therefore, BcGR1.1 could improve the scavenging ability of reactive oxygen species (ROS) by increasing the activity of GR, antioxidant enzymes and the utilization of AsA, and then enhance the copper stress tolerance of plants.

The multi metal-resistant bacterium Cupriavidus metallidurans CH34 affects growth and metal mobilization in Arabidopsis thaliana plants exposed to copper

Copper (Cu) is important for plant growth, but high concentrations can lead to detrimental effects such as primary root length inhibition, vegetative tissue chlorosis, and even plant death. The interaction between plant-soil microbiota and roots can potentially affect metal mobility and availability, and, therefore, overall plant metal concentration. Cupriavidus metallidurans CH34 is a multi metal-resistant bacterial model that alters metal mobility and bioavailability through ion pumping, metal complexation, and reduction processes. The interactions between strain CH34 and plants may affect the growth, metal uptake, and translocation of Arabidopsis thaliana plants that are exposed to or not exposed to Cu. In this study, we looked also at the specific gene expression changes in C. metallidurans when co-cultured with Cu-exposed A. thaliana. We found that A. thaliana’s rosette area, primary and secondary root growth, and dry weight were affected by strain CH34, and that beneficial or detrimental effects depended on Cu concentration. An increase in some plant growth parameters was observed at copper concentrations lower than 50 µM and significant detrimental effects were found at concentrations higher than 50 µM Cu. We also observed up to a 90% increase and 60% decrease in metal accumulation and mobilization in inoculated A. thaliana. In turn, copper-stressed A. thaliana altered C. metallidurans colonization, and cop genes that encoded copper resistance in strain CH34 were induced by the combination of A. thaliana and Cu. These results reveal the complexity of the plant-bacteria-metal triad and will contribute to our understanding of their applications in plant growth promotion, protection, and phytoremediation strategies.

Deepening the knowledge on the removal of Cr(VI) by L. minuta Kunth: removal efficiency and mechanisms, lipid signaling pathways, antioxidant response, and toxic effects

Lemna minuta Kunth was used to remove Cr(VI) from aqueous solutions, and some of the mechanisms involved in this process were analyzed. In addition, the cellular signaling mediated by phospholipase D activity as well as antioxidant responses was also evaluated during the process. Cr(VI) removal efficiencies were 40% for 0.5 mg/L, after 24 h, and up to 18% at metal concentrations as high as 5 mg/L. Removal mechanisms displayed by these macrophytes include bioadsorption to cell surfaces and, to a greater extent, Cr internalization and bioaccumulation within cells. Inside of them, Cr(VI) was reduced to Cr(III), a less toxic form of this metal. At the first hours of Cr(VI) exposure, plants were able to sense chromium, activating membrane signal transduction pathways mediated by phospholipase D and phosphatidic acid. Moreover, an increase in the activity of antioxidant enzymes such as superoxide dismutases and peroxidases was observed in the same time. These and other components of the antioxidant defense system would help to reduce the stress generated by the metal. The toxicity of the products formed during the removal process was assessed through Lactuca sativa L. and AMPHIAGU test. It was evidenced that Cr(VI) phytoremediation process by L. minuta plants did not generate acute toxicity neither for L. sativa seeds nor for embryos of Rhinella arenarum (Hensel, 1876). Thus, L. minuta plants could be considered as valuable species for the treatment of waters contaminated with Cr(VI).

OsMSR3, a Small Heat Shock Protein, Confers Enhanced Tolerance to Copper Stress in Arabidopsis thaliana

Copper is a mineral element essential for the normal growth and development of plants; however, excessive levels can severely affect plant growth and development. Oryza sativa L. multiple stress-responsive gene 3 (OsMSR3) is a small, low-molecular-weight heat shock protein (HSP) gene. A previous study has shown that OsMSR3 expression improves the tolerance of Arabidopsis to cadmium stress. However, the role of OsMSR3 in the Cu stress response of plants remains unclear, and, thus, this study aimed to elucidate this phenomenon in Arabidopsis thaliana, to further understand the role of small HSPs (sHSPs) in heavy metal resistance in plants. Under Cu stress, transgenic A. thaliana expressing OsMSR3 showed higher tolerance to Cu, longer roots, higher survival rates, biomass, and relative water content, and accumulated more Cu, abscisic acid (ABA), hydrogen peroxide, chlorophyll, carotenoid, superoxide dismutase, and peroxidase than wild-type plants did. Moreover, OsMSR3 expression in A. thaliana increased the expression of antioxidant-related and ABA-responsive genes. Collectively, our findings suggest that OsMSR3 played an important role in regulating Cu tolerance in plants and improved their tolerance to Cu stress through enhanced activation of antioxidative defense mechanisms and positive regulation of ABA-responsive gene expression.

Effects of Pisolithus tinctorius and Cenococcum geophilum inoculation on pine in copper-contaminated soil to enhance phytoremediation

We used Pisolithus tinctorius and Cenococcum geophilum to determine the copper (Cu) resistance of ectomycorrhizal (ECM) fungi and their potential for improving phytoremediation of Cu-contaminated soil by Chinese red pine (Pinus tabulaeformis). The results showed that nutrient accumulation in C. geophilum mycelium was significantly lower under higher Cu concentrations in the soil, which was not observed in P. tinctorius. Meanwhile, P. tinctorius exhibited greater Cu tolerance than C. geophilum. Inoculation with ECM fungi significantly improved the growth of pine shoots planted in polluted soil in pot experiments (p < 0.01). The total accumulated Cu in pine seedlings planted in Cu-contaminated soil increased by 72.8% and 113.3% when inoculated with P. tinctorius and C. geophilum, respectively, indicating that ECM fungi may help their host to phytoextract heavy metals. Furthermore, the majority of the total absorbed metals remained in the roots, confirming the ability of ECM fungi to promote heavy metal phytostabilization. There were no differences between the effects of the two fungi in helping the host stabilize and absorb Cu, even though they have different Cu tolerances. Inoculation with ECM fungi can benefit plant establishment in polluted environments and assist plants with phytoremediating heavy-metal-contaminated soils.

Arsenic stress induces changes in lipid signalling and evokes the stomata closure in soybean

Soybean (Glycine max) is often exposed to high arsenic (As) level in soils or through irrigation with groundwater. In previous studies on As-treated soybean seedlings we showed deleterious effect on growth, structural alterations mainly in root vascular system and induction of antioxidant enzymes. However, there are not reports concerning signal transduction pathways triggered by the metalloid in order to develop adaptive mechanisms. Phosphatidic acid (PA), a key messenger in plants, can be generated via phospholipase D (PLD) or via phospholipase C (PLC) coupled to diacylglycerol kinase (DGK). Thus, changes in PA and in an enzyme involved in its metabolism (PLD) were analysed in soybean seedlings treated with 25 μM AsV or AsIII. The present study demonstrated that As triggers the PA signal by PLD and also via PLC/DGK mainly after 48 h of As treatment. DGPP, other lipid messenger produced by phosphorylation of PA by PAK increased in As treated roots. Arsenic also induced rapid and significant stomatal closure after 1.5 h of treatment, mainly with AsIII, probably as an adaptive response to the metalloid to reduce water loss by transpiration. This report constitute the first evidence that shows the effects of As on lipid signalling events in soybean seedlings which would be crucial in adaptation and survival of soybean seedlings under As stress.

Symbiotic association between Salix purpurea L. and Rhizophagus irregularis: modulation of plant responses under copper stress

There are increasing concerns about trace metal levels such as copper (Cu) in industrial sites and the broader environment. Different studies have highlighted the role of mycorrhizal associations in plant tolerance to trace metals, modulating some of the plant metabolic and physiological responses. In this study, we investigated the role of the symbiotic association betweenRhizophagus irregularisandSalix purpureaL. in modulating plant responses under Cu stress. We measured Cu accumulation, oxidative stress-related, photosynthetic-related and hydraulic traits, for non-inoculated (non-arbuscular mycorrhizal fungi) and inoculated saplings exposed to different Cu concentrations. We found thatS. purpureais a suitable option for phytoremediation of Cu, acting as a phytostabilizer of this trace metal in its root system. We observed that the symbiotic association modulates a broad spectrum of metabolic and physiological responses inS. purpureaunder Cu conditions, including (i) a reduction in gas exchange associated with chlorophyll content changes and (ii) the sequestration of Cu into the cell walls, modifying vessels anatomy and impacting leaf specific conductivity (KL) and root hydraulic conductance (LP). UpholdingKLandLPunder Cu stress might be related to a dynamic Aquaporin gene regulation ofPIP1;2along with an up-regulation ofTIP2;2in the roots of inoculatedS. purpurea.

The Dynamic Changes of the Plasma Membrane Proteins and the Protective Roles of Nitric Oxide in Rice Subjected to Heavy Metal Cadmium Stress

The heavy metal cadmium is a common environmental contaminant in soils and has adverse effects on crop growth and development. The signaling processes in plants that initiate cellular responses to environmental stress have been shown to be located in the plasma membrane (PM). A better understanding of the PM proteome in response to environmental stress might provide new insights for improving stress-tolerant crops. Nitric oxide (NO) is reported to be involved in the plant response to cadmium (Cd) stress. To further investigate how NO modulates protein changes in the plasma membrane during Cd stress, a quantitative proteomics approach based on isobaric tags for relative and absolute quantification (iTRAQ) was used to identify differentially regulated proteins from the rice plasma membrane after Cd or Cd and NO treatment. Sixty-six differentially expressed proteins were identified, of which, many function as transporters, ATPases, kinases, metabolic enzymes, phosphatases, and phospholipases. Among these, the abundance of phospholipase D (PLD) was altered substantially after the treatment of Cd or Cd and NO. Transient expression of the PLD fused with green fluorescent peptide (GFP) in rice protoplasts showed that the Cd and NO treatment promoted the accumulation of PLD in the plasma membrane. Addition of NO also enhanced Cd-induced PLD activity and the accumulation of phosphatidic acid (PA) produced through PLD activity. Meanwhile, NO elevated the activities of antioxidant enzymes and caused the accumulation of glutathione, both which function to reduce Cd-induced H2O2 accumulation. Taken together, we suggest that NO signaling is associated with the accumulation of antioxidant enzymes, glutathione and PA which increases cadmium tolerance in rice via the antioxidant defense system.

Endophytic bacteria take the challenge to improve Cu phytoextraction by sunflower

Endophytic bacteria from roots and crude seed extracts of a Cu-tolerant population of Agrostis capillaris were inoculated to a sunflower metal-tolerant mutant line, and their influence on Cu tolerance and phytoextraction was assessed using a Cu-contaminated soil series. Ten endophytic bacterial strains isolated from surface-sterilized A. capillaris roots were mixed to prepare the root endophyte inoculant (RE). In parallel, surface-sterilized seeds of A. capillaris were crushed in MgSO4 to prepare a crude seed extract containing seed endophytes (SE). An aliquot of this seed extract was filtered at 0.2 μm to obtain a bacterial cell-free seed extract (SEF). After surface sterilization, germinated sunflower seeds were separately treated with one of five modalities: no treatment (C), immersion in MgSO4 (CMg) or SEF solutions and inoculation with RE or SE. All plants were cultivated on a Cu-contaminated soil series (13-1020 mg Cu kg(-1)). Cultivable RE strains were mostly members of the Pseudomonas genera, and one strain was closely related to Labrys sp. The cultivable SE strains belonged mainly to the Bacillus genera and some members of the Rhodococcus genera. The treatment effects depended on the soil Cu concentration. Both SE and SEF plants had a higher Cu tolerance in the 13-517 mg Cu kg(-1) soil range as reflected by increased shoot and root DW yields compared to control plants. This was accompanied by a slight decrease in shoot Cu concentration and increase in root Cu concentration. Shoot and root DW yields were more promoted by SE than SEF in the 13-114 mg Cu kg(-1) soil range, which could reflect the influence of seed-located bacterial endophytes. At intermediate soil Cu (416-818 mg Cu kg(-1) soil), the RE and CMg plants had lower shoot Cu concentrations than the control, SE and SEF plants. At high total soil Cu (617-1020 mg Cu kg(-1)), root DW yield of RE plants slightly increased and their root Cu concentration rose by up to 1.9-fold. In terms of phytoextraction efficiency, shoot Cu removal was increased for sunflower plants inoculated with crude and bacterial cell-free seed extracts by 1.3- to 2.2-fold in the 13-416 mg Cu kg(-1) soil range. Such increase was mainly driven by an enhanced shoot DW yield. The number and distribution of endophytic bacteria in the harvested sunflower tissues must be further examined.

Specific mechanisms of tolerance to copper and cadmium are compromised by a limited concentration of glutathione in alfalfa plants

The induction of oxidative stress is a characteristic symptom of metal phytotoxicity and is counteracted by antioxidants such as glutathione (GSH) or homoglutathione (hGSH). The depletion of GSH│hGSH in fifteen-day-old alfalfa (Medicago sativa) plants pre-incubated with 1mM buthionine sulfoximine (BSO) affected antioxidant responses in a metal-specific manner under exposure to copper (Cu; 0, 6, 30 and 100μM) or cadmium (Cd; 0, 6 and 30μM) for 7 days. The phytotoxic symptoms observed with excess Cu were accompanied by an inhibition of root glutathione reductase (GR) activity, a response that was augmented in Cd-treated plants but reverted when combined with BSO. The synthesis of phytochelatins (PCs) was induced by Cd, whereas the biothiol concentration decreased in Cu-treated plants, which did not accumulate PCs. The depletion of GSH│hGSH by BSO also produced a strong induction of oxidative stress under excess Cu stress, primarily due to impaired GSH│hGSH-dependent redox homeostasis. In addition, the synthesis of PCs was required for Cd detoxification, apparently also determining the distribution of Cd in plants, as less metal was translocated to the shoots in BSO-incubated plants. Therefore, specific GSH│hGSH-associated mechanisms of tolerance were triggered by stress due to each metal.

Involvement of phospholipase D-related signal transduction in chemical-induced programmed cell death in tomato cell cultures

Phospholipase D (PLD) and its product phosphatidic acid (PA) are incorporated in a complex metabolic network in which the individual PLD isoforms are suggested to regulate specific developmental and stress responses, including plant programmed cell death (PCD). Despite the accumulating knowledge, the mechanisms through which PLD/PA operate during PCD are still poorly understood. In this work, the role of PLDα1 in PCD and the associated caspase-like proteolysis, ethylene and hydrogen peroxide (H(2)O(2)) synthesis in tomato suspension cells was studied. Wild-type (WT) and PLDα1-silenced cell lines were exposed to the cell death-inducing chemicals camptothecin (CPT), fumonisin B1 (FB1) and CdSO(4). A range of caspase inhibitors effectively suppressed CPT-induced PCD in WT cells, but failed to alleviate cell death in PLDα1-deficient cells. Compared to WT, in CPT-treated PLDα1 mutant cells, reduced cell death and decreased production of H(2)O(2) were observed. Application of ethylene significantly enhanced CPT-induced cell death both in WT and PLDα1 mutants. Treatments with the PA derivative lyso-phosphatidic acid and mastoparan (agonist of PLD/PLC signalling downstream of G proteins) caused severe cell death. Inhibitors, specific to PLD and PLC, remarkably decreased the chemical-induced cell death. Taken together with our previous findings, the results suggest that PLDα1 contributes to caspase-like-dependent cell death possibly communicated through PA, reactive oxygen species and ethylene. The dead cells expressed morphological features of PCD such as protoplast shrinkage and nucleus compaction. The presented findings reveal novel elements of PLD/PA-mediated cell death response and suggest that PLDα1 is an important factor in chemical-induced PCD signal transduction.

Copper regulates primary root elongation through PIN1-mediated auxin redistribution

The heavy metal copper (Cu) is an essential microelement required for normal plant growth and development, but it inhibits primary root growth when in excess. The mechanism underlying how excess Cu functions in this process remains to be further elucidated. Here, we report that a higher concentration of CuSO4 inhibited primary root elongation of Arabidopsis seedlings by affecting both the elongation and meristem zones. In the meristem zone, meristematic cell division potential was reduced by excess Cu. Further experiments showed that Cu can modulate auxin distribution, resulting in higher auxin activities in both the elongation and meristem zones of Cu-treated roots based on DR5::GUS expression patterns. This Cu-mediated auxin redistribution was shown to be responsible for Cu-mediated inhibition of primary root elongation. Additional genetic and physiological data demonstrated that it was PINFORMED1 (PIN1), but not PIN2 or AUXIN1 (AUX1), that regulated this process. However, Cu-induced hydrogen peroxide accumulation did not contribute to Cu-induced auxin redistribution for inhibition of root elongation. When the possible role of ethylene in this process was analyzed, Cu had a similar impact on the root elongation of both the wild type and the ein2-1 mutant, implying that Cu-mediated inhibition of primary root elongation was not due to the ethylene signaling pathway.

The influence of EDDS on the metabolic and transcriptional responses induced by copper in hydroponically grown Brassica carinata seedlings

To improve the knowledge about the use of plants for the removal of toxic metals from contaminated soils, metabolic and transcriptional responses of Brassica carinata to different forms of copper (Cu) were studied. Two-week-old hydroponically grown seedlings were exposed for 24 h to 30 μM CuSO₄ or CuEDDS. CuSO₄ appeared to be more toxic than CuEDDS as roots showed higher levels of thiobarbituric acid reactive substances (TBARS) and increased relative leakage ratios (RLR), although the superoxide dismutase (SOD, EC 1.15.1.1) activity increased following both exposures. In CuSO₄-exposed seedlings the higher toxicity was underlined by increased transcription of lipoxygenases (EC 1.13.11.12) and NADPH oxidases (EC 1.6.99.6) and by the higher Cu accumulation in both tissues compared to CuEDDS exposure. The presence of EDDS increased Cu translocation, which resulted 5-times higher than when exposed to CuSO₄. Decreases in catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) activities together with increases of reduced glutathione (GSH) and tocopherols and a reduction of lipoic acid (LA) were observed in roots of CuSO₄-exposed seedlings. On the contrary, CuEDDS exposure induced a general increase in enzyme activities and decreases in ascorbate (AsA) and tocopherol levels. In the primary leaves, in both exposures Cu differently affected the oxidative stress responses indicating that the cellular redox balance was anyway maintained. EDDS plays a crucial role in B. carinata tolerance to oxidative stress induced by Cu and might be proposed to improve the efficiency of Cu phytoextraction.

The cellular redox state as a modulator in cadmium and copper responses in Arabidopsis thaliana seedlings

The cellular redox state is an important determinant of metal phytotoxicity. In this study we investigated the influence of cadmium (Cd) and copper (Cu) stress on the cellular redox balance in relation to oxidative signalling and damage in Arabidopsis thaliana. Both metals were easily taken up by the roots, but the translocation to the aboveground parts was restricted to Cd stress. In the roots, Cu directly induced an oxidative burst, whereas enzymatic ROS (reactive oxygen species) production via NADPH oxidases seems important in oxidative stress caused by Cd. Furthermore, in the roots, the glutathione metabolism plays a crucial role in controlling the gene regulation of the antioxidative defence mechanism under Cd stress. Metal-specific alterations were also noticed with regard to the microRNA regulation of CuZnSOD gene expression in both roots and leaves. The appearance of lipid peroxidation is dual: it can be an indication of oxidative damage as well as an indication of oxidative signalling as lipoxygenases are induced after metal exposure and are initial enzymes in oxylipin biosynthesis. In conclusion, the metal-induced cellular redox imbalance is strongly dependent on the chemical properties of the metal and the plant organ considered. The stress intensity determines its involvement in downstream responses in relation to oxidative damage or signalling.

Exogenously induced expression of ethylene biosynthesis, ethylene perception, phospholipase D, and Rboh-oxidase genes in broccoli seedlings

In higher plants, copper ions, hydrogen peroxide, and cycloheximide have been recognized as very effective inducers of the transcriptional activity of genes encoding the enzymes of the ethylene biosynthesis pathway. In this report, the transcriptional patterns of genes encoding the 1-aminocyclopropane-1-carboxylate synthases (ACSs), 1-aminocyclopropane-1-carboxylate oxidases (ACOs), ETR1, ETR2, and ERS1 ethylene receptors, phospholipase D (PLD)-alpha1, -alpha2, -gamma1, and -delta, and respiratory burst oxidase homologue (Rboh)-NADPH oxidase-D and -F in response to these inducers in Brassica oleracea etiolated seedlings are shown. ACS1, ACO1, ETR2, PLD-gamma1, and RbohD represent genes whose expression was considerably affected by all of the inducers used. The investigations were performed on the seedlings with (i) ethylene insensitivity and (ii) a reduced level of the PLD-derived phosphatidic acid (PA). The general conclusion is that the expression of ACS1, -3, -4, -5, -7, and -11, ACO1, ETR1, ERS1, and ETR2, PLD-gamma 1, and RbohD and F genes is undoubtedly under the reciprocal cross-talk of the ethylene and PA(PLD) signalling routes; both signals affect it in concerted or opposite ways depending on the gene or the type of stimuli. The results of these studies on broccoli seedlings are in agreement with the hypothesis that PA may directly affect the ethylene signal transduction pathway via an inhibitory effect on CTR1 (constitutive triple response 1) activity.

Accumulation of lead in the roots of grass pea (Lathyrus sativus L.) plants triggers systemic variation in gene expression in the shoots

The impact of lead nitrate (Pb(NO(3))(2); 0.5mM) on steady-state accumulation of messengers corresponding to stress responsive genes was studied in two local lines of 11-d grass pea (Lathyrus sativus L.) plants exposed for 96 h in a hydroponic system. Real-time reverse transcription polymerase chain reaction technique was used with grass pea-specific primers designed from newly isolated partial cDNA. Increases in accumulation of glutathione reductase, ascorbate peroxidase and glutathione S-transferase transcripts suggested that roots enhanced detoxification mechanisms involving glutathione. In the leaves where no lead was translocated, the pollutant indirectly triggered increases in expression of several genes. This process probably resulted from systemic signals originating from the roots where lead accumulated in large amounts, approximately 150 mg Pbg(-1) dry weight. A preventive and/or adaptive role for the signal is assumed, since it concerned genes implicated in reactive oxygen species scavenging (ascorbate peroxidase), protein protection (heat shock protein 70) and proteolysis (cysteine and aspartic proteases).

Moving up, down, and everywhere: signaling of micronutrients in plants

To cope with the variable availability of micronutrients, plants have evolved a complex set of physiological and developmental processes, which are under tight control of short-range and long-range signaling pathways. These signals act at the cellular and whole-plant scale to coordinate micronutrient homeostasis at the systemic and local level. Recently, several molecular components of the local and long-distance regulatory circuits as well as their putative positions in the signaling cascade have been identified. Since among the micronutrients comparatively most is known on the signaling of Fe, this review sets a focus on Fe, for which the regulatory pathway most likely involves signaling compounds such as nitric oxide and hormones (e.g. ethylene and cytokinin) that act upstream of a set of transcription factors.

Copper homeostasis

Copper (Cu) is a cofactor in proteins that are involved in electron transfer reactions and is an essential micronutrient for plants. Copper delivery is accomplished by the concerted action of a set of evolutionarily conserved transporters and metallochaperones. As a result of regulation of transporters in the root and the rarity of natural soils with high Cu levels, very few plants in nature will experience Cu in toxic excess in their tissues. However, low Cu bioavailability can limit plant productivity and plants have an interesting response to impending Cu deficiency, which is regulated by an evolutionarily conserved master switch. When Cu supply is insufficient, systems to increase uptake are activated and the available Cu is utilized with economy. A number of Cu-regulated small RNA molecules, the Cu-microRNAs, are used to downregulate Cu proteins that are seemingly not essential. On low Cu, the Cu-microRNAs are upregulated by the master Cu-responsive transcription factor SPL7, which also activates expression of genes involved in Cu assimilation. This regulation allows the most important proteins, which are required for photo-autotrophic growth, to remain active over a wide range of Cu concentrations and this should broaden the range where plants can thrive.

Implication of phospholipase D in response of Hordeum vulgare root to short-term potassium deprivation

To verify the possible involvement of lipids and several other compounds including hydrogen peroxide (H(2)O(2)) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) in the response of Hordeum vulgare to early potassium deprivation, plants were grown in hydroponic conditions for 30d with a modified Hewitt nutrient solution containing 3mM K(+). They were then incubated for increasing periods of time ranging from 2 to 36h in the same medium deprived of K(+). In contrast to leaves, root K(+) concentration showed its greatest decrease after 6h of treatment. The main lipids of the control barley roots were phospholipids (PL), representing more than 50% of the total lipids. PL did not change with treatment, whereas free sterols (FS) decreased following K(+) deprivation, showing a reduction of approximately 17% after 36h. With respect to the individual PL, 30h K(+) deprivation led to a reduction in phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI) levels, whereas phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and phosphatidic acid (PA) levels increased. The maximum PA accumulation and the highest phospholipase D (PLD) activation, estimated by an accumulation of phosphatidylbutanol (PtBut), were observed after 24h of K(+) starvation. At the root level, H(2)O(2) showed the maximum value after 6h of incubation in -K solution. In parallel, G3PDH activity reached its minimum. On the basis of a concomitant stimulation of PLD activity and, consequently, PA accumulation, enhancement of H(2)O(2) production, and inhibition of G3PDH activity, we suggest a possible involvement of these three compounds in an early response to K(+) deprivation.

Enhanced induction of microspore embryogenesis after n-butanol treatment in wheat (Triticum aestivum L.) anther culture

The aim of this study was the improvement of embryo production in wheat anther culture. Three butanol alcohols, n-butanol, sec-butanol and tert-butanol, were evaluated for their effect on microspore embryogenesis in two spring cultivars of wheat, Pavon and Caramba. Application of n-butanol, at 0.1 and 0.2% (v/v) in the induction media for 5 h, highly improved embryo production in both cultivars. Sec- and tert-butanol performed similarly to control plates. Regeneration ability was unaffected by any butyl-alcohol treatment. As a consequence of the higher embryo production after n-butanol treatment, the number of green regenerated plants increased up to five times in cultivar Pavon and up to three times in cultivar Caramba. The percentage of green plants was improved or unaffected by the treatment. Doubled haploid plant production was between 2 and 4 times higher after n-butanol treatment than in control plates. Therefore, n-butanol was successfully applied in the production of wheat doubled haploids. This primary alcohol is known as an activator of phospholipase D and has been previously reported to disrupt cortical microtubules and detach them from the plasma membrane in plants. Its effects on androgenetic induction could confirm the importance of microtubule regulation in plant cell fate, specifically in microspore development. A possible implication of phospholipase D is discussed.

Early production of activated oxygen species in root apoplast of wheat following copper excess

Wheat seedlings (Triticum durum Desf.) were incubated in a solution containing 100 microM CuSO(4) for increasing time ranging from 1 min to 6h. Copper rapidly accumulated into the roots, and its amount increased significantly until 360 min. During the experiment, copper did not cause any lipid peroxidation and K(+) leakage. Up to 60 min of copper treatment the superoxide (O2(*-)) production in root apoplast decreased concomitantly with increase in superoxide dismutase (SOD) activity. In contrast, after 60 min of incubation, SOD decreased and this facilitated an increase in O2(*-) production. In the presence of the SOD inhibitor diethyldithiocarbamic acid, O2(*-) production was more than two times higher and showed a biphasic increase. Very high SOD activity in the apoplast, due to the presence of three different isozymes, one Mn-SOD and two CuZn-SODs, dismutated the radical giving rise, at least in part, to an increase in hydrogen peroxide. The highest value of H(2)O(2) was detected at 15 min, when peroxidase (POD) activity reached the lowest value. Root apoplast showed the presence of at least five different isoforms of PODs, whose pattern did not change during the entire treatment.