In-gel detection of urease with nitroblue tetrazolium and quantification of the enzyme from different crop plants using the indophenol reaction

Effect on N release by urea coating with chitosan, starch and urease inhibitor

Food production often relies on nitrogen fertilizers, which can harm the environment when dispersed in agroecosystems. A new urea coating additive, made from chitosan, starch, and N-(n-butyl) thiophosphoric triamide (a urease inhibitor), has been developed to mitigate these effects. The additive was tested for its impact on ammonium (NH4) production and urea release in water, characterized using Fourier transform infrared spectroscopy (FTIR), and subjected to bioassays on lettuce and rocket. The additive decreased the urea release rate in water by 12 %, as predicted by the Korsmeyer and Peppas model, indicating Fickian diffusion controlled by concentration gradients. FTIR analysis revealed that the interaction between chitosan's amine groups and urea's hydroxyl groups slowed the release. In lettuce and rocket, the additive enhanced root development, increasing surface area by 97 %, root volume by 100 %, and thin and thick root growth by 65 % and 131 %, respectively. After 24 h, the fertilizer produced less ammonium when in contact with urease. The production cost of this fertilizer was only 20 % higher than conventional fertilizers, showing that applying NBPT, starch, and chitosan to urea can reduce waste and improve key aspects of sustainable food production.

The Hormesis effect of cadmium on Panax notoginseng and corresponding impact on the rhizosphere microorganism

Panax notoginseng is a famous Chinese traditional medicinal. However, soil cadmium pollution seriously affected the yield and quality of notoginseng. This study systematically investigated the effects of soil Cd stress at different concentrations on the growth of one-year-old notoginseng. The results indicate that Cd exhibits a typical low-dose stimulation and high-dose inhibition effect on the development of notoginseng. At low concentrations (1 mg/kg), Cd promotes the growth of plants, including increased biomass (∼40 % of root dry weight) and higher saponin contents (∼30 % of total saponins). At high concentrations, Cd inhibits the overall growth and metabolism of notoginseng. Meanwhile, the impact of Cd on the rhizospheric micro-environment shows dose dependency. In a low Cd stress environment, the total and unique microbial populations increase, including Rhizobiaceae, Streptomycetaceae, and Mesorhizobium. Conversely, under strong Cd stress, the richness and diversity of the rhizospheric microbial community decrease, while the abundance of cadmium-tolerant species increases, such as Deinococcus and Rhodanobacter.

Biodegradation of phenol-contaminated soil and plant growth promotion by Myroides xuanwuensis H13

Physicochemical methods for remediating phenol-contaminated soils are costly and inefficient, making biodegradation an environmentally friendly alternative approach. This study aims to screen for potential phenol-degrading bacteria and to verify the removal capacities of a selected strain in a bioaugmentation experiment at the greenhouse level using Brassica chinensis L. (Chinese cabbage) as the model plant and phenol-contaminated soil. In parallel, pot experiments were conducted using a collaborative approach based on this model system. We found that Myroides xuanwuensis strain H13 showed a high degradation capability, with a 97.67% efficiency in degrading 100 mg/L phenol. Under shaking flask conditions, H13 facilitated the solubilization of tricalcium phosphate and potassium feldspar powder. Pot experiments suggested a phenol removal percentage of 89.22% and enhanced availability of soil phosphorus and potassium for plants with H13 inoculation. In this case, the abundance of soil microbes and the activity of soil enzymes significantly increased as well. Furthermore, both photosynthesis and the antioxidant system in Chinese cabbage were enhanced following H13 inoculation, resulting in its increased yield and quality. Partial least squares path modeling revealed that H13 can primarily affect plant root growth, with a secondary impact on photosynthesis. These findings highlight the potential of biodegradation from phenol-degrading bacteria as a promising strategy for efficient phenol removal from soil while promoting plant growth and health.IMPORTANCEThis study is significant for environmental remediation and agriculture by its exploration of a more environmentally friendly and cost-effective bio-strategy in treating phenol-contaminated soil. These findings have essential implications for environmental remediation efforts and sustainable agriculture. By utilizing the biodegradation capabilities of Myroides xuanwuensis strain H13, it is possible to remove phenol contaminants from the soil efficiently, reducing their negative effects. Furthermore, the enhanced growth and health of the Chinese cabbage plants indicate the potential of this approach to promote sustainable crop production.

Biodegradation of aliphatic polyurethane foams in soil: Influence of amide linkages and supramolecular structure

Polyurethane (PU) foams are classified as physically nonrecyclable thermosets. The current effort of sustainable and eco-friendly production makes it essential to explore methods of better waste management, for instance by modifying the structure of these frequently used polymers to enhance their microbial degradability. The presence of ester links is known to be a crucial prerequisite for the biodegradability of PU foams. However, the impact of other hydrolysable groups (urethane, urea and amide) occurred in PU materials, as well as the supramolecular structure of the PU network and the cellular morphology of PU foams, is still relatively unexplored. In this work, fully aliphatic PU foams with and without hydrolyzable amide linkages were prepared and their aerobic biodegradation was investigated using a six-month soil burial test. Besides the variable chemical composition of the PU foams, the influence of their different supramolecular arrangement and cellular morphologies on the extent of biodegradation was also evaluated. Throughout the soil burial test, the release of carbon dioxide, and enzyme activities of proteases, esterases, and ureases were measured. At the same time, phospho-lipid fatty acids (PLFA) analysis was conducted together with an assessment of microbial community composition achieved by analysing the genetic information from the 16S rRNA gene and ITS2 region sequencing. The results revealed a mineralization rate of 30-50 % for the PU foams, indicating a significant level of degradation as well as indicating that PU foams can be utilized by soil microorganisms as a source of both energy and nutrients. Importantly, microbial biomass remained unaffected, suggesting that there was no toxicity associated with the degradation products of the PU foams. It was further confirmed that ester linkages in PU foam structure were easily enzymatically cleavable, while amide linkages were not prone to degradation by soil microorganisms. In addition, it was shown that the presence of amide linkages in PU foam leads to a change in the supramolecular network arrangement due to increased content of hard segments, which in turn reduces the biodegradability of PU foam. These findings show that it is important to consider both chemical composition and supramolecular/macroscopic structure when designing new PU materials in an effort to develop environmentally friendly alternatives.

Exploring a high-urease activity Bacillus cereus for self-healing concrete via induced CaCO3 precipitation

The structural integrity and esthetic appeal of concrete can be compromised by concrete cracks. Promise has been shown by microbe-induced calcium carbonate precipitation (MICP) as a solution for concrete cracking, with a focus on urease-producing microorganisms in research. Bacillus cereus was isolated from soil and employed for this purpose in this study due to its high urease activity. The strain exhibited strong tolerance for alkaline media and high salt levels, which grew at a pH of 13 and 4% salt concentration. The repair of concrete cracks with this strain was evaluated by assessing the effects of four different thickeners at varying concentrations. The most effective results were achieved with 10 g/L of sodium carboxymethyl cellulose (CMC-Na). The data showed that over 90% repair of cracks was achieved by this system with an initial water penetration time of 30 s. The study also assessed the quantity and sizes of crystals generated during the bacterial mineralization process over time to improve our understanding of the process. KEY POINTS: • MICP using Bacillus cereus shows potential for repairing concrete cracks. • Strain tolerates alkaline media and high salt levels, growing at pH 13 and 4% salt concentration. • Sodium carboxymethyl cellulose (CMC-Na) at 10 g/L achieved over 90% repair of cracks.

Pyrimidine catabolism is required to prevent the accumulation of 5-methyluridine in RNA

5-Methylated cytosine is a frequent modification in eukaryotic RNA and DNA influencing mRNA stability and gene expression. Here we show that free 5-methylcytidine (5mC) and 5-methyl-2'-deoxycytidine are generated from nucleic acid turnover in Arabidopsis thaliana, and elucidate how these cytidines are degraded, which is unclear in eukaryotes. First CYTIDINE DEAMINASE produces 5-methyluridine (5mU) and thymidine which are subsequently hydrolyzed by NUCLEOSIDE HYDROLASE 1 (NSH1) to thymine and ribose or deoxyribose. Interestingly, far more thymine is generated from RNA than from DNA turnover, and most 5mU is directly released from RNA without a 5mC intermediate, since 5-methylated uridine (m5U) is an abundant RNA modification (m5U/U ∼1%) in Arabidopsis. We show that m5U is introduced mainly by tRNA-SPECIFIC METHYLTRANSFERASE 2A and 2B. Genetic disruption of 5mU degradation in the NSH1 mutant causes m5U to occur in mRNA and results in reduced seedling growth, which is aggravated by external 5mU supplementation, also leading to more m5U in all RNA species. Given the similarities between pyrimidine catabolism in plants, mammals and other eukaryotes, we hypothesize that the removal of 5mU is an important function of pyrimidine degradation in many organisms, which in plants serves to protect RNA from stochastic m5U modification.

Construction of a ratiometric fluorescent probe for visual detection of urea in human urine based on carbon dots prepared from Toona sinensis leaves and 5-carboxyfluorescein

In this work, pH-sensitive blue fluorescent carbon dots (CDs) with high fluorescence quantum yield (17.24%) were synthesized by hydrothermal method using Toona sinensis leaves and ethylenediamine (EDA) as raw materials. The CDs can detect urea with a limit of detection (LOD) of 6.700 mmol L^-1. For more sensitive detection of urea, we constructed a ratiometric fluorescent probe (CDs@5-FAM) using CDs and 5-carboxyfluorescein (5-FAM). The CDs@5-FAM probe can rapidly and sensitively detect urea according to the changes of I₅₁₄/I₄₀₅, with LOD as low as 0.014 mmol L^-1. Furthermore, with the help of a smartphone and RGB analysis software, urea's visual intelligent detection was realized using a CDs@5-FAM probe. The method proposed in this paper is consistent with the standard method, which indicates that the pH-sensitive ratiometric fluorescent probe CDs@5-FAM is accurate and reliable for practical application. It provides a new way for rapid and visual detection of urea.

Biodegradable microplastics impact the uptake of Cd in rice: The roles of niche breadth and assembly process

Biodegradable microplastics (MPs) can impact the accumulation of cadmium (Cd) by plants, however, its mechanisms have not been fully understood. In this study, two biodegradable MPs, polypropylene carbonate (PPC) and polylactic acid (PLA), were used to examine their influences on the uptake of Cd in rice plants. Results showed that PPC significantly reduced the accumulation of Cd in rice root and aerial part, whereas PLA increased the Cd concentrations in rice root. The random forest analysis revealed that the bacterial biomarkers enriched by two MPs were different at genus level. Niche breadths were significantly reduced under Cd stress, and PPC alleviated this environmental pressure for entire bacterial community, whereas PLA reduced the niche breadth for whole community and abundant taxa, which was further verified by co-occurrence network and normalized stochasticity ratio model. The abundant taxa of group PPC were primarily governed by deterministic process while rare taxa were more driven by stochastic process. Structural equation model and Mantel analysis identified that the niche breadth imposed a strong selection on Cd accumulation after co-exposure. This study reveals the underlying mechanism of assembly process and niche breadth of rice rhizosphere microbiome on Cd accumulation by rice plants.

Strain Screening and Particle Formation: a Lysinibacillus boronitolerans for Self-Healing Concrete

Microbial-induced calcite precipitation is a promising technology to solve the problem of cracks in soil concrete. The most intensively investigated microorganisms are urease-producing bacteria. Lysinibacillus that is used as urease-producing bacteria in concrete repair has rarely been reported. In this study, Lysinibacillus boronitolerans with a high urease activity was isolated from soil samples. This strain is salt- and alkali-tolerance, and at pH 13, can grow to ~OD₆₀₀ 2.0 after 24 h. At a salt concentration of 6%, the strain can still grow to ~OD₆₀₀ 1.0 after 24 h. The feasibility of using this strain in self-healing concrete was explored. The data showed that cracks within ~0.6 mm could be repaired naturally with hydration when spores and substrates were added to the concrete in an appropriate proportion. Moreover, the number and morphology of CaCO₃ crystals that were produced by bacteria can be influenced by the concrete environment. An efficiency method to elucidate the process of microbial-induced calcium carbonate crystal formation was established with Particle Track G400. This study provides a template for future studies on the theory of mineralization based on microorganisms. IMPORTANCE The formation of calcium carbonate crystals in concrete by urease-producing bacteria is not understood fully. In this study, a Lysinibacillus boronitolerans strain with a high urease activity was isolated and used to analyze the counts and sizes of the crystals and the relationship with time. The data showed that the number of crystal particles increases exponentially in a short period with sufficient substrate, after which the crystals grow, precipitate or break. In concrete, the rate-limiting steps of calcium carbonate crystal accumulation are spore germination and urease production. These results provided data support for the rational design of urease-producing bacteria in concrete repair.

Concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities during Impranil biodegradation by Alicycliphilus denitrificans BQ1

The concerted action of commercial esterases, proteases and amidases has been demonstrated to be relevant in polyurethane (PU) degradation by in vitro experiments. However, the spatial and temporal dynamics of these activities during PU biodegradation by PU-degrading bacteria have not been addressed. Here, we examined the capability of Alicycliphilus denitrificans BQ1 to biodegrade the polyester (PS)-PU Impranil, analyzed the temporal and spatial coordination between the extracellular and cytoplasmic esterase and urethane-cleaving activities, and their independent and combined effects on Impranil biodegradation. A. denitrificans BQ1 grew in Impranil, and its clearing was correlated with the cleavage of ester and urethane groups since early times, with decrements of some Impranil compounds and the appearance of biodegradation products. While extracellular esterase was active at early times with its maximum at 18 h, urethanase appeared at this time and increased up to the end of the analysis (48 h), with the cytoplasmic activities behaving similarly but with lower levels than the extracellular ones. Both enzymatic activities exhibited distinct substrate specificity depending on their cellular localization and cultivation times, suggesting they cleave differentially located groups. As the urethane cleavage occurred since early times, when no urethane-cleaving activity was detected, different proteins should be acting at early and late times. In vitro experiments with independent or combined cellular protein fractions supported the previous deduction and confirmed the concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities. A two-stage process for Impranil degradation by A. denitrificans BQ1 is proposed.

Smartphone-assisted point-of-care colorimetric biosensor for the detection of urea via pH-mediated AgNPs growth

Smartphone-assisted point-of-care (POC) bioassay has brought a giant leap in personal healthcare system and environmental monitoring advancements. In this study, we developed a rapid and reliable colorimetric urea biosensor assisted by a smartphone. We employed hydrolysis of urea into NH₃ by urease, which activates the reduction power of tannic acid, to generate silver nanoparticles for a dramatic colorimetric response. The proposed urea biosensor was validated in a solution to provide high selectivity against various interferents in human urine. It had high sensitivity, with a limit of detection as low as 0.0036 mM, and a high reliability of 99% ± 2.9% via the standard addition method. The urea biosensor was successfully implanted on a paper to facilitate smartphone-assisted POC readout with a limit of detection of 0.58 mM and wide detection range of 500 mM, whereby direct diagnosis of human urine without dilution was realized. Our smartphone-assisted POC colorimetric urea biosensor will pave the way for daily monitoring systems of renal and hepatic dysfunction diseases.

Urease activity according to the different inhibitors

The objective of this study was to evaluate NBPT, zeolite and humic acid in different concentrations as inhibitors of the activity of the enzyme urease. The activity of the urease enzyme was quantified by the methods proposed by May and Douglas (1976) and Witte and Medina-Escobar (2001). For this reason, two experiments were conducted in a completely randomized design in split plots, in which the incubation periods are the plots and the fertilizers with the inhibitors at the different concentrations are the subplots with three replications. Fifteen fertilizers based on NBPT-coated urea, humic acid and zeolite were used in different concentrations. The two methods of analysis used in the experiment confirmed the efficiency of NBPT in inhibiting the enzymatic action even at low concentration, with 0.02% (m/m) being sufficient to inhibit urease, with no difference between inhibitor concentrations. The addition of humic acid reduced the activity of urease after 36 hours of reaction when the activity of the enzyme was evaluated by the method proposed by May and Douglas (1976). Zeolite did not influence the activity of the urease enzyme when analyzed by the May and Douglas method (1976).

Coprophagous features in carnivorous Nepenthes plants: a task for ureases

Most terrestrial carnivorous plants are specialized on insect prey digestion to obtain additional nutrients. Few species of the genus Nepenthes developed mutualistic relationships with mammals for nitrogen supplementation. Whether dietary changes require certain enzymatic composition to utilize new sources of nutrients has rarely been tested. Here, we investigated the role of urease for Nepenthes hemsleyana that gains nitrogen from the bat Kerivoula hardwickii while it roosts inside the pitchers. We hypothesized that N. hemsleyana is able to use urea from the bats’ excrements. In fact, we demonstrate that ¹⁵N-enriched urea provided to Nepenthes pitchers is metabolized and its nitrogen is distributed within the plant. As ureases are necessary to degrade urea, these hydrolytic enzymes should be involved. We proved the presence and enzymatic activity of a urease for Nepenthes plant tissues. The corresponding urease cDNA from N. hemsleyana was isolated and functionally expressed. A comprehensive phylogenetic analysis for eukaryotic ureases, including Nepenthes and five other carnivorous plants’ taxa, identified them as canonical ureases and reflects the plant phylogeny. Hence, this study reveals ureases as an emblematic example for an efficient, low-cost but high adaptive plasticity in plants while developing a further specialized lifestyle from carnivory to coprophagy.

The assembly of the plant urease activation complex and the essential role of the urease accessory protein G (UreG) in delivery of nickel to urease

Urease is a ubiquitous nickel metalloenzyme. In plants, its activation requires three urease accessory proteins (UAPs), UreD, UreF, and UreG. In bacteria, the UAPs interact with urease and facilitate activation, which involves the channeling of two nickel ions into the active site. So far this process has not been investigated in eukaryotes. Using affinity pulldowns of Strep-tagged UAPs from Arabidopsis and rice transiently expressed in planta, we demonstrate that a urease-UreD-UreF-UreG complex exists in plants and show its stepwise assembly. UreG is crucial for nickel delivery because UreG-dependent urease activation in vitro was observed only with UreG obtained from nickel-sufficient plants. This activation competence could not be generated in vitro by incubation of UreG with nickel, bicarbonate, and GTP. Compared with their bacterial orthologs, plant UreGs possess an N-terminal extension containing a His- and Asp/Glu-rich hypervariable region followed by a highly conserved sequence comprising two potential HXH metal-binding sites. Complementing the ureG-1 mutant of Arabidopsis with N-terminal deletion variants of UreG demonstrated that the hypervariable region has a minor impact on activation efficiency, whereas the conserved region up to the first HXH motif is highly beneficial and up to the second HXH motif strictly required for activation. We also show that urease reaches its full activity several days after nickel becomes available in the leaves, indicating that urease activation is limited by nickel accessibility in vivo Our data uncover the crucial role of UreG for nickel delivery during eukaryotic urease activation, inciting further investigations of the details of this process.

Biodegradative Activities of Selected Environmental Fungi on a Polyester Polyurethane Varnish and Polyether Polyurethane Foams

Polyurethane (PU) is widely used in many aspects of modern life because of its versatility and resistance. However, PU waste disposal generates large problems, since it is slowly degraded, there are limited recycling processes, and its destruction may generate toxic compounds. In this work, we isolated fungal strains able to grow in mineral medium with a polyester PU (PS-PU; Impranil DLN) or a polyether PU (PE-PU; Poly Lack) varnish as the only carbon source. Of the eight best Impranil-degrading strains, the six best degraders belonged to the Cladosporium cladosporioides complex, including the species C. pseudocladosporioides, C. tenuissimum, C. asperulatum, and C. montecillanum, and the two others were identified as Aspergillus fumigatus and Penicillium chrysogenum The best Impranil degrader, C. pseudocladosporioides strain T1.PL.1, degraded up to 87% after 14 days of incubation. Fourier transform infrared (FTIR) spectroscopy analysis of Impranil degradation by this strain showed a loss of carbonyl groups (1,729 cm(-1)) and N-H bonds (1,540 and 1,261 cm(-1)), and gas chromatography-mass spectrometry (GC-MS) analysis showed a decrease in ester compounds and increase in alcohols and hexane diisocyanate, indicating the hydrolysis of ester and urethane bonds. Extracellular esterase and low urease, but not protease activities were detected at 7 and 14 days of culture in Impranil. The best eight Impranil-degrading fungi were also able to degrade solid foams of the highly recalcitrant PE-PU type to different extents, with the highest levels generating up to 65% of dry-weight losses not previously reported. Scanning electron microscopy (SEM) analysis of fungus-treated foams showed melted and thinner cell wall structures than the non-fungus-treated ones, demonstrating fungal biodegradative action on PE-PU.

IMPORTANCE

Polyurethane waste disposal has become a serious problem. In this work, fungal strains able to efficiently degrade different types of polyurethanes are reported, and their biodegradative activity was studied by different experimental approaches. Varnish biodegradation analyses showed that fungi were able to break down the polymer in some of their precursors, offering the possibility that they may be recovered and used for new polyurethane synthesis. Also, the levels of degradation of solid polyether polyurethane foams reported in this work have never been observed previously. Isolation of efficient polyurethane-degrading microorganisms and delving into the mechanisms they used to degrade the polymer provide the basis for the development of biotechnological processes for polyurethane biodegradation and recycling.

Molecular docking of Glycine max and Medicago truncatula ureases with urea; bioinformatics approaches

Urease (EC 3.5.1.5) is a nickel-dependent metalloenzyme catalyzing the hydrolysis of urea into ammonia and carbon dioxide. It is present in many bacteria, fungi, yeasts and plants. Most species, with few exceptions, use nickel metalloenzyme urease to hydrolyze urea, which is one of the commonly used nitrogen fertilizer in plant growth thus its enzymatic hydrolysis possesses vital importance in agricultural practices. Considering the essentiality and importance of urea and urease activity in most plants, this study aimed to comparatively investigate the ureases of two important legume species such as Glycine max (soybean) and Medicago truncatula (barrel medic) from Fabaceae family. With additional plant species, primary and secondary structures of 37 plant ureases were comparatively analyzed using various bioinformatics tools. A structure based phylogeny was constructed using predicted 3D models of G. max and M. truncatula, whose crystallographic structures are not available, along with three additional solved urease structures from Canavalia ensiformis (PDB: 4GY7), Bacillus pasteurii (PDB: 4UBP) and Klebsiella aerogenes (PDB: 1FWJ). In addition, urease structures of these species were docked with urea to analyze the binding affinities, interacting amino acids and atom distances in urease-urea complexes. Furthermore, mutable amino acids which could potentially affect the protein active site, stability and flexibility as well as overall protein stability were analyzed in urease structures of G. max and M. truncatula. Plant ureases demonstrated similar physico-chemical properties with 833-878 amino acid residues and 89.39-90.91 kDa molecular weight with mainly acidic (5.15-6.10 pI) nature. Four protein domain structures such as urease gamma, urease beta, urease alpha and amidohydro 1 characterized the plant ureases. Secondary structure of plant ureases also demonstrated conserved protein architecture, with predominantly α-helix and random coil structures. In structure-based phylogeny, plant ureases from G. max, M. truncatula and C. ensiformis were clearly diverged from bacterial ureases of B. pasteurii and K. aerogenes. Glu, Thr, His and Gly were commonly found as interacting residues in most urease-urea docking complexes while Glu was available in all docked structures. Besides, Ala and Arg residues, which are reported in active-site architecture of plant and bacterial ureases were present in G. max urea-urease complex but not present in others. Moreover, Arg435 and Arg437 in M. truncatula and G. max, respectively were identified as highly mutable hotspot residues residing in amidohydro 1 domain of enzyme. In addition, a number of stabilizing residues were predicted upon mutation of these hotspot residues however Cys and Thr made strong implications since they were also found in codon-aligned sequences as substitutions of hotspot residues. Comparative analyses of primary sequence and secondary structure in 37 different plants demonstrated quite conserved natures of ureases in plant kingdom. Structure-based phylogeny indicated the presence of a possible prokaryote-eukaryote split and implicated the subjection of bacterial ureases to heavy selection in prokaryotic evolution compared to plants. Urea-urease docking complexes suggested that different species could share common interacting residues as well as may have some other uncommon residues at species-dependent way. In silico mutation analyses identified mutable amino acids, which were predicted to reside in catalytic site of enzyme therefore mutagenesis at these sites seemed to have adverse effects on enzyme efficiency or function. This study findings will become valuable preliminary resource for future studies to further understand the primary, secondary and tertiary structures of urease sequences in plants as well as it will provide insights about various binding features of urea-urease complexes.

Deciphering the mechanisms involved in Portulaca oleracea (C4) response to drought: metabolic changes including crassulacean acid-like metabolism induction and reversal upon re-watering

Portulaca oleracea is a C(4) plant; however, under drought it can change its carbon fixation metabolism into a crassulacean acid metabolism (CAM)-like one. While the C(3) -CAM shift is well known, the C(4) -CAM transition has only been described in Portulaca. Here, a CAM-like metabolism was induced in P. oleracea by drought and then reversed by re-watering. Physiological and biochemical approaches were undertaken to evaluate the drought and recovery responses. In CAM-like plants, chlorophyll fluorescence parameters were transitory affected and non-radiative energy dissipation mechanisms were induced. Induction of flavonoids, betalains and antioxidant machinery may be involved in photosynthetic machinery protection. Metabolic analysis highlights a clear metabolic shift, when a CAM-like metabolism is induced and then reversed. Increases in nitrogenous compounds like free amino acids and urea, and of pinitol could contribute to withstand drought. Reciprocal variations in arginase and urease in drought-stressed and in re-watered plants suggest urea synthesis is strictly regulated. Recovery of C(4) metabolism was accounted by CO(2) assimilation pattern and malate levels. Increases in glycerol and in polyamines would be of importance of re-watered plants. Collectively, in P. oleracea multiple strategies, from induction of several metabolites to the transitory development of a CAM-like metabolism, participate to enhance its adaptation to drought.

Molecular and functional characterization of allantoate amidohydrolase from Phaseolus vulgaris

Allantoate degradation is an essential step for recycling purine-ring nitrogen in all plants, but especially in tropical legumes where the ureides allantoate and allantoin are the main compounds used to store and transport the nitrogen fixed in nodules. Two enzymes, allantoate amidohydrolase (AAH) and allantoate amidinohydrolase (allantoicase), could catalyze allantoate breakdown, although only AAH-coding sequences have been found in plant genomes, whereas allantoicase-related sequences are restricted to animals and some microorganisms. A cDNA for AAH was cloned from Phaseolus vulgaris leaves. PvAAH is a single-copy gene encoding a polypeptide of 483 amino acids that conserves all putative AAH active-site domains. Expression and purification of the cDNA in Nicotiana benthamiana showed that the cloned sequence is a true AAH protein that yields ureidoglycine and ammonia, with a Km of 0.46 mM for allantoate. Optimized in vitro assay, quantitative RT-PCR and antibodies raised to the PvAAH protein were used to study AAH under physiological conditions. PvAAH is ubiquitously expressed in common bean tissues, although the highest transcript levels were found in leaves. In accordance with the mRNA expression levels, the highest PvAAH activity and allantoate concentration also occurred in the leaves. Comparison of transcript levels, protein amounts and enzymatic activity in plants grown with different nitrogen sources and upon drought stress conditions showed that PvAAH is regulated at posttranscriptional level. Moreover, RNAi silencing of AAH expression increases allantoate levels in the transgenic hairy roots, indicating that AAH should be the main enzyme involved in allantoate degradation in common bean.

BASIC AMINO ACID CARRIER 2 gene expression modulates arginine and urea content and stress recovery in Arabidopsis leaves

In plants, basic amino acids are important for the synthesis of proteins and signaling molecules and for nitrogen recycling. The Arabidopsis nuclear gene BASIC AMINO ACID CARRIER 2 (BAC2) encodes a mitochondria-located carrier that transports basic amino acids in vitro. We present here an analysis of the physiological and genetic function of BAC2 in planta. When BAC2 is overexpressed in vivo, it triggers catabolism of arginine, a basic amino acid, leading to arginine depletion and urea accumulation in leaves. BAC2 expression was known to be strongly induced by stress. We found that compared to wild type plants, bac2 null mutants (bac2-1) recover poorly from hyperosmotic stress when restarting leaf expansion. The bac2-1 transcriptome differs from the wild-type transcriptome in control conditions and under hyperosmotic stress. The expression of genes encoding stress-related transcription factors (TF), arginine metabolism enzymes, and transporters is particularly disturbed in bac2-1, and in control conditions, the bac2-1 transcriptome has some hallmarks of a wild-type stress transcriptome. The BAC2 carrier is therefore involved in controlling the balance of arginine and arginine-derived metabolites and its associated amino acid metabolism is physiologically important in equipping plants to respond to and recover from stress.

Comparison of inhibition of N2 fixation and ureide accumulation under water deficit in four common bean genotypes of contrasting drought tolerance

BACKGROUND AND AIMS

Drought is the principal constraint on world production of legume crops. There is considerable variability among genotypes in sensitivity of nitrogen fixation to drought, which has been related to accumulation of ureides in soybean. The aim of this study was to search for genotypic differences in drought sensitivity and ureide accumulation in common bean (Phaseolus vulgaris) germplasm that may be useful in the improvement of tolerance to water deficit in common bean.

METHODS

Changes in response to water deficit of nitrogen fixation rates, ureide content and the expression and activity of key enzymes for ureide metabolism were measured in four P. vulgaris genotypes differing in drought tolerance.

KEY RESULTS

A variable degree of drought-induced nitrogen fixation inhibition was found among the bean genotypes. In addition to inhibition of nitrogen fixation, there was accumulation of ureides in stems and leaves of sensitive and tolerant genotypes, although this was higher in the leaves of the most sensitive ones. In contrast, there was no accumulation of ureides in the nodules or roots of stressed plants. In addition, the level of ureides in the most sensitive genotype increased after inhibition of nitrogen fixation, suggesting that ureides originate in vegetative tissues as a response to water stress, probably mediated by the induction of allantoinase.

CONCLUSIONS

Variability of drought-induced inhibition of nitrogen fixation among the P. vulgaris genotypes was accompanied by subsequent accumulation of ureides in stems and leaves, but not in nodules. The results indicate that shoot ureide accumulation after prolonged exposure to drought could not be the cause of inhibition of nitrogen fixation, as has been suggested in soybean. Instead, ureides seem to be produced as part of a general response to stress, and therefore higher accumulation might correspond to higher sensitivity to the stressful conditions.

Nickel affects xylem Sap RNase a and converts RNase A to a urease

BACKGROUND

Nickel (Ni) is an essential micronutrient; however, its metabolic or physiological functions in plants and animals are largely uncharacterized. The ribonucleases (RNase, e.g., RNase A) are a large family of hydrolases found in one form or many forms facilitating nitrogen (N) cycling. It is currently unknown how either a deficiency or excess of Ni influences the functionality of ribonucleases, like RNase A. This is especially true for perennial crops possessing relatively high Ni requirements.

RESULTS

We report that the 'rising' xylem sap of pecan [Carya illinoinensis (Wangenh.) K. Koch, a long-lived tree] at bud break contains a 14 kDa RNase A (aka, RNase 1), which amount has a 33% greater in Ni-deficient as in Ni-sufficient trees when exposed to Ni ions exhibits ureolytic activity. The homologous 13.4 kDa bovine pancreatic RNase A likewise exhibits ureolytic activity upon exposure to Ni ions. Ni therefore affects enzymatic function of a typically non-metalloenzyme, such as it transforms to an enzyme capable of hydrolyzing a linear amide; thus, converting an endonuclease esterase into a urease.

CONCLUSIONS

We conclude that Ni potentially affects the level and activity of RNase A present in the spring xylem sap of pecan trees, and probably in other crops, it has the same influence. The catalytic property of RNase A appears to shift from a nuclease to a urease relying on Ni exposure. This is suggestive that RNase A might possess novel metabolic functionality regarding N-metabolism in perennial plants. The ability of Ni to convert the activity of plant and animal RNase A from that of a ribonuclease to a urease indicates a possible unrecognized beneficial metabolic function of Ni in organisms, while also identifying a potential detrimental effect of excessive Ni on N related metabolic activity if there is sufficient disruption of Ni homeostasis.

Factors required for activation of urease as a virulence determinant in Cryptococcus neoformans

Urease in Cryptococcus neoformans plays an important role in fungal dissemination to the brain and causing meningoencephalitis. Although urea is not required for synthesis of apourease encoded by URE1, the available nitrogen source affected the expression of URE1 as well as the level of the enzyme activity. Activation of the apoenzyme requires three accessory proteins, Ure4, Ure6, and Ure7, which are homologs of the bacterial urease accessory proteins UreD, UreF, and UreG, respectively. A yeast two-hybrid assay showed positive interaction of Ure1 with the three accessory proteins encoded by URE4, URE6, and URE7. Metalloproteomic analysis of cryptococcal lysates using inductively coupled plasma mass spectrometry (ICP-MS) and a biochemical assay of urease activity showed that, as in many other organisms, urease is a metallocentric enzyme that requires nickel transported by Nic1 for its catalytic activity. The Ure7 accessory protein (bacterial UreG homolog) binds nickel likely via its conserved histidine-rich domain and appears to be responsible for the incorporation of Ni²⁺ into the apourease. Although the cryptococcal genome lacks the bacterial UreE homolog, Ure7 appears to combine the functions of bacterial UreE and UreG, thus making this pathogen more similar to that seen with the plant system. Brain invasion by the ure1, ure7, and nic1 mutant strains that lack urease activity was significantly less effective in a mouse model. This indicated that an activated urease and not the Ure1 protein was responsible for enhancement of brain invasion and that the factors required for urease activation in C. neoformans resemble those of plants more than those of bacteria.

Cryptococcus neoformans is the major fungal agent of meningoencephalitis in humans. Although urease is an important factor for cryptococcal brain invasion, the enzyme activation system has not been studied. We show that urease is a nickel-requiring enzyme whose activity level is influenced by the type of available nitrogen source. C. neoformans contains all the bacterial urease accessory protein homologs and nickel transporters except UreE, a nickel chaperone. Cryptococcal Ure7 (a homolog of UreG) apparently functions as both the bacterial UreG and UreE in activating the Ure1 apoenzyme. The cryptococcal urease accessory proteins Ure4, Ure6, and Ure7 interacted with Ure1 in a yeast two-hybrid assay, and deletion of any one of these not only inactivated the enzyme but also reduced the efficacy of brain invasion. This is the first study showing a holistic picture of urease in fungi, clarifying that urease activity, and not Ure1 protein, contributes to pathogenesis in C. neoformans

The physiological implications of urease inhibitors on N metabolism during germination of Pisum sativum and Spinacea oleracea seeds

The development of new nitrogen fertilizers is necessary to optimize crop production whilst improving the environmental aspects arising from the use of nitrogenous fertilization as a cultural practice. The use of urease inhibitors aims to improve the efficiency of urea as a nitrogen fertilizer by preventing its loss from the soil as ammonia. However, although the action of urease inhibitors is aimed at the urease activity in soil, their availability for the plant may affect its urease activity. The aim of this work was therefore to evaluate the effect of two urease inhibitors, namely acetohydroxamic acid (AHA) and N-(n-butyl) thiophosphoric triamide (NBPT), on the germination of pea and spinach seeds. The results obtained show that urease inhibitors do not affect the germination process to any significant degree, with the only process affected being imbibition in spinach, thus also suggesting different urease activities for both plants. Our findings therefore suggest an activity other than the previously reported urolytic activity for urease in spinach. Furthermore, of the two inhibitors tested, NBPT was found to be the most effective at inhibiting urease activity, especially in pea seedlings.

Carbon availability triggers fungal nitrogen uptake and transport in arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) symbiosis, formed between the majority of land plants and ubiquitous soil fungi of the phylum Glomeromycota, is responsible for massive nutrient transfer and global carbon sequestration. AM fungi take up nutrients from the soil and exchange them against photosynthetically fixed carbon (C) from the host. Recent studies have demonstrated that reciprocal reward strategies by plant and fungal partners guarantee a "fair trade" of phosphorus against C between partners [Kiers ET, et al. (2011) Science 333:880-882], but whether a similar reward mechanism also controls nitrogen (N) flux in the AM symbiosis is not known. Using mycorrhizal root organ cultures, we manipulated the C supply to the host and fungus and followed the uptake and transport of N sources in the AM symbiosis, the enzymatic activities of arginase and urease, and fungal gene expression in the extraradical and intraradical mycelium. We found that the C supply of the host plant triggers the uptake and transport of N in the symbiosis, and that the increase in N transport is orchestrated by changes in fungal gene expression. N transport in the symbiosis is stimulated only when the C is delivered by the host across the mycorrhizal interface, not when C is supplied directly to the fungal extraradical mycelium in the form of acetate. These findings support the importance of C flux from the root to the fungus as a key trigger for N uptake and transport and provide insight into the N transport regulation in the AM symbiosis.

Short term physiological implications of NBPT application on the N metabolism of Pisum sativum and Spinacea oleracea

The application of urease inhibitors in conjunction with urea fertilizers as a means of reducing N loss due to ammonia volatilization requires an in-depth study of the physiological effects of these inhibitors on plants. The aim of this study was to determine how the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) affects N metabolism in pea and spinach. Plants were cultivated in pure hydroponic culture with urea as the sole N source. After 2 weeks of growth for pea, and 3 weeks for spinach, half of the plants received NBPT in their nutrient solution. Urease activity, urea and ammonium content, free amino acid composition and soluble protein were determined in leaves and roots at days 0, 1, 2, 4, 7 and 9, and the NBPT content in these tissues was determined 48h after inhibitor application. The results suggest that the effects of NBPT on spinach and pea urease activity differ, with pea being most affected by this treatment, and that the NBPT absorbed by the plant caused a clear inhibition of the urease activity in pea leaf and roots. The high urea concentration observed in leaves was associated with the development of necrotic leaf margins, and was further evidence of NBPT inhibition in these plants. A decrease in the ammonium content in roots, where N assimilation mainly takes place, was also observed. Consequently, total amino acid contents were drastically reduced upon NBPT treatment, indicating a strong alteration of the N metabolism. Furthermore, the amino acid profile showed that amidic amino acids were major components of the reduced pool of amino acids. In contrast, NBPT was absorbed to a much lesser degree by spinach plants than pea plants (35% less) and did not produce a clear inhibition of urease activity in this species.

Urea metabolism in plants

Urea is a plant metabolite derived either from root uptake or from catabolism of arginine by arginase. In agriculture, urea is intensively used as a nitrogen fertilizer. Urea nitrogen enters the plant either directly, or in the form of ammonium or nitrate after urea degradation by soil microbes. In recent years various molecular players of plant urea metabolism have been investigated: active and passive urea transporters, the nickel metalloenzyme urease catalyzing the hydrolysis of urea, and three urease accessory proteins involved in the complex activation of urease. The degradation of ureides derived from purine breakdown has long been discussed as a possible additional metabolic source for urea, but an enzymatic route for the complete hydrolysis of ureides without a urea intermediate has recently been described for Arabidopsis thaliana. This review focuses on the proteins involved in plant urea metabolism and the metabolic sources of urea but also addresses open questions regarding plant urea metabolism in a physiological and agricultural context. The contribution of plant urea uptake and metabolism to fertilizer urea usage in crop production is still not investigated although globally more than half of all nitrogen fertilizer is applied to crops in the form of urea. Nitrogen use efficiency in crop production is generally well below 50% resulting in economical losses and creating ecological problems like groundwater pollution and emission of nitric oxides that can damage the ozone layer and function as greenhouse gasses. Biotechnological approaches to improve fertilizer urea usage bear the potential to increase crop nitrogen use efficiency.

Identification and characterization of proteins involved in rice urea and arginine catabolism

Rice (Oryza sativa) production relies strongly on nitrogen (N) fertilization with urea, but the proteins involved in rice urea metabolism have not yet been characterized. Coding sequences for rice arginase, urease, and the urease accessory proteins D (UreD), F (UreF), and G (UreG) involved in urease activation were identified and cloned. The functionality of urease and the urease accessory proteins was demonstrated by complementing corresponding Arabidopsis (Arabidopsis thaliana) mutants and by multiple transient coexpression of the rice proteins in Nicotiana benthamiana. Secondary structure models of rice (plant) UreD and UreF proteins revealed a possible functional conservation to bacterial orthologs, especially for UreF. Using amino-terminally StrepII-tagged urease accessory proteins, an interaction between rice UreD and urease could be shown. Prokaryotic and eukaryotic urease activation complexes seem conserved despite limited protein sequence conservation for UreF and UreD. In plant metabolism, urea is generated by the arginase reaction. Rice arginase was transiently expressed as a carboxyl-terminally StrepII-tagged fusion protein in N. benthamiana, purified, and biochemically characterized (K(m) = 67 mm, k(cat) = 490 s(-1)). The activity depended on the presence of manganese (K(d) = 1.3 microm). In physiological experiments, urease and arginase activities were not influenced by the external N source, but sole urea nutrition imbalanced the plant amino acid profile, leading to the accumulation of asparagine and glutamine in the roots. Our data indicate that reduced plant performance with urea as N source is not a direct result of insufficient urea metabolism but may in part be caused by an imbalance of N distribution.

Nitrate modifies the assimilation pattern of ammonium and urea in wheat seedlings

BACKGROUND

In certain plant species, ammonium or urea nutrition can cause negative effects on plant development which can result in toxic symptoms. Some authors suggest that the presence of nitrate can alleviate these symptoms by increasing ammonium and urea assimilation, avoiding its accumulation. In order to study this hypothesis, wheat (Triticum aestivum L.) seedlings were grown with various nitrogen supplies containing the main nitrogen forms (ammonium, nitrate and urea). Amino acids content and the activity of the three main enzymes involved in nitrogen assimilation (nitrate reductase, glutamine synthetase and urease) were studied.

RESULTS

The application of nitrate along with urea and/or ammonium was not associated with a time-sustained increase in the activity of glutamine synthetase and urease. Amino acid analysis revealed that nitrate induced changes in amino acid metabolism enhancing its concentration. Likewise the content of protein was also higher in nitrate-treated plants.

CONCLUSION

These results suggest that the effect of nitrate is compatible with a rapid and transient increase in the activity of glutamine synthetase and urease during the first hour after the onset of treatments. Nevertheless, a possible effect of nitrate reducing ammonium accumulation through the activation of alternative metabolic pathways different from that involving glutamine synthetase cannot be ruled out. Finally, nitrate effects on amino acid concentration indicate that, whereas ammonium assimilation takes place principally in the root, urea and nitrate assimilation occurred in the shoot, under the conditions of the experiment.

Silver(I) ions ultrasensitive detection at carbon electrodes-analysis of waters, tobacco cells and fish tissues

We used carbon paste electrodes and a standard potentiostat to detect silver ions. The detection limit (3 Signal/Noise ratio) was estimated as 0.5 μM. A standard electrochemical instrument microanalysis of silver(I) ions was suggested. As a working electrode a carbon tip (1 mL) or carbon pencil was used. Limits of detection estimated by dilution of a standard were 1 (carbon tip) or 10 nM (carbon pencil). Further we employed flow injection analysis coupled with carbon tip to detect silver(I) ions released in various beverages and mineral waters. During first, second and third week the amount of silver(I) ions releasing into water samples was under the detection limit of the technique used for their quantification. At the end of a thirteen weeks long experiment the content of silver(I) ions was several times higher compared to the beginning of release detected in the third week and was on the order of tens of nanomoles. In subsequent experiments the influence of silver(I) ions (0, 5 and 10 μM) on a plant model system (tobacco BY-2 cells) during a four-day exposition was investigated. Silver(I) ions were highly toxic to the cells, which was revealed by a double staining viability assay. Moreover we investigated the effect of silver(I) ions (0, 0.3, 0.6, 1.2 and 2.5 μM) on guppies (Poecilia reticulata). Content of Ag(I) increased with increasing time of the treatment and applied concentrations in fish tissues. It can be concluded that a carbon tip or carbon pencil coupled with a miniaturized potentiostat can be used for detection of silver(I) ions in environmental samples and thus represents a small, portable, low cost and easy-to-use instrument for such purposes.

Sunflower Plants as Bioindicators of Environmental Pollution with Lead (II) Ions

In this study, the influence of lead (II) ions on sunflower growth and biochemistry was investigated from various points of view. Sunflower plants were treated with 0, 10, 50, 100 and/or 500 μM Pb-EDTA for eight days. We observed alterations in growth in all experimental groups compared with non-treated control plants. Further we determined total content of proteins by a Bradford protein assay. By the eighth day of the experiment, total protein contents in all treated plants were much lower compared to control. Particularly noticeable was the loss of approx. 8 μg/mL or 15 μg/mL in shoots or roots of plants treated with 100 mM Pb-EDTA. We also focused our attention on the activity of alanine transaminase (ALT), aspartate transaminase (AST) and urease. Activity of the enzymes increased with increasing length of the treatment and applied concentration of lead (II) ions. This increase corresponds well with a higher metabolic activity of treated plants. Contents of cysteine, reduced glutathione (GSH), oxidized glutathione (GSSG) and phytochelatin 2 (PC2) were determined by high performance liquid chromatography with electrochemical detection. Cysteine content declined in roots of plants with the increasing time of treatment of plants with Pb-EDTA and the concentration of toxic substance. Moreover, we observed ten times higher content of cysteine in roots in comparison with shoots. The observed reduction of cysteine content probably relates with its utilization for biosynthesis of GSH and phytochelatins, because the content of GSH and PC2 was similar in roots and shoots and increased with increased treatment time and concentration of Pb-EDTA. Moreover, we observed oxidative stress caused by Pb-EDTA in roots where the GSSG/GSH ratio was about 0.66. In shoots, the oxidative stress was less distinctive, with a GSSG/GSH ratio 0.14. We also estimated the rate of phytochelatin biosynthesis from the slope of linear equations plotted with data measured in the particular experimental group. The highest rate was detected in roots treated with 100 μM of Pb-EDTA. To determine heavy metal ions many analytical instruments can be used, however, most of them are only able to quantify total content of the metals. This problem can be overcome using laser induced breakdown spectroscopy, because it is able to provide a high spatial-distribution of metal ions in different types of materials, including plant tissues. Data obtained were used to assemble 3D maps of Pb and Mg distribution. Distribution of these elements is concentrated around main vascular bundle of leaf, which means around midrib.

In-gel detection of urease activity by nitroprusside-thiol reaction

A new staining method for urease activity in non-denaturing polyacrylamide gels is described. The increase in local pH of the gel, resulting from ureolytic activity of urease, causes a purple red coloured band after incubation of the polyacrylamide gel with urea. Staining of urease activity using this method is very specific for catalytically active urease even in crude preparations. Detection of urease activity by this method is rapid, simple and economical. The described method is also more sensitive than existing methods of urease staining. A minimum of 0.25 mU of urease activity can be detected after 5 min of incubation with the substrate. The method has been used to demonstrate the presence of different charge isoforms of urease in a member of the plant family Cucurbitaceae.

Identification, biochemical characterization, and subcellular localization of allantoate amidohydrolases from Arabidopsis and soybean

Allantoate amidohydrolases (AAHs) hydrolize the ureide allantoate to ureidoglycolate, CO(2), and two molecules of ammonium. Allantoate degradation is required to recycle purine-ring nitrogen in all plants. Tropical legumes additionally transport fixed nitrogen via allantoin and allantoate into the shoot, where it serves as a general nitrogen source. AAHs from Arabidopsis (Arabidopsis thaliana; AtAAH) and from soybean (Glycine max; GmAAH) were cloned, expressed in planta as StrepII-tagged variants, and highly purified from leaf extracts. Both proteins form homodimers and release 2 mol ammonium/mol allantoate. Therefore, they can truly be classified as AAHs. The kinetic constants determined and the half-maximal activation by 2 to 3 microm manganese are consistent with allantoate being the in vivo substrate of manganese-loaded AAHs. The enzymes were strongly inhibited by micromolar concentrations of fluoride as well as by borate, and by millimolar concentrations of L-asparagine and L-aspartate but not D-asparagine. L-Asparagine likely functions as competitive inhibitor. An Ataah T-DNA mutant, unable to grow on allantoin as sole nitrogen source, is rescued by the expression of StrepII-tagged variants of AtAAH and GmAAH, demonstrating that both proteins are functional in vivo. Similarly, an allantoinase (aln) mutant is rescued by a tagged AtAln variant. Fluorescent fusion proteins of allantoinase and both AAHs localize to the endoplasmic reticulum after transient expression and in transgenic plants. These findings demonstrate that after the generation of allantoin in the peroxisome, plant purine degradation continues in the endoplasmic reticulum.

Multi-instrumental Analysis of Tissues of Sunflower Plants Treated with Silver(I) Ions - Plants as Bioindicators of Environmental Pollution

The aim of this work is to investigate sunflower plants response on stress induced by silver(I) ions. The sunflower plants were exposed to silver(I) ions (0, 0.1, 0.5, and 1 mM) for 96 h. Primarily we aimed our attention to observation of basic physiological parameters. We found that the treated plants embodied growth depression, coloured changes and lack root hairs. Using of autofluorescence of anatomical structures, such as lignified cell walls, it was possible to determine the changes of important shoot and root structures, mainly vascular bungles and development of secondary thickening. The differences in vascular bundles organisation, parenchymatic pith development in the root centre and the reduction of phloem part of vascular bundles were well observable. Moreover with increasing silver(I) ions concentration the vitality of rhizodermal cells declined; rhizodermal cells early necrosed and were replaced by the cells of exodermis. Further we employed laser induced breakdown spectroscopy for determination of spatial distribution of silver(I) ions in tissues of the treated plants. The Ag is accumulated mainly in near-root part of the sample. Moreover basic biochemical indicators of environmental stress were investigated. The total content of proteins expressively decreased with increasing silver(I) ions dose and the time of the treatment. As we compare the results obtained by protein analysis – the total protein contents in shoot as well as root parts – we can assume on the transport of the proteins from the roots to shoots. This phenomenon can be related with the cascade of processes connecting with photosynthesis. The second biochemical parameter, which we investigated, was urease activity. If we compared the activity in treated plants with control, we found out that presence of silver(I) ions markedly enhanced the activity of urease at all applied doses of this toxic metal. Finally we studied the effect of silver(I) ions on activity of urease in in vitro conditions.

Characterization of the polyurethanolytic activity of two Alicycliphilus sp. strains able to degrade polyurethane and N-methylpyrrolidone

Two bacterial strains (BQ1 and BQ8) were isolated from decomposed soft foam. These were selected for their capacity to grow in a minimal medium (MM) supplemented with a commercial surface-coating polyurethane (PU) (Hydroform) as the carbon source (MM-PUh). Both bacterial strains were identified as Alicycliphilus sp. by comparative 16S rRNA gene sequence analysis. Growth in MM-PUh showed hyperbolic behavior, with BQ1 producing higher maximum growth (17.8 +/- 0.6 mg.ml(-1)) than BQ8 (14.0 +/- 0.6 mg.ml(-1)) after 100 h of culture. Nuclear magnetic resonance, Fourier transform infrared (IR) spectroscopy, and gas chromatography-mass spectrometry analyses of Hydroform showed that it was a polyester PU type which also contained N-methylpyrrolidone (NMP) as an additive. Alicycliphilus sp. utilizes NMP during the first stage of growth and was able to use it as the sole carbon and nitrogen source, with calculated K(s) values of about 8 mg.ml(-1). Enzymatic activities related to PU degradation (esterase, protease, and urease activities) were tested by using differential media and activity assays in cell-free supernatants of bacterial cultures in MM-PUh. Induction of esterase activity in inoculated MM-PUh, but not that of protease or urease activities, was observed at 12 h of culture. Esterase activity reached its maximum at 18 h and was maintained at 50% of its maximal activity until the end of the analysis (120 h). The capacity of Alicycliphilus sp. to degrade PU was demonstrated by changes in the PU IR spectrum and by the numerous holes produced in solid PU observed by scanning electron microscopy after bacterial culture. Changes in the PU IR spectra indicate that an esterase activity is involved in PU degradation.

Combination of reversible male sterility and doubled haploid production by targeted inactivation of cytoplasmic glutamine synthetase in developing anthers and pollen

Reversible male sterility and doubled haploid plant production are two valuable technologies in F(1)-hybrid breeding. F(1)-hybrids combine uniformity with high yield and improved agronomic traits, and provide self-acting intellectual property protection. We have developed an F(1)-hybrid seed technology based on the metabolic engineering of glutamine in developing tobacco anthers and pollen. Cytosolic glutamine synthetase (GS1) was inactivated in tobacco by introducing mutated tobacco GS genes fused to the tapetum-specific TA29 and microspore-specific NTM19 promoters. Pollen in primary transformants aborted close to the first pollen mitosis, resulting in male sterility. A non-segregating population of homozygous doubled haploid male-sterile plants was generated through microspore embryogenesis. Fertility restoration was achieved by spraying plants with glutamine, or by pollination with pollen matured in vitro in glutamine-containing medium. The combination of reversible male sterility with doubled haploid production results in an innovative environmentally friendly breeding technology. Tapetum-mediated sporophytic male sterility is of use in foliage crops, whereas microspore-specific gametophytic male sterility can be applied to any field crop. Both types of sterility preclude the release of transgenic pollen into the environment.

Identification of three urease accessory proteins that are required for urease activation in Arabidopsis

Urease is a nickel-containing urea hydrolase involved in nitrogen recycling from ureide, purine, and arginine catabolism in plants. The process of urease activation by incorporation of nickel into the active site is a prime example of chaperone-mediated metal transfer to an enzyme. Four urease accessory proteins are required for activation in Klebsiella aerogenes. In plants urease accessory proteins have so far been only partially defined. Using reverse genetic tools we identified four genes that are necessary for urease activity in Arabidopsis (Arabidopsis thaliana; ecotypes Columbia and Nössen). Plants bearing T-DNA or Ds element insertions in either the structural gene for urease or in any of the three putative urease accessory genes AtureD, AtureF, and AtureG lacked the corresponding mRNAs and were defective in urease activity. In contrast to wild-type plants, the mutant lines were not able to support growth with urea as the sole nitrogen source. To investigate whether the identified accessory proteins would be sufficient to support eukaryotic urease activation, the corresponding cDNAs were introduced into urease-negative Escherichia coli. In these bacteria, urease activity was observed only when all three plant accessory genes were coexpressed together with the plant urease gene. Remarkably, plant urease activation occurred as well in cell-free E. coli extracts, but only in extracts from cells that had expressed all three accessory proteins. The future molecular dissection of the plant urease activation process may therefore be performed in vitro, providing a powerful tool to further our understanding of the biochemistry of chaperone-mediated metal transfer processes in plants.

Absorption of mulberry root urease to the hemolymph of the silkworm, Bombyx mori

Mulberry leaves are the sole diet of the silkworm, Bombyx mori. The host urease is incorporated into the larval hemolymph and involved in nitrogen metabolism in the insect. To investigate the selective absorption of the host urease to the larvae, crude urease was prepared from mulberry leaves and roots. Root urease was identical to leaf urease on the basis of electrophoretic analyses: (1) the urease activity appeared in the same migration position in a native gel; (2) There was no difference in molecular mass of the subunit. The root urease was orally injected to the fifth instar larvae of the silkworm. Just before spinning, the larvae absorbed intact urease from the midgut lumen to the hemolymph without the loss of activity. The capacity to absorb urease occurred only at the specific stage. Localization of host urease in midgut tissue was observed using confocal laser scanning microscopy and transmission electron microscopy. Based on spatial distribution of immunofluorescent signals and immunogold particles, host urease specifically attached to the surfaces of microvilli existing in the apical side of columnar cells and appeared in the cytoplasm of the cells for transport to the hemolymph. The incorporation efficiency of root urease into the hemolymph was significantly higher than for ureases from jack bean seeds and Bacillus pasteurii. The urease that was transported to the hemolymph was electrophoretically altered, compared with the host urease extracted.

Urease biogenesis in Streptococcus thermophilus

Urease biogenesis was monitored in the lactic acid bacterium Streptococcus thermophilus during the growth cycle using in-gel detection and a phenol-hypochloride assay. Zymogram analysis, performed in a non-denaturing polyacrylamide gel, enabled visualization of a complex profile of bands whose number and intensity were dependent on the growth phase and culture conditions. The monitoring of urease biogenesis in batch fermentations revealed the onset of enzyme synthesis starting from the mid-exponential growth phase, with a maximum reached during the late exponential phase. Urease activity strongly increased at acidic pH but to a lesser extent when urea and nickel ions were added to the culture medium. When S. thermophilus cells were cultured with pH maintained at a neutral value, urease activity was detectable only in gel with extremely low signals. Evaluation of beta-glucuronidase activity in strain DSM 20617(T) harboring a transcriptional fusion between a DNA fragment containing the putative urease promoter and the gusA reporter evidenced significant expression at neutral pH that strongly increased in an acidic environment. Further experiments carried out on p(ureI)-gusA recombinant strain revealed that expression of ure genes was not affected by carbohydrates, nickel or urea availability. The presence of consistent expression of ure genes at neutral pH and the absence of induction of expression by carbohydrate availability demonstrated that the transcription of ure genes in S. thermophilus is regulated differently compared with that of the closely related S. salivarius. These differences are discussed taking into consideration the different habitats colonized by the two bacterial species.

Rapid one-step protein purification from plant material using the eight-amino acid StrepII epitope

Beyond the rewards of plant genome analysis and gene identification, characterisation of protein activities, post-translational modifications and protein complex composition remains a challenge for plant biologists. Ideally, methods should allow rapid isolation of proteins from plant material achieving a high degree of purity. We tested three purification strategies based on the eight-amino acid StrepII, six-amino acid His(6) and 181-amino acid Tandem Affinity Purification (TAP) affinity tags for enrichment of a membrane-anchored protein kinase, Nt CDPK2, and a soluble protein, At SGT1b, from leaf extracts. Transiently expressed StrepII-tagged Nt CDPK2 was purified from Nicotiana benthamiana to almost complete homogeneity in less than 60 min and was directly suitable for enzymatic or mass-spectrometric analyses, allowing the identification of in planta phosphorylation sites. In contrast, purification of Nt CDPK2 via His(6) tag yielded partially oxidised protein of low purity. At SGT1b could be isolated after transient expression from N. benthamiana or from transgenic Arabidopsis thaliana as either TAP-tagged or StrepII-tagged protein. While StrepII-tag purification achieved similar yield and high purity as the TAP-tag strategy, it was considerably easier and faster. Using either tagging strategy, a protein was co-purified with At SGT1b from N. benthaniana and A. thaliana leaf extracts, suggesting that both the StrepII and TAP tags are suitable for purification of protein complexes from plant material. We propose that the StrepII epitope, in particular, may serve as a generally utilizable tag to further our understanding of protein functions, post-translational modifications and interaction dynamics in plants.

Interallelic complementation at the ubiquitous urease coding locus of soybean

Soybean (Glycine max [L.] Merrill) mutant aj6 carries a single recessive lesion, aj6, that eliminates ubiquitous urease activity in leaves and callus while retaining normal embryo-specific urease activity. Consistently, aj6/aj6 plants accumulated urea in leaves. In crosses of aj6/aj6 by urease mutants at the Eu1, Eu2, and Eu3 loci, F(1) individuals exhibited wild-type leaf urease activity, and the F(2) segregated urease-negative individuals, demonstrating that aj6 is not an allele at these loci. F(2) of aj6/aj6 crossed with a null mutant lacking the Eu1-encoded embryo-specific urease showed that ubiquitous urease was also inactive in seeds of aj6/aj6. The cross of aj6/aj6 to eu4/eu4, a mutant previously assigned to the ubiquitous urease structural gene (R.S. Torisky, J.D. Griffin, R.L. Yenofsky, J.C. Polacco [1994] Mol Gen Genet 242: 404-414), yielded an F(1) having 22% +/- 11% of wild-type leaf urease activity. Coding sequences for ubiquitous urease were cloned by reverse transcriptase-polymerase chain reaction from wild-type, aj6/aj6, and eu4/eu4 leaf RNA. The ubiquitous urease had an 837-amino acid open reading frame (ORF), 87% identical to the embryo-specific urease. The aj6/aj6 ORF showed an R201C change that cosegregated with the lack of leaf urease activity in a cross against a urease-positive line, whereas the eu4/eu4 ORF showed a G468E change. Heteroallelic interaction in F(2) progeny of aj6/aj6 x eu4/eu4 resulted in partially restored leaf urease activity. These results confirm that aj6/aj6 and eu4/eu4 are mutants affected in the ubiquitous urease structural gene. They also indicate that radical amino acid changes in distinct domains can be partially compensated in the urease heterotrimer.

Leaf urea metabolism in potato. Urease activity profile and patterns of recovery and distribution of (15)N after foliar urea application in wild-type and urease-antisense transgenics

The influence of urease activity on N distribution and losses after foliar urea application was investigated using wild-type and transgenic potato (Solanum tuberosum cv Désirée) plants in which urease activity was down-regulated. A good correlation between urease activity and (15)N urea metabolism (NH(3) accumulation) was found. The general accumulation of ammonium in leaves treated with urea indicated that urease activity is not rate limiting, at least initially, for the assimilation of urea N by the plant. It is surprising that there was no effect of urease activity on either N losses or (15)N distribution in the plants after foliar urea application. Experiments with wild-type plants in the field using foliar-applied (15)N urea demonstrated an initial rapid export of N from urea-treated leaves to the tubers within 48 h, followed by a more gradual redistribution during the subsequent days. Only 10% to 18% of urea N applied was lost (presumably because of NH(3) volatilization) in contrast to far greater losses reported in several other studies. The pattern of urease activity in the canopy was investigated during plant development. The activity per unit protein increased up to 10-fold with leaf and plant age, suggesting a correlation with increased N recycling in senescing tissues. Whereas several reports have claimed that plant urease is inducible by urea, no evidence for urease induction could be found in potato.