Selenium-mediated differential response of beta-glucosidase and beta-galactosidase of germinating Trigonella foenum-graecum.

Abstract: Selenium-accumulating plants such as Brassica juncea (Indian mustard) concentrate the element in plant shoots and roots. Such behavior may provide a cost-effective technology to clean up contaminated soils and waters that pose major environmental and human health problems (phytoremediation). Such ability to transform selenium into bioactive compounds has important implications for human nutrition and health. Element selective characterization of B. juncea grown in the presence of inorganic selenium under hydroponic conditions provides valuable information to better understand selenium metabolism in plants. The present work determines both previously observed organoselenium species such as selenomethionine and Se-methylselenocysteine and for the first time detects the newly characterized S-(methylseleno)cysteine in plant shoots and roots when grown in the presence of selenate or selenite as the only selenium source. A key feature of this study is the complementary role of selenium and sulfur specific chromatographic detection by HPLC with interfaced inductively coupled plasma mass spectrometry (ICP-MS) detection and by derivatization GC with interfaced atomic spectral emission. HPLC–ICP-MS limits of detection for such species were in the range 5–50 ng Se mL −1 in the injected extracts. Speciation profiles are compared with those of selenium-enriched yeast by both HPLC–ICP-MS and GC–AED.

Abstract: Selenium (Se) is considered a beneficial chemical element for plants, but in high concentrations it may present symptoms of toxicity. The present study aimed to evaluate 11 concentrations of Se (0; 0.1; 0.5; 1; 5; 10; 20; 40; 80; 400; 800 mg.L-1) to determine the low and high (toxicity) critical levels to seed germination of cowpea (Vigna unguiculata). In addition, alterations in the rate of photosynthetic pigments, lipid peroxidation and sugars during the initial growth development of seedlings were analysed. Seeds exposed to 800 mg.L-1 of Se showed a decrease of 20% of seed germination index compared to the control treatment. The decrease in seedling growth reflected in the increase of total sugars and sucrose concentration in both the shoot and root in response to exposure to Se concentration. There was a decrease in the concentration of leaf chlorophyll, carotenoids and pheophytin from seedlings exposed to high Se concentration. The rate of lipid peroxidation and the hydrogen peroxide concentration in the shoot was reduced up to the concentration of 1 mg.L-1 with subsequent increase in response to Se concentration applied. In the roots, the lipid peroxidation rate increased at concentrations higher than 80 mg.L-1. The highest oxidation rate of the cellular lipid membrane in response to Se occurred in the shoot, due to oxidation reactions in the chloroplast. Degradation of photosynthetic pigments and accumulation of total sugars and sucrose can be considered efficient biomarkers to indicate the toxicity of Se in cowpea seedlings and probably in other crops.

Abstract: Breeding plants to be more efficient at micronutrient accumulation is a proposed strategy for fighting worldwide malnutrition of humans. Selection for increased selenium (Se) in Brassica oleracea L. is possible. However, when present at high levels, micronutrients such as Se can affect seed germination and subsequently hamper breeding efforts. The objectives of this study were: (1) to evaluate the accumulation of Se in seeds of B. oleracea; and (2) to determine effects that Se accumulation may have on seed germination. Plants of a rapid‐cycling B. oleracea population were grown in nutrient solutions with sodium selenate (Na2SeO4) concentrations up to 7 mg L−1 (2.93 mg Se L−1). Seeds and leaves were harvested from the selenized plants and analyzed for Se content using atomic absorption spectrophotometry. Germination percentage and rate were determined by sowing seeds in moistened towels, placing them in an incubator at 21°C, and observing radicle emergence. Selenium accumulated in the seeds, but a...

Abstract: Selenium compounds break dormancy of seeds of Townsville stylo (Stylosanthes humilis) through the induction of ethylene production. This was supported by the fact that antiethylenic substances inhibited germination of Se-treated dormant seeds. Under these conditions germination was restored by ethylene-producing compounds. Efficacy of the compounds was monitored through an Efficiency Index (Ief) which takes into account not only the maximal germination but also the optimal concentration responsible for eliciting the process. The most efficient compounds were SeCl4, SeO2 and Na2SeO3 and the least efficient were selenourea, H2SeO4 and selenomethionine. Although ethylene was required for dormancy breakage the compounds triggering the highest ethylene productions were not necessarily the same ones leading to the largest Ief(s). Hence it was concluded that the index is an overall integrating parameter, encompassing uptake of the compound, arrival to target cells and also post-ethylene biosynthesis effects.

Abstract: Salinity (NaCl) is a major abiotic stress that limits crop production, especially under rainfed conditions. Selenium (Se), as an important micronutrient, plays a vital role in mitigating the detrimental effects of different abiotic stresses. The objective of this research was to examine the effect of Se fertilization on sage (Salvia officinalis L.) under different salt stresses. The results showed that Se treatments caused significant improvements in the dry weight (DW) of sage under salt stress. It was found that the DW was increased in the combined treatment of 10 ppm of Se and 100 mM/L of NaCl and was reduced at the highest level of NaCl (100 mM/L). The highest essential oil percentages were recorded in the first harvest (5 ppm of Se), and the control treatment in the second and third harvests but significantly affected the low and high NaCl levels in the sage. Additionally, the results in this study showed that the application of Se from 2.5 ppm to 10 ppm significantly increased the essential oil components when under salt stress. The results showed that 5 ppm of Se and 50 mM/L of NaCl increased SO42− and PO43− concentrations in the first and third harvests. In addition, significant increases in K+ uptakes and decreases in Na+ uptakes were detected when the Se was added while the sage was under salt stress, and the highest Ca2+ and Mg2+ concentrations were all found in the Se treatments as well as in the combined treatments of Se and NaCl.

Abstract: Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins, a number of modified analytical procedures utilizing this reagent have been reported for the determination of proteins in serum, in antigen-antibody precipitates, and in insulin. Although the reagent would seem to be recommended by its great sensitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard to effects of variations in pH, time of reaction, and concentration of reactants, permissible levels of reagents commonly used in handling proteins, and interfering substances. Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.

Abstract: When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase.

Abstract: The amino acid sequences of 301 glycosyl hydrolases and related enzymes have been compared. A total of 291 sequences corresponding to 39 EC entries could be classified into 35 families. Only ten sequences (less than 5% of the sample) could not be assigned to any family. With the sequences available for this analysis, 18 families were found to be monospecific (containing only one EC number) and 17 were found to be polyspecific (containing at least two EC numbers). Implications on the folding characteristics and mechanism of action of these enzymes and on the evolution of carbohydrate metabolism are discussed. With the steady increase in sequence and structural data, it is suggested that the enzyme classification system should perhaps be revised.

Abstract: The crystal structure of bovine erythrocyte glutathione peroxidase has been refined by a combined procedure of restrained crystallographic refinement and energy minimization at 0.20 nm resolution. The final R value at this resolution is 0.178. The r.m.s. deviation of main-chain atoms of the two independently refined monomers is 0.019 nm. The structure at 0.28 nm resolution, which has been determined by multiple isomorphous replacement, served as a starting model. The refined model allowed a detailed survey of the hydrogen-bonding pattern and of the subunit contact areas in the molecule. The model contains 165 solvent molecules per dimer, all taken as water molecules. The mobility of the structure was derived from the individual atomic temperature factors. The complete tetramer, including the active sites, seems to be rather rigid, except for narrow loops near to the N-terminal ends and some β turns exposed to solvent. The active centres of glutathione peroxidase are found in flat depressions on the molecular surface. The catalytically active selenocysteine residues could be located at the N-terminal ends of α helices forming βαβ substructures together with two adjacent parallel β strands. In the vicinity of the reactive group some aromatic amino acid side-chains could be localized. Especially Trp-148, which could be hydrogen bonded to SeCys-35, may play a functional role during catalysis. The results of substrate and inhibitor binding studies in solution and in the crystalline state could be interpreted by an apparent half-site reactivity of glutathione peroxidase. The enzyme seems to react in the sense of negative cooperativity with dimers being the functional units. Based on difference Fourier analyses of appropriate derivatives a reasonable model of glutathione binding is presented. Among the residues which could be of functional importance are Arg-40, Gln-130 and Arg-167, presumably forming salt bridges and a hydrogen bond to the glutathione molecule. In conclusion, a general picture of a minimal reaction mechanism, which is in good agreement with functional and structural data, is proposed. The main reaction of the catalytic cycle presumably shuttles between the selenolate and the selenenic acid state of SeCys-35.