This work was focused on the role of silicon (Si) in amelioration of manganese (Mn) toxicity caused by elevated production of hydroxyl radicals (·OH) in the leaf apoplast of cucumber (Cucumis ...sativusL.). The plants were grown in nutrient solutions with adequate (0.5 μM) or excessive (100 μM) Mn concentrations with or without Si being supplied. The symptoms of Mn toxicity were absent in the leaves of Si-treated plants subjected to excess Mn, although the leaf Mn concentration remained extremely high. The apoplastic concentration of free Mn²⁺ and H₂O₂ of high Mn-treated plants was significantly decreased by Si treatment. Si supply suppressed the Mn-induced increased abundance of peroxidase (POD) isoforms in the leaf apoplastic fluid, and led to a rapid suppression of guaiacol-POD activity under excess Mn. The spin-trapping reagent 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide was used to detect ·OH by electron paramagnetic resonance spectroscopy. Although supplying Si markedly decreased the accumulation of ·OH in the leaf apoplast with excess Mn, adding monosilicic acid to the Mn²⁺/H₂O₂ reaction mixture did not directly affect the Fenton reactionin vitro. The results indicate that Si contributes indirectly to a decrease in ·OH in the leaf apoplast by decreasing the free apoplastic Mn²⁺, thus regulating the Fenton reaction. A direct inhibitory effect of Si on guaiacol-POD activity (demonstratedin vitro) may also contribute to decreasing the POD-mediated generation of ·OH.
Apoplastic antioxidative constituents (enzymes, primary and secondary metabolites, ROS) from different root zones of hydroponically grown maize (Zea mays L.) were investigated using a noninvasive ...isolation procedure: filter strip method. Filter strips were placed at specific positions on the root surface: apical zone (tip) and basal zone (base) to absorb apoplastic fluid. Three major classes of low‐weight metabolites (organic acids, sugars, and phenolics) have been identified by HPLC‐ECD. The longitudinal distribution of sugars and organic acids had the same pattern: higher concentration in the tip than the base, while it was vice versa for phenolics. The specific activities of guaiacol peroxidase, superoxide dismutase, and ascorbate peroxidase were higher in the apoplastic fluid from the root base than the tip, and their different isoforms were separated by isoelectric focusing. Electron paramagnetic resonance (EPR) spectroscopy coupled with the spin‐trapping method using DEPMPO showed a persistent generation of hydroxyl radical in the root tip. In vivo EPR imaging of the whole maize root with membrane‐permeable and impermeable aminoxyl spin‐probes, enabling real‐time detection of ROS formation within and outside the membranes, demonstrated ROS accumulation on the root surface, while endodermis and central cylinder were ROS free. For the first time in plant research, 2D EPR images enabled the direct demonstration of site‐specific free radical production along the root. Highly sensitive analytical techniques combined with the filter strips, as a non‐invasive tool, have increased our knowledge of metabolic processes occurring in the apoplast and their spatial–temporal changes in small regions of the intact root tissue.
Indigo carmine is a commonly used industrial blue dye. To determine its concentration in a commercially available food dye composed of a mixture of indigo carmine and D-glucose, this paper ...characterizes it through (ATR, KBr) FTIR micro-Raman as well as UV/Vis and clock: Briggs–Rauscher (BR) oscillatory reaction methods. The indigo carmine was detected in the bulk food dye only by applying micro-Raman spectroscopy, indicating a low percentage of the indigo carmine present. This research provides an improvement in the deviations from the experimental Raman spectrum as calculated by the B97D/cc-pVTZ level of theory one, resulting in a better geometrical optimization of the indigo carmine molecule compared to data within the literature. The analytical curves used to determine indigo carmine concentrations (and quantities) in an aqueous solution of food dye were applied by means of UV/Vis and BR methods. BR yielded significantly better analytical parameters: 100 times lower LOD and LOQ compared to commonly used UV/Vis. The remarkable sensitivity of the BR reaction towards indigo carmine suggests that not only does indigo carmine react in an oscillatory reaction but also its decomposition products, meaning that the multiple oxidation reactions have an important role in the BR’s indigo carmine mechanism. The novelty of this research is the investigation of indigo carmine using a clock BR reaction, opening new possibilities to determine indigo carmine in other complex samples (pharmaceutical, food, etc.).
The application of digital technology in teaching physical education provides a basis for its improvement in the direction of promoting physical activity and student development. As one of the most ...important subjects of the teaching process, teachers have a fundamental role in achieving the goals and tasks of physical education. Physical education teachers are required to develop competences based on which they would implement digital technology in physical education classes in compliance with the imperatives of modern digital education. Therefore, this research is focused on the competences of physical education teachers in education supported by digital technology. The aim of this research is to determine the competences of physical education teachers necessary to fulfil their role in education supported by digital technology. The method used in this theoretical research is the method of theoretical analysis. The technique of content analysis was used. The research instrument consists of the relevant literature on this topic. The theoretical analysis points to a need to expand and improve the digital competences of physical education teachers, which can be achieved by joint action of formal and informal education systems in developing programs that would provide a basis for the professional development and empowerment of physical education teachers to use digital technology with more certainty and purpose in teaching physical education.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The causal relationship between salinity and oxidative stress tolerance is well established, but specific downstream targets and the role of specific antioxidant compounds in controlling cellular ...ionic homeostasis remains elusive. In this work, we have compared antioxidant profiles of leaves of two quinoa genotypes contrasting in their salt tolerance, with the aim of understanding the role of enzymatic and non-enzymatic antioxidants in salinity stress tolerance. Only changes in superoxide dismutase activity were correlated with plant adaptive responses to salinity. Proline accumulation played no major role in either osmotic adjustment or in the tissue tolerance mechanism. Among other non-enzymatic antioxidants, rutin levels were increased by over 25 fold in quinoa leaves. Exogenous application of rutin to glycophyte bean leaves improved tissue tolerance and reduced detrimental effects of salinity on leaf photochemistry. Electrophysiological experiments revealed that these beneficial effects were attributed to improved potassium retention and increased rate of Na+ pumping from the cell. The lack of correlation between rutin-induced changes in K+ and H+ fluxes suggest that rutin accumulation in the cytosol scavenges hydroxyl radical formed in response to salinity treatment thus preventing K+ leak via one of ROS-activated K+ efflux pathways, rather than controlling K+ flux via voltage-gated K+-permeable channels.
Cucumber plants (Cucumis sativus L. cv. Chinese long) were grown in nutrient solution with increasing manganese (Mn) concentrations (0.5, 50, and 100 µM) with (+Si) or without silicon (–Si) supplied ...as silicic acid at 1.5 mM. High external Mn supply induced both growth inhibition of the whole plant and the appearance of Mn‐toxicity symptoms in the leaves. The application of Si alleviated Mn toxicity by increasing the biomass production. Although the total Mn concentration in the leaves did not differ significantly between +Si and –Si plants, symptoms of Mn toxicity were not observed in Si‐treated plants. The concentrations of phenolic compounds, particularly in the leaf extracts of cucumber plants grown at high external Mn concentrations, differed from those of plants grown without Si. The increased tissue concentrations of phenols (e.g., coniferyl alcohol, coumaric and ferulic acids) were in agreement with enhanced enzymes activities, i.e., peroxidases (PODs) and polyphenol oxidases (PPO) in the tissues of –Si plants. The activities of both enzymes were kept at a lower level in the tissue extracts of +Si plants grown at high external Mn concentrations. These results suggest that Si nutrition modulates the metabolism and utilization of phenolic compounds mainly at the leaf level, most probably as a consequence of the formation of Si‐polyphenol complexes.
•Experimental analysis shows strong influence of l-Tyrosine on the oscillatory dynamics of the Bray-Liebhafsky reaction.•Two reaction pathways based on the interaction of l-Tyrosine with HIO or I2O ...were investigated to explain the experimental results.•The reaction pathway between l-Tyrosine and I2O showed better agreement with the experimental results.
The impact of L-tyrosine on the dynamics of the Bray-Liebhafsky (BL) oscillatory reaction was investigated both experimentally and numerically. The study focused on the examination of the sensitivity of the BL reaction to L-tyrosine perturbation. The results obtained indicated possible pathways of influence. Simulations were carried out with and without L-tyrosine. The interaction of L-tyrosine with the BL reaction system was tested with two possible reactions.
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Phenolic compounds of 25 newly introduced strawberry cultivars were profiled using spectrophotometry, electron paramagnetic resonance (EPR) spectroscopy, and high-performance liquid ...chromatography-mass spectrometry. Total phenolic and anthocyanin content (TPC and TACY, respectively), as well as vitamin C, and concentrations of individual phenolic compounds in fruits were evaluated to identify the most promising cultivars according to their phenolic profile. The highest values of TPC, TACY, and vitamin C were recorded in 'Premy' (1.53 mg eq GA g
FW), 'Sandra' (30.60 mg eq Pg-3-g 100 g
FW), and 'Laetitia' (56.32 mg 100 g
FW), respectively. The DPPH and •OH radicals scavenging activity of fruit methanolic extracts was estimated using EPR spectroscopy. All cultivars are almost uniformly effective in the scavenging of •OH radical, while 'Tea', 'Premy', and 'Joly' were marked as highly potent cultivars (over 70%) in terms of DPPH-antiradical activity. Specific peroxidase activities were the highest in 'Garda', 'Federica', and 'Rumba' (0.11, 0.08, and 0.06 U mg
prot, respectively). 'Laetitia', 'Joly', 'Arianna', 'Tea', and 'Mila' cultivars were distinguished from others as the richest concerning almost all flavonoids and phenolic acids, including some other parameters of bioactivity. These cultivars could be recommended to consumers as functional fruit foods.
The Briggs–Rauscher reaction containing malonic acid may undergo a sudden transition from low (state I) to high iodide and iodine (state II) concentration states after a well-defined and strongly ...reproducible oscillatory period. This study clearly shows that even though the time-dependent behavior of the oscillatory state is reproducible, the time lag necessary for the appearance of the state I to state II transition after the system leaves the oscillatory state becomes irreproducible for an individual kinetic run. This crazy clock behavior of the state I to state II transition is identified by repeated experiments in which stirring rate is taken as a control parameter and all other parameters such as initial conditions, temperature, vessel surface, and the age of solution were kept constant. Surprisingly, a better stirring condition does not make the transition reproducible; it simply does not allow the transition to happen at all. The proposed mechanism, additional explanations, and proposals for this irreproducibility of state I to state II transition have been presented. Considering the fact that the number of crazy clock reactions is only a few, this study may contribute to a better understanding of fundaments of this phenomenon.
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