The upregulation of thiamine (vitamin B1) biosynthesis in Arabidopsis thaliana seedlings under salt and osmotic stress conditions is mediated by abscisic acid at the early stages of this stress response

<p>Abstract</p> <p>Background</p> <p>Recent reports suggest that vitamin B₁(thiamine) participates in the processes underlying plant adaptations to certain types of abiotic and biotic stress, mainly oxidative stress. Most of the genes coding for enzymes involved in thiamine biosynthesis in <it>Arabidopsis thaliana </it>have been identified. In our present study, we examined the expression of thiamine biosynthetic genes, of genes encoding thiamine diphosphate-dependent enzymes and the levels of thiamine compounds during the early (sensing) and late (adaptation) responses of Arabidopsis seedlings to oxidative, salinity and osmotic stress. The possible roles of plant hormones in the regulation of the thiamine contribution to stress responses were also explored.</p> <p>Results</p> <p>The expression of Arabidopsis genes involved in the thiamine diphosphate biosynthesis pathway, including that of <it>THI1</it>, <it>THIC</it>, <it>TH1 </it>and <it>TPK</it>, was analyzed for 48 h in seedlings subjected to NaCl or sorbitol treatment. These genes were found to be predominantly up-regulated in the early phase (2-6 h) of the stress response. The changes in these gene transcript levels were further found to correlate with increases in thiamine and its diphosphate ester content in seedlings, as well as with the enhancement of gene expression for enzymes which require thiamine diphosphate as a cofactor, mainly α-ketoglutarate dehydrogenase, pyruvate dehydrogenase and transketolase. In the case of the phytohormones including the salicylic, jasmonic and abscisic acids which are known to be involved in plant stress responses, only abscisic acid was found to significantly influence the expression of thiamine biosynthetic genes, the thiamine diphosphate levels, as well as the expression of genes coding for main thiamine diphosphate-dependent enzymes. Using Arabidopsis mutant plants defective in abscisic acid production, we demonstrate that this phytohormone is important in the regulation of <it>THI1 </it>and <it>THIC </it>gene expression during salt stress but that the regulatory mechanisms underlying the osmotic stress response are more complex.</p> <p>Conclusions</p> <p>On the basis of the obtained results and earlier reported data, a general model is proposed for the involvement of the biosynthesis of thiamine compounds and thiamine diphosphate-dependent enzymes in abiotic stress sensing and adaptation processes in plants. A possible regulatory role of abscisic acid in the stress sensing phase is also suggested by these data.</p

Monolayers of the HSA dimer on polymeric microparticles-electrokinetic characteristics

Human serum albumin dimer (dHSA) enhances the accumulation and retention of anti-tumor drugs. In this work, monolayers of dHSA on polystyrene microparticles were prepared and thoroughly characterized. The changes in the electrophoretic mobility of microparticles upon the addition of controlled amounts of dHSA were measured using Laser Doppler Velocimetry (LDV) technique. These dependencies were quantitatively interpreted in terms of the 3D electrokinetic model. This allowed to determine the coverage of dHSA on microparticles under in situ conditions. Additionally, the maximum coverage of dHSA was precisely determined by the concentration depletion method. At physiological ionic strength, the maximum coverage of dHSA monolayer on microparticles was 1.05 mg m−2. This agrees with the theoretical value predicted from the random sequential adsorption approach by assuming a side-on orientation of molecules. A high stability of the monolayers under pH cycling was confirmed, which proved irreversibility of the protein adsorption on the microparticles. The obtained results can be exploited to prepare and characterize polymeric drug-capsule conjugated with albumin dimer

High density monolayers of plasmid protein on latex particles : experiments and theoretical modelling

Monolayers obtained by adsorption of the plasmid protein KfrA on negatively charged polystyrene latex particles under diffusion-controlled conditions at pH 3.5 were interpreted in terms of the random sequential adsorption (RSA) model. A quantitative agreement of the theoretical results derived from these calculations with experimental data was attained for the ionic strength from 0.15 up to 10_{−2} M. This confirmed the adsorption mechanism of KfrA molecules on latex in the form of tetramers up to 10_{−2} M. On the other hand, for the ionic strength of 10_{−3} M the experimental coverage agreed with theoretical predictions under the assumption that screening of electrostatic interaction is enhanced by the presence of counterions and negatively charged polymer chains stemming from latex particles

Recombinant Albumin Monolayers on Latex Particles

The adsorption of recombinant human serum albumin (rHSA) on negatively charged polystyrene latex micro-particles was studied at pH 3.5 and the NaCl concentration range of 10^–3 to 0.15 M. The electrophoretic mobility of latex monotonically increased with the albumin concentration in the suspension. The coverage of adsorbed albumin was quantitatively determined using the depletion method, where the residual protein concentration was determined by electrokinetic measurements and AFM imaging. It was shown that albumin adsorption was irreversible. Its maximum coverage on latex varied between 0.7 mg m^–2 for 10^–3 M NaCl to 1.3 mg m^–2 for 0.15 M NaCl. The latter value matches the maximum coverage previously determined for human serum albumin on mica using the streaming potential method. The increase in the maximum coverage was interpreted in terms of reduced electrostatic repulsion among adsorbed molecules. These facts confirm that albumin adsorption at pH 3.5 is governed by electrostatic interactions and proceeds analogously to colloid particle deposition. The stability of albumin monolayers was measured in additional experiments where changes in the latex electrophoretic mobility and the concentration of free albumin in solutions were monitored over prolonged time periods. Based on these experimental data, a robust procedure of preparing albumin monolayers on latex particles of well-controlled coverage and molecule distribution was proposed

Physicochemical and Biological Study of 99mTc and 68Ga Radiolabelled Ciprofloxacin and Evaluation of [99mTc]Tc-CIP as Potential Diagnostic Radiopharmaceutical for Diabetic Foot Syndrome Imaging

This paper presents the application of ciprofloxacin as a biologically active molecule (vector) for delivering diagnostic radiopharmaceuticals to the sites of bacterial infection. Ciprofloxacin-based radioconjugates containing technetium-99m or gallium-68 radionuclides were synthesised, and their physicochemical (stability, lipophilicity) and biological (binding study to Staphylococcus aureus and Pseudomonas aeruginosa) properties were investigated. Both the tested radiopreparations met the requirements for radiopharmaceuticals, and technetium-99m-labelled ciprofloxacin turned out to be a good radiotracer for the tomography of diabetic foot syndrome using SPECT