Study of Aqueous Chemical Forms of Silicon in Organic-rich Waters

The study of silicon species in organic-rich waters is a very significant problem. This type of waters is widely spread all over the world. It is characterized by a high content of humic substances, high color of water and low pH. In this regard, a certain determination of silicon concentration in this type of waters is impossible without a preliminary investigation of silicon species. The aim of this research is therefore an investigation of the ratio of silicon dissolved forms in organic-rich waters depending on the silicon concentration and the acidity of the water. The study of pH influence on silicic acids and a silicon-humic matter interaction was carried out using model solutions and natural bog waters (Tomsk region). It has been found that the degree of polymerization of silicic acids essentially depends on the acidity of a solution. Scanning of spectrophotometric measurements has shown that silicon does not form stable complexes with fulvic and humic acids in weak-acid media (рН 3-4). Studying the bog waters of Tomsk Region has shown that they (рН=3.66-3.80) contain only monomeric-dimeric and polymeric forms of silicic acids

Investigating the biosynthesis of cuticular alkanes in Arabidopsis thaliana : Characterization of SCD2 and chemical analysis of double CER mutant waxes

The plant cuticle is a hydrophobic layer that seals the surface of primary aerial organs of terrestrial plants and serves in protecting the tissues from abiotic and biotic stresses. Lipids are synthesized in the plastid and in the endoplasmic reticulum (ER) of epidermal cells for eventual export and deposition on the surface. Great progress has been made by genetic studies in the model plant Arabidopsis thaliana in elucidating fatty acid elongation, but knowledge of alkane biosynthesis is still scarce. The current work was focused on expanding our current understanding of alkane biosynthesis in Arabidopsis thaliana. A recent discovery of Susceptible to Coronatine-Deficient Pst DC3118-2 (SCD2) whose mutant has a leaf-specific increase in aldehydes and a decrease in alkanes suggests that SCD2 has a role in converting aldehydes to alkanes. In this thesis, further characterization of SCD2 revealed that alkanes are decreased in two mutant lines, the wax of mutants was restored by transgene complementation with the native gene, the transcript is abundant in leaves, and the promoter is active in the phloem of vasculature. Finally, the protein localized to the ER, consistent with its role in wax biosynthesis. This work provided evidence for yet another gene whose product is involved in formation of cuticular alkanes in Arabidopsis thaliana. Double mutants were generated to further study wax biosynthesis in both stems and leaves. The cer1cer3 mutant had greatly reduced total stem and leaf wax amounts compared to wild-type, as well as a substantial reduction of alkanes. It has an increase in C30 primary alcohol levels like the cer3 parent, indicating epistasis. This suggests that CER3 precedes CER1 in alkane formation. Furthermore, it is severely male-sterile with a reduction in epicuticular wax crystals. Wax biosynthesis is similar in stems and leaves of cer1cer3, cer1cer4 and cer3cer4. The cer1cer3 will be an important tool to test domain functionality of CER1 and CER3 and may shed more light on the mechanisms of alkane formation in Arabidopsis thaliana.Science, Faculty ofBotany, Department ofGraduat

COP1 is required for UV-B-induced nuclear accumulation of the UVR8 photoreceptor

The UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) promotes UV-B acclimation and tolerance in Arabidopsis thaliana UVR8 localizes to both cytosol and nucleus, but its main activity is assumed to be nuclear. UV-B photoreception stimulates nuclear accumulation of UVR8 in a presently unknown manner. Here, we show that CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is required for UV-B-induced nuclear accumulation of UVR8, but bypassing the COP1 requirement for UVR8 nuclear accumulation did not rescue the cop1 mutant UV-B phenotype. Using a glucocorticoid receptor (GR)-based fusion protein system to conditionally localize GR-UVR8 to the nucleus, we have demonstrated that both photoactivation and nuclear localization of UVR8 are required for UV-B-induced photomorphogenic responses. In contrast, there was no UV-B response when UV-B-activated UVR8 was artificially retained in the cytosol. In agreement with a predominantly nuclear activity, constitutively active UVR8(W285A) accumulated in the nucleus also in the absence of UV-B. Furthermore, GR-COP1 expression lines suggested that UV-B-activated UVR8 can be coimported into the nucleus by COP1. Our data strongly support localization of UVR8 signaling in the nucleus and a dual role for COP1 in the regulation of UV-B-induced UVR8 nuclear accumulation and in UVR8-mediated UV-B signaling

Mechanisms of UV-B light-induced photoreceptor UVR8 nuclear localization dynamics

Light regulates the subcellular localization of plant photoreceptors, a key step in light signaling. Ultraviolet-B radiation (UV-B) induces the plant photoreceptor UV RESISTANCE LOCUS 8 (UVR8) nuclear accumulation, where it regulates photomorphogenesis. However, the molecular mechanism for the UV-B-regulated UVR8 nuclear localization dynamics is unknown. With fluorescence recovery after photobleaching (FRAP), cell fractionation followed by immunoblotting and co-immunoprecipitation (Co-IP) assays we tested the function of UVR8-interacting proteins including CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 in the regulation of UVR8 nuclear dynamics in Arabidopsis thaliana. We showed that UV-B-induced rapid UVR8 nuclear translocation is independent of COP1, which previously was shown to be required for UV-B-induced UVR8 nuclear accumulation. Instead, we provide evidence that the UV-B-induced UVR8 homodimer-to-monomer photo-switch and the concurrent size reduction of UVR8 enables its monomer nuclear translocation, most likely via free diffusion. Nuclear COP1 interacts with UV-B-activated UVR8 monomer, thereby promoting UVR8 nuclear retention. Conversely, RUP1and RUP2, whose expressions are induced by UV-B, inhibit UVR8 nuclear retention via attenuating the UVR8-COP1 interaction, allowing UVR8 to exit the nucleus. Collectively, our data suggest that UV-B-induced monomerization of UVR8 promotes its nuclear translocation via free diffusion. In the nucleus, COP1 binding promotes UVR8 monomer nuclear retention, which is counterbalanced by the major negative regulators RUP1 and RUP2