IST Austria Thesis

The development and growth of Arabidopsis thaliana is regulated by a combination of genetic programing and also by the environmental influences. An important role in these processes play the phytohormones and among them, auxin is crucial as it controls many important functions. It is transported through the whole plant body by creating local and temporal concentration maxima and minima, which have an impact on the cell status, tissue and organ identity. Auxin has the property to undergo a directional and finely regulated cell-to-cell transport, which is enabled by the transport proteins, localized on the plasma membrane. An important role in this process have the PIN auxin efflux proteins, which have an asymmetric/polar subcellular localization and determine the directionality of the auxin transport. During the last years, there were significant advances in understanding how the trafficking molecular machineries function, including studies on molecular interactions, function, subcellular localization and intracellular distribution. However, there is still a lack of detailed characterization on the steps of endocytosis, exocytosis, endocytic recycling and degradation. Due to this fact, I focused on the identification of novel trafficking factors and better characterization of the intracellular trafficking pathways. My PhD thesis consists of an introductory chapter, three experimental chapters, a chapter containing general discussion, conclusions and perspectives and also an appendix chapter with published collaborative papers. The first chapter is separated in two different parts: I start by a general introduction to auxin biology and then I introduce the trafficking pathways in the model plant Arabidopsis thaliana. Then, I explain also the phosphorylation-signals for polar targeting and also the roles of the phytohormone strigolactone. The second chapter includes the characterization of bar1/sacsin mutant, which was identified in a forward genetic screen for novel trafficking components in Arabidopsis thaliana, where by the implementation of an EMS-treated pPIN1::PIN1-GFP marker line and by using the established inhibitor of ARF-GEFs, Brefeldin A (BFA) as a tool to study trafficking processes, we identified a novel factor, which is mediating the adaptation of the plant cell to ARF-GEF inhibition. The mutation is in a previously uncharacterized gene, encoding a very big protein that we, based on its homologies, called SACSIN with domains suggesting roles as a molecular chaperon or as a component of the ubiquitin-proteasome system. Our physiology and imaging studies revealed that SACSIN is a crucial plant cell component of the adaptation to the ARF-GEF inhibition. The third chapter includes six subchapters, where I focus on the role of the phytohormone strigolactone, which interferes with auxin feedback on PIN internalization. Strigolactone moderates the polar auxin transport by increasing the internalization of the PIN auxin efflux carriers, which reduces the canalization related growth responses. In addition, I also studied the role of phosphorylation in the strigolactone regulation of auxin feedback on PIN internalization. In this chapter I also present my results on the MAX2-dependence of strigolactone-mediated root growth inhibition and I also share my results on the auxin metabolomics profiling after application of GR24. In the fourth chapter I studied the effect of two small molecules ES-9 and ES9-17, which were identified from a collection of small molecules with the property to impair the clathrin-mediated endocytosis. In the fifth chapter, I discuss all my observations and experimental findings and suggest alternative hypothesis to interpret my results. In the appendix there are three collaborative published projects. In the first, I participated in the characterization of the role of ES9 as a small molecule, which is inhibitor of clathrin- mediated endocytosis in different model organisms. In the second paper, I contributed to the characterization of another small molecule ES9-17, which is a non-protonophoric analog of ES9 and also impairs the clathrin-mediated endocytosis not only in plant cells, but also in mammalian HeLa cells. Last but not least, I also attach another paper, where I tried to establish the grafting method as a technique in our lab to study canalization related processes

Home bias persistence in foreign direct investments

The purpose of this paper is to analyse the issues related to home bias and foreign direct investments (FDIs). We study the role of physical, cultural, and institutional distances from home on FDI decisions taken by corporations to assess whether the globalization of the past two decades has reduced their influence. Using the ‘home bias’ framework from the finance literature and the gravity model from the economics literature, we utilize a large sample of both developed and emerging markets, using FDI flows of 6263 unique bilateral country pairs over a 30-year period. We find strong empirical evidence of persistent home bias in FDI outflows, and we show that not only physical distance but also cultural and institutional similarities between host and source countries remain a decisive factor in foreign corporate investment decisions. We also show that such home bias is persistent over time and is observed around the world

Herding in foreign direct investment

This paper, to our knowledge, is the first to examine herding in foreign direct investment (FDI). We investigate it from two perspectives, first the number of countries investing in the host country and then the dollar volumes of those investments. Our results provide strong evidence of herding in FDI. We also show herding in the divestures of these investors. We show that herding in FDI is related to host country characteristics and governance parameters

SUCCESS FOR REMOVING OR BYPASSING INSTRUMENTS FRACTURED BEYOND THE ROOT CANAL CURVE – 45 CLINICAL CASES

The aim of the study is to compare success rates for ultrasonic removal or bypassing endodontic instruments, fractured below the curve of root canals. Methods: 45 clinical cases – 30 MB and 5 ML root canals of mandibular molars, as well as 8 MB, 2 DB root canals of maxillary molars were selected from the authors’ private practice. 18 of the fragments are stainless steel files, 6 are rotary Ni-Ti files and 21 – lentulos. Fragments, to which visual access could be achieved by safe straightening of the root canal (26) were treated ultrasonically under dental microscope (OPMI Pico, Carl Zeiss) with magnification 10x and 16x. Bypass is chosen for fragments (19) without visibility. Results: Ultrasonic group: 22 of 26 fragments (84,61%) were totally removed, and full working length was consequently reached in 69,23% of the cases (18 fragments). Four fragments (15,38%) separated additionally from the vibrations and could not be totally ultrasonically removed. Bypass group: only 7 of 19 fragments (36,84%) could be successfully bypassed. Conclusions: Ultrasonic technique for broken instruments removal is significantly more successful than bypassing. Straight visible access to the fragment under dental microscope is crucial for successful fragments retrieval

Mathematical Modeling for Studying Microbial Processes – Some Examples

Mathematical modeling may have different purposes in chemical and biochemical engineering sciences. One of them is to confirm or to reject kinetic models for certain processes, or to evaluate the importance of some transport phenomena on the net chemical or biochemical reaction rate. In the present paper different microbial processes are considered and modeled for evaluation of kinetic constants for batch and continuous processes accomplished by free and immobilized microbial cells. The practical examples are from the field of wastewater treatment and biosynthesis of products, like enzymes, lactic acid, gluconic acid, etc. By the aid of mathematical modeling the kinetics and the type of inhibition are specified for microbial wastewater denitrification and biodegradation of halogenated hydrocarbons. The importance of free and immobilized cells and their separate contribution to the overall microbial process is also evaluated for some fermentation processes: gluconic acid production, dichloroethane biodegradation, lactic acid fermentation and monochloroacetic acid biodegradation

Наследяване на височината на растенията и броя на листата при хибридни комбинации тютюн Виржиния

The aim of current research is to determine genetic effects in relation to inheritance of plant height and leaves number regard to their use for the Virginia tobacco breeding. The experimental work was carried out on the field of the Tobacco and tobacco products Institute, Markovo, Bulgaria. Coefficient of heritability and selection, the number of genes, transgressions and heterosis of plant height and leaves number were studied. For this purpose P1, P2, F1 and F2 populations of seven hybrid combinations were analyzed. The data from conducted analysis showed that inheritance of the plant height and tobacco leaves number is overdominantly, in the direction of the parent with the higher trait values. The number of genes influencing the plant height expression varies in a wide range (14-17) and genes number affecting tobacco leaves is 1 or 2. Negative epistasis was observed for the plant height inheritance, while epistatic interactions of genes controlling leaves number was weaker but positive one. There were establish high values for heritability coefficient of plant height and average one of leaves number. Based on the conducted analysis it was found that the mass selection by phenotype for studied traits would be more effective in the F5-F6 hybrid generations.Целта на настоящото проучване е да се установи характерът на унаследяване на височината на растенията и броят на листата при хибридни комбинации тютюн Виржиния, във връзка с тяхното използване в селекционноподобрителната работа при тази култура. Експериментът е извършен на територията на Институт по тютюна и тютюневите изделия, Марково, България. Определени са унаследяването, коефициентите за наследяемост и отбор, броят на гените, проявите на трансгресия и хетерозис по отношение на изследваните признаци при кръстоски тютюн Виржиния. За целта са проучени P1, P2, F1 и F2 популациите на седем хибридни комбинации. Данните от хибридологичния анализ показват, че при изследваните в настоящото проучване образци, унаследяването на височината на растенията и броя на листата е свръхдоминантно винаги в посока на родителя, проявяващ по-висока стойност на признака. Броят на гените, влияещи върху проявлението на признака височина на растенията е от 14 до 17, а при брой листа – 1 или 2. По отношение височината се наблюдава отрицателен епистаз, а при броя на листата, по-слаб, но положителен такъв. Установени са високи стойности за коефициента на наследяемост за височината на растенията и средни стойности относно признака брой листа от растение. Коефициентите за наследяемост и за ефективност на масовия отбор по фенотип показват, че отборът на генотипове с по-големи стойности на височината на растенията и на генотипове с по голям брой листа ще бъде по-ефективен в F5-F6 генерациите

Sources and variations of tropospheric ozone in central Siberia: observations and model simulations

IOP Conference Series: Earth and Environmental Science, Climate change: causes, risks, consequences, problems of adaptation and management" 26-28 November 2019, Moscow, Russian Federatio