Many orchid species are seriously endangered at present. Reasons for their disappearing from natural habitats remain often unclear. Orchids depend on mycorrhizal symbiosis in nature, however only little is known about this symbiosis. Seeds of some species do not germinate in vitro, making their cultivation for scientific and rescue purposes impossible. We found that seed germination of one of such reluctant species, Pseudorchis albida, is strongly inhibited by nitrates even at extremely low concentrations. As this species prefers oligotrophic mountain meadows, nitrate-induced inhibition probably take place in natural conditions. Surprisingly, we found similar but slightly weaker inhibitory effect also in typical mesophillic species and even in slightly eutrophic ones. The sensitivity to nitrates correlates with trophy level of species canopy. This inhibitory effect of nitrates could be weakened by application of a range of growth regulators, including auxins, cytokinins and gibberellins, and also by mycorrhizal fungi. The action of nitratereductase is essential for this inhibitory effect of nitrates. Experiments with NO donors, scavengers, and NO quantification are pointing right at NO as compound which perhaps mediates nitrate inhibitory effect. Based on these results, the nitrate inhibitory...

This thesis deals with the preparation, characterization methods and in vitro imaging of nanoparticles with great potential for medical diagnostics. A key role in this work occupy nanoparticles comprising a core of calcium tungstate, CaWO4, covered by a natural polysaccharide together serve as a suitable model contrast agent for cell imaging techniques. CaWO4 natural properties such as the absorption of X-rays, natural fluorescence capabilities and capacities for doping fluorescently active lanthanides, makes from nanoparticles suitable candidates for the position of contrast agents for imaging in the diagnosis of oncological diseases. Moreover, by coverage of the inorganic core by natural polysaccharide nanoparticles reach the desired size and the possibility of active targeting to specific or nonspecific interactions with the cell membrane, which are key factors in in vitro cell studies. It was found the most suitable synthesis both doped and undoped core of this model reaching the formation of spherical particles of colloidal dimensions. Doping was realized by red fluorescent trivalent europium, Eu3+ , and green fluorescent trivalent terbium, Tb3+ , and neither of these dopants affected the original crystalline structure CaWO4. In the next stage, these fluorescent nuclei successfully dispersed...