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Auxin transport in algae
Skokan, Roman ; Petrášek, Jan (advisor) ; Bíšová, Kateřina (referee)
Phytohormone auxin plays an important role in regulating plant development. Directional (polar) cell-to-cell auxin transport creates auxin gradients within plant tissues, which trigger a specific developmental response. The vast majority of available data concerns angiosperms. Lower land plants have been much less explored in this regard, but the important auxin-related mechanisms (including polar auxin transport) are already present in mosses. To uncover the origins of auxin action, one must focus on green algae, especially of clade Streptophyta, which are the direct ancestors of all land plants. In this study, the possible effects of auxins, both native and synthetic, were investigated on two algae: basal, unicellular Chlorella lobophora and advanced, filamentous Spirogyra sp. The latter received comparably more attention, since it belongs to a clade now acknowledged as a sister group to land plants. Chlorella lobophora culture growth was irresponsive to synthetic auxin NAA. The average Spirogyra sp. cell length was, however, changed by auxins at high concentrations. By conducting accumulation assays of radioactively labelled auxins and HPLC analysis, auxin metabolism and transport was investigated in Spirogyra sp. This alga was able to metabolize the plant-native IAA, but not synthetic auxins...
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Cytokinines and their role in plant cell division, with accent on G2/M transition
Prášilová, Jana ; Ševčíková, Hana (advisor) ; Bíšová, Kateřina (referee)
The eukaryotic cell cycle is well understood mainly in yeasts and animals. Basic regulatory mechanisms, with cyclin-dependent kinases (CDKs) playing crucial roles, are similar in all eukaryotes including plants. CDKs operate mainly at the key cell cycle checkpoints, G1/S and G2/M. Phosphorylation and dephosphorylation of CDKs by kinases and phosphatases have both negative and positive effect. Negative regulator at the G2/M transition is WEE1 kinase which phosphorylates conserved amino acid residues T14 and Y15 of CDK. Phosphatase CDC25 removes this inhibitory phosphate in yeasts and animals and forces cells into mitosis. Plant cell cycle exhibits remarkable differences. Importantly, it is controlled by phytohormones, and some key points of regulation remain obscure - a functional plant homologue of yeast CDC25 phosphatase has not been found in plants yet though Y15 inhibitory phosphorylation by WEE1 kinase blocks mitosis entry in plants as well. Thus, the regulatory mechanism of G2/M transition in plant cells is still to be found. Phytohormones play a key role, not only in the plant cell cycle, but in whole plant development. Interplay between the two groups of phytohormones: auxins and cytokinins, is crucial. Especially cytokinins significantly influence the regulation of G2/M checkpoint. It is...
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Gamma-Tubulin forms and functions in microtubule organization and beyond
Kourová, Hana ; Binarová, Pavla (advisor) ; Šolc, Petr (referee) ; Bíšová, Kateřina (referee)
Microtubules are highly dynamic structures forming complex arrays changing accordingly to cellular requirements. In most eukaryotes, microtubules are nucleated from defined organizing centres like centrosomes or spindle pole bodies. Despite conservation of the major cytoskeletal components in plants and animals, plant cells lack centrosome-like structures and have evolved a unique mechanism to control microtubule assembly and organization. γ-Tubulin is an essential component of microtubule organizing centres, highly conserved in all eukaryotes with a prominent role in microtubule nucleation. However, growing body of evidence suggests γ-tubulin as a multifunctional protein. Next to microtubule nucleation, γ-tubulin controls microtubule plus-end dynamics, regulates gene expression, associates with DNA repair proteins and is implemented in mitotic and cell cycle regulation. We focused on γ-tubulin complexes and aimed to characterize interactors of γ-tubulin and their function in Arabidopsis. Next to characterizing microtubule dependent functions, we analyzed cell cycle and division. We also studied DNA damage response and involvement of E2F/RBR (retinoblastoma related) pathway and possible link to γ-tubulin. We characterized NodGS protein as a novel interactor of γ-tubulin in Arabidopsis and proposed...
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Cytokinines and their role in plant cell division, with accent on G2/M transition
Prášilová, Jana ; Ševčíková, Hana (advisor) ; Bíšová, Kateřina (referee)
The eukaryotic cell cycle is well understood mainly in yeasts and animals. Basic regulatory mechanisms, with cyclin-dependent kinases (CDKs) playing crucial roles, are similar in all eukaryotes including plants. CDKs operate mainly at the key cell cycle checkpoints, G1/S and G2/M. Phosphorylation and dephosphorylation of CDKs by kinases and phosphatases have both negative and positive effect. Negative regulator at the G2/M transition is WEE1 kinase which phosphorylates conserved amino acid residues T14 and Y15 of CDK. Phosphatase CDC25 removes this inhibitory phosphate in yeasts and animals and forces cells into mitosis. Plant cell cycle exhibits remarkable differences. Importantly, it is controlled by phytohormones, and some key points of regulation remain obscure - a functional plant homologue of yeast CDC25 phosphatase has not been found in plants yet though Y15 inhibitory phosphorylation by WEE1 kinase blocks mitosis entry in plants as well. Thus, the regulatory mechanism of G2/M transition in plant cells is still to be found. Phytohormones play a key role, not only in the plant cell cycle, but in whole plant development. Interplay between the two groups of phytohormones: auxins and cytokinins, is crucial. Especially cytokinins significantly influence the regulation of G2/M checkpoint. It is...
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Auxin transport in algae
Skokan, Roman ; Petrášek, Jan (advisor) ; Bíšová, Kateřina (referee)
Phytohormone auxin plays an important role in regulating plant development. Directional (polar) cell-to-cell auxin transport creates auxin gradients within plant tissues, which trigger a specific developmental response. The vast majority of available data concerns angiosperms. Lower land plants have been much less explored in this regard, but the important auxin-related mechanisms (including polar auxin transport) are already present in mosses. To uncover the origins of auxin action, one must focus on green algae, especially of clade Streptophyta, which are the direct ancestors of all land plants. In this study, the possible effects of auxins, both native and synthetic, were investigated on two algae: basal, unicellular Chlorella lobophora and advanced, filamentous Spirogyra sp. The latter received comparably more attention, since it belongs to a clade now acknowledged as a sister group to land plants. Chlorella lobophora culture growth was irresponsive to synthetic auxin NAA. The average Spirogyra sp. cell length was, however, changed by auxins at high concentrations. By conducting accumulation assays of radioactively labelled auxins and HPLC analysis, auxin metabolism and transport was investigated in Spirogyra sp. This alga was able to metabolize the plant-native IAA, but not synthetic auxins...
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Characterization of gamma-tubulin protein interactions and their functions in acentrosomal cells
Doskočilová, Anna ; Binarová, Pavla (advisor) ; Dráber, Pavel (referee) ; Bíšová, Kateřina (referee)
The long term goal of the Laboratory of Functional Cytology is to characterize the roles of γ-tubulin in acentrosomal plant model. Besides characterizing γ-tubulin interactions with plant homologues of proteins of γ-tubulin complexes (GCPs) and determination of their canonical role in microtubule nucleation, we also collect the evidence for γ-tubulin association with proteins that are not directly involved in microtubule nucleation. These γ-tubulin interacting proteins have been of high interest since their characterization might provide a platform for understanding the novel, yet not fully understood functions of γ-tubulin. The major aim of the laboratory is to determine signalling that regulates γ-tubulin complexes and their role in multiple processes in plants. Specifically, the cell cycle regulatory signalling in regulation of microtubular cytoskeleton nucleation and organization is of high interest.
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Cirkadiální hodiny se neúčastní načasování buněčného dělení v řase Chlamydomonas reinhardtii
Vítová, Milada ; Bišová, Kateřina ; Hendrychová, Jana ; Čížková, Mária ; Zachleder, Vilém
To determine whether the circadian clock functions in control the entry of algal cells into the cell cycle, we have tested the green alga Chlamydomonas reinhardtii in a wide range of growth conditions both light intensity and temperature. We monitored the course of the cell cycles in asynchronous as well as in synchronized cultures. The cultures were grown either at the continuous light or at alternating light/dark periods. The length of the cell cycle was monitored also at different temperatures and in “circadian” mutant. We have evidenced that the length of the cell cycle corresponding to circadian times can be attained only under relatively narrow range of growth conditions and even in this case the “circadian time” is a result of given growth conditions and not of any circadian gating. These results suggest that the intrinsic circadian clock does not play any role in timing of the cell cycle division in the green alga Chlamydomonas
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Plastoskeletální protein FtsZ a dělení chloroplastů v zelených řasách
Vítová, Milada ; Hendrychová, Jana ; Bišová, Kateřina
FtsZ protein, an ancestral homologue of eukaryotic tubulin, is the key effector in regulation of bacterial division. In plants, the FtsZ protein participates in chloroplast division. We have studied the chloroplast division in the green unicellular alga Scenedesmus quadricauda. To uncouple chloroplast and nucleocytoplasmic division cycles, we used 5-fluorodeooxyuridine (FdUrd). The amount and localization of FtsZ during the cell cycle was followed using immunoblotting and immunofluorescence staining on semi-thin sections. Antibody against FtsZ reacts with 49kD protein in Scenedesmus quadricauda and this protein is localized in chloroplast.The level of FtsZ protein increases during growth phase with maximum in time of chloroplast division. Localization of FtsZ protein is changing during the cell cycle, but we have not observed Z-ring, described in higher plants
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