|
| |
|
|
Mechanisms of physical dormancy and germination of orchid seeds
Jiroušková, Anna ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Orchid seeds are called dust seeds because of very reduced structure. A mature dust seed is composed of living embryo and two seed coats which are formed by dead cells. While the outer seed coat is distinctive, the inner seed coat (known as carapace) is very thin and tightly surrounds the embryo. Seed coat is hydrophobic and prevents water from entering embryo. To induce germination artificially, calcium hypochlorite or sodium hypochlorite solutions are often used. However, the effect of chemical scarification on seed coats is poorly understood. I focused on seeds of Epipactis helleborine and Dactylorhiza majalis and I analysed changes in seeds induced by calcium hypochlorite treatment using germination of seeds in vitro, permeability tests of seed coats and histochemical analyses of selected components of seed coats. The most prominent change observed was decrease of amount of lignin in the outer seed coat. This is likely related to increase in permeability of seeds and stimulation of in vitro germination rate in Dactylorhiza majalis which has only thin and less complex inner seed coat. However, this relationship was less evident in Epipactis helleborine, which has thicker and more complex inner seed coat which is more resistant to hypochlorite scarification. This could indicate existence of...
|
|
|
Ecophysiological relevance of extreme sensitivity of orchids to nitrates
Figura, Tomáš ; Ponert, Jan (advisor) ; Tylová, Edita (referee)
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...
|
|
|
Mechanisms that control physiological seed dormancy
Řezková, Natálie ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Physiological dormancy is an important developmental trait ensuring that seed does not germinate when the environmental factors are appropriate only temporary. The transition from seed dormancy to germination is regulated by a large number of factors and the phytohormone abscisic acid (ABA) plays a crucial role. Enhanced response to ABA and its biosynthesis is a key mechanism in dormancy induction and maintenance. ABA interacts antagonistically with gibberellins (GAs). Therefore GA biosynthesis and ABA catabolism are positive germination regulators. However, other phytohormones are also involved in the regulation of dormancy and germination. The most studied is ethylene which supports germination similarly to GA. Numerous factors affect dormancy at molecular level, namely chromatin remodeling, gene products that function only in dormancy regulation [e.g. DELAY OF GERMINATION 1 (DOG1)] or gene products that mediate seed response to environmental factors. The dormancy, its induction, depth and release, is driven not only by environmental conditions affecting mature seeds, but also by conditions acting during seed maturation in a maternal plant when the primary dormancy is induced. Requirements for dormancy release and germination induction may vary considerably between species. The physiological...
|
|
|
Stanovení mikroflóry osiva vybraných druhů zeleniny a možnosti ochrany
Chalupová, Lenka
The aim of this diploma thesis is assessing the determination and evaluation of pathogens species spectrum in carrot (Daucus carota), parsley (Petroselinum crispum) and pepper (Capsicum annum) seeds. The microflora was determined in laboratory conditions. The surface disinfected seeds and non-disinfected seeds were cultivated on culture medium PDA and filter paper. The level of bacterial and yeast contamination was low. The major part of pathogenswere fungi pathogens. The most often found pathogens were species from Alternaria and Cladosporium genus. The species spectrum was not different between individual varieties of carrot, parsley and pepper. In most cases, non-disinfected seeds had significantly higher amount of pathogens than the disinfected seeds.
|
|
|
Physical dormancy of seeds
Jiroušková, Anna ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Physical dormancy of seeds is a widespread adaptation, allowing plant seeds to time the germination to a suitable season. Seeds with physical dormancy possess hard seed coats, which are impermeable to water and sometimes also to gases. This allows seeds to create a long-term seed bank and to wait for favourable conditions even for years. There are two main mechanisms, which break physical dormancy and enable water to enter the seed. The seed coat can be disrupted through the whole surface, or in one specialized place only. The disruption through the whole surface is common in the seeds dispersed by endozoochory. In this case, the long-distance seed dispersal brings an important advantage. In physically dormant seeds, which are dispersed by other ways, a complicated structure called water gap is usually present in the seed coat. Water gap responds to exogenous signals and controls when the water enters the seed. In such a case, physical dormancy can be broken as a response to annual or diurnal temperature fluctuations, which times germination into a proper time of the year. Another species germinate in response to high temperatures during a fire. This ensures, that seedlings emerge in suitable conditions with a high level of available nutrients, low competition and that they can restore the damaged...
|
|
|
Evaluation of modifications in content of selected bioactive substances in flax (\kur{Linum usitatissimum} L.) seeds during germination
HAŠKOVÁ, Kateřina
This thesis focus on analysing effect of germination on some groups of bioactive compounds in flaxseed. We used flaxseed variety named Libra. Its germination was 10 days long, done in two different conditions: in the dark and fully iluminated for 24 hours daily. Samples were taken on 2nd, 4th, 6th, 8th and 10th day. Following analyses were performed: determination of dry matter content, lipid content, content of nitrogenous compounds, content of proteins and protein spectrum, chlorophyll content, content of total polyphenolic compounds and antioxidant activity. Content of dry mater was proved to decrease during germination as well as lipid content regardless of light conditions. Amount of nitrogenous compounds stayed relatively unchanged during germination. Whereas amount of proteins increased depending on duration of germination and light conditions. Hydrolysis of proteins during germination was proved by protein spectrum analysis. Content of chlorophyll inreased in light-germinated seeds only. Increasing effect of germination on total polyphenolic compounds content and antioxidant activity was proven as well. Moreover aproximately two-fold rise of values was reported after defatting of samples.
|
|
|
Mechanisms that control physiological seed dormancy
Řezková, Natálie ; Ponert, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Physiological dormancy is an important developmental trait ensuring that seed does not germinate when the environmental factors are appropriate only temporary. The transition from seed dormancy to germination is regulated by a large number of factors and the phytohormone abscisic acid (ABA) plays a crucial role. Enhanced response to ABA and its biosynthesis is a key mechanism in dormancy induction and maintenance. ABA interacts antagonistically with gibberellins (GAs). Therefore GA biosynthesis and ABA catabolism are positive germination regulators. However, other phytohormones are also involved in the regulation of dormancy and germination. The most studied is ethylene which supports germination similarly to GA. Numerous factors affect dormancy at molecular level, namely chromatin remodeling, gene products that function only in dormancy regulation [e.g. DELAY OF GERMINATION 1 (DOG1)] or gene products that mediate seed response to environmental factors. The dormancy, its induction, depth and release, is driven not only by environmental conditions affecting mature seeds, but also by conditions acting during seed maturation in a maternal plant when the primary dormancy is induced. Requirements for dormancy release and germination induction may vary considerably between species. The physiological...
|
|
|
Changes in timing of germination caused by neighbouring seeds and how it is connected with species traits.
Kos, Pavel ; Weiser, Martin (advisor) ; Hadincová, Věroslava (referee)
The time when the seed germinates is very important. Ability to change the time of germination may be very advantageous. It allows the emerging seed to choose the best time according to abiotic conditions, and also to avoid of competition with neighbouring individuals. The seed reacts not only on adult plants and seedlings, but also on other seeds, with which is able to communicate. For a better understanding to this mechanism I conducted an experimental study with twenty-six species. The species were selected according to their position in long succession seres of mesic/xeric abandoned fields in Český kras. The seeds were left to germinate in pairs in all combinations among them. Here I present the results where I show how the time of emergence changes, depending on presence of neighbouring seed. Also, I show how these changes in germination are related to species specific traits. Out of this, I tried to influence communication between seeds by adding activated carbon. Activated carbon should stop the communication by highly absorbing surface. The time of germination of seeds which germinated alone was not proportional to the time of germination of seeds which germinated with neighbours. This correlation showed up like nonlinear, late-emerging seeds emerging unproportionally later when emerging...
|
|
|
Seed germination of selected crops after low-temperature treatment
PETRÁŠKOVÁ, Kamila
The influence of low-temperature plasma on the different seeds is currently one of the most used techniques in agriculture. The aim of my bachelor thesis is to monitor and evaluate the effect of low-temperature plasma on the seeds of maize sow (Zea mays L.) and oilseed rape (Brassica napus L. napus), particularly on the germination of the seeds, germination rate and germination energy. These characteristics were measured by germination tests and they are expressed as a percentage. The submitted thesis informs whether the stimulation of the seeds by plasma affects these plants and if so, whether the influence is positive or negative.
|
guest ::
