The effect of water stress on the gas exchange (CO2, H2O), distribution, water potential (T*), membrane permeability and chlorophyll content was studied in two maize hybrids, of the high and low drought tolerance, in the vegetative phase of growth. Diťferences in the responses to drought between both hybrids were clearly marked. After 5 d of drought the decrease in the net photosynthetic rate uptake and losses, transpiration rate (E) and increase of stomata resistance (r^ were greater in the drought-resistant hybrid than in the drought-susceptible one. On the contrary, after 10 or 15 d of drought, the decrease of and 'P in whole seedlings was greater in the susceptible hybrid than in the resistant one. Significant differences between hybrids were also observed in the accumulation of *'^C, the membrane permeability and the chlorophyll content. For all treatments the amount of carbon accumulation in roots of the resistant hybrid increased, while that of the susceptible one decreased. In the drought-resistant hybrid we observed a greater chlorophyll stability and a smaller damage of cell membranes than in the sensitive one.
Lichen thalli were exposed to 4 regimes differing in irradiance and duration of irradiation. Photosynthetic efficiency of thalli was monitored by chlorophyll fluorescence parameters and xanthophyll cycle analysis. Maximal quantum yield of photosystem 2 (FV/FM) decreased gradually with time in long-term treatment. The effect of additional short-term high irradiance (HI) treatment applied each 24 h was not significant. Nevertheless, short-term HI applied repeatedly on thalli kept in the dark led to a significant decrease of FV/FM. Non-photochemical quenching recorded during the long-term treatment corresponded to the content of zeaxanthin (Z). In short-term treatment, however, proportion of Z (and antheraxanthin) to total amount of xanthophyll cycle pigments recovered to the initial values every 24 h after each repeated short-term HI event in thalli kept in dark. Thus duration of irradiation rather than irradiance and frequency of HI events is important for a decrease in primary photosynthetic processes in wet thalli of Lasallia pustulata. Rapidly responding photoprotective mechanisms, such as conversion of xanthophyll cycle pigments, are involved mainly in short-term irradiation events, even at HI. and M. Barták ... [et al.].
The first part of the paper deals with the key question of the Searle-Derrida debate, namely, with the question of conceptual ''exactness'' and applicability of concepts to facts. I argue that Derrida makes a strict distinction between the exactness in the realm of concepts and the exactness in the realm of facts. Supposing that it is not correct to argue against him - as Searle does - that concepts cannot be exact because there are no strict boundaries between facts. The second part of the paper deals with a distinction used by John Searle: The distinction between linguistic meaning and speaker’s meaning. According to Searle linguistic meaning is constituted outside a particular context of use whereas speaker’s meaning is embedded in a particular situation. I argue this distinction is problematic as far as any meaning is constituted in a particular utterance and in a particular context of use., První část práce se zabývá klíčovou otázkou debaty Searle-Derrida, konkrétně otázkou konceptuální ,,přesnosti'' a aplikovatelnosti konceptů na fakta. Tvrdím, že Derrida rozlišuje mezi přesností v oblasti pojmů a přesností v oblasti faktů. Předpokládejme, že není správné argumentovat proti němu - jak to dělá Searle -, že pojmy nemohou být přesné, protože mezi fakty neexistují striktní hranice. Druhá část práce se zabývá rozlišením, které používá John Searle: Rozlišení mezi jazykovým významem a významem mluvčího. Podle Searle je lingvistický význam vytvořen mimo konkrétní kontext použití, zatímco význam mluvčího je zakotven v určité situaci., and Tomáš Koblížek
The photosynthesis and related plant productivity aspects of plants and cyanobacteria depend upon the functioning of photosystem 2 (PS2), associated with D1 and D2 heterodimer reaction centre core proteins. The D1 protein is encoded by psbA gene, genetically localized on the plastid genome (cpDNA), contains functional cofactors of PS2 in association with D2 protein, and also functions for radiant energy transformation through oxidation of water and reduction of plastoquinone. Surprisingly, D1 protein accounts for even less than 1% of the total thylakoid membrane protein content. In spite of that, its rate of turnover is very much comparable to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) large subunit, most abundantly present in green tissue. The normal functioning of PS2 possesses damage-repair cycles of D1 protein. Generally, rate of photodamage does not exceed the rate of repair under optimal growth conditions, therefore, no adverse effect on photosynthetic efficiency is manifest. However, under strong irradiance coupled with elevated temperature, level of photodamage exceeds the rate of repair, resulting in photoinhibition, photodegradation of D1 protein, and lowering photosynthetic efficiency linked with plant productivity eventually. The features of D1 turnover process are reviewed, particularly with respect to molecular mechanisms.
Dostupné vodíkové technologie mohou dramaticky omezit znečišťování životního prostředí a produkci skleníkových plynů. Přechod na vodíkové palivo bude nicméně vyžadovat silnou politickou vůli., Joan M. Ogdenová ; přeložila Andrea Cejnarová., and Obsahuje seznam literatury