As compared with the swamp reed (SR) ecotype of Phragmites communis growing in the desert region of northwest China, plants of the dune reed (DR) ecotype from the same region possessed lower chlorophyll (Chl) content in leaves, and less thylakoids and grana stacks in chloroplasts. Tube gel electrophoresis without stain showed that the contents of Chl-protein (Pro) components related to photosystem 2 (PS2) were markedly lower in the DR thylakoid membranes than in the SR thylakoid membranes, while the contents of Chl-Pro components associated with PS1 were almost the same in both types. SDS-PAGE analysis indicated that the content of polypeptides of the light-harvesting Chl a/b complex of PS2 (LHC2) was lower in the DR thylakoids. Besides, the conformation of LHC2 within the DR thylakoid membranes was also altered as indicated by circular dichroism spectra. Hence in the DR, reduced energy harvesting by declining the size of LHC2 might be responsible for the down-regulated PS2 activity. Chl fluorescence parameters. Fv/Fm and quantum efficiency of PS2 (ΦPS2), were lower in the DR leaves than in the SR ones. However, non-photochemical quenching coefficient (qN) was greater in DR than that in SR, implying other energy dissipation way exists in the DR photosynthetic membranes. and X. Y. Zhu, S. M. Wang, C. L. Zhang.
The influence of surplus normál oř deficient nitrogen nutrition on the organization of maize chloroplast pigment apparatus was investigated. The amoímt of light- harvesting pigment-protein complexes (LHC) was the highest in chloroplasts fi^om high-nitrogen plants. Nitrogen deficiency resulted in a strong reduction of LHC, especially of its oligomer form. The fine structure of low temperature chloroplast absorption spectra revealed a relative decrease in the intensity of the 663, 666 and 678 nm components, while that of the components at 672 and 674 nm was increased. The changes in fine structure of the red fluorescence excitation spectra (F720 and F736) reflected similar changes in absorbance spectra. The changes do not allow to draw conclusions about the disturbance in energy transfer efficiency between some chlorophyll forms.
The genus Acanthamoeba includes more than 20 morphological species, but classification is problematical. Recently, the discovery of substantial interstrain differences in ribosomal DNA (rDNA) sequences has prompted questions about the relatedness of strains of the same species. In this study, therefore, we have investigated relationships between two isolates of A. polyphaga, CCAP 1501/3c and ATCC 30871, using morphological, biochemical, physiological, molecular and cytotoxicity assays. We observed that A. polyphaga ATCC 30871 exhibited up to six arms in endocyst while A. polyphaga CCAP 1501/3c exhibited a maximum of 5 arms thus indicating their position in group 2 and 3, respectively. Acanthamoeba polyphaga ATCC 30871 exhibited growth at 37°C and growth on 1M mannitol plates while A. polyphaga CCAP 1501/3c did not. In addition, both isolates exhibited differences in isoenzyme banding patterns and rDNA restriction fragment polymorphisms. More importantly, A. polyphaga ATCC 30871 produced cytotoxicity on corneal epithelial cells while A. polyphaga CCAP 1501/3c had no effects, suggesting differences in pathogenicity. Thus, all the results provide evidence for significant differences between the strains and further provided the basis for reclassification of the isolates. Implications of these results in the clinical diagnosis of pathogenic Acanthamoeba are discussed.
Tobacco plants accumulating high levels of soluble sugars due to the cytosolic expression of an inorganic pyrophosphatase from Escherichia coli were ušed to study adaptation to the osmotic stress that these plants are continuously faced with. In the course of differential RNA screening between wild type and transgenic plants three cDNA dones could be isolated, which after sequencing were identified as pathogenesis-related proteins (PR-proteins). Two cDNAs, PRlb and PR-P, belong to the acidic PRl and PR3 groups of PR-proteins, and the third cDNA, SAR8.2, has so far been associated with systemic acquired resistance in tobacco plants. The expression of PR-proteins transcripts in generál was well correlated with the steady- state level of total soluble sugars present in the tobacco plants. The induction of PR protein transcripts resulted in an accumulation of corresponding proteins. Moreover, the complete set of acidic PR-proteins induced by potato virus Y was also present in the sugar-accumulating transgenic plants. The induction of PR-proteins might be a generál response to the osmotic stress in tobacco plants.
The article presents a brief summary of newly discovered wooden structures in the well-known polycultural site Mohelnice – štěrkovna (also “U cukrovaru” or Za cukrovarem) in the Mohelnice cadastre and its vicinity. Earlier discoveries at this site include Neolithic timbered wells and a sensational find of an oak monoxylon from the La Tène period of the 4th/3rd century BC (dendro 281 or 301 BC). It was found trapped in its home port on the banks of the meandering river Morava and dating has revealed the same age as the absolutely dated simple wooden pole construction. It is the northernmost found monoxylon known in the Czech Republic and also presents the oldest evidence for such use of ships on Czech rivers. The manufacture and use of such ships has been known since the Mesolithic period continuing until modern times. The subsequent exploration of the shores of the Moravičany Lakes banks revealed a number of smaller wooden structures below the water surface, either made up of pointed stakes themselves, or a combination of smaller stakes and branches built into a tapered corridor resembling a structure used for fishing. The latest discovery is a massive oak-fir structure manufactured from stakes, longitudinal and transverse planks and stones, interpretable as a timber trackway, or a bridge. It has been dendrochronologically dated to 1547–1560 and archival sources indicate the structure was repaired in 1645. The structure spans the former meander between Třeština and Mohelnice near one of the mills. The existence of this route is documented on 18th-century maps. Significant discoveries from various times of mainly wooden buildings underscore at least the European significance of the Mohelnice site. It may yield many valuable finds in the future.
After 45 d of limited water supply, cassava (Manihot esculenta Crantz) exhibited pronounced reduction in shoot growth, high leaf fall, and decreased stomatal conductance. However, the water status of the remaining leaves was unaffected. This was combined with an amplified heliotropic response and drooping which minimises radiant energy interception at mid-day, suggesting that leaves are sensitive to high irradiance (I). In well-irrigated plants, CO2-saturated oxygen evolution and net photosynthetic rate (PN) in air were markedly higher (5-fold) in young (expanding) leaves than in mature leaves. Water limitation did not strongly modify CO2-saturated oxygen evolution but it altered PN in air for both types of leaves, although differently. The mature leaves of drought-adapted plants displayed residual rate of P N and deteriorated photosystem 2 (PS2) photochemistry estimated from chlorophyll (Chl) a fluorescence measurements. In young leaves at moderate I, PN was depressed by only 66 % in stressed plants. Moreover, the photochemical quenching of Chl a fluorescence and the quantum efficiency of PS2 photochemistry in young leaves were comparable in both control and stressed plants. In contrast at high I, PN was almost null and marked decreases in the two fluorescence parameters were apparent. Hence the strong heliotropic response and drooping displayed by young leaves under water limitation is an important strategy for avoiding inactivation of PN by high I and therefore for cassava tolerance to drought. and P.-A. Calatayud ... [et al.].
Cesta k objevu a následnému zkoumání vlastností kosmického zářeni byla a je stejně klikatá jako dráhy nabitých částic tohoto záření v propastech vesmíru. Ohlédnutí za prehistorií i historií výzkumu kosmických paprsků by mohlo být podnětem k vyřešení záhad, které se ani po stoletém úsilí mnoha badatelů nepodařilo rozluštit., The path to the discovery and subsequent study of the properties of the rather mysterious cosmic rays was, and still is as tortuous as the trajectories of charged particles in the depths of the universe. Looking back to the prehistory and history of cosmic-ray research might therefore serve as a stimulus for deciphering the puzzles that resist to be solved in spite of a hundred-year effort by many brilliant scientists., Jiří Grygar., and Obsahuje seznam literatury
The effects of a high temperature on leaf photosynthetic response of Lupinus albus, a species native from the Mediterranean zone, were studied under varying tissue water status and irradiance (/). At leaf temperatures optimal (25 °C) or near-optimal (15 ®C) for carbon assimilation in lupins, photosynthetic capacity (P^) was decreased at leď relative water content (RWC) around 60 %. The temperature above the optimum (e g. 35 oC) decreased at high RWC (80 %). Irrespective of the leaf water status the optimum leaf temperature for in lupins was around 25 "C. The inhibition of P^ by lupin leaf discs at 35 °C was greatly enhanced at high I. Leaf disc treatment at 35 in the dark did not change quantum yield or Pn. When in addition to 35 the leaves were subjected to high I (TS + IS) or to high I and dehydration (TS + IS + WS), then a substantial decrease was observed in the quantum yield (66 and 77 % of the values in Controls, respectively) and in (31 and 56 %, respectively).