Zooplankton decline in the Černé Lake (Šumava Mountains,Bohemia) as reflected in the stratification of cladoceran remains in the sediment

Stratigraphy of cladoceran remains in the upper 18 cm of a sediment core from the Lake Černé was studied. The successive disappearance of Bosmina longispina, Daphnia longispina and Ceriodaphnia quadrangula from the upper layers of the sediment corresponds with our knowledge concerning the disappearance of these species from the open water.     

Changes in basin geomorphology after implementation of the Oosterschelde estuary project

The completion in 1986/87 of an open storm-surge barrier in the inlet and of secondary dams in the landward parts of the Oosterschelde tidal basin (SW Netherlands) has had and will continue to have a significant impact on geomorphological developments. An analysis of historic data, and of recent detailed bathymetric and morphodynamic process data, indicates that former trends have reversed. At present the Oosterschelde is a sedimentation basin with a degrading intertidal area and silting up of channels. The continuing reduction in intertidal area, the decreasing geomorphological gradients, the increasing fine sediment content of channel deposits, combined with a general reduction in hydrodynamics, imply significant ecological effects.     

Grana stacking and protection of Photosystem II in thylakoid membranes of higher plant leaves under sustained high irradiance: An hypothesis

We propose yet another function for the unique appressed thylakoids of grana stacks of higher plants, namely that during prolonged high light, the non-functional, photoinhibited PS II centres accumulate as D1 protein degradation is prevented and may act as dissipative conduits to protect other functional PS II centres. The need for this photoprotective mechanism to prevent high D1 protein turnover under excess photons in higher plants, especially those grown in shade, is due to conflicting demands between efficient use of low irradiance and protection from periodic exposure to excessive irradiance.     

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K⁺ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K⁺-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K⁺-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K⁺ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.     

Differences in the metabolic responses of root tips of wheat and rye to aluminium stress

The effects of aluminium (Al) ions on the metabolism of root apical meristems were examined in 4-day-old seedlings of two cereals which differed in their tolerance to Al: wheat cv. Grana (Al-sensitive) and rye cv. Dakowskie Nowe (Al tolerant). During a 24 h incubation period in nutrient solutions containing 0.15 mM and 1.0 mM of Al for wheat and rye, respectively, the activity of first two enzymes in the pentose phosphate pathway (G-6-PDH and 6-PGDH) decreased in the sensitive cultivar. In the tolerant cultivar activities of these enzymes increased initially, then decreased slightly, and were at control levels after 24 h. In the Al-sensitive wheat cultivar a 50% reduction in the activity of 6-phosphogluconate dehydrogenase was observed in the presence of Al. Changes in enzyme activity were accompanied by changes in levels of G-6-P- the initial substrate in the pentose phosphate pathway. When wheat was exposed for 16 h to a nutrient solution containing aluminium, a 90% reduction in G-6-P concentration was observed. In the Al-tolerant rye cultivar, an increase and subsequently a slight decrease in G-6-P concentration was detected, and after 16 h of Al-stress the concentration of this substrate was still higher than in control plants. This dramatic Al-induced decrease in G-6-P concentration in the Al-sensitive wheat cultivar was associated with a decrease in both the concentration of glucose in the root tips as well as the activity of hexokinase, an enzyme which is responsible for phosphorylation of glucose to G-6-P. However, in the Al-tolerant rye cultivar, the activity of this enzyme remained at the level of control plants during Al-treatment, and the decrease in the concentration of glucose occurred at a much slower rate than in wheat. These results suggest that aluminium ions change cellular metabolism of both wheat and rye root tips. In the Al-sensitive wheat cultivar, irreversible disturbances induced by low doses of Al in the nutrient solution appear very quickly, whereas in the Al-tolerant rye cultivar, cellular metabolism, even under severe stress conditions, is maintained for a long time at a level which allows for root elongation to continue.Abbreviations G-6-PDH glucose-6-phosphate dehydrogenase - 6-PGDH 6-phosphogluconate dehydrogenase - G-6-P glucose-6-phosphate - TEA triethanolamine     

Mapping of two new markers within the smallest interval harboring the spinal muscular atrophy locus by family and radiation hybrid analysis

The locus responsible for the childhood-onset proximal spinal muscular atrophies (SMA) has recently been mapped to an area of 2–3 Mb in the region q12–13.3 of chromosome 5. We have used a series of radiation hybrids (RHs) containing distinct parts of the SMA region as defined by reference markers. A cosmid library was constructed from one RH. Thirteen clones were isolated and five of these were mapped within the SMA region. Both RH mapping and fluorescence in situ hybridization analysis showed that two clones map in the region between loci D5S125 and D5S351. One of the cosmids contains expressed sequences. Polymorphic dinucleotide repeats were identified in both clones and used for segregation analysis of key recombinant SMA families. One recombination between the SMA locus and the new marker 9Ic (D5S685) indicates that 9Ic is probably the closest distal marker. The absence of recombination between the SMA locus and marker Fc (D5S684) suggests that Fc is located close to the disease gene. These new loci should refine linkage analysis in SMA family studies and may facilitate the isolation of the disease gene.     

Haematological changes in an Antarctic teleost,Trematomus bernacchii,following stress

The effect of an acute increase in temperature, exhaustive exercise and hypoxia on the haematology of the benthic Antarctic teleost, Trematomus bernacchii was investigated. High temperature and hypoxia caused the biggest changes to the blood, with increases in haematocrit, haemoglobin concentrations and plasma chloride levels. The spleen decreased in mass. Exercise produced the smallest changes. Changes were substantially less than reported for the more active cryopelagic species Pagothenia borchgrevinki. The magnitude of the haematocrit increase is discussed in relation to life-style of fish living in the Antarctic.     

Cloning and expression analysis of an ADP-ribosylation factor from Solanum tuberosum L.

Summary A cDNA clone encoding an ADP-ribosylation factor from potato (Solanum tuberosum L.) was isolated. The nucleotide and deduced amino acid sequences show high homology to known ADP-ribosylation factor sequences from Arabidopsis, yeast, cow and man. In northern blot experiments, all tissues analysed showed expression of the corresponding mRNA. Strongest expression was found, however, in potato tubers.Abbreviations ARF, ADP ribosylation factor - BSA bovine serum albumin - EDTA ethylenediaminetetraacetic acid - SDS sodium dodecyl sulfate - SSC sodium saline citrate     

Localization of a New Type of X-Linked Liver Glycogenosis to the Chromosomal Region Xp22 Containing the Liver α-Subunit of Phosphorylase Kinase (PHKA2)

We describe here a new type of X-linked liver glycogen storage disease. The main symptoms include liver enlargement and growth retardation. The clinical and biochemical abnormalities of this glycogenosis are similar to those of classical X-linked liver glycogenosis due to phosphorylase kinase deficiency (XLG). However, in contrast to patients with XLG, the patients described here have no reduced phosphorylase kinase activity in erythrocytes and leukocytes, and no enzyme deficiency could be found. Linkage analysis of four families with this X-linked type of liver glycogenosis assigned the disease gene to Xp22. Lod scores obtained with the markers DXS987, DXS207, and DXS999 were 3.97, 2.71, and 2.40, respectively, all at 0% recombination. Multipoint linkage analysis localized the disease gene between DXS143 and DXS989 with a maximum lod score of 4.70 at θ = 0, relative to DXS987. As both the classical XLG gene and the liver α-subunit of PHK (PHKA2) are also located in Xp22, this variant type of XLG may be allelic to classical XLG, and both diseases may be caused by mutations in PHKA2. Therefore, we propose to classify XLG as XLG type I (the classical type of XLG) and XLG type II (the variant type of XLG).