Niche differentiation with respect to light utilization among coexisting dwarf shrubs in a subarctic woodland

Summary Canopy structure, shoot design, and photosynthetic light recruitment were used to compare four coexisting dwarf shrub species with respect to light utilization. All four species showed different shoot designs which probably result in different light interception properties. Leaves of Vaccinium uliginosum showed the highest levels of photosynthetic light saturation but in situ the shoots of this species reached their maximum photosynthetic rate at the lowest photon flux densities. No consistent differences with respect to photosynthetic light responses were found between deciduous and evergreen species. At sites dominated by one of the deciduous species (Vaccinium uliginosum or V. myrtillus), the two evergreen species studied (V. vitis-idaea and Empetrum hermaphroditum) occurred in the understory, i.e., with their leaf distribution slightly below that of the deciduous species. Sites dominated by one of the evergreen species showed less vertical differentiation in leaf distribution between species.     

Nucleation and growth of ice crystals inside cultured hepatocytes during freezing in the presence of dimethyl sulfoxide.

A three-part, coupled model of cell dehydration, nucleation, and crystal growth was used to study intracellular ice formation (IIF) in cultured hepatocytes frozen in the presence of dimethyl sulfoxide (DMSO). Heterogeneous nucleation temperatures were predicted as a function of DMSO concentration and were in good agreement with experimental data. Simulated freezing protocols correctly predicted and explained experimentally observed effects of cooling rate, warming rate, and storage temperature on hepatocyte function. For cells cooled to -40 degrees C, no IIF occurred for cooling rates less than 10 degrees C/min. IIF did occur at faster cooling rates, and the predicted volume of intracellular ice increased with increasing cooling rate. Cells cooled at 5 degrees C/min to -80 degrees C were shown to undergo nucleation at -46.8 degrees C, with the consequence that storage temperatures above this value resulted in high viability independent of warming rate, whereas colder storage temperatures resulted in cell injury for slow warming rates. Cell damage correlated positively with predicted intracellular ice volume, and an upper limit for the critical ice content was estimated to be 3.7% of the isotonic water content. The power of the model was limited by difficulties in estimating the cytosol viscosity and membrane permeability as functions of DMSO concentration at low temperatures.     

The solution structure of the CBM4-2 carbohydrate binding module from a thermostable Rhodothermus marinus xylanase

The solution structure is presented for the second family 4 carbohydrate binding module (CBM4-2) of xylanase 10A from the thermophilic bacterium Rhodothermus marinus. CBM4-2, which binds xylan tightly, has a beta-sandwich structure formed by 11 strands, and contains a prominent cleft. From NMR titrations, it is shown that the cleft is the binding site for xylan, and that the main amino acids interacting with xylan are Asn31, Tyr69, Glu72, Phe110, Arg115, and His146. Key liganding residues are Tyr69 and Phe110, which form stacking interactions with the sugar. It is suggested that the loops on which the rings are displayed can alter their conformation on substrate binding, which may have functional importance. Comparison both with other family 4 cellulose binding modules and with the structurally similar family 22 xylan binding module shows that the key aromatic residues are in similar positions, and that the bottom of the cleft is much more hydrophobic in the cellulose binding modules than the xylan binding proteins. It is concluded that substrate specificity is determined by a combination of ring orientation and the nature of the residues lining the bottom of the binding cleft.     

Overlapping and specific patterns of GDNF,c-ret and GFR alpha mRNA expression in the developing chicken retina

GDNF and the GDNF receptors, c-Ret, GFR alpha 1 and 2 mRNA is expressed in the developing chicken retina. GDNF labelling was mainly found in embryonic day 4-5 retina but weak labelling could also be found over scattered retinal cells at later stages. c-ret labelling was found over ganglion cells, amacrine and horizontal cells; the preferred GDNF receptor (GFR alpha 1) over amacrine and horizontal cells; and the less preferred GDNF receptor (GFR alpha 2) over ganglion cells, amacrine cells and photoreceptors.     

Controlling the cortical actin motor

Actin is the essential force-generating component of the microfilament system, which powers numerous motile processes in eukaryotic cells and undergoes dynamic remodeling in response to different internal and external signaling. The ability of actin to polymerize into asymmetric filaments is the inherent property behind the site-directed force-generating capacity that operates during various intracellular movements and in surface protrusions. Not surprisingly, a broad variety of signaling pathways and components are involved in controlling and coordinating the activities of the actin microfilament system in a myriad of different interactions. The characterization of these processes has stimulated cell biologists for decades and has, as a consequence, resulted in a huge body of data. The purpose here is to present a cellular perspective on recent advances in our understanding of the microfilament system with respect to actin polymerization, filament structure and specific folding requirements.     

Proton NMR and fast-atom bombardment mass spectrometry analysis of the melanoma-associated ganglioside 9-O-acetyl-GD3

A glycolipid antigen, detected by a monoclonal antibody (ME 311) obtained by immunizing mice with a human metastatic melanoma cell line (WM 46), was isolated and structurally characterized. Using immunostaining on thin-layer chromatograms for monitoring, 1.0 mg of a pure alkali-labile disialoganglioside was obtained from 23 g of packed melanoma cells (WM 164). Fractionation of the lipid extract was done on DEAE-Sepharose columns into total disialogangliosides which were repeatedly separated by high-pressure liquid chromatography. On mild alkaline treatment, the ganglioside was converted to a slower migrating species identical with a ganglioside GD3 isolated from the same source (Neu5Ac alpha 2----8Neu5Ac alpha 2----3Gal beta 1----4Glc beta 1----1-cer-amide) and specifically detected by monoclonal antibody R24. Comparison of the two gangliosides by fast-atom bombardment mass spectrometry (revealing an acetyl group on the terminal sialic acid on the alkali-labile species) and by 1H NMR (indicating the position of the acetyl group) suggested the following structure: Neu5,9Ac2 alpha 2----8Neu5Ac alpha 2----3Gal beta 1----4Glc beta 1----1-ceramide. This is identical with a ganglioside proposed earlier to exist in melanoma cells (Cheresh, D. A., Varki, A. P., Varki, N. M., Stallcup, W. B., Levine, J., and Reisfeld, R. A. (1984) J. Biol. Chem. 259, 7453-7459). Immunostaining with ME 311 antibody of cell extracts on thin-layer chromatography chromatograms revealed only this ganglioside in the melanoma cells, while normal human brain was negative. However, in one of the total ganglioside extracts tested for presence of binding with antibody ME 311, three gangliosides were found to bind. No evidence was obtained for the presence of the antigenic epitope in mucins or glycoproteins of the melanoma cells.     

Influence of sodium chloride on hydrophobic adsorption of PEGylated lysozyme

Interaction of macromolecules in aqueous salt‐containing solution with a hydrophobic adsorbent is studied by adsorption equilibrium measurements and by independent isothermal titration calorimetry. The macromolecules are native as well as mono‐, di‐, and tri‐PEGylated lysozyme and four pure PEGs. The hydrophobic adsorbent is Toyopearl PPG‐600M. The salt is sodium chloride. The sodium chloride concentration in the aqueous 25 mM sodium phosphate buffer is varied from 2000 to 4500 mM at pH 7.0 and 25°C. PEGylation of the lysozyme is carried using 5 and 10 kDa PEG chains. The molar enthalpy of adsorption is calculated from the adsorption equilibrium and the calorimetric data. The results show that the adsorption of the PEGylated lysozyme is caused by both the interaction of the lysozyme and the interaction of the PEG chains with the adsorbent, respectively, but the interaction of the lysozyme is stronger than that of PEG. The comparison of the results of the present study on the influence of sodium chloride with a corresponding study on the influence of ammonium sulfate shows that the adsorption mechanism changes upon the variation of the salt. The knowledge of the adsorption mechanisms supports the systematic development of chromatographic purification steps.     

PDGF-C is a new protease-activated ligand for the PDGF alpha-receptor

Platelet-derived growth factors (PDGFs) are important in many types of mesenchymal cell. Here we identify a new PDGF, PDGF-C, which binds to and activates the PDGF alpha-receptor. PDGF-C is activated by proteolysis and induces proliferation of fibroblasts when overexpressed in transgenic mice. In situ hybridization analysis in the murine embryonic kidney shows preferential expression of PDGF-C messenger RNA in the metanephric mesenchyme during epithelial conversion. Analysis of kidneys lacking the PDGF alpha-receptor shows selective loss of mesenchymal cells adjacent to sites of expression of PDGF-C mRNA; this is not found in kidneys from animals lacking PDGF-A or both PDGF-A and PDGF-B, indicating that PDGF-C may have a unique function.     

Characterization of the intermediates in the reaction of mixed-valence state soluble cytochrome oxidase with oxygen at low temperatures by optical and electron-paramagnetic-resonance spectroscopy.

The reaction of soluble mixed-valence-state (a3+CuA 2+.CuB + A32+) cytochrome oxidase with O2 at low temperature was studied by optical and e.p.r. spectroscopy. The existence of three intermediates [Clore & Chance (1978) Biochem. J. 173, 799-8101] was confirmed. From the e.p.r data it is clear that cytochrome a and CuA remain in the low-spin ferric and cupric states respectively throughout the reaction. No e.p.r. signals attributable to cytochrome a3 or CuB were seen in the intermediates. The difference spectra (intermediates minus unliganded mixed-valence-state cytochrome oxidase) and absolute spectra of the three intermediates were obtained. The chemcal nature of the three intermediates is discussed in terms of their spectroscopic properties. A catalytic cycle for cytochrome oxidase is proposed.     

Spatio-temporal processing of surface EMG signals from the sternocleidomastoideus muscle to assess effects of radiotherapy on motor unit conduction velocity and firing rate—A pilot study

Radiation therapy causes both muscle and nerve tissue damage. However, the evolution and mechanisms of these damages are not fully understood. Information on the state of active muscle fibres and motoneurons can be obtained by measuring sEMG signals and calculating the conduction velocity (CV) and firing rate of individual motor units, respectively. The aim of this pilot study was to evaluate if the multi-channel surface EMG (sEMG) technique could be applied to the sternocleidomastoideus muscle (SCM) of radiotherapy patients, and to assess if the CV and firing rate are altered as a consequence of the radiation.

Surface EMG signals were recorded from the radiated and healthy SCM muscles of 10 subjects, while subjects performed isometric rotation of the head. CV and firing rate were calculated using two recently proposed methods based on spatio-temporal processing of the sEMG signals. The multi-channel sEMG technique was successfully applied to the SCM muscle and CV and firing rates were obtained. The measurements were fast and simple and comfortable for the patients. Sufficient data quality was obtained from both sides of seven and four subjects for the CV and firing rate analysis, respectively. No differences in CV or firing rate were found between the radiated and non-radiated sides (p = 0.13 and p = 0.20, respectively). Firing rate and CV were also obtained from a myokymic discharge pattern. It was found that the CV decreased significantly (p = 0.01) during the bursts.