Ionic relations and the regulation of turgor pressure in the marine alga,Valonia macrophysa

Summary Ionic composition and turgor pressure in the giant celled marine alga,Valonia macrophysa, were measured at environmental salinities ranging from 15 to 60 (11–44 atm). The steady-state turgor pressure, which is normally about 1.5 atm, changes only 2.5 atm in response to a 25 atm change in seawater osmotic pressure. Thus, turgor regulation is 90% effective. The salts important in turgor regulation are KCl and NaCl. During turgor regulation changes in intracellular KCl concentration account for 85% of the change in sap osmolality, and changes in NaCl account for the remaining 15%. Potassium is actively transported into the vacuole, whereas chloride appears to be passively transported as the counter ion. Thus, potassium transport, which we have shown previously to be sensitive to the turgor pressure, accounts for most of the turgor regulation at all salinities.     

Crystallite Features of Valonia cellulose by Electron Diffraction and Dark-Field Electron Microscopy

Individual cellulose crystallites from the cell wall of Valonia ventricosa have been studied by electron diffraction and observed by dark-field electron microscopy. These two techniques reveal that the crystalline zones which run along the fibrils are above 1000 Å in length without any longitudinal periodicity. The width of the crystallites covers the width of the microfibrils and ranges from 140 to 180Å without persistent 35 Å subunits. In several instances, the crystalline zones terminate in the manner of a fork with two arms of 30 to 40 Å in width.     

Electron diffraction of Valonia cellulose. A quantitative interpretation

The crystal structure of native cellulose (Valonia) has been analyzed by electron diffraction. Possible models for the structure were refined by rigid-body least squares methods, which incorporated parameters defining the preferred orientation of the fibrils around their long axes in the cell wall lamellae. The structure was found to consist of an array of chains having the same sense (i.e., parallel), with packing parameters similar to those recently determined by X-ray diffraction. The eight-chain unit cell could be approximated adequately by a two-chain monoclinic unit cell with dimensions a = 8.18 Å, b = 7.84 Å, c = 10.38 Å (fiber axis), and γ = 97.04°; the space group is P2₁.     

On the polarity of cellulose in the cell wall of Valonia

The orientation of the triclinic phase of cellulose in the cell wall of Valonia ventricosa J. Agardh was investigated by X-ray- and electron-diffraction analysis. In addition to the well-documented uniplanar-axial organization of the cell wall which requires that the a ^* axis should be always perpendicular to the wall surface, the direction of this axis was also found to be pointing outward from the plasma membrane side of the wall. This unidirectionality was persistent throughout the various layers that constitute the cell wall and also for the three microfibrillar orientations that occur in Valonia cell walls. The unidirectionality of the a ^* axis indicates, in particular, that the Valonia cellulose microfibrils are not twisted along their axis. These observations are consistent with a cellulose biosynthetic scheme where a close association exists between terminal-complex orientations and those of the cellulose microfibrils. In this context, the unidirectionality of the a ^* axis of cellulose seems to be related to the restricted mobility of the terminal complexes which are able to slide in the plasma membrane but not to rotate along their long axis.Abbreviations TC terminal complex This work was initiated during a visit of J.F.R at Grenoble in the framework of a France-Québec exchange program. J.S. was recipient of a CNRS fellowship. The diagram in Fig. 8 was kindly drawn for us by Miss Yukie Saito from the Department of Forest Products, the University of Tokyo.     

Action of exo- and endo-type cellulases from Irpex lacteus on Valonia cellulose

Cellulolytic mode of action of the two highly purified exo- and endo-type cellulases from Irpex lacteus on pure Valonia cellulose was investigated. Electron microscopy substantiated that both cellulases are adsorbed preferentially into the internal parts of microfibrils in the network structure of the cellulose at initial stages before enzymatic hydrolysis, and that the adsorption ratio of both cellulases onto the external surfaces of microfibrils increased with incubation time although this tendency was less remarkable with the exo-type cellulase than with the endo-type one. The exo-type cellulase exhibited relatively high activity producing cellobiose throughout 12-h incubation, while the endo-type cellulase produced small amounts of cellooligosaccharides. The degree of polymerization was far more suppressed by the endo-type cellulase than by the exo-type one. Degradation by the cellulases in typical exo- and endo-fashions yielded quite different morphological patterns in the microfibrils. Exo-type cellulase loosened the network structure of microfibrils and made them slightly thinner, while endo-type cellulase caused conspicuous swelling and dissolution of individual microfibrils.     

Preparation of sulfoacetate derivatives of cellulose by direct esterification

A new and efficient method for the preparation in one step of water-soluble cellulose acetate sulfate derivatives (CAS) is reported. Acetylation and sulfation were carried out simultaneously, using a mixture of acetic anhydride and sulfuric acid in glacial acetic acid. The reaction time and the amount of acetic anhydride were optimized and the method provided water-soluble esters, with a degree of acetylation in the range 1.6 and 2.4 and a degree of sulfation of 0.3. This method has been successfully applied to pure cellulose and to cellulose-enriched materials obtained from agricultural by-products. The product exhibited a high viscosity in aqueous solution suggesting interesting rheological properties.     

Crystalline cellulose degradation by a strain of Cellulomonas and its mutant derivatives

Summary Mutant derivatives of a strain of Cellulomonas (CS1-1) were shown to be able to degrade crystalline cellulose (cotton wool) more efficiently compared to the parent strain. These mutants were also more effective in the accumulation of reducing sugar in the growth medium under certain environmental conditions. Differences between the mutant derivatives and CS1-1 were reflected by assay of the amount and distribution of various cellulolytic enzymes.     

Intraspecific variability of pollen morphology as revealed by elliptic Fourier analysis

Pollen grains have long fascinated biologists who used their remarkable interspecific diversity as a marker to infer profiles of past and present vegetations and environment. This study addresses the question of the diversity of the morphology of pollen grains at the intraspecific level: how different are pollen grains of the same species sampled in different populations? Such differences are expected, and are actually well known to palynologists, but at the same time technically challenging to quantify. We used elliptic Fourier analysis, a powerful morphometric approach for the comparison of outlines, on equatorial and polar views of 30 pollen grains sampled in two different populations for each of five tropical species, thus yielding 600 outlines. Multivariate analysis of variance revealed intraspecific variation of shape of the pollen grains in three out of the five species studied. Our goal here was to test if there were differences in the shape of pollen. This, to our knowledge, would be the first such study of this particular aspect of palynology. We also discuss some relevant evolutionary hypotheses. Further studies using outline analysis, coupled with a choice of appropriate sampling strategies, to suit varying environmental conditions, would prove of great value in testing such hypotheses.     

The morphology of bone mineral as revealed by small-angle X-ray scattering

Diffuse small-angle X-ray scattering of oriented bone from bovine femur and canine femur was described in terms of an ideal isotropic two-dimensional two-phase system which consists of mineral phase and organic phase. The microstructure of powdered, randomly-oriented bone from bovine femur was found to be affected by grinding. An analysis of small-angle scattering from oriented bone showed that bone mineral was to a large extent in the form of needle-like particles with a 50-60 A the diameter, and the dimension of organic phase transverse to the longitudinal axis of long bone was in the range 45-55 A. The intersect distribution function was directly calculated from the scattering intensities, and the results strongly suggested the presence of needle-like mineral with sharp edges.     

Architectural dynamics of the meiotic spindle revealed by single-fluorophore imaging

Bipolarity of the meiotic spindle, required for proper chromosome segregation, is maintained throughout cell division despite rapid microtubule turnover. How this is achieved has remained mysterious, as determining the organization of individual spindle microtubules has been difficult. Here, we develop single-fluorophore speckle imaging to examine microtubule organization in the vertebrate meiotic spindle. We find that the mean length of microtubules is approximately 40% of spindle length. Long and short filaments distribute randomly throughout the spindle and those in close proximity can move in the same direction with highly heterogeneous velocities. The ratio between microtubule and spindle lengths remains unchanged as spindles elongate upon dynein-dynactin inhibition. However, maintaining this ratio depends on proper kinesin-5 function. Our data suggest that force transmission within the spindle must be understood in terms of the crosslinking dynamics of a tiled array of individual filaments, most of which do not span the distance from the pole to the metaphase plate.