Maurice Demarty

Polyanionic characteristics of purified sulphated homofucans from brown algae

Abstract Sulphated fucans were fractionated from different brown algae using quaternary ammonium detergents. Purified fractions from different species had the same general chemical composition, that of a typical sulphated homofucans, or fucoidan. The interaction of univalent and divalent counter-ions with fucoidan was investigated by viscometry and polarimetry, and by measuring the counter-ion activites and conductance coefficients in salt-free solutions. The activity and conductance coefficients were found to be independent of the polyanion concentration and approximately the same within each family of counter-ions. This indicates that cation binding in salt-free solutions of fucoidan is purely electrostatic. The conductivity results were in good agreement with the Mannings condensation polyelectrolyte model. The density charge parameter was 2.08 and the mean length of the monomeric unit was 4.5 A. Both the reduced viscosity and the optical rotation were dependent on the valency of the counter-ions used. Coupled with the data obtained from light-scattering measurements. ( M W = 1.7 10 6 and R g = 1760 A ), our results suggest that fucoidan in aqueous solution is an extended, flexible coil.

Partial purification of Flax cell wall pectin methylesterase.

Abstract Cell walls of Linum usitatissimum calli exhibited ca 1 μkat g−1 of pectin methylesterase activity (EC 3.1.1.11). Ion exchange and size exclusion chromatography gave three active fractions. The major one, representing 20% of the initial activity, with a chromatographic Mr of 100 000, and a SDS-PAGE one of 43 000 consisted of three isoforms with pIs of 5.5, 7.3 and 7.8, respectively. The second fraction, 3.5% of the initial activity, had a chromatographic Mr of 110 000, and was separated into five isoforms with pIs of 5.5, 7, 7.3, 7.8 and 8.8. The minor active fraction, 1 % of the initial activity, revealed one isoform (pI close to 10) but was contaminated with non-active proteins. The major active fraction had a Km of 0.147 mg ml−1 for a specific activity of 3.3 mkat g−1 and a complex behaviour in the presence of NaCl.

Structural features of CDTA-soluble pectins from flax hypocotyls

Polymers extracted with CDTA-Na2 (trans-diaminocyclohexane-a-tetra-acetic acid partially neutralized with NaOH) after a boiling water treatment from cell walls of 3-day-old seedlings of flax, germinated on water and in darkness, contained three main components: (1) rhamnogalacturonan I (RG-I)-like polymers with ratios of rhamnose to galacturonic acid which increased with their molecular mass; (2) neutral polysaccharides including galactans as well as arabinans; and (3) galacturonic-acid enriched polymers. n nHigh degrees of acetylation were estimated for most of the rhamnogalacturonans but a minor RG-I-like fraction with a ratio of rhamnose to galacturonic acid of unity was acetylated (29%) as well as methylesterified (40%). n nHowever, the calcium activity coefficients of the fractionated polymers measured in solution were quite high which implies that these polyelectrolytes did not behave like linear ones. These polymers which reacted in solution as well as in situ not only with ruthenium red but also with ferric hydroxylamine, and which contained large amounts of acetylated RG-I-like blocks might be considered as early markers of the differentiation of the cellulosic fibre cells in flax.

Degradation of flax polysaccharides with purified endo-polygalacturonase

Abstract An endo-polygalacturonase was purified from a commercial preparation of Aspergillus by cation exchange and size exclusion chromatographies. It degraded a polysaccharide extracted from under-retted flax into three general size classes. The first product was a polysaccharide of high molecular weight (close to 100 000), enriched in galactose and characterized by a ratio of galacturonic acid:rhamnose 2:1. The second product was an acidic polysaccharide (the molecular weight of which was close to 10 000) enriched in glucose and rhamnose, which reacted little with the usual colorimetric methods for uronic acids and gave a negative circular dicroism bond. The last and major products were oligomers rich in galacturonic acids.

Cambium pre-activation in beech correlates with a strong temporary increase of calcium in cambium and phloem but not in xylem cells

Using secondary ion mass spectrometry (SIMS), calcium was imaged in cambium cells and in the adjacent secondary phloem and xylem cells during the different phases of cambium functioning in beech (Fagus sylvatica L.). At the end of the period of quiescence, immediately before the resumption of cell divisions (i.e. at the cambium pre-activation phase), a strong temporary increase of calcium concentration was observed to take place in cambium and phloem but not in xylem cells.

SIMS determination of the distribution of the main mineral cations in the depth of the cuticle and the pecto-cellulosic wall of epidermal cells of flax stems: problems encountered with SIMS depth profiling

Depth profiles of C, Na, Mg, Al, K and Ca were performed in the cuticle and wall of epidermal cells of flax hypocotyls, with current densities ranging from 0.2 to 1 pA μm−2. The crater bottoms were never flat, but exhibited fairly complex, filiform or alveolar structures. The profiles of K, Ca and Mg were reasonably parallel to one another. The Ca/Mg signal ratio was in the magnitude of 3.5 in the cuticle. The Na profile, except perhaps in the cuticle, did not parallel the K, Ca and Mg profiles, but rather paralleled the C profile. At the outset of the depth profiles, ie in the cuticle, the intensity of the Na signal, although fairly variable, was usually above that of K; then there was an abrupt decrease of the Na signal, possibly at the border of the cuticle and of the wall. The Al signal usually began to increase, thus revealing the occurrence of perforations through the epidermis sample, after 80 min sputtering at a current density of 1 pA μm−2; the mean sputtering rate was thus estimated to be in the order of 1 μm h−1.

Modelling autocatalytic networks with artificial microbiology

Cells can usefully be equated to autocatalytic networks that increase in mass and then divide. To begin to model relationships between autocatalytic networks and cell division, we have written a program of artificial chemistry that simulates a cell fed by monomers. These monomers are symbols that can be assembled into linear (non-branched) polymers to give different lengths. A reaction is catalysed by a particular polymer or enzyme that may itself be a reactant of that reaction (autocatalysis). These reactions are only studied within the confines of the cell or reaction chamber. There is a flux of material through the cell and eventually the mass of polymers reaches a threshold at which we analyse the cell. Our results indicate a similarity between the connectivity of the reaction network and that of real metabolic networks. Developing the model will entail attributing increased probabilities of reactions to polymers that are colocalised to evaluate the consequences of the dynamics of large assemblies of diverse molecules (hyperstructures) and of cell division.

Inorganic Ions in Morphogenetic Responses of Plants

Signal transduction (i.e. the chain of events between reception and expression), depends on the interaction of organic molecules (e.g. hormones) with stereospecific cellular sites. However, inorganic ions also may be involved (Davies, 1987b; Desbiez and Thellier, 1987).