Evaluation of Mechanical Properties of Polysaccharide Films Prepared from Furcellaria Lumbricalis and Gigartina Skottsbergii Seaweeds by PF-QNM Technique

Films from Furcellaria lumbricalis (FL) and Gigartina skottsbergii (GS) seaweed extracts were prepared and their properties were investigated. According to NMR analysis of GS ultrasonic water (GSUW) extraction (1-3)-α-glycan 6-sulfate was isolated. The analogical treatment with carbonate-peroxide solution (GSUCP) resulted in a mixture of the same glycan and carrageenan hybrids µ-D6S and ν-D2S,6S observed for the first time in this study. The extraction of GS in boiling water under reflux (GSW) in comparison to FL (FLW), indicates that GSW consisted of the most complex mixture of α-, β-, κ-, ι-, θ-, ζ-carrageenans, (1-3)-α-glycan partially sulfated at C6, and µ-D6S and ν-D2S,6S hybrids. The analogical FLW extract contained α-, θ-, λ-, µ-, ν- and ζ-carrageenans and (1-3)-α-glycan partially sulphated at C6. SEC-MALS results indicate that molecular weight of chromatographic main peak (Mp) is decreasing: GSUCP (994 kg/mol) > GSUW (565 kg/mol) > FLW (498 kg/mol) > ι-carrageenan (264 kg/mol) > κ-carrageenan (174 kg/mol) > furcellaran (144 kg/mol) > GSW (78 kg/mol). Macromolecules conformation is varying from flexible random coil for κ-carrageenan to nearly compact spheres for ι-carrageenan. Furcellaran conformation is intermediate between κ-carrageenan and ι-carrageenan, specifically a little more compact than κ-carrageenan. XRD analysis confirmed no cellulose content in all prepared films. AFM and PF-QNM analysis showed relations between values of Rg and Mp and the values of surface roughness, reduced moduli, stiffness and adhesion.

Optical polarised phase function of the HR 4796A dust ring

Context. The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. Aims. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR 4796 A in polarised optical light. Methods. We obtained high-contrast polarimetric images of HR 4796 A in the wavelength range 600–900 nm with the SPHERE/ZIMPOL instrument on the Very Large Telescope. Results. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles.

Centriole and centrosome cycle in the early Drosophila embryo

Centriole and centrosome cycles were examined by indirect immunofluorescence and electron microscopy techniques in the early Drosophila embryo. The centrosomes, which are already divided at interphase, appear as compact spheres during prophase and metaphase, expand and flatten from anaphase to telophase and split into two units in late telophase. Centriole separation starts in late metaphase, becomes evident in anaphase and increases during telophase. Procentrioles appear during the following interphase.

Incorporation of tritiated cytochalasin B into ectodermal explants of the amphibian gastrula

Ectodermal explants from gastrulae of Triturus alpestris were exposed to tritiated cytochalasin B (5 and 10µg/ml) for ½–2½ h. The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yolk platelets, but were also scattered over other cellular components. Areas containing pigment granules or the feltwork material, present in the apices of dissociating cells of the superficial layer, exhibited higher activity than areas containing mitochondria or cytoplasmic matrix. Lipid droplets and nuclei showed comparatively little activity. The results are discussed in relation to previous findings on the uptake of tritiated cytochalasin D by cell fractions.