Glycoconjugate Synthesis During Gastrulation in Xenopus laevis

Xenopus laevis gastrulae show more incorporation of isotopicallyabelled glucosamine and galactose into TCA-insoluble materialsthan blastulae. These materials are high molecular weight anddegraded by pronase as judged by their behavior in various gelfiltration media. Labelled materials migrate slowly on celluloseacetate electrophoresis, bind to DEAE—cellulose and eluteat low ionic strength, but are not precipitated by cetyl pyridiniumchloride (CPC) in the presence of added carrier hyaluronic acid. Pulse—chase labelling experiments and light microscopicautoradiography were used to examine secretion and depositionof glucosamine and galactose—labelled materials in differentstages of developing Xenopus laeins embryos. After a 30-minpulse, grains are predominantly over cytoplasmic structures.After a 30-min pulse and a 60-min pulse chase, grains are commonlyencountered over cytoplasmic structures but are predominantlylocalized over extracellular materials. Scanning electron microscopic studies show that extracellularfibrillar materials increase in number during gastrulation inXenopus laevis. Increasing numbers of extracellular fibrillarstructures occur in the blastocoel cavity and along the inneraspect of the roof of the lastocoel (Nakatsuji and Johnson,1983).     

Cellular Differentiation in a Highly Specialized Insect Secretory Organ

The colleterial glands of insects are accessory reproductive structures which produce secretions that are applied to eggs after fertilization and which serve a number of protective functions. The colleterial glands of lepidoptera are of particular interest in the study of the events of cellular differentiation because they undergo rapid development, generally during the pupal adult transformation, and contain highly specialized cells which produce large amounts of a restricted variety of secretory products. The extreme specialization of these organs facilitates parallel studies of differentiation at the biochemical and morphological level. This communication describes the changes in the ultrastructure of cells which will form the protein-secreting segment of the colleterial gland of the moth Actias luna during the period of transition from the undifferentiated state to the acquisition of secretory ability.
An initial stage of general cellular proliferation by mitosis in the presumptive colleterial tissue mass is followed by differentiation of the cells in the absence of further mitosis. Four distinctive cell types are recognized during the phase of differentiation. These types include a chitogenous cell which forms the chitin lining of the main duct, and three cells which cooperate in the formation of a secretory apparatus. Cell A forms two temporary flagella-like structures which assist in the formation of a ductule, which eventually leads from the secretory cell to the main duct. Near the end of the differentiative phase, Cell A degenerates and is phagocitized by Cell B. Cell B becomes the actual secretory element, and acquires cytoplasmic features such as extensive rough endoplasmic reticulum and Golgi apparatus which are associated with synthesis and secretion of protein. The final element, Cell C, remains associated with the ductule which it helps to construct and which traverses its cytoplasm.     

Biochemical Changes Associated with Zygotic Pine Embryo Development

Johnson, M. A., Carlson, J. A., Conkey, J. H. and Noland, T.L. 1987. Biochemical changes associated with zygotic pine embryodevelopment.—J. exp. Bot. 38: 518–524. At intervals during the period from pre-fertilization to nearmaturation, pine (Pinus resinosa Ait. and Pinus strobus L.)ovules were analysed for several biochemical constituents, andthe results were expressed on a fresh weight basis. Lipid accumulatedin parallel with the growth of the developing seeds. Solubleprotein also accumulated but only in the initial stages of development.ATP content peaked approximately 2 weeks after fertilization,followed about one week later by the energy charge; these peakswere associated with maximal growth stages of the developingembryos. Likewise, peaks of glutathione (GSH) and ascorbic acid(AA), two water-soluble reductants, preceded or coincided withthe ATP maximum. At late stages of seed development, dissectionof the more mature ovules into embryos and gametophytes foranalysis revealed that the ATP, GSH, and AA were more concentratedin the embryonic tissue. On the other hand, this segregationshowed that virtually no proanthocyanidin was located in thedeveloping embryos proper, although they contained other reductants,some of which were probably phenolics. Also, general stainingwith reagents for phenolics and thiols indicated that the formeroccurred primarily in non-embryonic tissue, whereas GSH wasin the embryo per se. These findings are consistent with rolesfor ATP, GSH, and AA in the growth and development of zygoticpine embryos; however, it would appear that lipid and proteinare being stored for subsequent germination events and thatmuch of the phenolic component is segregated from the developingembryo. Key words: Pine, embryogenesis, biochemistry     

Biochemical investigations of retinotectal adhesive specificity

The preferential adhesion of chick neural retina cells to surfaces of intact optic tecta has been investigated biochemically. The study uses a collection assay in which single cells from either dorsal or ventral halves of neural retain adhere preferentially to ventral or dorsal halves of optic tecta respectively. The data presented support the following conclusions: (a) The adhesion of ventral retina to dorsal tecta seems to depend on proteins located on ventral retina and on terminal β-N-acetylgalactosamine residues on dorsal tecta. (b) The adhesion of dorsal retina to ventral tecta seems to depend on proteins located on ventral tecta and on terminal β- N-acetylgalactosamine residues on dorsal retina. (c) A double gradient model for retinotectal adhesion along the dorsoventral axis is consistent with the data presented. The model utilizes only two complementary molecules. The molecule suggested to be concentrated dorsally in both retina and tectum seems to require terminal β-N-acetylgalactosamine residues for adhesion. Its activity is not affected by protease. A molecule fitting these qualifications, the ganglioside GM(2), could not be detected in a gradient, but lecithin vesicles containing GM(2) adhered preferentially to ventral tectal surfaces. The second molecule, concentrated ventrally in both retina and tectum, is a protein and seems capable of binding terminal β-N- acetylgalactosamine residues. One enzyme, UDP-galactose:GM(2) galactosyltransferase, has been found to be more concentrated in ventral retina than dorsal, but only by 30 percent.     

Variations in Depleted Uranium Sorption and Solubility with Depth in Arid Soils

This study examined the ability of alkaline desert soils to sorb depleted uranium (DU) as a function of soil horizon and assessed the solubility of corrosion and migration products from two DU kinetic energy penetrators exposed on the desert surface for a 22-y period. Both uranium corrosion products on the surface, and subsurface uranium originating from the dissolution of surface corrosion products followed by reprecipitation or sorption, were examined. A four-step sequential extraction method was used to classify uranium solubility at each site. Results show that distribution coefficient for uranium is highly variable, but can be correlated with the clay content (r = 0.55) and soil pH (r = 0.73) of the soil horizon considered. Surface corrosion products and near-surface uranium easily dissolve in a weak acid solution (25% acetic acid for two hours), suggesting a uranyl hydroxide form. As uranium migrates beyond several centimeters in depth, it forms insoluble aggregates with silicate minerals and requires strong acids to leach it. The formation of uranium-silicate mineral aggregates appears to be the limiting factor in vertical vadose zone transport of DU at the site investigated.