Structure of shells of eggs of Callisaurus draconoides (Reptilia, Squamata, Iguanidae)

Female zebra-tailed lizards (Iguanidae: Callisaurus draconoides ) lay roughly ovoid eggs with thin, highly extensible shells. The outer surface of the eggshell is a thin, calcareous crust of calcium carbonate in the calcite morph. Immediately beneath the crystalline matrix is a shell membrane composed of multiple layers of fibres organized into an undulating series of troughs and crests, apparent in both cross-section and surface view. The outer surface of the shell membrane is differentiated into a tightly woven fibrous mat that may serve to anchor the calcareous layer to the membrane. Organization of the eggshell into a series of troughs and crests serves to increase the surface area available for contact with the substrate and, presumably, to increase the capacity of the eggshell to stretch as the egg absorbs water.     

A feeling for the micro-organism: structure on a small scale. Biofilms on plant roots

Biofilms are structured communities of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface; they have clinical, industrial and environmental impacts. Biofilms that are established by bacteria on plants are found on the surfaces of roots, leaves, seeds and internal vascular tissues where the microbes live in commensal, mutualistic or parasitic/pathogenic associations with their host. The study of the structure of plant-associated biofilms has been considerably helped by the development of techniques using fluorescent markers coupled with confocal scanning laser microscopy as well as scanning electron microscopy. We review several of these techniques as well as some of the research that has dealt with plant-associated biofilms. Our investigations focus on biofilm formation in the early stages of the Rhizobium –legume symbiosis, in which Gram-negative rhizobia provide fixed nitrogen to a host legume, and in return, the legume provides carbon-containing molecules. Because root colonization is an important early step in the establishment of the nitrogen-fixing symbiosis, we looked at Sinorhizobium meliloti attachment and biofilm establishment on the roots of its legume hosts, Medicago sativa L. and Melilotus alba Desr. We also examined biofilm formation by Rhizobium leguminosarum bv. viciae on the roots of Arabidopsis thaliana (L.) Heynh., a non-legume and non-host. Our ultimate goal is to characterize the rhizobial genes involved in aggregation and attachment to roots because several of these appear to be shared in biofilm formation and rhizobial entry of legume root cells.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 79–88.     

A developmental study of the phylloclades of Ruscus aculeatus L.

Lateral phylloclades of Ruscus aculeatus are found in the axils of reduced scale leaves on the orthotropic, photosynthetic stem. The terminal phylloclade results from the elongation and flattening of the main shoot apex after the lateral appendages have been initiated. Studies of the development of both lateral and terminal phylloclades point to their cauline nature. The hypothesis that the phylloclade results from the congenital fusion of a reduced short shoot and its prophyll is not supported.     

Ras is active throughout the cell cycle,but is able to induce cyclin D1 only during G2 phase

The control of cell cycle progression has been studied in asynchronous cultures using image analysis and time lapse techniques. This approach allows determination of the cycle phase and signaling properties of individual cells, and avoids the need for synchronization. In past studies this approach demonstrated that continuous cell cycle progression requires the induction of cyclin D1 levels by Ras, and that this induction takes place during G2 phase. These studies were designed to understand how Ras could induce cyclin D1 levels only during G2 phase. First, in studies with a Ras-specific promoter and cellular migration we find that endogenous Ras is active in all cell cycle phases of actively cycling NIH3T3 cells. This suggests that cyclin D1 induction during G2 phase is not the result of Ras activation specifically during this cell cycle period. To confirm this suggestion oncogenic Ras, which is expected to be active in all cell cycle phases, was microinjected into asynchronous cells. The injected protein induced cyclin D1 levels rapidly, but only in G2 phase cells. We conclude that in the continuously cycling cell the targets of Ras activity are controlled by cell cycle phase, and that this phenomenon is vital to cell cycle progression.