Über die Mitosenverteilung im Meristem der Wurzelspitzen

Ohne ZusammenfassungMit 11 Textabbildungen.     

Acidic fibroblast growth factor enhances peripheral nerve regeneration in vivo

When added to a collagen-filled nerve guide, purified acidic fibroblast growth factor (aFGF) increased the number of myelinated axons that regenerated across a 5-mm nerve gap distance. In addition, a greater number of primary sensory and motor neurons extended axons through the nerve guide in animals treated with aFGF. Thus the effect of aFGF on peripheral nerve regeneration is not simply an increase in axonal branching within the nerve guide tube. This is the first highly purified growth factor since nerve growth factor that has been shown to promote nerve regeneration in vivo. This experimental model provides a convenient and quantitative means to assess the effects of putative neuronotropic factors on peripheral nerve regeneration in vivo.     

Nature of amino acid side chain and alpha-helix stability.

In order to investigate the ability of neutral amino acids to support the α-helix conformation, the coil–helix transition of poly(L -lysine) and of lysine copolymers with these amino acids was studied in water/methanol using circular dichroism. The transtions were recorded at constant pH adding buffer to the methanol/water mixtures. With poly(L -lysine), experiments were performed at several constant pH's; the transition midpoint on the water (methanol) concentration scale was found to depend strongly upon pH; the helix stability region is shifted towards higher water concentrations, when the pH is increased. Copolymers of lysine and several neutral amino acids revealed the same effect in that increasing amounts of, for example, norleucine also shifted the transition midpoint to higher water concentrations. A series of copolymers containing L -lysine as the host and different hydrophobic amino acids were synthesized and the helix–coil transition in water/methanol was observed at constant pH. Different copolymers of equal composition showed significant differences with respect to the nature of the amino acid incorporated into polylysine. From these studies an α-helix-philic scale (in decreasing order): Leu, Nle, Ile, Ala, Phe, Val, Gly is deduced and discussed; the results obtained were compared with those of different procedures.     

Decreased Laminin Expression by Human Lung Epithelial Cells and Fibroblasts Cultured in Acellular Lung Scaffolds from Aged Mice

The lung changes functionally and structurally with aging. However, age-related effects on the extracellular matrix (ECM) and corresponding effects on lung cell behavior are not well understood. We hypothesized that ECM from aged animals would induce aging-related phenotypic changes in healthy inoculated cells. Decellularized whole organ scaffolds provide a powerful model for examining how ECM cues affect cell phenotype. The effects of age on ECM composition in both native and decellularized mouse lungs were assessed as was the effect of young vs old acellular ECM on human bronchial epithelial cells (hBECs) and lung fibroblasts (hLFs). Native aged (1 year) lungs demonstrated decreased expression of laminins α3 and α4, elastin and fibronectin, and elevated collagen, compared to young (3 week) lungs. Proteomic analyses of decellularized ECM demonstrated similar findings, and decellularized aged lung ECM contained less diversity in structural proteins compared to young ECM. When seeded in old ECM, hBECs and hLFs demonstrated lower gene expression of laminins α3 and α4, respectively, as compared to young ECM, paralleling the laminin deficiency of aged ECM. ECM changes appear to be important factors in potentiating aging-related phenotypes and may provide clues to mechanisms that allow for aging-related lung diseases.     

Implication of the visual system in the regulation of activity cycles in the absence of solar light: 2-[125I]iodomelatonin binding sites and melatonin receptor gene expression in the brains of demersal deep-sea gadiform fish

Relative eye size, gross brain morphology and central localization of 2-[¹²⁵I]iodomelatonin binding sites and melatonin receptor gene expression were compared in six gadiform fish living at different depths in the north-east Atlantic Ocean: Phycis blennoides (capture depth range 265 to 1260 m), Nezumia aequalis (445 to 1512 m), Coryphaenoides rupestris (706 to 1932 m), Trachyrincus murrayi (1010 to 1884 m), Coryphaenoides guentheri (1030 m) and Coryphaenoides (Nematonurus) armatus (2172 to 4787 m). Amongst these, the eye size range was 0.15 to 0.35 of head length with a value of 0.19 for C. (N.) armatus, the deepest species. Brain morphology reflected behavioural differences with well-developed olfactory regions in P. blennoides, T. murrayi and C. (N.) armatus and evidence of olfactory deficit in N. aequalis, C. rupestris and C. guentheri. All species had a clearly defined optic tectum with 2-[¹²⁵I]iodomelatonin binding and melatonin receptor gene expression localized to specific brain regions in a similar pattern to that found in shallow-water fish. Melatonin receptors were found throughout the visual structures of the brains of all species. Despite living beyond the depth of penetration of solar light these fish have retained central features associated with the coupling of cycles of growth, behaviour and reproduction to the diel light–dark cycle. How this functions in the deep sea remains enigmatic.     

Divergence in germination traits among arctic and alpine populations of <Emphasis Type="Italic">Koenigia islandica</Emphasis>: light requirements

Light is known to regulate conservative germination strategies and the formation of seed banks. Although these strategies are crucial to survival in tundra environments—especially for annuals—light requirements for germination in arctic–alpine species are seldom investigated. Furthermore, environmental differences between arctic and alpine regions are expected to lead to evolutionary divergence among conspecific populations in seed germination strategies. In this study, we report important differences in germination light requirements among six arctic and alpine populations of the annual Koenigia islandica. Light had little effect on germination of the seeds from Iqaluit (Nunavut, Canada), Yukon (Canada), and Jasper (Alberta, Canada), whereas the seeds from the most severe climates, Svalbard (Norway) and Colorado (USA), had strong light requirements. Stratification of the seeds had little influence on their germination light requirements, with the exception of the population from Dovre (Norway), in which it induced a strong light requirement. Possible adaptive explanations and some implications of these observed germination patterns are discussed.