Fire and late-Holocene expansion of Quercus ilex and Pinus pinaster on Corsica

Abstract. The natural origin of old Quercus ilex (holm oak) forests on the west coast of Corsica is a matter of dispute. This paper discusses the use of pedoanthracology, especially adapted to approach topics in palaeoecology requiring a high spatial precision. It also shows the importance of fire in vegetation change during the Holocene. Pedoanthracology relies on botanical identification and AMS ¹⁴C dating of micro-charcoal found in soil. Three test pits were dug in a forest currently protected within the ‘Man and Biosphere’ program. These pits yielded large quantities of charcoal. There is evidence that Pinus nigra ssp. laricio (laricio pine) and understorey heather species (Ericaceae) played an important role in the vegetation at the beginning of the Subatlantic (ca. 2500 BP). The importance of Pinus pinaster (maritime pine), Quercus ilex and a few mesophilic species increased between 2000 and 1000 BP. Charcoal fragments found in the soil show the role of fire in the vegetation changes recorded. The late expansion of P. pinaster results from a high fire frequency. The hypothesis proposed in the paper suggests that fires destroyed the remaining toxic humus that had accumulated during the millennia which preceded the arrival of Q. ilex to our study sites. The late development of holm oak forest is a combination of the migration of the species and the increase of fire frequency since 2500 BP, most probably resulting from slash-and-burn agriculture.     

Middle Holocene vegetation and human impact in central Sudan: charcoal from the neolithic site at Kadero

Charcoal recovered from middens and graves in the neolithic site of Kadero, north of Khartoum, Sudan was analysed. The site lies within the semi-desert vegetation zone at present. During the occupation period (5960-5030 uncal B.P.), a scrub and thorn savanna grew around the site. It is further suggested that the vegetation during the neolithic period at Kadero was already under strong human impact through controlled fires, felling and grazing.     

Effects of Selenium and Exendin-4 on Glucagon-Like Peptide-1 Receptor, IRS-1, and Raf-1 in the Liver of Diabetic Rats

Selenium and exendin-4 exert antidiabetic effects by unknown mechanisms. Herein, we investigated their effects on the expression of glucagon-like peptide-1 receptor (GLP-1R), insulin receptor substrate-1 (IRS-1), and Raf-1 in the livers of rats with streptozotocin-induced diabetes. Diabetic rats were injected intraperitoneally with exendin-4 (0.03?μg/kg body weight) twice daily or treated with 5?ppm selenium as sodium selenite in drinking water for 4?weeks. Both selenium and exendin-4 reduced the hyperglycemia in diabetic rats. Induction of diabetes mellitus resulted in decreased level of GLP-1R and increased levels of IRS-1 and Raf-1 in the liver. Treatment of diabetic rats with selenium or exendin-4 resulted in increased level of GLP-1R and decreased levels of IRS-1 and Raf-1 in the liver, compared with the levels in diabetic rats. Therefore, the antidiabetic actions of selenium and exendin-4 involve their effects on GLP-1R, IRS-1, and Raf-1 levels in the liver.     

Redox interconversions of geraniol and nerol in higher plants

Use of ¹⁴C, ³H-labelled precursors showed that for feedings carried out in winter, isothujone (trans-thujan-3-one) was formed in Tanacetum vulgare from nerol (3,7-dimethyl-octa-cis-2,6-dien-1-ol) without loss of hydrogen from C-1 of the precursor. In contrast, formation from geraniol (the corresponding trans-isomer) involved stereospecific loss ofthe pro-(1S) hydrogen. This suggests that geraniol and nerol were interconverted by a redox system. Similar studies at other seasons with T. vulgare and on the biosynthesis of α- and β-pinenes (pin-3-ene; pin-2-(10)-ene) in Pinus pinaster; 1,8-cineole (1,8-oxidomethane) in Mentha piperita and Eucalyptus globulus; and carvone (menth-6,8(9)-dien-2-one) in M. spicata did not lead to such unambiguous conclusions. The results may be rationalized if (i) the redox system was reversible and/or (ii) tracer at C-1 of the phosphate esters of the precursors was scrambled by action of a phosphatase that induced CO bond fission.     

Carbonic anhydrase activity in primary sensory neurons

Neuronal subpopulations of dorsal root ganglion (DRG) cells in the chicken exhibit carbonic anhydrase (CA) activity. To determine whether CA activity is expressed by DRG cells maintained in in vitro cultures, dissociated DRG cells from 10-day-old chick embryos were cultured on a collagen substrate. The influence exerted by environmental factors on the enzyme expression was tested under various conditions of culture. Neuron-enriched cell cultures and mixed DRG-cell cultures (including numerous non-neuronal cells) were performed either in a defined medium or in a horse serum-supplemented medium. In all the tested conditions, subpopulations of cultured sensory neurons expressed CA activity in their cell bodies, while their neurites were rarely stained; in each case, the percentage of CA-positive neurons declined with the age of the cultures. The number and the persistence of neurons possessing CA activity as well as the intensity of the reaction were enhanced by addition of horse serum. In contrast, the expression of the neuronal CA activity was not affected by the presence of non-neuronal cells or by the rise of CO2 concentration. Thus, the appearance and disappearance of neuronal subpopulations expressing CA activity may be decisively influenced by factors contained in the horse serum. The loss of CA-positive neurons with time could result from a cell selection or from genetic repression. Analysis of the time curves does not support a preferential cell death of CA-positive neurons but suggests that the eventual conversion of CA-positive neurons into CA-negative neurons results from a loss of the enzyme activity. These results indicate that the phenotypic expression of cultured sensory neurons is dependent on defined environmental factors.     

Unsteady and three-dimensional simulation of blood flow in the human aortic arch

A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.     

Zinc-phosphorus relationship in the nutrition of corn plants (Zea mays L.) grown on some calcareous soils

Summary Positive relationships were observed between Zn and P in the studied calcareous soils and in the corn plants grown thereon. The high content of carbonates in these soils affected greatly the levels of extractable Zn and the Zn–P relationships. In the pot experiment, application of P increased the Zn content of the corn plants and application of Zn increased that of P.     

Flow-activated ion channels in vascular endothelium

The ability of vascular endothelial, cells (ECs) to respond to fluid mechanical forces associated with blood flow is essential for flow-mediated vasoregulation and arterial wall remodeling. Abnormalities in endothelial responses to flow also play a role in the development of atherosclerosis. Although our understanding of the endothelial signaling pathways stimulated by flow has greatly increased over the past two decades, the mechanisms by which ECs sense flow remain largely unknown. Activation of flow-sensitive ion channels is among the fastest known endothelial responses to flow; therefore, these ion channels have been proposed as candidate flow sensors. This review focuses on: 1) describing the various types of flow-sensitive ion channels that have been reported in ECs, 2) discussing the implications of activation of these ion channels for endothelial function, and 3) proposing candidate mechanisms for activation of flow-sensitive ion channels.