Two proxy records revealing the late Holocene fire history at a site on the central coast of New South Wales,Australia

Abstract: The local fire history of a coastal swamp catchment in New South Wales was reconstructed using two proxy records of fire: sedimentary macroscopic charcoal and fire‐scar analyses of Xanthorrhoea johnsonii. The charcoal analysis provided a record of fire activity spanning the last 2800 years, while the Xanthorrhoea record covered the last approx. 300 years. The ability of each method to accurately record fire events was verified by cross referencing against the recent (post 1968) historic fire record. Fire history was then extrapolated beyond the historic record, to reveal an unprecedented level of fire activity in the last 35 years, which coincides with increased human activity in the area. In the prehistoric period charcoal and fire scars are comparatively rare, which is most parsimoniously ascribed to little fire activity, but perhaps represents skilful fire manipulation, as is often attributed to Aboriginal people. The comparatively minor fluctuations in macroscopic charcoal during the prehistoric period were approximately coeval with previous evidence of late Holocene environmental change in south‐eastern Australia, suggesting that fire frequency at the site responded to climatic variability. The longer temporal perspective of this palaeoenvironmental approach provides information for the contemporary management of fire in this conservation reserve.     

Effects of Mechanical Impedance on Root Growth in Barley (Hordeum vulgare L.): III. OBSERVATIONS ON THE MECHANISM OF RESPONSE

The effects of mechanical stress on whole root systems was investigatedusing beds of solid glass spheres (ballotini) continuously suppliedwith aerated nutrient solution. As noted in earlier experiments,increased mechanical impedance slowed root extension and alteredcell size and number; it also caused distortion of the rootapex, stimulated growth of lateral shoot meristems, and inducedthe formation of nodal roots. The development of lateral branchroots was enhanced and where root axes curved around ballotinilateral roots formed preferentially on the outer (convex) sidewhereas root hairs developed on the inner (concave) side. After roots were relieved from mechanical stress at least 3d elapsed before the rate of extension growth equalled thatof unimpeded plants. When intact Zea mays root apices first made contact with ballotinitheir elongation was slowed by 70% for about 10 min; where rootcaps were removed before the roots made contact, no such effectswere seen. We discuss the general nature of the mechanism of response tomechanical stress.     

Stem Cell Factor Regulates Human Melanocyte-Matrix Interactions

Stem cell factor (SCF) is hypothesized to play a critical role in the migration of melanocytes during embryogenesis because mutations in either the SCF gene, or its ligand, c-kit, result in defects in coat pigmentation in mice and in skin pigmentation in humans. In this report we directly show that SCF alters the adhesion and migration of human melanocytes to extracellular matrix (ECM) ligands and regulates integrin expression at the protein level. SCF decreased adhesion of neonatal and fetal cells to collagen IV, and increased attachment of fetal cells to laminin. Attachment of fetal cells to fibronectin was decreased, but was unchanged in neonatal cells. Flow cytometry analysis of neonatal melanocytes showed that SCF down-regulated the expression of the α2 receptor, and up-regulated the expression of the α3, α5 and β1 integrin receptors. SCF down-regulated expression of α2, α5 and β1 integrins by fetal melanocytes, and up-regulated expression of the αv and α3 integrin receptors. Analysis of melanocyte migration using time-lapse videomicroscopy showed that SCF significantly increased migration of neonatal, but not fetal, melanocytes on fibronectin (FN). We conclude that SCF regulates integrin expression at the protein level and that SCF has pleiotropic effects on melanocyte attachment and migration on ECM ligands. We suggest that this may be one mechanism by which SCF regulates melanocyte migration during development of the skin.