Microtubules and Filaments Beneath the Fission Furrow of Stentor coeruleus1

ABSTRACT. The ultrastructure of the cortex beneath the fission furrow of dividing Stentor coeruleus was examined using scanning and transmission electron microscopy. During division, basal bodies, axonemes, and km fibers beneath the furrow were absorbed near the moving primordial oral apparatus, and a circumferential band of microtubules and filaments was formed at the base of the furrow. The location and orientation of this fibrous band suggest that it may be an important component of the cytokinetic machinery. Treatment with vinblastine sulfate (4 × 10^-5 M) disrupted the circumferential microtubules and blocked division, which is consistent with this hypothesis.     

Vegetation of pastoralist campsites within the coastal grassland of central Somalia

Seasonal occupancy of pastoralist campsites where livestock are bedded down at night has created islands of soil fertility within the coastal grassland of central Somalia. Soil organic matter, nitrogen, phosphorous, and potassium concentrations were greatest at the centre of the campsites and decreased towards the perimeter. The vegetation on the campsites differed from the surrounding grassland, presumably in response to soil fertility and intense grazing. The fast-growing, grazing-tolerant, stoloniferous grass, Cynodon dactylon , and the non-palatable, annual forbs, Cleome tenella and Gisekia pharnaceoides , occupied the centre of the campsites. The campsite perimeters were dominated by the slow-growing, grazing-sensitive, perennial plants Cencrhus ciliaris and Indigofera intricata .

Résumé

L'occupation saisonnière des lieux de campement où le bétail est rentré pendant la nuit a créé des ilots au sol fertile dans la partie côtière de la Somalie centrale. La matière organique du sol, les concentrations en azote, phosphore et potassium, étaient plus élevées au centre du campement et diminuaient vers la périphérie. La végétation à l'intérieur des campements différait de la prairie environnante, résultat sans doute de la fertilité du sol et du pâturage intense. L'herbe à la croissance rapide, résistante au pâturage et stolonifèhe, Cynodon dactylon , et les désagréables et annuelles Cleome tenella et Gisekia pharnaceoides , occupaient le centre des campements. Le périmètre des campements était dominé par les plantes à croissance lente, sensibles au pâturage et perennes, Cenchrus ciliaris et Indigofera intricata .     

Bone Load Estimation for the Proximal Femur Using Single Energy Quantitative CT Data

A density-based load estimation method was applied to determine femoral load patterns. Two-dimensional finite element models were constructed using single energy quantitative computed tomography (QCT) data from two femora. basic load cases included parabolic pressure joint loads and constant tractions on the greater trochanter. An optimization procedure adjusted magnitudes of the basic load cases, such that the applied mechanical stimulus approached the ideal stimulus throughout each model. Dominant estimated load directions were generally consistent with published experimental data for gait. Other estimated loads suggested that loads at extreme joint orientations may be important to maintenance of bone structure. Remodeling simulations with the estimated loads produced density distributions qualitatively similar to the QCT data sets. Average nodal density errors between QCT data and predictions were 0·24 g/cm³ and 0·28 g/cm³. The results indicate that density-based load estimation could improve understanding of loading patterns on bones.     

Assessment of Canada Lynx Research and Conservation Needs in the Southern Range: Another Kick at the Cat

Abstract The ecology of Canada lynx (Lynx canadensis) and their main prey, snowshoe hares (Lepus americanus), is poorly understood in southern Canada and the contiguous United States compared to the boreal forest of Canada and Alaska, USA, where both species are well studied. However, given recent listing of lynx under the Endangered Species Act, accurate understanding of lynx and snowshoe hare ecology and conservation requirements in the United States is a high priority. We critically examined unchallenged perceptions and important research needs related to lynx and hare ecology and conservation at the southern extent of their range. Contrary to popular dogma, lynx do not require old-growth forest for denning, but further research on lynx and hare use of fragmented landscapes at lower latitudes is required. The contention that southern lynx are subject to higher interference or exploitative competition compared to their northern counterparts remains without strong empirical support. Lynx rely more on red squirrels (Tamiasciurus hudsonicus) and possibly other alternate prey at lower latitudes, but hares are the predominant food type for lynx across their range. Southern lynx and hare populations do not exhibit periodic cyclicity, but harvest statistics suggest that lynx abundance in the southern range is highly variable, implying that numerical fluctuations likely are fueled by immigration from Canada. Southern lynx population viability in the absence of ingress is suspect and thus maintaining connectivity with northern areas of occupancy should be a priority. Successful conservation of lynx populations in the contiguous United States will require 1) improved understanding of lynx population and habitat ecology at lower latitudes, 2) protection and management of large tracts of lynx and snowshoe hare habitat, and 3) ensured connectivity between lynx populations at the core and periphery of the species' range. However, in light of the numerous challenges facing conservation of populations of many species at their southern distributional limit, the long-term prognosis for lynx in the southern range currently is uncertain.     

The Health and Nutrition of a Medieval Nubian Population

Human remains from two cemeteries at Kulubnarti in Sudanese Nubia present an ideal opportunity to assess the biological impact of political and economic change. Remains from the early cemetery come from Nubia's medieval period, characterized by political unification and important achievements in art and architecture. Remains from the second cemetery come from the later emergent feudal age, characterized by regional isolation and return to a subsistence economy. Patterns of mortality, growth, development, nutrition, and disease revealed by the remains converge on one conclusion: the transformation from the medieval to the feudal age at Kulubnarti witnessed an improvement in human health and survival.     

Experimental Boron Neutron Capture Therapy for Melanoma: Systemic Delivery of Boron to Melanotic and Amelanotic Melanoma

The boron-containing melanin precursor analogue p-boronophenylalanine (BPA) has previously been shown to selectively deliver boron to pigmented murine melanomas when administered in a single intragastric dose. If boron neutron capture therapy is to become a clinically useful method of radiation therapy for human malignant melanoma, the boron carrier must be capable of delivering useful amounts of boron to remote tumor sites (metastases) and to poorly pigmented melanomas. We have now determined the ability of BPA to accumulate in several nonpigmented melanoma models including human melanoma xenografts in nude mice. The absolute amount of boron in the nonpigmented melanomas was about 50% of that observed in the pigmented counterparts but was still selectively concentrated in the tumor relative to normal tissues in amounts sufficient for effective neutron capture therapy. Single intragastric doses of BPA resulted in selective localization of boron in the amelanotic Greene melanoma carried in the anterior chamber of the rabbit eye and in a pigmented murine melanoma growing in the lungs. The ratio of the boron concentration in these tumors to the boron concentration in the immediately adjacent normal tissue was in the range of 3:1 to 4:1. These distribution studies support the proposal that boron neutron capture therapy may be useful as a regional therapy for malignant melanoma.     

Abscission in Coleus: Light and Phytohormone Control

Light control of leaf abscission in Coleus (Coleus blumei Benthcv. Ball 2719 Red) appears to be regulated by the quantity ofendogenous auxin transported from the leaf blade to the abscissionzone. Gas chromatographic—mass spectrophotometric analysisindicated that diffusate collected from leaf tissue treatedwith red light contained significantly higher levels of auxinthan dark and far-red light-treated leaf tissue. In addition,diffusate from red light-treated tissue inhibited abscissionof leafless petioles while diffusate from far-red light-treatedtissue promoted abcission when compared with diffusate fromdark-treated tissue. The effect of red light on abscission couldbe mimicked by IAA, but not by other phytohormones. An auxintransport inhibitor, 2, 3, 5-triiodobenzoic acid (TIBA), appliedeither as a lanolin ring around the petiole or vacuum infiltratedinto tissue, could completely eliminate any red light effecton abscission. The data are consistent with a phytochrome-mediatedlight regulation of endogenous auxin level in the leaf whichthen controls abscission. Key words: Abscission, Coleus, IAA, plant hormones, red (far-red) light, TIBA