The evolution and maintenance of white spruce woodlands on the Mackenzie Delta, N.W.T., Canada

White spruce forests on the most elevated surfaces of the Mackenzie Delta are dying out and are being replaced by open spruce/lichen-heath or spruce/bog woodlands. Soil profiles indicate that these woodlands have not received flood-deposited sediments for many years. The active layer is only 20 to 50 cm deep by mid-summer, and the organic soils are colder and more acidic than soils under white spruce forests flooded during spring ice breakup in 1961, 1972, and 1982. Spruce regeneration is limited to those stands that are flooded periodically, have moderately-closed canopies, and have a ground cover of herbs rather than feathermosses and lichens. It is proposed that a decrease in flood frequency is primarily responsible for the poor regeneration of white spruce on the most elevated delta surfaces. Spruce woodlands on the delta could succeed to tundra vegetation if present fluvial regimes continue.     

Luminescence-based detection of Erwinia carotovora associated with rotting potato tubers

A luminescence-based marker system has been used to follow rotting of potato tubers by Erwinia carotovora. The early stages of infection could be detected by visual observation of areas of luminescence developing from the point of inoculation. During later stages luminescence was limited to peripheral regions and to central regions where the structure of the potato was destroyed. Luminometry demonstrated reduction in aerobic activity of infecting cells due to oxygen limitation. The system enables rapid and sensitive detection of active marked populations and distinction between aerobic and fermentative activity.     

Hormonal regulation of myoblast proliferation and myotube production in vivo: influence of prostaglandins

The study of myoblast proliferation and fusion to form myotubes in vivo has centered around the role of the innervating motoneurones. Hormonal factors such as prostaglandin E1 (PGE1) are important during in vitro myogenesis, but their role in vivo has yet to be elucidated. In vitro, PGE1 appears to switch myoblast from a mitotic to a fusion mode. Consistent with this hypothesis, administration of PGE1 to chicken embryos decreased the number of myonuclei incorporated into their muscles. The effect of inhibitors of prostaglandin synthesis (aspirin and indomethacin) on in vivo myogenesis was not, however, as expected. Both drugs decreased the number of myonuclei incorporated into the muscles of treated embryos, which is the opposite of what would have been expected if they were enabling myoblasts to undergo additional divisions by delaying their onset from the mitotic cycle. The simplest explanation of this observation is that the effect of aspirin and indomethacin is mediated by a prostaglandin other than E1, or by a systemic factor whose levels are regulated by a prostaglandin. The maximum extent of the reduction caused by PGE1 and the inhibitors of prostaglandin synthesis was only 25-30%, suggesting that only a subpopulation of myoblasts is effected by these drugs. The number of myotubes formed in the treated embryos closely paralleled the total number of myonuclei, indicating that the number of myoblasts fusing to form a myotube is constant even when the total number of available myoblasts is diminished.     

Primary veloplasty or primary palatoplasty: some preliminary findings

Staged palatal closure was carried out in 30 children. The soft palate was closed at 9 months and the hard palate at 5 years. These patients were followed up for 7 years, and it was found that although the incidence of lateral crossbite was reduced in both unilateral and bilateral cases, the speech results were less satisfactory than those obtained with total palatal closure. In this series, there were two fistulae at the junction of the hard and soft palate. This was related to difficulty in closing this area in some patients at the time of the second operation. As a result, the procedure is not advised. An alternative palatal closure technique is described. This technique consists of nasal layer closure, careful dissection and reconstruction of the levator musculature, transverse division of the nasal layer, insertion of a buccal flap for lengthening, and closure of the oral layer with Veau flaps without dissection behind the tuberosities and with almost total closure of the lateral donor sites on the palatal shelves. In this way there is minimal scarring, particularly in the retrotuberosity area. This is felt to be important since it would seem from studies of facial growth that this is a much more significant area than the palatal shelves.     

Cupin: A candidate molecular structure for the Nep1-like protein family

Background  

NEP1-like proteins (NLPs) are a novel family of microbial elicitors of plant necrosis. Some NLPs induce a hypersensitive-like response in dicot plants though the basis for this response remains unclear. In addition, the spatial structure and the role of these highly conserved proteins are not known.     

CLADOGRAM VERSATILITY: EVOLUTION AND BIOGEOGRAPHY OF ACANTHUROID FISHES

A highly corroborated cladogram of acanthuroid fishes is used to explore several aspects of the biogeographic and microevolutionary events during the evolution of the group. Five events in acanthuroid evolution are documented here, which demonstrate not only the power of cladograms to provide adaptational hypotheses, but also how they can be used to frame significant questions for further research. Biogeographic analysis indicates that basal cladogenesis of the acanthuroids must have occurred prior to the Eocene (50-55 mya), because at least the basal lineages of the Acanthuridae, one of the last acanthuroid families to have evolved, were present at that time. In addition, optimization of current distributions suggests that the ancestors of the Acanthurinae, of the Acanthuridae, and of the Acanthuroidei each had an Indo–West Pacific distribution. Subsequent dispersion and/or speciation in one or more of these lineages may have been related either to the closure of the Tethys (ca 20 mya), or to colonization from the Pacific of the Caribbean/Atlantic prior to the formation of the Panamanian isthmus. Hypotheses about adaptation in acanthuroids begin with a discussion of several cases of dietary plasticity. The importance of information from fossils is illustrated in an investigation of predorsal bone evolution. Morphologically divergent and convergent tendencies in the modification of the pelvic fins concludes the examples. The morphologically most derived genus, Ctenochaetus, seems the least active taxon evolutionarily in the characters investigated.     

The action of some analogues of the excitatory amino acids in the dentate gyrus of the rat

We have confirmed that gamma-D-glutamylglycine and the L-isomer of 2-amino-4-phosphonobutyric acid, and have shown also that L-2-amino-5-phosphonovaleric (L-APV) acid, are antagonists of synaptic excitations of dentate granule cells induced from both lateral and medial perforant paths. The N-methyl-D-aspartic acid (NMDA) antagonist D-APV is without effect. The synaptic antagonists reduce the presynaptic fibre volley particularly in the lateral path, suggesting that a reduced transmitter output contributes to their action. NMDA receptors exist upon the granule cells, but they are not involved with these synaptic process.     

Relationship between muscle size and motoneurone survival in temporarily paralyzed embryos

Neuronal cell death has been postulated to occur as a consequence of there being a limited availability of target. This hypothesis was examined by delaying the onset of motoneurone cell death, by temporary paralysis of chick embryos, until the size of the target had increased. Despite the availability of this enlarged periphery, the extent of cell death was unaltered, although the rate of cell death was retarded. It is argued that the extent of cell death is not simply related to target size and may instead be governed by differences in the capacity of particular motoneurones to compete successfully for target cells.