Development, structure and function of rhinoceros enamel

Vertical enamel prism decussation in the inner-layer enamel of rhinoceroses occurs as the result of vertical translation, in opposite senses, of zones of ameloblasts, which begins very shortly after amelogenesis commences at the enamel-dentine junction. Prisms in the centre of the decussating zones are stacked in the Pattern 3 arrangement. Zone boundary prisms adopt intermediate orientations, are locally nearly perpendicular to the enamel surface, and have a cylindrical, Pattern 1 cross-section. Decussation also continues in the outer-layer enamel, but the prisms all have occlusal-going courses: the occlusal-going zones of the inner enamel continue as the more occlusally oriented zones of the outer layer. Abrasion resistance to diamond polishing and soft abrasive projectile erosion (air-polishing with NaHCOs) and resistance to ion beam erosion is greater with distance from the nearest prism boundary discontinuity. Polished surface areas containing longitudinally sectioned prisms are more prone to 'air-polishing' and 'airbrading' erosion than areas with transversely sectioned prisms. These observed relationships fully explain the relief developed at natural wear surfaces.     

A Method for the Isolation of Stable Mesophyll Protoplasts from Tomato Leaves throughout the Year under Standard Conditions

A method is described, based on growing tomato plants under low light intensities and feeding with calcium nitrate, whereby stable protoplasts can be isolated throughout the year under standard conditions. Plants are grown in the equivalent of spring and winter light intensities (i. e. incoming solar radiation 2.52 to 10.8 MJ m^?2 day^?1 15 h day) in the glasshouse on peat compost supplied with a balanced fertilizer containing nitrate and urea as nitrogen sources and given a supplementary feed of calcium nitrate. Under these conditions, high yields of protoplasts can be isolated on incubation in the dark using low enzyme concentrations at 25°C for 2 h. Protoplasts isolated in this way can support tobacco mosaic virus replication and are capable of cell division.     

Influence of Anthropogenic Structures on Northern Bobwhite Space Use in Western Oklahoma

ABSTRACT Anthropogenic structures associated with energy development and other activities are a growing concern in wildlife conservation because of habitat loss and fragmentation. We conducted a retrospective analysis of effects of barbed-wire fences, oil-extraction structures, aboveground power lines, resurfaced roads, and artificial water sites on space use by northern bobwhite (Colinus virginianus)in western Oklahoma, USA. Nest location data accrued during 1991–2002 and radiolocation data during 1997–2002. Data suggested fences had a weak repellent effect at distances <300 m, oil structures had neutral effects at distances <800 m, aboveground power lines had neutral effects at distances <250 m, resurfaced roads attracted at distances <350 m, and water sites had neutral effects at distances <250 m. Generally, anthropogenic structures seemed compatible with bobwhite populations on our study area, given density and dispersion of the structures that existed.     

Modelling the ecosystem effects of nitrogen deposition: Simulation of nitrogen saturation in a Sitka spruce forest,Aber, Wales,UK

A new model for simulating nitrogen leaching fromforested ecosystems has been applied to data from anexperimentally manipulated 30-year-old Sitka sprucestand. The manipulation experiment (at Aber, in north-western Wales, UK) was part of the European NITREXproject and involved five years of additions ofinorganic nitrogen to the spruce stand. The model(MERLIN) is a catchment-scale, mass-balance model thatsimulates both biotic and abiotic processes affectingnitrogen in ecosystems.The structure of MERLIN includes representationsof the inorganic soil, one plant compartment and twosoil organic compartments. Fluxes in and out of thesimulated ecosystem and transfers between compartmentsare regulated by atmospheric deposition, hydrologicaldischarge and biological processes such as plantuptake, litter production, immobilization,mineralization, nitrification and denitrification.Rates of nitrogen uptake, cycling and release amongpools are regulated by carbon productivity, inorganicnitrogen availability and the C:N ratios of theorganic pools. Inputs to the model are temporalsequences of carbon fluxes and pools, hydrologicaldischarge and external sources of nitrogen.The NITREX experiment at Aber began in 1990 withweekly additions of ammonium nitrate(NH4NO3) at a rate of 35 kg N ha-1 yr-1.Data were collected from both control andtreatment plots within the stand. The site-intensivedata from the control plots at Aber were augmented bydata taken from a chronosequence of 20 Sitka sprucestands and data from a survey of 5 moorland catchmentsin the same region to providecalibration data for the model. The data were used toestablish current conditions at the Aber site and toreconstruct historical sequences of carbon fluxes andpools from 1900 to the present day with which to drivethe model. The reconstructed sequences included anincrease in nitrogen deposition and a vegetationchange from moorland to plantation forest in 1960. Thecalibrated model was then used to predict the effectsof the experimental nitrogen additions begun in 1990.MERLIN successfully reproduced the observedincrease in NO3 leaching from aging spruce standsthat results from forest maturation and increasednitrogen deposition (as inferred from thechronosequence and forest survey data in the region).MERLIN also correctly predicted the increases insoilwater NO3 concentrations, the changes innitrogen content of tree and soil organic matterpools, and the changes in nitrogen fluxes that occurin spruce stands in response to increased nitrogeninputs (as observed in the nitrogen additionexperiment).     

Polymorphic microsatellite loci in Mimulus guttatus and related species

The evolution of self-fertilization from outcrossing is one of the most common evolutionary transitions in flowering plants. One goal of our research is to develop a linkage map based upon microsatellite loci in Mimulus guttatus and the selfing derivative M. nasutus in order to examine the genetics of one such transition. Here we present 19 primer pairs that detect polymorphisms between these two species. Within-population allelic surveys demonstrate the value of these markers for detailed analysis of population structure. We have found also that many of the microsatellites are conserved in more distantly related Mimulus species, and may thus serve as useful genetic markers for population genetic and comparative mapping studies within this diverse genus.     

Wind Flow Characteristics on a Soybean Leaf Compared with a Leaf Model

The purpose of this paper is to describe momentum boundary layer flow parameters on a soybean leaf [Glycine max (L.) Merrill] at various velocities of the bulk air stream and these data are compared with similar measurements on an artificial leaf. The wind structure is measured at three different bulk air velocitìes (u_∞= 39, 148 and 271 centimeters per second) on an individual soybean leaf and is compared to structural effects on an artificial leaf (flat metal plate) in a small closed-circuit wind tunnel. The boundary layers were homogeneous for the metal plate, but only at the lower velocity for the soybean leaf. The boundary layer thicknesses decrease with increasing bulk air velocity for laminar flow regimes, whereas in the turbulent flow regime the boundary layer thickness greatly increases. The effect of turbulence on the soybean leaf boundary layer made the eddy diffusivities at least three times greater than in the laminar flow regime at the calculated roughness height above the leaf surface. The structure of the leaf boundary layer flow is comparable to that of the metal plate only at the lower bulk air velocity.