The distribution and abundance of species of Danthonia DC on the New England Tablelands (Australia)

The distribution and percent frequency of the 13 species and one variety of Danthonia recorded on the New England Tablelands were examined in a survey of 110 predominantly pastoral sites. The relationships between site factors and the presence and percent frequency of the different Danthonia species were subjected to canonical correlation analysis. Individual species were found to have particular sets of environmental factors associated with their distribution and percent frequency; a fact not well recognized in the past. The most common factor associated with the abundance of Danthonia was either a long time since the last cultivation or no cultivation at all. Other factors such as altitude, drainage, soil parent material, soil texture and total soil phosphorus status were also of some importance. The six species most commonly recorded throughout the New England Tablelands were D. racemosa RBr, D. pilosa RBr, D. laevis J. Vickery, D. linkii Kunth., D. richardsonii Cashmore and D. tenuior (Steud.) Conert. Of these the first three are ecologically wide species. The first two can coexist with other naturalized species under grazing while D. laevis tends to disappear with disturbance. D. linkii and D. richardsonii require fairly narrow habitat conditions but these conditions and consequently these species are common. Both species respond positively to disturbance. Danthonia linkii increases with cultivation and D. richardsonii colonizes eroded soil surfaces. Danthonia tenuior has more restricted requirements and is not so frequent The other seven species and one variety did not occur often enough for detailed study and the occurrence of two of these species, D. carphoides and D. caespitosa must be considered as rare.     

Comparative in vitro and in vivo beta-oxidation of N-nitrosodiethanolamine in different animal species

The metabolism of N-nitrosodiethanolamine (NDELA) was studied to assess whether the formation of the beta-oxidated metabolites N-(2-hydroxyethyl)-N-(formylmethyl)nitrosamine (EFMN) and N-(2-hydroxyethyl)-N-(carboxymethyl)nitrosamine (ECMN) is involved in the mechanism of tumor induction in various animal species with different susceptibility to NDELA carcinogenicity. In vitro studies using liver S9 fractions from rats, hamster, B6C3F1 and CD-1 mice and rabbits showed that all the animal species metabolize NDELA through the beta-oxidation pathway, although to different extents. Urinary excretion of NDELA and its metabolite ECMN in rats, hamsters and mice after 5 mg X kg-1 NDELA i.p. confirmed these findings. The results suggest there is no correlation between carcinogenesis by NDELA and its beta-oxidation. The possibility that ECMN formation might represent a detoxifying metabolic pathway for NDELA is discussed.     

Radioimmunoassay of chenodeoxycholic acid-3-sulfate in urine

A sensitive and specific radioimmunoassay (RIA) for the measurement of urinary total chenodeoxycholic acid-3-sulfate (SCDCA) was developed and the accuracy was confirmed. SCDCA bound to bovine serum albumin as the antigen and emulsified with Freund's complete adjuvant was injected into rabbits. The antiserum obtained was capable of binding 75% of [11,12-3H]SCDCA at 1:1000 dilution. The percentage of bound radioactivity decreased linearly with logarithmic increases in unlabeled SCDCA, from 8 to 200 pmol/ml. The antiserum showed an extremely high specificity for SCDCA (free and conjugated), and the values determined by RIA indicated a close correlation with those found by gas-liquid chromatography. The daily urinary SCDCA level was determined using SCDCA-RIA in 12 disease-free humans and 74 patients with chronic liver diseases. In the normal subjects the daily urinary SCDCA level was 0.74 +/- 0.83 mg/day and increased levels were evident in all groups with chronic liver diseases. The daily urinary SCDCA level corresponds closely with the extent of hepatic dysfunction.     

Comparative incidence of reticuloendothelial tumors in C57BL mice after exposure to tritiated water

A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types.     

The role of oxygen availability in the embryonation of Heterakis gallinarum eggs.

The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.     

Calculation of effective diffusivities for biofilms and tissues.

In this study we describe a scheme for numerically calculating the effective diffusivity of cellular systems such as biofilms and tissues. This work extends previous studies in which we developed the macroscale representations of the transport equations for cellular systems based on the subcellular-scale transport and reaction processes. A finite-difference model is used to predict the effective diffusivity of a cellular system on the basis of the subcellular-scale geometry and transport parameters. The effective diffusivity is predicted for a complex three-dimensional structure that is based on laboratory observations of a biofilm, and these numerical predictions are compared with predictions from a simple analytical solution and with experimental data. Our results indicate that, under many practical circumstances, the simple analytical solution can be used to provide reasonable estimates of the effective diffusivity.