Modelling the distribution of diameter growth along the stem in Scots pine

This paper presents an empirical model for the distribution of diameter growth along the stem in Scots pine (Pinus sylvestris L.) and for the consequent stem form over time. First, the distribution of annual mass growth in the stem is determined as a function of the total annual growth in stem mass, current stem mass and the distribution of the latter along the stem. Second, the distribution of diameter growth is obtained by converting the fraction of annual growth in the stem mass at a given height in the stem into the thickness of the annual ring at the same height. Application of the model to Scots pine data sets including both young and mature trees not used in parameter estimation showed that the model was capable of reconstructing the distribution of diameter growth from the stem butt to the apex and from the pith to the stem surface at any height in the stem in both young and mature trees. The resulting empirical model was also linked to a physiological, process-based model in order to study its performance in a simulated stand. Simulations representing trees grown in unthinned and thinned Scots pine stands with trees of different status (from dominant to suppressed) showed that the response in tree growth to thinning in terms of the distribution of diameter growth along the stem was quite realistic relative to measured data.     

Plasmid-Borne Type E Neurotoxin Gene Clusters in Clostridium botulinum Strains

A collection of 36 Clostridium botulinum type E strains was examined by pulsed-field gel electrophoresis (PFGE) and Southern hybridization with probes targeted to botE and orfX1 in the neurotoxin gene cluster. Three strains were found to contain neurotoxin subtype E1 gene clusters in large plasmids of about 146 kb in size.     

Is reproduction of the Australian house mouse (<Emphasis Type="Italic">Mus domesticus</Emphasis>) constrained by food? A large-scale field experiment

Food quantity and especially food quality are thought to be key factors driving reproductive changes in the house mouse, Mus domesticus, leading to outbreaks of house mouse populations in the Australian grain-growing region. Characteristic changes during an incipient mouse plague are an early start of breeding, a high proportion of females breeding at a young age and a prolonged breeding season. We conducted a large-scale food manipulation during an incipient mouse plague, which started with early breeding and relatively high spring numbers of mice. We measured background food availability in four farms throughout the study and conducted a food manipulation experiment from November to March in two of them. After harvest in December 100-200 kg/ha spilled grain remained in the stubble. This was depleted by March. In two treatment farms we added high-protein food pellets on a weekly basis between November and March and two farms served as controls. We measured changes in mouse numbers by capture-mark-recapture trappings and changes in reproduction by scoring embryos and recent placental scars at necropsy. Mouse numbers did not differ between treatments and controls. There were no differences in the litter size or the proportion of females breeding between treatments and controls. We observed the normal pattern of high litter size in spring and decreasing litter size towards the end of summer in treatments and controls. In all farms reproduction stopped in March. Mouse numbers were high but not at plague densities. Contrary to our prediction we did not observe food constraint affecting the reproduction of female mice. Our field experiment seems to rule out food quality as the driving factor for improved reproduction and formation of an outbreak of mice. We suggest that physiological mechanisms in mice might not enable them to take advantage of food with a high protein content in arid summers in southeastern Australian grain fields because of the lack of free-standing water.     

Amino acid biosynthesis and metabolic flux profiling of Pichia pastoris.

Amino acid biosynthesis and central carbon metabolism of Pichia pastoris were studied using biosynthetically directed fractional (13)C labeling. Cells were grown aerobically in a chemostat culture fed at two dilution rates (0.05 h(-1), 0.16 h(-1)) with glycerol as the sole carbon source. For investigation of amino acid biosynthesis and comparison with glycerol cultivations, cells were also grown at 0.16 h(-1) on glucose. Our results show that, firstly, amino acids are synthesized as in Saccharomyces cerevisiae. Secondly, biosynthesis of mitochondrial pyruvate via the malic enzyme is not registered for any of the three cultivations. Thirdly, transfer of oxaloacetate across the mitochondrial membrane appears bidirectional, with a smaller fraction of cytosolic oxaloacetate stemming from the mitochondrial pool at the higher dilution rate of 0.16 h(-1) (for glucose or glycerol cultivation) when compared to the glycerol cultivation at 0.05 h(-1). Fourthly, the fraction of anaplerotic synthesis of oxaloacetate increases from 33% to 48% when increasing the dilution rate for glycerol supply, while 38% is detected when glucose is fed. Finally, the cultivation on glucose also allowed qualitative comparison with the flux ratio profile previously published for Pichia stipitis and S. cerevisiae grown on glucose in a chemostat culture at a dilution rate of 0.1 h(-1). This provided a first indication that regulation of central carbon metabolism in P. pastoris and S. cerevisiae might be more similar to each other than to P. stipitis.