Differences in chemical composition of plants grown at constant relative growth rates with stable mineral nutrition

Summary Leaf chemistry of a willow clone (Salix aquatica Smith) differed significantly when grown at constant relative growth rates depending upon the relative availability of nutrients and light. Concentration of amino acids and nitrate were high in plants grown with a relative surplus of nutrients. Concentrations of starch, tannin, and lignin, on the other hand, were high in plants grown with a relative surplus of carbon. Photosynthetic rates, expressed per unit leaf area, were similar when plants were grown under high light conditions, regardless of nutrient availability. Dark respiration was much higher in plants supplied with abundant nutrients than in those with a more limited supply, reflecting differences in nitrogen concentration of the tissue. The experimental approach allows plants to be grown to a standard size with differing, but highly uniform chemistry. Plants grown in such a manner may provide good experimental material to evaluate interactions between herbivores or pathogens and their hosts.     

Animal models for respiratory chain disease

Elucidation of the pathogenesis in respiratory chain diseases is of great importance for developing specific treatments. The limitations inherent to the use of patient material make studies of human tissues often difficult and the mouse has therefore emerged as a suitable model organism for studies of respiratory chain diseases. In this review, we present an overview of the field and discuss in depth a few examples of animal models reproducing pathology of human disease with primary and secondary respiratory chain involvement.     

Scale down of recombinant protein production: a comparative study of scaling performance

A large bioreactor is heterogeneous with respect to concentration gradients of substrates fed to the reactor such as oxygen and growth limiting carbon source. Gradient formation will highly depend on the fluid dynamics and mass transfer capacity of the reactor, especially in the area in which the substrate is added. In this study, some production-scale (12 m³ bioreactor) conditions of a recombinant Escherichia coli process were imitated on a laboratory scale. From the large-scale cultivations, it was shown that locally high concentration of the limiting substrate fed to the process, in this case glucose, existed at the level of the feedpoint. The large-scale process was scaled down from: (i) mixing time experiments performed in the large-scale bioreactor in order to identify and describe the oscillating environment and (ii) identification of two distinct glucose concentration zones in the reactor. An important parameter obtained from mixing time experiments was the residence time in the feed zone of about 10 seconds. The size of the feed zone was estimated to 10%. Based on these observations the scale-down reactor with two compartments was designed. It was composed of one stirred tank reactor and an aerated plug flow reactor, in which the effect of oscillating glucose concentration on biomass yield and acetate formation was studied. Results from these experiments indicated that the lower biomass yield and higher acetate formation obtained on a large scale compared to homogeneous small-scale cultivations were not directly caused by the cell response to the glucose oscillation. This was concluded since no acetate was accumulated during scale-down experiments. An explanation for the differences in results between the two reactor scales may be a secondary effect of high glucose concentration resulting in an increased glucose metabolism causing an oxygen consumption rate locally exceeding the transfer rate. The results from pulse response experiments and glucose concentration measurements, at different locations in the reactor, showed a great consistency for the two feeding/pulse positions used in the large-scale bioreactor. Furthermore, measured periodicity from mixing data agrees well with expected circulation times for each impeller volume. Conclusions are drawn concerning the design of the scale-down reactor.     

Synthesis of human walking: A planar model for single support

A mathematical model for the single support phase of normal, level, human walking is formulated. The motion of the lower extremity is synthesized using a preprogrammed set of inputs, recognized by the model as a simple collection of applied joint moments.

Two mechanisms are forwarded as candidates for producing the observed peaks in the vertical ground reaction. The first, stance knee flexion-extension, generates the necessary level of whole-body vertical acceleration during the initial region of single support (opposite toe-off to heel-off). A model accounting for the determinants of foot and knee interaction then predicts the second peak to be the result of an increasing ankle moment in the region from heel-off to opposite heel-strike.     

Environmentally induced morphological variation in the Barnacle Goose,Branta leucopsis

The environmental conditions to which juvenile barnacle geese (Branta leucopsis) were exposed during growth were found to affect their body size at fledging as well as their final adult body size. Small juveniles showed compensatory growth from the time of fledging up to one year of age, but this did not fully compensate the differences in body size that were established before fledging. The variation in protein content in plants eaten during growth could probably explain the observed body size differences, sometimes of more than 10%, between different categories of adult geese. Our results imply that one cannot infer selection on morphological characters from differences between samples of adult birds from different localities or from different cohorts within a population, without first showing that environmental conditions during growth do not affect the development of the characters under study.     

Few intra-lake variations of physiological parameters in perch, Perca fluviatilis

Intra-lake variations in physiological parameters, representing haematology, plasma ion composition and carbohydrate metabolism, were investigated in perch (Perca fluviatilis), inhabiting a comparatively unpolluted lake. Provided the perch were subjected to a standardized procedure for capture, handling, recovery after capture, and sampling, only few and minor differences were observed in 21 parameters investigated when 3 groups were compared to a control group of perch. It is concluded that the experimental design used is suitable for the examination of the physiological status of perch in the field.     

Distribution of ACTH-like immunoreactivity in rat brain and gastrointestinal tract.

Immunocytochemistry reveals ACTH-like immunoreactivity to reside not only in the pituitary but also in central nerves and in central nerves and in antral gastrin cells. In all probability, the central nerves store a peptide identical with or closely resembling true ACTH. Their pattern of distribution is, in some regions, similar to that of enkephalin-immunoreactive nerves. The antiserum demonstrating ACTH-like immunoreactivity in central nerves and in antral gastrin cells is directed towards the COOH-terminal part of the hormone. A peptide corresponding to this part, the corticotrophin-like intermediate peptide (CLIP) is manufactured by the pars intermedia of the pituitary. CLIP is devoid of adrenocortical activity, but has recently been shown to possess insulin-releasing activity. The occurrence of CLIP-like peptides in antral gastrin cells may indicate a role for such peptides in the gastrointestinal regulation of insulin release. The simultaneous occurrence of enkephalin-like and ACTH-like immunoreactivity in the antral gastrin cells is of particular interest since a large precursor molecule, containing both the enkephalin and the ACTH sequence has recently been identified.