Data-Driven Modeling of Intracellular Auxin Fluxes Indicates a Dominant Role of the ER in Controlling Nuclear Auxin Uptake

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Seasonal distribution of sympagic amphipods near Chesterfield Inlet, N.W.T., Canada

The seasonal distribution of sympagic amphipods was investigated in the Chesterfield Inlet area of northwestern Hudson Bay (63°30′N). Amphipod abundance was measured by photographic samples and species composition was determined by sweep net samples. Twelve species of amphipods were collected, the most common being Ischyrocerus anguipes, Pontogeneia inermis, Apherusa megalops and Weyprechtia pinguis. The major environmental variable affecting amphipod distribution was water depth. Amphipod abundance was highest near 20 m and near zero past 50 m. The maximum recorded abundance was 1367 m⁻². A minor factor affecting the distribution of amphipods was snow depth, through its modifying effect on light and thereby the growth of ice algae. Amphipods began to inhabit the sea ice shortly after its formation. From the beginning of March, the number of amphipods on the ice increased steadily to about the 3rd week of April, after which numbers declined. This pattern coincided with the seasonal ice algae abundance. Amphipods reduced ice algal biomass over 20-m depth by 63%. No evidence of diurnal changes in abundance was observed. Received: 15 May 1996 / Accepted: 4 November 1996     

Extreme differences in rates of molecular evolution of foraminifera revealed by comparison of ribosomal DNA sequences and the fossil record

Foraminifera have one of the best known fossil records among the unicellular eukaryotes. However, the origin and phylogenetic relationships of the extant foraminiferal lineages are poorly understood. To test the current paleontological hypotheses on evolution of foraminifera, we sequenced about 1,000 base pairs from the 3' end of the small subunit rRNA gene (SSU rDNA) in 22 species representing all major taxonomic groups. Phylogenies were derived using neighbor- joining, maximum-parsimony, and maximum-likelihood methods. All analyses confirm the monophyletic origin of foraminifera. Evolutionary relationships within foraminifera inferred from rDNA sequences, however, depend on the method of tree building and on the choice of analyzed sites. In particular, the position of planktonic foraminifera shows important variations. We have shown that these changes result from the extremely high rate of rDNA evolution in this group. By comparing the number of substitutions with the divergence times inferred from the fossil record, we have estimated that the rate of rDNA evolution in planktonic foraminifera is 50 to 100 times faster than in some benthic foraminifera. The use of the maximum-likelihood method and limitation of analyzed sites to the most conserved parts of the SSU rRNA molecule render molecular and paleontological data generally congruent.      

Enzymology of the oxidation of ammonia to nitrite by bacteria

The enzymes which catalyze the oxidation of ammonia to nitrite by autotrophic bacteria are reviewed. A comparison is made with enzymes which catalyze the same reactions in methylotrophs and organotrophic heterotrophic bacteria.     

Loads on an internal spinal fixation device during sitting.

Sitting is often assumed to involve high loads on the spine as well as on implants for stabilising the spine. Loads on internal spinal fixation devices were therefore measured in ten patients sitting on several types of seats, including a stool, a stool with a padded wedge, a chair, a physiotherapy ball, a knee-stool, and a bench. The patients also successively sat relaxed and erect on a stool. In addition, six of them sat on a special chair allowing different inclinations of the backrest. Implant loads were also measured for standing up and sitting down. There were only minor differences in fixator loads for sitting on the different types of seats. Sitting erect caused an average of 11% higher implant loads than sitting relaxed. Implant loads decreased with increasing inclination of the upper body while sitting on a chair with an adjustable backrest. Implant loads were about 27% higher for standing up and sitting down than for sitting.     

Averaging of strongly varying signals.

Forces acting at the hip joint during a given activity often vary much between trials and subjects. Large variations are also encountered in many other biomechanical signals. Arithmetic mean curves then lead to falsified results, especially if extreme values occur at very different times. A method was developed for calculating a typical curve from such varying, time dependent signals. All cycle times are first averaged and the signals are then more and more smoothed using Fourier series with decreasing numbers of harmonics. The remaining extrema are analysed to decide whether they are typical for all curves or not. This is done by systematically cutting off a varying number of extrema at the beginning or end of all curves. After this an equal number of extrema remains in all curves. These extrema are then shifted to average positions in time, i.e. the times between consecutive extrema are compressed or expanded, and the standard deviation of all curves is calculated. The combination of cut off extrema which results in the smallest standard deviation is then used further on. The same time distortions are applied to the original curves and their arithmetic mean finally results in the typical signal. This procedure is well suited for averaging hip contact forces and other varying signals as long as their complexity and variation is not extremely large.     

Neutral sterols of rat epididymis. High concentrations of dehydrocholesterols in rat caput epididymidis.

Phospholipids and sterols are known to have multiple functions in reproductive tissue of mammals. High concentrations of the cholesterol precursor desmosterol have been described in testis, epididymis, and spermatozoa of various species. These findings and the recent discovery of some cholesterol precursors as meiosis-activating sterols suggest important functions of cholesterol precursors in fertility. Many sterol intermediates appear from the 19-step conversion of lanosterol, the first sterol synthesized in the cascade of cholesterol synthesis, to cholesterol. The biochemical basis of the genetically inherited Smith-Lemli-Opitz syndrome has been described as a defective conversion of 7-dehydrocholesterol to cholesterol. Since this discovery, interest has focused on this special cholesterol precursor. Here, we report high concentrations of 7- and 8-dehydrocholesterol in caput epididymidis and spermatozoa derived from caput epididymidis of Sprague-Dawley and Wistar rats, which comprised up to 30% of total sterols. In contrast to caput epididymidis, 7- and 8-dehydrocholesterol were barely detected in cauda epididymidis or testis. Desmosterol increased several times from caput to cauda epididymidis.This is the first report of the natural appearance of high concentrations of dehydrocholesterols in mammalian tissue, and it underlines the putative importance of cholesterol precursors in reproductive tissue.