Codon usage and G+C content in Bradyrhizobium japonicum genes are not uniform

To date, the sequences of 45 Bradyrhizobium japonicum genes are known. This provides sufficient information to determine their codon usage and G+C content. Surprisingly, B. japonicum nodulation and NifA-regulated genes were found to have a less biased codon usage and a lower G+C content than genes not belonging to these two groups. Thus, the coding regions of nodulation genes and NifA-regulated genes could hardly be identified in codon preference plots whereas this was not difficult with other genes. The codon frequency table of the highly biased genes was used in a codon preference plot to analyze the RSRj9 sequence which is an insertion sequence (IS)-like element. The plot helped identify a new open reading frame (ORF355) that escaped previous detection because of two sequencing errors. These were now corrected. The deduced gene product of ORF355 in RSRj9 showed extensive similarity to a putative protein encoded by an ORF in the T-DNA of Agrobacterium rhizogenes. The DNA sequences bordering both ORFs showed inverted repeats and potential target site duplications which supported the assumption that they were IS-like elements.     

Numerical simulation of thermal bone necrosis during cementation of femoral prostheses

The implant of a femoral prosthesis is a critical process because of the relatively high temperature values reached at the bone/cement interface during the cementation of the infibulum. In fact, the cement is actually a polymer that polymerizes in situ generating heat. Moreover, the conversion of monomer into polymer is never 100%; this is dangerous because of the toxicity of the monomer. In this paper, we present a 3-D axisymmetric mathematical model capable of taking into account both the geometry of the implant and the chemical/physical properties of the cement. This model, together with its numerical simulation, thus represents a useful tool to set up the optimal conditions for the new materials developed in this orthopaedic field. The real complex geometry is assumed to be a bone/cement/metallic system having cylindrical symmetry, thus allowing the model to be reduced to two space variables. The cementation process is described by the Fourier heat equation coupled with a suitable polymerization kinetics. The numerical approximation is accomplished by semi-implicit finite differences in time and finite elements in space with numerical quadrature. The full discrete scheme amounts to solve linear positive definite symmetric systems preceded by an elementwise algebraic computation. We present various numerical simulations which confirm some critical aspects of this orthopaedic fixing technique such as thermal bone necrosis and the presence of unreacted residual monomer.This work was partially supported by MURST (Fondi per la Ricerca Scientifica 40%) and CNR (IAN, Contract 880032601, and Progetto Finalizzato Sistemi Informatici e Calcolo Parallelo, Sottoprogetto Calcolo Scientifico per Grandi Sistemi) of Italy     

The effect of geochemical factors on prevalences of dental diseases for prehistoric inhabitants of the state of Missouri

In previous epidemiological studies, it has been suggested that geochemical factors besides fluoride may affect the prevalences of dental diseases. Our objective in this study was to determine whether the prevalences of periodontal diseases, coronal caries, and root caries for prehistoric inhabitants vary between geochemical regions of the state of Missouri. Burial sites were located on unique maps that depict geochemical variation among regions of the state. Data on dental caries and alveolar bone loss were gathered from 179 of the best preserved skeletal remains of the Late Woodland (A.D. 400-900) and Mississippian (A.D. 900-1700) periods. Mean caries scores and proportions of individuals with caries were calculated for these geochemical regions. Average alveolar bone loss was regressed on age for the individuals of these regions. Significant differences in caries and bone loss were found between several regions. These differences cannot be adequately explained by fluoride concentrations or by diet. It is suggested that geochemical factors, in addition to fluoride, may have affected the prevalences of dental diseases.     

Trace element distributions in some saline lakes of the Vestfold Hills,Antarctica

The distributions of trace elements in Shield, Ace and Burton Lakes of the Vestfold Hills were investigated. Three aspects are discussed as follows: (1) the vertical distribution of 18 trace elements in the three lakes, (2) the behaviour of trace elements in the lakes, especially that of manganese in Shield Lake, and (3) the origin of trace elements in antarctic saline lakes.High concentrations of trace elements were found in these coastal saline lakes, when compared to open ocean water.We suggest that the peak of total extractable manganese, found at 20 m in Shield Lake, was related to the oxic/anoxic water interface brought about by microbiological activity. Solid phase manganese at the upper oxic layer may have precipitated and then reached the anoxic boundary to be there reduced to manganese ion. This dissolved manganese may then have diffused upwards to be reoxidized to a solid form. This cycle, repeated many times, may have produced the Mn profile.The alkali, alkaline earth elements and Cl were probably derived from relict seawater. Other elements were present in similar concentration ratios to those of South Polar aerosols. Residence time calculations indicate that fallout of aerosol particles, themselves derived from various sources, is capable of accounting for the measured concentrations of some trace elements in Shield Lake. This source of trace elements may be significant for other antarctic saline lakes.     

Molecular cloning of the c2 locus of Zea mays, the gene coding for chalcone synthase

Summary The c2 locus of Zea mays, identified as one of the genes affecting anthocyanin biosynthesis, was cloned using the transposable element En (Spm) as a gene tag. The Spm element present at the c2 locus in the autonomously mutating c2-m1 line was isolated using En1 element specific probes. Sequences flanking the element were identified as c2 locus specific and were used to clone the nonautonomous c2-m2 and wild-type alleles. The cloning and analysis of a cDNA complementary to the c2 locus provided evidence that this gene encodes the enzyme chalcone synthase.     

Effects of fertilization and liming on the chemical soil conditions and element distribution in forest soils

Summary The distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH₄NO₃ and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO₃-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer.     

黑腹果蝇P转座因子研究 Ⅰ.我国黑腹果蝇的P-M测定及其地理分布

采用性腺败育(GD不育)作为标准检定方法。对我国20个地方的黑腹果蝇的P因子活性和细胞型进行了测定。结果表明我国北部沿海城市为Q型;南部沿海和内地皆为M型。各地的M品系所产生的GD不育能力各不相同,但表现出与地理位置相关的梯度变化。这一变化规律为研究我国黑腹果蝇的P因子起源及P和M品系的形成提供了重要的理论依据。     

A comparison of within-plant karyological heterogeneity between agamospermous and sexualTaraxacum (Compositae) as assessed by the nucleolar organiser chromosome

Morphological variation for the NOR chromosome was studied for four half-siblings of a sexual outbreedingTaraxacum, for three siblings of the obligate agamospermT. pseudohamatum, and for two individuals of the agamospermT. brachyglossum. No rearrangement was detected for the 113 chromosomes of sexuals, or for 41 chromosomes of two agamospermous individuals. In the other three agamospermous individuals, 3/16, 5/50, and 5/20 chromosomes showed evidence of chromosomal rearrangement. The majority of rearrangement events (10/13) occurred to the satellite rather than to the body of the NOR-chromosome. It is considered that such high levels of somatic chromosomal rearrangement in agamospermousTaraxacum may be the result of activity by transposable genetic elements. This recombination may be of selective advantage to asexual plants which cannot generate genetic variability through the sexual process.