Modelling Nitrogen Content and Distribution in Cauliflower (Brassica oleracea L.botrytis )

A model of nitrogen uptake and distribution is presented whichdescribes these processes in relation to the amount of availablesoil nitrate and the rate of plant growth. Nitrogen uptake iseither sink or source limited. Sink limitation is based on maximumN-concentrations of plant compartments. The N-uptake model iscombined with a photosynthesis model based on the productivity-nitrogenrelationship at the single-leaf level. The model is parameterizedusing cauliflower as an example crop. Applied to an independentdata set, the combined model was able to predict leaf, stemand inflorescence nitrogen concentrations with correlation coefficientsbetween predicted and simulated values of 0.89, 0.66 and 0.86,respectively. The influence of nitrogen supply and light intensityon leaf nitrate-N could also be predicted with good accuracy(r² = 0.87). Dry matter production based on the productivity-Nrelationship and the partitioning into leaf, stem and inflorescencewas also reproduced satisfactorily (r² = 0.91, 0.93 and 0.92,respectively). Copyright 2000 Annals of Botany Company Brassica oleracea L. botrytis, cauliflower, nitrogen, nitrate, nitrogen supply, nitrogen uptake, nitrogen distribution, model     

Activation of V kappa gene rearrangement in pre-B cells follows the expression of membrane-bound immunoglobulin heavy chains.

During B cell development V kappa gene rearrangement seems to occur only in mu-positive pre-B cells. To study the role of the mu chain in the activation of the Ig kappa locus, we introduced expression vectors carrying different forms of the mu gene into null pre-B cells. The activation of the Ig kappa locus followed the expression of the membrane form (micron) of the mu chain. The expression of the secreted form (microS) did not result in the activation of the Ig kappa locus. We further show that both forms of the mu chain differ in their intracellular transport in pre-B cells.     

High-frequency disruption of the N-myc gene in embryonic stem and pre-B cell lines by homologous recombination.

Identification of gene function has often relied on isolation of mutant cells in which expression of the gene was inactivated. Gene targeting by homologous recombination in tissue culture now may provide a technology to rapidly and directly produce such mutant mammalian cells. We demonstrate that selection of embryonic stem and pre-B cell lines for expression of a promoterless construct containing murine N-myc genomic sequences fused to a gene encoding neomycin resistance allows highly efficient recovery of variants in which the endogenous N-myc gene is disrupted. The high frequency of N-myc gene disruption by this method should permit targeted disruption of both allelic N-myc copies in various cell lines to study N-myc function.     

The scid defect affects the final step of the immunoglobulin VDJ recombinase mechanism

Abelson murine leukemia virus-transformed precursor B lymphocytes from scid (severe combined immunodeficient) mice, like A-MuLV transformants from normal mice, actively rearrange segments of their Ig heavy chain variable region gene locus during growth in culture. Targeting of recombination to appropriate segments appears normal in these lines as evidenced by initial rearrangement of sequences from within the D and JH locus to form aberrant "DJH" rearrangements and secondary rearrangement of sequences from within the VH locus to the aberrant "DJH" intermediates. A detailed analysis of the joints in these rearrangements indicates that the VDJ recombinase in scid pre-B cells can correctly recognize heptamernonamer signal sequences and perform precise endonucleolytic scissions at these sequences. We propose that the scid defect involves the inability of scid precursor lymphocytes to join correctly the cleaved ends of the coding strands of variable region gene segments.     

Trichinella spiralis in the black bear (Ursus americanus) of Pennsylvania: distribution, prevalence and intensity of infection

Samples of tongue or diaphragm from 2,056 black bears harvested in Pennsylvania during the 1981-1983 hunting seasons were examined for larvae of Trichinella spiralis by peptic digestion. Sixteen males and 21 females were infected. The overall prevalence of infection was 1.8%. Infected animals were distributed widely throughout the range of the bear in Pennsylvania. In samples from infected bears, the geometric mean density of muscle larvae was 7.8 per g of tissue (LPG). There were neither sex- nor age-related differences in prevalence or intensity of infection. Virtually all bears harvested in Pennsylvania are consumed as food, which often is shared widely among hunters, their friends and relatives. Furthermore, high densities of larvae occurred in some bears (i.e., 300, 348, 465, 512, 555, and 912 LPG). Thus, a basis for potential, single-source outbreaks of severe human trichinosis exists.     

Use of191Pt radiotracer for the development of enrichment procedures to detect natural levels of platinum in biological and environmental materials

Biological Trace Element Research - The191Pt-radiotracer is a powerful tool to develop separation and preconcentration methods for Pt. The radiotracer was produced either through190Pt...     

Molecular basis of heavy-chain class switching and switch region deletion in an Abelson virus-transformed cell line.

We demonstrated that a subclone of an Abelson murine leukemia virus-transformed B-lymphoid cell line switched from mu to gamma 2b expression in vitro, by the classical recombination-deletion mechanism. In this line, the expressed VHDJH region and the C gamma 2b constant region gene were juxtaposed by a recombination event which linked the highly repetitive portions of the S mu and S gama 2b regions and resulted in the loss of the C mu gene from the intervening region. An additional recombination event in this subclone involved an internal deletion in the S mu region of the expressed (switched) allele. One end of this deletion occurred very close to the switch recombination point. Despite the recombination-deletion mechanism of switching, the gamma 2b-producing line retained two copies of the C mu gene and two copies of the sequence just 5' to the S gamma 2b recombination point. The possible significance of the retention of these sequences to the mechanism of class switching is discussed.     

Persistence of introduced Bradyrhizobium japonicum strains in forming nodules in subsequent years after inoculation in Wisconsin soils

Nodulation of soybeans by indigenous and inoculum strains of Bradyrhizobium japonicum was studied in field experiments in Wisconsin from 1983 to 86. Aqueous suspensions of bacteria were applied to seeds at the time of planting at levels of 7?×?10(7)-10(10) bacteria per 2.5-cm row. The predominant indigenous serogroup was 123 in these soils. Six different inoculum strains were used (two from serocluster 123, two from serogroup 110, and one each from serogroups 122 and C1). Nodule occupants were identified using spontaneous antibiotic-resistant mutations in the inoculum strains, phage typing, and serotyping. In the 1983 experiment, the majority of nodules were formed by the inoculum strains in almost all cases (up to 100% in some cases), in two different soils containing 3.5?×?10(5) indigenous B. japonicum per gram. After 2 years without inoculation at the same two site, the inoculum strains did not form many nodules on uninoculated soybeans (less than 10% in most cases; less than 30% in all cases). In inoculation experiments carried out in 1985 and 1986, four inoculum strains were used (3 members of 123 serocluster and USDA 110str); inocula containing 10(8) bacteria per 2.5-cm row formed less than42%ofthe nodules in soils containing 1?×?10(4)-4?×?10(4)B. japonicum per gram. The major conclusions are (i) the success of inoculation in Midwestern U.S. soils is highly variable, even with members of the (highly competitive) 123 serocluster, and (ii) successful inoculation in 1 year in a Wisconsin soil does not ensure that the inoculated strain will persist in forming nodules in that field in subsequent years without further inoculation. Key words: Bradyrhizobium japonicum, strain persistence, field trials.