Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

Population dynamics of a motile and a non-motile Azospirillum lipoferum strain during rice root colonization and motility variation in the rhizosphere

Abstract: Azospirillum lipoferum 4B and non-motile A. lipoferum 4T have been simultaneously isolated from rice rhizosphere at the same frequency. A. lipoferum 4T showed stable morphological and metabolic traits which are atypical for A. lipoferum species such as lack of motility, carbohydrate metabolism and laccase activity. Inoculation experiments showed that A. lipoferum 4T, but not A. lipoferum 4B, needed rice roots to stabilize in sterile soil. Both strains were able to colonize efficiently rice roots (10⁸ cfu g⁻¹ fresh roots) but motile form 4B remained dominant. In spite of their phenotypical differences, A. lipoferum 4B and 4T co-existed without exclusion in sterile soil (planted or not) and rice rhizosphere. Inoculation of rice roots with A. lipoferum 4B showed that rice rhizosphere enhanced the frequency of appearance of stable non-motile forms (40%). This percentage was weaker in plantlet growth medium (4%). However, these non-motile bacteria kept the same biochemical traits than the motile parental strain 4B (carbohydrates metabolism, laccase activity).     

Differential Protein Expression in Aortic Smooth Muscle Cells Cultured from Newborn and Aged Rats

Atherosclerosis is a complex disease in which smooth muscle cells (SMC) play a fundamental role. Work from several laboratories has suggested that in experimental models of atheromatosis SMC heterogeneity is important in the establishment of intimal thickening. Moreover, it has been shown that SMC cultured from different situations in vivo maintain distinct phenotypic features in vitro. In order to find proteins differentially expressed in SMC cultured from newborn and aged rats, total protein extracts were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), high-resolution maps were built, and differentially expressed spots were identified by automatic computer analysis. Of the 14 differentially expressed protein spots, 4 were present in SMC of newborn and 10 in SMC of old animals; we describe their molecular weights and isoelectric points. One of these proteins (expressed only in cultured SMC of old rats) was successfully microsequenced for 16 amino acids and it was found identical to cellular retinol-binding protein. This result provides, to our knowledge, the first suggestion that retinoids are implicated in the differentiation and aging of vascular SMC.     

Membrane topology and site-specific mutagenesis of Pseudomonas aeruginosa porin OprD

Pseudomonas aeruginosa OprD is a 420-amino-acid protein that facilitates the uptake of basic amino acids, imipenem and gluconate across the outer membrane. OprD was the first specific porin that could be aligned with members of the non-specific porin super-family. Utilizing multiple alignments in conjugation with structure predictions and amphipathicity calculations, an OprD-topology model was proposed. Sixteen β-strands were predicted, connected by short loops at the periplasmic side. The eight external loops were of variable length but tended to be much longer than the periplasmic ones. Polymerase chain reaction (PCR)-based site-specific mutagenesis was performed to delete separately short stretches (4-8 amino acid residues) from each of the predicted external loops. The mutants with deletions in the predicted external loops L1, L2, L5, L6, L7 and L8 were tolerated in both Escherichia coli and P. aeruginosa. The expressed mutant proteins maintained substantial resistance to trypsin treatment in the context of isolated outer membranes. Proteins with deletions in loops L1, L5, L6, L7 and L8 reconstituted similar imipenem supersusceptibility in a P. aeruginosa OprD::Ω background. The L2-deletion mutant only partially reconstituted supersusceptibility, suggesting that loop L2 is involved in imipenem binding. These data were generally consistent with the topology model.     

A 11 Mb YAC-Based Contig Spanning the Familial Juvenile Nephronophthisis Region (NPH1) Located on Chromosome 2q

A gene (NPH1) responsible for approximately 90% of the purely renal form of familial juvenile nephronophthisis, a progressive tubulo-interstitial kidney disorder, maps to human chromosome 2. We report the construction of a YAC-based contig spanning the critical NPH1 region and the flanking genetic markers. This physical map was integrated with a refined genetic map that restricted the NPH1 interval to about 2 cM; this interval corresponds in a maximum physical distance of 3.5 Mb. The entire contig covers 9 cM between the loci D2S135 and D2S121. The maximum physical distance between these two markers is approximately 11.3 Mb. Forty-five sequence-tagged sites, including six genes, have been located within this contig. PAX8, a member of the human paired box gene family, that is expressed in the developing kidney, was assigned outside the restricted NPH1 critical region and cannot therefore be regarded as a candidate gene. This set of overlapping clones represents a useful resource for further targeted development of genetic markers and for the characterization of candidate genes responsible for juvenile nephronophthisis.     

The RNase P ofDictostyelium discoideum

Ribonuclease P (RNase P) is a key enzyme involved in tRNA biosynthesis. It catalyses the endonucleolytic cleavage of nearly all tRNA precursors to produce 5-end matured tRNA. RNase P activity has been found in all organisms examined, from bacteria to mammals. Eubacterial RNase P RNA is the only known RNA enzyme which functionsin trans in nature. Similar behaviour has not been demonstrated in RNase P enzymes examined from archaebacteria or eukaryotes. Characterisation of RNase P enzymes from more diverse eukaryotic species, including the slime moldDictyostelium discoideum, is useful for comparative analysis of the structure and function of eukaryotic RNase P.Abbreviations RNase P ribonuclease P - MN micrococcal nuclease     

Myoblast Fusion Requires Fibronectin Degradation by Exteriorized m-Calpain

We recently reported that when myoblasts fuse, m-calpain could be exteriorized. Indeed, at present a number of works support this hypothesis because this enzyme was localized intercellularly and more particularly associated to extracellular matrix components. Knowing that the cell surface of the fusing myoblast is supposed to undergo many changes, we addressed the question whether m-calpain could be involved in the phenomenon of fusion via fibronectin cleavage or degradation. Using different digestion experiments, we demonstrated that soluble purified fibronectin and highly insoluble fibronectin fibrils represent very good substrates for this proteinase; moreover, at the burst of fusion, fibronectin proteolytic fragments could be identified. On the other hand, we have conducted biological assays on cultured myoblasts using a defined medium supplemented by exogenous factors capable of stimulating or inhibiting m-calpain activity. The effects of such factors on rat myoblast fusion and concomitantly on the targeted glycoprotein were analyzed and quantified. When m-calpain activity and the phenomenon of fusion were reduced (defined medium without insulin), the amount of the 220-kDa fibronectin band was increased by 43%. When m-calpain activity and myoblast fusion were prevented by addition of antibodies to m-calpain or calpain inhibitor II, the fibronectin concentration was higher since it was increased by 67 and 71%, respectively. In addition, when observed at the ultrastructural level, m-calpain seems to be localized at the potential fusion site of myoblasts and more particularly associated to the extracellular matrix when muscle cells were initially treated by anti-m-calpain IgG. Taken together, these results support the hypothesis that exteriorized m-calpain could be, in part, involved in myoblast fusion via fibronectin alteration or degradation.     

Establishment and immunocharacterization of an immortalized pancreatic cell line derived from the H-2Kb-tsA58 transgenic mouse

Summary This study describes the establishment and characterization of an immortalized cell line derived from the pancreas of an adult H-2K^b-tsA58 transgenic mouse. These cells, designated IMPAN for IMmortalized PANcreatic cells, displayed a cobblestone appearance typical of confluent epithelial cells and a distinct polarity in the organization of their cytoplasmic organelles. Immunocytochemical studies revealed that all IMPAN cells stained positively for a wide range of markers characteristic of pancreatic acinar cells, namely the secretory products α-amylase, chymotrypsinogen, DNAse, the lectinlike secretory protein PAP (pancreatitis associated protein), and the zymogen granule membrane proteins GP-2 and gp300. They also stained positively for carbonic anhydrase II and cytokeratin 19, two proteins characteristic of pancreatic duct cells, as well as for rab3A, a small GTP-binding protein specifically localized in pancreatic islet cells. No reactivity was ever obtained with insulin antibodies. Taken together, these results show that the IMPAN cells exhibit a phenotype comparable to exocrine pancreatic acinar cells. However the expression of some proteins more specific to duct and islet cells make them similar to in vivo or in vitro growing acinar cells. The cell line should be a valuable model to study the mechanisms of growth, differentiation, and transformation of the exocrine pancreatic acinar cell.     

Functional interactions between the proline-rich and repeat regions of tau enhance microtubule binding and assembly.

Tau is a neuronal microtubule-associated protein that promotes microtubule assembly, stability, and bundling in axons. Two distinct regions of tau are important for the tau-microtubule interaction, a relatively well-characterized "repeat region" in the carboxyl terminus (containing either three or four imperfect 18-amino acid repeats separated by 13- or 14-amino acid long inter-repeats) and a more centrally located, relatively poorly characterized proline-rich region. By using amino-terminal truncation analyses of tau, we have localized the microtubule binding activity of the proline-rich region to Lys215-Asn246 and identified a small sequence within this region, 215KKVAVVR221, that exerts a strong influence on microtubule binding and assembly in both three- and four-repeat tau isoforms. Site-directed mutagenesis experiments indicate that these capabilities are derived largely from Lys215/Lys216 and Arg221. In marked contrast to synthetic peptides corresponding to the repeat region, peptides corresponding to Lys215-Asn246 and Lys215-Thr222 alone possess little or no ability to promote microtubule assembly, and the peptide Lys215-Thr222 does not effectively suppress in vitro microtubule dynamics. However, combining the proline-rich region sequences (Lys215-Asn246) with their adjacent repeat region sequences within a single peptide (Lys215-Lys272) enhances microtubule assembly by 10-fold, suggesting intramolecular interactions between the proline-rich and repeat regions. Structural complexity in this region of tau also is suggested by sequential amino-terminal deletions through the proline-rich and repeat regions, which reveal an unusual pattern of loss and gain of function. Thus, these data lead to a model in which efficient microtubule binding and assembly activities by tau require intramolecular interactions between its repeat and proline-rich regions. This model, invoking structural complexity for the microtubule-bound conformation of tau, is fundamentally different from previous models of tau structure and function, which viewed tau as a simple linear array of independently acting tubulin-binding sites.