Nitrate reductase activity in nodules of pea inoculated with hydrogenase positive and hydrogenase negative strains of Rhizobium leguminosarum

The nitrate reductase (NR, EC 1.6.6.1) activity in root nodules formed by hydrogenase positive (Hup⁺) and hydrogenase negative (Hup⁻) Rhizobium leguminosarum strains was examined in symbioses with the pea cultivar Alaska ( Pisum sativum L.), Rates of activity were determined by the in vivo assay in nodules from plants that were only N₂-dependent or grown in the presence of 2 m M KNO₃. The rates varied widely among strains, regardless of the Hup phenotype of the R. leguminosarum strain used for inoculation, but the overall results indicated that nodules formed by Hup⁻ strains accumulated more nitrite in the incubation medium than did those with Hup⁻ phenotypes. Total plant dry weight and reduced nitrogen content of pea plants grown in the presence of 2 m M KNO₃ and inoculated with single Hup⁺ and Hup⁻ R. leguminosarum strains were statistically different among some strains. These observations suggest that the possible advantages derived from the presence of the Hup system on whole plant growth may be counteracted by the higher rates of NR activity in the Hup⁻ strains in the R. leguminosarum -pea symbiosis.     

Effect of D-galactosamine on nucleotides in the rat heart. Effects of cytidine and uridine administration

The treatment of rats by galactosamine (2 mmol/kg i.p.), which dramatically alters the metabolism of pyrimidine nucleotides in the liver, has been used to investigate the dynamics of pyrimidine nucleotides in the rat heart. Six hours after administration of the drug, the UTP and UDPG myocardial contents were decreased by respectively 40 and 52% while the sum of uracil nucleotides was increased by 66% and that of cytosine nucleotides by 15%. When administered 5 h after galactosamine treatment, cytidine (750 nmol/rat i.v.) induced a further increase in cytosine nucleotides (46% above control value 1 h later) without however effect on uracil nucleotides. On the other hand, the administration of uridine (250 nmol/rat, i.v. 5 h after galactosamine), while restoring UTP, UDPG and the pool of uracil nucleotides, provoked a decrease in cytosine nucleotide level (-17%). In the absence of galactosamine treatment, the administration of uridine and cytidine did not induce changes in nucleotide levels despite a rise in blood cytidine concentration. All these observations support the hypothesis that: 1. the pathway for cytosine nucleotide synthesis predominant in the heart is that utilizing preformed exogenous cytidine and 2. this pathway is mainly controlled by the intracellular concentration of UTP rather than that of CTP.     

Nitrate inhibition of nodulation can be overcome by the ethylene inhibitor aminoethoxyvinylglycine

Previously, we reported (a) a positive correlation between the nitrate concentrations in growth medium and ethylene evolved from uninoculated and inoculated alfalfa (Medicago sativa) roots and (b) a negative correlation between ethylene evolution and nodulation. Here, we report that the inhibitory effect of NO₃⁻ on nodulation of alfalfa can be eliminated by the ethylene inhibitor aminoethoxyvinylglycine (AVG). This effect was probably related to the strong inhibition (90%) of ethylene biosynthesis caused by AVG in these inoculated and NO₃⁻-treated roots. These results support our hypothesis that the inhibitory effect of NO₃⁻ is mediated through the phytohormone ethylene. A possible role of endogenous ethylene in the autoregulation of nodulation also is discussed. AVG at 10 micromolar significantly (P < 0.05) increased total nitrogenase activity (acetylene reduction) in 2.5 and 5 millimolar NO₃⁻-fed plants probably as a result of the very high stimulation of nodulation.     

Nucleosomal organization of chromatin in sperm nuclei of the bivalve mollusc Aulacomya ater

The sperm nuclei of Aulacomya ater, family Mitylidae, contain three proteins (X, Aa5 and Aa6) which are specific to this cell type coexisting with a set of five somatic-type histones. Information about the chromatin structure resulting from this kind of association is scarce. Therefore, we have probed the structure of this sperm chromatin through digestion with micrococcal nuclease in combination with salt fractionation. The data obtained have allowed us to propose a nucleosomal arrangement for this chromatin. However, two types of nucleosomes would be present in agreement with their protein components.     

Implication of nifA in regulation of genes located on a Rhizobium meliloti cryptic plasmid that affect nodulation efficiency.

We examined the contribution of a cryptic plasmid, pRmeGR4b, to the nodulation of Medicago sativa by strain GR4 of Rhizobium meliloti. A 905-base-pair PstI DNA fragment in pRmeGR4b was found to hybridize DNA of the R. meliloti fixA promoter region as a probe. Sequence analysis of the PstI fragment showed a 206-base-pair region displaying high homology with the DNA upstream of the RNA start points of the P1 and P2 symbiotic promoters. Putative nif promoter consensus sequences were conserved in this DNA segment. Expression of DNA downstream of the nif promoterlike sequence, monitored by beta-galactosidase activity of different lacZ fusions, was demonstrated to depend on a functional nifA gene, both in microaerobically free-living cells and in nodules. Individual transposon Tn3-HoHo1 insertions in this DNA region caused a reduced nodulation competitiveness. This new symbiotic region, occupying approximately 5 kilobases of pRmeGR4b DNA, was called nfe (nodule formation efficiency).     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Intraspecific diversity in the fungal speciesChaunopycnis alba: Implications for microbial screening programs

Intraspecific variation among 84 isolates of the anamorphic fungusChaunopycnis alba from 26 different geographical locations was analyzed by investigating optimal growth temperatures, differences in the production of secondary metabolites and presence or absence of the cyclosporin synthetase gene. The genetic diversity was assessed using random amplified polymorphic DNA (RAPD). Analysis of these data showed high genetic, metabolic and physiological diversity within this species. Isolates from the Antarctic represented the most homogeneous group withinC. alba and together with isolates from the Arctic these polar strains differed from alpine, temperate and tropical strains by low optimal growth temperatures and by low production of secondary metabolites. Isolates from tropical climes were characterized by high optimal growth temperatures and by the production of comparatively diverse metabolite spectra. Most of the isolates that were similar in the combination of their physiological and metabolic characters were also genetically related. Isolates from different geographical origins did not show many similarities, with the exception of the cyclosporin A-producing isolates, and large diversity could be observed even within a single habitat. This leads us to the suggestion that for pharmaceutical screening programs samples should be collected from a diversity of different geographical and climatic locations. For the selection of strains for screening the RAPD assay seems to be the most powerful tool. It reflected the highest intraspecific diversity and the results corresponded well with the other characteristics.     

Relationships between carbon and hydrogen isotope ratios and nitrogen levels in leaves ofClusia species and two other Clusiaceae genera at various sites and different altitudes in Venezuela

Samples of the Clusiaceae generaClusia, Oedematopus andDystovomita were collected at various sites and different altitudes in northern and south-western Venezuela. Analyses of stable isotopes of carbon and hydrogen and of leaf-nitrogen levels were performed on the dried samples. Correlations among these variables, i.e. carbon isotope discrimination (), hydrogen isotope ratio (D) and N-levels, and with altitude were assessed. In the samples, where values of above 15 indicate predominant performance of C₃ photosynthesis, there were slight tendencies of increasing , D and N-levels with increasing altitude and of increasing with increasing N. Although these correlations taken separately were not statistically significant, they support each other and indicate increasing transpiration and increased leaf-nutrient supply at increasing altitude. Performance of crassulacean acid metabolism (CAM) in species ofClusia appears to be restricted to altitudes below 1500 m a.s.l. There was a significant negative correlation of with altitude in the samples, where values of below 10 indicated predominant performance of CAM. This suggests that phases II and IV of CAM are progressively suppressed towards the upper altitudinal limit of CAM inClusia in northern Venezuela. It is concluded that among the large number of environmental factors and combinations thereof, which determine the expression of CAM inClusia and trigger C₃-CAM transitions in C₃/CAM intermediate species, low availability of water is the most important.