Diffusion du15N2 dans le sol pendant la mesure de fixation biologique de l'azote

Summary The kinetic of¹⁵N₂ diffusion has been measured in a system similar to that for the estimation of N₂ fixation in plant microorganism associations cultivated in soil. The¹⁵N₂ enrichment of the soil atmosphere reached an homogenous value one hour after injection of¹⁵N₂ and is identical to that obtained by calculation, indicating that no adsorption occurs in the soil particles.

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Diffusion du¹⁵N₂ dans le sol pendant la mesure de fixation biologique de l'azote

Résumé La cinétique de diffusion du¹⁵N₂ est mesurée sur un système identique à ceux pouvant être utilisés pour la mesure de fixation de l'azote chez les associations plantes-microorganismes cultivées sur sol. L'enrichissement homogène de l'atmosphère du sol est obtenu une heure environ après l'injection de¹⁵N₂ et correspond à l'enrichissement calculé, ce qui indique qu'aucune adsorption n'a lieu dans les particules du sol.

     

Oxo fatty acid esters from Cryptocoryne spiralis rhizomes

Two new compounds, isolated from the rhizomes of Cryptocoryne spiralis, have been characterized as ethyl 14-oxotetracosanoate and 15-oxoeicosanyl 14-oxoheptadecanoate by spectral data and chemical studies. Hentriacontane and sitosterol have also been isolated and identified.     

Requirements for antiribosomal activity of pokeweed antiviral protein

It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K⁺ and 3 mM Mg²⁺ retards the reaction, while 20 mM K⁺ and 2 mM Mg²⁺ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The K_m for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pK_a value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity.     

Ligation of highly modified bacteriophage DNA

After digestion by TaqI or nicking by DNAase I, five highly modified bacteriophage DNAs were tested as substrates for T4 DNA ligase. The DNAs used were from phages T4, XP12, PBS1, SP82, and SP15, which contain as a major base either glucosylated 5-hydroxymethylcytosine, 5-methylcytosine, uracil, 5-hydroxymethyluracil, or phosphoglucuronated, glucosylated 5-(4′,5′-dihydroxypentyl)uracil, respectively. The relative ability of cohesive-ended TaqI fragments of these DNAs and of normal, λ DNA to be ligated was as follows: $\text{λ}\text{DNA}\text{=}\text{XP}\text{12}\text{DNA}\text{>}\text{SP}\text{82}\text{DNA}\text{?}\text{nonglucosylated}\text{T}\text{4}\text{DNA}\text{>}\text{T}\text{4}\text{DNA}\text{=}\text{PBS}\text{1}\text{DNA}\text{?}\text{SP}\text{15}\text{DNA}$. TaqI-T4 DNA fragments were also inefficiently ligated by Escherichia coli DNA ligase. However, annealing-independent ligation of DNAase I-nicked T4, PBS1, and λ DNAs was equally efficient. We conclude that the poor ligation of TaqI fragments of T4 and PBS1 DNAs was due to the hydroxymethylation (and glucosylation) of cytosine residues at T4's cohesive ends and the substitution of uracil residues for thymine residues adjacent to PBS1's cohesive ends destabilizing the annealing of the restriction fragments. Only SP15 DNA with its negatively charged, modified base was unable to serve as a substrate for T4 DNA ligase in an annealing-independent reaction; therefore, its modification directly interfered with enzyme binding or catalysis.     

Serotonin Stimulates Both Cytosolic and Membrane-Bound Guanylate Cyclase in NG108–15 Cells

The cyclic GMP (cGMP) content was rapidly (greater than 30 s) increased by serotonin [5-hydroxytryptamine (5-HT)] (EC50 = 10 microM), and the increase lasted for greater than 10 min in NG108-15 cells. The 5-HT-induced elevation of cGMP level (EC50 = 10 microM) at 20 s ("fast" elevation) was inhibited by ICS 205-930 or MDL 72,222 and by Ca2+ deficiency in the reaction medium but not by organic Ca2+ antagonists. The 5-HT effect at 10 min ("slow" elevation) was not inhibited by several antagonists for 5-HT receptors of the 1A, 1B, 1C, 1D, 2, and 3 subtypes and was independent from external Ca2+ concentration. The fast and slow effects of 5-HT were similar to the effects of bradykinin and atrial natriuretic peptide (ANP), respectively, in aspects of both Ca2+ dependency and time course of the effects. Bradykinin transiently stimulated formation of inositol phosphates as well as accumulation of cGMP, a finding suggesting that intracellular Ca2+ is involved in bradykinin-induced cGMP accumulation as shown in the fast response to 5-HT. ANP, an activator of membrane-associated guanylate cyclase (mGC), slowly (approximately 60 s) increased the cGMP content (EC50 = 10 nM), a result lasting for greater than 10 min, and the effects were independent from external Ca2+, as shown in the slow response to 5-HT. 5-HT and ANP did not induce formation of inositol phosphates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interleukin-1 Hyperproduction by In Vitro Activated Peripheral Macrophages from Cerebellar Mutant Mice

Several mutations in mice produce complex patterns of neuronal degeneration of the cerebellum and of its afferent pathways. In the staggerer (sg/sg) mutant, atrophy of the lymphoid organs and immunological abnormalities have been described. To search for a possible link between the neurological and the immune disorders in this mutant, we studied the production by its peripheral macrophages of interleukin-1 (IL-1), which roles in both immune and nervous systems are well established. Suspensions of peritoneal and/or spleen macrophages from mutants and their appropriate controls were stimulated in vitro by lipopolysaccharide. Northern and dot blots, performed with murine IL-1 cDNA probes, revealed a clear-cut hyperexpression of IL-1 mRNA in staggerer macrophages. An IL-1 bioassay using the IL-1-responsive D10.G4 cell line also revealed a sixfold increase of IL-1 activity in the macrophage supernatants of staggerer mutant mice. The hyperproduction was found in 3-week to 1-year-old staggerer and also in heterozygous (+/sg) mice. A similar phenomenon existed in cerebellar mutants lurcher, Purkinje cell degeneration (pcd), and to a lesser extent reeler and wobbler, but was absent in the neurological mutants weaver, jimpy, and motor end plate disease (medH). These observations establish that in several point mutations in mice, central nervous degeneration is associated with dysregulation of IL-1 production by peripheral macrophages.     

Forests losing large quantities of nitrogen have elevated 15N:14N ratios

Summary Urea (U) and ammonium nitrate (AN) had been applied to a Scots pine (Pinus sylvestris L.) forest in northern Sweden for 18 consecutive years at four doses resulting in total N applications ranging from 0 to 1980 kg ha^–1. The ¹⁵N abundance ( ¹⁵N) of the grass Deschampsia flexuosa (L.) Trin. increased linearly (from –0.7 to 11.0) with application rate in the case of U. The response to AN was in the same direction but smaller. While others have shown that the initial response of nitrogen-limited systems to additions of N is a change of ¹⁵N abundance towards that of added N, this study shows that further and excessive additions leads to a retention of ¹⁵N. Monitoring ¹⁵N abundance over time in dose-response trials of this type thus opens new possibilities to estimate critical loads of N and the point of nitrogen saturation.     

Assessment of genetic variability for N2 fixation between and within provenances of Leucaena leucocephala and Acacia albida estimated by 15N labelling techniques

Nitrogen fixed in 13 provenances of Acacia albida and 11 isolines of Leucaena leucocephala inoculated with effective Rhizobium strains was measured by ¹⁵N techniques and the total N difference method. In the test soil, on the average, L. leucocephala derived about 65% of its total N from atmospheric N₂ fixation compared to about 20% by A. albida. Significant differences in the percentage of N derived from atmospheric N₂ (% Ndfa) occurred, between provenances or isolines within species. The % Ndfa ranged from 37 to 74% within L. leucocephala and from 6 to 37 within A. albida; (equivalent to 20–50 mg N plant^–1 and 4–37 mg N plant^–1 for the two species over three months, respectively) and was correlated with the nodule mass (r=0.91). The time course of N₂ fixation of three selected provenances (low, intermediate and good fixers) was followed at 12 weekly intervals over a 36 week period. The % Ndfa of all provenances and isolines increased with time; and except for one of the L. leucocephala provenances, % Ndfa was similar within species at the 36 weeks harvest. There was a significant correlation between % Ndfa and the amount of N₂ fixed (r=0.96). Significant interactions occurred between provenances and N treatments and often growth of uninoculated but N fertilized plants was less variable than for inoculated unfertilized plants.     

Influence of salt stress on primary metabolism of Zea mays L. seedlings of model genotypes

Short-term studies for comparing some primary metabolic and growth-responses to salt stress in seedlings of two maize genotypes differing in drought resistance were carried out under controlled conditions. Both genotypes revealed high yielding ability in favourable environments. Treatments: Control (Hoagland-Arnon No 1 solution) and salt stress (Hoagland-Arnon solution plus NaCl, _s = –0.84MPa). It was found that in both genotypes the activity of the principal metabolic pathway supplying reduced nitrogen (¹⁵N) for the synthesis of amino acids and proteins as well as the assimulatory number (¹⁴CO₂—assimilation relation rate per chlorophyll unit) were decreased under the effect of the stress. These effects were more marked in the resistant genotype. In this genotype the stress induced metabolic activity decline was accompanied by a corresonding reduction of the relative growth rate. Conversely, continuing growth, resulting probably from accumulation of solutes, was observed in the susceptible genotype.On the basis of these and other observations it is assumed that the resistant genotype manifests short-term energy saving stress reactions.     

Nitrogen fixation and growth of soybean as influenced by varying the methods of inoculation with Bradyrhizobium japonicum

The effects of inoculating soil with a water suspension of Bradyrhizobium japonicum (i) at seeding, (ii) 7, or (iii) 14 days after planting (DAP), (iv) seed slurry inoculation and (v) seed slurry supplemented with postemergence inoculation of a water suspension of Bradyrhizobium at 7 or (vi) 14 DAP, on nodulation, N₂ fixation and yield of soybean (Glycine max. [L.] Merrill) were compared in the greenhouse. The ¹⁵N isotope dilution technique was used to quantify N₂ fixed at flowering, early pod filling and physiological maturity stages (36, 52 and 70 DAP, respectively). On average, the water suspension inoculation formed the greatest number of nodules, and seed plus postemergence inoculation formed slightly more nodules than the seed-only inoculated plants (27, 19 and 12 nodules/plant respectively at physiological maturity). Seed slurry inoculation followed by postemergence inoculation at 14 DAP gave the highest nodule weight, with the plants fixing significantly more (P<0.05) N₂ (125 mg N plant⁻¹ or 56% N) than any other treatment (mean, 75 mg plant⁻¹ or 35% N). However, the higher N₂ fixation was not translated into higher N or dry matter yields. Estimates of N₂ fixed by the ostemergence Bradyrhizobium inoculations as well as plant yield were not significantly different from those of the seed slurry inoculation. Thus, delaying inoculation (e.g., by two weeks as in this study) did not reduce the symbiotic ability of soybean plants.