Nutrients and mass in litter and top soil of ten tropical tree plantations

The importance of litter to nutrient and organic matter storage and the possible influence of species selection on soil fertility in ten stands each consisting of a separate tree species were examined in this study. The plantations had been grown under similar conditions in an arboretum in the Luquillo Experimental Forest, Puerto Rico. The species involved were: Anthocephalus chinensis, Eucalyptus × patentinervis, E. saligna, Hernandia sonora, Hibiscus elatus, Khaya nyasica, Pinus caribaea var. hondurensis, P. elliottii var. densa, Swietenia macrophylla, and Terminalia ivorensis. After 26 yr, litter mass ranged from 5 mg ha^-1 in the H. sonora stand to 27.2 Mg ha^-1 in the P. caribaea stand. Nutrients in the litter (N, P, K, Ca, and Mg) also varied widely, but stands were ranked in different order when ranked by nutrients in the litter than then ranked according to accumulation of mass. Only E. saligna and A. chinensis stands were ranked similarly in accumulation of both nutrients and mass, and the stand of H. elatus was ranked higher with respect to nutrient accumulation than to accumulation of mass. The nutrient concentration in standing leaf litter generally increased in the order of recently fallen <old intact< fragmented. Nutrient concentration of standing leaf litter appears to increase with age and depth in the litter layer. The amount of nutrients stored in the litter compartment of these plantations was in the same order of magnitude as the quantity of available nutrients in the top 10-cm of mineral soil. Total litter mass was negatively correlated with the mass-weighted concentration of N, K, and Mg. The same relationship was found for Ca in the leaf litter and N in the fine wood litter compartments. In some stands (notably P. caribaea, P. elliottii, and E. saligna), leaf litter derived from species other than the species planted in that particular stand had higher nutrient concentration than leaf litter from the planted species. Soils of the 10 stands were classified in the same soil series and had similar texture (clay soils). However, significantly different chemical characteristics were found. Results obtained by analysis of covariance and by limiting comparisons to adjacent stands with similar soil texture, indicate that different species have had different influences on the concentration of available nutrients in soil.     

Effect of beta-lactoglobulin on the activity of pregastric lipase. A possible role for this protein in ruminant milk.

The interaction of bovine beta-lactoglobulin with palmitic and oleic acids has been studied by a partition equilibrium method. Bovine beta-lactoglobulin displays only one high affinity binding site for fatty acids whose association constants for palmitic and oleic acids are 4.2 x 10(6) and 2.3 x 10(6) M-1, respectively. However, other binding sites with low affinity are also present. The existence of one high affinity binding site is in accordance with the amount of fatty acids naturally bound to beta-lactoglobulin isolated from milk. The effect of beta-lactoglobulin on ruminant pregastric lipases from a pharyngeal extract has been assayed. The activity of pharyngeal lipase on a triglyceride emulsion is increased about 200%, 250% and 190% in the presence of 10 mg/ml, 20 mg/ml and 40 mg/ml of beta-lactoglobulin, respectively, the last concentration representing that found physiologically in colostrum. Albumin, another ligand-binding protein, increases the activity of this enzyme to a lesser extent and high levels tend to inhibit enzyme action. These results indicate that beta-lactoglobulin could participate in the digestion of milk lipids during the neonatal period by enhancing the activity of pregastric lipase through removal of the fatty acids that inhibit this enzyme.     

多聚酶链反应技术鉴别肾综合征出血热病毒血清型的初步研究

肾综合征出血热(HFRS)为一组抗原性密切相关的布尼亚科汉坦病毒引起的急性传染病。在我国存在至少两种临床表现、动物宿主及流行特征截然不同的血清型别,即血清Ⅰ型(汉坦型)和血清Ⅱ型(汉城型)。这两型病毒间的血清学定型已有报道。近年来,除啮齿类动物外,从临床病人以及非啮齿类动物体内也分离到了HFRS病毒。同时出现两类型别毒株共存,以及从家鼠体内分离到野鼠型毒株或从野鼠体内分离到家鼠型毒株的复杂情形。为此,准确检定并鉴别不同来源毒株型别,将为深入了解其病原学、流行病学以及制定疫苗生产策略提供重要信息。     

Leishmania infantum Nicolle, 1908 from southern Spain: Characterisation of the strains from human visceral and cutaneous leishmaniasis and from sandflies; with a numerical analysis of the isoenzymatic data

This study presents the results of the characterisation of 17 strains ofLeishmania by isoenzyme electrophoresis from a focus of leishmaniasis in southern Spain: two from human visceral leishmaniasis, four from human cutaneous leishmaniasis and 11 from sandflies. The 17 strains are grouped in 6 zymodemes characterised by their variability as regards to the electrophoretic mobility of the enzymes MDH, G6PD, NP and ME. Thus, we confirm the high intraspecific variability ofLeishmania (L.) infantum in a focus of southern Spain, as already suggested by previous studies. Zymodemes GR-15 and GR-17 are also described for the first time in Spain, and they characteristically possess the same relative electrophoretic mobility in the enzyme ME (93). Sixteen zymodemes of theL. infantum complex found in southern Spain were numerically analysed on the basis of the enzymatic profiles of 122Leishmania strains characterised from this area.     

Inositol 1,4,5-trisphosphate formation in leaves of winter oilseed rape plants in response to freezing, tissue water potential aed abscisic acid

Time courses of formation of inositol 1,4,5-trisphosphate (IP₃) were followed in the leaves of non-acclimated and cold (2°C)-acclimated winter oilseed rape ( Brassica napus L. var. oleifera ) plants, subjected to different freezing temperatures or to polyethylene glycol 8000 (PEG) and abscisic acid (ABA) treatments. Changes in water potential (Ψ_w) and in ABA level in the frost- and PEG-treated tissues were also determined. Results obtained indicate that temperatures sligthly higher than LT₅₀ induced a transient and substantial increase in IP₃ level, both in non-acclimated and cold-acclimated tissues. At comparable freezing temperature (–5°C) the response of cold-acclimated leaves was lower than that of non-acclimated ones. The PEG-depedent decrease in Ψ_w to –0.9 MPa or ABA (0.1 m M ) treatment gave rise to a transient increase in IP₃ content in non-acclimated tissues only. Collectively, the data indicate that cold acclimation of plants may lead to lower cell responsiveness to the factors studied in terms of induction of IP₃ formation. Changes in the IP₃ content, observed in the present experiments, support our previous suggestion that non-killing freezing temperatures may induce the phosphoinositide pathway, both in non-acclimated and cold-acclimated tissues. Lowering of tissue water potential to some threshold value or a high exogenous ABA supply may mimic the freezing-dependent reaction in the non-acclimated leaves.     

Development of persistent ovarian follicles during synchronization of estrus influences the superovulatory response to FSH treatment in cattle

The synchronization of estrus with synthetic progestins or progesterone (P(4)) results in the development of a large, persistent ovarian follicle. The objectives of the present study were to determine if development of a persistent ovarian follicle during synchronization of estrus suppresses recruitment of additional follicles during FSH treatment. On Day 5 of the estrous cycle (estrus = Day 0), beef cows were treated with 0.5 or 2.0 P(4) releasing intravaginal devices (PRIDs) for 8 d (Experiment 1, n = 20), 5 or 2 d (Experiment 2, n = 44) before initiation of FSH treatment. Prostaglandin F(2alpha) (25 mg) was administered on Days 5 and 6. Superovulation was induced with 24 mg of recombinant bovine FSH (rbFSH, Experiment 1) or 28 mg of FSH-P (Experiment 2) over a 3- or 4-d period, respectively. The PRIDs were removed concurrently with the 5th injection of rbFSH or FSH-P. There was a treatment-by-day interaction (P < 0.001) for the concentration of 17beta-estradiol in cows treated for 8, 5 or 2 d before FSH treatment. In Experiment 1, FSH treatment initiated 8 d after insertion of a 0.5 PRID did not affect the number of CL (6.9 +/- 1.4 vs 6.7 +/- 1.6), ova/embryos (3.7 +/-1.3 vs 3.0 +/- 1.3) and transferable embryos (2.4 +/- 0.9 vs 3.0 +/- 0.9) compared with that of the 2.0 PRIDs. In Experiment 2, FSH treatment initiated 5 d after insertion of a 0.5 PRID decreased the number of CL (4.0 +/- 0.5 vs 8.3 +/- 0.8; P < 0.001), ova/embryos (3.0 +/- 0.6 vs 5.9 +/- 1.2; P < 0.03) and transferable embryos (2.3 +/- 0.6 vs 5.1 +/- 1.0; P < 0.03) compared with that of a 2.0 PRID, respectively. Initiation of FSH treatment 2 d after insertion of a 0.5 PRID compared with a 2.0 PRID had no affect on the number of CL (8.0 +/- 2.1 vs 8.7 +/- 1.2), total ova (4.8 +/- 1.4 vs 6.9 +/- 1.4) and transferable embryos (2.9 +/- 1.2 vs 6.1 +/- 1.7). In conclusion, treatment with low doses of P(4) (0.5 PRID) for 5 d but not for 2 or 8 d before initiation of FSH treatment results in the development of a dominant ovarian follicle, which reduces recruitment of ovarian follicles, and the number of CL, total ova and transferable embryos.     

The SWISS-2DPAGE database of two-dimensional polyacrylamide gel electrophoresis, its status in 1995.

SWISS-2DPAGE is a database of proteins identified on two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). The current release contains 343 entries of human, yeast (Saccharomyces cerevisiae) and Escherichia coli origin, as well as virtual entries for each of the protein sequences in the SWISS-PROT database.     

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE₂ involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE₂ serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE₂ release per cell by CD8+; values of PGE₂ release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE₂ (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE₂ could play a role in resistance in mice infected with K98.     

Probability of mast cells to mediate anaphylaxis in skeletal muscle

Are there enough mast cells in denervated skeletal muscle to account for autopharmacological mediation of the antigen potentials (APs) elicited by microtaps? Through rough qualitative estimations, some authors have suggested a positive answer to this question. However, in view of measurements performed in this investigation of both the density of mast cells and the diffusion coefficient of antigens, the probability of such mediated effects was found to be relatively low:P=0.016 for egg albumin andP=0.004 for ferritin. Therefore, most APs induced by microtaps should be attributed to the direct effect of antigen over the sensitized muscle fibers. Yet, both the density of mast cells found in this work and the known amount of histamine they are capable of releasing when challenged with antigen, support the hypothesis regarding the involvement of these cells when antigen is massively superfused so as to induce Schultz-Dale reactions in muscle strips. Under this circumstance, the direct and mediated mechanisms may coexist.