Asynchronous fluctuation of soil microbial biomass and plant litterfall in a tropical wet forest

Carbon availability often controls soil microbial growth and there is evidence that at regional scales soil microbial biomass is positively correlated with aboveground forest litter input. We examined the influence of plant litterfall on annual variation of soil microbial biomass in control and litter-excluded plots in a tropical wet forest of Puerto Rico. We also measured soil moisture, soil temperature, and plant litterfall in these treatment plots. Aboveground plant litter input had no effect on soil microbial biomass or on its pattern of fluctuation. Monthly changes in soil microbial biomass were not synchronized with aboveground litter inputs, but rather preceeded litterfall by one month. Soil microbial biomass did not correlate with soil temperature, moisture, or rainfall. Our results suggest that changes in soil microbial biomass are not directly regulated by soil temperature, moisture, or aboveground litter input at local scales within a tropical wet forest, and there were asynchronous fluctuation between soil microbial biomass and plant litterfall. Potential mechanisms for this asynchronous fluctuation include soil microbial biomass regulation by competition for soil nutrients between microorganisms and plants, and regulation by below-ground carbon inputs associated with the annual solar and drying-rewetting cycles in tropical wet forests.     

Interaction between nickel and iron in the rat

The interaction between nickel and iron was confirmed in rat metabolism. In a fully-crossed, two-way, three by four, factorially designed experiment, female weanling rats were fed a basal diet supplemented with iron at 0, 25, 50, and 100 μg/g and with nickel at 0, 5, and 50 μg/g. The basal diet contained about 10 ng of nickel and 2.3 μg of iron/g. After nine weeks, dietary iron affected growth, hematocrit, hemoglobin, plasma cholesterol, and in liver affected total lipids, phospholipids, and the contents of copper, iron, manganese, and zinc. By manipulating the iron content of the diet, effects of dietary nickel were shown in rats that were not from dams fed a nickel-deprived diet. Nickel affected growth, hematocrit, hemoglobin, plasma alkaline phosphatase activity, plasma total lipids, and in liver affected total lipids, and the contents of copper, manganese, and nickel. The interaction between nickel and iron affected hematocrit, hemoglobin, plasma alkaline phosphatase activity, and plasma phospholipids, and in liver affected size, content of copper, and perhaps of manganese and nickel. In severely iron-deficient rats, the high level of dietary nickel partially alleviated the drastic depression of hematocrit and hemoglobin, and the elevation of copper in liver. Simultaneously, high dietary nickel did not increase the iron level in liver and was detrimental to growth and appearance of severely iron-deficient rats. In nickel-deprived rats fed the borderline iron-deficient diet (25 μg/g) hematocrit and hemoglobin also were depressed. However, 5 μg Ni/g of diet were just as effective as 50 μg Ni/g of diet in preventing those signs of nickel deprivation. The findings in the present study suggested that nickel and iron interact with each other at more than one locus.     

Genetic variation and ecology of stoneroller minnows

Genetic variation at 17 enzymic and other protein loci was examined for natural populations of stoneroller minnows, Campostoma oligolepis and C. anomalum. Species differences in levels of heterozygosity, standardized variance of gene frequencies and interpopulation heterogeneity appear to be a function of degree of demic isolation, rate of migration and potential for stochastic processes to structure genomes.     

The effects of a diet rich in fish oil on human neutrophils: identification of leukotriene B5 as a metabolite

Diets that are enriched with fish oil have been shown to alter arachidonic acid metabolism via the cyclooxygenase pathway. Recently it has been shown that one of the major component fatty acids of fish oil, eicosapentaenoate (EPA), is a substrate for the leukotriene B (LTB) pathway when added exogenously to human neutrophils in vitro. We fed a diet that contained 8-10gm/day of EPA to four human subjects for three weeks and compared the arachidonate metabolism of their neutrophils to the same functions while the subjects were on their usual diet. The fish oil-supplementation increased neutrophil EPA content from undetectable levels to 7.4 +/- 2.4% (p less than 0.01, expressed as % of total fatty acid), and decreased arachidonate from 15.4 +/- 2.3% to 12.8 +/- 2.3% (p less than 0.05). Leukotriene B5 was identified as a metabolite during the fish oil-diet by its chromatographic profile and mass spectrum. During the experimental diet LTB4, decreased from 160 +/- 37 ng/10(7) neutrophils to 120 +/- 12 (p less than 0.05), and LTB5 increased from 0 to 39 +/- 9 ng/10(7) neutrophils (p less than 0.005). The diet had no effect on neutrophil aggregation or adherence to nylon fibers.     

Intrawell Absorption of Antisera in a Template Thin-Film Gel Diffusion Method

This report describes a method for in situ absorption of antisera within the template wells used in thin-film microgel diffusion. The intrawell absorption of antisera offers several advantages over previously reported techniques for detecting the presence of given antigens in biological preparations. The procedure is time saving, antigens are conserved, optimum antigen-antibody ratios are easily determined, and tests of several different absorbing antigens can be made on a single plate.     

Interaction of Partially Purified Phytotoxins from Phytophthora cactorum on Apple Cell Plasma Membrane

The ‘crude’ filtrate (CF) of Phytophthora cactorum containing phytotoxin(s), having some properties similar to the toxins isolated from other Phytophthora species, was processed by three steps (acetone precipitation, dialysis and gel filtration chromatography). The CF fractions corresponding to the progressive steps of purification were tested for phytotoxicity on tomato seedlings and for activity on cell trans-membrane electrical potential (Em) of susceptible and resistant apple rootstocks (Malus domestica). The fractions (F4), obtained from chromatography on Sephadex G50 fine and eluted in the zone corresponding to a molecular weight of 15 ± 2 kD, induced a specific alteration on susceptible apple cell membranes. These metabolites, even though incompletely purified, are able to induce a high and specific activity on susceptible apple cell Em only, not on resistant ones. As a consequence, they may be of potential use in screening for insensitive cells.