Root growth inhibition of the holorganic layer of moder humus under spruce (Picae abies KARST.) and beech (Fagus Silvatica L.)

A test of root growth inhibition of spruce and beech roots, according to Lynch's procedure (1977), shows the inhibitory effects of soil solution extracted from the holorganic layers (Of₂-Oh) under beech and spruce. Molecular gel filtration of soil solutions shows that the molecular weights vary over a wide range, from less than 100 to over 40,000 daltons. Chemical analysis, using CGC, HPLC and sometimes MS shows only negligible concentrations of simple aliphatic (C₁-C₅) and aromatic acids in the free state. Using the fraction scheme of Forsyth (1977) and the carbazole procedure, it is shown that uronic acids represent only a small percentage of the carboxylic acids, and have no inhibitory effects on root growth. By analogy with results of other authors, the presence of polycarboxylic acids in the soil solution are considered to be the main cause of root growth inhibition.     

Haplotype analysis of the human apolipoprotein B mutation associated with familial defective apolipoprotein B100.

Haplotype analysis was conducted on the mutant allele of 14 unrelated subjects heterozygous for a mutation in the codon for amino acid 3500 of human apolipoprotein B100. This mutation is associated with defective binding of low-density lipoprotein to the low-density lipoprotein receptor and with moderate hypercholesterolemia. Ten markers were used for haplotyping: eight diallelic markers within the structural gene and two hypervariable loci flanking the gene. Seven of eight unequivocally deduced haplotypes were identical, and one revealed only a minor difference at one of the hypervariable loci. The genotypes of the six other affected subjects were consistent with this same assigned haplotype. These data are consistent with a common ancestral chromosome and provide no evidence for a recurrent mutation at this potentially hypermutable CG dinucleotide, despite the fact that this mutation is not rare.     

D-Cycloserine: Agonist turned antagonist

Summary D-Cycloserine can enhance activation of the NMDA receptor complex and could enhance the induction of long-term potentiation (LTP). In animals and humans, D-cycloserine can enhance performance in learning and memory tasks. This enhancing effect can disappear during repeated administration. The enhancing effects are also lost when higher doses are used, and replaced by behavioral and biochemical effects like those produced by NMDA antagonists. It has been reported that NMDA agonists, applied before or after tetanic stimulation, can block the induction of LTP. This may be the result of feedback inhibition of second messenger pathways stimulated by receptor activation. This may explain the antagonist-like effects of glycine partial agonists like D-cycloserine. In clinical trials of D-cycloserine in age-associated memory impairment (AAMI) and Alzheimer's disease, chronic treatment provided few positive effects on learning and memory. This may be due to inhibition of second messenger pathways following chronic stimulation of the receptor complex.     

Maximum growth temperature ranges of Aeromonas Spp. isolated from clinical or environmental sources

Only a limited number of phenotypic tests are available for the differentiation of all 13 known hybridization groups (HG) of Aeromonas spp. These organisms have a wide spectrum of warm-blooded and cold-blooded hosts. In the present study, the maximum growth temperatures (t_max) of the most common HGs of Aeromonas spp. originating from human fecal samples, food, water, and healthy and diseased fish were determined with a plate-type continuous temperature-gradient incubator. We observed that determination of the t_max can be applied for differentiation of HG 1 from HG 2 and 3 (phenospecies A. hydrophila); HG 6 from HG 4, 5A, and 5B (phenospecies A. caviae); HG 7 from HG 8/10 (phenospecies A. sobria); and HG 11 from HG 8/10 (phenospecies A. veronii). HG 1, 4, 8/10, and 13 strains occurring also in human clinical samples had a high t_max, about 40°C or higher. Hybridization group 2, 3, 5A, and 5B strains, which in most cases originated from water or food, had t_max values in the range of about 36–39°C, while HG 6, 7, and 11 had t_max values in the range of about 33–37°C. Fish pathogenic strains of A. salmonicida subsp. salmonicida and subsp. achromogenes had the lowest t_max values from about 30 to 35°C. Correspondence to: M.-L. Hdnninen     

The 1-Hz fluorometer: A new approach to fast and sensitive long-term studies of active chlorophyll and environmental influences

A new instrument for environmental monitoring, called at 1-Hz fluorometer, provides two modes of application. First, it enables a quantitative determination of algal concentrations down to 20 ng/l. Second, it can be used as a biosensor for changes in environmental conditions. The distinction between the signals from living chlorophyll-containing algae and other fluorescent material is achieved by using two modulated light-sources resulting in a mean fluence rate of 200 μE. The measuring light induces changes in chlorophyll fluorescence (yield) with a frequency of 1 kHz, and the actinic light modulates the redox state of the quenchers of PS II with a frequency of 1 Hz. This leads to a modulation of the yield which is detected by two phase-sensitive rectifiers (double correlation). Measurements from different sites in a river, and in the Baltic and North Seas, show that correction by the built-in simultaneously-measured attenuation is necessary in order to obtain values which are identical with those determined by a photometric analysis (Uvikon 860). This applies if the transmission becomes less than about 95%. Suspensions ofDunaliella salina exposed to ammonia and phosphate were used for illustrating the usage for environmental monitoring. It is shown that this system can measure changes in the chlorophyll fluorescence of living algae caused by changes in concentration of ammonia down to 1 μg/l and of phosphate down to 10 μg/l.     

Genetic variation for foot-rot and Fusarium head-blight resistances among full-sib families of a self-incompatible winter rye (Secale cereale L.) population

The amount of genetic variation for resistance to foot rot caused by Pseudocercosporella herpotrichoides, Fusarium spp., and Microdochium nivale and for resistance to head blight caused by Fusarium culmorum are important parameters when estimating selection gain from recurrent selection in winter rye. One-hundred and eighty-six full-sib families of the selfincompatible population variety Halo, representing the Petkus gene pool, were tested for foot-rot resistance at five German location-year combinations (environments) and for head-blight resistance in three environments with artificial inoculation in all but one environment. Foot-rot rating was based on 25 stems per plot scored individually on a 1–9 scale. Head-blight resistance was plotwise scored on a 1–9 scale and, additionally, grain-weight per spike was measured relative to the non-inoculated control plots. Significant estimates of genotypic variance and medium-sized heritabilities (h ²=0.51–0.69) were observed in the combined analyses for all resistance traits. In four out of five environments, the amount of genetic variance was substantially smaller for foot-rot than for head-blight rating. Considerable environmental effects and significant genotype-environment interactions were found for both foot-rot and head-blight resistance. Coefficients of error-corrected correlation among environments were considerably closer than phenotypic correlations. No significant association was found between the resistances to both diseases (r=-0.20 to 0.17). In conclusion, intra-population improvement by recurrent selection should lead to substantial higher foot-rot and head-blight resistances due to significant quantitative genetic variation within Halo. Selection should be carried out in several environments. Lack of correlation between foot-rot and head-blight resistance requires separate infection tests for improving both resistances.     

Intersegmental Coordination: Lessons from Modeling Systems of Coupled Non-Linear Oscillators

SYNOPSIS. Intersegmental coordination of both vertebrates andinvertebrates is poorly understood primarily because so littleis known about the substrate of the neural underpinnings andhow the elements interact to produce the complex timing relationshipsrequired by the organism. We describe here a systems approachcombining experimental and theoretical treatment of the lampreylocomotor central pattern generator. The central pattern generatoris viewed as a chain of coupled non-linear oscillators correspondingto segmental burst generators. We analyze various coupling schemesin terms of their ability to produce a stable traveling wavesimilar to that seen in the isolated spinal cord and the intactanimal. The role of long coordinating neurons is particularlydiscussed.