Pore water phosphorus and iron concentrations in a shallow,eutrophic lake — indications of bacterial regulation

Peak pore water SRP and iron(II) concentrations were found during summer in surface sediments in the shallow and eutrophic L. Finjasjön, Sweden, and the concentrations generally increased with water depth. The SRP variation in surface sediments (0–2 cm) was correlated with temperature (R² = 0.82–0.95) and iron(II) showed a correlation with sedimentary carbon on all sites (R² = 0.42–0.96). In addition, sedimentary Chla, bacterial abundances and production rates in surface sediments (0–2 cm) varied seasonally, with peaks during spring and fall sedimentation. Bacterial production rates were correlated with phosphorus and carbon in the sediment (R² = 0.90–0.95 and R² = 0.31–0.95, respectively), indicating a coupling with algal sedimentation. A general increase in sediment Chla and bacterial abundances towards sediments at greater water depth was found. Further, data from 1988–90 reveal that TP and TFe concentrations in the lake were significantly correlated during summer (R² = 0.81 and 0.76, in the hypolimnion and epilimnion, respectively). The results indicate that the increase in pore water SRP and Fe(II) in surface sediments during summer is regulated by bacterial activity and the input of organic matter. In addition, spatial and temporal variations in pore water composition are mainly influenced by temperature and water depth and the significant correlation between TP and TFe in the water suggests a coupled release from the sediment. These findings support the theory of anoxic microlayer formation at the sediment-water interface.     

Sensitive mRNA detection using unfixed tissue: combined radioactive and non-radioactive in situ hybridization histochemistry

Summary In the present study some experimental parameters for in situ hybridization histochemistry (ISHH) have been analysed using³⁵S-labelled and alkaline phosphatase-conjugated probes, in order to develop a reproducible double-labelling procedure. We have compared the total exclusion of tissue fixation with tissue sections fixed by immersion in formalin. In addition, the effect of dithiothreitol was assessed both when combining radiolabelled and non-radioactive probes on a single tissue section and when the probes were used separately. Hybridization of unfixed tissue resulted in stronger specific labelling and lower background both for radiolabelled and alkaline phosphatase-conjugated probes. No loss in tissue preservation was seen at the light microscopic level after hybridization of unfixed tissue. High concentrations (200 mM) of dithiothreitol strongly suppressed background when using³⁵S-labelled probes, whereas in the non-radioactive procedure, alkaline phosphatase labelling could only be achieved with very low dithiothreitol concentrations (<1 mM). This incompatibility led to a protocol using unfixed tissue sections and a sequential hybridization procedure, with the radiolabelled probe and high concentrations of dithiothreitol in the first step and the alkaline phosphatase-conjugated probe without dithiothreitol in the second step.     

Effects of donor plant environment and light during incubation on anther cultures of some spring wheat (Triticum aestivum L.) cultivars

Four different growth environments (field, two phytotron greenhouses and one growth chamber) were compared, using two genotypes of spring wheat, one recalcitrant and one responsive. Field-grown plants gave inferior results. Large improvements could be made by improving the conditions, embryoid frequencies in the two genotypes reaching 77.1% and 183.9% per 100 anthers, respectively. High light intensity during the induction phase strongly suppressed induction in both genotypes, but stimulated regeneration of green plants in the recalcitrant genotype, which had the lowest regeneration ability. Weak, diffuse light did not inhibit induction while the positive effect on regeneration was maintained. Also, another recalcitrant genotype was grown in the field, together with two F₁-hybrids (recalcitrant x recalcitrant and recalcitrant x responsive). Evidence for a three-factor system was obtained.     

Ipsdienol-specific receptor cells in bark beetles: structure-activity relationships of various analogues and of deuterium-labelled ipsdienol

Summary The specificity of receptor cells specialized for the bark beetle pheromone component, ipsdienol, was studied electrophysiologically (extracellular recordings) in species ofIps. Single cells were tested with both ipsdienol enantiomers, their racemate, and racemates of structurally similar compounds. The two cell types, keyed to (+)- and to (–)-ipsdienol, respectively, showed much weaker responses to the analogues, demonstrating the high specialization of the cells. The relationships between the dose-response curves of the two types were similar, favoring the concept of particular membrane receptor types (acceptors) in both cell types.The stimulatory efficacy of the various analogues suggested three key features of ipsdienol: (i) the free hydroxyl group at C-4, (ii) the C-2-C-3 double bond, and (iii) the diene system attached to C-5 which may be in acis-conformation.Substituting the C-4 hydrogen by deuterium did not affect the stimulatory effect of ipsdienol.     

Triloborhynchus psilastericola n. sp., a parasitic turbellarian (Fam. Pterastericolidae) from the starfish Psilaster andromeda (Müller and Troschel)

The turbellarian Triloborhynchus psilastericola n.sp. (family Pterastericolidae) occurs in the starfish Psilaster andromeda. On approaching maturation it moves from the host's coelom into the glandular pockets of the pyloric caeca with simultaneous loss of almost the entire ciliation. Mature turbellarians feed on the tissue of the pyloric caeca.     

Chemoreception of host volatiles in the bark beetleIps typographus

Summary In the bark beetleIps typographus the stimulating effects of host odour constituents were studied by linking a gas Chromatograph (GC) with electrophysiological recordings from single olfactory receptor cells. Cells were exposed to the complete aroma of natural bark, extracts from host and non-host trees and fractions of these stimuli separated via a GC column. Four minor fractions belonging to two extracts were found to excite olfactory receptor cells. Responsive cells were divided into two main groups reacting exclusively to one fraction and suggesting that the cells were highly specialized to a particular host odour constituent. However, an effective extract or fraction could not be found for half of the olfactory units responding to natural bark, indicating that the relevant stimulatory compounds were lost during the extraction and/or GC procedure.Abbreviations EAG electroantennogram - GC gas-chromatograph     

Über die Backfähigkeit schwedischer Weizensorten und die Möglichkeit ihrer Verbesserung durch Züchtung

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