Chemotaxis,induced gene expression and competitiveness in the rhizosphere

Rhizobia are soil bacteria which symbiotically infect legume roots and generate nodules in which they fix atmospheric nitrogen for the plant in exchange for photosynthetically fixed carbon. A crucial aspect of signal exchange between these symbionts is the secretion of phenolic compounds by the host root which induce nodulation gene expression in the bacteria. Stimulation of nod gene expression by host phenolics is required for nodule formation, is biochemically specific at 10^-6 M, and is mediated by nodD. We and others have shown that rhizobia display chemotaxis to 10^-9 M of the same phenolic compounds. Chemotaxis to inducer phenolics is selectively reduced or abolished by mutations in certain nod genes governing nodulation efficiency or host specificity. Conversely, mutations in rhizobia that affect general motility or chemotaxis have substantial effects on nodulation efficiency and competitiveness. These findings suggest that microbes entering the rhizosphere environment may utilize minor, non-nutrient components in root exudates as signals to guide their movement towards the root surface and elicit changes in gene expression appropriate to this environment.     

Elicitor-induced metabolic changes in cell cultures of chickpea (Cicer arietinum L.) cultivars resistant and susceptible to Ascochyta rabiei

Cell-suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant (ILC 3279) and susceptible (ILC 1929) to the fungus Ascochyta rabiei (Pass.) Lab., showed differential accumulation of the phytoalexins medicarpin and maackiain, and transient induction of related enzyme activities after application of an A. rabiei-derived elicitor. The chalcone-synthase (CHS) activity (EC 2.3.1.74) which is involved in the first part of phytoalexin biosynthesis exhibited a maximum 8–12 h after elicitation in the cells of both cultivars. Concomitant with the fivefold-higher phytoalexin accumulation, CHS activity increased twofold in the cells of the resistant cultivar. The maximum of the elicitor-induced CHS-mRNA activity was determined 4 h after onset of induction in the cultures of both cultivars, although in cells of cultivar ILC 3279 this mRNA activity was induced at a level twofold higher than that in cells of the susceptible race ILC 1929. Investigations of CHS isoenzymes by two-dimensional gel electrophoresis of immunoprecipitated in-vitro-translated protein indicated the presence of five proteins. In the cells of both cultivars only two of the isoenzymes were induced after elicitor treatment. Analysis of the total in-vitro-translated proteins by two-dimensional gel electrophoresis showed that the constitutively expressed patterns of mRNA activities in the cell cultures of the two cultivars were identical. After elicitation, considerably more translatable mRNAs were induced in the cells of cultivar ILC 3279. The few induced proteins, and their respective mRNA activities, which could be detected in the cells of the susceptible cultivar, all existed in the cells of the resistant cultivar, too. One highly induced protein (M_r 18 kDa) found in the cells of cultivar ILC 3279 reached its maximum mRNA activity 6 h after elicitor application. The amount of this protein was hardly increased in the cells of the susceptible cultivar. This protein appears to be excreted from the cells into the growth medium.Abbreviations CHS chalcone synthase - IEF isoelectric focussing - ILC international legume chickpea - PR-protein pathogenesis-related protein - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. The authors thank Dr. K. Hahlbrock (Max-Planck-Institut für Züchtungsforschung, Köln, FRG) for provision of antisera and the International Centre for Agricultural Research in the Dry Areas (Aleppo, Syria) for plant material.     

Selenium concentrations in the human thyroid gland

Recently, we found that prediagnostic serum selenium concentration was significantly lower for cases developing thyroid cancer (n=43) than for controls. We assumed that redistribution of serum selenium into the affected tissue took place in the prediagnostic period. The present study was carried out to determine the physiological concentration of selenium in the thyroid, since very few data are available in the literature. The concentrations of selenium in the thyroid (n=45) and liver samples from Norwegians who had died because of acute illness or accidents were determined by hydride generation atomic absorption spectrometry. The mean selenium concentration was found to be 0.72±0.44 μg/g in the thyroid and 0.45±0.11 μg/g in the liver tissue. The surprisingly high concentration of selenium in apparently normal thyroids indicates that selenium has important functions in this organ. The remarkably broad range, together with the observation that no significant correlation exists between thyroid and liver concentrations, suggest that factors other than the selenium status are important determinants for the selenium concentration in the thyroid gland. This observation is consistent with our hypothesis that in carcinogenesis, prediagnostic processes influence the serum-/thyroid-ratio of selenium.     

Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein

The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, Q_B-independent electron flow and Q_B-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and Q_B-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The Q_B-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the Q_B-site of D1-protein. Evidence for this comes from fluorescence relaxation kinetics following photoinhibition at 0°C which indicate a partial inactivation of Q_A ^--reoxidation. These results support the idea of D1-protein breakdown during photoinhibition as a two step process consisting of an initial inactivation at the Q_B-site of the protein followed by its degradation. The latter is accompanied by the loss of PS II-reaction centre function.Abbreviations Asc ascorbate - p-BQ 1, 4-benzoquinone - DAD diaminodurene - DPC diphenylcarbazide - DQH₂ duroquinole - Fecy ferricyanide - MV methylviologen - Q_A primary quinone acceptor of PS II - Q_B secondary quinone acceptor of PS II - SiMo silicomolybdate     

Aldosterone regulates paracellular pathway resistance in rabbit distal colon

Summary Regulation of the paracellular pathway in rabbit distal colon by the hormone aldosterone was investigated in vitro in Ussing chambers by means of transepithelial and microelectrode techniques. To evaluate the cellular and paracellular resistances an equivalent circuit analysis was used. For the analysis the apical membrane resistance was altered using the antibiotic nystatin. Under control conditions two groups of epithelia were found, each clearly dependent on the light: dark regime. Low-transporting epithelia (LT) were observed in the morning and high-transporting epithelia (HT) in the afternoon. Na⁺ transport was about 3-fold higher in HT than in LT epithelia. Incubating epithelia of both groups with 0.1 mol·1^-1 aldosterone on the serosal side nearly doubled in LT epithelia the short circuit current and transepithelial voltage but the transepithelial resistance was not influenced. Maximal values were reached after 4–5 h of aldosterone treatment. In HT epithelia due to the effect of aldosterone all three transepithelial parameters remained constant over time. Evaluation of the paracellular resistance revealed a significant increase after aldosterone stimulation in both epithelial groups. This increase suggests that tight junctions might have been regulated by aldosterone. The hormonal effect on electrolyte transport was also dependent on the physiological state of the rabbit colon. Since net Na⁺ absorption in distal colon is, in addition to transcellular absorption capacity, also dependent on the permeability of the paracellular pathway, the regulation of tight junctions by aldosterone may be a potent mechanism for improving Na⁺ absorption during hormone-stimulated ion transport.Abbreviations V _t transepithelial potential difference (mV) - R _t transepithelial resistance (·cm²) - G _t transepithelial conductance (mS·cm^-2) - I_sc calculated short circuit current (A·cm^-2) - V _a apical membrane potential difference (mV) - V _bl basolateral membrane potential difference (mV) - voltage divider ratio - R _a apical membrane resistance (·cm²) - R _bl basolateral membrane resistance (·cm²) - R _c cellular resistance ( of apical and basolateral resistance) (·cm²) - R _p resistance of the paracellular pathway (·cm²) - G _a apical membrane conductance (mS·cm^-2) - G _bl basolateral membrane conductance (mS·cm^-2) - G _p paracellular conductance (mS·cm^-2) - G _t transepithelial conductance (mS·cm^-2) - HT _contr high transporting control epithelia - LT _contr low transporting control epithelia - HT _aldo aldosterone incubated high transporting epithelia - LT _aldo aldosterone incubated low transporting epithelia     

The macrofauna and macroflora associated withLaminaria digitata andL. hyperborea at the island of Helgoland (German Bight,North Sea)

This paper describes the macroflora and macrofauna associated with two bull kelp species,Laminaria hyperborea andL. digitata, at the island of Helgoland, North Sea. During a study period of seven months (March–September 1987), 29 macroflora species and 125 macrofauna species were found. The dominant taxonomic groups were Polychaeta (25 species), Bryozoa (17), Amphipoda (14), Hydrozoa (10) and Ascidiae (8). The species maximum was in July. In general,L. hyperborea was preferred as a substrate for settlement toL. digitata. Composition of the communities associated with kelp changed during the season according to exposure to wave action, and according to location on the kelp thallus. The rhizoid community of both kelps bore more species at exposed locations. Wave-exposedL. digitata lacked obvious faunal settlement on both phylloid and cauloid. Phylloid and cauloid ofL. hyperborea were chosen as an attractive substrate at both sheltered and wave-exposed locations, showing an association of encrusting bryozoan and hydrozoan colonies.     

Different influences of cytochalasin B on the activation of human neurophils settled onto petri dishes displayed by simultaneously detected native and luminol-dependent luminescence

Cytochalasin B (CB) is known to interfere reversibly with the cytoplasmic contractile filamental network of mammalian cells. The role of the microfilament system in the mechanism of the reactive oxygen intermediates release of polymorphonuclear leukocytes (PMNL) was studied for different kinds of stimuli. PMNL from fresh human blood were treated with CB and stimulated by adherence on plastic surfaces, by opsonized zymosan, by phorbol myristate acetate and by N-formylmethionyl-phenylalaline. The production of reactive oxygen species were monitored by simultaneous detection of native, luminol-independent, luminescence (NL) and luminol-dependent luminescence (LDL) using a method of spectral discrimination. Different influences of CB on NL with respect to LDL as well stimuli-dependent influences of CB on the luminescence response of PMNL were observed. Especially phagocytosis-associated activation of PMNL was strongly inhibited by CB, whereas LDL was reduced to a much greater extent in comparison with NL. A firm involvement of the microfilament system is indicated, but it depends on the kind of stimulus engaged.     

Colony orientation and successful defence behaviour in the conifer aphid, Schizolachnus pineti

We studied colony structure and body orientation behaviour of Schizolachnus pineti, a specialised aphid feeding on needles of Scots pine. Aphids feeding at the margin of a colony always face towards the centre of the colony, bounding the colony with their legs. This behaviour increased the defence success aginst the specialised parasitoid (Pauesia unilachni) and the specialised predator (Scymnus nigrinus). Both enemies had less success when attacking S. pineti from the abdominal site when compared to the front. We assume that the defence orientation displayed by marginally feeding aphids has an adaptive nature and is particularly effective when feeding in a row on linear plant structures such as needles.     

Langzeit-Erfassung brutbiologischer Parameter beim KleiberSitta europaea in zwei norddeutschen Untersuchungsr?umen

Zusammenfassung Der Zusammenstellung liegen Befunde zu den brutbiologischen Parametern Gelegestärke, Schlüpftermin und Anzahl flügger Junge zugrunde, die von 1970–1995 an rund 1500 Erstbruten des Kleibers in Versuchsgebieten mit künstlichen Nisthöhlen bei Braunschweig und Essen gewonnen wurden. Die Vollgelege-Eizahl beträgt im Durchschnitt 6,8 Eier (nur Daten aus dem Braunschweiger Raum), der durchschnittliche Schlüpftermin fällt auf den 9. Mai (Braunschweig) und 6. Mai (Essen) und die Anzahl flügger Nestlinge liegt in erfolgreichen Bruten im Mittel bei 5,6 (Braunschweig) bzw. 5,2 (Essen). Im Untersuchungszeitraum kam es in beiden Gebietsregionen zu einer signifikanten Verfrühung des Bruttermins. Doch werden wohl erst die Befunde der kommenden Jahre zeigen können, ob die rezente Häufung früher Brutjahre beim Kleiber (diese Arbeit) und bei Kohl- und Blaumeisen (Winkel &Hudde unveröff.) bereits eine Folge des anthropogen bedingten global warming ist oder noch das normale Auf und Ab der Witterung widerspiegelt.

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Long-term changes of breeding parameters of NuthatchesSitta europaea in two study areas of northern Germany

Between 1970 and 1995, nestbox data about clutch size, hatching date and fledging success were collected for a total of around 1500 first broods of Nuthatches in two north German study areas (near Brunswick 52.16 N 10.32 E and near Essen 51.24 N 6.59 E). The average clutch size was 6.8 eggs (Brunswick), the average hatching date 9 May (Brunswick) and 6 May (Essen), and the mean number of fledglings per successful brood 5.6 (Brunswick) and 5.2 (Essen). Over time hatching dates significantly advanced in both areas. Data of further years are needed to clarify if the recent unusual sequence of early breeding years in the Nuthatch is already a consequence of the anthropogenic greenhouse effect or just due to normal variation of weather conditions.