Protonmotive force in freshwater sulfate-reducing bacteria,and its role in sulfate accumulation in Desulfobulbus propionicus

The protonmotive force in several sulfate-reducing bacteria has been determined by means of radiolabelled membrane-permeant probes (tetraphenyl-phosphonium cation, TPP⁺, for , and benzoate for pH). In six of ten freshwater strains tested only the pH gradient could be determine, while the membrane potential was not accessible due to nonspecific binding of TPP⁺. The protonmotive force of the other four strains was between –110 and –155 mV, composed of a membrane potential of –80 to –140 mV and a pH gradient between 0.25 and 0.8 (inside alkaline) at pH_out=7. In Desulfobulbus propionicus the pH gradient decreased with rising external pH values. This decrease, however, was compensated by an increasing membrane potential. Sulfate, which can be highly accumulated by the cells, did not affect the protonmotive force, if added in concentrations of up to 4 mM. The highest sulfate accumulation observed (2500-fold), which occurred at external sulfate concentrations below 5 M, could be explained by a symport of three protons per sulfate, if equilibrium with the protonmotive force was assumed. At higher sulfate concentrations the accumulation decreased and suggested an electroneutral symport of two protons per sulfate. At sulfate concentrations above 500 M, the cells stopped sulfate uptake before reaching an equilibrium with the protonmotive force.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - MOPS morpholinopropanesulfonic acid - TPP⁺ tetraphenylphosphonium cation - EDTA ethylenediaminetetraacetic acid - pH transmembrane pH gradient (pH_in-pH_out) - transmembrane electrical potential difference     

Differenzierung in Schilddrüsenkulturen erwachsener Hühner

Zusammenfassung Ebeling hat im Jahre 1925 über Differenzierung und Follikelbildung in Schilddrüsenkulturen 18–19 Tage alter Hühnerembryonen berichtet. Diese Versuche wurden mit den Schilddrüsen erwachsener Hähne nachgeprüft. Dabei zeigte es sich, daß unter den von Ebeling angegebenen Bedingungen keine morphologische Differenzierung eintritt. Die von ihm beobachteten und fälschlich als neu entstanden bezeichneten Follikel sind Reste der Mutterstücke, d.h. des ursprünglich ausgepflanzten voll ausdifferenzierten Schilddrüsenfragmentes.     

Fusion of cultured dog kidney (MDCK) cells: I. Technique,fate of plasma membranes and of cell nuclei

Summary The evaluation of the intracellular signal train and its regulatory function in controlling transepithelial transport with electrophysiological methods often requires intracellular measurements with microelectrodes. However, multiple impalements in epithelial cells are hampered by the small size of the cells. In an attempt to avoid these problems we fused cells of an established cell line, Madin Darby canine kidney cells, originally derived from dog kidney, to giant cells by applying a modified polyethylene glycol method. During trypsin-induced detachment from the ground of the petri dish, individual cells grown in a monolayer incorporate volume and mainly lose basolateral plasma membrane by extrusion. By isovolumetric cell-to-cell fusion, spherical giant cells are formed within 2 hr. During this process a major part of the individual cell plasma membranes is internalized. Over three weeks following cell plasma membrane fusion degradation of single cell nuclei and cell nuclear fusion occurs. We conclude that this experimental approach opens the possibility to investigate ion transport of epithelia in culture by somatic cell genetic techniques.     

Delta-Cytomembranen und lamelläre Cytosomen

Zusammenfassung Im Epithel der Kiemenbüschel von Axolotl (Amblystoma mexicanum) findet sich ein besonderer Typ von cytoplasmatischen Membranen, den wir mit -Cytomembran bezeichnen. -Cytomembranen sind schichtweise in Schleifen oder Spiralen angeordnet und bestehen aus einer 30–45 Å dicken osmiophilen Schicht mit einem 60 Å breiten intermembranösen Intervall. Die -Cytomembranen differenzieren sich im perinucleären Bereich des Cytoplasmas aus einer homogenen, elektronendichten Substanz und stellen die Vorstufen der lamellären Cytosomen dar. Die -Cytomembranen und die lamellären Cytosomen sind aus einem Kohlenhydrat-Protein-Komplex mit möglicher Bindung an Phospholipoide zusammengesetzt. Wir glauben, daß diese besondere Gruppe von submikroskopischen Strukturen wichtige Funktionen für die Synthese der Mucopolysaccharide im allgemeinen und für die Schleimsekretion im speziellen hat.Stipendiat der Deutschen Forschungsgemeinschaft.     

A MACROMUTATION IN TRIPSACUM DACTYLOIDES (POACEAE): CONSEQUENCES FOR SEED SIZE,GERMINATION, AND SEEDLING ESTABLISHMENT

A recessive allele of a gene in Tripsacum dactyloides L. (eastern gamagrass) changes staminate florets to pistillate or hermaphrodite, and restores fertility to suppressed florets. There were ten to 25 times more seeds in the mutant pistillate form, and these were 0.32 to 0.59 times smaller than seeds from the normal form. Seeds from pistillate plants had significantly lower germination rates (22% vs. 50%), and seedlings grew 20% slower than those of normal plants in a greenhouse experiment. Pistillate seedling survival rates were lower in both high- (18.8% vs. 62.6%) and low- (52.8% vs. 72.6%) competition environments in a field experiment, and surviving seedlings were smaller. The maternal parent of volunteer seedlings next to a plantation of normal and pistillate plants was determined by dissecting the attached fruitcases of 1,313 seedlings. Pistillate plants in the plantation produced 90% of all seeds falling on the site but only 29% of the volunteer seedlings. The pistillate macromutation is not likely to spread in the wild due to morphological constraints on seed size and packaging.     

Time- and order-dependent changes in functional and NO-mediated dilation during exercise training

Lash, Julia M., and H. Glenn Bohlen. Time- andorder-dependent changes in functional and NO-mediated dilation during exercise training. J. Appl. Physiol.82(2): 460-468, 1997.Arterial vessel responses to sodiumnitroprusside (SNP) and acetylcholine (ACh) were measured in thespinotrapezius muscle of sedentary (Sed) and treadmill-trained (Tr)rats to determine whether these endothelium-dependent (ACh) and-independent (SNP) mechanisms contribute to thetraining-induced increase in functional vasodilation previouslyobserved. Control and maximal vessel diameters were similar between Sedand Tr. After 8 wk of training, functional dilation (2-, 4-, and 8-Hzcontractions) was enhanced in all orders of vessels studied[terminal feed artery (FA), largest arterioles (1A), andintermediate-sized arterioles (2A)], but responses to SNP wereincreased only in FA. Responses to ACh were not significantly increasedin any vessel order. After 16 wk of training, functional dilation hadregressed in Tr such that only the FA response to 4 Hz wassignificantly elevated relative to Sed. However, the FA and 1Aresponses to SNP were significantly greater in Tr than in Sed, as werethe 1A and 2A responses to ACh. These results show a dissociation offunctional dilation and SNP- or ACh-mediated responses, as well asage-dependent interactions, a time-dependent progression, and vesselorder specificity in the adaptations to training.

     

Die Rezeptoren an den ersten Antennen vonLeptestheria dahalacensis Rüppel (Crustacea,Conchostraca)

Zusammenfassung Bei dem ConchostracenLeptestheria dahalacensis kommen auf den ersten Antennen etwa 600 gleich aussehende Sinneshaare vor, die in Gruppen von jeweils 25–30 zusammengefaßt sind. Diese Sinneshaare sind in zwei Teile gegliedert, die durch das lichtmikroskopisch gut sichtbare Basalstück (basal bead) voneinander getrennt sind. Dieses bildet die Basis des Haares, dessen Wand im wesentlichen aus Epicuticula besteht. Apikal wird das Haar durch das Endkügelchen (terminal pellet) abgeschlossen. Das Basalstück wird von der untersten Lage der Epicuticula gebildet. Die 4–10 Receptorcilien, die jeweils einzeln ebensovielen Dendriten aufsitzen, ziehen aus dem inneren Teil des Rezeptors, der von insgesamt 5 Hüllzellen umgeben wird, durch das Basalstück, in dem sie stark eingeengt werden und verzweigen sich dann im äußeren Teil des Rezeptors. Sie ziehen bis zum Endkügelchen, in das sie durch einen Porus, den man als Häutungsporus ansprechen kann, eintreten. In der Häutungsvorbereitung wird der Haarbalg von der Hüllzelle 5, das Basalstück von der Hüllzelle 4, der Haarschaft dagegen von der Hüllzelle 3 gebildet. Dabei spaltet sich die Hüllzelle 3 ringspaltförmig auf, so daß in diesem Spalt der neuangelegte Haarschaft handschuhfingerförmig eingestülpt liegt. Die Hüllzelle 2 formt die Spitze des neuen Haares, während die Dendritenscheide von der Hüllzelle 1 abgegeben wird.

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The receptors on the first antennae ofLeptestheria dahalacensis Rüppel (Crustacea, Conchostraca)

Summary On the antennulae ofLeptestheria dahalacensis (Conchostraca) nearly 600 sensory setae of one type are found. They are gathered in groups of 25–30. The single sensory seta is divided into two parts by the basal bead which is easily visible in the light microscope. The basal bead is the socket of the seta, whose wall is mainly built up by the epicuticle. The terminal pellet closes the tip of the seta. The basal bead is derived from the innermost layer of the epicuticle. 4–10 dendrites each with one receptorcilium innervate the receptor. The receptorcilia stretch through the interior part of the receptor and the basal bead into the exterior part, where they branch. They enter the terminal pellet in a porus, which seems to be a moulting porus. The interior part of the receptor is surrounded by 5 sheath cells. During the premoult it becomes obvious, that the socket of the seta is built by the sheath cell 5, the basal bead by the sheath cell 4 and the shaft by the sheath cell 3. For this the sheath cell 3 is divided into two parts. Between this two parts the newly formed cuticle is invaginated. The sheath cell 2 formes the tip and the sheath cell 1 the cuticular sheath of the new bristle.

     

The Arabidopsis mitogen-activated protein kinase kinase MKK3 is upstream of group C mitogen-activated protein kinases and participates in pathogen signaling

Although the Arabidopsis thaliana genome contains genes encoding 20 mitogen-activated protein kinases (MAPKs) and 10 MAPK kinases (MAPKKs), most of them are still functionally uncharacterized. In this work, we analyzed the function of the group B MAPK kinase, MKK3. Transgenic ProMKK3:GUS lines showed basal expression in vascular tissues that was strongly induced by Pseudomonas syringae pv tomato strain DC3000 (Pst DC3000) infection but not by abiotic stresses. The growth of virulent Pst DC3000 was increased in mkk3 knockout plants and decreased in MKK3-overexpressing plants. Moreover, MKK3 overexpression lines showed increased expression of several PR genes. By yeast two-hybrid analysis, coimmunoprecipitation, and protein kinase assays, MKK3 was revealed to be an upstream activator of the group C MAPKs MPK1, MPK2, MPK7, and MPK14. Flagellin-derived flg22 peptide strongly activated MPK6 but resulted in poor activation of MPK7. By contrast, MPK6 and MPK7 were both activated by H(2)O(2), but only MPK7 activation was enhanced by MKK3. In agreement with the notion that MKK3 regulates the expression of PR genes, ProPR1:GUS expression was strongly enhanced by coexpression of MKK3-MPK7. Our results reveal that the MKK3 pathway plays a role in pathogen defense and further underscore the importance and complexity of MAPK signaling in plant stress responses.