Induction by antimycin A of cyanide-resistant respiration in heterotrophic Euglena gracilis: Effects of growth,respiration and protein biosynthesis

The addition of antimycin A during the logarithmic phase of growth of heterotrophic Euglena gracilis cultures (in lactate or glucose medium) was immediately followed by decreased respiration and a cessation of grwoth. Induced cyanideresistent respiration appeared 5 h after the addition of the inhibitor then the cells started to grow again and could be cultured in the presence of antimycin A. Thus the cells exhibited a cyanide-and antimycin-resistant respiration which was, in addition, sensitive to salicylhydroxamic acid and propylgallate. Antimycin-adapted Euglena and control cells were compared for their biomass production and protein synthesis. The difference in growth yield between control and antimycin-adapted cells was not as high as would be expected if only the first phosphorylation site of the normal respiratory chain was active in the presence of antimycin A. Furthermore, the ability to incorporate labelled valine into proteins, under resting-cell conditions, was not changed. Strong correlations were established between the effects of respiratory effectors on O₂ consumption and valine incorporation. These results suggest that sufficient energy for protein synthesis and growth is provided by the operation of the cyanide-resistant respiratory pathway in antimycin-adapted Euglena.Abbreviations DNP dinitrophenol - PG propylgallate - SHAM salicylhydroxamic acid     

Clostridium neopropionicum sp. nov., a strict anaerobic bacterium fermenting ethanol to propionate through acrylate pathway

Strain X4 was isolated several years ago from an anaerobic mesophilic plant treating vegetable cannery waste waters. It was the first example of propionic fermentation from ethanol. Morphologic and physiologic characterizations of the strain are presented here. This strain is described as type strain of a new species, Clostridium neopropionicum sp. nov. Whole cells of strain X4 ferment [1-¹³C]ethanol and CO₂ to [2-¹³C]propionate, [1-¹³C]acetate and [2-¹³C]propanol, suggesting the absence of a randomizing pathway during the propionate formation. Enzymes involved in this fermentation were assayed in cell-free extracts of cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase, phosphate acetyl transferase, acetate kinase, pyruvate synthase, lactate dehydrogenases, and the enzymes of the acrylate pathway were detected at activities sufficient to be involved in ethanol fermentation. The same pathway may be used for the degradation of lactate or acrylate to acetate.     

Sex determination and differentiation in organisms other than higher plants

The understanding of sex determination in general, but in particular in mammals, has been a subject of scientific speculation for a long time. It has been shown that in many vertebrate and invertebrate species, the sex of an individual is determined by the individual's chromosomal constitution. Initial studies of classical genetic searching for sex-transforming mutations and the scrupulous analyses of modified phenotypes have shed light on the mechanism(s) of sex-determination. They paved the road to successful studies at molecular level. After a brief review on sex determination in chosen model species, the “Drosophila system” is presented to exemplify a possible general principle for sex determinism.     

Characterization of different forms of yeast acid trehalase in the secretory pathway

The biosynthesis and processing of the vacuolar (lysosomal) acid trehalase (molecular mass about 220 kDa) was followed in vivo using mutants conditionally defective in the secretory pathway. A precursor of 41 kDa was found in sec61 mutant cells deficient in translocation of secretory protein precursors into the lumen of the endoplasmic reticulum. Endoglycosidase H and N-glycosidase F treatment of purified acid trehalase in vitro resulted in a 41 kDa band, indicating that the precursor form found in sec61 mutant cells corresponds to the carbohydrate-free form of the enzyme. sec 18 mutant cells, blocked in the delivery of secretory proteins from the endoplasmic reticulum to the Golgi body accumulate a form with a molecular mass of 76 kDa which probably corresponds to a partially glycosylated precursor of the mature acid trehalase. This precursor partially disappears in favour of the appearance of a higher molecular weight component of 180 kDa in sec7 mutants which are blocked in the delivery step of secretory proteins from the Golgi body to the vacuole. In wild-type cells the fully glycosylated mature form of acid trehalase of about 220 kDa was observed accompanied by some 180 kDa and 76 kDa material.     

A visually evoked escape response of the housefly

Summary Flies (Musca domestica) avoid danger by initiating a rapid jump followed by flight. To identify the visual cues that trigger the escape response in the housefly, we measured the timing and probability of escapes when the fly was presented with a variety of visual stimuli created by moving targets toward it. Our results show that an escape response is triggered by an approaching dark disk, but not by a receding dark disk. On the other hand, a bright disk elicits escape only when it recedes. A disk with black and white rings is less effective at eliciting escape than is a dark solid disk of the same size. This indicates that the darkening contrast produced by an approaching stimulus is a more crucial parameter than expansion cues contained in the optical flow. Escape is also triggered by a horizontally moving dark edge, but not by a moving bright edge or by a grating. An examination of several visual parameters reveals that the darkening contrast, measured from the onset of stimulation to the start of escape is nearly constant for a variety of stimuli that trigger escape reliably. Thus darkening contrast, coupled with motion may be crucial in eliciting the visually evoked escape response. Other visual parameters such as time-to-contact or target angular velocity seem to be relatively unimportant to the timing of escapes.Abbreviations P _s Probability of successful escape - r _disk radius of disk target - r _arena radius of shielding arena - v _disk linear velocity of disk target - v _edge linear velocity of edge - d _disk angular velocity of disk target boundary - _edge angular velocity of edge - _escape target distance at escape - d _start target distance before onset of target movement - h _edge height of the edge above fly - x _start distance from corner of triangle to start position of edge (0 or 50 mm) - x _escape distance from corner of triangle to the position of the edge when the fly escapes - x _center distance from corner of triangle to point above the center of the pad - x _total distance from the corner of the triangle to the base (height of triangle = base of triangle)     

Subcellular localization of the common shikimate-pathway enzymes in Pisum sativum L.

5-Enolpyruvylshikimate 3-phosphate (EPSP) synthase (3-phosphoshikimate 1-carboxyvinyltransferase; EC 2.5.1.19), 3-dehydroquinate dehydratase (EC 4.2.1.10) and shikimate: NADP⁺ oxidoreductase (EC 1.1.1.25) were present in intact chloroplasts and root plastids isolated from pea seedling extracts by sucrose and modified-silica density gradient centrifugation. In young (approx. 10-d-old) seedling shoots the enzymes were predominantly chloroplastic; high-performance anion-exchange chromatography resolved minor isoenzymic activities not observed in density-gradientpurified chloroplasts. The initial enzyme of the shikimate pathway, 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (EC 4.1.2.15) was also associated with intact density-gradient-purified chloroplasts. 3-Dehydroquinate synthase (EC 4.6.1.3) and shikimate kinase (EC 2.7.1.71) were detected together with the other pathway enzymes in stromal preparations from washed chloroplasts. Plastidic EPSP synthase was inhibited by micromolar concentrations of the herbicide glyphosate.Abbreviations DAHP 3-deoxy-d-arabino-heptulosonate 7-phosphate - DEAE diethylaminoethyl - DHQase 3-dehydroquinate dehydratase - DTT dithiothreitol - EPSP 5-enolpyruvylshikimate 3-phosphate - SORase shikimate:NADP⁺ oxidoreductase     

A sodium ion gradient as energy source for Peptostreptococcus asaccharolyticus

The determination of enzymatic activities in cell-free extracts of Acidaminococcus fermentans and Peptostreptococcus asaccharolyticus led to a refined scheme for the pathway of glutamate fermentation via (R)-2-hydroxyglutarate to acetate and butyrate. From the ratio of these products the amount of ATP generated by substrate level phosphorylation was calculated. Growth experiments with the organisms including Clostridium symbiosum and Clostridium tetanomorphum indicated that a sodium gradient contributed additional energy for growth. The high growth yields found in organisms containing the biotin dependent sodium pump glutaconyl-CoA decarboxylase could be reduced by the sodium ionophor monensin. In P. asaccharolyticus energy equivalent up to 0.6 mol ATP per mol of glutaconyl-CoA decarboxylated was conserved via the Na⁺ gradient. The data may explain the growth promoting effects of monensin in cattle.     

Vegetation succession on the dunes near Oostvoorne,The Netherlands,since 1934, interpreted from air photographs and vegetation maps

The vegetation succession on the dunes near Oostvoorne, The Netherlands has been followed by means of a novel combination of repeated large-scale vegetation mapping and air photograph interpretation. Vegetation units have been discerned on the formation level because these could be distinguished fairly easily on the photographs and because the rates of change are appropriate to the time interval chosen. Nineteen formations were distinguished. Five 1:6250 maps were constructed, reflecting the formation pattern in 1934, 1943, 1959, 1972 and 1980. An overlay with 2736 grid points at 25 m field distance was used to quantify changes in the formation pattern.The results suggest a pronounced multiple pathway succession with nevertheless three principal trajectories of succession from pioneer to woodland vegetation. The outer dunes, which have originated since 1910, are distinct in successional characteristics from the inner dunes, which already existed but were released from heavy grazing pressure in 1910. The rate of change in the outer dunes was high in the beginning and is slowly decreasing eversince. In the inner dunes it went the other way around. Through visual extrapolation the likely formation patterns in 1910 and in 2000 were estimated.Transition frequencies proved highly variable for most formations. Moreover, strong spatial dependence was found. Limitations in the use of Markov models in cases of long-term succession in heterogeneous environments are discussed.Nomenclature follows the same sources as in van der Maarel et al. (1984).Field work carried out 1980–1981 when the authors were at the Division of Geobotany, University of Nijmegen. We thank Jos Rijntjes, Nijmegen, for his cooperation in the field. Vegetation maps were prepared and calculations performed at Uppsala. We thank the Foundation Het Zuid-Hollands Landschap, Rotterdam, for providing facilities and a grant for fieldwork as well as additional means to reproduce the vegetation maps. Two reviewers gave useful comments.     

Influence of osmotic stress on the respiration of potato tuber callus

Potato tuber ( Solanum tuberosum L. cv. Bintje) callus shows a decrease in fresh weight and an increase in dry weight upon transfer to nutrient medium supplemented with 0.3 or 0.5 M mannitol. The osmolarity of the intracellular fluid increases simultaneously. Probably mannitol is taken up from the medium till the osmolarity of the tissue is in equilibrium with that of the medium. After osmotic adaptation, on a medium with 0.5 M mannitol, growth is negligible, although the tissue retains its viability.
Respiration increases upon transfer to medium with extra mannitol, especially when expressed on a fresh weight basis. On this basis cytochrome and alternative pathway capacities do not change appreciably. The respiratory increase is exclusively caused by an increased engagement of the alternative pathway. The participation of this pathway in uninhibited respiration increases from about 10 to 90% upon transfer to medium with extra mannitol. The increase in respiration is partly correlated with the decrease in fresh weight upon transfer. Per disc, the capacities of the cytochrome and alternative pathway decline. Yet, total respiration per disc significantly increases due to the increased participation of the alternative pathway. This results in an almost equal ATP-production per disc before and after transfer. We suggest, that the alternative pathway functions as a reserve capacity in potato callus, which is switched on when ATP-production coupled to the cytochrome pathway is impaired.     

Anatomical and physiological characteristics of individual neurones in the central antennal pathway of insects

Signals of tens up to hundreds of thousands of (mostly olfactory) receptor cells on an insect antenna are switched to a comparatively low number of neurones in the antennal lobe of the deutocerebrum in circumscribed units of neuropile, the glomeruli. Each glomerulus is connected via its output neurone to two separate neuropiles (calyces of mushroom body, and lateral lobe) of the protocerebrum. Local interneurones interconnect between the glomeruli. Certain modes of convergence between receptors and central neurones provide for a very high sensitivity of the latter to certain odours and their sensitivity for complex odour stimuli, and in many cases for a marked multimodality. Anatomical and physiological data are given especially for pheromone sensitive neurones and their projections.