Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability

Summary Centaurea maculosa seedlings were grown in pots to study the effects of root herbivory by Agapeta zoegana L. (Lep.: Cochylidae) and Cyphocleonus achates Fahr. (Col.: Curculionidae), grass competition and nitrogen shortage (each present or absent), using a full factorial design. The aims of the study were to analyse the impact of root herbivory on plant growth, resource allocation and physiological processes, and to test if these plant responses to herbivory were influenced by plant competition and nitrogen availability. The two root herbivores differed markedly in their impact on plant growth. While feeding by the moth A. zoegana in the root cortex had no effect on shoot and root mass, feeding by the weevil C. achates in the central vascular tissue greatly reduced shoot mass, but not root mass, leading to a reduced shoot/root ratio. The absence of significant effects of the two herbivores on root biomass, despite considerable consumption, indicates that compensatory root growth occurred. Competition with grass affected plant growth more than herbivory and nutrient status, resulting in reduced shoot and root growth, and number of leaves. Nitrogen shortage did not affect plant growth directly but greatly influenced the compensatory capacity of Centaurea maculosa to root herbivory. Under high nitrogen conditions, shoot biomass of plants infested by the weevil was reduced by 30% compared with uninfested plants. However, under poor nitrogen conditions a 63% reduction was observed compared with corresponding controls. Root herbivory was the most important stress factor affecting plant physiology. Besides a relative increase in biomass allocation to the roots, infested plants also showed a significant increase in nitrogen concentration in the roots and a concomitant reduction in leaf nitrogen concentration, reflecting a redirection of the nitrogen to the stronger sink. The level of fructans was greatly reduced in the roots after herbivore feeding. This is thought to be a consequence of their mobilisation to support compensatory root growth. A preliminary model linking the effects of these root herbivores to the physiological processes of C. maculosa is presented.     

Physical mapping of the MHC and grc by the pulse field electrophoresis

The development of the physical map of the major histocompatibility complex of the rat was undertaken using pulse field gel electrophoresis of fragments of genomic DNA from the BIL/2 (grc ⁺) and BIL/1 (grc ^–) strains obtained primarily from single and double digests with the enzymes Mlu I, Not I, and Sfi I and hybridized with a variety of mouse, rat, and human probes. Both strains are maintained by inbreeding the BIL heterozygote (forced heterozygosity; F31); hence, their differences lie almost entirely in the MHC-grc regions. The MHC-grc region was contained in five fragments of DNA comprising 3000–3200 kilobases (kb); thus, its size appears to be closer to that of the human MHC than to that of the mouse MHC. This didstance may be an underestimate of the size of the entire region, however, because the cluster of class I loci in the RT1.A region could not be defined in detail in this study. The most striking difference between the BIL/2 strain, which has normal growth and reproductive characteristics, and the BIL/1 strain, which has growth and reproductive defects and an enhanced susceptibility to chemical carcinogens, is a deletion of approximately 70 kb in the latter strain. The studies og grc ⁺ and grc ^– strain suggest that the phenotypic defects of the grc ^– stains may be due to the loss of genes that are normally present in this deleted region. Address correspondence and offprint request to: T. J. Gill III.     

Pulse-modulated photoacoustic measurements reveal strong gas-uptake component at high CO2-concentrations

The effect of high CO₂-concentration on photoacoustic signals from tobacco leaves is studied by means of a recently developed pulse modulation method which provides simultaneous information on photothermal and photobaric components in the millisecond time domain. High CO₂-concentrations are found to induce large gas-uptake signals. Simultaneous measurements of chlorophyll fluorescence suggest that the uptake signals are correlated with energy-dependent fluorescence quenching. Very similar CO₂-concentration dependencies are found in the absence and presence of methylviologen, which is known to catalyze O₂-reduction, and in the presence of glyceraldehyde, which blocks Calvin cycle and photorespiration. It is suggested that the CO₂-enhanced uptake signal is likely to reflect O₂-uptake in the Mehler reaction. However, it is not ruled out that also rapid CO₂-solubilisation or CO₂-binding caused by light-induced stroma alkalisation are involved. Strong uptake is also induced when the CO₂-concentration in the closed photoacoustic chamber increases due to dark-respiration. The consequences of these findings with respect to the interpretation of photoacoustic data (e.g., low-light effect) and to the regulatory role of O₂-dependent electron flow are discussed.     

K+ current stimulation by Cl- in the midgut epithelium of tobacco hornworm (Manduca sexta)

Summary Chloride-stimulated K⁺ secretion by Manduca sexta midgut (5th-instar larvae) was measured as K⁺-carried short-circuit current of the tissue mounted in an Ussing chamber. Microscopic parameters, such as single-channel current and channel density for the rate-determining passive transport step across the basolateral goblet cell membrane (i.e. K⁺ channels), were estimated by means of current-fluctuation analysis of the K⁺ channel blockade by haemolymph-side Ba²⁺ ions. Ba²⁺ was equally effective with Cl^- or gluconate (Glu^-) as the principal ambient anion. The Ba²⁺-induced K⁺ channel conduction noise is reflected by a Lorentzian, or relaxation, noise component in the power spectrum of the K⁺ current fluctuations. A reduced Lorentzian plateau value, but an unchanged corner frequency, were observed when Cl^- was replaced by Glu^-. The results from the analysis of a two-state model of K⁺ channel block by Ba²⁺, with respect to the anion-replacement effects, suggest that the observed changes in K⁺ current and Lorentzian plateau value mirror a complex change of the underlying parameters: Cl^- omission reduces single channel current but increases channel density so that the product of single channel current and channel density is smaller in Glu^- than in Cl^-. It seems likely that basolateral K⁺ channels (1) are subject to anionic gating ligands, and (2) depend on anions with respect to the rate of K⁺ transfer through and open K⁺ channel.Abbreviations a.c. alternating current - single-channel conductance - E _K K⁺ Nernst potential - f frequency contained in current noise - f _c corner frequency - Glu^- gluconate - G _t transepithelial conductance - I _sc short-circuit current - I _K K⁺ current - I _K(max) maximal K⁺ current - i single-channel current - K _Ba barium inhibition constant - K _m Michaelis constant of saturating K⁺ current - k ₀₁ and k ₁₀ barium association and dissociation rate constant, respectively - M K⁺ channel density - S _f power density - S _o Lorentzian plateau value - P _o channel-open probability - P _K K⁺ permeability - V _sc cellular potential at short-circuit These results have already been presented in part, at the 1989 joint meeting of the German and Israel Physiological Societies in Jerusalem (Zeiske et al. 1990).     

Mechanism of freeze-thaw damage to liver alcohol dehydrogenase and protection by cryoprotectants and amino acids

Multiple freeze-thaw (FT) cycles, with complete melting between cycles, resulted in an exponential decline in liver alcohol dehydrogenase (LADH) enzyme activity. The reduction in activity of LADH as a result of FT damage was proportional to the decrease in the intensity of the tryptophan fluorescence of the enzyme. Treatment with urea resulted in a similar relationship between tryptophan fluorescence intensity and inactivation. Evidence from fluorescence and activity studies from the same sample, as well as gel electrophoresis, indicates that damage to LADH from a FT cycle, resulting in inactivation, is likely an unfolding of the enzyme rather than separation of subunits or aggregation of enzymes at the enzyme concentrations and cooling rates used. A nonexponential decline in enzyme activity, as a function of the number of FT cycles, can be achieved if complete melting between cycles is not allowed or if the samples are stored at +4 degrees C for 24 hr following the last FT cycle, prior to assay. In the latter case, a partial recovery in enzyme activity is seen. "Seeding," while lowering the enzyme activity, is desirable to achieve consistent results without the artifacts that are introduced if not used. Amino acids were tested for their effectiveness as cryoprotectants. From the results of this study, the mean fractional area loss of amino acid residues upon incorporation in globular proteins (f) is inversely proportional to the FT protection by these free amino acids. Thus, amino acid residues which tend to be found at the surface of proteins (e.g., glutamate) improve the FT survival of LADH, when added as the free amino acid, while those amino acids which are found in the interior of proteins (e.g., valine, leucine) sensitize LADH to FT damage. The pattern of protection ("fingerprint") of LADH by various amino acids is different from that of living cells. Furthermore, unlike the case with cells, glutamine and DMSO do not act independently when protecting LADH.     

Einfluß der Konzentration der Zuckerlösung auf den Gesang und das Balzverhalten des Gelbbauchnektarvogels (Nectarinia venusta)*

Different concentrations of a sucrose solution vary the courtship song and behaviour of the male yellow-bellied sunbird Nectarinia venusta- the duration of subsong, total singing duration, and the absolute number of full song phrases. With high concentrations the sunbird sings more full song phrases but less subsong during the courtship season than otherwise. The various effects are described.     

Stimulation of the anaerobic growth ofSalmonella typhimurium by reduction ofl-carnitine,carnitine derivatives and structure-related trimethylammonium compounds

In view of the development of al-carnitine deficiency, the metabolism ofl-carnitine and structure-related trimethylammonium compounds was studied inSalmonella typhimurium LT₂ by means of thin-layer chromatography (TLC).l-Carnitine, crotonobetaine and acetyl-l-carnitine stimulated the anaerobic growth in a complex medium significantly. The stimulation depended on the formation of -butyrobetaine. The reduction ofl-carnitine proceeded in two steps: (1) Dehydration of thel-carnitine to crotonobetaine, (2) hydrogenation of crotonobetaine to -butyrobetaine. The reduction of crotonobetaine was responsible for the growth stimulation. Terminal electron acceptors of the anaerobic respiration such as nitrate and trimethylamine N-oxide, but not fumarate, suppressed the catabolism ofl-carnitine completely. Glucose fermentation, too, inhibited the reduction ofl-carnitine but optimal growth with a high carnitine catabolism was achieved byd-ribose. The esters of carnitine with medium- and long-chain fatty acids inhibited the growth considerably because of their detergent properties.Abbreviations TLC thin-layer chromatography     

Effect of organic matter on growth and cell yield of ammonia-oxidizing bacteria

The effect of various organic compounds on the growth of ammonia-oxidizing bacteria was examined.Nitrosococcus oceanus, a strongly halophilic bacterium, had a very low tolerance to organic matter compared with other organisms tested. Organic compounds scarcely affected the growth of theNitrosomonas strains whereas nitrite formation by bothNitrosococcus mobilis strains was inhibited by nearly all of the substances tested. The growth ofNitrosospira strain Nsp₁ was enhanced more than 30% by acetate and formate, but not growth was detectable in the presence of pyruvate. On the contrary,Nitrosospira strain Nsp₅ was stimulated only by pyruvate. Nitrite formation by the twoNitrosovibrio tenuis strains tested was similar. The growth of both strains was enhanced considerably by formate and glucose; acetate and, to a greater extent, pyruvate inhibited these bacteria.In batch culture, the energy efficiency of autotrophically grown ammonia-oxidizing bacteria varied from strain to strain. The cell yield of mixotrophically grown cultures, per unit of ammonia oxidized, was increased in comparison with autotrophic ones. No heterotrophic growth was detected.     

Electron microscope investigation of synapses,synapse-like structures,and possible sites of release of neurosecretory material in the buccal ganglia of Helix pomatia (Mollusca)

Summary In the buccal ganglia of Helix pomatia synapses and sites of possible release of neurosecretory material were investigated electron microscopically. There is one chemical synapse and one electrotonic synapse in the neuropile of the ganglion. No synapses could be detected in the buccal nerves, cerebro-buccal connectives, or in the buccal commissure. The synaptic cleft of the chemical synapse is about 25 nm wide and contains electron-dense material whereas the cleft of the electrotonic synapse is only 5 nm wide. The presynaptic fibre of the chemical synapse contains clear vesicles and dense core vesicles. The release sites of neurosecretory material are found at the initial segment of the axons, at perikarya of neurones, and at the perineurium of the ganglion. If the terminals are located at the plasmalemma of a nerve cell, these release sites are called synapse-like structures according to Roubos and Moorer-van Delft (1979). The synapse-like structures show all structural elements of synapses, except the 25 nm cleft containing dense material; the cleft is only 15–20 nm wide here like the normal cleft between neurones and glial cells or between two fibres. If the secretory material is released at the periphery through the perineurium the terminal is called synaptoid according to Scharrer (1970). In all cases, i.e. synapses, synapse-like structures, and synaptoids, clear vesicles were found in the axon terminal. This finding provides further evidence that clear vesicles always accompany the release of substances from axon endings.     

Isolation of RNA polymerases from the water mold Achlya

The DNA-dependent RNA polymerases I, II, and III (ribonucleosidetriphosphate: RNA nucleotidyl-transferase, EC 2.7.7.6) from Achlya ambisexualis E87 (male), have been isolated. The highly purified RNA polymerase I was found to be composed of polypeptides with the following molecular weights (·10^-4): 18.5, 14, 11.8, 7.3, 6.1, 4.9, 4.4, 2.8. RNA polymerase II showed a 400-fold higher resistance against -amanitin than mammalian or higher plant RNA polymerase II.