Effects of plant hybridization on herbivore-parasitoid interactions

We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hybrid and parental willow plants in the field and in a common garden experiment. P. salicifoliella survival differed significantly among three willow taxa in the field in 1994 but not in the field in 1995 or in the common garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in their survival. In the field in 1995, host feeding predation varied significant among taxa. The theory of tritrophic interactions predicts that plant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation in survival and eulophid parasitism was also found among genotypes within taxa in the field in both years and in the common garden experiment. The common garden results show that genetic differences in plants affect the herbivore-parasitoid interaction. Variation among years in the patterns of survival and causes of mortality among field plants suggest that genotype by environment interactions may be important. Received: 1 March 1996 / Accepted: 4 November 1996     

Galactosylation of antibiotics using the β-galactosidase from Aspergillus oryzae

The β-galactosidase from Aspergillus oryzae has been shown to catalyze the synthesis of β-galactosides of antibiotics such as chlorphenisin and chloramphenicol using β-lactose as the galactosyl donor. Among the water-miscible organic solvents tested, 20% (v/v) acetonitrile in the reaction mixture gave the highest yield in galactoside synthesis. The products obtained were purified by preparative TLC and liquid chromatography and analyzed by ¹H-and ¹³C-NMR, and MS (FAB). Chlorphenisin and chloramphenicol were galactosylated exclusively at their primary hydroxy groups. The pH optimum for the transgalactosylation reaction was between pH 4–5. Increasing concentrations of galactosyl donor and aglycon caused increasing yields of galactosides. When the resulting galactosylated antibiotic was withdrawn from the sample, further synthesis was observed. This could be accelerated either by withdrawing the resulting monosaccharides (glucose and galactose) or exchanging them for mannose.     

Structure—function studies of the hammerhead ribozyme

Elucidation of the catalytic mechanism and structure—function relationship studies of the hammerhead ribozyme continue to be an area of intensive research. A combination of diverse approaches, such as X ray crystallography, spectral studies, chemical modifications, sequence variations and kinetic analyses, have provided valuable insight into the cleavage mechanism of this ribozyme. The hammerhead ribozyme crystal structures have provided valuable insight into conformational deformations needed to attain the catalytically active structure. Similarly, determination of ribozyme solution structure by spectroscopic analyses and the effect of divalent metal ions on RNA folding has further aided in the construction of a model for hammerhmead catalysis.     

Counteracting the mutagenic effect of hydrolytic deamination of DNA 5-methylcytosine residues at high temperature: DNA mismatch N-glycosylase Mig.Mth of the thermophilic archaeon Methanobacterium thermoautotrophicum THF.

Spontaneous hydrolytic deamination of DNA 5-methylcytosine residues gives rise to T/G mismatches which are pre-mutagenic lesions requiring DNA repair. For fundamental reasons, the significance of this and other processes lowering genetic fidelity must be accentuated at elevated temperatures, making thermophilic organisms attractive objects for studying how cells cope with thermal noise threatening the integrity of their genetic information. Gene mig of Methanobacterium thermoautotrophicum THF, an anaerobic archaeon with an optimal growth temperature of 65 degrees C, was isolated and its product (Mig.Mth; EC3.2.2-) shown to be a T/G-selective DNA thymine N-glycosylase with the properties required for counteracting the mutagenic effect of hydrolytic 5-meC deamination. The enzyme acts on T/G and U/G oppositions with similar efficiency; G/G, A/G, T/C and U/C are minor substrates; no other opposition of common nucleobases is attacked and no removal of U from single-stranded DNA is observed. Substrate preferences are modulated by sequence context. Together with the results presented here, one example of an enzyme directed against the hydrolytic deamination damage of 5-meC is known from each of the three phylogenetic kingdoms; entry into the repair pathway is glycosylytic in the eukaryotic and the archaeal case, whereas the eubacterial repair starts with an endonucleolytic DNA incision.     

Influence of substrate supply on the production of sophorose lipids by Candida bombicola ATCC 22214

Summary Candida (Torulopsis) bombicola ATCC 22214 produces 180 g/l sophorose lipids using glucose and oleic acid (technical grade) as combined substrates in an extended fed-batch cultivation. Excess of oleic acid generated a paste-like product. However, only when oleic acid was not detectable during the whole run of cultivation, a microcrystalline product precipitated. The unsaturated C-18 fatty acids of the technical grade oleic acid were transferred unchanged into the sophorose lipid.     

Dietary cholesterol enhances torpor in a rodent hibernator

Dietary cholesterol can affect both body lipid composition and steroid hormone concentration. We investigated whether a diet rich in cholesterol influences torpor patterns of hibernating chipmunks (Tamias amoenus) and, if so, whether these changes are better explained by diet-induced changes in body lipid composition or the concentration of testosterone, which at high levels inhibits torpor. Two groups of chipmunks were maintained either on a cholesterol diet (rodent chow containing 10% cholesterol) or a control diet (rodent chow) during pre-hibernation fattening and throughout the hibernation season. Torpid chipmunks on the cholesterol diet had significantly lower minimum body temperatures (−0.2 ± 0.2 vs +0.6 ± 0.2 °C), lower metabolic rates (0.029 ± 0.002 ml O₂ g⁻¹h⁻¹ vs 0.035 ± 0.001 ml O₂ g⁻¹h⁻¹), and longer torpor bouts at −1 °C (6.8 ± 0.5 vs 4.1 ± 1.0 days) than chipmunks on the control diet. Dietary cholesterol resulted in a significant increase in blood plasma cholesterol (sevenfold), liver cholesterol content (6.9-fold) and liver triglyceride content (3.5-fold) in comparison to controls. In contrast, dietary cholesterol had no detectable effect on the concentration of plasma testosterone, which was very low in both groups. Since torpor was deeper and longer in animals on the cholesterol diet our study suggests that torpor patterns of chipmunks were either directly affected by the dietary cholesterol or via changes in body lipid composition. Accepted: 22 January 1997     

Effects of Brefeldin A on Synthesis and Intracellular Transport of Ganglioside GT3 by Chick Embryo Retina Cells

Abstract: Ganglioside GT3 is the precursor of c-series gangliosides. It is synthesized by sialylation of GD3 and is expressed in nervous tissue of birds and mammals at early stages of development. In this study we examined the sub-Golgi location of GT3 synthesis and the mechanism of its transport from the site of synthesis to the plasma membrane in chicken embryo retina cells in culture. Neural retina cells from 10-day-old chick embryo were cultured with [³H]galactose in the absence (control cells) or in the presence of 1 µg/ml brefeldin A (BFA). At the end of the labeling period, the fraction of labeled gangliosides transported to the plasma membrane was determined. For this, cells were treated with C . perfringens neuraminidase in conditions to desialylate only those gangliosides that were transported to the plasma membrane and consequently accessible to the enzyme. After neuraminidase treatment of cells, gangliosides were isolated, purified, and the pattern of radioactivity analyzed by HPTLC-fluorography. It was found that BFA blocked the synthesis of complex gangliosides without affecting the synthesis of GM3, GD3, and GT3. Furthermore, in BFA-treated cells, GM3, GD3, and GT3 were protected from the action of added neuraminidase, indicating an intracellular localization and, hence, an inhibition of their transport to the plasma membrane. The results indicate that synthesis of the first intermediates of a-, b-, and c- series gangliosides occurs in a proximal Golgi compartment and that the proximal Golgi-synthesized gangliosides (GM3, GD3, and GT3) use a transport mechanism that is dependent on ADP ribosylation factor and coatomer proteins.     

Investigations on the regioselective hydrolysis of a branched β-1,3-glucan

Schizophyllan, an extracellular polysaccharide secreted by the fungus Schizophyllum commune ATCC 38548, shows interesting technical and pharmaceutical applications. Especially in the degraded form, this homoglucan is applicable as an antitumor, antihepatitis, anti-HIV and antiviral agent. Due to the fact that the side chains of the biopolymer are essential for its activities, a regioselective degradation of the β-1,3 basic chain by maintaining the β-1,6 side chains is necessary. This paper covers investigations which deal with the regioselective cleavage of the basic chain.

It was found that the hydrolysis of aqueous polysaccharide solutions by incubation in DURAN glass bottles at 121 °C and 1 bar was the most successful method. A slight decrease of pH, a rapid loss of viscosity, a constant increase in reducing end groups and a continual release of glucose over an incubation time of 100 h indicated a degradation especially at the basic chain. Stepwise ultrafiltration of degraded solutions yielded fractions with varying molar masses and the ratio of the fractions depended on the total incubation time. The maintenance of the side chains was verified by ¹³C-NMR spectra. The regioselectivity of this degradation method can be explained by a pore theory. One attempt to justify this theory is the suppression of hydrolysis after hydrophobization of the glass surface by using dichloromethylsilane.