Reductive Pentose Cycle and Formate Assimilation in Rhodopseudomonas palustris

Rhodopseudomonas palustris assimilated formate autotrophically as carbon dioxide and hydrogen arising from the activity of the formic hydrogenlyase system. Kinetic analyses of cell suspensions pulse-labeled with (14)C-formate or (14)C-bicarbonate showed similar distributions of incorporated radioactivity. In both cases phosphate esters were the first assimilation products. Ribulose diphosphate carboxylase, phosphoribose isomerase, and phosphoribulokinase, characteristic enzymes of the reductive pentose cycle, were present in extracts of cells grown on formate.     

Studies on the Bohr Effect of Sheep Hemoglobin

A simple method is described for the measurement of pH changes in hemoglobin solutions on oxygenation and reduction. Data are presented establishing the absence of a Bohr effect in p-chloromercuribenzoate [PCMB] treated hemoglobin. The influence of a number of sulfhydryl inhibitors on the Bohr effect of a hemoglobin solution is reported and an interpretation based on steric factors in the protein is proposed.     

Genetic transformation of apple (Malus pumila Mill.) using a disarmed Ti-binary vector

The disamed Ti-binary vector pBIN 6 in Agrobacterium tumefaciens has been used in leaf disc transfomations to produce transgenic apple (Malus pumila Mill.) plants with a nomal phenotype except for a somewhat reduced capacity to root. The presence of the genes for nopaline synthase and neomycin phosphotrans ferase (conferring kanamycin resistance), inserted into the host genome by the vector, was confirmed by Southern blot analysis, the detection of nopaline synthase activity and rooting in the presence of the antibiotic.The nopaline synthase gene continued to be expressed in glasshouse-grown plants several months after removal from in vitro growth conditions.     

A Hydrogen-Oxidizing, Fe(III)-Reducing Microorganism from the Great Bay Estuary, New Hampshire

A dissimilatory Fe(III)- and Mn(IV)-reducing bacterium was isolated from bottom sediments of the Great Bay estuary, New Hampshire. The isolate was a facultatively anaerobic gram-negative rod which did not appear to fit into any previously described genus. It was temporarily designated strain BrY. BrY grew anaerobically in a defined medium with hydrogen or lactate as the electron donor and Fe(III) as the electron acceptor. BrY required citrate, fumarate, or malate as a carbon source for growth on H₂ and Fe(III). With Fe(III) as the sole electron acceptor, BrY metabolized hydrogen to a minimum threshold at least 60-fold lower than the threshold reported for pure cultures of sulfate reducers. This finding supports the hypothesis that when Fe(III) is available, Fe(III) reducers can outcompete sulfate reducers for electron donors. Lactate was incompletely oxidized to acetate and carbon dioxide with Fe(III) as the electron acceptor. Lactate oxidation was also coupled to the reduction of Mn(IV), U(VI), fumarate, thiosulfate, or trimethylamine n-oxide under anaerobic conditions. BrY provides a model for how enzymatic metal reduction by respiratory metal-reducing microorganisms has the potential to contribute to the mobilization of iron and trace metals and to the immobilization of uranium in sediments of Great Bay Estuary.     

Effects of the diatom-Emiliana huxleyi succession on photosynthesis, calcification and carbon metabolism by size-fractioned phytoplankton

Changes in the species composition, photosynthesis, calcification and size-fractionated carbon metabolism by natural phytoplankton assemblages were monitored in three mesocosms under different nutrient conditions during May 1993. In the 3 enclosures, the decline of the diatom-dominated assemblages was followed by the development of a bloom of the coccolithoporid Emiliania huxleyi. Highest growth of E. huxleyi was observed in the mesocosm with a high N : P ratio, suggesting this species is a good competitor at low phosphate concentrations. The transition from diatom- to E. huxleyi-dominated assemblages brought about a sharp reduction of the phytoplankton standing stock and carbon-specific photosynthetic rate. The relative contribution of the smaller size fraction to total photosynthesis increased as the succession progressed. Calcification rate and E. huxleyi cell-specified calcite production were highest during the early stages of development of the E. huxleyi bloom. Distinct changes in the patterns of ¹⁴C allocation into biomolecules were noticed during the diatom-E. huxleyi succession. The diatom-dominated assemblage showed high relative ¹⁴C incorporation into low molecular weight metabolites (LMWM), whereas proteins and, specially, lipids accounted for the largest proportion of carbon incorporation in the E. huxleyi bloom. The patterns of photoassimilated carbon metabolism proved to be strongly dependent on cellular size, as protein relative synthesis was significantly higher in the smaller than in the larger size fraction, irrespective of the nutrient regime and the successional stage. These results are discussed in relation to the ecological and physiological features of small phytoplankton.     

Cold acclimation and photoinhibition of photosynthesis in Scots pine

Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO₂ uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.Abbreviations APX ascorbate peroxidase - DHA dehydroascorbate - DHAR dehydroascorbate reductase - Fm maximal fluorescence when all reaction centres are closed - Fv/Fm maximum photochemical yield of PSII - GR glutathione reductase - GSH reduced glutathione - Je rate of photosynthetic electron transport - MDAR monodehydroascorbate reductase - q_N nonphotochemical quenching of fluorescence - q_P photochemical quenching of fluorescence - SOD superoxide dismutase This work was supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China.     

Pressure Stabilization of Proteins from Extreme Thermophiles

We describe the stabilization by pressure of enzymes, including a hydrogenase from Methanococcus jannaschii, an extremely thermophilic deep-sea methanogen. This is the first published report of proteins from thermophiles being stabilized by pressure. Inactivation studies of partially purified hydrogenases from an extreme thermophile (Methanococcus igneus), a moderate thermophile (Methanococcus thermolithotrophicus), and a mesophile (Methanococcus maripaludis), all from shallow marine sites, show that pressure stabilization is not unique to enzymes isolated from high-pressure environments. These studies suggest that pressure stabilization of an enzyme may be related to its thermophilicity. Further experiments comparing the effects of increased pressure on the stability of α-glucosidases from the hyperthermophile Pyrococcus furiosus and Saccharomyces cerevisiae support this possibility. We have also examined pressure effects on several highly homologous glyceraldehyde-3-phosphate dehydrogenases from mesophilic and thermophilic sources and a rubredoxin from P. furiosus. The results suggest that hydrophobic interactions, which have been implicated in the stabilization of many thermophilic proteins, contribute to the pressure stabilization of enzymes from thermophiles.     

Behavioral responses of Colorado potato beetle larvae to combinations of temperature and insolation, under field conditions

In short-term field trials at combinations of ambient temperature (°C) and insolation (W·m⁻²), larval Colorado potato beetles (Leptinotarsa decemlineata [Say] [Coleoptera: Chrysomelidae]) were observed after their release on the adaxial surface of leaflets on potato plants (Solanum tuberosum L. Solanaceae). The larvae either began feeding or moved under the leaflet; mean interval from release to expression of these behaviors (2.9±0.05 min [n =358]) was independent of air temperature and insolation. Proportion of larvae moving under the leaflet increased logistically with both air temperature and insolation. A 1 W·m⁻² change in insolation (P) evoked the same effect on this proportion as a 0.0838 °C change in air temperature (T _a ), so the two quantities were combined as T^*=T _a +P·0.0838 °C/(W·m⁻²), which has units of °C. The proportion of larvae moving under the leaflet increased logistically with T^*. In 1-day field trials we monitored air temperature, insolation and proportion of larvae under the leaflet, and compared the latter to predictions from the logistic regression derived from the short-term trials. Consistently more larvae occurred under leaflets than predicted from the logistic regression; this bias diminished as T^* increased until at T^*≥40 °C, observed and predicted proportions were equal. This pattern of deviation from the predictions of the logistic regression is consistent with a thermoregulatory strategy in which larvae move away from hostile conditions, rather than seek optimal conditions.     

Catecholamine stimulated lipolysis in differentiated human preadipocytes in a serum-free,defined medium

Adipocyte precursors from the stromal vascular fraction of human adipose tissue were allowed to differentiate in serum-free defined medium, whereafter their catecholamine stimulated lipolytic response was compared to that of mature isolated human adipocytes. Seventy-five to ninety percent of the fibroblast-like cells accumulated lipid droplets and glycerol-3-phosphate dehydrogenase activities of 1,000–2,800 mU/mg protein were measured in cell homogenates of differentiated cells. Lipolysis could be stimulated by both isoproterenol and norepinephrine in both differentiated preadipocytes as well as mature adipocytes. The results obtained with β-adrenergic agents suggested the presence of a higher affinity receptor in differentiated preadipocytes as compared to mature adipocytes. Mature adipocytes responded well to β-adrenergic agents, but no antilipolytic α₂-adrenergic response was observed in the differentiated preadipocytes. The presence of Gi proteins in the differentiated preadipocytes was suggested by the antilipolytic effect of adenosine as well as the lipolytic activity generated by pertussis toxin. In conclusion, our medium supported the differentiation of a very high percentage of human preadipocytes which developed a sensitive β-adrenergic lipolytic response but which lacked an α₂-adrenergic antilipolytic response.