The structural nif genes of the cyanobacteria Gloeothece sp. and Calothrix sp. share homology with those of Anabaena sp., but the Gloeothece genes have a different arrangement.

Probes carrying the Anabaena sp. strain PCC 7120 nitrogenase reductase (nifH) and nitrogenase (nifK and nifD) genes were hybridized to Southern blots of DNA from the unicellular, aerobic nitrogen-fixing cyanobacterium Gloeothece sp. strain PCC 6909 and from the filamentous cyanobacterium Calothrix sp. strain PCC 7601. These data suggest that the Gloeothece sp. nif structural proteins must be similar to those of other diazotrophs and that the ability for aerobic nitrogen fixation does not reside in the nif protein complex. We also found that the nif structural genes of Gloeothece sp. are clustered, whereas those of Calothrix sp. are arranged more like those of Anabaena sp.     

Selenium as a growth factor for plankton algae in laboratory experiments and in some Swedish lakes

The growth requirements of inorganic and organic selenium (Se) for the dinoflagellate Peridinium cinctum fa. westii and the diatom Stephanodiscus hantzschii var. pusillus and eight species of green algae are demonstrated. A new mineral culture medium for P. cinctum is presented. Using P. cinctum as a test alga, bioassays were carried out on waters from a calciferous lake and from some acidified, fertilized, lime-enriched or humic lakes for determination of their contents of bioavailable forms of Se (bioactive Se). Some of the results were related to Tot-Se and selenite-Se, measured chemically, to pH and the occurrence of ambient phytoplankton. In calcium-rich Lake Erken (pH ～ 8) blooms and decline of algae coincided with decreases (from >70 to ～20 ng Se · l^?1) and increases (up to >80 ng · l^?1) of bioactive Se, indicating uptake and release of inorganic or organic forms of Se. Acidified lakes (pH < 5) generally demonstrated much lower concentrations of bioactive Se (<20 ng · l^?1) than neutral, fertilized, lime-enriched, slightly acidic or humic lakes (>20 ng · l^?1). The correlation between pH and bioactive Se was positive (r ～ 0.92; n = 7). The ecological importance of Se is suggested for some common species of phytoplankton.     

Analysis of two chloride requirements for sodium-dependent amino acid and glucose transport by intestinal brush-border membrane vesicles of fish

Intestinal brush border vesicles of a Mediterranean sea fish (Dicentrarchus labrax) were prepared using the Ca²⁺-sedimentation method. The transport of glucose, glycine and 2-aminoisobutyric acid is energized by an Na⁺ gradient ($\text{out > in}$). In addition, amino acid uptake requires Cl^? in the extravesicular medium (2-aminoisobutyric acid more than glycine). This Na⁺- and Cl^?-dependent uptake is electrogenic, since it can be stimulated by negative charges inside the vesicles. The specific Cl^? requirement of glycine and 2-aminoisobutyric acid transport is markedly influenced by pH, a change from 6.5 to 8.4 reducing the role played by Cl^?. In the presence of Cl^?, the $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ of 2-aminoisobutyric acid uptake is reduced and its $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ is enhanced. Cl^? affects also a non-saturable Na⁺-dependent component of this amino acid uptake. Amino acid transport is also increased by intravesicular Cl^? (2-aminoisobutyric acid less than glycine). This effect is more concerned with glucose uptake, which can be then multiplied by 2.3. A concentration gradient ($\text{in > out}$) as well as the presence of Na⁺ in the incubation medium seems to enter into this requirement. This intravesicular Cl^? effect is not influenced by pH between 6.5 and 8.4.     

Teleonomical optimization of a fractal model of the pulmonary arterial bed

Modeling the pulmonary arterial tree (PAT) is considered here as an optimal synthesis problem. Firstly, a class of candidate models is specified: the three-dimensional symmetric dichotomous fractal trees of elastic tubes described by Womersley's equations. Secondly, the parameters are shown to be constrained by interactions of PAT with the rest of the body; these constraints are used to limit the volume of the parametric space to which attention will be directed in the synthesis step. Thirdly, a teleonomical hypothesis is proposed: a naturally selected PAT must have a minimal input impedance under conditions keeping total arterial volume and distensibility as small as possible. This hypothesis is translated in mathematical terms and the resulting cost-function minimized in the limited parametric volume. The optimal model has parameter values and an impedance spectrum corresponding satisfactorily with real data. Moreover this model gives a clear picture of the internal hemodynamic behavior of PAT as an impedance matching device.     

Production and purification of monoclonal antibodies to Pisum and Avena phytochrome

At least nine monoclonal antibodies against phytochrome from Pisum sativum L. and 20 against phytochrome from Avena sativa L. have been obtained from mouse hybridomas that were produced by fusion of spleen cells with SP 2/O-Ag14 myeloma cells. Hybridomas were selected and cloned in a single step by plating on a semisolid methylcellulose medium. Eight antibodies to Pisum and one to Avena phytochrome were immunopurified from hybridoma medium or ascitic fluid. When necessary, secreted antibodies were verified to be against phytochrome by demonstrating to be against phytochrome by demonstrating immunoadsorption of phytochrome, detected as loss of photoactivity and-or by appearance of the approx. 120,000-dalton phytochrome band upon sodium dodecyl sulfate polyacrylamide gel electrophoresis.     

Glutamate synthase in rice roots. Studies on the electron donor specificity

Rice root glutamate synthase activity was assayed with various reducing systems. Ferredoxin-dependent glutamate synthase (EC 1.4.7.1) and pyridine nucleotide-dependent glutamate synthase (NADH, EC 1.4.1.14; or NADPH, EC 1.4.1.13) exhibited a strict specificity for the electron donor. The ferredoxin-dependent glutamate synthase from rice roots could accept electrons from photoreduced ferredoxin in an illuminated reconstituted spinach chloroplast system. Thioredoxin, a potent electron carrier, was not able to provide either ferredoxin-dependent or pyridine nucleotide-dependent glutamate synthase with electrons as no glutamate formation was detected in the presence of reduced thioredoxin f or m.     

Distribution of corticotropin-releasing factor in ovine brain determined by radioimmunoassay

We have developed and used a sensitive and specific radioimmunoassay to demonstrate the presence of CRF-like immunoreactivity in extra-hypothalamic areas of ovine brain. Synthetic CRF displaced antibody bound tracer at an ED50 value of 200 pg and there was no cross-reactivity with LHRH, TRH, ACTH, beta-endorphin and several other peptides. Displacement of bound 125I-CRF by brain extracts exhibited curves parallel to synthetic CRF standards. Highest concentrations (1 ng/mg tissue) of CRF-like immunoreactivity were found in the median eminence but surprisingly, high concentrations of CRF-like immunoreactivity were found in frontal, parietal, occipital and particularly temporal areas of cerebral cortex. Much lower concentrations were found in other brain areas including the basal ganglia, limbic system and brain stem.