Kinetics of nitrogen and phosphorus release in varying food supplies byDaphnia magna

Rates of nitrogen and phosphorus release from individualDaphnia magna were determined by measuring ammonia and soluble reactive phosphorus in successive 10-min incubations in small (0.05 ml) vessels after the animals were removed from their food. Release rates of both nutrients were generally highest initially and decreased with time after removal. The ratio of nitrogen to phosphorus released increased with time after animals were removed from an artificial detritus/bacterial food; ratios were lower and changed with time less for animals fed algae. These data suggest errors may be introduced by assumptions of constant stoichiometry for nutrient release in varying environments.GLERL Contribution No. 268     

Proteoid root morphology and function inLupinus albus

Summary Current theories of phosphorus uptake by plants imply that they can augment diffusion to their root axes by the development of abundant root hairs or mycorrhizas. Some phosphorus efficient plants have root morphology with multi-branched roots and localised regions of densely packed root hairs, which we suggest is better suited to the retention of substances exuded by the roots than uptake of substances moving to the root by diffusion. Evidence of substantial exudation by the proteoid roots ofLupinus albus is presented.     

Breast-feeding and respiratory syncytial virus infection.

The pattern of breast-feeding in 127 infants admitted to hospital with respiratory syncytial virus infection was compared with that in 503 age-matched controls. Thirty per cent of children with infection had been breast-fed compared with 49% of controls. The approximate relative risk of being admitted to hospital with respiratory syncytial virus infection if not breast-fed was 2.2. Several other factors were also considered, including an assessment of maternal care and home environment; the mother''s age, marital state, and smoking habits; the number of siblings; and gestation. Adverse factors were all associated with an increased risk of admission with infection, but breast-feeding still appeared to provide protection after controlling for these other factors in turn. These findings provide further support for encouraging mothers to breast-feed their infants and should prompt further studies into the immune status of mothers and into the nature of the protective factors in their breast milk.     

Characterization of a site-specific restriction endonuclease from Rhodopseudomonas sphaeroides.

A type II restriction endonuclease, RshI, has been partially purified from photoheterotrophically grown Rhodopseudomonas sphaeroides strain 2.4.1. The enzyme preparation, after a single DE-52 column fractionation, is free of 5' exonuclease and phosphatase activities but contains a trace of 3' exonuclease activity. Based upon deoxyribonucleic acid (DNA) sequencing data in the vicinity of the enzyme-promoted cleavage of pBR322 DNA, we have concluded that RshI probably recognizes the palinodromic hexanucleotide sequence 5'-CGATCG-3' and cleaves between the T and C. lambda cI857 DNA contains three RshI sites, two of which lie in the replaceable region. The plasmid pBR322, which carries resistances to ampicillin and tetracycline, contains a single RshI site in the ampicillin resistance determinant. Insertion of DNA into the RshI site of pBR322 results in loss of ampicillin resistance but retention of tetracycline resistance, thereby providing a convenient screening procedure for recombinant plasmids.     

Fibronectin: a chromatin-associated protein?

We have previously reported that chromatin preparations from human cultured fibroblasts contain a single homologous serum protein. In this paper we present evidence, based on immunological identity and physicochemical properties, that this serum protein is fibronectin. Furthermore, using a radioimmunoassay system, we have estimated that fibronectin represents about 0.7% of the total protein in both chromatin preparations and whole fibroblasts. Using a nitrocellulose filter assay system, we also show that fibronectin is a DNA-binding protein having an equilibrium constant of 4.6 x 10(-6) M. Equilibrium competition experiments have demonstrated that fibronectin has the ability to differentiate among nucleotides, indicating that fibronectin-DNA interaction is at least partially specific, and that a minimum polymer length of 12-18 nucleotides is required for effective binding to occur. Fibronectin has been isolated readily from plasma using DNA-affinity chromatography. We do not have direct evidence that fibronectin is an actual nonhistone chromosomal protein, but fibronectin is a DNA-binding protein (at least under in vitro assay conditions) and appears to be a normal constituent of chromatin as chromatin is currently isolated from cell nuclei.     

Iron-deficiency anaemia and its effect on worker productivity and activity patterns.

The effects of iron-deficiency anaemia on workers productivity were studied in a tea plantation in Sri Lanka. The quantity of tea picked per day was studied before and after iron supplementation or placebo treatment. After one month''s treatment significantly more tea was picked when the haemoglobin (Hb) concentration was increased by iron supplementation than when it was not. The degree of improvement was greater in more-anaemic subjects (those with concentrations of 6.0-9.0 g Hb/dl). The level of physical activity of anaemic subjects in their everyday environment was also recorded for four or 24 hours continuously both before and after treatment. After three weeks these levels was significantly greater in the iron-treated than matched placebo-treated subjects. The economic implications of increased work productively with iron treatment are evident, particularly in developing countries. These results also provide strong evidence for the clinical impression that people with iron-deficiency anaemia suffer from tiredness and weakness.     

Effects of calcium and chelating agents on the ability of various agonists to increase cyclic GMP in pancreatic acinar cells.

In dispersed acinar cells from guinea pig pancreas we found that chelating extracellular calcium with EDTA did not alter cellular cyclic GMP but caused a 50% reduction in the increase in cyclic GMP caused by the synthetic C-terminal octapeptide of porcine cholecystokinin (cholecystokinin octapeptide). This effect was maximal within 2 min and preincubating the cells with EDTA for as long as 30 min caused no further reduction in the action of cholecystokinin octapeptide. In acinar cells preincubated without calcium, adding calcium caused a time dependent increase in the action of cholecystokinin octapeptide and this increase was maximal after 10 min of incubation. An effect of extracellular calcium on the action of cholecystokinin octapeptide could be detected with 0.5 mM calcium and was maximal with 2.0 mM calcium. Magnesium alone or with calcium did not alter the action of cholecystokinin octapeptide. Extracellular calcium did not alter the time course or the configuration of the dose vs. response curve for the action of cholecystokinin octapeptide on cellular cyclic GMP. Low concentrations of EGTA (0.1 mM) decreased the effect of cholecystokinin octapeptide on cellular cyclic GMP to the same extent as did EDTA or preincubating acinar cells without calcium. Increasing EGTA above 0.1 mM caused progressive augmentation of the action of cholecystokinin octapeptide on cellular cyclic GMP and this augmentation did not require extracellular calcium or magnesium. Results similar to those obtained with cholecystokinin octapeptide were also obtained with bombesin, carbamylcholine, litorin and eledoisin. In contrast, the action of sodium nitroprusside on cyclic GMP in pancreatic acinar cells was not altered by adding EDTA or EGTA. These results indicate that the ability of extracellular calcium to influence the action of cholecystokinin octapeptide and other agents on cyclic GMP results from changes in cellular calcium and not from effects of extracellular calcium per se. The action of low concentrations of EGTA on the increase in cyclic GMP caused by various agents reflects the ability of EGTA to chelate extracellular calcium. The actions of high concentrations of EGTA were independent of extracellular calcium or magnesium and appear to reflect a direct action of EGTA on pancreatic acinar cells.     

Amphotropic host range of naturally occuring wild mouse leukemia viruses.

Seven murine leukemia virus field isolates (uncloned) from wild mice (Musmusculus) of four widely separated areas in southern California show an unusually wide in vitro host range. They replicate well in human, feline, canine, guinea pig, rabbit, rat, and mouse cells, whereas bovine, hamster, and avian cells are resistant. Since this host range includes that of both mouse tropic (ecotropic) and xenotropic murine leukemia viruses, they are designated as "amphotropic". No purely xenotropic virus component is detectable in these field isolates. They may represent the "wild" or ancestral viruses from which the ecotropic and xenotrophic murine leukemia virus strains of laboratory mice have been derived.     

High molecular weight deoxyribonucleic acid polymerase from crown gall tumor cells of periwinkle (Vinca rosea).

A high molecular weight (6 S) plant DNA polymerase from axenic Vinca rosea tissue culture cells has been purified 2200-fold and characterized. The enzyme has a molecular weight of 105 000 (+/-5000). Sodium dodecyl sulfate-acrylamide gel electrophoresis of the purified enzyme yields polypeptide subunits having molecular weights of 70 000 and 34 000. The purified enzyme has a pH optimum of 7.5; a cation requirement optimum of 6 mM Mg2+ or 0.5 mM Mn2+; an apparent requirement for Zn2+; a Km of 1 muM for dTTP; and a 3.5-fold stimulation by 50 mM KCl. The enzyme is sensitive to N-ethylmaleimide (1 mM), heparin (0.1 muM), ethanol (5%), pyrophosphate (0.05 muM), and o-phenanthroline (0.1 mM) but is insensitive to rifamycin. Denatured DNA is found to be the best natural template, and only negligible activity can be demonstrated with the ribopolymer templates poly(dT)n-poly(rA)n and p(dT)10-poly(rA)n. In addition to the polymerization reaction, the enzyme catalyzes a pyrophosphate exchange reaction. Antibody to calf thymus 6-8S DNA polymerase does not inhibit DNA polymerase from Vinca rosea, suggesting no antigenic relationships between the mammalian and plant enzymes.