Biology of Azospirillum-Sugarcane Association: Enhancement of Nitrogenase Activity

Azospirillum brasilense was reisolated from associations with callus tissue cultures of sugarcane and compared with stock cultures of the inoculated bacterium and related strains. Although the reisolate had a growth rate similar to stock cultures, it exhibited a severalfold increase in maximum specific activity of nitrogenase. The reisolate and the parent culture had similar ultrastructure. The general ultrastructure of Azospirillum is described. The bacterium was capsulated when grown on nitrogen-free nutrient agar plates and on callus, but was not capsulated when growing in a subsurface zone in N-free semisolid nutrient agar, except rarely in aging cultures. Capsulation may be a protective mechanism against unfavorable pO₂ under dinitrogen-fixing conditions. Pleomorphism occurred in capsulated forms, and the ultrastructure of these forms is described.     

Social status and season of birth: a study of a metropolitan area in the southeastern United States

An analysis of live birth statistics obtained from the Health Department of Fulton County, Georgia for 1967-1977 indicated that seasonal variation in birth was significantly related to maternal social status. Mothers were assigned to social status classification on the basis of whether they lived in an upper, upper middle, lower middle, or lower socioeconomic census tract. Periodic regression analysis and analysis of variance was applied to the data. Specific findings were 1) upper status groups showed no significant variation in births; 2) upper and lower middle classes showed a similar and a significant degree of seasonal variation with depressed birth levels from January-June and elevated levels from July-December; 3) lower class birth patterns showed more seasonal variation than the other classes; 4) the periodic curve accounted for 92.3% of the monthly variation in births for the lower class, 70.6% for the lower middle class, and 64.6% for the upper middle class; 5) the relationship between social status and seasonal variation in births held for both whites and non-whites; 6) seasonal variations were somewhat more marked for non-whites than for white in the lower and lower middle class; and 7) the observed relationship held throughout the 11 year period of observation. The results were of special concern given previous studies which found that children born in September-October entered school on the average earlier than other children and did less well in school than other students. Major findings were presented in graphic and tabular form.     

Foetal glutamate as a possible precursor of placental glutamine in the guinea pig.

The role of foetal glutamate as a source of placental glutamine was investigated in the near-term pregnant guinea-pig placenta perfused in situ through the umbilical vessels. With normal foetal amino acid concentrations there was a significant two-way exchange of glutamate between the placenta and foetal perfusate, but a net release of the amino acid from the placenta. Radioactively labelled glutamate carbon entering the placenta by this exchange was freely incorporated into intracellular glutamine, but only 1.5% of it was found in glutamine transported out into the foetal circulation. In the guinea pig, therefore, foetal glutamate does not appear to be a precursor of glutamine released from the placenta on the foetal side.     

β-endorphin-induced increase in striatal dopamine turnover

Human β-endorphin administered intracisternally in a dose of 15 μg per rat increased striatal concentrations of the dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) as well as producing catalepsy. These effects were inhibited by naloxone. Pargyline-induced decreases in striatal DOPAC and HVA were greater in endorphin-treated than in saline-treated animals, supporting the concept that β-endorphin increases striatal dopamine turnover. β-endorphin increased the rate of decline in striatal dopamine concentration following synthesis inhibition with α-methyltyrosine, further suggesting that endorphin increases striatal dopamine turnover. β-endorphin and probenecid interacted competitively to decrease the effects of each other to increase striatal HVA. Naloxone prevented the effect of endorphin to decrease the HVA response to probenecid. Thus, probenecid cannot be used to assess the effects of endorphin on striatal dopamine turnover. If β-endorphin acts presynaptically to decrease dopamine release in striatum, the increases in striatal DOPAC and HVA probably represent a compensatory attempt to increase dopamine synthesis. Although turnover of dopamine to its metabolites is increased, dopamine release may be suppressed by β-endorphin.     

Effects of β-endorphin on brain serotonin metabolism

Human β-endorphin (15 μg) administered intracisternally increased concentrations of serotonin (5HT) and its metabolite, 5-hydroxyindoleacetic. acid (5-HIAA), in brain stem and hypothalamus and decreased 5-HIAA concentrations in hippocampus. These data are compatible with the hypothesis that β-endorphin increases 5HT turnover in brain stem and hypothalamus and decreases 5HT turnover in hippocampus. β-endorphin increased in brain stem and hypothalamus and decreased in hippocampus the rate of pargyline-induced decline of 5-HIAA. β-endorphin decreased the rate of pargyline-induced accumulation of 5HT in all these brain regions. The probenecid-induced accumulation of 5-HIAA in brain stem was decreased by β-endorphin. These data are compatible with the hypothesis that β-endorphin increases release of 5HT from neurons in brain stem and hypothalamus and decreases release of 5HT from neurons in hippocampus. The data require further a hypothesis that β-endorphin either decreases 5HT reuptake in these three brain regions or increases 5-HIAA egress from brain.     

The effect of AZT on in vitro lymphokine-activated killer (LAK) activity in human immunodeficiency virus type-1 (HIV-1) infected individuals

Human immunodeficiency virus type-1 (HIV-1)-infected individuals exhibit functional impairment in various forms of cell-mediated cytotoxicities (CMC) at all stages of disease. The purpose of this study was to determine (i) if peripheral blood mononuclear cells (PBMC) obtained from HIV-1-infected patients could be stimulated in vitro to yield lymphokine-activated killer (LAK) activity; (ii) if non-MHC-restricted gp120-specific CMC could be preserved; and (iii) what effect zidovudine (AZT) would have on LAK activity. Fourteen asymptomatic HIV-1 seropositive adults and five healthy seronegative adults (controls) were evaluated. PBMCs were isolated and incubated in media or supplemented with IL-2 for 4 or 72 hr. Lysis of the NK resistant target cell line, Daudi, was similar for the control and experimental group. The increase in activity after stimulation was elevated to a similar degree in both seronegative and seropositive groups (P less than 0.001). LAK activity was significantly decreased (P = 0.011) when AZT was added to LAK cultures. In addition, virus production may not have been completely inhibited by AZT in LAK cultures. Thus, PBMCs from asymptomatic HIV-1-infected patients could be stimulated to yield LAK activity. However, AZT can impair LAK generation. It is unclear if LAK activation results in virus production that cannot be inhibited by AZT in this system. Further definition in other patient populations is required prior to applying this information to clinical trials.     

Early gene interaction during prepupal expression of Drosophila arginine kinase

Arginine kinase displays a distinctive rise and fall in specific activity and specific protein levels during the prepupal stage of Drosophila development with maximal activity occurring at morphological stage P3. This developmentally regulated peak is under the influence of ecdysone. Altered doses of the major ecdysone-inducible “early” genes at cytological regions 75B and 2B5 alter this pattern of expression while altered doses of another major “early” gene at 74EF have no effect. We hypothesize that a product of the 2B5 locus and a product of the 75B locus interact to effect this developmental pattern of expression of Drosophila arginine kinase. © 1992 Wiley-Liss, Inc.