The dependence of glyceroglycolipid orientation and dynamics on head-group structure

The head-group orientations and molecular dynamics of three glyceroglycolipids in aqueous dispersions, as determined by 2H-NMR, are compared. 1,2-Di-O-tetradecyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (alpha-DTGL) and 1,2-di-O-tetradecyl-3-O-(alpha-D-mannopyranosyl)-sn-glycerol (alpha-DTML), selectively 2H-labelled on the pyranose ring, at the exocyclic hydroxymethyl group, and at C3 of glycerol, have been studied by 2H-NMR and the results compared with those reported earlier for 1,2-di-O-tetradecyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol (beta-DTGL). The alpha-glucolipid exhibits a gel-to-liquid crystal phase transition and a lamellar to hexagonal mesophase transition at temperatures which are similar to those of the beta-anomer, beta-DTGL. However, alpha-DTGL exhibits head group orientations and molecular ordering in the lamellar and hexagonal phases which differ strikingly with those reported for the corresponding beta-glucolipid. Whereas the head group of beta-DTGL is extended away from the bilayer surface into the aqueous phase, that of alpha-DTGL is almost parallel to the bilayer surface. alpha-DTGL exhibits a molecular order parameter of 0.56 which is substantially greater than that of its anomer, beta-DTGL, 0.45. The latter indicates that the head group region of the alpha-glyceroglucolipid is characterized by smaller angular fluctuations than that of beta-DTGL. On entering the hexagonal mesophase the pyranose ring of the beta-glucolipid undergoes a large reorientation relative to the motional axis of the head group, whereas the alpha-anomer exhibits only a small orientational change. 1,2-Di-O-tetradecyl-3-O-(alpha-D-mannopyranosyl)-sn-glycerol (alpha-DTML) undergoes a phase transition at 47 degrees C, attributed to the unusual lamellar gel to hexagonal phase transition. The pyranose ring of alpha-DTML, in a mixture with dimyristoylphosphatidylcholine (1:9 mol ratio) to give a lamellar liquid crystalline phase, is oriented away from the bilayer surface into the aqueous environment and has an Smol of 0.75. The results for alpha-DTML, 2H-labelled at the C3 position of glycerol, suggest that this segment also has high molecular ordering. alpha-DTML in a lamellar environment has the least flexible membrane surface of the glyceroglycolipids investigated to date. 2H-NMR spin lattice relaxation times have been used to probe the head group motions of the glycolipids. The results indicate that the rate of head group motion increases in the order alpha-DTML less than alpha-DTGL less than beta-DTGL.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dwarf pea response to gibberellic acid applied to soil through a drip irrigation system,and gibberellic acid biodegradation in soil

Gibberellic acid (29 or 290 M) injected into drip irrigation lines significantly stimulated internode elongation of dwarf peas, and the 290-M soil treatment produced significantly taller plants than did the 29-M treatment. GA₃ uptake may limit GA-induced internode elongation when GA₃ is applied to soil, in contrast to results obtained for hydroponically grown plants, where uptake initially appeared to exceed the rate of hormone metabolism (andersonet al.). It is likely that biodegradation or chemical inactivation limited the plant-availability of GA₃ in the soil. Degradation of moderate GA₃ concentrations in a moist, aerobic loamy fine sand was nearly complete within five days, indicating that the inefficiency of soil applications may outweight the benefits provided by reducing labor costs associated with foliar-spray applications.     

Binding of 125I-labelled human chorionic gonadotropin to cell membrane receptors in rabbit ovarian slices

The binding of 125I-labelled human chorionic gonadotropin (HCG) was studied using thick slices (300 micron) of rabbit ovarian tissue. Binding was saturable, reversible, stereospecific, and of high affinity. The amount of binding was proportional to the number of slices used and could be destroyed by boiling. Ovarian slices from eight individual rabbits were found to have two binding sites for 125I-labelled HCG with KD values of 272 +/- 64 and 1263 +/- 274 pM and Bmax values of 25.7 +/- 5.3 and 94.1 +/- 18.8 fmol/mg protein, respectively. In a comparative study the KD and Bmax values were 351 +/- 151 pM and 25.3 +/- 11.1 fmol/mg protein with slices from one ovary and 134 +/- 24 pM and 109 +/- 32 fmol/mg protein with membranes from the contralateral ovary. These data suggest that the binding of HCG can be determined in live tissue.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

Studies on the developmental pattern of rat ovarian 3 alpha-hydroxysteroid dehydrogenase: inhibition of the postpubertal activity with medroxyprogesterone acetate in vivo

The developmental pattern of rat ovarian 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) activity was determined with respect to age, vaginal opening, ovarian histology and serum 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol). The enzyme was assayed by the incubation of [3H]dihydrotestosterone with a portion of whole ovarian cytosol in the presence of 5 X 10(-4) M NADPH. Serum levels of 3 alpha-diol declined from 11.1 +/- 1.2 ng/ml on day 22-3.4 +/- 0.3 ng/ml on day 30 (P less than 0.01). There was no significant change in 3 alpha-HSD during that period which fluctuated from 6.0 +/- 4.0 nmol/h/organ on day 22-8.4 +/- 1.9 nmol/h/organ on day 39. A significant increase on day 42 of 21.1 +/- 6.1 nmol/h/organ occurred well after vaginal opening, corpus luteum formation and the presence of ovarian progesterone; the activity plateaued on day 49 at 31.2 +/- 3.7 nmol/h/organ. In an attempt to inhibit the developmental increase in 3 alpha-HSD activity, medroxyprogesterone acetate (MPA), known inhibitor in vitro was administered to three groups of developing rats in vivo. The administration of MPA at doses of 0.1, 1.0 and 10.0 mg/kg to 30 and 36 day did not inhibit activity when assayed on day 44. In 44-day old rats, the administration of MPA failed to inhibit 3 alpha-HSD activity at 24 h (C-21.1 +/- 2.6; 0.1 mg/kg-19.4 +/- 5.5; 1.0 mg/kg-20.7 +/- 3.7; 10.0 mg/kg-21.1 +/- 3.0 nmol/h/organ) yet there was a significant reduction of 3 alpha-HSD activity when assayed at 48 h (C-21.1 +/- 1.5; 01 mg/kg-9.6 +/- 1.3; 1.0 mg/kg-8.5 +/- 1.9; and 10 mg/kg 5.2 +/- 2.0 nmol/h/organ).     

The effects of ionophores and metabolic inhibitors on methanogenesis and energy-related properties of Methanobacterium bryantii

The effects of numerous ionophores and inhibitors were tested on methane synthesis, intracellular ATP and potassium concentrations, and the proton motive force of the methanogenic archaebacterium Methanobacterium bryantii. M. bryantii had an internal pH near 6.8 (and hence little ΔpH during growth) with an electrical potential of ?127 mV in growth medium and ?105 mV in a pH 6.5 buffer. The study has identified agents which, in M. bryantii, can effectively cause a decline of intracellular ATP (gramicidin, acetylene) and potassium concentrations (gramicidin, nigericin), inhibit methane synthesis (acetylene, gramicidin, nigericin, triphenylmethylphosphonium bromide), eliminate the electrical potential (high extracellular potassium ion concentrations), and dissipate artificially imposed, inside alkaline, pH gradients (monensin, nigericin, carbonyl cyanide m-chlorophenylhydrazone). Carbonyl cyanide m-chlorophenylhydrazone was generally ineffective in media or buffers reduced with cysteine-sulfide but could be effective in cysteine-free solutions reduced with hydrogen sulfide.     

Production of live offspring with predicted genotypes using PCR-RFLP analysis of polar bodies from mouse oocytes

Accurate identification of genotypes in gametes and early embryos could facilitate the efficient production of offspring with desirable traits. This study demonstrates the feasibility of producing offspring with predictable genotypes from micromanipulated mouse oocytes. The Polymerase Chain Reaction (PCR) was used to amplify genes in the IA subregion of the major histocompatibility complex of the mouse. The validity of the approach was demonstrated in experiment 1 with IA haplo-types of unfertilized mouse ova amplified via PCR and distinguished by restriction fragment length polymorphism (RFLP) analysis. In experiment 2, fertilized oocytes were micromanipulated to remove the first and second polar bodies, which were then genotyped by validated PCR-RFLP procedures. Primary oocytes of heterozygous females contain two copies of each of the different alleles. Following meiosis I and II, the genotype of the ovum was predicted by subtracting the alleles observed in micromanipulated polar body samples. Sixty-two fertilized ova were micromanipulated and transferred to recipient females resulting in 27 live offspring (44%). The correct maternal contribution to the embryonic genotype was predicted in 19 of 27 (71%) offspring as confirmed by PCR-RFLP analysis of DNA from pup tails. Predicted genotypes of two pups were not confirmed (7%), whereas no prediction could be made in six cases (22%). © 1995 Wiley-Liss, Inc.     

Localization of flagellin genes on the physical map of Methanococcus voltae

Methanococcus voltae DNA, digested individually with the restriction enzymes ApaI, SacII, BamHI, or EagI, was resolved by pulsed-field gel electrophoresis reproducing the previously published digestion patterns. Hybridization of a flagellin gene-specific probe to such gels dried down (unblots) resulted in the identification of one band per enzyme harboring the flagellin genes. These bands all overlapped, revealing that an approximately 15-kb BamHI/EagI DNA fragment should harbor the flagellin genes. Double digestion with BamHI and EagI resulted in the resolution of two bands in the 15-kb region of the gel. Separation of these two fragments prior to blotting and probing with a flagellar gene-specific probe revealed that one of these fragments possessed the flagellar sequences. The presence of an EagI restriction site in flaB3 localized the flagellin genes precisely at the junction of EagI fragments Ea2 and Ea5 at approximately the 1800-kb position of the physical map.     

Nitrogen fixation efficiency,natural15N abundance,and morphology of mesquite (Prosopis glandulosa) root nodules

Summary The relative nitrogen fixation efficiencies (RE 1-[H₂ evolved÷C₂H₂ reduced]·100) of four mesquite (Prosopis glandulosa var.torreyana) rhizobia (Strains WR 1001, WR 1002, L5, L9) and a cowpea rhizobia (Strain 176A32) on mesquite were evaluated in a glasshouse experiment. Plant yield, shoot N accumulation, and the natural¹⁵N abundance (¹⁵N) of nodule tissue were determined. Strain WR 1002 failed to nodulate mesquite and strain L5 produced ineffective nodules. Among the three effective strains (WR 1001, L9, 176A32) the cowpea strain (176A32) and strain L9 had significantly higher RE than strain WR 1001. Differences in RE, however, were not accompanied by significantly higher plant yield and shoot N accumulation. The difference in¹⁵N abundance between foliar tissue and nodules (nodules minus leaves) was 0.47 ¹⁵N for the ineffective L5 nodules, while for the effective WR 1001, L9, and 176A32 nodules, respectively, this difference was 8.35, 7.81, and 8.35 ¹⁵N. This indicates a similar relationship between N₂-fixing effectiveness and natural¹⁵N enrichment of nodules that was previously observed in soybeans (Glycine max, L. Merr.). Strains WR 1001 and L9 produced elongate, indeterminate nodules typical for mesquite. The ineffective L5 nodules had few infected cells and an abundance of cortical amyloplasts. Mesquite nodules produced by the cowpea strain were spherical and were somewhat more similar in internal morphology to determinate nodules typical of cowpea than indeterminate nodules normally associated with mesquite.     

Formation and regeneration ofHalobacterium spheroplasts

Spheroplasts ofHalobacterium cutirubrum were formed upon suspension of cell pellets in 0.1M MES buffer, pH 7.0, containing 0.5M sucrose, 0.25M NaCl, and 0.01M MgCl₂. The spheroplasts regenerated into rod-shaped bacteria when plated on a complex medium containing 15% (wt/vol) sucrose, undergoing several divisions as spherical bodies before the rod shape developed. The frequency of regeneration was approximately 5% of the total spheroplasts plated. The yield of regenerants was increased significantly (to approximately 35%) when bovine serum albumin was present in the spheroplasting buffer and dilution media. The conditions for spheroplast formation and regeneration inH. cutirubrum were also found effective forHalobacterium salinarium but not forHalobacterium halobium.NRCC Paper no. 23080.