Bee visitation rates to trees of Prockia crucis differing in flower number

Summary Annual flower production ranged over four orders of magnitude among individuals of the tropical tree Prockia crucis (Flacourtiaceae), but the number of visits per flower by bees did not increase with flower number. In a population in Jalisco, México, the trees flower for about one week each year, offering only pollen to the bees (mostly solitary species). In a small group of trees, the number of visits per flower was less on trees with greater flower production but in a large group visitation did not vary between trees. Pollen flow probably was not directed from large to small trees or vice versa, because the number of flowers per tree did not determine the schedule of visits. The ratio of pollinators to pollen thieves decreased rapidly through the day, while individuals of both groups foraged more rapidly. Most bee species were rare, and only a small subset of medium-sized to large bees were effective pollinators. Large and small groups of trees differed in the relationship between individual flower crop and abundance and diversity of both pollinators and thieves.     

Axonal patterns of disc-shaped cells in the central nucleus of the cat inferior colliculus

The axonal patterns of disc-shaped cells (Dsc) and their distribution within the central nucleus (Cn) of the inferior colliculus was studied in young cats with the rapid Golgi method. Dsc were subdivided in three main cell varieties according to their axonal branching pattern. The first type possesses local axonal collaterals inside the lamina of origin but also gives collaterals and probably terminals to adjacent lamina. The second variety is characterized by a dense axonal plexus with a restricted zone of arborization. The third axonal pattern is distributed in a radiate fashion. These results demonstrate that Dsc contribute to the intrinsic axonal system of the Cn to a larger degree than previously supposed. Axon terminals of Dsc probably establish axo-dendritic contacts with medium sized Stc which probably establish contacts with neighbouring Dsc. This suggests that reciprocal connections between Dsc and Stc could exist in the Cn.     

A method for calibration of flow cytometric wavelength shift fluorescence measurements

Recently, new fluorescent dyes have been introduced into flow cytometry which alter their spectral characteristics when changes occur in certain cell features, e.g., intracellular pH or calcium ion concentration. Such changes may be determined by measuring the fluorescence intensity ratio in two different wavelength ranges (5). Here a new method is described, which simplifies the use of steadily flowing fluids for calibration. The pulse electronics of a flow cytometer cannot process the static fluorescence signals of a streaming fluid. If, however, the exciting or emitted fluorescence light of a calibration fluid is made pulsating, the flow cytometer electronics can evaluate those pulses. The new calibration procedure uses measurement of two wavelength windows shown in a two-parameter display to generate an absolute calibration scale. Measurement of the spectral shift in calibration fluids under identical instrumental settings provides absolute values that measurements of intracellular concentrations can be referred to.     

Inhibition by cortisol of human natural killer (NK) cell activity

The effects of cortisol on the natural killer (NK) activity of human peripheral blood mononuclear (PBM) cells were studied in vitro using a direct 4-h 51Cr-release assay and K 562 cell line as a target. Preincubation for 20 h of PBM cells drawn from healthy donors with 1 X 10(-8) to 1 X 10(-5) M cortisol resulted in a significant decrease of NK cell activity. The magnitude of the suppression was directly related to the steroid concentration and inversely related to the number of effector cells. Cortisol was able to minimize the enhancement of NK cytotoxicity obtainable in the presence of immune interferon (IFN-gamma). A significantly higher suppression was achieved after sequential exposure of PBM cells to cortisol and equimolar levels of prostaglandin E2 (PgE2). The concomitant incubation with theophylline and isobutyl-methylxanthine failed to enhance the cortisol-induced suppression, whereas PgE2-dependent inhibition significantly increased after exposure of PBM cells to methyl-xanthines. The inhibitory effect of cortisol was partially or totally prevented by the concomitant incubation with equimolar amounts of 11-deoxycortisol and RU 486 but not of progesterone. Treatment of NK effectors with a monoclonal anti-human corticosteroid-binding globulin (CBG) antibody produced an enhancement of the spontaneous NK activity and a partial suppression of cortisol-mediated effects. Our results suggest that endogenous glucocorticoids play a role in the regulation of NK cell-mediated cytotoxicity. Since the effect of cortisol was additive to that of PgE2 and was not changed by phosphodiesterase inhibitors, it is conceivable that the hormone acts at a level different from the adenylate cyclase-phosphodiesterase system. Data obtained with the use of antiglucocorticoids and the anti-CBG antibody are compatible with a role both of high-affinity glucocorticoid receptors and of CBG in mediating cortisol action on the human NK cell activity.     

Cloning and expression in Escherichia coli of the homoserine kinase (thrB) gene from Brevibacterium lactofermentum

Summary Five DNA fragments carrying the thrB gene (homoserine kinase E.C. 2.7.1.39) of Brevibacterium lactofermentum were cloned by complementation of Escherichia coli thrB mutants using pBR322 as vector. All the cloned fragments contained a common 3.1 kb DNA sequence. The cloned fragments hybridized among themselves and with a 9 kb BamHI fragment of the chromosomal DNA of B. lactofermentum but not with the DNA of E. coli. None of the cloned fragments were able to complement thrA and thrC mutations of E. coli. Plasmids pULTH2, pULTH8 and pULTH11 had the cloned DNA fragments in the same orientation and were very stable. On the contrary, plasmid pULTH18 was very unstable and showed the DNA inserted in the opposite direction. E. coli minicells transformed with plasmids pULTH8 or pULTH11 (both carrying the common 3.1 kb fragment) synthesize a protein with an M _r of 30,000 that is similar in size to the homoserine kinase of E. coli.Abbreviations SSC 0.15 M NaCl, 0.015 M sodium citrate - SDS sodium dodecyl sulphate - TSB tripticase soy broth - m-DAP meso-diaminopimelic acid - Sm^r, Cp^r, Km^r, Am^r, Ap^r, Tc^r, MA15^r resistance to streptomycin, cephalotin, kanamycin, amykacin, ampicillin, tetracycline and microcin A 15, respectively     

Formation of ion-translocating oligomers by nigericin

Summary At pH 4.0, >10^–7 m nigericin was found capable of conducting net charge transfer across bimolecular lecithin membranes, with a stoichiometry of three uncharged ionophore moieties per cation. At neutral or alkaline pH, nigericin catalyzed the transfer of net charge through dimer forms. In agreement with these results, quantitative analysis of nigericin-potassium complexes formed at pH 4.0 showed a 31 ratio, and a 21 ratio at neutral or alkaline pH. A 11 stoichiometry was observed when the ionophore complex was not transferred from methanol-water to chloroform. Moreover,¹H-NMR spectra of nigericin-cation complexes formed at pH 4.0, displayed clear-cut chemical shift variations different to those observed at neutral or alkaline pH. Thus, it is apparent that acid pH causes a transition from dimeric to trimeric forms of nigericin-cation complexes. The membrane conductance increased up to ten times when negatively charged phosphatidyl glycerol was used, while the conductance decreased in positively charged cetylpyridinium containing membranes at pH 4.0. These results suggest that the nigericin-K⁺ oligomeric complex is positively charged. In this respect, pK _a values around 8.0 were obtained for the nigericin carboxylate group in media of different dielectric constant, indicating that this chemical group is undissociated under these conditions. Moreover, the values for the complex formation constants as well as the G values calculated for the dimers and trimers indicated that such ionophore cation oligomeric complexes are thermodynamically stable.     

Minimal moisture content for growth and aflatoxin production by Aspergillus parasiticus in mixed feeds

Minimal moisture content for growth and aflatoxin production by Aspergillus parasiticus in mixed feeds was studied. Minimal moisture content for growth is 16.51%+/–0.45. Very low amounts of aflatoxins are accumulated at days 1 or 2 after the growth started when the initial moisture content of the mixed feed was 17% or lower; on the other hand, significant amounts of aflatoxin are detected when it was 18% or higher.     

Analysis of Rhizobium meliloti Sym Mutants Obtained by Heat Treatment

Deletions in the pSym megaplasmid of Rhizobium meliloti were produced at a high frequency, and their lengths varied according to incubation temperature. Morphological differentiation into large and small colonies occurred after heat treatment. Small colonies elicited pseudonodules on alfalfa roots.     

Influence of thyroid function upon "Substance P" induced secretion of saliva by submaxillary glands

The effects of changes in thyroid function on the action of "Substance P" upon the secretion of saliva by the submaxillary glands was studied in male Wistar rats, with parasympathetic decentralization on the left side. The dose-response curves to increasing doses of "Substance P" showed in hyperthyroid animals increased salivary secretion while in hypothyroid animals the dose-response curve to the drug was decreased. Every animal showed supersentivity to "Substance P" in the decentralized gland. The influence of changes in thyroid function in the denervated glands was the same as that in the unoperated side, increased salivary secretion in hyperthyroidism and decreased in hypothyroidism.     

Inversion of sucrose by immobilized beta-fructooxidase in an integral reactor

Experimental runs on the inversion of sucrose by means of immobilized beta-fructooxidase are reported. External mass-transfer and axial dispersion phenomena have been analyzed. It has been observed that external mass-transfer plays a significative role in the overall kinetics, while axial dispersion phenomena are negligible.