Altered expression of flowering class B and class C genes in the Appendix tobacco mutant

 In the tobacco (Nicotiana tabacum) Appendix mutant, anthers are tipped by a miniature style and stigma. The outgrowth appears on the anther when it is already differentiating and follows the developmental timing of the central carpel. The Appendix mutation thus represents a late homeotic transformation suggesting that the APPENDIX (APX) gene either could be a misregulated organ identity gene or could be involved in regulating the expression of such genes. RFLP analysis with two class B (TM6 and NTGLO) and a class C (NAG) probes revealed that the Appendix phenotype is not caused by a mutation in one of these genes. However, in situ hybridization showed important changes in the expression of NTGLO and NAG in the mutant when compared with wild-type tobacco. Surprisingly, although no phenotypic alteration other than the style and stigma outgrowth is observed in the Appendix mutant, changes in class B and class C gene expession were not restricted to the anther tip cells from which the outgrowth originates. As expected, NAG was expressed in the Appendix outgrowth but it was also overexpressed in the normal third and fourth whorl organs at the time the outgrowth, as well as the central styles and stigmas, differentiated. Overexpression of a class C gene is probably responsible for the Appendix phenotype. In normal and mutant flowers, NTGLO was expressed in the second, third and fourth whorls up to the time of carpel fusion. Expression of this class B gene then ceased in the fourth whorl organs but was reactivated at later stages only in the styles and stigmas as well as in the outgrowths of the mutant. It thus seems that the function of the APX gene is either to regulate the late expression of organ identity genes or to control cell proliferation in such a way that, in the mutant, some cells are in a state where they respond in an unusual way to developmental signals. Received: 17 October 1997 / Revision accepted: 24 March 1998     

Clumping factor B (ClfB), a new surface-located fibrinogen-binding adhesin of Staphylococcus aureus

The surface-located fibrinogen-binding protein (clumping factor; ClfA) of Staphylococcus aureus has an unusual dipeptide repeat linking the ligand binding domain to the wall-anchored region. Southern blotting experiments revealed several other loci in the S. aureus Newman genome that hybridized to a probe comprising DNA encoding the dipeptide repeat. One of these loci is analysed here. It also encodes a fibrinogen-binding protein, which we have called ClfB. The overall organization of ClfB is very similar to that of ClfA, and the proteins have considerable sequence identity in the signal sequence and wall attachment domains. However, the A regions are only 26% identical. Recombinant biotinylated ClfB protein bound to fibrinogen in Western ligand blots. ClfB reacted with the α- and β-chains of fibrinogen in the ligand blots in contrast to ClfA, which binds exclusively to the γ-chain. Analysis of proteins released from the cell wall of S. aureus Newman by Western immunoblotting using antibody raised against the recombinant A region of ClfB identified a 124 kDa protein as the clfB gene product. This protein was detectable only on cells that were grown to the early exponential phase. It was absent from cells from late exponential phase or stationary phase cultures. Using a clfB mutant isolated by allelic replacement alone and in combination with a clfA mutation, the ClfB protein was shown to promote (i) clumping of exponential-phase cells in a solution of fibrinogen, (ii) adherence of exponential-phase bacteria to immobilized fibrinogen in vitro, and (iii) bacterial adherence to ex vivo human haemodialysis tubing, suggesting that it could contribute to the pathogenicity of biomaterial-related infections. However, in wild-type exponential-phase S. aureus Newman cultures, ClfB activity was masked by the ClfA protein, and it did not contribute at all to interactions of cells from stationary-phase cultures with fibrinogen. ClfB-dependent bacterial adherence to immobilized fibrinogen was inhibited by millimolar concentrations of Ca²⁺ and Mn²⁺, which indicates that, like ClfA, ligand binding by ClfB is regulated by a low-affinity inhibitory cation binding site.     

Effects of grazing on plant species composition and spatial distribution in rangelands of the Sahel

The effects of grazing by livestock on plant species composition and spatial distribution have been studied at Sadoré, Niger. Herbaceous species were recorded in plots of increasing size from 1/64 to 1024 m² in ten fallow plots subjected to five different grazing treatments over the previous three years. Treatments consisted of three intensities of grazing, and of protection from grazing for either 3 or 14 years. For all treatments, the number of species fitted a normal distribution with the log (ln) of the area inventoried. However, the fit improved slightly when the model included two successive log-normal distributions respectively considered as species distribution within a patch and at the patch mosaic scale. Across treatments, the optimal sampling areas averaged 3.8 ± 1.1 m² for the within-patch and 725 ± 113 m² for the mosaic scale distributions. It is argued that similarity between treatments in the overall log-normal distribution resulted from compensations between the divergent trends that affected species distribution within and across patches depending on the grazing status. Long-term protection resulted in a regular spatial arrangement of highly contrasted, but internally homogeneous patches. Heavy grazing ensued the dominance of a few species in contagious patches but also left niches for scattered individuals of other species. Tests of the relative frequency of each plant species, together with the average area needed to record that species, were used to characterize specific response to grazing. A majority of species encountered in old Sahelian fallows were either fostered by grazing, indifferent or tolerant to grazing. However, more than a third of the species appeared sensitive to heavy grazing, and no relationships were found between species response to grazing and palatability.     

A Comparison of Sibutramine and Dexfenfluramine in the Treatment of Obesity

Objective : Because long-term weight reduction is often unsuccessful with dietary restriction alone, pharmacological agents have been used to promote weight loss. We have compared the novel (multiple monoamine neurotransmitter reuptake inhibitor) antiobesity drug sibutramine (10 mg once daily) with the extensively studied serotonin-releasing antiobesity agent dexfenfluramine (15 mg twice daily). Research Methods and Procedures : 226 healthy outpatients (aged 18 to 65 years; body mass index ≥27 kg/m²) were included in a 12-week, randomized, double-blind, parallel group study. The main outcome measures were changes in weight, body mass index, waist and hip circumference and ratio, and safety profiles. Results : Mean (±SEM) absolute weight loss was 4.5 ± 0.4 kg in the sibutramine group (n = 112) and 3.2 ± 0.3 kg in the dexfenfluramine group (n=112) (endpoint analysis); 4.7 ± 0.4 kg in the sibutramine group (n=101); and 3.6 ± 0.3 kg in the dexfenfluramine group (n = 94) (completers analysis). Comparing the two treatments under the conventional null hypothesis of equality as a secondary analysis, weight loss at endpoint in patients receiving sibutramine was significantly greater than that achieved with dexfenfluramine (p<0.05). Both drugs had similar adverse events profiles: 174 patients (77%) experienced adverse events; 17 patients withdrew due to adverse events (sibutramine, n = 6; dexfenfluramine, n = 11). Pulse rate increased significantly in sibutramine-treated patients (3.6 bpm), but decreased in dexfenfluramine-treated patients (-0.9 bpm). Discussion : Sibutramine (10 mg once daily) is at least as effective as dexfenfluramine (15 mg twice daily) in achieving weight loss in patients with obesity.     

Effects of low-molecular-weight aluminum complexes on brain tissue calcium homeostasis

The in vitro effects of low-molecular-weight aluminum complexes (citrate, lactate, and ATP complex) on the Ca²⁺ uptake and aluminum-induced lipid peroxidation of brain tissue show that the modification of the calcium homeostasis is determined by the nature of the ligand and that there is no correlation between the aluminum-induced lipid peroxidation and the Ca²⁺ uptake. The same characteristics have been shown by a similar study performed with Ehrlich carcinoma cells. The electrophoretic analyses of the aluminum lactate-albumin and aluminum lactate-ATP interactions indicate an aluminum transfer from the lactate to the albumin and ATP ligands. The increased Ca²⁺ uptake when ATP is present in the incubation medium with aluminum citrate and aluminum lactate corroborates the suggested mediator role of ATP in cellular calcium homeostasis modification induced by iron.     

A new acanthocolpid cercaria (Digenea) from Cantharus dorbignyi (Prosobranchia) in the Western Mediterranean

A new cercaria is recorded from the prosobranch snail Cantharus dorbignyi from the sublittoral region off the coast of Corsica. The redia, cercaria and metacercaria (the latter experimentally developed in the labrid fishes Symphodus ocellatus and S. rostratus) are described, along with the behaviour of naturally emitted cercariae. In view of the morphology of the larval stages, the parasite is thought likely to be an acanthocolpid. The morphology of the cercaria and metacercaria are compared with both known and suspected acanthocolpid cercariae and with adult acanthocolpids known to occur in the Mediterranean. Morphological and circumstantial evidence suggests that this cercaria may be a species of the genus Tormopsolus.     

Somaclonal variation and chilling tolerance improvement in rice: Changes in fatty acid composition

The relationship between chilling tolerance of six rice cultivars – Facagro 57, Facagro 76, Fujisaka 5, Kirundo 3, Kirundo 9 and IR64 -and the fatty acid composition in total lipids, phospholipids, galactolipids and neutral lipids from leaves was studied. Higher double bond index and proportions of linolenic acid in the phospholipid and galactolipid classes were related to cultivar chilling tolerance, but this was not so for the total lipids nor the neutral lipid class. The somaclonal families derived from Facagro 76, Kirundo 3 and Kirundo 9 that showed enhanced chilling tolerance as compared to their original parental cultivar were analyzed for fatty acid composition in phospholipids and galactolipids from leaves. Altered proportions in fatty acid composition in phospholipids, galactolipids or both were found in the somaclonal families derived from Facagro 76 and Kirundo 9, but not from Kirundo 3. These changes most usually resulted in higher double bond index and higher proportions in linoleic and linolenic acids which were related either to lower ratio of C16 to C18 fatty acids or to higher unsaturation in the C18 fatty acid fraction. Different mechanisms thus seem to be implicated in the altered fatty acid composition of somaclones, which may be related to the chilling tolerance improvement of some somaclonal families.     

Time-resolved electron transfer at the donor side of Rhodopseudomonas viridis photosynthetic reaction centers in whole cells

We have studied the electron transfer reactions from the tetraheme cytochrome of Rhodopseudomonas viridis to the oxidized primary donor in whole cells with a new high sensitivity spectrophotometer. In this apparatus the monochromatic detecting flashes are provided by a YAG pumped Optical Parametric Oscillator, allowing a 10 ns time resolution. When four hemes are reduced the observed electron transfer reaction sequence is the following: first the low-potential c552 heme (the number refers to the maximum absorption wavelength in the alpha-band region) is oxidized with a half time of 130 ns, in agreement with previous reports of measurements performed with purified reaction centers. Then, the electron hole is transferred to the low potential c554 heme with a half time of 2.6 µs. When only the two high potential hemes are reduced the observed electron transfer sequence is the following: oxidation of the high potential c559 heme in the hundreds of ns time range (410 ns), reduction of this heme by the high potential c556 heme in the µs time range (2.7 µs). This confirms the first steps of electron transfer observed in isolated reaction centers. However, in the microsecond time domain, the overall amount of oxidized hemes increases suggesting that, in vivo, the equilibrium constant between the P⁺/P and the c559^ox/c559^red couples is significantly lower than expected from the difference in their midpoint potentials.