Zinc sulphate improved microspore embryogenesis in barley

The effect of ZnSO₄ concentration on barley (Hordeum vulgare L.) microspore embryogenesis was investigated using cultivars of different androgenetic response. Concentrations from 0 (control) to 600 μM in the stress pre-treatment medium alone or in combination with 30 (control) to 600 μM in the embryo induction medium were assayed in anther culture. Incorporation of Zn²⁺ in the pre-treatment medium itself did not affect microspore embryogenesis. The optimum concentration in the stress pre-treatment and induction media was 180 μM for cultivars (cvs.) Igri and Reinette, and 90 μM for cv. Hop. A significant increase of 30 and 300% in cv. Igri and Reinette, respectively, were produced with 180 μM ZnSO₄ in both the number of embryos and green plants. In order to confirm the effect of Zn²⁺ on microspore embryogenesis this micronutrient was incorporated in the induction medium of isolated microspore cultures of cv. Igri. Concentrations of 90–300 μM ZnSO₄ resulted in an increase of 40–53% in the number of embryos and green plants. All these results indicate that the beneficial effect of Zn²⁺ is exerted mainly during the culture phase, increasing the number of embryos, leading to an increased number of green plants, but it had no effect on percentage of regeneration or green plants.     

A theoretical analysis of the Ti(IV)-catalyzed glycoaminocyanation reaction

The chelation of the Lewis acid Ti(OiPr)(4) provides the necessary conformational control to induce pi-facial selectivity on the cyanation process. The steric hindrance imposed by the alpha-substituent restrains the addition for l-amino acid derivatives.     

An osmoregulatory basis for shape oscillations in regenerating hydra

The freshwater polyp Hydra has considerable regeneration capabilities. A small fragment of tissue excised from an adult animal is sufficient to regenerate an entire Hydra in the course of a few days. During the initial stages of the regeneration process, the tissue forms a hollow sphere. Then the sphere exhibits shape oscillations in the form of repeated cycles of swelling and collapse. We propose a biophysical model for the swelling mechanism. Our model takes the osmotic pressure difference between Hydra's inner and outer media and the elastic forces of the Hydra shell into account. We validate the model by a comprehensive experimental study including variations in initial medium concentrations, Hydra sphere sizes and temperatures. Numerical simulations of the model provide values for the swelling rates that are in agreement with the ones measured experimentally. Based on our results we argue that the shape oscillations are a consequence of Hydra's osmoregulation.     

Cicada acoustic communication: potential sound partitioning in a multispecies community from Mexico (Hemiptera: Cicadomorpha: Cicadidae)

Multispecies cicada communities in neotropical rainforests produce a complex and intense acoustic environment. In a fragment of a Mexican rainforest (Veracruz, Mexico), a cicada community at the end of the dry season consisted of nine species ( Daza montezuma; Pacarina schumanni; Miranha imbellis; Dorisiana sutori; Fidicinoides picea; Fidicinoides pronoe; Quesada gigas; one species of the genus Neocicada and one uncaught canopy species). Seven of the nine species formed dense choruses at dawn and at dusk. Each species showed preferences in the height of calling sites. Males of the species were solitary or gregarious, and followed a 'call-fly' or a 'call-stay' calling strategy. Acoustic signals of each species had particular time and frequency patterns. All these specific features appear to separate the nine species acoustically and lead to a partitioning of the acoustic environment. The acoustic partitioning might decrease the risk of heterospecific courting and mating.© 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 379–394.     

Effects of colchicine on anther and microspore culture of bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The aim of this work was to study the effects of colchicine application on chromosome doubling and androgenic response in anther and microspore culture of different bread wheat genotypes. Colchicine was applied during a mannitol stress pretreatment or during the first 48 h of culture at concentrations of 0, 150 and 300 mg l⁻¹. When colchicine was applied during stress pretreatment, the percentage of doubling depended on genotype and concentration. A significant increase in doubling was observed with 300 mg l⁻¹ in the low androgenic responding cv. Caramba. Colchicine incorporation during the first hours of culture improved percentage of doubling in all genotypes, in both anther and microspore culture. Application of 300 mg l⁻¹ colchicine improved the percentage of doubling in the two low responding genotypes, to 118% of control in DH24033, and 75% in Caramba in microspore and anther culture, respectively. Concerning the androgenic response, the effect of colchicine on embryo formation and percentage of green plants depended on the genotype and on the culture method. In cv. Pavon, a 2- and a 3-fold increase in percentage of embryogenesis and green plants, respectively, were obtained with 300 mg l⁻¹ colchicine in microspore culture. However, no significant differences in these two variables were observed in anther culture. The number of green doubled haploid (DH) plants reflects the index of success of the procedure. Regardless of the culture method, when colchicine was incorporated during the first hours of culture, the number of green DH plants increased significantly in three of four genotypes. These results confirm the usefulness of colchicine application during the first hours of culture in wheat breeding programs.     

DiI as a marker for cellular transplantation into solid organs.

Research in cellular transplantation is frequently compromised by an inability to identify transplanted cells engrafting into orthotopic sites if they exhibit normal morphology and no unique antigenic markers. A method is described for using the fluorescent dye DiI as a marker for cell transplantation studies. This dye is not metabolized or exchanged between cells in vitro or in vivo and enables identification of engrafted cells by fluorescence microscopy, flow cytometry or fluorescence-activated cell sorting. Applications are described in autologous hepatocellular and thyroid follicular cell transplantation.     

Synthesis and Cu(II) coordination of two new hexaamines containing alternated propylenic and ethylenic chains: Kinetic studies on pH-driven metal ion slippage movements

The synthesis of the open-chain and cyclic polyamines, 1,5,8,12,15,19-hexaazaheptadecane (L1) and 2,6,9,13,16,20-hexaaza[21]-(2,6)-pyridinophane (L2), are described. The protonation constants and interaction constants with Cu(II) have been determined by potentiometric measurements carried out at 298.1 K in 0.15 mol dm⁻³ NaClO₄. The values obtained are discussed as a function of the open-chain or cyclic nature of the ligands and compared with analogous polyamines containing different sets of hydrocarbon chains between the nitrogen donors. Kinetic studies on the acid-promoted dissociation of the Cu(II) complexes indicate that the mono and binuclear complexes of L1 decompose with different kinetics, a behavior unprecedented for open-chain polyamines. In contrast, the dissociation of the first metal ion is accelerated in the binuclear complexes of L2 and so, all the mono and binuclear complexes of L2 decompose with the same kinetics. The voltammetric response of Cu(II)-L1 and Cu(II)-L2 complexes has been studied in order to correlate electrochemical and structural data.     

An assessment of the floristic composition,structure and possible origin of a liana forest in the Guayana Shield

Liana is a life form that possesses high importance in many Neotropical forests. Density of climbers apparently increases with the intervention rate (e.g. logging). The aim of this work is to characterize the structure, floristic composition and soils of a sector classified as Liana Forest (LF). We identified an LF sector in a not-logged area; three 1 ha square plots were measured (individuals ≥ 10 cm dbh, “diameter at breast height”). In each plot, we evaluate four 100 m² square understory subplots (all spermatophyta individuals < 10 cm dbh). LF has a low canopy ( < 15 m) and is dominated by Alexa imperatricis and Pentaclethra macroloba. Basal area (20.4 m²ha^? 1) and diversity (H′ = 2.6) are lower than other surrounding plots. Understory is dominated by gnarled climbers, and the most important are Cheiloclinium hippocrateoides and Bauhinia scala-simiae. Soil is extremely acidic, with very low fertility but is similar to neighboring places. We conclude that LF was neither originated by edaphic restrictions nor logging; LF probably suffered a hurricane wind that fell down most of the canopy trees, thick individuals of climber species also disappeared, and the current successional stage favors a recovery dominated with thin individuals of this life form.