Floral development and expression of floral homeotic genes are influenced by cytokinins

Tobacco plants that are somatic mosaics for the expression of a cytokinin-synthesizing gene have viviparous leaves. Epiphyllous buds can be either vegetative or floral. Floral adventitious buds can be either normal or abnormal. Abnormalities of floral development correlate with: (i) a local activation of the cytokinin-synthesizing gene, (ii) a drastic increase in floral cytokinin content, and (iii) a decrease in the steady-state levels of mRNA homologues of the homeotic genes DEFA , GLO and PLENA of Antirrhinum majus . Thus, these data show in planta that cytokinins, a class of phytohormones, are able to alter the development of floral organs and to decrease the expression of three homeotic floral genes.     

Life cycle of Cyclops vicinus in relation to food availability, predation, diapause and temperature

The seasonal cycle of Cyclops vicinus was studied during a 5year period in the shallow and hypertrophic Lake Søbygård.The annual number of generations varied between three and sixand sometimes included midsummer generations. Naupliar and copepoditedensity was extremely high, the maximum recorded being 1313and 745 1^–1 respectively. The seasonal fluctuation inthe abundance of C.vicinus was related to the concentrationof edible phytoplankton (EDP): when diatoms and cryptomonadswere abundant, nauplii and copepodites were also abundant, whereaswhen greens such as Scenedesmus spp. were dominant, no cohortswere observed. The maximum density of copepodites in the separatecohorts and the amount of EDP, expressed as carbon content,were found to be significantly correlated. The development ofthe second cohort also seemed to depend on the occurrence ofa peak in rotifer density. High number of eggs per female generallycoincided with high biovolume of EDP, suggesting that algaeconstituted a major part of the diet of adult C. vicinus. Theduration of the naupliar stage was inversely related to temperatureand is one of the shortest times that have been recorded inthe literature. The short duration is probably attributableto the abundance of food. Fish composition and the calculatedsex ratio of C.vicinus indicate low predation pressure fromplanktivorous fish. The high density of C.vicinus during thesummer, when the whole population would be expected to haveentered diapause, is probably attributable to the concurrenceof low predation and the abundance of food.     

THE MARINE DINOFLAGELLATE ALEXANDRIUM OSTENFELDII: PARALYTIC SHELLFISH TOXIN CONCENTRATION,COMPOSITION, AND TOXICITY TO A TINTINNID CILIATE1

The composition of paralytic shellfish toxins in the marine dinoflagellate Alexandrium ostenfeldii (Paulsen) Balech et Tangen grown in unialgal culture was determined by high-performance liquid chromatography. The toxin profile revealed that the low-potency sulfamate toxin B₂ was dominant (90 molar % of total toxins), but small amounts of the weakly toxic 21-N-sulfocarbamoyl derivatives C₁₊₂ and trace amounts of the carbamate toxins GTX₂ and GTX₃ were also present. The mammalian toxicity was confirmed by a modification of the conventional AOAC mouse bioassay (0.6–1.4 pg STX_eq· cell^-1). The acute toxicity to a potential predator, the tintinnid ciliate Favella ehrenbergi (Clap, et Lach.) Jörg., was also investigated. The ciliate was able to graze on A. ostenfeldii when the cell concentration of the dinoflagellate was low (<2000 cells · mL^-1). At higher concentrations the ciliate was affected by exudates (presumably PSP toxins) that induced backward swimming followed by swelling and lysis of the cell. Fluorescence microscopy of calcofluor-stained cells was employed as an easy and rapid method to identify this and other thecate dinoflagellates.     

Heterostyly in the Canarian endemic Jasminum odoratissimum (Oleaceae)

Jasminum odoratissimum is a Madeira and Canary Islands endemic showing classic heterostyly, i.e. with long-styled flowers with anthers at a low level in the corolla tube and short-styled flowers with anthers at a high level in the corolla tube. Short-styled flowers have large pollen, whereas long-styled flowers have small pollen. The two types are present in equal frequencies in the population.     

On peptide bond formation, translocation, nascent protein progression and the regulatory properties of ribosomes. Derived on 20 October 2002 at the 28th FEBS Meeting in Istanbul.

High-resolution crystal structures of large ribosomal subunits from Deinococcus radiodurans complexed with tRNA-mimics indicate that precise substrate positioning, mandatory for efficient protein biosynthesis with no further conformational rearrangements, is governed by remote interactions of the tRNA helical features. Based on the peptidyl transferase center (PTC) architecture, on the placement of tRNA mimics, and on the existence of a two-fold related region consisting of about 180 nucleotides of the 23S RNA, we proposed a unified mechanism integrating peptide bond formation, A-to-P site translocation, and the entrance of the nascent protein into its exit tunnel. This mechanism implies sovereign, albeit correlated, motions of the tRNA termini and includes a spiral rotation of the A-site tRNA-3' end around a local two-fold rotation axis, identified within the PTC. PTC features, ensuring the precise orientation required for the A-site nucleophilic attack on the P-site carbonyl-carbon, guide these motions. Solvent mediated hydrogen transfer appears to facilitate peptide bond formation in conjunction with the spiral rotation. The detection of similar two-fold symmetry-related regions in all known structures of the large ribosomal subunit, indicate the universality of this mechanism, and emphasizes the significance of the ribosomal template for the precise alignment of the substrates as well as for accurate and efficient translocation. The symmetry-related region may also be involved in regulatory tasks, such as signal transmission between the ribosomal features facilitating the entrance and the release of the tRNA molecules. The protein exit tunnel is an additional feature that has a role in cellular regulation. We showed by crystallographic methods that this tunnel is capable of undergoing conformational oscillations and correlated the tunnel mobility with sequence discrimination, gating and intracellular regulation.     

On-line membrane inlet mass spectrometry for feed-back control of precursor concentration in penicillin fermentation

Summary A sampling system which enables on-line measurements of the precursor phenoxyacetic acid (POAA) in penicillin fermentation by membrane inlet mass spectrometry is presented and its capacity for feed-back regulation of POAA to a low predefined concentration in a penicillin-V fermentation over 150 hours is demonstrated. The system measures alternately filtered sample and standard solution in a measuring cycle which is shorter than the response time of membrane inlet mass spectrometry (MIMS) but sufficiently long to decide whether the concentration of POAA in the sample is higher or lower than in the standard solution at set point concentration. The decision is used for on-off regulation of the addition of POAA.     

Antihypertensive effects of captopril without adverse effects on glucose tolerance in hyperinsulinemic rhesus monkeys

The rhesus monkey (Macaca mulatta), which has been found to develop spontaneous obesity, non-insulin dependent diabetes mellitus (NIDDM; Type 2), and hypertension, was used to evaluate the potential blood pressure-lowering effects of captopril as well as the specific effects, if any, on the prediabetic state. Intravenous and oral glucose tolerance testing was carried out with oral captopril dosing. Results showed that captopril significantly decreased both systolic and diastolic blood pressure in all monkeys and significantly decreased fasting plasma glucose levels. Based on these preliminary studies in monkeys, we conclude that captopril exerted antihypertensive effects without adverse effects on glucose metabolism.     

Synergism of thidiazuron and benzyladenine in axillary shoot formation depends on sequence of application in Miscanthus X ogiformis ‘Giganteus’

Shoots of Miscanthus X ogiformis Honda Giganteus transferred from medium with benzyladenine (BA) to thidiazuron (TDZ) formed significantly more axillary shoots than shoots grown continuously on either medium, or transferred from TDZ to BA. Shoot formation on axillary shoots transferred from BA-containing media to media with kinetin or isopentenyladenine (2iP) or transferred from media with TDZ, kinetin or 2iP to media with BA, corresponded to the number of shoots formed in the previous subculture. Shoot formation on shoots transferred from medium containing BA to media containing combinations of BA and/or TDZ increased with increasing concentrations of TDZ in the first subculture, whereas shoot formation in the second and third subculture depended on the BA concentration. When shoots were transferred from media with BA to media with TDZ, the time for shoot formation, as well as shoot size, indicate that the combined effect of BA and TDZ is expressed only during the early phase of the subculture. The results suggest that adenine- and phenylurea-type cytokinins have a common binding site in the plant cell, and a model is proposed.Abbreviations BA 6-benzyladenine - CBP cytokinin-binding protein - 2iP isopentenyladenine - KIN kinetin - MS Murashige & Skoog - TDZ thidiazuron     

Apoplastic pH of intact leaves of Vicia faba as influenced by light

The fluorochrome FITC-dextran was used to measure the effectof light on the apoplastic pH of intact Vicia faba leaves withthe ratio imaging technique. In darkadapted leaves the apoplasticpH varied depending on the leaf between 5.2 and 5.9. Red light(660 nm, 4–12 W m^–2) leads to multiphasic responses:in the first seconds an alkalinization ({small tilde}0.3 pHunits), and thereafter an acidification of the leaf apoplast({small tilde}0.4 pH units) were observed. Both effects couldbe inhibited by DCMU. While variation of CO₂ concentration revealedno effect on light-induced apoplastic pH changes, a decreasein O₂ concentration decreased the effect. On the basis of ourdata it is suggested that the influence of photosynthesis onplasmalemma H⁺ ATPase is responsible for the observed effects,rather than altered CO₂ uptake. Key words: Leaf apoplast, apoplastic pH, light, ratio imaging, pH-sensitive fluorescent dye, Vicia fab     

Glycan modification of a thermostable recombinant (1-3,1-4)-β-glucanase secreted fromSaccharomyces cerevisiae is determined by strain and culture conditions

High level biosynthesis and secretion of the thermostable hybrid (1-3,1-4)--glucanase H(A16-M) has been achieved inSaccharomyces cerevisiae by means of the yeast vacuolar endoprotease B promoter (PRB1_p) and theBacillus macerans (1-3,1-4)--glucanase signal peptide. The N-glycans present on the yeast-secreted H(A16-M), denoted H(A16-M)-Y, were released by endoglycosidase H, and identified by proton NMR spectroscopy to be a homologous series of Man_8-13GlcNAc₂, although only traces of Man₉GlcNAc₂ were found. Therefore, processing of N-glycans on H(A16-M)-Y is similar to that on homologous proteins. Most of the N-glycans (88%) were neutral while the remainder were charged due to phosphorylation. Site-directed mutagenesis of Asn to Gln in two of the N-glycosylation sequons, and subsequent analysis of the N-glycans on the yeast-secreted proteins together with analysis of the N-glycans from the individual sites of H(A16-M)-Y suggest the presence of steric hindrance to glycan modification by the glycans themselves. H(A16-M)-Y produced under control of either the yeast protease B or the yeast 3-phosphoglycerate kinase promoter, each in two differentSaccharomyces strains revealed a dependence of N-glycan profile on both strain and culture conditions. The extent of O-glycosylation was found to be nine mannose units per H(A16-M)-Y molecule. An attempt to identify the linkage-sites for the O-glycans by amino acid sequencing failed, suggesting non-stoichiometric or heterogeneous O-glycosylation. The possible modes in which N-glycans might contribute to resistance of H(A16-M)-Y to irreversible thermal denaturation are discussed with respect to structural information available for H(A16-M)-Y. Abbreviations: AMY,B. amyloliquefaciens (1-3,1-4)--glucanse; MAC,B. macerans (1-3,1-4)--glucanase H(A16-M), H(A36-M), H(A78-M),H(A107-M) and H(A152-M), hybrid (1-3,1-4)--glucanases containing 16, 36, 78, 107 and 152 N-terminal amino acids, respectively, derived from AMY with the remaining amino acids derived from MAC; similar enzyme abbreviations followed by Y, e.g. H(A16-M)-Y, denote the enzymes secreted from yeast cells; PCR, polymerase chain reaction; PGK_p, yeast 3-phosphoglycerate kinase promoter; PRB1_p, yeast protease B promoter; LB, Luria-Bertani medium; SC, minimal medium; CNBr, cyanogen bromide; Endo H_f, endoglycosidase H fusion protein; PNGase F, peptide:N-glycosidase F; HPAEC; high pH anion exchange chromatography; HVE, high voltage paper electrophoresis; CPY, yeast carboxypeptidase Y.