Evidence for the involvement of ethylene in the expression of specific RNAs during maturation of the orange,a non-climacteric fruit

Twelve cDNAs corresponding to mRNAs inducible by ethylene were isolated by differential screening of a cDNA library from ethylene-treated Citrus sinensis fruits. Northern analysis of RNA extracted from flavedo of ethylene-treated fruits and from fruits at different maturation stages showed that some of the mRNAs corresponding to these cDNAs were regulated both by ethylene treatment and during fruit maturation. The effect of exogenous ethylene on leaves and of endogenous ethylene on flowers showed that gene induction was not restricted to the flavedo tissue. The possible role of ethylene during maturation of the non-climacteric Citrus fruit is discussed.     

Distribution of the phytoplankton from the Guri Reservoir (Venezuela)

The distribution of phytoplankton species of a tropical blackwater reservoir is discussed on the basis of spatial differences in water composition and of species abundance and diversity. Spatial heterogeneity in water composition identified three different environments within the reservoir itself: (1) strongly colored waters, high turbidity and iron concentrations at the inflow; (2) calcium enriched, nearly uncolored waters at El Pao Bay; (3) lightly colored water, higher transparency and a higher ratio monovalent to divalent cations in the main body of the reservoir. Three corresponding phytoplankton associations were found. Principal Component Analysis helped to explore the relationship of particular species with the abiotic factors. Among them, water color, turbidity, and mineralization proved to be determinant in habitat diversification.     

Seasonal body weight, lipid content, and impact of starvation and water stress on adult survivorship and longevity ofNezara viridula andEuschistus heros

Fresh and dry body weights (FW, DW) were greater for adult southern green stink bug,Nezara viridula (L.) than for the brown stink bug,Euschistus heros F. throughout the year in southern Brazil. FemalesN. viridula significantly increased FW and DW in late summer-early autumn, and during mid-spring; femaleE. heros did not show the same rates of increase in FW and DW. FemaleN. viridula were heavier than males, particularly during summer; however, female and maleE. heros were generally similar in weight.E. heros contained significantly greater amounts of lipid thanN. viridula, during mid-autumn to early-spring (April–September). Survivorship (%) and total longevity ofE. heros adults provided water only was greater (34.6–24.6 days, for females and males) than that forN. viridula (14.8–13.0 days); without water and food, longevity was drastically reduced (<7 days) for both species.     

Solution conformation and dynamics of a tetrasaccharide related to the LewisX antigen deduced by NMR relaxation measurements

¹H-NMR cross-relaxation rates and nonselectivelongitudinal relaxation times have been obtained at two magnetic fields (7.0and 11.8 T) and at a variety of temperatures for the branchedtetrasaccharide methyl3-O--N-acetyl-galactosaminyl--galactopyranosyl-(14)[3-O--fucosyl]-glucopyranoside (1), an inhibitor of astrocyte growth. Inaddition, ¹³C-NMR relaxation data have also been recorded atboth fields. The ¹H-NMR relaxation data have been interpretedusing different motional models to obtain proton–proton correlationtimes. The results indicate that the GalNAc and Fuc rings display moreextensive local motion than the two inner Glc and Gal moieties, since thosepresent significantly shorter local correlation times. The¹³C-NMR relaxation parameters have been interpreted in termsof the Lipari–Szabo model-free approach. Thus, order parameters andinternal motion correlation times have been deduced. As obtained for the¹H-NMR relaxation data, the two outer residues possess smallerorder parameters than the two inner rings. Internal correlation times are inthe order of 100 ps. The hydroxymethyl groups have also different behaviour,with the exocyclic carbon on the glucopyranoside unit showing the highestS². Molecular dynamics simulations using a solvated systemhave also been performed and internal motion correlation functions have beendeduced from these calculations. Order parameters and interproton distanceshave been compared to those inferred from the NMR measurements. The obtainedresults are in fair agreement with the experimental data.     

Allergenic and antigenic proteins released in the apertural sporoderm during the activation process in grass pollen grains

A combination of transmission electron microscopy with immunocytochemical methods was used to localize antigenic and allergenic proteins during the maturation and activation processes of Poaceae pollen grains. The intine undergoes a series of modifications that play a decisive role in these processes. Allergenic and antigenic proteins were detected particularly in the intine of activated in vitro grass pollen grains. Labelling of antigenic proteins was more abundant and less specific than that of allergenic proteins. At the time of hydration, the operculum was lifted up, the intine was swollen and labelling of allergenic proteins appeared highly localized in the Zwischenkörper. No significant labelling was observed when the Zwischenkörper gelatinized. Immunolocalization of allergenic proteins in the activated Zwischenkörper indicated the presence of proteins related to activation of the pollen grains. This confirms that the intine function is involved in the processes of pollen tube formation and fertilization, and also suggests the possible mechanism activated in the pollen grains when allergenic proteins reach the mucosa of sensitive subjects.     

Assessment of survival during starvation ofEscherichia coli andKlebsiella pneumoniae in artificial urine: analysis of the kinetics of colony formation

A kinetic model of colony formation was proposed by Hattori, based on a count of the colonies that appear on a plate in successive short intervals of time. In this model, three parameters (,t _r and N) are defined, which reflect the ability of a bacterium to yield colonies and allow us to described the dynamics of bacterial populations in soil and ofE. coli at different growth phases. In this paper we report a reparametrization of the kinetic model of colony formation, with the aim of facilitating more accurate calculation of andt _r. Moreover, we observed that during the starvation ofE. coli andK. pneumoniae in urine, can be used to assess survival, since this parameter clearly decreases during starvation. Retardation time values (t _r) were similar inE. coli andK. pneumoniae throughout the starvation experimental period.     

Hemagglutination properties of Enterococcus

In total, 86 enterococcal strains including representatives of most of the described species were tested for the ability to agglutinate human, sheep, and rabbit erythrocytes. Five strains did not react with any of the erythrocytes tested, and 81 (94.2%) strains agglutinated only rabbit erythrocytes. The hemagglutination titers ranged from 2 to 64. Loss of the hemagglutination activity was observed when rabbit erythrocytes were treated with trypsin or neuraminidase. Trypsin treatment of the bacterial suspensions also caused loss of the agglutination ability. On the other hand, heat treatment of bacterial suspensions increased the efficiency of the interactions, and higher titers were obtained. Assays for inhibition of hemagglutination were performed with -d-fucose, -d-galactose, -d-galactose, d-glucose, N-acetyl-galactosamine, N-acetyl-glucosamine, N-acetylneuraminic acid, N-acetylneuraminic acid-lactose, and fetuin. Only fetuin was able to inhibit the hemagglutination reactions. The results showed that hemagglutination properties are common to the different enterococcal species tested. They also suggest that enterococci possess hemagglutinins of proteic and non-proteic nature that are involved in the attachment to sialic acid-containing receptors on the surface of rabbit erythrocytes.     

Effects of prenatal cocaine exposure in the retinal ganglion cell layer of the rat

To study the effects of prenatal cocaine-exposure on the developing retinal ganglion cell layer of the rat, female Wistar rats were administered subcutaneously (sc) cocaine hydrochloride (60 mg/kg body wt/d) or saline, or were not manipulated from gestational d 8–22. Male offspring were sacrificed at postnatal day 14 and 30. Radial semithin sections of epon-embedded flat mounts of the retinal quadrants were used to evaluate the following parameters along the centroperipheral axis:

1. Thickness of ganglion cell plus nerve fiber layer;
2. Nuclear size of ganglion cell layer neurons; and
3. Linear density (number per unit length) of ganglion cell layer neurons.

To study the effects of cocaine and age on the retinal areas (temporal/nasal, dorsal/ventral), a repeated measures analysis of variance was used for each of the parameters mentioned above. All parameters were affected by prenatal exposure to cocaine. The thickness of the ganglion cell plus nerve fiber layer was reduced in cocaine-exposed rats in comparison with the saline group. Nuclear diameters were smaller in the cocaine than in the saline and control groups. The linear density was higher in the cocaine-exposed group than in the control and saline groups. The linear decrease in the linear density from postnatal day 14–30 was higher in the cocaine-exposed rats than in the saline group; the decrease in the linear density along the centroperipheral axis found in both the control and saline groups was not significant in the cocaine-treated group. These morphometric findings strongly support the view that prenatal cocaine-exposure induces marked changes in the organization of the developing retina.     

An overview of the multispecies VPA — theory and applications

Summary Multispecies virtual population analysis is an attempt to take species interactions into account when assessing the status of fish stocks. It was introduced primarily with the aim of lowering the uncertainty in the natural mortality rate as used in single species VPA and to take account of variability between years and ages by calculating inside the model the part of the mortality rate caused by predation. The output of the MSVPA is therefore —in addition to stock sizes and fishing mortality rates as in single species VPA —the amounts consumed of the various species by the predators included in the analysis.The MSVPA model of the predation interactions results in a set of coupled non-linear equations which must be solved for each time step in the analysis. Key parameters in the model are the so-called suitability coefficients, measuring the relative suitability of one species as prey for another species. These parameters must be estimated inside the model and this estimation requires data on the stomach contents of the predators in the model. The MSVPA makes two key assumptions: constant ration size (i.e. independent of time for each species-age combination) and hence fixed weights-at-age and a model of prey selection which leads to a type ii functional feeding response. These assumptions do not hold for all areas and therefore limit the applicability of the MSVPA in its present form.The MSVPA is probably one of the more successful multispecies models in fisheries. Its main application to date has been to the North Sea, and although it has not been used directly as a management tool it has provided input values of parameters used in assessment models as well as valuable insights into the system. For example, it has demonstrated that an increase in mesh size can result in lower long-term yields, an effect opposite to what is predicted if species interactions are ignored. Such insights into the dynamics of the system are useful and MSVPA may therefore have an indirect role to play in management. Nevertheless, due to many uncertainties involved in multispecies modelling in general and MSVPA in particular, it seems doubtful that the use of MSVPA in fisheries management will be much greater in the immediate future than it is at present.     

Batch culture of Candida utilis in a medium deprived of a phosphorous source

Summary Candida utilis var. major NRRL-Y-1084 was grown in a defined medium without a phosphorous (P) source. During the exponential phase, cells divided according to a specific growth rate of 0.32 h^-1, which is lower than the usual rate for a balanced medium (0.4–0.6 h^-1). The relative P content of the biomass decreased from 2.70% to 0.75% over a period of 6 h, including 2 h of cell division arrest. At the end of this period there was another interruption of cell division. After that, multiplication restarted at a considerably lower rate and it deviated slightly from the exponential pattern. The stationary phase began when biomass P content reached 0.4%–0.5%, slowly decreasing afterwards to 0.25–0.20%. Biomass synthesis was less affected than cell division by the relative decrease of endogenous P, the two processes differing partially in their kinetics. Cell lysis started shortly before the stationary phase and affected about 20% of the population by the end of the assay. RNA and P content of the resulting biomass were 2.4% and 0.25% respecitvely, P being mainly incorporated to RNA.The relationship of biomass production to glucose uptake was very low, probably because the marked P deficiency called for an increase in energy consumption for growth and specially for maintenance. Compared with yeasts grown in a balanced medium, 40% increase in glycogen was observed, whereas no mean changes in the content of cell wall carbohydrates (glucan and mannan) and that of true protein were found.Member of the Scientific Researcher's Career of the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET). Agrentina