Karyotype differentiation among Spondias species and the putative hybrid Umbu-cajá (Anacardiaceae)

Spondias L. comprises at least nine Neotropical species, including the widely cultivated S. monbim and S. tuberosa. Umbu‐cajá, a putative hybrid between these two species, is also grown. In this paper, the karyotypes of five Spondias species and Umbu‐cajá were analysed for evidence of this hybridization. Chromosome banding with chromomycin A₃ and the distribution of 5S and 45S rDNA sites were used to characterize the plants, also genomic in situ hybridization using nuclear DNA from both putative parents and the hybrid as probes. All material presented the same chromosome number (2n = 32) and morphology, but differed in the number and distribution of bands. Spondias monbim and S. tuberosa, the supposed relatives of Umbu‐cajá, displayed similar banding patterns, with five to six chromosome pairs having terminal bands, whereas Umbu‐cajá exhibited bands on both members of nine chromosome pairs. The three other species, S. venulosa, S. cytherea and S. purpurea, showed less closely related karyotypes, with bands in 12–18 chromosome pairs. In situ hybridization with 5S and 45S rDNA probes revealed one site of each probe per haploid chromosome complement in all material. However, in S. tuberosa, the location of 5S rDNA was different from the other species and found no counterpart in Umbu‐cajá. Several tests with total DNA from S. mombin and S. tuberosa against metaphase chromosomes of Umbu‐cajá failed to differentiate the individual genomes in the hybrid. From the chromosome banding and the distribution of rDNA sites, as well as from the genomic in situ hybridization, it seems clear that Umbu‐cajá is related closely to S. monbim and S. tuberosa, but it is karyotypically homozygous and distinct from theses other species. Karyotypically, the three other investigated species were related less closely to Umbu‐cajá. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 541–547.     

The effects of shrimps on benthic material in a Brazilian island stream

1. Shrimps are abundant in many tropical coastal streams. Studies in Central America and the Caribbean have demonstrated the importance of shrimps in removing sediments and altering the composition of the benthos. Previous work in our study area showed that ephemeropterans and not shrimps were important in removing benthic material. 2. Here we used an experimental exclusion to test the hypothesis that shrimps exert strong influence on sediment dynamics with direct and indirect effects on the benthic algal and faunal community at a site where they are the predominant element of macrofauna. We used electricity to exclude Macrobrachium olfersi and Potimirim glabra from small quadrats (0.135 m²) for 34 days in a stream located at Ilha Grande, Rio de Janeiro state, Brazil. We analysed benthic sediment dynamics and community colonisation during this period on artificial substrates in electrified and not‐electrified quadrats. 3. Significantly higher sediment accrual had occurred in the electrified treatment after 14 days and persisted for the 34‐day course of the experiment; substrates protected from shrimps contained about four times as much ash‐free dry mass (AFDM) as those of the controls. After 34 days, significantly more pennate diatoms were present in the exclusion treatment, but chlorophyll was not significantly different between treatments. Densities of baetid ephemeropteran nymphs were significantly higher in the presence of shrimps. 4. We attribute all these effects to the atyid P. glabra, the more abundant and active shrimp observed in the control treatment. Our results suggest that atyid shrimps played an important role related to sediment removal on hard substrate by direct ingestion and ‘bioturbation’. They reduced certain components of the periphyton (pennate diatoms) without affecting primary production (chlorophyll a). The activity of these shrimps on periphyton affected also faunal components such as baetid ephemeropterans and seems to determine the composition of the benthic community.     

Surface Anionic Groups in Symbiote-Bearing and Symbiote-Free Strains of Crithidia deanei1

The surface anionic groups of symbiote-bearing and symbiote-free strains of Crithidia deanei were compared by determining cellular electrophoretic mobility, by ultrastructural cytochemistry, and by identification of sialic acids by thin-layer and gasliquid chromatography. Symbiote-free Crithidia deanei has a highly negative surface charge (-0.9984 μm?s^-1? V^-1? cm), which is slightly reduced (-0.8527 μm?s^-1? V^-1? cm) by the presence of the endosymbiote. Treatment of both strains of C. deanei with neuraminidase decreased significantly the electrophoretic mobility of cells toward the cathodic pole, indicating the existence of exposed sialic acid residues responsible for the negative charge on the protozoan cell surface. Thin-layer and gas-liquid chromatography showed that N-glycolyl- and N-acetylneuraminic acids were present in both strains of C. deanei.     

Contribution of transpiration to forest ambient vapour based on isotopic measurements

Using a simple isotope mixing model, we evaluated the relative proportion of water vapour generated by plant transpiration and by soil evaporation at two sites in the Amazon basin. Sampling was carried out at two different soil covers (forest and pasture), in a seasonal tropical rainforest at eastern Amazon where major deforestation is the result of land-use change, and compared to a less seasonal central Amazon forest. In both forests, vapour from transpiration was responsible for most, if not all, of the water vapour generated in the forest, while it could not be detected above the grassy pastures. Thus the canopy transpiration may be a major source of water vapour to the forest and perhaps to the atmosphere during the dry season. The results are discussed in relation to predictive models based on net radiation that usually are not able to distinguish between transpiration and evaporation.     

Mechanism of Acquired Immunity Induced by “Leptomonas pessoai” against Trypanosoma cruzi in Mice*

Living culture forms of “Leptomonas pessoai” cross protected mice against T. cruzi challenge infection. Circulating antibodies have been detected in the immunized mice by immunodiffusion analysis, passive hemagglutination, complement fixation test and antibody binding assay; these antibodies cross reacted with T. cruzi extracts. A cellular immune response was indicated by leucocyte migration inhibition using L. pessoai and T. cruzi antigens, strongly suggesting a role for cell-mediated immunity in the mechanism of protection induced by L. pessoai.     

Fine Structure and Cytochemistry of the Nucleus and the Kinetoplast of Epimastigotes of Trypanosoma cruzi1

ABSTRACT. Ultrastructural cytochemical techniques were used to analyze the nucleus and the kinetoplast of epimastigotes of Trypanosoma cruzi. With the use of ethanolic phosphotungstic acid, which detects basic proteins, reaction product was seen in the chromatin and at the periphery of the kinetoplast. Thallium alcoholate, which interacts with DNA, stained strongly the whole kinetoplast and the chromatin. With the use of a silver impregnation method that detects acidic nucleolar proteins, silver granules were seen preferentially located in the central region of the nucleolus. With the EDTA method, which reveals the presence of ribonucleoproteins, staining was observed in the nuclear pores. Also 6–8 nm fibrils, 25 nm and 40 nm granules, which correspond to the perichromatin fibers, interchromatin granules and the perichromatin granules, respectively, were identified in the nucleus. The EDTA method also revealed the presence of 40 nm granules in the kinetoplast. These granules were seen mainly at the two extremities of the kinetoplast. Freeze-fracture images indicate that the nuclear membrane contains ca. 9 pores/μm² of nuclear surface area. The mean diameter of the pores was 80 nm. All these results suggest that epimastigotes of T. cruzi have a very active nucleus and a high rate of nucleocytoplasmic interchange.     

Surface Charge of Trypanosoma cruzi. Binding of Cationized Ferritin and Measurement of Cellular Electrophoretic Mobility*

SYNOPSIS The surface charge of epimastigote and trypomastigote forms of Trypanosoma cruzi was evaluated by means of binding of cationized ferritin to the cell surface as visualized by electron microscopy, and by direct measurements of the cellular microelectrophoretic mobility (EPM). Epimastigote forms had a mean EPM of -0.52 μm^.s^-1.V^-1.cm and were lightly labeled with cationized ferritin. In contrast, bloodstream trypomastigotes had a much higher EPM (-1.14), and the surface was heavily labeled with cationized ferritin. When trypomastigotes from stationary phase cultures were isolated on DEAE cellulose columns, the mean EPM was found to be significantly lower (-0.63), and labeling with cationized ferritin decreased. With a mixed population containing epimastigote, trypomastigote, and intermediate forms, EPM values ranging between -0.70 to -1.14 were found. From these observations we conclude that there is a definite increase in negative surface charge during development from epi- to trypomastigote forms of T. cruzi.