Isolation of clones on chromosome 7 that contain recognition sites for rare-cutting enzymes by oligonucleotide hybridization

Five G/C-containing oligonucleotides that include the recognition sequences of rare-cutting restriction enzymes have been used to isolate almost 100 different genomic segments from chromosome 7 that contain recognition sites for those enzymes. Hybridization and washing at 27 degrees C allow the use of 8-bp radiolabeled oligonucleotides to detect specific G/C-containing sequences in less than 1 ng of cloned DNA. This method was used to isolate 9 positive clones from 138 previously isolated single-copy probes from a flow-sorted chromosome 7 library. The specificity of the method was confirmed by showing that clones that gave positive hybridization signals also contained the corresponding restriction site. The oligonucleotides were also used to analyze approximately 12,000 kb of genomic sequence from a newly constructed chromosome 7 cosmid library that yielded 88 positive cosmids from 350 analyzed. The average distances between binding sites ranged from 200 to 690 kb and was independent of the number of CpG residues present in the oligonucleotide. Confirmation that clones containing restriction sites for these rare-cutting enzymes are located near genes was obtained by hybridization to RNA and cross-species DNA blots.     

Labeled nitrogen fertilizer research with urea in the semi-arid tropics

Summary Field studies with bordered microplots were conducted on an Alfisol in the semiarid tropics of India to determine (1) the fate of¹⁵N-labeled urea applied to dryland sorghum in two successive rainy seasons and (2) the effect of method of application on N fertilizer efficiency. Recoveries of¹⁵N-labeled fertilizers by above-ground plant parts ranged from 46.7% to 63.6% in 1981 when the rainfall was above the average and from 54.4% to 66.9% in 1980 when the rainfall was near the average. Small (0.014 g) pellets of urea applied twice as postemergent applications in separate 5 cm deep bands were more effective than single preemergent applications either surface applied or incorporated. Both banding and the split applications contributed to overall fertilizer efficiency. Large (1.0 g) pellets of urea (supergranules) placed at a depth of 5 cm were also superior to the incorporated, small-pellet treatment in 1981. The¹⁵N-balance data for the soil (0–90 cm in depth)-plant system in 1981 showed that the unaccounted-for fertilizer N ranged from 5.1% to 20.6%. An important finding was that high grain yields, in excess of 6,000 kg/ha, with N fertilizer losses of less than 10% could be obtained through fertilizer management during a very wet season. The data from the Alfisol experiments were compared with data from similar Vertisol experiments; N fertilizer losses resulting from incorporated and surface applications were greater for Vertisols than for Alfisols in the wetter year.     

The effect of habitat fragmentation on the scorpion assemblage of a Brazilian Atlantic Forest

Habitat fragmentation is a topic widely studied in ecology; however, its effects on the assemblage of the order Scorpiones is less well understood. Aiming to fill this gap, this study assessed the effect of fragmentation on the assemblage of these arachnids in 12 Brazilian Atlantic forest fragments. Five environmental variables were measured (depth and dry mass of litter, understory density, canopy openness, and diameter at breast height of the trees), and the fragment area, vegetation cover, connectivity and elevation assessed. The animals were collected during the dry season and, identified at night with the use of ultraviolet light lamps. The analyzed scorpion assemblage in the landscape was characterized by the species Tityus pusillus, T. stigmurus, T. neglectus, T. brazilae, and Ananteris mauryi, with a maximum of three species co-occurring per fragment. Only the fragment size and the dry mass of litter showed a positive relationship with the composition of scorpions. These results suggest that the habitat of scorpions responds to environmental attributes and landscape metrics at both higher (fragment size) and lower (leaf litter) scales. Our study was able to expand our knowledge of how scorpions respond to habitat changes in the Atlantic Forest. We conclude that fragmentation and habitat quality are determining factors for the assemblage of these arachnids.     

Chaos and the (un)predictability of evolution in a changing environment

Among the factors that may reduce the predictability of evolution, chaos, characterized by a strong dependence on initial conditions, has received much less attention than randomness due to genetic drift or environmental stochasticity. It was recently shown that chaos in phenotypic evolution arises commonly under frequency‐dependent selection caused by competitive interactions mediated by many traits. This result has been used to argue that chaos should often make evolutionary dynamics unpredictable. However, populations also evolve largely in response to external changing environments, and such environmental forcing is likely to influence the outcome of evolution in systems prone to chaos. We investigate how a changing environment causing oscillations of an optimal phenotype interacts with the internal dynamics of an eco‐evolutionary system that would be chaotic in a constant environment. We show that strong environmental forcing can improve the predictability of evolution by reducing the probability of chaos arising, and by dampening the magnitude of chaotic oscillations. In contrast, weak forcing can increase the probability of chaos, but it also causes evolutionary trajectories to track the environment more closely. Overall, our results indicate that, although chaos may occur in evolution, it does not necessarily undermine its predictability.     

Karyotype differentiation of four Cestrum species (Solanaceae) revealed by fluorescent chromosome banding and FISH

The karyotypes of four South American species of Cestrum (C. capsulare,C. corymbosum,C. laevigatum and C. megalophylum) were studied using conventional staining, C-CMA/DAPI chromosome banding and FISH with 45S and 5S rDNA probes. The karyotypes showed a chromosome number of 2n = 2x = 16, with metacentric chromosomes, except for the eighth submeta- to acrocentric pair. Several types of heterochromatin were detected, which varied in size, number, distribution and base composition. The C-CMA(+) bands and 45S rDNA were located predominantly in terminal regions. The C-CMA (+) /DAPI (+) bands appeared in interstitial and terminal regions, and the C-DAPI (+) bands were found in all chromosome regions. The 5S rDNA sites were observed on the long arm of pair 8 in all species except C. capsulare, where they were found in the paracentromeric region of the long arm of pair 4. The differences in band patterns among the species studied here, along with data from other nine species reported in the literature, suggest that the bands are dispersed in an equilocal and non-equilocal manner and that structural rearrangements can be responsible for internal karyotype diversification. However, it is important to point out that the structural changes involving repetitive segments did not culminate in substantial changes in the general karyotype structure concerning chromosome size and morphology.     

Resprouting Ability of Six Atlantic Shrub Species

Resprouting from subterranean structures is a principal method of vegetative regeneration that many shrub species show after a disturbance. This study, therefore, aims to determine the resprouting capacity and intensity of six dominant species in an Atlantic shrubland area located in the NW of the Iberian Peninsula and compare their resprouting and germinating strategies. Resprouting intensity is measured using three variables: individual probability of resprouting, number of resprouts and length of these sprouts in three plant-age classes. The intensity for each species was calculated using a simple index (IRI) that included the three measured variables. All studied species, excepting Erica umbellata, could resprout. According to the IRI values, there are three groups of species: strong resprouters (Ulex europaeus, Ulex minor and Pterospartum tridentatum), weak resprouters (Ulex micranthus and Genista triacanthos) and non-resprouters (E. umbellata). The germination of strong resprouters is highly stimulated by fire. Frequent disturbances remove the non- and weak resprouter populations and promote the strong resprouter ones.     

Les larges vacuoles des têtes spermatiques sont-elles associées à des altérations du noyau ou de l’acrosome du spermatozoïde ?

Objective

The aim of this study was to detect acrosome and nucleus alterations in isolated spermatozoa with large vacuoles detected by MSOME (Motile Sperm Organelle Morphology Examination), named type 3 spermatozoa and defined by the presence of one or more vacuoles occupying more than 13% of the sperm head area.

Material and methods

Twenty infertile men were included in this study. Whole sperm and isolated spermatozoa were compared. Spermatozoa acrosome and nucleus were explored using 1) proacrosin immunostaining with a monoclonal antibody (4D4), 2) DNA fragmentation with TUNEL assay, 3) chromatin condensation with aniline blue staining, and 4) aneuploidy after fluorescence in situ hybridization (FISH) and analysis by electron transmission and confocal microscopy.

Results

Acrosome abnormalities were significantly increased in type 3 spermatozoa compared towhole sperm(77.8 ± 2.49% vs. 70.6 ± 2.62%). DNA fragmentation was similar in type 3 spermatozoa compared towhole sperm(14.5 ± 3.45%vs. 11.5 ± 1.25%). Chromatin condensation was significantly altered in isolated spermatozoa as well as aneuploidy frequencies (50.4 ± 3.10% vs. 26.5 ± 2.60% and 7.8 ± 1.98% vs. 1.3 ± 0.18%). Large vacuoles have an exclusive nuclear location, confirmed by electron and confocal microscopy.

Conclusion

Large vacuoles are probably due to sperm nucleus maturation dysfunction during spermiogenesis.     

Characterization of the orf1glnKamtB operon of Herbaspirillum seropedicae

Herbaspirillum seropedicae is an endophytic nitrogen-fixing bacterium that colonizes economically important grasses. In this organism, the amtB gene is co-transcribed with two other genes: glnK that codes for a PII-like protein and orf1 that codes for a probable periplasmatic protein of unknown function. The expression of the orf1glnKamtB operon is increased under nitrogen-limiting conditions and is dependent on NtrC. An amtB mutant failed to transport methylammonium. Post-translational control of nitrogenase was also partially impaired in this mutant, since a complete switch-off of nitrogenase after ammonium addition was not observed. This result suggests that the AmtB protein is involved in the signaling pathway for the reversible inactivation of nitrogenase in H. seropedicae.     

Nesting biology of Centris flavifrons (Friese) (Hymenoptera: Apidae, Centridini), one of the main pollinators of Byrsonima crassifolia L. Kunth in Maranhão, Brazil

The Centridini has almost 176 species distributed mainly in the tropic regions of America. Although they are considered key pollinators in the maintenance of many vegetal species, data about their bionomics are restrict. Nesting activity is known for 11 species, out of the 21 that are considered pollinators of murici, Byrsonima crassifolia L. Kunth, a valuable biomonitoring specie. A study of the nesting biology of Centris flavifrons (Friese) was conducted in the state of Maranh?o, Brazil, during the active period of the adults (May through December). Nests were aggregated. The females excavated their nests on flat surfaces of hard soils. Fifteen nests were dug and we only found cells in six of them. The nests architecture consisted of a single unbranched tunnel, with only one cell in the vertical position at the end, which was 25 cm to 50 cm away from the entrance. Nocturnal activity was observed in the nests building. The pollen analysis of the contents of four cells allowed to identify 23 floral species, six of them Malpighiaceae. Six floral species were registered visiting C. flavifrons by the first time: Lecythis lurida (Miers) Mori, Hymenea courbaril L., Myrcea sp., Protium sp., Tetrapterys sp. and Thalisia sp.