Cytotaxonomy of species of Vernonia, section Lepidaploa, group Axilliflorae (Asteraceae, Vernonieae)

Mitotic chromosomes of eight populations of six species of Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa , group Axilliflorae ) were studied to assess the validity of maintaining the genus as proposed currently ( sensu Baker) or of splitting it into several smaller genera ( sensu Robinson). The species were collected in areas of 'cerrado' and 'campo rupestre' in southern and central-western Brazil. The chromosome numbers were 2 n  = 20–40 and karyotypic analysis showed a predominance of metacentric chromosomes, with some submetacentrics. B chromosomes were seen in one population of V. geminata . The chromosomes varied in length from 0.9 to 4.6 µm, with a total chromatin length of 29.7–45.0 µm and a symmetry index of 41.2–46.9%. The intrachromosomal asymmetry index varied from 0.13 to 0.29, and the interchromosomal asymmetry index varied from 0.15 to 0.21. The dispersion diagram showed that population 1 of V. geminata had the most asymmetrical karyotype. These results do not provide sufficient evidence for a conclusive cytotaxonomic discussion of Vernonia , mainly because of the impossibility of associating any infrageneric group with specific karyotypic characters, and also because of the small number of species analysed so far.  © 2007 The Linnean Society of London. Botanical Journal of the Linnean Society , 2007, 154 , 99–108.     

Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon

Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondônia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha^–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha^–1 y^–1 between the third and the eighteenth years after abandonment. CO₂ sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.     

Recombination indices in species of Erythrina L. (Leguminosae, Papilionoideae)

Darlington's recombination indices were calculated for eight species of Erythina by adding the mean chiasma frequency and the haploid chromosome number of each species. The recombination indices distinguished subgenus Erythraster (two species with greater mean chiasma frequency) from subgenera Micropteryx and Eythrina. This discrimination corroborates literature data on pollen morphology. It was not possible to separate groups at sectional level using recombination index. The recombination indices were also compared with data on breeding system and pollinators, available in literature, to investigate Grant's hypothesis on the occurrence of compensatory mechanisms in the regulation of recombination in plants. The data on breeding systems in Eythrina are very incomplete and it was not possible to correlate values of recombination indices with autogamy or allogamy. Species visited by hummingbirds showed lower recombination indices than species visited by other kind of pollinators.     

In Vitro Development of Exoerythrocytic Forms of Plasmodium Gallinaceum Sporozoites In Avian Macrophages

ABSTRACT Exoerythrocytic forms of Plasmodium gallinaceum were cultured in vitro using salivary gland sporozoites extracted from experimentally infected Aedes fluviatilis mosquitoes. the host cells were macrophage precursors from chicken bone marrow. At various times after introduction of Sporozoites, the cultures were stained by Giemsa or by immunofluorescence assay (IFA) using anti-sporozoite-specific monoclonal antibodies (MAb). the time to complete parasite development in vitro was 50-70 h. By 70 h, ruptured segmenters and free merozoites were visible within the cells. Inoculation of normal chickens with infected cultures induced parasitemia after a pre-patent period of 10-11 days. In vitro young exoerythrocytic forms, late schizonts that include the matured segmenters, and free merozoites shared common antigens with the sporozoites as revealed by IFA using anti-sporozoite-specific MAbs. Our data indicate that macrophages support development of P. gallinaceum sporozoites and that the circumsporozoite proteins are present until Ac end of the primary exoerythrocytic schizogony.     

Karyology of some Brazilian species of Alismataceae

The family Alismataceae ( sensu Cronquist) comprises 11 genera and 75 species of aquatic and semiaquatic herbs. In Brazil, only the two most speciose genera, Echinodorus Rich. ex Engelm. and Sagittaria L., are present. The chromosome number 2 n  = 22 is common to all species. We present karyotypes for eight species, together with their asymmetry index (TF%) and total chromatin length (TCL). All karyotypes have high karyotypic asymmetry and TCL, due to their large and mostly acrocentric chromosomes. The chromosomal evolution of the Alismatidae group is discussed.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 159−164.     

Litter decomposition in grasslands of Central North America (US Great Plains)

One of the major concerns about global warming is the potential for an increase in decomposition and soil respiration rates, increasing CO₂ emissions and creating a positive feedback between global warming and soil respiration. This is particularly important in ecosystems with large belowground biomass, such as grasslands where over 90% of the carbon is allocated belowground. A better understanding of the relative influence of climate and litter quality on litter decomposition is needed to predict these changes accurately in grasslands. The Long‐Term Intersite Decomposition Experiment Team (LIDET) dataset was used to evaluate the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon : nitrogen, and lignin : nitrogen ratios) on leaf and root decomposition in the US Great Plains. Wooden dowels were used to provide a homogeneous litter quality to evaluate the relative importance of above and belowground environments on decomposition. Contrary to expectations, temperature did not explain variation in root and leaf decomposition, whereas precipitation partially explained variation in root decomposition. Percent lignin was the best predictor of leaf and root decomposition. It also explained most variation in root decomposition in models which combined litter quality and climatic variables. Despite the lack of relationship between temperature and root decomposition, temperature could indirectly affect root decomposition through decreased litter quality and increased water deficits. These results suggest that carbon flux from root decomposition in grasslands would increase, as result of increasing temperature, only if precipitation is not limiting. However, where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands. Under homogeneous litter quality, belowground decomposition was faster than aboveground and was best predicted by mean annual precipitation, which also suggests that the high moisture in soil accelerates decomposition belowground.     

Identification of multi‐component trail pheromones in the most evolutionarily derived termites,the Nasutitermitinae (Termitidae)

In the present study, trail pheromone blends are identified for the first time in termites. In the phylogenetically complex Nasutitermitinae, trail‐following pheromones are composed of dodecatrienol and neocembrene, the proportions of which vary according to species, although neocembrene is always more abundant than dodecatrienol (by 25–250‐fold). Depending on species, termites were more sensitive to dodecatrienol or to neocembrene but the association of both components always elicited significantly higher trail following, with a clear synergistic effect in most of the studied species. A third component, trinervitatriene, was identified in the sternal gland secretion of several species, but its function remains unknown. The secretion of trail pheromone blends appears to be an important step in the evolution of chemical communication in termites. The pheromone optimizes foraging, and promotes their ecological success. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 20–27.     

Amphotericin B-Induced Carbohydrate Changes on the Trypanosoma cruzi Surface Membrane

ABSTRACT Changes in the cell surface carbohydrates of Trypanosoma cruzi epimastigotes induced by Amphotericin B (AmB) were assessed by chemical methods and by agglutination assay employing a panel of highly purified lectins of various sugar specificities, Escherichia coli K12 with mannose-sensitive fimbriae was also used as an agglutination probe. Amphotericin B caused a decrease in the total carbohydrate content of all glycoconjugate fractions isolated. Exposure to AmB strongly affected the mannose/galactose ratio (1:5) in the CHCI3/methanol/H2O soluble fraction. These sugars in 1.4:1 ratio were the major hexose components of control cells. The decrease in the mannose content (48 to 15%) after AmB treatment agrees with the marked decrease in the T. cruzi cell surface receptors for fimbriated E. coli K12. Also, an increase in the galactose content (74%) as compared with control cells (34%) is in agreement with the peanut agglutinin and Euonymus europaeus lectins agglutination results. Differences in the cell surface carbohydrates induced by AmB could be associated with alterations in the membrane structure and organization.     

Development and cytology of pollen in Dahlstedtia Malme (Leguminosae: Papilionoideae)

Microsporogenesis, chromosome number, meiotic behaviour and meiotic index were investigated in Dahlstedtia pinnata and D . pentaphylla , two legume species occurring largely in Brazil, in order to ascertain whether the pollen could limit fertilization events. Archesporial cells originate primary sporogenous and anther wall precursor cells, the tapetum is uniseriate, uninucleate and glandular. Tetrads are tetrahedric or decussate, and cytokinesis is of the simultaneous type. Mature pollen grains are tricolpate and bicellular. No abnormalities in microsporogenesis were found. In both species the chromosome number is n = 11, a number not reported previously. The base number for Dahlstedtia is also 11, because cytological observations include both species of Dahlstedtia . D. pentaphylla has a higher meiotic index and lower individual variation values, and it is considered meiotically stable. Its pollen grains do not limit fertilization. D. pinnata has a lower meiotic index, and the pollen is one of the factors which limit fertilization. Furthermore, D. pinnata has numerous adventitious shoots, which suggest that vegetative propagation is important in its reproductive process. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 138 , 461–471.