Identification and genetic diversity of Fusarium sacchari associated with pokkah boeng disease of sugarcane in Northeast Brazil

Isolates from the Fusarium fujikuroi species complex, mainly F. sacchari, have been reported to be the causal agents of pokkah boeng in sugarcane in Brazil. However, inadequate information was available on the occurrence and genetic diversity of F. sacchari in Northeast Brazil, which is a limiting factor on management. Thus, isolates of F. subglutinans sensu lato from sugarcane plants with symptoms of pokkah boeng were evaluated using the sexual cross-fertility to determine species. All the isolates produced black perithecia when they were crossed with the test isolates of F. sacchari. Three weeks after the crossing, the formation of fertile ascospores cirri was observed. Thirty-four isolates were self-sterile hermaphrodites, while 21 were fertile only as males. Five isolates were homothallic. The effective size [N_e(f)] of the population as a function of the frequency of hermaphrodites and female sterile strains was 95.5%. The F. sacchari isolates were separated into four genetic groups independent of geographic location. The mean of polymorphism among all populations was 79%, and the average unbiased genetic diversity (uh) was considered moderate (0.31). This study in addition to confirming that F. sacchari as the main species associated with pokkah boeng in sugarcane in Northeast Brazil, reveals the relationship of mating type and genetic diversity of F. sacchari. The unrestricted gene flow between regions is probably the best explanation for the low geographic correlation. This knowledge will help in the adoption of management measures with fungicides or resistant cultivars.     

Safeguarding sloths and anteaters in the future: Priority areas for conservation under climate change

Sloths and anteaters form the monophyletic order Pilosa, which is currently represented by only 16 extant species distributed exclusively in the Neotropics. This present-day low species richness is an inheritance of the Pleistocene megafaunal extinctions, where over 65 Pilosa species known from the fossil record went extinct. The large number of species lost in the recent past suggests that this group is greatly vulnerable to extinction. Here, we propose long-term priority conservation areas for the order Pilosa, considering different future climate change scenarios, biotic stability, and the multiple dimensions of the group's biodiversity, such as species richness, species endemism, and phylogenetic diversity. Projections of species distribution for future scenarios show increased fragmentation and clear habitat loss as the Amazon Forest is replaced by savanna-like habitats. Conservation solutions were highly congruent for the different dimensions of biodiversity, with priority areas emerging mainly in the Atlantic Forest, Amazonian wetlands, highlands of Ecuador, and the Central American isthmus. Expanding the currently protected areas network by 6% with the proposed priority areas, independently of which future climatic scenario is considered, can increase sloths and anteaters' coverage in the future by 12%. As a group of high phylogenetic and ecological importance, future conservation planning should deliberately aim to protect areas favorable to Pilosa, especially given the current scenario of environmental dismantling and neglect of critical Neotropical biomes.     

Mechanism of chromium(VI) carcinogenesis

Since chromium(VI) is unreactive toward DNA under physiological conditions in vitro, the ability of carcinogenic chromium(VI) compounds to damage DNA depends on the presence of cellular redox components that reduce chromium(VI) to reactive species capable of interacting with DNA. We have examined the role of glutathione and hydrogen peroxide in chromium(VI)-induced DNA damage in vitro. Upon reaction with chromium(VI), glutathione produced chromium(V) and glutathione thiyl radical reactive intermediates, whereas hydrogen peroxide produced chromium(V) and hydroxyl radical. Reaction of DNA with chromium(VI) in the presence of glutathione resulted in binding of chromium and glutathione to DNA with little or no DNA strand breakage. Reaction of DNA with chromium(VI) in the presence of hydrogen peroxide produced the 8-hydroxydeoxy-guanosine adduct and extensive DNA strand breakage in the absence of significant Cr-DNA adduct formation. These results suggest that the nature of chromium(VI)-induced DNA damage will be strongly dependent on reactive intermediates such as chromium(V), glutathione thiyl radical, and hydroxyl radical, produced by cellular components active in chromium(VI) metabolism. In order to assess the ability of chromium(VI)-induced DNA damage to affect the normal template function of DNA, we investigated the effects of chromium(VI) on steady-state mRNA levels of various genes in chick embryo liver in vivo, and compared the effects to the levels of DNA damage observed. Chromium(VI) induced DNA-protein and DNA interstrand cross-links in chick embryo liver in vivo and suppressed the induction of 5-aminolevulinic acid synthase and cytochrome P-450 mRNA expression by porphyrinogenic drugs. In contrast, chromium(VI) increased the basal levels of expression of these two inducible genes, but had little or no effect on the expression of the constitutive albumin, β-actin, and conalbumin genes. Comparison of the time course of formation and repair of DNA damage with that of changes in gene expression suggests that chromium(VI) may form a mono-adduct prior to formation of DNA cross-links, and that chromium(VI)-induced DNA lesions may target certain classes of genes and lead to changes in their expression.     

The lateral spread of signal between bipolar cells of the tiger salamander retina

When mapped with a small spot of light, the central receptive fields of bipolar cells in the salamander retina are much larger than the extent of bipolar cell dendrites. Furthermore responses of bipolar cells to distant spots of light are considerably delayed relative to proximal spots. Using quantitative modelling, electrical coupling between bipolar cells is examined and rejected as a sufficient explanation of the data. An active process appears to shape signal waveform as signals spread laterally in the bipolar cell layer. Chemical synaptic coupling between bipolar cells is considered and shown to be inconsistent with the data. It is suggested that local, transient negative feedback from amacrine cells is involved in shaping bipolar cell signals.     

Resistance ofBradyrhizobium japonicum strains to selected antibiotics

The majority of the 50Bradyrhizobium japonicum strains tested were resistant to ampicillin, kanamycin, streptomycin and tetracycline in concentrations below 100 g/ml but resistant to chloramphenicol in concentrations equal to or above 100 g/ml. Two strains had high levels of resistance to ampicillin and to streptomycin and six strains were very sensitive to several antibiotics.

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Résumé La majorité de la cinquantaine de souches deBradyrhizobium japonicum s'est révélée résistante à l'ampicilline, à la kanamycine, à la streptomycine et à la tétracycline aux concentrations intérieures à 100g/ml mais au chloramphenicol aux concentrations égales ou supérieures à 100 g/ml. Deux souches présentalent un haut degré de résistance à l'ampicilline et à la streptomycine. Six souches étaient très sensibles à plusleurs antibiotiques.

     

Patterns of ribosomal RNA evolution in salamanders

Sequence comparisons are presented for four segments of the large subunit of ribosomal RNA, including divergent domains D7a and D7b, portions of the large divergent domains D2, D3, and D8, and evolutionarily conservative sequences flanking divergent domains. These results resolve phylogenetic relationships among exemplars of seven families of salamanders and the three amphibian orders. Phylogenetic analysis confirms the prediction that divergent domains feature the highest relative rates of base substitution and length variation within the ribosome, but the divergent domains evolve more slowly than nuclear noncoding DNA and the silent sites of structural genes. Base substitutions demonstrate approximately twice as many transitions as transversions and an uneven distribution among sites within the divergent domains but no apparent bias in base composition. Length mutations are primarily small insertions and deletions, with deletions predominating. The divergent domains appear to be a good source of phylogenetic information for evolutionary events occurring approximately 100-200 million years ago.      

Drivers of diversity in Macaronesian spiders and the role of species extinctions

Aim To identify the biogeographical factors underlying spider species richness in the Macaronesian region and assess the importance of species extinctions in shaping the current diversity. Location The European archipelagos of Macaronesia with an emphasis on the Azores and Canary Islands. Methods Seven variables were tested as predictors of single‐island endemics (SIE), archipelago endemics and indigenous spider species richness in the Azores, Canary Islands and Macaronesia as a whole: island area; geological age; maximum elevation; distance from mainland; distance from the closest island; distance from an older island; and natural forest area remaining per island – a measure of deforestation (the latter only in the Azores). Different mathematical formulations of the general dynamic model of oceanic island biogeography (GDM) were also tested. Results Island area and the proportion of remaining natural forest were the best predictors of species richness in the Azores. In the Canary Islands, area alone did not explain the richness of spiders. However, a hump‐shaped relationship between richness and time was apparent in these islands. The island richness in Macaronesia was correlated with island area, geological age, maximum elevation and distance to mainland. Main conclusions In Macaronesia as a whole, area, island age, the large distance that separates the Azores from the mainland, and the recent disappearance of native habitats with subsequent unrecorded extinctions seem to be the most probable explanations for the current observed richness. In the Canary Islands, the GDM model is strongly supported by many genera that radiated early, reached a peak at intermediate island ages, and have gone extinct on older, eroded islands. In the Azores, the unrecorded extinctions of many species in the oldest, most disturbed islands seem to be one of the main drivers of the current richness patterns. Spiders, the most important terrestrial predators on these islands, may be acting as early indicators for the future disappearance of other insular taxa.     

Lipophilic phenolic antioxidants: Correlation between antioxidant profile,partition coefficients and redox properties

Lipophilic compounds structurally based on caffeic, hydrocaffeic, ferulic and hydroferulic acids were synthesized. Subsequently, their antioxidant activity was evaluated as well as their partition coefficients and redox potentials. The structure–property–activity relationship (SPAR) results revealed the existence of a clear correlation between the redox potentials and the antioxidant activity. In addition, some compounds showed a proper lipophilicity to cross the blood–brain barrier. Their predicted ADME properties are also in accordance with the general requirements for potential CNS drugs. Accordingly, one can propose these phenolic compounds as potential antioxidants for tackling the oxidative status linked to the neurodegenerative processes.     

Plasticity comparisons between plants and animals: Concepts and mechanisms

This review attempts to present an integrated update of the issue of comparisons of phenotypic plasticity between plants and animals by presenting the problem and its integrated solutions via a whole-organism perspective within an evolutionary framework. Plants and animals differ in two important aspects: mobility and longevity. These features can have important implications for plasticity, and plasticity may even have facilitated greater longevity in plants. Furthermore, somatic genetic mosaicism, intra-organismal selection, and genomic instability contribute to the maintenance of an adaptive phenotype that is especially relevant to long-lived plants. It is contended that a cross-kingdom phylogenetic examination of sensors, messengers and responses that constitute the plasticity repertoire would be more useful than dichotomizing the plant and animal kingdoms. Furthermore, physicochemical factors must be viewed cohesively in the signal reception and transduction pathways leading to plastic responses. Comparison of unitary versus modular organisms could also provide useful insights into the range of expected plastic responses. An integrated approach that combines evolutionary theory and evolutionary history with signal-response mechanisms will yield the most insights into phenotypic plasticity in all its forms.Key words: electrical signaling, genomic instability, mechanotransduction, phenotypic plasticity, plant volatiles, reactive oxygen species, ROS signaling