O período da contaminação com petróleo influencia a rebrota de Echinochloa polystachya (H.B.K.) Hitchcock em solo de várzea da Amazônia central?

Several factors may influence the impact of oil on the environment. However, although it is understood that the effect of pollutants may change throughout the year according to seasonal variations in environmental parameters, this effect is poorly studied in the tropical region. The effects of Urucu's crude oil on the vegetative propagation and growth of Echinochloa polystachya were evaluated in a 63 days period, in two experiments, "A" (July-September) and "B" (September-November) planting the species in a greenhouse. In both experiments parts of stems were placed in 2 L of várzea soil contaminated by 6 oil doses, ranging from 0 to 0.231 L oil m-2 soil. In response to dosage increase there was a decrease of total biomass, ratio of live /total biomass, the leaf length and number of leaves. The period of planting influenced the response of plants to the dosage applied due to climate change, with negative effects in the "B" period of higher temperatures. We concluded that the exposure period influence the vegetative propagation and growth of the seedlings, being a spill in the period of the higher temperatures more dangerous for this specie

The developmental pattern of homologous and heterologous tRNA methylation in rat brain differential effect of spermidine

Using S -adenosyl- L -[Me- 14 C] methionine, rat cerebral cortex methyltransferase activity was determined during the early postnatal period in the absence of added Escherichia coli tRNA and in its presence. [Me- 14 C] tRNA was purified from both systems and its [Me- 14 C] base composition determined. The endogenous formation of [Me- 14 C] tRNA (homologous tRNA methylation) was totally abolished in the presence of 2.5 mM spermidine, whereas E. coli B tRNA methylation (heterologous methylation) was markedly stimulated. Only [Me- 14 C] 1-methyl guanine and [Me- 14 C] N 2 -methyl guanine were formed by homologous methylation, there being an inverse shift in their relative proportions with age. Heterologous tRNA methylation led, additionally, to the formation of [Me- 14 C] N 2 2 -dimethyl guanine, 5-methyl cytosine, 1-methyl adenine, 5-methyl uracil, 2-methyl adenine, and 1-methyl hypoxanthine. A comparison of heterologous tRNA methylation between the whole brain cortex (containing nerve and glial cells) and bulk-isolated nerve cell bodies revealed markedly lower proportions of [Me- 14 C] N 2 -methyl and N 2 2 -dimethyl guanine and significantly higher proportions of [Me- 14 C] 1-methyl adenine in the neurons. The present findings suggest (1) that homologous tRNA methylation may provide developing brain cells with continuously changing populations of tRNA and (2) that neurons are enriched in adenine residue-specific tRNA methyltransferases that are highly sensitive to spermidine.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45399/1/11064_2004_Article_BF00966229.pd

Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2,3,4,5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers