Application of dendrogeomorphology on the study of soil sediment deposition in the stems of Guarea guidonea trees in a disturbed riparian forest in Goias state, Brazil

The sediments resulting of natural or anthropic erosion are deposited on the soil surface and around the trunks of trees occurring in riparian forests. For assessment of the erosion, tree-rings of roots and stems were analyzed. Guarea guidonea trees from a riparian forest affected by the sedimentation of soil erosion from pastures and soybean fields in state of Goias were selected. Wood samples were extracted through a non-destructive method at three heights from trunks of trees located in three positions (top, middle and bottom) of a riparian slope. The evaluation revealed a deposition of a thick sediment layer up to 34 cm around the base of tree trunks during the past 24 years. The inter-correlations between the tree-rings widths present in wood samples at the base and at 50 and 100 cm from Guarea guidonea tree trunks presented low, medium and high values. These values resulted from the low tree-rings distinctiveness in the wood; the absence of some rings as well as the eccentricity of the pith. The analyses of dendrogeomorphology allowed the determination of the date of seed germination and tree growth and inference on the periods of sediment deposition in the trunk of the trees.

Redox regulation of the proteasome via S-glutathionylation

The proteasome is a multimeric and multicatalytic intracellular protease responsible for the degradation of proteins involved in cell cycle control, various signaling processes, antigen presentation, and control of protein synthesis. The central catalytic complex of the proteasome is called the 20S core particle. The majority of these are flanked on one or both sides by regulatory units. Most common among these units is the 19S regulatory unit. When coupled to the 19S unit, the complex is termed the asymmetric or symmetric 26S proteasome depending on whether one or both sides are coupled to the 19S unit, respectively. The 26S proteasome recognizes poly-ubiquitinylated substrates targeted for proteolysis. Targeted proteins interact with the 19S unit where they are deubiquitinylated, unfolded, and translocated to the 20S catalytic chamber for degradation. The 26S proteasome is responsible for the degradation of major proteins involved in the regulation of the cellular cycle, antigen presentation and control of protein synthesis. Alternatively, the proteasome is also active when dissociated from regulatory units. This free pool of 20S proteasome is described in yeast to mammalian cells. The free 20S proteasome degrades proteins by a process independent of poly-ubiquitinylation and ATP consumption. Oxidatively modified proteins and other substrates are degraded in this manner. The 20S proteasome comprises two central heptamers (β-rings) where the catalytic sites are located and two external heptamers (α-rings) that are responsible for proteasomal gating. Because the 20S proteasome lacks regulatory units, it is unclear what mechanisms regulate the gating of α-rings between open and closed forms. In the present review, we discuss 20S proteasomal gating modulation through a redox mechanism, namely, S-glutathionylation of cysteine residues located in the α-rings, and the consequence of this post-translational modification on 20S proteasomal function.

In-plane mapping of buried InGaAs quantum rings and hybridization effects on the electronic structure

This work reports the investigation on the structural differences between InAs quantum rings and their precursor quantum dots species as well as on the presence of piezoelectric fields and asymmetries in these nanostructures. The experimental results show significant reduction in the ring dimensions when the sizes of capped and uncapped ring and dot samples are compared. The iso-lattice parameter mapped by grazing-incidence x-ray diffraction has revealed the lateral extent of strained regions in the buried rings. A comparison between strain and composition of dot and ring structures allows inferring on how the ring formation and its final configuration may affect optical response parameters. Based on the experimental observations, a discussion has been introduced on the effective potential profile to emulate theoretically the ring-shape confinement. The effects of confinement and strain field modulation on electron and hole band structures are simulated by a multiband k.p calculation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733964]