S100B belongs to a family of calcium-binding proteins involved in cell cycle and cytoskeleton regulation. We observed an inhibitory effect of S100B on glial fibrillary acidic protein (GFAP) phosphorylation, when stimulated by cAMP or Ca2+/calmodulin, in a cytoskeletal fraction from primary astrocyte cultures. We found that S100B has no direct effect on CaM KII activity, the major kinase in this cytoskeletal fraction able to phosphorylate GFAP. The inhibition of GFAP phosphorylation is most likely due to the binding of S100B to the phosphorylation sites on this protein and blocking the access of these sites to the protein kinases. This inhibition was dependent on Ca2+. However, Zn2+ could substitute for Ca2+. The inhibitory effect of S100B was prevented by TRTK-12, a peptide that blocks S100B interaction with several target proteins including glial fibrillary acidic protein. These data suggest a role for S100B in the assembly of intermediate filaments in astrocytes.

Several tools of precision agriculture have been developed for specific uses. However, this specificity may hinder the implementation of precision agriculture due to an increasing in costs and operational complexity. The use of vegetation index sensors which are traditionally developed for crop fertilization, for site-specific weed management can provide multiple utilizations of these sensors and result in the optimization of precision agriculture. The aim of this study was to evaluate the relationship between reflectance indices of weeds obtained by the GreenSeekerTM sensor and conventional parameters used for weed interference quantification. Two experiments were conducted with soybean and corn by establishing a gradient of weed interference through the use of pre- and post-emergence herbicides. The weed quantification was evaluated by the normalized difference vegetation index (NDVI) and the ratio of red to near infrared (Red/NIR) obtained using the GreenSeekerTM sensor, the visual weed control, the weed dry matter, and digital photographs, which supplied information about the leaf area coverage proportions of weed and straw. The weed leaf coverage obtained using digital photography was highly associated with the NDVI (r = 0.78) and the Red/NIR (r = -0.74). The weed dry matter also positively correlated with the NDVI obtained in 1 m linear (r = 0.66). The results indicated that the GreenSeekerTM sensor originally used for crop fertilization could also be used to obtain reflectance indices in the area between rows of crops to support decision-making programs for weed control.

ResumoOs filamentos intermediários representam um dos principais componentes do citoesqueleto de células eucarióticas. O monômero desses filamentos em astrócitos é a GFAP ("glial fibrillary acidic protein"), cuja polimerização é modulada aparentemente pela fosforilação e pela interação com uma proteína ligante de cálcio, a 8100B. Neste estudo investigamos a polimerização in vitro da GFAP, usando um ensaio baseado na sedimentação induzida por imidazol/ alto magnésio. De fato, a GFAP solúvel (não polimerizada) aumentou em cerca de 25% na presença de 8100B ou PKA (proteína cinase A). Estes dados sugerem que ambos os mecanismos possam estar atuando no ciclo de polimerização/despolimerização da GFAP em momentos e/ou situações diferentes afetando a plasticidade glial. Palavras-chaves: GFAP, 8100B, fosforilação protéica, plasticidade glial. AbstractIntermediate filaments represent a major cytoskeleton constituent in eukaryotic cells. GFAP ("glial fibrillary acidic protein") is the monomer of these filaments in astrocytes and its polymerization is apparently modulated by phosphorylation and by interaction with S100B, a calcium-binding protein. In this study we investigate in vitro polymerization of GFAP, using an assay based on imidazol/high magnesium-induced sedimentation. In fact, soluble GFAP (nonpolymerized) increased about 25% in presence of S100B or PKA (protein kinase A). These data suggest that both mechanisms could be acting in the cycle of polymerization/depolymerization of GFAP at different times and/or conditions, therefore affecting glial plasticity.