RESUMO - Trinta e seis cordeiros (18 machos inteiros e 18 fêmeas) de três diferentes grupos genéticos: 12 cordeiros cruzas Texel x Bergamácia (T x B), 12 cordeiros cruzas Texel x Santa Inês (T x S) e 12 cordeiros puros Santa Inês (SI) foram alimentados com três diferentes dietas experimentais: A- sem casca de café; B. com casca de café in natura; e C- com casca de café, tratada com uréia e grão de soja moído. Os pesos das carcaças quente e fria, o rendimento de carcaça quente (RC), a quebra de peso da carcaça devido ao resfriamento, as medidas de comprimento interno e total da carcaça, o comprimento de perna, o comprimento total de perna (CTP), o perímetro da garupa (PG), a largura da garupa (LG), a profundidade do tórax (PT) e a gordura subcutânea (GS), de acordo com a dieta, o grupo genético e sexo foram avaliados. Não houve efeito das dietas sobre as variáveis avaliadas. Os cordeiros cruzas T x B e T x S apresentaram menor CTP e maiores PG, LG e GS. Os cordeiros T x B apresentaram valores superiores para PT. Houve superioridade dos animais cruzados nos pesos das carcaças quente e fria, não ocorrendo diferenças para o rendimento da carcaça quente entre os grupos genéticos. Não houve diferença entre machos e fêmeas para GS. As fêmeas apresentaram melhor RC que os machos. Para as outras características, os machos mostraram valores superiores em relação às fêmeas.

Xylella fastidiosa, the causal agent of citrus variegated chlorosis (CVC), colonizes plant xylem, reducing sap flow, and inducing internerval chlorosis, leaf size reduction, necrosis, and harder and smaller fruits. This bacterium may be transmitted from plant to plant by sharpshooter insects, including Bucephalogonia xanthopis. The citrus endophytic bacterium Methylobacterium mesophilicum SR1.6/6 colonizes citrus xylem and previous studies showed that this strain is also transferred from plant to plant by B. xanthopis (Insecta), suggesting that this endophytic bacterium may interact with X. fastidiosa in planta and inside the insect vector during co-transmission by the same insect vector. To better understand the X. fastidiosa behavior in the presence of M. mesophilicum, we evaluated the X. fastidiosa transcriptional profile during in vitro interaction with M. mesophilicum SR1.6/6. The results showed that during co-cultivation, X. fastidiosa down-regulated genes related to growth and up-regulated genes related to energy production, stress, transport, and motility, suggesting the existence of a specific adaptive response to the presence of M. mesophilicum in the culture medium.

Xylella fastidiosa is a xylem-limited bacterium responsible for important plant diseases, like citrus-variegated chlorosis (CVC) and grapevine Pierce's disease (PD). Interestingly, in vitro growth of X. fastidiosa in chemically defined media that resemble xylem fluid has been achieved, allowing studies of metabolic processes used by xylem-dwelling bacteria to thrive in such nutrient-poor conditions. Thus, we performed microarray hybridizations to compare transcriptomes of X. fastidiosa cells grown in 3G10-R, a medium that resembles grape sap, and in Periwinkle Wilt (PW), the complex medium traditionally used to cultivate X. fastidiosa. We identified 299 transcripts modulated in response to growth in these media. Some 3G10R-overexpressed genes have been shown to be upregulated in cells directly isolated from infected plants and may be involved in plant colonization, virulence and environmental competition. In contrast, cells cultivated in PW show a metabolic switch associated with increased aerobic respiration and enhanced bacterial growth rates.

Paracoccidioides brasiliensis is a thermodimorphic fungus associated with paracoccidioidomycosis (PCM), the most common systemic mycosis in Latin America. The infection is initiated by inhalation of environmentally dispersed conidia produced by the saprophytic phase of the fungus. In the lungs, P. brasiliensis assumes the parasitic yeast form and must cope with the adverse conditions imposed by cells of the host immune system, which includes a harsh environment, highly concentrated in reactive oxygen species (ROS). In this work, we used the ROS-generating agent paraquat to experimentally simulate oxidative stress conditions in order to evaluate the stress-induced modulation of gene expression in cultured P. brasiliensis yeast cells, using a microarray hybridization approach. The large-scale evaluation inherent to microarray-based analyses identified 2070 genes differentially transcribed in response to paraquat exposure, allowing an integrated visualization of the major metabolic changes that constitute the systemic defense mechanism used by the fungus to overcome the deleterious effects of ROS. These include overexpression of detoxifying agents, as well as of molecular scavengers and genes involved in maintenance of the intracellular redox potential. Particularly noteworthy was to verify that the oxidative stress resistance mechanism of P. brasiliensis also involves coordinated overexpression of a series of genes responsible for chitin-biosynthesis, suggesting that this pathway may constitute a specific regulon. Further analyses aiming at confirming and understanding the mechanisms that control such regulon may provide interesting new targets for chemotherapeutic approaches against P. brasiliensis and other pathogenic fungi.

Este artigo sintetiza reflexões sobre o processo de formação de conceitos teóricos na educação em Ciências baseada na teoria de P. Ya. Galperin. Tomamos como contexto algumas críticas tradicionalmente feitas à teoria, reforçadas (embora não intencionalmente) em estudos atuais de pesquisas no contexto brasileiro que abordam esse processo. Partimos da natureza lógica dialética dos conceitos teóricos e do papel de sua definição para justificar a formação da base orientadora do tipo III como mecanismo psicológico da aprendizagem desses conceitos. Na discussão, pretendemos oferecer um ponto de vista que se contrapõe com posturas teóricas que consideramos interpretações parciais ou mal-entendidos das ideias de Galperin, sempre reconhecendo suas limitações, próprias de qualquer teoria científica.