Organic acids are abundant constituents of ripe fruits and are responsible for their sourness. In addition, they contribute to their flavour. In many fruits, the most abundant organic acids are malic and citric. The aims of this review are two-fold. The first is to provide a clear overview of malic and citric acids in the flesh of fruits. The abundance of different organic acids in commercially grown fruits is described. How this abundance changes during fruit development is outlined. The metabolic pathways used in the synthesis and dissimilation of malic and citric acids in fruits are described. The functions of malic and citric acids in the flesh of fruits are discussed. Secondly, how environmental and cultural practices can alter the organic acid content of fruits is considered.

Los ácidos orgánicos son componentes abundantes de los frutos maduros y responsables de la acidez, además contribuyen en su sabor. En muchos frutos, los ácidos más abundantes son el málico y el cítrico. Los objetivos de esta revisión son, en primer lugar, proporcionar una reseña clara respecto de los ácidos málico y cítrico en los frutos. Se describe la abundancia de diferentes ácidos en frutos cultivados comercialmente, la manera en que esta abundancia cambia durante el desarrollo de los frutos y las rutas metabólicas usadas en la síntesis y la desasimilación de los ácidos málico y cítrico en los frutos; adicionalmente, se discute sobre las funciones de estos ácidos en la pulpa de los frutos. En segundo lugar, se aborda la manera en que las prácticas ambientales y culturales pueden alterar el contenido de los ácidos orgánicos en frutos.

The oocyst wall of coccidian parasites is a robust structure that is resistant to a variety of environmental and chemical insults. This resilience allows oocysts to survive for long periods, facilitating transmission from host to host. The wall is bilayered and is formed by the sequential release of the contents of two specialized organelles - wall forming body 1 and wall forming body 2 - found in the macrogametocyte stage of Coccidia. The oocyst wall is over 90% protein but few of these proteins have been studied. One group is cysteine-rich and may be presumed to crosslink via disulphide bridges, though this is yet to be investigated. Another group of wall proteins is rich in tyrosine. These proteins, which range in size from 8-31 kDa, are derived from larger precursors of 56 and 82 kDa found in the wall forming bodies. Proteases may catalyze processing of the precursors into tyrosine-rich peptides, which are then oxidatively crosslinked in a reaction catalyzed by peroxidases. In support of this hypothesis, the oocyst wall has high levels of dityrosine bonds. These dityrosine crosslinked proteins may provide a structural matrix for assembly of the oocyst wall and contribute to its resilience.

Este artigo examina as relações entre as características sociodemográficas das famílias de pequenos produtores na Amazônia e a hipótese do ciclo de vida no processo de tomada de decisão de desmatar. A análise foi conduzida combinando informações de sensoriamento remoto e de sistema de informações geográficas com dados primários de 153 pequenos produtores estabelecidos ao longo da rodovia Transamazônica. Análises de regressões foram efetuadas juntamente com testes de autocorrelação espacial. Os resultados levaram à conclusão de que as características sociodemográficas das famílias, bem como fatores institucionais e de mercado, influenciam a tomada de decisão de uso da terra. Esses resultados permitem concluir ainda que, apesar de não serem muito populares entre os cientistas sociais brasileiros, os dados obtidos através das imagens de satélite podem ser muito úteis neste tipo de estudo. Além disso, a pesquisa aqui apresentada indica que dados sociodemográficos da família, bem como os de mercado, podem resultar em problemas de má especificação do modelo. O mesmo se aplica a modelos que não incorporem análises espaciais.

This paper examines the relationships between the sociodemographic characteristics of small settlers in the Brazilian Amazon and the life cycle hypothesis in the process of deforestation. The analysis was conducted combining remote sensing and geographic data with primary data of 153 small settlers along the Transamazon Highway. Regression analyses and spatial autocorrelation tests were conducted. The results from the empirical model indicate that sociodemographic characteristics of households, as well as institutional and market factors, affect the land use decision. Although remotely sensed information are not yet very popular among Brazilian social scientists, these results confirm that they can be very useful for this kind of study. Furthermore, the research presented by this paper strongly indicates that family and sociodemographic data, as well as market data, may result in misspecification problems. The same applies to models that do not incorporate spatial analysis.