Sugar metabolism during coffee fruit development.

In this study, we investigated more particularly the sucrose synthase (Susy: EC2.4.1.13) at the biochemical and molecular levels during the development of coffee fruits. In addition, feeding experiments with 14C-sucrose and incubation of fruits with 14CO2 were carried out. Our results suggest that Susy is the main enzyme responsible for sucrose metabolism in coffee fruits. In the pulp and endosperm of fruits at the last stage of maturation, a peak of Susy activity was observed and correlates with an increase of sucrose. At the molecular level, we cloned two cDNAs encoding different Susy isoforms. We also showed that both Susy-encoding genes were expressed in coffee fruits, with differences regarding their spatial and temporal expression. The 14C-experiments showed that sugars are not only transported from the leaves to the fruits, but also there is an intense communication among the tissues composing the fruits

Biochemical and genomic analysis of sucrose metabolism during coffee (Coffea arabica) fruit development

Sucrose metabolism and the role of sucrose synthase were investigated in the fruit tissues (pericarp, perisperm, and endosperm) of Coffea arabica during development. Acid invertase, sucrose phosphate synthase, and sucrose synthase activities were monitored and compared with the levels of sucrose and reducing sugars. Among these enzymes, sucrose synthase showed the highest activities during the last stage of endosperm and pericarp development and this activity paralleled closely the accumulation of sucrose in these tissues at this stage. Carbon partitioning in fruits was studied by pulse-chase experiments with C-14-sugars and revealed high rates of sucrose turnover in perisperm and endosperm tissues. Additional feeding experiments with (CO2)-C-14 showed that leaf photosynthesis contributed more to seed development than the pericarp in terms of photosynthate supply to the endosperm. Sugar analysis, feeding experiments, and histological studies indicated that the perisperm plays an important role in this downloading process. It was observed that the perisperm presents a transient accumulation of starch which is degraded as the seed develops. Two full-length cDNAs (CaSUS1 and CaSUS2) and the complete gene sequence of the latter were also isolated. They encode sucrose synthase isoforms that are phylogenetically distinct, indicating their involvement in different physiological functions during cherry development. Contrasting expression patterns were observed for CaSUS1 and CaSUS2 in perisperm, endosperm, and pericarp tissues: CaSUS1 mRNAs accumulated mainly during the early development of perisperm and endosperm, as well as during pericarp growing phases, whereas those of CaSUS2 paralleled sucrose synthase activity in the last weeks of pericarp and endosperm development. Taken together, these results indicate that sucrose synthase plays an important role in sugar metabolism during sucrose accumulation in the coffee fruit.57123243325

A autoavaliação da aprendizagem de inglês como língua estrangeira em um ambiente tandem a distância Self-assessment of English as a foreign language learning in a distance tandem setting

Este trabalho visa discutir as características do processo de autoavaliação da aprendizagem de inglês como língua estrangeira em um contexto tandem a distancia. Trata-se, mais especificamente, da apresentação de uma pesquisa na qual se analisam os dados coletados no ambiente teletandem (TELLES, 2005) por uma brasileira (aprendiz de inglês), durante suas interações via chat com dois parceiros norteamericanos (aprendizes de português). A análise enfoca as metas e estratégias de aprendizagem em relação aos parâmetros e critérios adotados pela brasileira em seu processo de autoavaliação.<br>This work aims at discussing the characteristics of self-assessment process in a tandem language learning setting. It is the presentation of a study in which the data were collected by a Brazilian participant (learner of English as a foreign language) during her interactions via chat with two North American teletandem (TELLES, 2005) partners (learners of Portuguese as a foreign language). The analysis focused on the learning goals and strategies in relation to the parameters and criteria defined by the Brazilian learner in her self-assessment process