Treatment with 1-MCP and the role of ethylene in aroma development of mountain papaya fruit

Moya-Leon, M.A. Laboratorio de Fisiología Vegetal, Instituto de Biología Vegetal y Biotecnología, Universidad de Talca, Casilla 747, Talca, Chile. Centro de Investigación en Biotecnología Silvoagrícola (CIBS), Chile.Mountain or highland papaya (Vasconcellea pubescens) is a climacteric fruit which develops a strong and characteristic aroma during ripening. The dynamics of aroma volatile production during ripening of whole papaya fruit were analysed by headspace-SPME. The main compounds produced by the fruit were esters (aliphatic and branched) and alcohols: the most abundant esters were ethyl acetate, ethyl butanoate, methyl butanoate and butyl acetate, comprising 88% of the volatiles in fully ripe fruit; butanol was the most abundant alcohol. Among the volatiles produced, ethyl butanoate, ethyl acetate, ethyl hexanoate and ethyl 2-methylbutanoate were found to be the most potent odour compound

Diet breadth and its relationship with genetic diversity and differentiation: The case of southern beech aphids (Hemiptera: Aphididae)

Herbivorous insect species with narrow diet breadth are expected to be more prone to genetic differentiation than insect species with a wider diet breadth. However, a generalist can behave as a local specialist if a single host-plant species is locally available, while a specialist can eventually behave as a generalist if its preferred host is not available. These problems can be addressed by comparing closely related species differing in diet breadth with overlapping distributions of insect and host populations. In this work, diet breadth, genetic diversity and population differentiation of congeneric aphid species from southern beech forests in Chile were compared. While at the species level no major differences in genetic diversity were found, a general trend towards higher genetic diversity as diet breadth increased was apparent. The aphid species with wider diet breadth, Neuquenaphis edwardsi (Laing), showed the highest genetic diversity, while the specialist Neuquenaphis staryi

Structural characterization and substrate specificity of VpAAT1 protein related to ester biosynthesis in mountain papaya fruit

Morales-Quintana, L (Morales-Quintana, Luis)1; Fuentes, L (Fuentes, Lida)1; Gaete-Eastman, C (Gaete-Eastman, Carlos)1; Herrera, R (Herrera, Raul)1; Moya-Leon, MA (Alejandra Moya-Leon, Maria)1Univ Talca, Inst Biol Vegetal & Biotecnol, Lab Fisiol Vegetal & Genet Mol, Talca, ChileThe aroma in fruits is an important attribute of quality that influences consumer's acceptance. This attribute is a complex character determined by a set of low molecular weight volatile compounds. In mountain papaya fruit (Vasconcellea pubescens) the aroma is determined mainly by esters, which are produced through an esterification reaction catalyzed by the enzyme alcohol acyltransferase (AAT) that utilizes alcohols and acyl-CoAs as substrates. In order to understand the molecular mechanism involved in the production of esters in this fruit, an AAT gene which has been previously cloned and characterized from mountain papaya (VpAAT1) was expressed in yeasts, and the highest enzyme activity of the recombinant protein was obtained when the enzyme was tested for its ability to produce benzyl acetate. On the other hand, to gain insight the mechanism of action at the molecular level, a structural model for VpAAT1 protein was built by comparative modelling methodology, which was validated and refined by molecular dynamics simulation. The VpAAT1 structure consists of two domains connected by a large crossover loop, with a solvent channel in the center of the structure formed between the two domains. Residues H166 and D170, important for catalytic action, displayed their side chains towards the central cavity of the channel allowing their interaction with the substrates. The conformational interaction between the protein and several ligands was explored by molecular docking simulations, and the predictions obtained were tested through kinetic analysis. Kinetic results showed that the lowest K(M) values were obtained for acetyl-CoA and benzyl alcohol. In addition, the most favorable predicted substrate orientation was observed for benzyl alcohol and acetyl CoA, showing a perfect coincidence between kinetic studies and molecular docking analysis. (C) 2010 Elsevier Inc. All rights reserved