Antioxidant and Cytoprotective Activities of Grapevine Stilbenes.

Grapevine stem extracts are viticulture byproducts rich in stilbenes that are increasingly studied for their potential biological activities. This study aimed to investigate some biological activities of a grape byproduct with high stilbenoid content and to point out the molecules responsible of these beneficial activities. As a consequence, the extract was subjected to a bioguided fractionation and separation by centrifugal partition chromatography. The obtained fractions were characterized by liquid chromatography coupled to mass spectrometry and nuclear magnetic resonance. Fractions were purified further by column chromatography and resulted in the purification of the main constituents. Thirteen stilbenes have been quantified. The most abundant compounds were ε-viniferin, resveratrol, and, in lesser amounts, isohopeaphenol and ampelopsin A. The extract, fractions, and major stilbenes were tested for their antioxidant activity by oxygen radical absorbance capacity and their cyprotective effects against ß-amyloid on rat pheochromocytoma cells. Among them, fraction 5 showed significant antioxidant activity and fraction 2 had a significant cytoprotective effect against ß-amyloid-induced toxicity. Two putative inhibitors of ß-amyloid toxicity have been identified: ampelopsin A and piceatannol.

Respiration climacteric in tomato fruits elucidated by constraint-based modelling.

Tomato is a model organism to study the development of fleshy fruit including ripening initiation. Unfortunately, few studies deal with the brief phase of accelerated ripening associated with the respiration climacteric because of practical problems involved in measuring fruit respiration. Because constraint-based modelling allows predicting accurate metabolic fluxes, we investigated the respiration and energy dissipation of fruit pericarp at the breaker stage using a detailed stoichiometric model of the respiratory pathway, including alternative oxidase and uncoupling proteins. Assuming steady-state, a metabolic dataset was transformed into constraints to solve the model on a daily basis throughout tomato fruit development. We detected a peak of CO2 released and an excess of energy dissipated at 40 d post anthesis (DPA) just before the onset of ripening coinciding with the respiration climacteric. We demonstrated the unbalanced carbon allocation with the sharp slowdown of accumulation (for syntheses and storage) and the beginning of the degradation of starch and cell wall polysaccharides. Experiments with fruits harvested from plants cultivated under stress conditions confirmed the concept. We conclude that modelling with an accurate metabolic dataset is an efficient tool to bypass the difficulty of measuring fruit respiration and to elucidate the underlying mechanisms of ripening.

Modelling central metabolic fluxes by constraint-based optimization reveals metabolic reprogramming of developing Solanum lycopersicum (tomato) fruit.

Modelling of metabolic networks is a powerful tool to analyse the behaviour of developing plant organs, including fruits. Guided by our current understanding of heterotrophic metabolism of plant cells, a medium-scale stoichiometric model, including the balance of co-factors and energy, was constructed in order to describe metabolic shifts that occur through the nine sequential stages of Solanum lycopersicum (tomato) fruit development. The measured concentrations of the main biomass components and the accumulated metabolites in the pericarp, determined at each stage, were fitted in order to calculate, by derivation, the corresponding external fluxes. They were used as constraints to solve the model by minimizing the internal fluxes. The distribution of the calculated fluxes of central metabolism were then analysed and compared with known metabolic behaviours. For instance, the partition of the main metabolic pathways (glycolysis, pentose phosphate pathway, etc.) was relevant throughout fruit development. We also predicted a valid import of carbon and nitrogen by the fruit, as well as a consistent CO2 release. Interestingly, the energetic balance indicates that excess ATP is dissipated just before the onset of ripening, supporting the concept of the climacteric crisis. Finally, the apparent contradiction between calculated fluxes with low values compared with measured enzyme capacities suggest a complex reprogramming of the metabolic machinery during fruit development. With a powerful set of experimental data and an accurate definition of the metabolic system, this work provides important insight into the metabolic and physiological requirements of the developing tomato fruits.

Deciphering genetic diversity and inheritance of tomato fruit weight and composition through a systems biology approach.

Integrative systems biology proposes new approaches to decipher the variation of phenotypic traits. In an effort to link the genetic variation and the physiological and molecular bases of fruit composition, the proteome (424 protein spots), metabolome (26 compounds), enzymatic profile (26 enzymes), and phenotypes of eight tomato accessions, covering the genetic diversity of the species, and four of their F1 hybrids, were characterized at two fruit developmental stages (cell expansion and orange-red). The contents of metabolites varied among the genetic backgrounds, while enzyme profiles were less variable, particularly at the cell expansion stage. Frequent genotype by stage interactions suggested that the trends observed for one accession at a physiological level may change in another accession. In agreement with this, the inheritance modes varied between crosses and stages. Although additivity was predominant, 40% of the traits were non-additively inherited. Relationships among traits revealed associations between different levels of expression and provided information on several key proteins. Notably, the role of frucktokinase, invertase, and cysteine synthase in the variation of metabolites was highlighted. Several stress-related proteins also appeared related to fruit weight differences. These key proteins might be targets for improving metabolite contents of the fruit. This systems biology approach provides better understanding of networks controlling the genetic variation of tomato fruit composition. In addition, the wide data sets generated provide an ideal framework to develop innovative integrated hypothesis and will be highly valuable for the research community.

Metabolic acclimation to hypoxia revealed by metabolite gradients in melon fruit.

A metabolomics approach using (1)H NMR and GC-MS profiling of primary metabolites and quantification of adenine nucleotides with luciferin bioluminescence was employed to investigate the spatial changes of metabolism in melon fruit. Direct (1)H NMR profiling of juice collected from different locations in the fruit flesh revealed several gradients of metabolites, e.g. sucrose, alanine, valine, GABA or ethanol, with increase in concentrations from the periphery to the center of the fruit. GC-MS profiling of ground samples revealed gradients for metabolites not detected using (1)H NMR, including pyruvic and fumaric acids. The quantification of adenine nucleotides highlighted a strong decrease in both ATP and ADP ratios and the adenylate energy charge from the periphery to the center of the fruit. These concentration patterns are consistent with an increase in ethanol fermentation due to oxygen limitation and were confirmed by observed changes in alanine and GABA concentrations, as well as other markers of hypoxia in plants. Ethanol content in melon fruit can affect organoleptic properties and consumer acceptance. Understanding how and when fermentation occurred can help to manage the culture and limit ethanol production.