Cécile Cabasson

Effects of long-term cadmium exposure on growth and metabolomic profile of tomato plants

The response of tomato plants to long-term cadmium exposure was evaluated after a 90-days long culture in hydroponic conditions (0, 20, and 100 μM CdCl(2)). Cadmium preferentially accumulated in roots, and to a lower extent in upper parts of plants. Absolute quantification of 28 metabolites was obtained through (1)H NMR, HPLC-PDA, and colorimetric methods. The principal component analysis showed a clear separation between control and Cd treated samples. Proline and total ascorbate amounts were reduced in Cd-treated leaves, whereas α-tocopherol, asparagine, and tyrosine accumulation increased, principally in 100 μM Cd treated leaves. Carotenoid and chlorophyll contents decreased only in 100 μM Cd-mature-leaves, which correlate with a reduced expression of genes essential for isoprenoid and carotenoid accumulations. Our results show that tomato plants acclimatize during long-term exposure to 20 μM Cd. On the contrary, 100μM Cd treatment results in drastic physiological and metabolic perturbations leading to plant growth limitation and fruit set abortion.

Prolonged root hypoxia induces ammonium accumulation and decreases the nutritional quality of tomato fruits

Here we examined the effects of root hypoxia (1-2% oxygen) on the physiology of the plant and on the biochemical composition of fruits in tomato (Solanum lycopersicum cv. Micro-Tom) plants submitted to gradual root hypoxia at first flower anthesis. Root hypoxia enhanced nitrate absorption with a concomitant release of nitrite and ammonium into the medium, a reduction of leaf photosynthetic activity and chlorophyll content, and an acceleration of fruit maturation, but did not affect final fruit size. Quantitative metabolic profiling of mature pericarp extracts by (1)H NMR showed that levels of major metabolites including sugars, organic acids and amino acids were not modified. However, ammonium concentration increased dramatically in fruit flesh, and ascorbate and lycopene concentrations decreased. Our data indicate that the unfavorable effects of root hypoxia on fruit quality cannot be explained by two of the well-known effects of root hypoxia on the plant, namely a decrease in photosynthesis or an excess in ethylene production, but may instead result from disturbances in the supply of either growth regulators or ammonium, by the roots.

Chapter One – High-Resolution 1H-NMR Spectroscopy and Beyond to Explore Plant Metabolome

During the past decade, metabolomics has become a crucial functional genomic tool. Tremendous advances in instrumentation, automation, data handling capabilities and statistical analyses have boosted this discipline. Today, most investigations of the plant metabolome tend to be based on either nuclear magnetic resonance (NMR) spectrometry or mass spectrometry (MS), with or without hyphenation with chromatography or capillary electrophoresis. Although less sensitive than MS, NMR provides a powerful complementary technique for the identification and quantification of metabolites in plant extracts. High-resolution one-dimensional (1D) proton NMR spectroscopy (1H-NMR) is a robust technique, highly reproducible, non-selective and non-destructive, able to produce structural information and quantitative data. In this review, we highlight important technical prere-quisites for sample preparation, acquisition parameters, as well as recent developments in NMR and resources available for spectra annotation, which are necessary to pursue plant 1H-NMR metabolomics studies. 1H-NMR is the ideal nucleus for most metabolomics studies. On the one hand, multivariate analysis of unassigned 1H-NMR spectra (concept of metabolite fingerprinting) is used to compare the overall metabolic composition of plant extracts. On the other hand, identification and quantification of 20–60 metabolites (concept of metabolite profiling) in unfractionated extracts are used to spot the major metabolites in plant extracts. Both strategies generate key information concerning the plant metabolome, but in an incomplete way. Several applications of NMR fingerprinting and profiling approaches are presented from the characterization of food or medicinal plants to plant functional genomics, showing the key role that 1H-NMR plays in data provision for food and plant sciences. The future challenges for 1H-NMR metabolomics are linked with the developments in NMR spectroscopy technology that provide improvement in signal detection and quantitation and also the facility to use shared databases.

Respiration climacteric in tomato fruits elucidated by constraint-based modelling

Summary 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 CO 2 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.