France
October 14, 2011
Melon is a fruit of economic importance as its consumption is recommended in the diet, in compliance with the nutritional guidelines of the "Five fruits and vegetables a day" programme. It contains essential nutrients (such as isoprenoids), vitamins and minerals. To a considerable extent, its appreciation by consumers is based on its aroma and sugar content. In the context of the European META-PHOR project, a study by the INRA Fruit Biology and Pathology Unit in Bordeaux, in collaboration with other teams, has demonstrated that the spatial and developmental variability of the metabolite and mineral composition of this fruit has major effects on the organoleptic and nutritional quality of melon, and identified groups of compounds with coordinated development profiles.
The melon variety chosen for this research was "Escrito", which was cultivated in open fields (at a density of 9200 plants/hectare) in Moissac, France, between April and August 2008. Management of the crop complied with current professional guidelines. The melons were harvested at three developmental stages: before development of the corky skin of the fruit (stage 1), at the very beginning of ripeness (stage 2) and at the start of fruit abscission (stage 3, or "market ripeness"). At each stage, three homogeneous batches of three melons were made up. Two, 1-cm thick slices were cut at the broadest circumference of the fruit. After removal of the skin and pips, the analysis concerned five concentric circles of flesh from the external area to the centre. At the three developmental stages of the fruit, fleshy tissues from the outer envelope to the pips underwent extractions and then analyses, which enabled the quantification of 2000 metabolite signatures and 15 mineral elements.
Using six complementary analytical platforms, the profiles of the metabolites and minerals in each section of fruit, at each stage, could be mapped. This concerned primary metabolites, secondary volatile metabolites, secondary non-volatile metabolites and mineral elements. The results confirmed that metabolism is re-programmed during ripening and displays spatial variations in the composition of metabolites and mineral elements in the fruit. These spatial variations may be linked to the distribution of vascular bundles and to the production of plant hormones by pips and their gradual diffusion through the melon flesh. If this is confirmed, then varietal selection for fruits with a more homogeneous composition should focus on homogenising the vascular structure of tissues, and preferably target pip-free fruits.
This research was also able to demonstrate numerous correlations, firstly between primary and secondary non-volatile metabolites, and secondly between the latter and volatile compounds. Visualisation of the correlations between metabolites, in the form of association networks, was able to highlight points of "metabolic cross-talk", involving sucrose, aspartic acid, 2-isopropylmalic acid, β-caroten, phytoene and dihydroseudoione, which may become candidate metabolites to be monitored during genetic improvement programmes targeting fruit quality.
From the aroma point of view, the research confirmed the close links between the concentrations of certain primary metabolites and that of certain volatile compounds with different chemical properties (esters, aldehydes, alcohols and sulphurated compounds). Furthermore, unexpected links between the levels of certain mineral elements and certain metabolites were demonstrated and should be taken account during selection.
This work on melon, partly pursued in the context of another European project, SAFQUIM (Plant KBBE 2010), has demonstrated the importance of taking account of a metabolomic approach in selection programmes, with respect to both nutritional and organoleptic quality. By exploring the relationships between the presence of metabolites and fruit quality, new opportunities are now available for improvement programmes.
Scientific leaders:
Annick MOING
Benoit BIAIS
Catherine DEBORDE
Stéphane BERNILLON
Yves GIBON
UMR 1332 BFP Biologie du Fruit et Pathologie
INRA Domaine de la Grande Ferrade
71 avenue Edouard Bourlaux
33140 VILLENAVE D'ORNON CEDEX
For further information:
A Moing, A Aharoni, B Biais, IRogachev, S Meir, L Brodsky, J. W Allwood, A Erban, W B. Dunn, L Kay, S de Koning, R de Vos, H Jonker, R Mumm, C Deborde, M Maucourt, S Bernillon, Y Gibon, T H. Hansen, S Husted, R Goodacre, J Kopka, J Schjoerring, D Rolon, R D. Hall, "Extensive metabolic cross-talk in melon fruit revealed by spatial and developmental combinatorial metabolomics", New Phytologist, 2011,10.1111/j.1469-8137.2010.03626.x
Photo: © Inra-J. Weber
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