Off-the-Vine Ripening of Tomato Fruit Causes Alteration in the Primary Metabolite Composition

Abstract

The influence of postharvest fruit ripening in the composition of metabolites, transcripts and enzymes in tomato (Solanum lycopersicum L.) is poorly understood. The goal of this work was to study the changes in the metabolite composition of the tomato fruit ripened off-the-vine using the cultivar Micro-Tom as model system. Proton nuclear magnetic resonance (1H NMR) was used for analysis of the metabolic profile of tomato fruits ripened on- and off-the-vine. Significant differences under both ripening conditions were observed principally in the contents of fructose, glucose, aspartate and glutamate. Transcript levels and enzyme activities of -amino butyrate transaminase (EC 2.6.1.19) and glutamate decarboxylase (EC 4.1.1.15) showed differences in fruits ripened under these two conditions. These data indicate that the contents of metabolites involved in primary metabolism, and conferring the palatable properties of fruits, are altered when fruits are ripened off-the-vine.

Figure 1

Principal component analysis (PCA) of ¹H NMR spectra of tomato fruit. ¹H NMR spectra of samples of pericarp extract of green (green line), red ripened on-the-vine (red line) and red ripened off-the-vine (blue line) Micro-Tom fruits were analyzed considering the whole spectra (each spectrum was normalized to a maximum intensity of 1, the water region was removed) and distinct spectral regions.

Figure 2

PCA analysis performed on metabolite concentrations for all the studied samples. Panels show (a) the scores plots, in which each point corresponds to one sample, and (b) the loading plots, in which each point is a metabolite concentration. Green, red and blue colors indicate maturation stage of fruits as described in Figure 1, and 2-OG indicates 2-oxoglutarate.

Figure 3

Metabolism of glutamate and GABA in tomato fruit. Enzymes and metabolites measured in mature green fruit (upper part), and fruits ripened on- and off-the-vine (lower part) are shown. Colored arrows and letters indicate increased levels in mature green fruit (green), on-the-vine (red) or off-the-vine (blue). Thickness of arrows and size of letters are proportional to corresponding reaction activity (taken from Table 2) and metabolite accumulation, respectively. At the bottom, a violet scale representing the content of each metabolite (taken from Table 1) is shown.