Characterization and content of flavonoid glycosides in genetically modified tomato (Lycopersicon esculentum) fruits.

There is a growing interest in producing food plants with increased amounts of flavonoids because of their potential health benefits. Tomatoes contain small amounts of flavonoids, most of which are located in the peel of the fruit. It has been shown that flavonoid accumulation in tomato flesh, and hence an overall increase in flavonoid levels in tomato fruit, can be achieved by means of simultaneous overexpression of the maize transcription factors LC and C1. Fruit from progeny of two modified lines (2027 and 2059) was selected for a detailed analysis and individual identification of flavonoids, at different stages of maturity. Nine major flavonoids were detected in the flesh of transgenic ripe tomatoes. LC/NMR, LC/MS, and LC/MS/MS enabled us to identify these as kaempferol-3,7-di-O-glucoside (1), kaempferol-3-O-rutinoside-7-O-glucoside (2), two dihydrokaempferol-O-hexosides (3 and 4), rutin (5), kaempferol-3-O-rutinoside (6), kaempferol-3-O-glucoside (7), naringenin-7-O-glucoside (8) and naringenin chalcone (9), which were quantified by HPLC/DAD. All but 5, 6, and 9 were detected in tomato for the first time. The total flavonoid glycoside content of ripe transgenic tomatoes of line 2059 was about 10-fold higher than that of the controls, and kaempferol glycosides accounted for 60% of this. Kaempferol glycosides comprised around 5% of the flavonoid glycoside content of ripe control tomatoes (the rest was rutin and naringenin chalcone). The rutin concentration in both transgenic and control fruits was similar.

Metabolite profiling of tomato (Lycopersicon esculentum) using 1H NMR spectroscopy as a tool to detect potential unintended effects following a genetic modification.

The maize transcription factors LC and C1 were simultaneously overexpressed in tomato with the aim of producing lines with increased amounts of flavonols. The metabolite composition of these genetically modified tomatoes has been compared with that of azygous (nonmodified) controls grown side-by-side under the same conditions. It has been possible to observe metabolic changes in both types at different stages of maturity. (1)H NMR spectra showed that the levels of glutamic acid, fructose, and some nucleosides and nucleotides gradually increase from the immature to the ripe stage, whereas some amino acids such as valine and gamma-aminobutyric acid were present in higher amounts in unripe tomatoes. Apart from the significantly increased content of six main flavonoid glycosides (mainly kaempferol-3-O-rutinoside, with additional increases in kaempferol-3,7-di-O-glucoside (1), kaempferol-3-O-rutinoside-7-O-glucoside (2), kaempferol-3-O-glucoside, a dihydrokaempferol-O-hexoside (3), and naringenin-7-O-glucoside), the levels of at least 15 other metabolites were found to be different between the two types of red tomato. Among them were citric acid, sucrose, phenylalanine, and trigonelline. However, although statistically significant, these changes in mean values were relatively minor (less than 3-fold) and within the natural variation that would be observed in a field-grown crop. Nevertheless, this study clearly showed that NMR combined with chemometrics and univariate statistics can successfully trace even small differences in metabolite levels between plants and therefore represents a powerful tool to detect potential unintended effects in genetically modified crops.