Flavonoids are phenolic compounds derived ultimately from phenylalanine which impart much of the color and flavor of fruits, vegetables, nuts and seeds. The first committed step in flavonoid biosynthesis is the conversion of the precursor 4-coumaroyl-CoA into chalcone by the enzyme chalcone synthase. Chalcone is then derivatized in a series of enzymatic steps to eventually form different classes of flavonoids, such as flavanones, dihydroflavonols and finally to the anthocyanins, the major water-soluble pigments in flowers and fruits (Schijlen et al. 2004). Tomato is an excellent candidate for transgenic enhancement of flavonoid content. It is an important food crop worldwide; however, its flavonoid content is generally low and largely confined to the tomato peel. Constitutive, high level overexpression of a petunia chalcone isomerase in tomato resulted in up to 78-fold increases in the levels flavonoids in the peel (Muir et al. 2001). However, since the peel accounts for only about 5% of fruit mass the overall increase was rather low. A 3.5-fold increase in fruit flavonol content of tomato was achieved by RNAi-mediated suppression of the tomato DET1 gene, which encodes a transcription factor negatively regulating photomorphogenic responses (Davuluri et al. 2005).
Coordinate transcriptional control of biosynthetic genes has emerged as a major mechanism dictating the final levels of secondary metabolites in plant cells. In various plant species the tissue-specific regulation of the structural genes involved in flavonoid biosynthesis is controlled by the combination of regulators from two transcription factor families (Schijlen et al. 2004). Consequently, overexpression of Lc and C1, two transcription factors that control flavonoid biosynthesis in maize, resulted in tomato fruit containing 20-fold higher flavonol content than the respective control. In a similar approach, Butelli et al. (2008) expressed the Del and Ros1 genes from snapdragon in the fruit of transgenic tomatoes. Both genes encode transcription factors that interact with each other to induce anthocyanin biosynthesis in snapdragon flowers. The fruit of the transgenic tomato plants accumulated anthocyanins at levels substantially higher than previously reported. Evidence for a health promoting effect of these engineered tomato fruits comes from a pilot study in which a cancer-susceptible mouse strain showed a significant extension of life span when fed on high-anthocyanin tomatoes (Butelli et al. 2008).
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Interested In Canning Juicy Tomatoes? Here's How You Can Prepare Canned Tomatoes At Home. A Comprehensive Guide On Tomato Canning. The process of canning tomatoes at home has been a family tradition with many generations. Making home canned or home tinned tomatoes is something that is remembered by families for years! You must have surely seen your granny canning tomatoes at home in order to prepare for the approaching winters. In winters, one is usually unsure of getting fresh tomatoes.