Generation of stress-resistant transgenic tomato containing a large amount of ascorbic acid

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Man is unable to synthesize ascorbic acid (vitamin C) and so depends on external sources such as plants for its supply. L-ascorbic acid attracts so much attention because of its important role in plants and relevance to man. It acts as an enzyme cofactor and an antioxidant and is involved in many different essential processes within the plant cell, including hormone and cell wall biosynthesis, stress resistance, photo-protection and cell growth. It has been established that GDP-D-mannose is involved in plant ascorbic acid biosynthesis. GDP-mannose is used for the biosynthesis of ascorbic acid, glycoprotein, L-fucose and cell wall polysaccharide. Any change in the expression of GDP-mannose pyrophosphorylase catalyzing the formation of GDP-mannose may affect the biosynthesis of ascorbic acid. The L-galactose which is released, through yet unclear steps, is oxidized to L-galactono-1,4-lactone and later converted to L-ascorbic acid by L-galactono-1,4-lactone dehydrogenase.I have investigat … More ed biosynthesis pathway and biological function of tomato plant. L-galactono-1,4-lactone dehydrogenase and GDP-mannose pyrophosphorylase are the vital enzymes in the proposed biosynthetic pathway for ascorbic acid in plants. The cDNAs encoding L-galactono-1,4-lactone dehydrogenase and GDP-mannose pyrophosphorylase have been cloned and sequenced from tomato. Northern hybridization analysis indicated that their relative mRNA levels correlated with the changing ascorbic acid content of tomato tissues, suggesting that L-galactono-1,4-lactone dehydrogenase and GDP-mannose pyrophosphorylase are involved in ascorbic acid biosynthesis.Acerola (Malpighia glabra L.) is one of the richest known natural sources of ascorbic acid (vitamin C). Thus, the expression of ascorbic acid-biosynthesizing enzymes is markedly high. Thus, I challenged to generate transgenic tomato containing a large amount of ascorbic acid in which acerola genes for ascorbic acid-biosynthesizing enzymes are introduced and over-expressed. Finally, the possibility of the generation of transgenic tomato that has resistance to environmental stresses by increasing their ascorbic acid content has been discussed. Less