The challenge of increasing vitamin C content in plant foods

Abstract

The term "vitamin" is used to define a number of organic compounds that have to be obtained from different foods because the organism itself cannot synthesize them in the quantities needed to sustain life. Vitamin C is the common name for L-ascorbic acid. In humans, the principal role of this molecule is to scavenge reactive oxygen species, due to its antioxidant capacity, and to serve as cofactor for many enzymes. A deficiency of L-ascorbic acid is traditionally linked to human diseases such as scurvy. Plant foods are the principal source of L-ascorbic acid for humans. There is a high variability of L-ascorbic acid content in the various plant organs that are used for human consumption. This diversity is related to the specific functions played by L-ascorbic acid in the different plant tissues. The net content of L-ascorbic acid in plants is determined through a balance of the activities of different biosynthetic, recycling, and catabolic pathways. Here we review the importance of L-ascorbic acid for human health, the current knowledge on its metabolism and function in plants, and the efforts that have already been made by genetic modification to improve its content in plant organs used for human food. We provide a current and forward looking perspective of how plant science can contribute to improving the L-ascorbic acid content in crop species using gene transformation, quantitative trait loci and association mapping-based approaches.

Overexpression of the Monodehydroascorbate Reductase Gene from Non-heading Chinese Cabbage Reduces Ascorbate Level and Growth in Transgenic Tobacco

“…PMM and GMP increase AsA level when overexpressed (Badejo et al 2008(Badejo et al , 2009Cruz-Rus et al 2012), but are not considered key regulatory points of AsA biosynthesis. Many studies suggest that GME and GGP are the key regulatory points of AsA in plants (Cruz-Rus et al 2012;Linster and Clarke 2008;Ren et al 2013). However, increased expression of GME was found in this study, indicating that the regulatory role of GME in AsA biosynthesis is complex.…”

“…In plants, the AsA synthesis pathway involves a complex network of D-mannose/L-galactose (D-Man/L-Gal), L-glucose, D-galacturonate, and myo-inositol (MI) as entry points into the network (Cruz-Rus et al 2012). The D-Man/L-Gal pathway, commonly called the Smirnoff-Wheeler pathway, is considered the main route of AsA biosynthesis (Cruz-Rus et al 2012).…”

“…In plants, the AsA synthesis pathway involves a complex network of D-mannose/L-galactose (D-Man/L-Gal), L-glucose, D-galacturonate, and myo-inositol (MI) as entry points into the network (Cruz-Rus et al 2012). The D-Man/L-Gal pathway, commonly called the Smirnoff-Wheeler pathway, is considered the main route of AsA biosynthesis (Cruz-Rus et al 2012). Therefore, the transcript levels of eight genes in the pathway were analyzed, namely D -mannose-6-phosphate isomerase (PMI), phosphomannomutase (PMM), GDP-mannose pyrophosphorylase (GMP), GDP-mannose-3′,5′-epimerase (GME), GDP-L-galactosephosphorylase (GGP), L-galactose-1-phosphate phosphatase (GPP), L-galactose dehydrogenase (GDH), and L-galactono-1,4-lactone dehydrogenase (GLDH).…”

“…Therefore, a deficiency in AsA could lead to various human diseases, such as scurvy and cancer (Mandl et al 2009). Fresh fruit and vegetables are the major sources of AsA for humans, primates, a few other mammals and passerines that are unable to synthesize it (Cruz-Rus et al 2012). Thus, a number of strategies and studies have been published to improve AsA level in plants through metabolic engineering (Gest et al 2013;Badejo et al, 2009;Tokunaga et al 2005;Gallie 2013;Ishikawa et al 2006;Chen et al 2003;Qin et al 2011).…”

Isolation and Characterization of GDP-L-Galactose Phosphorylase Gene of Vitamin C Biosynthesis Pathway from Kiwi

“…Vitamin C is a common name of L-ascorbic acid (AsA) that derived from a six-carbon sugar (L-threo-hex-2-enono-1,4-lactone). 1 Vitamin C is a water-soluble antioxidant that has a predominantly protective role and acts as a cofactor in the synthesis of carnitine and collagen requirement of cardiovascular function, repair, and maintenance of cartilage, bone, and teeth. It also acts as an important component of the skin, scar tissue, tendons, ligaments and blood vessels, as well as the development of immune cells and iron absorption, and is necessary for healing.…”