Abstract
Vitamin C participates in several physiological processes, among others, immune stimulation, synthesis of collagen, hormones, neurotransmitters, and iron absorption. Severe deficiency leads to scurvy, whereas a limited vitamin C intake causes general symptoms, such as increased susceptibility to infections, fatigue, insomnia, and weight loss. Surprisingly vitamin C deficiencies are spread in both developing and developed countries, with the latter actually trying to overcome this lack through dietary supplements and food fortification. Therefore new strategies aimed to increase vitamin C in food plants would be of interest to improve human health. Interestingly, plants are not only living bioreactors for vitamin C production in optimal growing conditions, but also they can increase their vitamin C content as consequence of stress conditions. An overview of the different approaches aimed at increasing vitamin C level in plant food is given. They include genotype selection by “classical” breeding, bio-engineering and changes of the agronomic conditions, on the basis of the emerging concepts that plant can enhance vitamin C synthesis as part of defense responses.
Highlights
Ascorbate (ASC) is a major soluble redox molecule with pivotal roles in allowing several metabolic pathways to work properly
It is interesting to notice that plants, which produce a great amount of ASC in almost all their tissues (ASC reaches several tens of millimolar concentrations in green tissues), have evolved a synthesizing pathway with the last step catalyzed by a dehydrogenase (L-Galactono-1,4-γ-lactone dehydrogenase GaLDH) that does not produce H2O2 (Figure 1)
An allele of MDHAR has been proposed as major candidate gene for high ASC level in tomato fruit (Stevens et al, 2008); whereas in strawberry candidate genes for stable QLT correlated to high ASC have identified in alternative biosynthesis pathways, such as Galacturonate reductase (GalUR) e Myo-inositol oxygenase (MIOX) (Zorrilla-Fontanesi et al, 2011)
Summary
Ascorbate (ASC) is a major soluble redox molecule with pivotal roles in allowing several metabolic pathways to work properly. ASC regenerates other metabolites, among which tocopherols, from oxidative damages and protects the catalytic site of a number of enzymes (e.g., hydroxylases) from irreversible oxidation, possibly caused by reactive oxygen species (ROS) in both animal and plant cells It can be used as substrate or enzyme cofactor in various biological reactions (Lodge, 2008; De Gara et al, 2010). Among which guinea pig, some birds, humans, and primates in general, ASC is a vitamin (vitamin C), since during their evolution, they have lost the capability to synthesize it In human this was caused by the loss of functionality of gulono-1,4 γ-lactone oxidase (GuLO), the enzyme catalyzing the last step of animal ASC biosynthesis (Nishikimi et al, 1992, 1994; Figure 1). Recommended dietary allowance (RDA) for vitamin C is a controversial matter, since different countries provide different advice; for example RDAs for adult men are 40 mg/day in UK; www.frontiersin.org
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