# Vitamin C in Plants: From Functions to Biofortification
## 1 Introduction
As a result of vitamin C deficiency, especially in the nucleus, the requirements of TETs or some JmjC-domain-containing histone demethylases may not be met, leading to alterations in the methylation-demethylation dynamics of DNA and histones, which can subsequently contribute to phenotypic alterations or even diseases. By regulating the epigenome, vitamin C can be involved in embryonic development, postnatal development and aging, and cancer and other diseases [24]. Being able to modulate the epigenome, vitamin C has been proposed as an effective molecule in anticancer therapies [25]. Vitamin C is considered a vitamin only for a few vertebrate species, including humans, that are unable to synthesize it [26]. Indeed, vitamin C can be synthesized by plants and most animals [27]. Primates, guinea pigs, bats, some species of birds, insects, invertebrates, and fish are examples of species not able to synthesize this vitamin [26; 27]. The inability of humans to synthesize vitamin C lies in the functional loss of the gene coding \(\upmu\)-gulonolactone oxidase, the last enzyme involved in the animal biosynthetic pathway of this vitamin [26]. The best way for humans to obtain vitamin C is by diet, and plant foods represent the primary source of this vitamin. Although synthetic vitamin C is chemically indistinguishable from the plant-derived vitamin, fruits and vegetables have different micronutrients and phytochemicals that can affect its bioavailability [28]. Many studies conducted on vitamin-C-deficient animals have shown that vitamin C in plant foods has greater bioavailability than that found in drugs or supplements [28]. For instance, in homozygote Gulo mice, the uptake and tissue distribution of vitamin C were higher when the vitamin was furnished by kiwifruit gel than when it was added as a synthetic supplement in drinking water [29]. Nevertheless, studies conducted on humans have not shown significant differences in bioavailability between synthetic and plant-derived vitamin C [28]. Despite the comparable dosage and bioavailability, it has been shown that orange juice and not synthetic vitamin C drink protects leukocytes from oxidative DNA damage [30]. Probably, the improved effects of vitamin C dispensed with fruits and vegetables is due to the interaction with other micronutrients, such as vitamin E [31] and iron [32]. Consistently, plant-derived vitamin C is related to reduced occurrence of different chronic diseases [33]. The loss of the capability to synthesize vitamin C in our ancestors would not have been a disadvantage with a diet rich in vegetables and fruits, which could have provided enough vitamin C [34]. On the contrary, since \(\iota\)-gulonolactone oxidase produces the potentially toxic H\({}_{2}\)O\({}_{2}\), this loss could have been an evolutionary improvement in the control of redox homeostasis [35]. Nowadays, very low levels of vitamin C are present in main crops, with the consequence that diet does not provides enough intake of this vitamin. Thus, obtaining plant foods with enhanced vitamin C content represents an important goal for human health. In-depth knowledge of the metabolism and functions of vitamin C in plants is needed to achieve biofortification.