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Among such vital organic compounds, one of the important vitamins is Vitamin-C (Ascorbic

acid).

Figure 1

ASCORBIC ACID AND ITS BIOSYNTHESIS IN PLANTS:

Ascorbic acid which is also known as L-Ascorbic acid is a naturally occurring chiral vitamin
as shown in Fig 1. The opposite enantiomer of ascorbic acid (D-ascorbic acid), is biologically

inactive, and thus it does not produced in the biosynthesis or in major industrial synthesis of
ascorbic acid (Crawford, 1982, Davey et al., 2000, EFSA, 2013a; EFSA, 2013b and EFSA,

2015). Thus, ascorbic acid is always refer as L-Ascorbic acid. It is synthesized by plants,
whereas in animals including primates, they lack biosynthesis capacity due to loss of function

due to mutations in the one of the vital enzyme L-gulono-1,4-lactoneoxidase (Drouin et al.,

2007) and thus have to obtain ascorbic acid from different sources like plants. Ascorbate
biosynthesis pathways differ in animals and green plants (Wheeler et al., 2015 and Smirnoff

et al., 2001). In green plants, the biosynthesis of ascorbic acid is takes place by Smirnoff-
Wheeler pathway (D-mannose/L-galactose pathway) (Ishikawa et al., 2008).

To explain the biosynthesis of ascorbic acid in plants, which is one of the chaotic work, took

more than a decade. “The biosynthesis of ascorbic acid in higher plants is takes place in
mitochondria via several proposed routes” (Akram et al., 2017). Among the different

proposed pathway for biosynthesis of ascorbic acid, the most accepted pathway is Smirnoff-
Wheeler pathway (D-mannose / L-galactose pathway) (Wheeler et al., 1998). Another three

ways are proposed for the biosynthesis of ascorbic acid; the gulose pathway, the myoinositol

pathway and the galacturonate pathway (Wolucka et al., 2003; Lorence et al., 2004 and
Agius et al., 2004). The Smirnoff-Wheeler pathway in plants involves the generation of L-

ascorbic acid from L-galactose (Wheeler et al., 1998) (Figure 2). L-Galactose is generated
from mannose-1-phosphate by the conversion of guanosine diphosphate (GDP)-mannose to

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