Abstract
Chinese jujube (Ziziphus jujuba Mill.) is the most economically important member of the Rhamnaceae family and contains a high concentration of ascorbic acid (AsA). To explore the metabolic mechanism of AsA accumulation, we investigated the abundance of AsA in the fruit development stages, the leaf and flower of Z. jujuba cv Junzao, and the mature fruit of one type of wild jujube (Z. jujuba var. spinosa Hu, Yanchuan sour jujube). And the expression patterns of genes involved in AsA biosynthesis, degradation, and recycling were analyzed. The result showed that AsA biosynthesis during early fruit development (the enlargement stage) is the main reason for jujube high accumulation. The L-galactose pathway plays a predominant role in the biosynthesis of AsA during jujube fruit development, and the genes GMP1, GME1, GGP, and GaLDH involved in the determination of AsA concentration during fruit development and in different genotypes; the myo-inositol pathway along with the genes GME2 and GMP2 in the L-galactose pathway play a compensatory role in maintaining AsA accumulation during the ripening stage. These findings enhance our understanding of the molecular mechanism in regulating AsA accumulation for jujube.
Highlights
Ascorbic acid (AsA), called vitamin C, is an important antioxidant that plays important roles in several plant biological processes including defense mechanisms, cell division, and photosynthesis (Smirnoff, 2011)
Two biosynthetic pathways were annotated in Junzao: the L-galactose and myo-inositol pathways
Expression of GDP-l-galactose phosphorylase (GGP) thought to be the key regulatory gene of ascorbic acid (AsA) accumulation via the L-galactose pathway in many fruits (Bulley et al, 2012; Mellidou et al, 2012a,b) was up-regulated rapidly when the AsA accumulation rate increased rapidly. These findings indicate that the L-galactose AsA biosynthetic pathway may play a predominant role during jujube fruit development, and that GMP1, GME1, GGP, galactose-1-phosphate phosphatase (GPP), and GaLDH genes are involved in the determination of AsA concentration during fruit development
Summary
Ascorbic acid (AsA), called vitamin C, is an important antioxidant that plays important roles in several plant biological processes including defense mechanisms, cell division, and photosynthesis (Smirnoff, 2011). AsA, which cannot be synthesized by human body, is an important dietary supplement for humans. Fruits and vegetables synthesize relative high levels of AsA, AsA content varies markedly among plant tissues and plant species. The AsA content of a tissue is determined by its biosynthesis and recycling. In AsA recycling, AsA is produced by a reduction of oxidized forms of AsA, including monodehydroascorbate and dehydroascorbate which contributes to determination of the AsA content (Alós et al, 2013)
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