Abstract
To elucidate metabolism of ascorbic acid (AsA) in sweet cherry fruit (Prunus avium ‘Hongdeng’), we quantified AsA concentration, cloned sequences involved in AsA metabolism and investigated their mRNA expression levels, and determined the activity levels of selected enzymes during fruit development and maturation. We found that AsA concentration was highest at the petal-fall period (0 days after anthesis) and decreased progressively during ripening, but with a slight increase at maturity. AsA did nevertheless continue to accumulate over time because of the increase in fruit fresh weight. Full-length cDNAs of 10 genes involved in the L-galactose pathway of AsA biosynthesis and 10 involved in recycling were obtained. Gene expression patterns of GDP-L-galactose phosphorylase (GGP2), L-galactono-1, 4-lactone dehydrogenase (GalLDH), ascorbate peroxidase (APX3), ascorbate oxidase (AO2), glutathione reductase (GR1), and dehydroascorbate reductase (DHAR1) were in accordance with the AsA concentration pattern during fruit development, indicating that genes involved in ascorbic acid biosynthesis, degradation, and recycling worked in concert to regulate ascorbic acid accumulation in sweet cherry fruit.
Highlights
Ascorbic acid (AsA) has several essential functions in plant physiology
We examined the pattern of expression of five genes involved in the degradation pathways and five genes involved in AsA recycling during fruit maturation
AsA concentrations in plant cells are highly regulated by developmental processes such as fruit development
Summary
Ascorbic acid (AsA) has several essential functions in plant physiology. AsA is the most abundant water-soluble antioxidant in higher plants, participates in the detoxification of reactive oxygen species, and has an important role in promoting resistance to senescence [1] and numerous environmental stresses, such as ozone [2, 3], dehydration stress [4, 5], high light [6] and salt stress [7]. AsA operates as a cofactor and take part in the regulation of some fundamental cellular processes (e.g. photoprotection, the cell cycle and cell expansion) and biosynthesis of important plant hormones (e.g. including ethylene, jasmonic acid, salicylic acid, abscissic acid gibberellic acid) [8, 9]. Fruit and vegetables are a primary source of dietary intake of vitamin C for humans, because primates and some other animals lack the ability to synthesize AsA [10]. Because of these unique functions, as well as its benefits to human health, mounting attention has been paid to AsA metabolism and regulation in plant tissues. De novo biosynthesis is PLOS ONE | DOI:10.1371/journal.pone.0172818 February 28, 2017
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