Ascorbic acid metabolism is influenced by oxidation, recycling, synthesis and transport during fruit development of Malpighia emarginata

This study evaluated gene expression and activity of key enzymes associated with L-ascorbic acid metabolism during the development of acerola. Acerola cv. Flor-branca shows a double sigmoid growth curve reaching physiological maturity at 17 days after anthesis (DAA) and is fully ripe at 21 DAA. Thus, fruits were analyzed at 15, 17, 19, 21 and 23 DAA. Total L-ascorbic acid (T-AsA) concentration declined 60% from immature green (15 DAA) to the fully ripe stage (21 DAA), with a relative increase in the content of the reduced form L-ascorbic acid (AsA). Regarding AsA biosynthesis, L-GalLDH activity increased during fruit development from 15 to 19 DAA. Oxidative enzyme activity patterns differed during ripening, APX was initially higher and decreased, while ascorbate oxidase (AO) activity was initially lower and then increased until 21 DAA. The activity patterns of recycling enzymes monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were similar and increased during fruit development. The genes associated with AsA biosynthesis (GalLDH, GMP and GME) showed similar expression profiles during fruit maturation (after 17 DAA) and may be related to the increase in L-GalLDH activity. The profile of genes linked to AsA degradation showed that AO isoform 2 is mainly involved in oxidation during fruit development. The high concentration of T-AsA in immature acerola seems related to cellular intake from phloem due to the high expression of the l-ascorbic acid transporter NAT3 gene. The data observed here gives an insight into the key points of regulation of AsA metabolism during acerola development that enables further fresh market and industrial uses, besides genetic manipulation efforts.

Graphical abstract