Distribution and metabolism of ascorbic acid in apple fruits ( Malus domestica Borkh cv. Gala)

• Published in: Plant science (Limerick) 2008-06, Vol.174 (6), p.606-612
• Main Authors: Li, Ming-Jun, Ma, Feng-Wang, Zhang, Min, Pu, Fei
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; amino acid metabolism; Apple fruits; apples; ascorbate peroxidase; Ascorbic acid; Biological and medical sciences; Distribution; Economic plant physiology; enzyme activity; Fructification, ripening. Postharvest physiology; fruiting; Fundamental and applied biological sciences. Psychology; glutathione dehydrogenase (ascorbate); glutathione reductase (NADPH); Growth and development; Malus domestica; Metabolism; monodehydroascorbate reductase; ripening; tissue distribution
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2008.03.008

The objective of this study was to determine ascorbic acid (AsA) distribution, biosynthesis and recycling in different tissues of young and mature fruit of cv. Gala apple ( Malus domestica Borkh). Our results showed that the peel of ‘Gala’ apple had the highest AsA levels among all the tissue types, which resulted from a combination of, lower ascorbate peroxidase (APX, EC 1.11.1.11) activity consuming AsA, and higher dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities used to recycle AsA. Exogenous feeding of AsA synthesis precursors demonstrated that the peel was capable of de nono AsA biosynthesis via l-galactose and d-galacturonic acid pathways whereas the flesh and seed were only able to synthesize AsA via l-galactose pathway. The young fruit had higher AsA concentration and stronger capability of AsA biosynthesis and recycling. The sun-exposed peel had higher AsA concentration and stronger capability of recycling AsA than the shaded peel, while there was no difference in the flesh between the sun-exposed side and the shaded side. Abundant AsA was found in fruit vascular tissue, which suggests that AsA can be transported to vascular tissues of fruit or vascular tissues could synthesize AsA itself in ‘Gala’ apple.