Abstract
Ascorbate accumulation levels, distribution and key enzyme activities involved in synthesizing via Smirnoff-Wheeler pathway and recycling in different pear fruit tissues during development were studied. Results show that the ascorbate contents increased with the fruit development, and reached the highest titers in 30 days after anthesis (DAA), then decreased and maintained a level. The higher contents of ascorbate in the peel of pear fruit were observed, which results from a combination of higher activities of L-galactose dehydrogenase (GalDH) and L-galactono-1,4-lactone (GalLDH) involving ascorbate biosynthesis and higher dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities used to recycle ascorbate. Exogenous feeding of ascorbate synthesis precursors demonstrated that the peel had stronger capability of de novo ascorbate biosynthesis via Smirnoff-Wheeler pathway and uronic acid pathway whereas the flesh and core had lower capability for ascorbate synthesis. These results suggest that the pear fruit is able to cause de novo ascorbate biosynthesis and the peel had higher capability for ascorbate biosynthesis than the flesh and core. Key words: Pyrus pyrifolia, ascorbate, biosynthesis.
Highlights
L-Ascorbic acid (AsA), called vitamin C (Vc) or ascorbate (ASC), is a vital antioxidant compound that plays a critical role in the cellular metabolism of plants and animals (Banhegyi et al, 1997; Noctor and Foyer, 1998)
The higher contents of ascorbate in the peel of pear fruit were observed, which results from a combination of higher activities of L-galactose dehydrogenase (GalDH) and L-galactono-1,4-lactone (GalLDH) involving ascorbate biosynthesis and higher dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities used to recycle ascorbate
These results suggest that the pear fruit is able to cause de novo ascorbate biosynthesis and the peel had higher capability for ascorbate biosynthesis than the flesh and core
Summary
L-Ascorbic acid (AsA), called vitamin C (Vc) or ascorbate (ASC), is a vital antioxidant compound that plays a critical role in the cellular metabolism of plants and animals (Banhegyi et al, 1997; Noctor and Foyer, 1998). Plants and most animals can synthesize AsA, a few mammalian species including primates, humans and guinea pigs have lost this capability (Nishikimi et al, 1994), for lacking L-gulono-1,4-lactone oxidase, an enzyme essential for its synthesis. Humans are unable to synthesize AsA in their bodies and deficiency state occurs with a wide spectrum of clinical manifestations. Scurvy is one of the Abbreviations: DAA, Days after anthesis; GalDH, L-galactose dehydrogenase; GalDH, L-galactose dehydrogenase; DHAR, dehydroascorbate reductase; MDHAR, monodehydroascorbate reductase; AsA, ascorbic acid. Clinical expressions of ascorbate deficiency, which is a lethal condition unless appropriately treated (Diplock et al, 1998). In order to survive humans must ingest vitamin C, mainly from fresh fruits, vegetables and other crop produce (Li and Schellhorn, 2007)
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