Apoplastic degradation of ascorbate: Novel enzymes and metabolites permeating the plant cell wall

M A Green, S C Fry

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A significant minority of the vitamin C in plants is located in the apoplast. We discuss recent progress towards mapping the pathway by which apoplastic L-ascorbate is converted to oxalate plus L-threonate. At least two novel compounds have been detected as apoplastic intermediates in the pathway: namely, 4-O-oxalyl-L-threonate and cyclic oxalyl di-ester(s) of L-threonate. In addition, evidence is presented for a dehydroascorbate oxidase activity and two novel oxalyl-esterase activities involved in the pathway. The operation of the pathway may augment the proposed role of ascorbate as a pro-oxidant since several steps in the pathway potentially generate H2O2. We argue that, whether acting as a pro-oxidant or in its better-known capacity as an anti-oxidant, apoplastic ascorbate may loosen the cell wall and hence promote cell expansion and/or fruit softening.

Original languageEnglish
Pages (from-to)27
Number of pages6
JournalPlant Biosystems - An International Journal Dealing with all Aspects of Plant Biology
Issue number1
Publication statusPublished - Mar 2005

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