부산대학교 도서관

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. [ABSTRACT FROM AUTHOR]