Identification of the Elusive Chloroplast Ascorbate Transporter Extends the Substrate Specificity of the PHT Family

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Most of the enzymatic reactions of ascorbate biosynthesis occur in the cytosol, with the exception of the terminal step, catalyzed by L-galactono-1,4-lactone dehydrogenase, which is localized on the inner mitochondrial membrane. Given the location of L-galactono-1,4-lactone dehydrogenase, the rate of ascorbate biosynthesis is intimately associated with the rate of mitochondrial respiration (Nunes-Nesi et al., 2005). Ascorbate has legion roles in the plant cell including mitosis, cell division, expansion and cell wall hydroxylation, hormone biosynthesis, signal transduction, programmed cell death, as well as protection against environmental stresses via detoxification of reactive oxygen species and regeneration of other antioxidants.