Identification of Arabidopsis VTC3 as a putative and unique dual function protein kinase::protein phosphatase involved in the regulation of the ascorbic acid pool in plants.

Ascorbic acid (AsA) is present at high levels in plants and is a potent antioxidant and cellular reductant. The major plant AsA biosynthetic pathway is through the intermediates D-mannose and L-galactose. Although there is ample evidence that plants respond to fluctuating environmental conditions with changes in the pool size of AsA, it is unclear how this regulation occurs.