Identification of ascorbic acid-deficient Arabidopsis thaliana mutants

Vitamin 6 (L-ascorbic acid) is a potent antioxidant and cellular reductant present at millimolar concentrations in plants. This small molecule has rol es in the reduction of prosthetic metal ions, cell wall expansion, cell div ision, and in the detoxification of reactive oxygen generated by photosynth esis and adverse environ mental conditions. However, unlike in animals, the biosynthesis of ascorbic acid (AsA) in plants is only, beginning to be unr aveled. The previously described AsA-deficient Arabidopsis mutant vtc1 (vit amin c-1) was recently shown to have a defect in GDP-mannose pyrophosphoryl ase, providing strong evidence for the recently proposed role of GDP-mannos e in AsA biosynthesis. To genetically define other AsA biosynthetic loci, w e have used a novel AsA assay to isolate four vtc mutants that define three additional VTC loci. We have also isolated a second mutant allele of VTC1. The four loci represented by the vtr mutant collection have been genetical ly characterized and mapped onto the Arabidopsis genome. The vtc mutants ha ve differing ozone sensitivities. In addition, two of the mutants, vtc2-1 a nd vtc2-2, have unusually low levels of AsA in the leaf tissue of mature pl ants.