L-galactono-γ-lactone dehydrogenase is present in calcium oxalate crystal idioblasts of two plant species

Abstract

Recent studies of calcium oxalate (Caox) crystal producing plant species have revealed that ascorbic acid is likely the primary precursor of the oxalic acid (OxA) used in crystal formation. Thus far, the evidence is based on pulse-chase labeling studies coupled with microautoradiography. In addition, some studies have used the same methods to investigate the biosynthetic pathway giving rise to the ascorbic acid being used to produce OxA. Strong evidence indicates that ascorbic acid is being produced via the pathway proposed by Wheeler and Smirnoff. Further evidence in support of this biosynthetic pathway is now being pursued in the form of identification and purification of key enzymes involved in the catalysis. The final enzyme in the synthesis, L-galactono-γ-lactone dehydrogenase (EC 1.3.2.3) has been isolated and purified from two plant species, cauliflower and sweet potato. Antibodies have been raised against the purified protein from sweet potato. In this study, we employed this antibody to gather further evidence that ascorbic acid is being produced in crystal idioblasts cells via the Wheeler-Smirnoff pathway by localization of this key enzyme. We used two Caox crystal producing species, Pistia stratiotes L. and Medicago truncatula Gaertn. as model systems.