Enhanced heavy metal sensitivity of tobacco cultured cells overexpressing RmGLP2, an azalea germin-like protein with oxalate oxidase activity

Abstract

Although known as a harmful food ingredient of plant origin, oxalate has been considered in plants to contribute to cellular protection against heavy metal toxicity by exerting chelating effects. During our research of functional characterization of an NO₂-inducible germin-like protein (RmGLP2) from azalea leaves¹, we found that recombinant RmGLP2 proteins, when overexpressed in tobacco cultured cells, were destined for the apoplast where they exhibited enzymatic activities for both superoxide dismutase and oxalate oxidase (OxO). In parallel with the increased OxO activity in the apoplast, there was a marked decrease in oxalate levels in the transformed cells. In the presence of heavy metals, transformed cells showed the hypersensitivity and significantly impaired biomass production. These results strongly suggest the plant physiological importance of oxalate accumulation in suppressing heavy metal toxicity.
¹Kondo et al. (2008) Biochem. Biophys. Res. Commun. 377: 857-861.