GABA shunt deficiencies and accumulation of reactive oxygen intermediates: insight from Arabidopsis mutants

In plants, succinic semialdehyde dehydrogenase (SSADH)-deficiency results in the accumulation of reactive oxygen intermediates (ROI), necrotic lesions, dwarfism, and hypersensitivity to environmental stresses [Bouché, N., Fait, A., Moller, S.G. and Fromm, H. (2003) Proc. Natl. Acad. Sci. USA. 100, 6843-6848]. We report that Arabidopsis ssadh knockout mutants contain five times the normal level of γ-hydroxybutyrate (GHB), which in SSADH-deficient mammals accounts for phenotypic abnormalities. Moreover, the level of GHB in Arabidopsis is light dependent. Treatment with γ-vinyl-γ-aminobutyrate, a specific γ-aminobutyrate (GABA)-transaminase inhibitor, prevents the accumulation of ROI and GHB in ssadh mutants, inhibits cell death, and improves growth. These results provide novel evidence for the relationship between the GABA shunt and ROI, which may, in part, explain the phenotype of SSADH-deficient plants and animals.