Characterization of a mutation in the IDH-II subunit of the NAD+-dependent isocitrate dehydrogenase from Arabidopsis thaliana

Abstract The mitochondrial NAD + -dependent isocitrate dehydrogenase (EC 1.1.1.41) is a key enzyme in the Krebs cycle of most organisms. The role of the IDH-II subunit of this protein in Arabidopsis thaliana was investigated using an idh-II knockout mutant where the IDH-II gene was disrupted by the Dissociation , ( Ds ), insertion element. These mutant plants showed no detectable differences in growth and development compared to wildtype Landsberg plants. Mitochondria from the idh-II mutant had substantially less NAD + -isocitrate dehydrogenase activity when measured in vitro but this did not appear to alter rates of tissue respiration or photosynthesis. These results suggest that the other NAD + -isocitrate dehydrogenase subunits can substitute for the missing IDH-II protein and that NAD + -IDH activity does not limit whole plant respiration as suggested by the low in vitro activity of this enzyme.