Further insights into the isoenzyme composition and activity of glutamate dehydrogenase in Arabidopsis thaliana

Abstract

Following the discovery that in Arabidopsis, a third isoenzyme of NA DH-dependent glutamate dehydrogenase (GDH) is expressed in the mitochondria of the root companion cells, we have re-examined the GDH isoenzyme composition. By analyzing the NA DH-GDH isoenzyme composition of single, double and triple mutants deficient in the expression of the three genes encoding the enzyme, we have found that the α, β and γ polypeptides that comprise the enzyme can be assembled into a complex combination of heterohexamers in roots. Moreover, we observed that when one or two of the three root isoenzymes were missing from the mutants, the remaining isoenzymes compensated for this deficiency. The significance of such complexity is discussed in relation to the metabolic and signaling function of the NA DH-GDH enzyme. Although it has been shown that a fourth gene encoding a NA DPH-dependent enzyme is present in Arabidopsis, we were not able to detect corresponding enzyme activity, even in the triple mutant totally lacking NA DH-GDH activity. © 2013 Landes Bioscience.