Resolving the Role of Plant Glutamate Dehydrogenase: II. Physiological Characterization of Plants Overexpressing the Two Enzyme Subunits Individually or Simultaneously

Glutamate dehydrogenase (GDH; EC 1.4.1.2) is able to carry out the deamination of glutamate in higher plants. In order to obtain a better understanding of the physiological func-tion of GDH in leaves, transgenic tobacco (Nicotiana taba-cum L.) plants were constructed that overexpress two genes from Nicotiana plumbaginifolia (GDHA and GDHB under the control of the Cauliflower mosiac virus 35S promoter), which encode the a- and b-subunits of GDH individually or simul-taneously. In the transgenic plants, the GDH protein accu-mulated in the mitochondria of mesophyll cells and in the mitochondria of the phloem companion cells (CCs), where the native enzyme is normally expressed. Such a shift in the cellular location of the GDH enzyme induced major changes in carbon and nitrogen metabolite accumulation and a re-duction in growth. These changes were mainly characterize