Mitochondrial Complex I Impairment and Nitrate Reductase Activity in Leaves of Nicotiana sylvestris

Loss of major mitochondrial complex I subunit Nad 7 in the leaves of CMS II mutant of Nicotiana sylvestris caused increase in both in vivo and in vitro nitrate reductase activities and the per cent activation state of NR was also higher in CMS II as against wild type. The differences suggest a possibility for export of mitochondrial NADH due to impairment of complex I, a major and high affinity sink for NADH. Loss of complex I subunit also resulted in constitutive expression of alternate oxidase (Aox) thereby providing a mechanism for continuous supply of carbon skeletons required for nitrate assimilation. The possibility of close coordination between mitochondrial redox perturbation and nitrate reduction and its further assimilation is discussed.