Inhibitory effects of nitric oxide on oxidative phosphorylation in plant mitochondria

Plant nitrate reductase (NR) produces nitric oxide (NO) when nitrite is pro vided as the substrate in the presence of NADH [H. Yamasaki and Y. Sakihama (2000) FEBS Lett. 468, 89-92]. Using a NR-dependent NO producing system, w e investigated the effects of NO on the energy transduction system in plant mitochondria isolated from mung bean (Vigna radiata). Plant mitochondria a re known to possess two respiratory electron transport pathways-the cytochr ome and alternative pathways. When the alternative pathway was inhibited by n-propyl gallate, the addition of NR strongly suppressed respiratory O-2 c onsumption driven by the cytochrome pathway. In contrast, the alternative p athway measured in the presence of antimycin A was not affected by NO. The extent of the steady-state membrane potential (Delta psi) generated by resp iratory electron transport rapidly declined in response to NO production. T he addition of bovine hemoglobin, a quencher of NO, resulted in the recover y of Delta psi to the uninhibited level. Consistent with its inhibition of Delta psi, NO produced by NR strongly suppressed ATP synthesis in the mitoc hondria. These results provide substantial evidence to confirm that the pla nt alternative pathway is resistant to NO and support the idea that the alt ernative pathway may lower respiration-dependent production of active oxyge ns under conditions where NO is overproduced, (C) 2001 Academic Press