Nitrite-dependent nitric oxide production pathway: implications for involvement of active nitrogen species in photoinhibition in vivo

Air pollution studies have shown that nitric oxide (NO), a gaseous free rad ical, is a potent photosynthetic inhibitor that reduces CO2 uptake activity in leaves. It is now recognized that NO is not only an air pollutant hut a lso an endogenously produced metabolite, which may play a role in regulatin g plant cell functions. Although many studies have suggested the presence o f mammalian-type NO synthase (NOS) in plants, the source of NO is still not clear. There has been a number of studies indicating that plant cells poss ess a nitrite-dependent NO production pathway which can be distinguished fr om the NOS-mediated reaction. Nitrate reductase (NR) has been recently foun d to be capable of producing NO through one-electron reduction of nitrite u sing NAD(P)H as an electron donor. This review focuses on current understan ding of the mechanism for the nitrite-dependent NO production in plants. Im pacts of NO produced by NR on photosynthesis are discussed in association w ith photo-oxidative stress in leaves.