Nitric oxide and plant mitochondria

Study of the interactions between nitric oxide (NO) and mitochondria are important for two major reasons. First, mitochondrial respiration is responsible for energy production in many metabolic functions in plant cells. Second, both apoptosis and necrosis, the two types of cell death, are closely linked to mitochondrial functions. NO can act at the mitochondrial level by binding to cytochrome oxidase, the terminal enzyme of the respiratory chain, thus inhibiting respiration. This interaction is thought to be responsible for the pro-apoptotic action of NO, since in NO treated cells various processes are observed, including the release of cytochrome c, production of reactive oxygen species, a decrease in the concentration of ATP, and opening of the permeability transition pore. However, NO-induced inhibition of respiration may also play a protective role. In reality, under limiting concentrations of O2, NO plays a major role in reducing plant cell metabolism in order to decrease the consumption of O2 and avoid anoxia. It has been suggested that NO may provide a sensing mechanism for O2, allowing the cell to perceive variations in O2 tension at O2 concentrations well above limiting concentrations for mitochondrial electron transport.