Ammonium-dependent respiratory increase is dependent on the cytochrome pathway in Arabidopsis thaliana shoots

Oxygen uptake rates are increased when concentrated ammonium instead of nitrate is used as sole N source. Several explanations for this increased respiration have been suggested, but the underlying mechanisms are still unclear. To investigate possible factors responsible for this respiratory increase, we measured the O₂ uptake rate, activity and transcript level of respiratory components, and concentration of adenylates using Arabidopsis thaliana shoots grown in media containing various N sources. The O₂ uptake rate was correlated with concentrations of ammonium and ATP in shoots, but not related to the ammonium assimilation. The capacity of the ATP-coupling cytochrome pathway (CP) and its related genes were up-regulated when concentrated ammonium was sole N source, whereas the ATP-uncoupling alternative oxidase did not influence the extent of the respiratory increase. Our results suggest that the ammonium-dependent increase of the O₂ uptake rate can be explained by the up-regulation of the CP, which may be related to the ATP consumption by the plasma-membrane H+ -ATPase.