Abstract
Plant mitochondrial respiratory chain has not only the cytochrome pathway, which is common to animals, but the alternative oxidase (AOX). AOX is uncoupled with proton extrusion. Thus, AOX apparently wastes the energy, but can dissipate the excess reductants effectively. In the plant cells, substantial reductants are consumed by nitrate reduction. This suggests both AOX and nitrate reduction can be regarded as the reductant-consuming systems. This study clarified any interaction between the nitrate reduction and AOX. Thus, we examined whether the activity of nitrate reduction could influence the AOX activity. Nitrate reduction was inhibited by tungstate, which is the inhibitor of Nitrate reducase (NR). The extent of decrease in NR activity was positively correlated with that of increase in AOX capacity. This result indicated that the excess reductants accompanied by decrement in nitrate reduction could be consumed by AOX. We also examined mechanism of interaction in detail.
