Abstract
Many studies on responses of higher plant respiration to nitrogen environments were concerned with relationships between respiration rates and tissue nitrogen contents. There were few studies as to underlying mechanisms of this relationship and physiological roles of respiration under limited nitrogen environments. Under a limited nitrogen environment, starch accumulates, which can down-regulate photosynthesis. Leaf respiration will consume excess carbohydrates in leaves so that C:N ratio would be well-balanced. The cyanide-resistant alternative pathway (AOX) is suggested to consume excess carbohydrates, but this significance was not clarified. In this study, we examined (1) respiration rates with various nitrogen environments, (2) amounts and maximal activities of respiratory enzymes, (3) oxygen uptake of respiratory chain, and (4) in vivo activity of AOX with 18O in spinach leaves. In this paper, we discuss regulatory mechanisms and physiological roles of respiration under low nitrogen environments.
