Abstract
Many studies on responses of 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 limited nitrogen environments, starch accumulates, which can down-regulate photosynthesis. AOX, which is uncoupled from ATP synthesis, is suggested to consume excess carbohydrates, but this significance was not clarified. In this study, we examined respiratory properties in leaves of spinach, which was cultivated under different nitrogen conditions. Under the lower nitrogen condition, both rates of photosynthesis and respiration in the leaves were slower. These leaves had smaller amounts of mitochondrial proteins and lower capacities of COX on the leaf area basis. On the other hand, AOX capacities were much higher in the leaves of low-N spinach. AOX would efficiently consume excess carbohydrates under the limited nitrogen conditions.
