Interactions Between Day Respiration, Photorespiration, and N and S Assimilation in Leaves

Abstract

Respiration of illuminated leaves (day respiration) represents a minor carbon flux as compared to photosynthesis and photorespiration under usual gaseous conditions. However, it is crucial for leaf primary metabolism, since it sustains N assimilation and provides ATP that can be used for sucroseSucrosesynthesis in the light. Although available data on interactions between photosynthesis, photorespiration, respiration, and nutrient assimilation are still rather limited, recent works taking advantage of isotopic labelingLabelingand metabolomicsMetabolomicssuggest that changes in photosynthetic and photorespiratory conditions (or the carboxylation-to-oxygenation ratio, vc/vo) influence N assimilation, S incorporation into methionineMethionine, and possibly, displace the equilibrium between C1-metabolites. The crossroad of all of these pathways is mitochondrial metabolism. Therefore, day respiration is probably of considerable importance not only for nutrient assimilation but also for cellular metabolic coordination. This view agrees with data obtained in respiratory mutants.