Leaf nitrate accumulation influences the photorespiration of rice (Oryza sativaL.) seedlings

Aims The form of nitrogen (N) supply influences photorespiration in C3 plants, but whether nitrate (NO3-) regulates photorespiration and, if so, the underlying mechanisms for such regulation are still unclear. Methods Three hydroponic experiments were conducted in a greenhouse to investigate the relationships between leaf NO(3)(-)concentrations and photorespiration rates in rice (Oryza sativaL.) genotypescv.'Shanyou 63' hybridindicaand 'Zhendao 11' hybridjaponicaor using mutants that overexpressNRT2.1(incv.'Nipponbare' inbred japonica). We estimated photorespiratory rate from the CO(2)compensation point in the absence of daytime respiration (Gamma*) using the biochemical model of photosynthesis. Results Higher Gamma* values under high N level or NO(3)(-)were significantly and positively correlated with leaf NO(3)(-)concentrations. Further elevating leaf NO(3)(-)concentrations by either resuming NO(3)(-)nutrition supply after N depletion (incv.'Shanyou 63' hybridindicaand 'Zhendao 11' hybridjaponica) or using mutants that overexpressNRT2.1(incv.'Nipponbare' inbred japonica) increased Gamma* values. Additionally, the activities of leaf nitrate reductase (Nr) and concentrations of organic acids involving in the tricarboxylic acid (TCA) cycle synchronously changed as environmental conditions were varied. Conclusions Photorespiration rate is related to the leaf NO(3)(-)concentration, and the correlation may links to the photorespiration-TCA derived reductants required for NO(3)(-)assimilation.