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

Aims The form of nitrogen (N) supply influences photorespiration in C3 plants, but whether nitrate (NO 3 − ) 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 sativa L.) genotypes cv. ‘Shanyou 63’ hybrid indica and ‘Zhendao 11’ hybrid japonica or using mutants that overexpress NRT2.1 (in cv. ‘Nipponbare’ inbred japonica). We estimated photorespiratory rate from the CO 2 compensation point in the absence of daytime respiration (Γ*) using the biochemical model of photosynthesis. Results Higher Γ* 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 (in cv. ‘Shanyou 63’ hybrid indica and ‘Zhendao 11’ hybrid japonica ) or using mutants that overexpress NRT2.1 (in cv. ‘Nipponbare’ inbred japonica) increased Γ* 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.