Department of Plant Sciences

Root exudates are derived from plant metabolites and the composition is affected by plant nutrient status. Acid phosphatase and organic acids are well-known root exudates in soils with low phosphorus (P) status. We applied metabolite profiling technique to investigate rice root exudates under P deficiency. Oryza sativa (cv. Nipponbare) was grown in solution culture at P concentrations between 0 to 258 µM for several weeks. Root exudates and root extracts were collected and their metabolites were determined by capillary electrophoresis / time-of-flight mass spectrometry (CE-TOF MS). Shoot P concentration and dry weight of rice plants grown at low P levels were lower than those at high P levels. Twenty-nine anionic and 51 cationic compounds and 15 anionic and 32 cationic compounds were identified in root extracts and in root exudates, respectively. More than 80% of metabolites in the root exudates showed higher concentration at low P levels than at high P levels. On the other hand, only 20% of metabolites in the root extracts showed higher concentration at low P levels than at high P levels. These results suggest that rice roots exude many metabolites in response to P deficiency.