Metabolite profiling of soybean root exudates under phosphorus deficiency

Root exudates are derived from plant metabolites and their composition is affected by the plant nutritional status. The purpose of this study was to examine soybean root exudates under phosphorus (P) deficiency using a metabolite profiling technique. Glycine max L. (cv. Suzuyutaka) was grown in a culture solution at P concentrations of 0 (P0) and 8 (P8) mg P L-1 for 1, 5, 10 and 15days after transplanting. Shoot extract, root extract and root exudates were collected and their metabolites were determined by capillary electrophoresis/time-of-flight mass spectrometry (CE-TOF MS). The shoot P concentration and dry weight of soybean plants grown at P0 were lower than those at P8. One hundred and eight, 116 and 79 metabolites were identified in the shoot extract, root extract and root exudates, respectively. The concentrations of several metabolites including amino acids and organic acids in root exudates were higher at P0 than at P8, irrespective of the P concentration in the shoot or root extract. These findings suggest that soybean roots actively release metabolites in response to P deficiency.