Compositional changes of selected amino acids, organic acids, and soluble sugars in the xylem sap of N, P, or K-deficient tomato plants.

Xylem sap plays a major role in long-distance transport of water, nutrients, and metabolites. However, there is little information on the behavior of metabolites in mineral-deficient xylem sap. For this reason, the time-dependent changes in selected metabolites (amino acids, organic acids, and soluble sugars) from tomato xylem sap in response to nitrogen (N), phosphorus (P), or potassium (K)-deficient condition were investigated. Tomato plants ( Solanum lycopersicum L.) were grown hydroponically in liquid culture under three different mineral regimes: N-deficient [0.5 mM Ca(NO3)2 and 0.5 mM KNO3], P-deficient (0.05 mM KH2PO4), and K-deficient (0.5 mM KNO3), respectively. Xylem sap was collected at 10:00 am after 1, 5, 15, and 30 d, and the selected metabolites were analyzed with liquid chromatography. All N, P, or K deficiencies led to a substantial increase in metabolites in the xylem sap. The predominant amino acid in the xylem sap was glutamine and, interestingly, all mineral deficiencies resulted in a substantial amount of γ-aminobutyric acid (GABA). Additionally, organic acids (citrate and malate) and soluble sugars were strongly increased in all mineral deficiencies, and, in particular, the level of shikimate was greatly affected by N deficiency. Based on these data, it is necessary to clearly elucidate an unknown event taking place in xylem loading in a variety of environmental impacts, and we are now studying to expand our knowledge on metabolic and proteomic responses using GC-MS and LC-MS. [ABSTRACT FROM AUTHOR]