Chemical composition of xylem sap of tomato grown on bicarbonate containing medium

Abstract

Incorporation of bicarbonate (HCO₃ ^‐) by the roots of tomato seedlings resulted in an increase in biomass production and changed the chemical composition of xylem sap. In the xylem sap of seedlings grown on a medium enriched with HCO₃ ^‐ (5.68 mM dm^‐3, series II) compared with the control (series I) the element content increased by about 27% and 33% for cations and anions, respectively. Potassium was the major cation in the xylem sap and constituted 69% of the total concentration of all the inorganic cations determined. Calcium attained 19% of this amount. The anionic load in the xylem sap was chiefly nitrate, constituting about 90% of the content of all the inorganic anions. The exudate was analysed for seven organic acids. In general, malic (MA), maleic, and citric (CA) occurred in xylem exudate at greater concentrations, constituting about 95% of the total content of organic acids. Cultivation of seedlings on the medium enriched with HCOJ brought about an increased content of organic acids, exceeding the control by about 60%. The concentration of MA increased by about 104% and that of CA and maleic acid exceeded the control by about 40% and 14%, respectively. Twenty amino acids were identified in tomato xylem sap. Glutamic, aspartic and y‐arninobutyric acid, and particularly the amides aspargine and glutamine occurred in greater amounts. Their total concentration was about 60% and 70% of the total amino acid content in series I and II, respectively. The remaining amino acids occurred at concentrations ≥ 90 μM. The cultivation of plants on the medium containing HCO₃ ^‐ resulted in an increase in amino acid content in xylem sap by about 28% as compared with the control. The ratio of amino acid to organic acid content was 2: 2.5 and 2: 3 for series I and II, respectively. The similar value of the ratio in the two series suggests that the synthesis of both groups of compounds be equally favoured by the carbon source (endogenous in the control and from the medium enriched with HCO₃ ^‐ in series II). The increased level of elements and organic compounds in xylem sap in the case of plants supplied with HCO₃ ^‐ is discussed in the work in respect of metabolic processes of roots.