THE INFLUENCE OF SALINITY ON THE UTILIZATION OF ROOT ANAPLEROTIC CARBON AND NITROGEN-METABOLISM IN TOMATO SEEDLINGS

In hydroponically grown Lycopersicon esculentum (L,) Mill. cv. F144 the site of NO3- reduction and assimilation within the plant was shifted from the shoot to the root by salinity. Uptake of NO3- from the root solution was strongly inhibited by salinization. Consequently, NO3- concentrations in the leaf, stem and root tissues as well as the nitrate reductase activities of the leaves were lower in salinized than in control plants, Lower NO3- but higher reduced-N, concentrations were observed in the xylem sap as a result of the enhanced participation of the root in NO3- reduction in salinized plants. Lower stem K+ concentrations and leaf malate concentrations were found in salinized compared to control plants which indicates reduced functioning of the K+-shuttle in the salinized plants, Incorporation of inorganic carbon by the root was determined by supplying a pulse of (NaHCO3)-C-14 followed by extraction and separation of the labelled products on ion exchange resins. The rate of (HCO3-)-C-14 incorporation was c, 2-fold higher in control than in salinized plants, In salinized plants the products of (HCO3-)-C-14 incorporation within the roots were diverted into amino acids, while the control plants diverted relatively more C-14 into organic acids. Products of inorganic carbon incorporation in the roots of salinized plants provide an anaplerotic source of carbon for assimilation of reduced NO3- into amino acids, while in control plants the products were predominantly organic acids as part of mechanisms to maintain ionic balance in the cells and in the xylem sap.