EFFECT OF ROOT-ZONE TEMPERATURE ON THE MINERAL-COMPOSITION OF XYLEM SAP AND PLASMA-MEMBRANE K-MG++-ATPASE ACTIVITY OF GRAFTED-CUCUMBER AND GRAFTED-FIGLEAF-GOURD ROOT SYSTEMS()

Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber- (C G) or figleaf gourd- (FG, Cucurbita ficifolia Bouche) seedlings in ord er to determine the effect of solution temperature (12, 22, and 32 deg rees C) on the mineral composition of xylem sap and the plasma membran e K+-Mg++-ATPase activities of the roots. Low solution temperature (12 degrees C) lowered the concentration of NO3- and H2PO4- in xylem sap of CG plants but not of FG plants. Concentrations of K+, Ca++ and Mg+ in xylem sap were less affected than anions by solution temperature. The plasma membrane of FG plants grown in 12 degrees C solution temper ature showed the highest K+Mg++-ATPase activity at all ATP concentrati ons up to 3 mM and at low reaction temperature up to 12 degrees C, ind icating resistance of figleaf gourd to low root temperature.