ION BALANCE IN TOMATO CULTIVARS DIFFERING IN SALT TOLERANCE .1. SODIUM AND POTASSIUM ACCUMULATION AND FLUXES UNDER MODERATE SALINITY

The magnitude of sodium and potassium fluxes in Lycopersicon esculentum cultivars Ace and Edkawi (Edkawi is considered more salt-tolerant) was evaluated in plants grown for 10 days in aerated Hoagland solution with the addition of 25 or 100 mM NaCl. Ion accumulation in different plant parts, ion concentration in xylem exudate, transpiration and membrane leakiness were measured. Bath cultivars responded very similarly to these levels of salinity in terms of growth. No conspicuous differences in membrane leakiness were observed. Net uprake rates were calculated from ion contents data. Potassium uptake rates were lower in salinized plants than in controls, especially in cv. Ace. Potassium/sodium selectivity ratios were much higher in Edkawi than in Ace, and higher in shoot uptake rates than in xylem exudate. This indicates that Edakwi has a higher capacity to retain potassium under salinity, a character which could contribute to its salt-tolerance.