EFFECT OF POTASSIUM ON GROWTH, WATER RELATIONS, THE INORGANIC AND ORGANIC SOLUTE CONTENTS 2 MAIZE CULTIVARS GROWN UNDER SALINE CONDITIONS

Two cultivars (''Spirit'' and ''Jubileo'') of maize (Zea mays L.) were studied to compare their response to various levels of potassium (K+) (0.1, 1, and 6 mol/m(3)) and sodium chloride (NaCl) (0 and 50 mol/m(3)) in nutrient solutions with 16 h photoperiod, day/night temperature regime of 25/20 degrees C, and a photon flux density of 380 mu mol/m(2)/sec. 'Spirit' produced about 1.5 times more biomass than 'Jubileo' at 6 mol/m(3) K+ in the control treatment, while at 0.1 mol/m(3) K+ the growth of both cultivars was similar. Plant fresh weight was reduced by 20% in 'Spirit' and by 30% in 'Jubileo' with 50 mol/m(3) NaCl and 6 mol/m(3) K+. Growth reduction of maize plants by salinity was associated with an excessive accumulation of sodium (Na+) and chloride (Cl-) rather than an effect on water relations. The higher salt tolerance of 'Spirit' can be related to its greater capacity to exclude Na+ and Cl- from the leaves and to maintain a higher K+/Na+ ratio. Increasing the K+ supply in the rooting media did not improve growth reduction imposed by the 50 mol/m(3) NaCl treatment. 'Jubileo' had a lower turgor potential than 'Spirit'. High concentrations of Na+ in the leaves may help to maintain turgor, but cannot substitute for K+ to give adequate growth of maize. The accumulation in leaf tissue of inorganic ions was sufficient for osmotic adjustment in both cultivars and no single organic solute appears to be important in this process.