EFFECTS OF NACL AND NA2SO4 ON IONIC EXCHA NGE AND ON ENERGETIC COST OF GROWTH IN BARLEY (HORDEUM-VULGARE L) CULTIVATED ON NO3-NH4+ MEDIA

Twelve-day-old barley seedlings were grown for 3 wk on media containin g either NO3- or NH4+ as N source and supplied with either NaCl, 205 m M (-0.9 MPa) or Na2SO4, 170 mM (-0.9 MPa). The effect of NaCl on growt h and mineral nutrition was independent of N source; that of Na2SO4 wa s more severe, particularly in NH4+ medium. Patterns of ion exchange b etween medium, roots and shoots were established. It appears that on N O3- medium with NaCl or Na2SO4 added, the chloride and sulfate anions substitute for carboxylates in order to balance cation excess. On NH4 medium these 2 salts have different effects. In the presence of NaCl, cation excess in leaves is balanced mainly by Cl-. In the presence of Na2SO4, an imbalance in favour of mineral anions (sulfate), is such t hat high synthesis of organic cations is required. Adjustment of acido -basic and osmotic balances depends on salt treatments. The energetic cost which is associated with this is increased by the addition of Na2 SO4 to the medium, irrespective of the nitrogen source. in contrast, N aCl increases the energetic cost associated with NH4+ assimilation and decreases that associated with NO3- assimilation.