The effect of sodium chloride on the Ca2+, K+ and Na+ concentrations of the seed coat and embryo of Acacia tortilis and A-coriacea

The uptake of Na+ and the loss of Ca2+ and K+ by seeds of Acacia tortilis ( Forsk.) Hayne (salt tolerant) and A. coriacea DC. (salt sensitive) were det ermined after 24 h soaking in 250 mol m(-3) NaCl or in distilled water. Na uptake was higher by the seed coat than by the embryo of both species and higher by A. coriacea than by A. tortilis. The greater Na+ uptake by A. cor iacea was associated with greater Ca2+ and K+ leakage. The Na+ concentratio n of solution imbibed by the embryo of both species was lower than the Naconcentration in the external solution, indicating an exclusion of Na+. Whe n A. tortilis and A. coriacea seeds were treated with a series of NaCl conc entration (0-400 mol m(-3)), the exclusion mechanism was particularly clear with A. tortilis at lower concentrations (50 and 150 mol m(-3)) of NaCl. I n contrast, the seed coat of both species accumulated Na+ Thus the seed coa t may play an important role in ion exchange. These results show that it is important to consider the seed coat and embryo separately rather than the whole seed when considering ion exchange in relation to salinity tolerance.