The effect of sodium chloride on germination and the potassium and calcium contents of Acacia seeds

Acacia bivenosa DC. Prod., A. coriacen DC., A. elata A. Cunn. Ex Benth., A. farnesiana (L.) Willd., A. nilotica Willd. Ex Del., A. salicina Lindl., A. saligna (Labill.) K. Wendl., A. senegal (L.) Willd., A. tortilis (Forsk.) Hayne and A. tumida F. Muell. ex Benth. were screened for their salt tolerance during seed germination in the presence of NaCl. The uptake of water, and the levels of Na+, K+ and Ca2+ of A. coriacea (salt sensitive), A. nilotica (intermediate) and A. tortilis (salt tolerant), before and after imbibition, were measured to ascertain the contributions of ionic and osmotic factors to the observed differences in response to salt stress. Imbibition by seeds incubated on NaCl solutions was reduced by only approximately 1% for each 100 mol m(-3) increase in NaCl concentration. The relationship between Nat concentration applied to the seeds and the Na+ concentration of the solution imbibed did not differ significantly among the species and there was no indication that selective uptake or exclusion of Na+ contributed to the differences in salinity tolerance. A. tortilis seeds had significantly lower initial K+ concentration and lost significantly less K+ in response to Na+ uptake than did either A. nilotica or A. coriacea. In contrast, the initial concentration of Ca2+ was significantly higher in A. tortilis than in the other two species, and the loss of Ca+ in response to Na+ was higher in A. tortilis than in A. coriacea. The adverse effects of NaCl on seed germination, observed in this study, appear to result from internal osmotic or ion toxicity effects rather than from a restriction of imbibition.