Effect of artificial ageing on the germination, ion leakage and salinity tolerance of Acacia tortilis and A-coriacea seeds

The final germination of Acacia tortilis seeds in either distilled water (D W) or 375 mol m(-3) NaCl (the concentration which reduces germination by 50 % in this species (LD50)) was significantly reduced by artificial ageing at 55 or 80 degrees C with very high relative humidity. In contrast, the germ ination rate in DW was unaffected but in NaCl it increased with ageing at 8 0 degrees C. The leakage of K+ and Ca2+ from A. tortilis seeds into DW and NaCl was increased by ageing. The reduced germination and greater ion leaka ge may be related to the loss of viability and membrane leakage. Despite th ese generally adverse effects on germination and ion leakage from A. tortil is seeds, there was no evidence for a greater sensitivity of germination to NaCl in aged than in unaged seeds, relative to the germination of each typ e in DW. Thus, the germination in NaCl of unaged A. tortilis seeds and seed s aged at 55 degrees C and 80 degrees C was 51, 50 and 52%, respectively, o f the germination in DW. With A. coriacea, ageing at 80 degrees C increased germination rate in NaCl (LD50 = 125 mol m(-3)) but other effects of agein g at either 55 or 80 degrees C on final germination or germination rate of A. coriacea in DW or NaCl were not demonstrated. The ageing treatments also had no adverse effect on ion leakage from A. coriacea, with the leakage of K+ unaffected by ageing and the leakage of Ca2+ into either DW or NaCl red uced by ageing at 55 or 80 degrees C. Despite the apparently less adverse e ffect of ageing on A. coreacea seeds, there was some evidence of a slightly increased sensitivity of aged seeds to NaCl, with the germination in NaCl of unaged A. coriacea seeds and seeds aged at 55 degrees C and 80 degrees C was 75, 55 and 60%, respectively, of the germination in DW.