Tolerance of submerged germinating rice to 50-200 mM NaCl in aerated solution

This paper concerns tolerance to 50-200mMNaCl of submerged rice (Oryza sativa cv. Amaroo) during germination and the first 138-186h of development in aerated solution. Rice was able to germinate and the seedlings even tolerated exposure to 200mMNaCl, albeit with severe growth restrictions. After return to 0.3mMNaCl, growth increased, indicating that even at 200mMNaCl there was no irreparable injury. Osmotic adjustment was achieved by using Na+ and Cl- as the major osmotica. At 200mMNaCl commenced at sowing, the shoot Na+ and Cl- concentrations between 50-110h were about 210 and 260mM, respectively, i.e. above the external concentration. Thus, there was a high tissue tolerance to NaCl. The internal concentrations declined subsequently, concurrent with a decline in growth. At 50-200mMNaCl, the contributions from ions to (sap) were 81-92% in roots and 62-74% in shoots. The assessed turgor pressures at 200mMNaCl were 0.33MPa in shoots and 0.15MPa in roots, compared to 0.62 and 0.43MPa at 0.3mMNaCl. In the General Discussion section, we compare the different responses of submerged seedlings to the responses of transpiring rice plants, reported in the literature, and suggest that the submerged system is useful to evaluate effects of NaCl on turgor pressure and particularly to establish whether there are specific effects of Na+ and Cl- in tissues.