Biphasic response to elevated levels of NaCl in Nicotiana occidentalis subspecies obliqua Burbidge

Abstract The seedling growth response of N. occidentalis subspecies obliqua Burbidge to elevated levels of NaCl was studied under various conditions with respect to light/dark cycle and temperature. When cultured at 28 °C under continuous light, the seedlings showed a unique biphasic response to NaCl; the seedlings died in the presence of 75 mM NaCl, while they survived in the presence of 150 mM NaCl. The results of Na + and K + accumulation in leaves suggested that this biphasic response was not due to the disruption of ion homeostasis under 75 mM NaCl. A similar phenomenon was observed when NaCl was replaced with KCl. Moreover, seedlings survived in the coexistence of 75 mM KCl or KNO 3 even under 75 mM NaCl. These results implied that the seedling response may be determined by the differential expression of salt-inducible gene(s) rather than specific ion toxicity. The biphasic response may be useful for understanding the salt tolerance mechanisms and for isolating the involved gene(s).