Growth Response to Ionic and Osmotic Stress of NaCl in Salt-tolerant and Salt-sensitive Maize

Salt-tolerant maize (STM) and salt-sensitive maize (SSM) were treated with 100 mM NaCl for 1, 3 and 6 d and the contents of Na+ and Cl- (cps) of different organelles of leaf cells determined by X-ray microanalysis. The results showed that Na+ and Cl- entered the cytoplasm, vacuole, chloroplast and apoplast simultaneously. When STM and SSM were treated in 100 mM NaCl at atmospheric pressure (-P) and with pressure equivalent to the osmotic pressure of the NaCl (+P), the dry weights of STM (+P) and SSM (+P) plants were greater than that of STM (-P) and SSM (-P) plants, showing that the inhibitory effect of salt on plant growth was at least partially due to the osmotic effect of the NaCl. When STM and SSM were treated with NaCl and iso-osmotic polyethlene glycol, the dry weights of plants given the iso-osmotic polyethlene glycol treatment were lower for both maize lines than that of the NaCl-treated plants. Our data show that under NaCl stress, both STM and SSM seedlings simultaneously suffered from osmotic and ion stresses.