Abstract: Abstract：The effect of sodium chloride（NaCl），sodium ion（Na+）and chloride ion（Cl-）solution
on the production of nitric oxide（NO）and active oxygen（ROS）and the membrane lipid peroxidation of
Malus hupehensis seedling roots was investigated by water culture. The results showed that，the production
rates of NO and superoxide anions，as well as the accumulation of malondiadehyde（MDA）and
hydrogen peroxide（H₂O₂），were all increased under iso-osmotic NaCl，Na⁺ and Cl^- salt solutions of the
same concentration，and the increasing extent was in the following order：NaCl >Cl^->Na⁺. In addition，
the increasing content caused by NaCl stress was lower than the sum of that caused by Na+ and Cl- stress. It
was demonstrated that Cl^- took more important part in the induction of oxidation damage under NaCl stress，
and stress response caused by NaCl treatment were not simple stack of those caused by Na⁺ and Cl- stress
individually.

Key words: Malus hupehensis, roots, nitric oxide, active oxygen, chloride ion, sodium ion