The ultrastructural distribution and active location of ATPase and the ultrastructural variations were investigated in mesophyll cells of Cyclocarya paliurus seedlings after iso-osmotic salt/water treatments in combination with calcium regulation. C. paliurus seed- lings were treated with five groups （control, 85 mM NaCl, 85 mM NaCl＋ 12 mM Ca（NO3）2, PEG iso-osmotic to 85 mM NaCl and PEG iso-osmotic to 85 mM NaCl＋12 mM Ca（NO））2） in a hydroponic system in a phytotron. Results show that under normal growth conditions the ATPase activity was low and the enzyme was primarily located on the nucleus. After 12 days of iso-osmotic salt/water treatments, ATPase activity on the tonoptast increased. Osmiophilic globules for iso-osmotic water treatment were greater than that for iso-osmotie salt treatments. The ATPase activity increased and was mostly transferred onto the nucleus for calcium regulation treatment under iso- osmotic salt/water stresses, and the osmiophilic globules significantly decreased under iso-osmotic water stress with calcium regulation. The ATPase located on the nucleus indicated that the degree of salt/drought damage that seedlings suffered was slighter, while the amount of the enzyme located on the tonoplast showed that the degree of salt/drought damage there was more serious. After 4 and 20 days of iso- osmotic treatments, the injury suffered by the leaf ultrastructures of C. paliurus seedlings for iso-osmotic treatment with calcium regula- tion was lower than those without calcium regulation, especially for the iso-osmotic water treatments. Preliminary analysis suggests that the iniury suffered by C. paliurus seedlings was lower for iso-osmotic salt treatments than for iso-osmotic water treatments, while the effect of calcium regulation under iso-osmotic water stress was greater than that of the iso-osmotic salt stress.
