Abstract: Experiments were carried out to study the effects of rhizosphere nitrate and ammonium on the level of cytokinins in different organs and the leaf growth of Malus hupenensis Rehd. seedlings under water culture condition. Results indicated that the concentration of zeatin and zeatin riboside (Z+ZR) both in roots and in leaves increased quickly in 0.5 hour after nitrate supp ly, and the levels of Z+ZR were always higher than ammonium treatment and the control within 24 hours. In stems, the concentration of Z+ZR increased significantly in 1 hour after nitrate treatment, but there was no significant difference between the treatment and the control. The concentration of isopentenyladenine and isopentenyladenosine (iP+iPA) was higher in roots in nitrate treatment and in leaves in ammonium treatment. No significant difference was noticed in stems between the treatment and the control. The leaf growth in nitrate treatmentwas better than ammonium treatment, suggesting that itmay be involved in higher Z+ZR level and lower ABA level.

Key words: Malus hupenensis Rehd., NO₃^-, NH₄⁺, Cytokinins, Z + ZR, Leaf, Growth