Abstract: Endogenous hormone regulation should be very important for apple dwarfing mechanism. Starking and its compact mutants , rootstocks in different warfing level were used to determine endogenous hormone content. The results were as follows : Compared to Red Delicious , its compact mutants had lower GA₁₊₃ and higher CTKs. CTKs/ GA₁₊₃ for dwarfing cultivars were 4. 78 to 6. 24 times of that for general cultivar. ABA , IAA content differed a little between compact and general apple cultivars. GA₁₊₃, ABA and CTKs in shoot tips and leaves varied about 13 % - 20 % for normal and dwarfing rootstocks. However , IAA in M9 leaves was 53. 7 % less than that in normal rootstock during the rest period of shoot growth. Using M26 as inter rootstock , IAA in scion leaves and fine roots of basic rootstocks dropped 34. 6 % and 25. 6 %. But the plant with Starkrimson as inter rootstock did not have this effect . So GA was very important for compact varieties. It erformed directly on above ground. But Dwarfing mechanism for rootstocks maybe was closed to polar transition of IAA.

Key words: Apple, Compact mutants, Dwarf rootstocks, Endogenous hormone