Abstract: Diploid and autotetraploid‘Hanfu’apple seedlings were treated with 200 mmol ? L-1 NaCl for 8 d in 1/2 Hoagland nutrient solution，and determined the physiological characteristics and the expression of aquaporin-related genes in leaves at different treatment time. The results showed that the morpholoy of autotetraploid was better than diploid. The relative water content（RWC）kept decreasing in diploid and autotetraploid leaves over time，but the latter was higher than the former in the whole process. The content of proline and the accumulation of malondialdehyde（MDA）remained higher in the diploid than the autotetraploid，with both increasing over time. The RWC of leaves in autotetraploid was 8% higher than the diploid，the concentration of MDA in autotetraploid was 4.466 nmol ? g-1FW lower than the diploid and the accumulation of Pro in diploid was about 1.18 fold that in the autotetraploid by 8 d after the imposition of stress. The tendences of MdPIP1;1，MdPIP2;1，MdTIP1;1，MdTIP2;1 all showed first decreasing then increasing trend，but the expression level in autotetraploid was higher，especially for 24 htreatment. This study found that the salt tolerance of autotetraploid was strongger than the diploid，which may be associated with the higher expression of aquaporin-related genes in autotetraploid under salt stress.

Key words: apple, polyploidization, salt stress, aquaporins