Abstract: Three-year-old apple trees 〔Malus domestica Borkh. ‘Rehd Fuji ’ /Malus hupehensis (Pamp) Rehd. 〕were used asmaterials in this experiment. The effect of abscisic acid (ABA) , salicylic acid ( SA) and oxalic acid (OA) on proline accumulation and the response of plant to water stress were studied
with app le leaves. The results showed that SA increased the p roline content by 7.87% at the second day of pretreatment. At the 9 th day of pretreatment, natural drought (ND) , ABA, SA and OA increased the proline content by 96.30% , 110.67%, 135.12% and 115.96% respectively. At the 5 th day of water stress after 9 day pretreatment, ND, ABA, SA and OA increased water use efficiency (WUE) by 286.77% , 75.76%,79.04% and 100.44% respectively, with increasing of proline content. At the 10 th day of water stress after 9
day pretreatment, ND, ABA and SA increased proline content by 5.33% , 262.76% and 92.32% , respectively. Those results suggested that the pretreatments of ND, ABA, SA and OA all could help to increase the
drought resistance of apple tree via increasing proline content and WUE of leaf, in which effect of ABA was best and salicylic acid secondly. The effective duration of oxalic acid was shorter.