Abstract: The physiological and root morphology responses of two apple rootstocks under zincdeficiency stress were investigated for exploring the difference of endurance and sensitivity to zinc-deficiency stress between cultivars of two apple rootstocks. The experiment was carried out with the seedlings of two apple rootstocks cultivars（Malus hupehensis Rehd. and Malus xiaojinensis Cheng et Jiang）under zinc-deficiency stress with hydroponics. The changes in the biomass，the morphology and architecture of root，the activity of root，and the zinc accumulation in plant shoot and root were studied. There were significant differences between different apple rootstocks cultivars in response to zinc-deficiencystress. The obtained results showed that many obvious zinc-deficiency symptoms were observed in the two apple rootstocks seedling receiving no Zn supply，such as，the plant dwarfed，the new leaves etiolated and
rosetted，the length of stem node decreased and the root tips enlarged. The results also indicated that zinc-deficiency treatment delayed the occurrence of zinc-deficiency symptoms of the Malus xiaojinensis Cheng et Jiang seedling by 7 days than the Malus hupehensis Rehd. The biomass of Malus hupehensis
Rehd. root system was significantly inhibited under zinc-deficiency stress. Root is more sensitive to zinc deficiency than that of shoot. Cultured for 20 days in a zinc-deficiency solution，the root length，root surface area，root volume and the number of root tips of the two apple rootstocks cultivars are both decreased seriously，and the decreased ranges of Malus xiaojinensis Cheng et Jiang are smaller than those of Malus hupehensis Rehd.，contrarily，the average diameter of two cultivars roots are increased under zinc-deficiency condition. Malus hupehensis Rehd. treatment plant had the maximum value of root activity of Malus hupehensis Rehd. treatment plant appeared at the 30th day，while that of Malus xiaojinensis Cheng et Jiang appeared at 45th day. The content of Zn of two cultivars under zinc-deficiency stress was in the order as below：Root > stem > leaf. Control plants > Malus xiaojinensis Cheng et Jiang > Malus hupehensis Rehd. treatment plant. The sensitivity and endurance of the two apple rootstocks seedlings to zinc-deficiency stress were different. The Malus hupehensis Rehd. was more sensitive to zinc deficiency and its root was vulnerable to zinc-deficiency stress，while Malus xiaojinensis Cheng et Jiang presented less decrease in its zinc content and had better endurance and resistance to the zinc-deficiency stress.

Key words: Malus hupehensis, Malus xiaojinensis, rootstock, zinc-deficiency stress, root system architecture, zinc accumulation