Abstract: Effects of water stress on nucleic acid metabolisms and changes of free radicals in Malus hupehensis pamp Reld. and Malus sieversii (Ledeb) Roem. seedings were studied with polyethylene glycol (PEG6000) treatment . Under water stress , the contents of RWC , DNA and RNA in leaves decreased , while the content of O₂^-· and H₂O₂, the activities of DNase and RNase increased. Compared with RNA , the less decrement of DNA content was
accompanied with higher activity of DNase. The changing extents in RWC , active oxygen , DNA , RNA , DNase and RNase in the drought tolerant variety M. sieversii were lower than the drought resistant variety M. hupehensis. Under water stress , there are high significant correlation between DNA , RNA content and DNase , RNase , RWC ,O₂^-·, H₂O₂ in M. hupehensis pamp Reld. and M. sieversii (Ledeb) Roem. seedings.

Key words: Malus, Water stress, Nucleic acid metabolism, Free radicals