Studies On Growth Characteristics And Rhythm Regulation Of Apple Plantlets Repeatedly Subcultured In Vitro

The organogenesis characteristics of apple (Malns domestica Borkh.) shoot explants repeatedly subcultured in vitro were examined by analysis of the shoot multiplication, rooting and adventitious bud regeneration rate from leaves, to make sure whether the growth and reproduction ability of apple in vitro has changed after subcultured a long time; Changing temperature, improving osmotic pressures , supplying growth inhibitor to delay the growth of apple in vitro and reduce subculture times, the changes of the number of buds and the growth amount, SOD,POD activity and MDA amount during conservation period in subculture media and recovery process were applied to explants during conservation in vitro in order to achieve the optimal status for retardant growth. The result showed:1. The results showed low propagation ability for the shoot explants subcultured in vitro for five times or less at the beginning of inoculation in terms of its shoot multiplication, rooting and adventitious bud regeneration rate from leaves.2. Apple shoot plantlets being subcultured for 13 times, shoot multiplication, rooting and adventitious bud regeneration rate from leaves of the organs enhanced and remained at a high level, the growth and regeneration ability of the organs don not have changed after 20 years more than 100 times subculture(Fuji moer than 200 times).3. A low incubation temperature can significantly retard the growth of explants. The optimal incubation temperature was 8℃after an incubation at 25℃for 5～10 d succeeding on inoculation of new plantlets, and these plantlets could be persevered for one and a half years with a survival rate of 100%.4. The increase of osmotic pressure in subculture media by enhancing the concentration of Agar, Sugar, and Mannitol could retard the growth of the explants. An increase of pressure retarded the amount of explant growth. But some explants died in media with a high concentration of Agar and Mannitol. The combination of osmotic pressure and temperature suggests that explants under incubation at a temperature at 8℃and supplying 60 g/L Sugar in a medium would maintain their healthy status at the lowest growth rate. The effect had variation between cultivars with favorable results in Fuji when compared to Jonagold.5. The effect of supplying 80mg/L B₉ is better than supplying other kinds of plant-growth regulators such as B₉,CCC,PP₃₃₃,ABA at room temperature. The conditions and survival rates are better than supplying CCC,ABA and PP333.6. The increase of osmotic pressure in subculture media by enhancing the concentration of Agar, Sugar, Mannitol or supplying B9, CCC, PP333 all can increase SOD and POD activity and decrease MDA amount of Jonagold and Fuji. The effects of SOD and POD activity and MDA amount are different between different treatments. This difference of SOD and POD activity and MDA amount disappeared when the explants were transferred to the conventional medium for recovery growth culture.