The Study On Relation Of Releases From Dormancy And Active Oxygen Metabolism In Flower Buds Of Pear

North deciduous fruit trees evolved into biomechanism of dormancy for a long time to adapte to environmental and climatical changes in winter. The physiological and biochemical metabolisms did not stop, but even were inactivited. Some pear cultivars including 'dangshansu', 'bayuehong', '5-16', 'cupili' and 'zaosu' were selected as material in this experiment to study systemically effects of temperature daily cycle and maintained low temperature treatment on the accumulation of chilling requirment and the opening of flower buds., and elucidating the changes of active oxygen and antioxidative system during temperature daily cycle and winter dormancy and after applying thioureas. The results were as follows:1. Differences were found in budbreak between two exposures of maintained low temperature (4 ) and temperature daily cycle (20 4h/4 20h). All materials were exposed to the continuous low temperature for 20 days, the budbreak rate of flower bud only in 'zaosu' pear reached beyong 50%. This meant that there were differences in chilling requrement among cutivars in same pear species. After 20 days exposure of temperature daily cycle, the budbreak rates of these cutivars were all beyong 50% except 'beyuehong'. The budbreak rates of exposure to temperature daily cycle treatment were higher than those of 'cupili', '5-16' and 'dangshansu' exposed to maintained low temperature except 'zaosu' ( at significantly different level 0.05). Results indicated that accumulation of chilling of exposure to temperature daily cycle more effective than that of exposure to maintained low temperature.2. Active oxygen and the antioxidative system changed much during natural dormancy. The production rate of O2 increased at early stage and then decreased. Increases in H2O2 appeared as soon as dormancy began, decreases at the end of dormancy and during the period of budbreak. The SOD activity in antioxidative system dropped , thePOD activity increased continuously, the CAT activity showed the same result caused probably by the content of H2O2 during winter dormancy. Two important antioxidants AsAand GSH decreased with the process of dormancy, and then increased at the last time of dormancy. Two of key enzymes in ascorbate-glutation cycle changed similarily, increased in process of dormancy, then decreased finally.3. Active oxygen and the antioxidative system also changed much in both temperature daily cycle and thioureas treatment. The production rate of O 2 rised up, the content of H2O2 too increased . The activity of SOD decreased with the extended time of exposure, however, both the POD activity and the CAT activity went up. The contents of antioxidant AsA and GSH decreased after exposure of temperature daily cycle, increases after exposure of thioureas. Both two treatments all increased the activity of APX and GR.