| The experiment had been carried out in Taian Qunxing orchard from 2005 to 2007 with 7-year-old nectarine trees of cv Shuguang(Prunus persica var. Nectarina.cv.Shuguang). The effects of short-term freezing at different temperature on the endodormancy breaking of peach buds were studied. The main results were as follows:1. Short-term freezing at the rest temperatures significantly released the peach bud endodormancy. When the plants were entering dormancy, an effect of short-term freezing was observed only if a sufficient level of dormancy had been reached, which appeared to be when chilling reached two-thirds of chilling requirement or more for P. persica. Short-term freezing at -4℃and -7℃showed little effect on the endodormancy release in P. persica, but short-term freezing at the rest temperatures efficiently released the peach bud endodormancy. Effects of short-term freezing on the release of dormancy were advanced by the postponement of treatment date, the decrease of treatment temperature and the prolonging of treatment time. Some buds died in the short-term freezing treatment, whereas the effects of short-term freezing on the dormancy breaking in the survival buds were significantly advanced.2. On November 30, compared with non-freezing treatment (CK), the effects of -4℃and -7℃freezing treatment were almost the same as CK, the bud burst, the ratio of free water to bound water and membrane permeability were nearly the same as CK. But the rest freezing treatments advanced the date of endodormancy release, the bud burst, the ratio of free water to bound water and membrane permeability were higher than CK. On December 10 and December 20, the effects of the freezing treatment on endodormancy release were the same as the treatment on November 30, and the effect was better as the treatment was later. The correlation between the rate of bud burst, the ratio of free water to bound water, and membrane permeability of the different freezing treatments indicated that the change from bound water to free water and the increase of membrane permeability were probably the signal of dormancy release.3. On November 30, the chang of content of soluble sugar and the content of starch were almost the same as CK on -4℃and -7℃-freezing treatments. Whereas the rest-freezing treatments had the significant effects that the content of soluble sugar was higher and the content of starch was lower. On December 10 and December 20, the effects of rest-freezing treatments on dormancy release were the same as the treatment on November 30, and the effect of the former was superior to the latter. The correlation between the content of soluble sugar, the content of starch and the rate of bud burst of the different freezing treatments indicated that the transition of starch to soluble sugar was probably the charctristic of dormancy release.4. On November 30, -4℃and -7℃-freezing treatment nearly had the same results as CK on the following factors, including the rate of production in O2-·and·OH, the content of H2O2 , the activity of CAT ,SOD and POD enzyme .But all of them were higher than CK on the rest-freezing treatments except that the activity of SOD enzyme was lower. On December 10 and December 20, the effects of freezing treatments on dormancy release were the same as the treatments on November 30, and the effect of the former was superior to the latter. The significant increase of reactive oxygen content and production rate were probably the cause of dormancy release.5. On November 30, compared with CK, the content of total phenolics , the activity of PPO and PAL enzyme showed little difference at -4, -7 and -10℃, but the activity of POD enzyme became higher from -10℃-freezing treatment. The rest freezing treatments had the significant effects on them, and the activity of PPO and POD enzyme were higher than CK while the content of total phenolics and the activity of PAL were lower. On December 10 and December 20, the effects of the freezing treatment on dormancy release were the same as the treatment on November 30, and the effect of the former was superior to the latter. The correlation of the bud burst rate and the content of total phenolics of the different treatments indicated that short-term freezing significantly released the peach bud endodormancy and played down the content of total phenolics through reducing the activity of PAL enzyme and increasing the activity of PPO and POD enzyme.
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