High temperature stress (HT) is efficient in breaking endo-dormancy of perennial trees. The effects of HT (50°C) on the respiration of dormant nectarine (Prunus persica var. nectariana cv. Shuguang) vegetative buds were evaluated in the research. We found that bud respiration was transiently inhibited by HT and the pentose phosphate pathway (PPP) and the cytochrome C pathway (CYT) were significantly affected. On the substrate level, PPP was activated in the HT-treated buds compared with the control group. However, the activation did mot occur until hours after HT treatment. The tricarboxylic acid cycle (TCA) in both the HT-treated buds and in the control group proceeded at a low level most of the time compared with total respiration. On the electron transfer level, CYT was transiently inhibited by HT but became significantly active in the later stage. CYT operation in the control group exhibited an attenuation process. The alternative pathway (ALT) fluctuated both in the HT-treated samples and in the control. The results suggest that the temporary CYT inhibition and the following PPP activation may be involved in HT-induced bud dormancy release and budburst mechanisms.

Shuguang (Prunus persica var. nectariana cv. Shuguang) nectarine was used to study effects of photoperiod on keyenzymeactivities of respiration during dormancy induction. The dormancy status was determined with sprouting ability.Spectrophotometry was used to investigate activities of phosphohexose isomerase (PGI), malic dehydrogenase (MDH),and glucose-6-phosphate dehydrogenase (G6PDH). The results revealed that short day (SD) treatment promoted dormancyinduction while long day (LD) treatment postponed the process. During dormancy induction, PGI activities declined,MDH activities changed little, and G6PDH activities increased both in flower buds and leaf buds. PGI activities and MDHactivities in SD treatment were lower than control, and G6PDH activities were higher, which was opposite with LDtreatment. The changes of respiratory key-enzyme activities were adjusted by photoperiod and correlated with thedevelopment of dormancy induction.

Characteristics of dormancy induction and alternative respiration pathway (also known as cyanide-resistant respiration) of nectarine flower buds in different photoperiods were studied to determine the function of photoperiod and alternative respiration pathway in dormancy induction. Oxygen-electrode system and respiratory inhibitors were used to measure total respiratory rates and rates of alternative respiration pathway. The results showed that total respiration rate (Vt) in flower buds showed to be double hump-shaped curves. Short day raised, brought the first-hump of Vt forward and delayed the second-hump, while long day delayed the whole curve. The capacity (Valt) and activity (ρValt) of SD and LD changed synchronously and both showed to be double hump-shaped curves. Short day made the first climax of Valt and ρValt existed much earlier, while long day increased their rates significantly. The length of day had little effects on the later period climax. Long day also increased the contributions of alternative respiration pathway in total respiration rate (ρValt/Vt). The changes in alternative respiration pathway were correlated with the induction of dormancy and adjusted by photoperiod. Short day promoted dormancy induction of nectarine trees, while long day delayed it.