Changes in Hydrogen Peroxide Content in Flower Buds of Japanese Pear(Pyrus pyrifolia Nakai) in Relation to Breaking of Endodormancy.

Abstract

Hydrogen peroxide (H2O2) content was determined in flower buds of Japanese pear (Pyrus pyrifolia Nakai cv. Kosui) trees under natural conditions during the development and their release from endodormancy. H2O2 content increased gradually as the developmental stage index (DVI) accumulated, peaking in late December when endodormancy was broken ; it then decreased during the ecodormancy stage. In unchilled flower buds from November 1 throughout the winter, H2O2 content did not change significantly and remained low. No budbreak was observed at the end of March which indicate that the increase in the level of H2O2 during chilling is closely associated with the breaking of endodormancy. H2O2 levels induced by applying hydrogen cyanamide to flower buds of cuttings throughout the endodormancy period promoted budbreak. This was accompanied by a depletion of H2O2 within one day, followed by a large increase 3-6 days later. However, cyanamide treatments at concentrations that had no promoting effect on budbreak resulted in a decrease in H2O2 content during the experimental period. The cumulative budbreak 22 days after cyanamide treatment was positively correlated with H2O2 content six days after the treatment, indicating that the endodormancy-breaking effect of cyanamide involves the elevation of H2O2 similar to that of chilling temperatures. These results suggest that H2O2 can substitute for the chilling requirement, and that the increase in H2O2 levels may trigger the sequence of reactions involved in the breaking of endodormancy.