Identification of the expressed protein and the impact of change in ascorbate peroxidase activity related to endodormancy breaking in Pyrus pyrifolia.

Endodormancy is an important feature of perennial deciduous fruit trees that survive in the extreme climates brought about by seasonal variation. To acquire a comprehensive knowledge of the biochemical processes occurring just before endodormancy breaking, the buds collected in the pre-breaking period (PP) phase were used as samples to identify the proteins related to the breaking of endodormancy in the Japanese pear (Pyrus pyrifolia Nakai). Using nano-ESI-LC-MS/MS analysis, 96 proteins were overlapped by analyses of three times and identified as expressed proteins at the PP stage. Among these proteins, dehydrin, several classes of heat shock proteins (HSP), auxin-binding protein, and auxin-induced protein were identified in the floral bud in the PP stage. The majority of these proteins were involved primarily in the oxidation-reduction process. We focused on catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) as enzymes regulating the levels of hydrogen peroxide (H2O2) in the bud. From measurements taken during the deepest period (DP), PP, mid-breaking period (MP), and late-breaking period (LP) of endodormancy, CAT activity decreased gradually, while APX activity also decreased from DP to MP, but then increased rapidly during LP. Protein data for PP and the rapid increase in APX activity observed in LP provided knowledge of the biochemical processes that regulate the consecutive transition from endodormancy breaking to ecodormancy induction in the Japanese pear.