title: Protein phosphorylation differs significantly among ontogenetic phases in Malus seedlings.
abstract: BACKGROUND
  Although protein phosphorylation is an important post-translational modification affecting protein function and metabolism, dynamic changes in this process during ontogenesis remain unexplored in woody angiosperms.
  
  
  METHODS
  Phosphorylated proteins from leaves of three apple seedlings at juvenile, adult vegetative and reproductive stages were extracted and subjected to alkaline phosphatase pre-treatment. After separating the proteins by two-dimensional gel electrophoresis and phosphoprotein-specific Pro-Q Diamond staining, differentially expressed phosphoproteins were identified by MALDI-TOF-TOF mass spectrometry.
  
  
  RESULTS
  A total of 107 phosphorylated protein spots on nine gels (three ontogenetic phases × three seedlings) were identified by MALDI-TOF-TOF mass spectrometry. The 55 spots of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) large-chain fragments varied significantly in protein abundance and degree of phosphorylation among ontogenetic phases. Abundances of the 27 spots corresponding to Rubisco activase declined between juvenile and reproductive phases. More extensively, phosphorylated β-tubulin chain spots with lower isoelectric points were most abundant during juvenile and adult vegetative phases.
  
  
  CONCLUSIONS
  Protein phosphorylation varied significantly during vegetative phase change and floral transition in apple seedlings. Most of the observed changes were consistent among seedlings and between hybrid populations.
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100193, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100193, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Changli Institute of Pomology, Hebei Academy of Agricultural and Forestry Sciences, Changli 066600, China.
authors.forename: Yong Bo
authors.initials: YB
authors.lastname: Zhao
authors.affiliation: Changli Institute of Pomology, Hebei Academy of Agricultural and Forestry Sciences, Changli 066600, China.
authors.forename: Dong Mei
authors.initials: DM
authors.lastname: Chen
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100193, China.
authors.forename: Zhen Hai
authors.initials: ZH
authors.lastname: Han
authors.affiliation: Institute for Horticultural Plants, China Agricultural University, Beijing 100193, China.
authors.forename: Xin Zhong
authors.initials: XZ
authors.lastname: Zhang
keywords: Apple; Floral transition; Phosphorylated proteomics; Vegetative phase change