Differential expression and modification of proteins during ontogenesis in Malus domestica.

Many morphological and physiological changes have been widely reported during ontogeny in higher plants. In order for the better understanding of the proteomic differences between ontogenetic phases, protein compositions between leaves of juvenile, adult vegetative and reproductive phases were compared in an apple (Malus domestica Borkh., Jonathan × Golden Delicious) seedling. Totally, 122 differentially expressed or modified protein spots were separated by DIGE. Of the 122 protein spots, 44, 17 and 29 were abundant in the leaf samples from the juvenile, adult vegetative and reproductive phases, respectively, two spots showed a lower level in the adult vegetative tissue, while the amount of protein increased in 21 spots during ontogeny and declined in nine spots. One hundred and fifteen spots were successfully picked and 95 spots were identified by MALDI-TOF-TOF high-resolution tandem mass spectrometry. Twenty-three juvenile phase abundant or down-regulated spots were photosynthesis-associated proteins, implying a juvenile phase-related photosynthesis enhancement. The expression of 10 enzymes and coenzymes involved in protein synthesis and catabolism was elevated in the adult reproductive phase or up-regulated during ontogeny, contributing a phase change-related activation in protein metabolism. Six proteins generated 30 differential gel spots via post-translational modifications. The differential expression of NADP-dependent D-sorbitol-6-phosphate dehydrogenase was confirmed by Western blotting in six seedlings derived from two hybrid populations. The results of semi-quantitative PCR indicate that some but not all of these proteomic changes were transcriptionally regulated.

Differential proteomic analysis during the vegetative phase change and the floral transition in Malus domestica.

In order to identify the proteomic changes of apple (Malus domestica Borkh.) during the vegetative phase change and the floral transition, leaf protein of juvenile, adult vegetative and reproductive phase in a seedling ('Jonathan' × 'Golden Delicious') was extracted and analyzed by 2-D electrophoresis and Matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Seventy two gel spots with significant expression differences between ontogenetic phases were obtained. Five protein spots were only detected in leaves of juvenile phase and 11 were not; 17 spots were found exclusively in adult vegetative leaves; and only one spot solely appeared in reproductive leaves while 12 did not. Twenty six of the differentially expressed proteins identified were involved in photosynthesis. Seven enzymes were related to respiration and carbohydrate metabolism. Fifteen other proteins also presented qualitative or quantitative differences among developmental phases. The spatial distribution of one differentially expressed protein, serine hydroxymethyltransferase, was confirmed by enzyme linked immunosorbent assay and immunohistochemistry. These results strongly support the idea that the vegetative phase change and the floral transition are regulated independently during developmental process.