Proteomic analysis during ontogenesis of secondary xylem in maritime pine

Secondary xylem (wood) is formed through an intricate biological process that results in a highly variable final product. Studies have focused on understanding the molecular events for wood formation in conifers. In this process environmental, ontogenic and genetic factors influence variation in wood characteristics, including anatomical, chemical and physical properties. The main objective of this study was to analyse the ageing (ontogenic) effect on protein accumulation in wood-forming tissues along a cambial age (CA) gradient, ranging from juvenile wood (JW) sampled at the top of the tree, to mature wood (MW) sampled at the bottom of the tree. A total of 62 proteins whose accumulation varied by at least 1.5-fold according to CA were selected and identified by ESI-MS/MS; 30 of these were more abundant in MW and 32 were more abundant in JW. Consistent with earlier findings, our results show that JW is a tissue characterized by a high energy demand with the accumulation of gene products involved in energy, protein fate and cellular transport, while proteins identified in MW (heat shock response, oxygen and radical detoxification, and the S-adenosyl methionine cycle) support the idea that this tissue undergoes extended cell-wall thickening and a delay of programmed cell death.