Pattern of carbohydrate changes in maturing xylem and phloem during growth to dormancy transition phase in Picea abies (L.) Karst.

Wood production is a metabolic process requiring high amount of soluble carbohydrates as source of carbon skeletons, energy, or signalling molecules. Nevertheless, the role of soluble sugars and starch has been rarely investigated in the growth to dormancy transition phase. The aim of this work was to investigate the carbohydrate concentrations and the transcription level of some candidate genes involved in cellulose and starch metabolisms in competitive carbon sinks such as phloem, maturing xylem, and xylem during the active growth to dormancy transition phase in Picea abies (L.) Karst. Stems were sampled every two weeks between July and October from potted eight-year-old Norway spruce plants. Results highlight that the cellulose biosynthesis regulated the pattern of carbohydrate changes in the phloem and maturing xylem during the transition to dormancy. In particular, the cessation of CesA (?-cellulose synthase) mRNA accumulation in maturing xylem determined a shift in the carbohydrate partitioning from the utilization sinks to the storage compartment. The content of carbohydrates was modulated in the maturing xylem by cellulose metabolism during the xylogenesis and by starch metabolism during the cambium dormancy. On the contrary, the carbon competition between utilization and storage sinks seemed to be less connected within the phloem. Since the amount of soluble carbohydrates within the maturing xylem and phloem has never been limited during the growth to dormancy transition phase, the cessation of the CesA transcription was probably determined by environmental conditions rather than by carbon limitation or sink competition.