Sucrose metabolism during somatic and zygotic embryogeneses in Norway spruce: content of soluble saccharides and localisation of key enzyme activities

Changes in soluble carbohydrate compounds and their amounts were analysed during the somatic embryo maturation and seed development of Norway spruce (Picea abies (L.) Karst.). The data were correlated to the localisation of key enzymes of carbohydrate metabolism (invertase, EC 3.2.1.26; sucrose synthase, EC 2.4.1.13; phosphoglucomutase, EC 5.4.2.2). The decrease in total carbohydrate content as well as the accumulation of sucrose in later stages was a common feature in both systems. At the beginning of somatic embryo maturation the activity of sucrose synthase was low, and it gradually increased during development. At the final cotyledonary stage the SuSy localisation in somatic embryos resembled the pattern observed in cotyledonary stage zygotic embryos. Activity of invertase (pH 6.0) was detected in the early stages of somatic embryo development. Afterwards the activity decreased to almost undetectable levels in mature cotyledonary embryos. Very low invertase activity was detected during the period of seed development studied. The activity of phosphoglucomutase was high throughout the whole process of maturation in both zygotic and somatic embryos. The results are discussed in respect to the transition of developing embryos from metabolic to storage sink and the possible signalling potential of the changes.