Ascorbic acid metabolism during white spruce somatic embryo maturation andgermination

Changes in ascorbic acid (AA) metabolism were investigated in 3 different c ell lines of white spruce; a non-embryogenic line (NE)WS and two embryogeni c lines with low (E)WS1 and high (E)WS2 percentage of embryo germination, D uring embryo maturation, a high AA/dehydroascorbate (DHA) ratio was observe d in the two embryogenic cultures, The increment of this ratio was mainly a scribed to the high ability of the (E)WSI and (E)WS2 lines to generate AA f rom its last precursor, L-galactono-gamma -lactone, since no increase in th e activities of the AA-recycling enzymes, i.e., AA free-radical reductase ( AFRR) and DHA reductase (DHAR), was observed as the embryos developed, Duri ng the partial drying treatment needed for successful embryo germination, t he ability to de novo generate AA continued to increase in the embryos of t he two embryogenic lines, although the total ascorbate pool (AA + DHA) shar ply decreased, A reactivation of the overall AA metabolism was observed at the inception of germination, especially in the (E)WS2 embryos. These resul ts suggest that (I) the ability to metabolically alter the AA/DHA ratio may be a fundamental requirement for somatic embryo maturation and (2) the res toration of the AA metabolism during the first days of germination may be n ecessary for successful embryo germination.