Exogenous Applications of Ascorbic Acid Enhance Shoot Apical Meristem Growth and Induce Shoot Organogenesis in Germinating White Spruce (Picea glauca) Somatic Embryos

Ascorbic acid (ASC) has been shown to improve the postembryonic growth of white spruce somatic embryos. In order to comprehend the effects of ASC applications on shoot apical meristem reactivation, structural studies were conducted. In control embryos, postembryonic growth was dependent on the quality of the shoot apical meristems since only well-organized meristems were able to resume mitotic activity at germination and undergo successful conversion. Resumption of cell division, in fact, was seldom observed in those embryos with poorly organized shoot meristems. ASC was found to rescue these structurally disorganized meristems by stimulating cell division in the apical pole. The newly divided cells were able to develop further and to generate a functional shoot primordium through the process of organogenesis. Mitotic divisions were also observed at the base of the cotyledons; this often resulted in the formation of an additional shoot apical meristem, especially if the main apex failed to develop.