| Abstract | Changes in cellular protein accumulation and in in vivo and in vitro protein synthesis, in somatic embryo tissues of white spruce during a 42 d maturation period were followed by two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (2-D SDS-PAGE). These investigations were complemented by an analysis of uptake and fate of fed abscisic acid (ABA) in somatic embryo tissues grown on maturation medium. When Stage 1 somatic embryos were cultured on ABA-containing maturation medium, many changes were observed in patterns of gene expression and in protein synthesis and accumulation which could be associated with embryo development. The polypeptides observed could be categorized as constitutive, embryo-abundant, embryo maturation-related and embryo stage-related, as well as those with non-specific changes. Accumulation of label from fed ³H-(+)-ABA in embryo tissues reached a plateau 3 d after Stage 1 somatic embryos were placed on maturation medium. ABA taken into tissues was rapidly metabolized, and 40% of radioactivity in tissues after 1 d of culture resulted from ABA metabolites. This value increased to 90% after 3 weeks culture. Conjugated ABA and oxidized ABA (phaseic acid and dihydrophaseic acid) were major forms of ABA metabolites in spruce embryo tissues. Using a single 42 d culture period following transfer to medium with ABA, the conditions that stimulate the sequence of developmental changes of somatic embryo maturation during the first 21 d do not reoccur during the second 21 d. Unless greater synchronization of Stage 1 cultures can be achieved, it is therefore unlikely that yields of mature somatic embryos will be increased by this method. |
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