DEVELOPMENT OF WHITE SPRUCE (PICEA-GLAUCA (MOENCH) VOSS) SOMATIC EMBRYOS DURING CULTURE WITH ABSCISIC-ACID AND OSMOTICUM, AND THEIR TOLERANCE TO DRYING AND FROZEN STORAGE

The limit of permeability of white spruce (Picea glauca [Moench.] Voss ) somatic embryo cell walls to molecules was in the order of 30 Angstr om. Polyethylene glycols (PEGs) and dextrans of molecular weights grea ter than 1000 and 6000, respectively, produced a non-permeating (non-p lasmolysing) water stress which improved embryo development. Somatic e mbryos converted to plantlets at frequencies of 76-84% following slow drying and storage at -20 degrees C for 1 year, which was similar to t he 77% recorded for control somatic embryos slowly dried then germinat ed without freezing or storage. Culture for 7-8 weeks with medium cont aining abscisic acid, 3% sucrose, and 7.5% PEG 4000 yielded somatic em bryos with five times the embryo storage lipid content recorded for zy gotic embryos. During culture with PEG the moisture content of the som atic embryos decreased from 96% for immature suspension-cultured somat ic embryos, to 47% for mature embryos. Somatic embryos cultured for 7- 8 weeks survived rapid drying to 5% moisture content, and converted to plantlets at frequencies of 60-70%, but no somatic embryos survived r apid drying when cultured for only 4 weeks; however, slow drying did i nduce desiccation tolerance in 3-week cultured somatic embryos. Abscis ic acid was important to maintain embryos in a developmental state, bu t ABA alone did not induce desiccation tolerance. In order to induce d esiccation tolerance a water stress treatment was required. Tolerance of rapid drying coincided with moisture contents below 55%, which occu rred after 5 weeks of culture in the presence of PEG 4000 and abscisic acid.