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Anatomical Changes and Peroxidase Activity After Cytokinin Treatments Inducing Adventitious Bud Formation on Embryos of Picea abies

Adventitious buds were initiated on embryos of Picea abies (L.) Karst. after a pulse treatment with benzyladenine (BA). The embryos released cytokinin-like substances into the culture medium for 16 h after pulse treatment. When embryos were cultured on medium containing the cytokinin-like substances for more than 6 days, elongation of cotyledons and roots was inhibited, and a meristematic layer was formed from epidermal and subepidermal cells. Meristematic centers and adventitious buds subsequently developed from this layer. In embryos transferred to fresh culture medium after the initial release of cytokinin-like substances, cotyledons and roots elongated to various extents. Frequency of cell division increased after the BA treatment, but no meristematic layer was formed. A few localized cell divisions in epidermal and subepidermal cells led to the organization of discrete meristematic centers from which adventitious buds subsequently developed. The developmental pattern for meristematic centers, the time course for the development of adventitious buds, and the final yield of adventitious buds were similar, irrespective of whether a meristematic layer was formed. The peroxidase activity in both water- and BA-treated embryos increased during the first 3 days in culture; thereafter, it remained at a high level for 18 days in BA-treated embryos, which developed a meristematic layer. The variation in peroxidase activity during the first 3 wk in culture was similar in water- and BA-treated embryos lacking a meristematic layer. Total peroxidase activity was not correlated with bud initiation.