Micromorphological studies of adventitious bud formation on Picea abies embryos treated with cytokinin

Embryos of Picea abies (L.) Karst were pulse-treated with water or cytokinin for 2 h and then cultured on medium lacking cytokinin. Adventitious buds developed on cytokinin-treated embryos, but not on water-treated embryos. The general appearance and the surface morphology were similar on water and BA (benzyladenine)-treated embryos after 3 days. The epidermal cells were elongating after 6 days on water-treated embryos, while they were dividing on cytokinin-treated embryos. Furthermore, the cells surrounding the stomata had started to proliferate on BA-treated embryos. This was the first micromorphological sign of bud initiation. During the second week prominent meristemoids developed from these cells. A stoma was observed on the top of each meristemoid. The variation in developmental pattern of meristemoids among different embryos as well as within each embryo was small. However, during the subsequent development of bud primordia and buds, the morphological variation was significant. The meristemoids continued to develop into cone-shaped bud primordia, which successively changed shape during the transition to adventitious buds. The epidermal cells divided and the epidermis did not rupture during the formation of adventitious bud primordia. The epidermis was identified as the protoderm of the bud primordium.