Development of white spruce somatic embryos: II. Continual shoot meristem development during germination

Abstract

This study compares the development of shoot apical meristems of white spruce somatic and zygotic embryos during germination. In mature somatic embryos, the functional part of the shoot apical meristem was bi-layered. After partial drying, a normal shoot meristem was formed from these two cell layers during germination. Other cells within the meristem were vacuolated and separated by intercellular air spaces. In the absence of the partial drying treatment, somatic embryos enlarged in size primarily due to vacuolation of cells and the formation of large intercellular air spaces. A majority of these somatic embryos failed to form a functional shoot apical meristem. Compared with somatic embryos, the shoot apical meristem of a mature zygotic embryo was well organized with a densely cytoplasmic apical layer. The cells within the meristem were tightly packed. Judging from the cell profiles during germination, all cells within the meristem of the zygotic embryo took part in the formation of the vegetative shoot apical meristem.