ACTIN DISTRIBUTION IN SOMATIC EMBRYOS AND EMBRYOGENIC PROTOPLASTS OF WHITE SPRUCE (PICEA-GLAUCA)

Examination of unfixed immature somatic embryos of white spruce (Picea glauca) with fluorescent rhodamine-labeled phalloidin revealed an ext ensive network of fine actin microfilaments (MFs) in the embryonal reg ion which were not detected cells contained fine in specimens fixed wi th formaldehyde. Transition cells linking the embryonal region and sus pensor were MFs as well as bundles of MFs. The large, highly vacuolate d suspensor cells ed the fine MFs from the embryonal region and transi tion cells, but characterized by actin MF cables only, Treatment of em bryos with cytochalasin B (CB) MF cables in suspensor cells were resis tant. Full recovery from CB treatment was observed in most somatic emb ryos. Embryogenic protoplasts capable of regenerating to somatic embry os in culture were released item only the embryonal many region of som atic embryos. Both uninucleate and multinucleate embryogenic. protopla sts retained the extensive network of fine actin MFs, In contrast, pro toplasts derived from vacuolated suspensor cells and vacuolated free-f loating cells contained thick MF bundles and were not embryogenic. Dis tinct MF cages enclosed nuclei in multinucleate protoplasts and may he responsible for preventing nuclear fusion. Microspectrophotometric an alyses showed that the DNA contents of embryonal cells in the embryo a nd embryogenic protoplasts were similar and characteristic of rapidly dividing cell populations, However, transition and suspensor cells whi ch released nonembryogenic protoplasts appeared io be arrested in G(1) , and suspensor cells showed signs of DNA degradation.