Actin distribution in somatic embryos and embryogenic protoplasts of white spruce (Picea glauca) |
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Authors: | P Binarova C Cihalikova J Dolezel S Gilmer L C Fowke |
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Institution: | (1) De Montfort University, Norman Borlaug Centre for Plant Sciences, Institute of Experimental Botany, The Academy of Science of the Czech Republic, Sokolovska 6, 772 00 Olomouc, Czech Republic;(2) Department of Biology, University of Saskatchewan, S7N 5E2 Saskatoon, Saskatchewan, Canada |
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Abstract: | Summary Examination of unfixed immature somatic embryos of white spruce (Picea glauca) with fluorescent rhodamine-labeled phalloidin revealed an extensive network of fine actin microfilaments (MFs) in the embryonal
region which were not detected in specimens fixed with formaldehyde. Transition cells linking the embryonal region and suspensor
cells contained fine MFs as well as bundles of MFs. The large, highly vacuolated suspensor cells were characterized by actin
MF cables only. Treatment of embryos with cytochalasin B (CB) removed the fine MFs from the embryonal region and transition
cells, but many MF cables in suspensor cells were resistant. Full recovery from CB treatment was observed in most somatic
embryos. Embryogenic protoplasts capable of regenerating to somatic embryos in culture were released from only the embryonal
region of somatic embryos. Both uninucleate and multinucleate embryogenic protoplasts retained the extensive network of fine
actin MFs. In contrast, protoplasts derived from vacuolated suspensor cells and vacuolated free-floating cells contained thick
MF bundles and were not embryogenic. Distinct MF cages enclosed nuclei in multinucleate protoplasts and may be responsible
for preventing nuclear fusion. Microspectrophotometric analyses showed that the DNA contents of embryonal cells in the embryo
and embryogenic protoplasts were similar and characteristic of rapidly dividing cell populations. However, transition and
suspensor cells which released nonembryogenic protoplasts appeared to be arrested in G1, and suspensor cells showed signs of DNA degradation. |
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Keywords: | actin microfilaments conifer cytoskeleton somatic embryogenesis |
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