, Volume 140, Issue 2, pp 173-186

First online:

High-voltage electron microscopy of whole, critical-point dried plant cells

2. Cytoskeletal structures and plastid motility inSelaginella
  • Guy CoxAffiliated withElectron Microscope Unit, University of Sydney
  • , C. R. HawesAffiliated withDepartment of Plant Sciences, Oxford University
  • , L. Van Der LubbeAffiliated withElectron Microscope Unit, University of Sydney
  • , B. E. JuniperAffiliated withDepartment of Plant Sciences, Oxford University

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The lower epidermis ofSelaginella Helvetica leaves has numerous chloroplasts. In the diffuse light of the plant's normal habitat these are distributed over the inner wall of the cell, while in bright sunlight they move to the lateral walls. High voltage electron microscopy of whole critical-point dried cells shows that in the diffuse-light position the chloroplasts are connected by bundles of tightly-packed parallel filaments; these are distinct from, but seem to interconnect with, the filaments of the cytomatrix. In thin sections these appear as conventional microfilament bundles, while staining with rhodamineconjugated phalloidin implies that they are composed of actin. In bright light, when the chloroplasts have moved to the lateral walls, these microfilament bundles completely disappear, while filaments of the cytomatrix system remain attached to the chloroplasts. These results suggest that the function of the microfilament bundles may be to anchor the chloroplasts as much as to move them, and that the cytomatrix system may play a part in the movement; it is possible that actin microfilament bundles may actually dissociate into separate filaments within the cytomatrix. Staining of cryo-sections with FITC-labelled antitubulin reveals a typical “cortical” pattern of microtubules which appears to play no part in chloroplast motility.


Chloroplast motility Cytoskeleton High-voltage electronmicroscope Actin microfilaments Cytomatrix Plant cells