Plasmatubules: fact or artefact?

Plasmatubules are tubular evaginations of the plasmalemma associated with sites where high solute flux occurs between apoplast and symplast. Plasmatubules of the scutellar epithelial cells of germinating barley (Hordeum vulgare L.) have been examined following a variety of fixation methods. Of the aqueous fixations, primary aldehyde fixation with osmium post-fixation and osmium as the primary fixative gave comparable images, whilst potassium permanganate resulted in some distortion of the tissue in general including dilation of the tubular evaginations of the plasmalemma. Freeze-fixation and substitution with acetone and acetone-osmium gave images of the plasmalemma comparable to those obtained by the aqueous aldehyde and osmium methods. The similarity of structure with aldehyde or osmium and freezing as the primary fixation is taken to indicate that plasmatubules are real and not artefacts resulting from the fixation procedure.