Glutaraldehyde-induced deposition of callose

Aldehyde fixation of Abutilon nectaries induces deposition of callose, probably at plasmodes-mata. The phenomenon was analysed by examining a range of other tissues, several of which show a similar response, and by varying the fixation conditions. Callose deposition occurs within 15 min of the onset of fixation in immature nectaries, and does not occur in mature nectaries. Low temperature controls show that the deposition is artefactual and that it may give an erroneous view of the structure of plasmodesmata.