Title: FINE STRUCTURE OF PHLOEM CELLS IN RELATION TO TRANSLOCATION IN THE COTTON SEEDLING
Abstract:When special precautions were taken to permit killing and fixation of sieve elements before they were cut, sieve pores were found to be open. Companion cells were shown to be highly resistant to freez...When special precautions were taken to permit killing and fixation of sieve elements before they were cut, sieve pores were found to be open. Companion cells were shown to be highly resistant to freezing injury and less plasmolyzable than phloem parenchyma. Plasmodesmata connected parenchyma to parenchyma, parenchyma to companion cells, and companion cells to sieve elements. Their general absence between parenchyma cells and sieve elements points to a specific role of companion cells in sieve tube functioning. EM studies of these cells revealed an ER system which connects the central core of the plasmodesma to the sieve tube. This system may be responsible for active sucrose transport. Callose was always present on sieve plates of mature functioning sieve elements even with the most rapid killing and fixing possible. Extra callose promoted by heating (45 C) an intact stem segment was found to constrict the sieve pores almost completely. Constriction of plasmodesmata in lateral sieve areas also was evident. Fine structure analysis of the blocking mechanism is in accord with evidence obtained by tracer studies.Read More
Publication Year: 1969
Publication Date: 1969-04-01
Language: en
Type: article
Indexed In: ['crossref']
Access and Citation
Cited By Count: 32
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