New insights on Laminaria digitata ultrastructure through combined conventional chemical fixation and cryofixation

Abstract

The objective of the present study is to examine the fine structure of vegetative cells of Laminaria digitata using both chemical fixation and cryofixation. Laminaria digitata was chosen due to its importance as a model organism in a wide range of biological studies, as a keystone species on rocky shores of the North Atlantic, its use of iodide as a unique inorganic antioxidant, and its significance as a raw material for the production of alginate. Details of the fine structural features of vegetative cells are described, with particular emphasis on the differences between the two methods used, i.e. conventional chemical fixation and freeze-fixation. The general structure of the cells was similar to that already described, with minor differences between the different cell types. An intense activity of the Golgi system was found associated with the thick external cell wall, with large dictyosomes from which numerous vesicles and cisternae are released. An interesting type of cisternae was found in the cryofixed material, which was not visible with the chemical fixation. These are elongated structures, in sections appearing tubule-like, close to the external cell wall or to young internal walls. An increased number of these structures was observed near the plasmodesmata of the pit fields. They are similar to the “flat cisternae” found associated with the forming cytokinetic diaphragm of brown algae. Their possible role is discussed. The new findings of this work underline the importance of such combined studies which reveal new data not known until now using the old conventional methods. The main conclusion of the present study is that cryofixation is the method of choice for studying Laminaria cytology by transmission electron microscopy.

Multicellularity and the Need for Communication—A Systematic Overview on (Algal) Plasmodesmata and Other Types of Symplasmic Cell Connections

“…Localization of the ‘preplasmodesmata’ determines the position of the mature PDLCs which develop while the membrane sacs expand laterally to form a complete ‘cell partitioning membrane’ and a young cell wall. Flat cisternae were still found in mature cells in the vicinity of all cell walls and they were densely aggregated at the pit fields, where many PDLCs are clustered [ 138 ]. It was speculated that the flat cisternae might have a general function in cell-wall deposition and maintenance and/or in PDLC transport.…”