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Survey of cell wall structure in some Florideophycidae Rusanowski, Paul Charles

Abstract

Cell wall structure was investigated in 20 different red algae. Representatives from all 4- families of the order Ceramiales and one family of the order Gigartinales were investigated. Of these, 3 genera, Polysiphonia, Pterosiphonia and Antithamnion were investigated with regards to both the cellulosic and mucilaginous portions of the cell wall. A new staining technique utilizing a combination of ruthenium red and osmium tetroxide as a postfixation was used in the latter portion of the study. The ultrastructure of pit connections was examined in all algae. The inner cellulosic portion of the cell wall consists of a reticulate pattern of microfibrils which appear densely stained, In Pterosiphonia this cellulosic portion was found to consist of 2 layers; an inner layer of microfibrils which ensheathed individual cells and an outer layer of microfibrils which ensheathed the entire thallus and was in contact with the mucilaginous coat. The microfibrils in the inner layer appear nearly cross-sectioned, while those in the outer layer appear more longitudinally oriented to the plane of sectioning. The outer mucilaginous coat covers the entire thallus. It consists of 4 layers. The first or outermost layer consists of loose bunches of microfibrils extending out from the second layer. The second layer consists of a zone of medium electron density approximately 750 A in thickness. The third layer is wholly contained within the second layer. It is composed of a densely staining band of microfibrils extending from a similarly staining membrane-like structure. The fourth layer is a densely stained membrane-like structure in contact with the cellulosic portion of the cell wall. An additional layer, the D layer, is sometimes found in the cell wall. When present it is found in the outermost portion of the cellulosic wall and obscures the fourth layer of the mucilaginous coat. It consists of a densely staining amorphous material. Investigation of the pit connection showed the occurrence of 2 stages of one basic pit structure. One stage, the single disc stage-pit structure, has been found in all algae investigated. It consists of a solid, lenticular, membrane-bound plug situated within an aperture in the cell wall. The plug consists of a granular material surrounded by a zone of densely staining amorphous material. The other stage, the double disc stage pit structure, is a modification of the single disc stage. It is not found in young cells near the apex of the thallus, but only in cells which have, or are undergoing, rapid elongation and vacuolation. This pit structure has only been observed in axial cells of the family Ceramiaceae in the order Ceramiales. The double disc stage pit structure differs from the single disc stage in that the granular material of the plug is segregated into 2 regions or plates, one on either side of the plug. The central region of the plug at first appears clear but later appears to be partially occupied by a granular to fibrillar material. The differentiation of the double disc stage pit structure from the single disc stage has been described. These observations are thought to support and confirm the earlier work of Jungers (25). However, his observations have been extended through the use of electron microscopy in this study. It has been proposed that the terms used in this study, single disc stage- and double disc stage pit structures, replace the terms Polysiphonia and Griffithsia pits used by Jungers.

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