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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. / Science, Faculty of / Botany, Department of / Graduate

Cell-cell contact must be made and maintained for normal development and eventual differentiation of D. discoideum to occur. Certain plasma membrane components are known to alter in activity or abundance during the organism's developmental cycle although no quantitative measurement of plasma membrane neutral lipid and phospholipid content has been reported to date. Optimal conditions for the extraction, separation and assay of lipid components were derived and tested by quantification of the neutral lipid and phospholipid components of intact cells of strain Ax-2. Development was initiated in D. discoideum populations suspended in aqueous buffer and plasma membrane fractions were purified from both exponentially growing and aggregation-phase cells by a modified procedure which minimized phospholipid degradation during the plasma membrane isolation. Neutral lipid and phospholipid compositions of the plasma membrane fractions PM1 and PM2 from exponentially growing cells and from those in early aggregation phase were determined. Exponential phase cells' plasma membranes contained large proportions of phosphatidylethanolamine, phosphatidylcholine and lysophosphatidylethanolamine. Lysophosphatidylcholine was absent. A significant quantity of phosphatidylinositol was detected and cardiolipin, phosphatidylglycerol, phosphatidic acid and lyso-phosphatidic acid were each present in small amounts. The presence of phosphatidylethanolamine plasmalogen was suspected but not proven. No acylglycerol components were detected, the major neutral lipid fraction being that of free sterol which largely comprised stigmast-22-en-3β-ol; sterol ester was present in extremely small quantities. An unidentified neutral lipid component of plasma membranes was detected by its characteristic absorption and fluorescence upon irradiation at ultraviolet wavelengths. After sixteen hours aggregation the phosphatidylcholine content of the plasma membranes was greatly reduced, a significant proportion of the phosphatidylethanolamine appeared to have been converted to lysophosphatidylethanolamine, and phosphatidylglycerol, phosphatidic acid and lysophosphatidic acid were all in greater abundance than in growing cells' membranes. The free sterol component remained relatively constant but sterol ester had increased dramatically (7 to 10-fold) and the fatty acid composition of the plasma membrane phospholipids was more saturated, primarily because of the accumulation of palmitate and stearate and a reduction of the octadeca-dienoic fatty acid components. / Science, Faculty of / Microbiology and Immunology, Department of / Unknown

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