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A Survey of Cell Wall Structure in Some Florideophycidae

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A Survey of Cell Wall Structure in Some Florideophycidae A SURVEY OF CELL WALL STRUCTURE IN SOME FLORIDEOPHYCIDAE by PAUL CHARLES RUSANOWSKI B.A., San Fernando Valley State College, 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Botany We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Paul Rusanowski (In absentia) Department of Botany The University of British Columbia Vancouver 8, Canada Date June 8, 1970 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 wecond 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. TABLE OF CONTENTS PAGE List of tables ................ iii List of plates iv List of appendicies • v INTRODUCTION . ............ 1 LITERATURE REVIEW . 2 Cell wall . .2 Pit connections • 3 MATERIALS AND METHODS 6 RESULTS . ........ 9 Light microscopy ........ 10 Electron microscopy 11 Cell wall ................ ..11 Pit ultrastructure • • 13 Cytoplasm • 17 DISCUSSION 20 Cell wall 20 Pit structure 22 CONCLUSIONS 29 BIBLIOGRAPHY 32 APPENDICIES . ' 36 Appendix I i 36 Appendix II . 38 Appendix III ........ 39 KEY TO ABBREVIATIONS . 41 (ii) LIST OF TABLES PAGE Table I. List of algae, collection and utilization data 7-8 (iii) TABLE OF PLATES PAGE Plates 1-2 -Light micrographs of apical region of the thallus and pits. with. both, fresh and fixed and sectioned material • .42-43 Plates 3-4 Ultrastructure of the apical cell and derivatives . .44-4-5 Plates 5-7 Ultrastructure of the single disc stage pit 46-48 Plate 8 Ultrastructure and development of the double disc stage pit ........ 49 Plates 9-12 Ultrastructure of cytoplasmic organelles and inclusions. • • 50-53 Plates 13-14 Ultrastructure of the cell wall .54-55 (iv) LIST OF APPENDICIES PAGE I. Culture formulae 36 II. Light microscope techniques and stains 38 III. Electron microscopy technique and formulae 39 Cv) 1 INTRODUCTION One of the unique features of the Rhodophyceae is the possession of pit connections. These pit connections are absent from the sub-class Bangiophycideae. They are a prominent feature of cell morphology in the sub-class Florideophycidae to which most of the red algae belong. Pit connections appear oval to circular in shape and are of variable size, depending on their age. In some red algae pit connections can occupy the entire wall between two cells. Although pit connections have been the subject of numerous investigations both their structure and function remain obscure. Recent investigations using electron microscopy have done much toward resolving the structure of pit connections, however, opinions are still divided as to their actual chemical and physical structure. The present studies were undertaken in an attempt to determine the structure of the cell wall and pit connection in several red algae, by means of electron microscopy. Of especial importance was an investi• gation into the structure of the outermost layer of the cell wall, the so-called pectic coat, using a previously untried staining procedure. In addition, a comparison of pit ultrastructure between different groups of algae utilizing the same preparative procedures was undertaken. Members of all four families of the order Ceramiales and one family of the order Gigartinales were investigated. 2 LITERATURE REVIEW CELL WALL The cell wall in the Florideophycidae is generally considered to be uniform in structure. It consists of two parts: an inner cellulosic portion and an outer pectic layer (16, 19, 28). In some cases a cuticle is also formed (28). In Porphyra, a member of the Bangiales, the cuticle has been shown to contain a very large amount of protein (20). In some algae, especially members of the family Ceramiaceae, cell walls show a distinct stratification (7, 19). The inner cellulosic portion of the cell wall consists of a pattern of reticulate microfibrils, which are easily seen under the electron microscope (11, 12, 4-0, 49). The microfibrils are embedded in an amorphous matrix (26). Preston (44) has classified wall material of algae into three groups: Group I, cellulose I being the main component with regularly oriented microfibrils; Group II, randomly oriented microfibrils of cellulose II, and Group III, wall composed of other microfibrils. The microfibrils have been identified as cellulose II in Griffithsia (37), and most red algal cell walls have been placed in Group II of Preston's classification (12, 13). The cellulosic layer •surrounds individual cells of the thallus (49). The mucilaginous or pectic coat, on the other hand, covers the outer surface of.the thallus only (12, 49). Dawes et al. (12) reported this mucilaginous coat to consist of reticulate microfibrils embedded in an amorphous matrix; while Bisalputra et al. (2) have been able to resolve it initio four distinct 3 layers of complex nature. Surface activities at the plasmalemma have been described and related to cell wall deposition (2). PIT CONNECTIONS Pit connections in the red algae have received considerable attention. One of the first workers, Schmitz, described the pit as being closed by a membrane in which two plates were situated, one on either side of the membrane (52). The plates stained densely with haematoxylin, and plasmodesmata were observed passing through the membrane separating the plates. Falkenberg, working with members of the Ceramiales, agreed with Schmitz, but could not find plasmodesmata (17). Mangenot, using Griffithsia (Ceramiales), claimed that the pit had no closing membrane and that the cytoplasm was continuous through the pit connection,(34). Miranda, using Bornetia (Ceramiales), was of the opinion that the closing membrane was present and that there were protoplasmic connecting strands (plasmodesmata) through the region (35). Jungers was the first to propose that the confusion in this area had probably resulted from the fact that there is more than one type of pit connection in the red algae (25). He recognized two types of pit structures, the Polysiphonia-type and the Griffithsia-type (25). The Polysiphonia-type has two densely stained plates separated by a membrane, with no plasmodesmata passing through the membrane; the Griffithsia-type was described as a dense, biconvex^lens-shaped body, without a closing membrane.
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