Takashi Sawa

THE STATOSPORE OF DINOBRYON DIVERGENS IMHOF: FORMATION AND GERMINATION IN A SUBARCTIC LAKE1

The population dynamics and the sequences of statospore development and germination of Dinobryon divergens from a shallow subarctic lake were examined. D. divergens showed a sharp increase in the vegetative cell population between June 19 and July 3, 1973, followed by a rapid formation of statospores from June 26 to July 3. Shortly after spore production, this species decreased sharply to an insignificant level in the phytoplankton. Statospore formation to as initialed by migration of the monad cell to the lorica mouth and proceeded by rounding up of the cytoplasm. There was then an unequal cleavage, silica wall formation around the larger portion of the cytoplasm including the nucleus and disintegration of the extracystic cytoplasm after development of the plug. The statospore was uninucleate throughout its development, and it was concluded that spore formation occurred asexually. Germination of statospores was observed in periphyton samples at depths of 20 and 80 cm on July 20–21, 1973 and in the sediments earlier the following year. During germination a cellulose chamber was produced from the pore of the statospore, followed, by cleavage of the cytoplasm within the spore and migration of approximately 4 daughter protoplasts into the cellulose chamber from which they eventually escaped. The present study proposes that chrysophycean statospores arising asexually and endogenously should be recognized as separate entities from those formed isogamously and autogamously but not necessarily endogenously. The latter statospores resulting from the sexual process have been given the term zygospore.

Cytochemical localization of oxidase activities with diaminobenizidine in the green algaChlamydomonas dysosmos

SummaryThe fine-structure of microbodies in the volvocalean green algaChlamydomonas dysosmos was studied and complimented with a cytochemical analysis of staining with diaminobenzidine (DAB). The organelle is spherical to ovate, delimited by a single membrane and possesses a matrix of moderate electron-opacity. The size of microbodies ranges from 0.25 to 0.9 microns in diameter. Close spatial association may occur between microbodies, mitochondria and the chloroplast. Deposition of oxidized DAB occurred in microbodies due to the presence of catalase, and in mitochondria because of mitochondrial cytochromes. Photooxidation of DAB by chloroplast lamellae is also described. Characteristic of these microbodies is the relative heterogeneity in DAB reactivity with certain individual microbodies of the population appearing DAB-insensitive.

18S Ribosomal Dna-Sequences Indicate a Monophyletic Origin of Charophyceae

Nuclear‐encoded small‐subunit (18S) ribosomal RNA genes of Chara australis R. Brown (C. corallina var. nobilis f. nobilis R.D.W.) and Nitella flexilis (L.) Ag. were amplified by polymerase chain reaction, cloned, and completely sequenced. Using structural criteria, the sequences were aligned with 18S ribosomal DNAs (rDNAs) from 11 other chlorophyll b‐containing algae and six higher plants (embryophytes). Phylogenetic trees were inferred by distance, neighbor‐joining, parsimony, and maximum‐likelihood approaches; confidence intervals were estimated by bootstrapping, and nonrandomness of tree structure was confirmed by permutation tests. 18S rDNAs of C. australis and two Nitella species were found to be specifically related and, together with 18S rDNAs of Chlorokybus atmophyticus Geitler, Klebsormidium flaccidum (A. Br.) Silva, Mattox, et Blackwell, and two Coleochaete species, support a robust monophyletic group (Charophyceae). Although most trees favored a specific sister‐group relationship between Charophyceae and embryophytes, statistical tests revealed that a sister‐group relationship between Charophyceae and Chlorophyceae could not be ruled out. Additional complete sequences from 18S rDNAs of lower land plants may be required to resolve phylogenetic relationships among these organisms.

COMPARATIVE ANATOMY OF CHAROPHYTA: II. THE AXIAL NODAL COMPLEX—AN APPROACH TO THE TAXONOMY OF LAMPROTHAMNIUM12

The present investigation on the axial nodes of 32 taxa belonging to the genera Chara, Lamprothamnium, Nitellopsis, Nitella and Tolypella confirms previous reports that within a given taxonomic group the structure of the main axial nodal complex is highly consistent. Besides the genera Nitella and Tolypella of the tribe Nitelleae, Lamprothamnium of the tribe Chareae is the only genus in which the central cells of the main axial nodal complex subdivide. This anatomical feature of the main axial nodal complex thus clearly separates the genus Lamprothamnium from the other genera of the tribe chareae. In 2 controversial species of the genus Chara, C. hornemannii and C. buckellii, the present study reveals that the central cells of their main axial nodal complexes do not subdivide. The transfer of these two species to the genus Lamprothamnium by Daily (1) may not be appropriate.

TWO NEW SPECIES OF TOLYPELLA(CHARACEAE) FROM NORTH AMERICA1,2

Two new species of the genus Tolypella (Characeae)–T. boldii Sawa sp. nov. and T. canadensis Sawa sp. nov.–were discovered in Texas, U.S.A., and Ontario, Canada, respectively. The species are recognized as additional members to the section Acutifolia because of the small and conical branchlet end cell and the oospore with a single basal impression. However, they differ from all the members previously described in the genus by the frequent and unique development of a terminal antheridium at the fertile branchlet node. A new and unexpected chromosome number of n = 8 for the genus was determined in both species, which, renders additional support to the conclusion that they represent a new taxonomic group in the section. The plants are described in detail in order to clarify some important morphological features which have been loosely interpreted by previous workers. Relationships between the new species and other members of the section are analyzed.

Occurrence, composition, and structure of microbody crystalloids in charophycean gametangial sheath cells

SummaryAn ultrastructural study was made of the cellular sheaths surrounding the sexual organs of five species of algae in the three genera ofCharophyceae: Nitella flexilis, N. mirabilis, Chara brattnii, Tolypella boldii andT. intricata. Microbodies similar in appearance, with crystalline nucleoids, were present in the sheath cells of all five species. The microbodies resembled in size and topographical associations those of other green algae. The hexagonal-shaped crystalloids consisted of parallel arrays of fine tubules of about 15 nm in diameter arranged parallel to the long axis of the crystalloid. In cross sections of the crystalloid, the close packing of the tubules showed hexagonal arrays. The intertubular distance is about 7 nm. At higher magnification there is a suggestion that the walls of these tubules are themselves constructed of smaller tubules. Further electron microscopic observations of diaminobenzidine (DAB)-treated preparations revealed pronounced deposition of reaction product in the microbodies, particularly on the crystalloids. The reaction was completely blocked by the catalase inhibitor, aminotriazole. These results strongly suggest that catalase is involved in this reaction and that catalase is located in the crystalloids.