Joe Scott

ULTRASTRUCTURE OF EARLY DEVELOPMENT IN THE FEMALE REPRODUCTIVE SYSTEM OF POLYSIPHONIA HARVEYI BAILEY (CERAMIALES, RHODOPHYTA)1

Prefertilization and immediate postfertilization development in the female reproductive branch of Polysiphonia harveyi (Bailey) was studied with the electron microscope. Results pertaining to prefertilization morphology and development are consistent with those established in earlier light microscopic studies, but several unexpected ultrastructural characteristics were discovered. The mature carpogonium was found to have double membrane‐bound vacuoles of nuclear origin and the carpogonial nucleus contained a nucleolus with a distinctive crystalline lattice. Trichogynes lacked a nucleus. Of particular interest was the discovery of a highly structured channel of smooth endoplasmic reticulum (SER) which extended uninterrupted, except for pit connections, through the carpogonial branch. It is suggested that the message of fertilization is conducted through the SER channel from the carpogonium to the support cell. Few observations were made on postfertilization branches, but evidence of direct fusion between the carpogonium and auxiliary cell was fairly conclusive. Pit plugs in the female branch were found to be of three morphological types differing by the presence and number of pit membranes. We have designated these plugs Type I–III since differential functioning was not fully ascertained. Our data suggest that pit membranes may serve to stabilize the plug and that those plugs without membranes are more readily dismantled to allow cytoplasmic continuity between cells.

Mitosis in the freshwater red algaBatrachospermum ectocarpum

SummaryMitotic ultrastructure was observed in meristematic cells of carposporophyte generations of the freshwater red algaBatrachospermum ectocarpum. Prior to nuclear division, cell elongation occurs resulting in the nucleus being located at the proximal end of the cell and separated by a large central vacuole from a distal “empty region” which the daughter nucleus eventually occupies. In late prophase, nuclear envelope-attached polar rings are situated adjacent to shallow nuclear invaginations. At prometaphase the nuclear invaginations extend deeply into the nucleus forming continuous cytoplasmic channels containing microtubules. Perinuclear ER and a typical equatorial chromosomal plate are formed by metaphase at which time the nuclear envelope lining the cytoplasmic channels has dispersed. Chromosomal and non-chromosomal microtubules converge at the poles where a single, large gap is seen in the otherwise intact nuclear envelope. Polar rings were not detected in the few mitotic cells observed beyond prometaphase but are thought to be present. During anaphase an interzonal midpiece is formed and the distal-most incipient daughter nucleus moves laterally past the central vacuole into the apical “empty region”. Features of mitosis inBatrachospermum are believed to be intermediate between those exhibited by the lower and higher orders of red algae, this being consistent with the taxonomic placement of the genus in theNemaliales, the least advanced order of the classFlorideophyceae.

ULTRASTRUCTURE OF CELL DIVISION AND REPRODUCTIVE DIFFERENTIATION OF MALE PLANTS IN THE FLORIDEOPHYCEAE (RHODOPHYTA): CELL DIVISION IN POLYSIPHONIA1

Cell division in the marine red algae Polysiphonia harveyi Bailey and P. denudata (Dillwyn) Kutzing was studied with the electron microscope. Cells comprising the compact spermatangial branches of male plants were used exclusively because of their small size, large numbers and the ease with which the division planes can be predetermined. Some features characterizing mitosis in Polysiphonia confirm earlier electron microscope observations in Membranoptera, the only other florideophycean algae in which mitosis has been studied in detail. Common to both genera are a closed, fenestrated spindle, perinuclear endoplasmic reticulum, a typical metaphase plate arrangement of chromosomes, conspicuous, layered kinetochores, chromosomal and non‐chromosomal microtubules, and nucleus associated organelles (NAOs) known as polar rings (PRs) located singly in large ribosome‐free zones of exclusion at division poles in late prophase. However, other features, unreported in Membranoptera, were observed consistently in Polysiphonia. These include the presence of PR pairs in interphase‐early prophase cells, the attachment of PRs to the nuclear envelope during all mitotic stages, the migration of a single PR to establish the division axis, a prominent, nuclear envelope protrusion (NEP) at both division poles at late prophase, the prometaphase splitting of PRs into proximal and distal portions, and the reformation of post‐mitotic nuclei by the separation of an elongated interzonal nuclear midpiece at telophase. During cytokinesis, cleavage furrows impinge upon a central vacuolar region located between the two nuclei and eventually pit connections are formed in a manner basically similar to that reported for other red algae. Diagrammatic sequences of proposed PR behavior during mitosis are presented which can account for events known to occur during cell division in Polysiphonia. Mitosis is compared with that reported in several other lower plants and it is suggested that features of cell division are useful criteria to aid in the assessment of phylogenetic relationships of red algae.

Observations on Purpureofilum apyrenoidigerum gen. et sp. nov. from Australia and Bangiopsis subsimplex from India (Stylonematales, Bangiophyceae, Rhodophyta)

Purpureofilum apyrenoidigerum gen et sp. nov. was obtained from a mangrove habitat in New South Wales, Australia. It had unbranched uniseriate to multiseriate filaments less than 1 mm tall, with a unicellular base. Each cell had a single multilobed parietal chloroplast without a pyrenoid. During reproduction vegetative cells were discharged directly as monospores that remained motile for several hours after release. Spores with long tails moved more slowly (0.053–0.195 μm sχ) than spores without tails (0.43–1.76 μm s′1). Phylo‐genetic analysis of sequences of the small subunit of the nuclear‐encoded rRNA and plastid‐encoded ribu‐lose bisphosphate carboxylase/oxygenase genes revealed that Purpureofilum is a member of the Stylonematales and is most closely related to the filamentous genus Bangiopsis. Bangiopsis differs from Purpureofilum by having longer (to 5 mm) multiseriate filaments, cells containing a stellate chloroplast, a conspicuous central pyrenoid, and monospores often formed in packets. Monospores of Bangiopsis were also motile. Transmission electron microscopy investigation of Purpureofilum and Bangiopsis revealed that the Golgi complexes are associated only with rough endo‐plasmic reticulum and that the plastid contains a peripheral thylakoid; this combination of features being the same as in all other multicellular members of the Stylonematales. The low molecular weight carbohydrates of Purpureofilum and Bangiopsis were digenea‐side and sorbitol, which were present in most other Stylonematales.

Neorhodella cyanea, a new genus in the Rhodellophyceae (Rhodophyta)

J. Scott, A. Yokoyama, C. Billard, J. Fresnel, Y. Hara, K.A. West and J.A. West. 2008. Neorhodella cyanea, a new genus in the Rhodellophyceae (Rhodophyta). Phycologia 47: 560–572. DOI: 10.2216/08-27.1 The red algal unicell Rhodella cyanea (Rhodellophyceae) was reinvestigated. The cell ultrastructure is clearly dissimilar to that of the two other Rhodella species, R. maculata Evans and R. violacea (Kornmann) Wehrmeyer. Consequently, we have established Neorhodella gen. nov. Neorhodella cyanea possesses a large parietal chloroplast with numerous lobes extending into the cell center. The inner region of each lobe terminates near the central nucleus and contains several thylakoids sparsely covered by opposed, disc-shaped phycobilisomes. These regions are interpreted as multiple pyrenoids. Thylakoids are more numerous in other chloroplast regions where phycobilisomes are alternately spaced. A peripheral encircling thylakoid is absent and plastoglobuli, in unicellular red algae found only in the Rhodellophyceae, are found at the cell periphery. Golgi bodies are exclusively perinuclear, similar to Dixoniella and Glaucosphaera in the class Rhodellophyceae. Golgi cisternae appear closely opposed during some cell cycle stages, a feature found in no other unicells except members of the Rhodellophyceae. Several stages of mitosis were observed in Neorhodella. These suggest a pattern fairly typical of other unicellular red algae. Nucleus-associated organelles are polar rings, the division poles have conspicuous gaps in the mostly intact nuclear envelope and microtubules emanate from a flattened plate of membranes and moderately electron dense material, attaching to small kinetochores during mitosis and terminating near the former poles of telophase nuclei during migration of daughter nuclei. The low molecular weight carbohydrate of Neorhodella is mannitol, similar to Rhodella and Dixoniella.

Phycobiliprotein composition and chloroplast structure in the freshwater red alga Compsopogon coeruleus (Rhodophyta)

Serial sections of uncorticated axial cells of Compsopogon coeruleus revealed a single interconnected parietal chloroplast. Phycobilisomes in such chloroplasts were hemidiscoidal in shape with a broad‐face diameter of ca. 25–30 nm. The molar ratio of phycobiliproteins in whole cell extracts was IPE:3PC:1APC, similar to isolated phycobilisomes. Two spectrally distinct C‐phycocyanin forms (A618 nm, F648 nm and A630 nm, F652 nm) were resolved in dissociated phycobilisomes along with B‐phycoerythrin and allophycocyanin.

ELECTRON MICROSCOPE OBSERVATIONS OF TELOPHASE II IN THE FLORIDEOPHYCEAE1

Tetrahedral tetrasporangia of several florideophycean red, algae were examined with the electron microscope for details of meiosis. Only telophase II nuclei are described since earlier stages were not, observed. Both divisions of meiosis are presumed to occur within the confines of the original tetrasporangial mother cell nuclear envelope. Four nuclei are then formed simultaneously. These observations essentially support Yamanouchis description of telophase II in Polysiphonia flexicaulis (Harvey) Collins (as P. violacea) and suggest that meiosis in these algae could be basically similar to “uninuclear meiosis” in the fungi Saprolegnia and Saccharomyces.

Ultrastructure of vegetative organization and cell division in the freshwater red algaCompsopogon

SummaryUniseriate filaments of the freshwater red algaCompsopogon coeruleus were examined by transmission electron microscopy for details of vegetative organization and cell division with the goal of providing useful taxonomic characters. Each cells single, complex chloroplast contains a peripheral encircling thylakoid, and unlike the vast majority of red algae, the cis-regions of dictyosomes are not consistently juxtaposed with mitochondria. These subcellular features, which are present in all examined genera in theCompsopogonales, Erythropeltidales, andRhodochaetales, along with certain unique reproductive characteristics, unify these three orders. During mitosis in uncorticated axial cells, a small, ring-shaped nucleus associated organelle (NAO) is located at each division pole, an intranuclear spindle comes to a moderately acute focus at the flattened, fenestrated metaphase-anaphase division poles and perinuclear ER partially encloses dividing nuclei, including a well-developed interzonal midpiece. The cleavage furrow penetrates the large, central vacuolar region to separate daughter nuclei. These cell division features most closely resemble the pattern described for the orderCeramiales. Our observations of vegetative and dividing cells ofC. coeruleus supplement the growing volume of evidence in favour of uniting all red algae into a single class without subclass designations.

Ultrastructure of meiosis in Dasya baillouviana (Rhodophyta). I: Prophase I

This first of two papers on ultrastructural observations of meiosis in the red alga Dasya baillouviana (Gmelin) Montague describes stages of prophase I of meiosis. Although the five stages of prophase were originally derived from light microscopic studies, the same stages were utilized for this study based on the developmental sequence of the synaptonemal complex, which has the same morphology and mode of development as those reported for other red algae. The cytoplasm in early prophase sporocytes was typically less electron dense than either vegetative cells or sporocytes in later stages of meiosis. The reduction in density suggests clearing of ribosomes and other cytoplasmic components prior to conversion from sporophyte to gametophyte control. Leptotene cells often had an amorphous, chromatin‐free area, function unknown, which was not obviously associated with any specific nuclear region. Diplotene cells were characterized by nuclei containing prominent ring‐shaped nucleoli composed of a dark staining ring of material surrounding an electron‐translucent “vacuole.” Packets of electron‐dense, fibrillar material were often noted in the cytoplasm of late prophase cells. These packets are thought to he “nuage,” a term applied to large cytoplasmic aggregations of RNA in germ cells of several other phyla. It is suggested that nuage may represent a new infusion of ribosomal and messenger RNA for post‐meiotic development. The division pales are established by late prophase and a single polar ring is found within each large “exclusion zone” in close association with a pore‐free area of nuclear envelope. Both annulate lamellae and small, numerous vesicles are located in the exclusion zones. The significance of the various aspects of prophase I is discussed with the overall observation that this phase of meiosis in red algae is very similar to the process in higher plant and animal cells.

Ultrastructure of cell division and reproductive differentiation of male plants in theFlorideophyceae (Rhodophyta). Mitosis inDasya baillouviana

SummaryMitosis in the marine red algaDasya baillouviana (Ceramiales, Florideophyceae) was observed with the electron microscope. Most details of the process are quite similar to those observed in the other macroscopic red algae studied to date. However, some minor variations were noted. At late prophase a very small nuclear envelope protrusion (NEP) is formed at each division pole subjacent to the “nucleus associated organelle” known as the polar ring (PR) and 2–3 cisternae of perinuclear endoplasmic reticulum (PER) are commonly present during metaphase-anaphase. In contrast, in the other florideophycean algae where mitosis has been reported, a prominent NEP is present at late prophase (McDonald personal communication,Scottet al. 1980) and only a single cisterna of PER is observed. Additionally, during mid-late interphase and in mitotically-quiescent cells ofDasya, a single cisterna of smooth-surfaced ER is always juxtaposed with each PR. The possible significance of PER in theFlorideophyceae and other multinucleate organisms is discussed as well as the likely functions of spindle-associated smooth ER. It is suggested that ultrastructural features of mitosis should be useful as criteria to aid in the interpretation of the phylogeny of red algae.