Karl R. Mattox

Comparative cytology, evolution and classification of the green algae with some consideration of the origin of other organisms with chlorophylls A and B

I. I n t r o d u c t o r y Review of Some Recen t Comparat ive Cytological Studies in the Green Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 II. A Classification of the Green Algae Based on Cytological Characterist ics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 III. Problems and Impl ica t ions of a Cytological Classification . . . . . . . . . 119 IV. The Origin of Land Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 V. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 VI. Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 VII. References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

MITOSIS, CYTOKINESIS, THE DISTRIBUTION OF PLASMODESMATA, AND OTHER CYTOLOGICAL CHARACTERISTICS IN THE ULOTRICHALES, ULVALES, AND CHAETOPHORALES: PHYLOGENETIC AND TAXONOMIC CONSIDERATIONS1

The results of previous research and a present survey of some of the cytological characteristics of 18 additional genera and 34 additional species are presented and discussed from the viewpoint of phylogenetic and taxonomic significance. A preliminary attempt is made to place these, algae, in 4 orders on the basis of comparative cytology, and in particular on the basis of variation in mitosis and cytokinesis and the distribution of plasmodesmata. Consideration is given to the evolution of the phragmoplast and to the hypothesis that the Chaetophorales are related to the ancestry of land plants.

CELLULAR ORGANIZATION, MITOSIS, AND CYTOKINESIS IN THE ULOTRICHALEAN ALGA, KLEBSORMIDIUM1,2,3

Mitosis, cytokinesis, and cellular organization during interphase are described. Interphase cells possess a single microbody‐like organdie which occurs between, and is appressed to, the chloroplast and nucleus. The microbody‐like organelle divides during mitosis and. the division of the chloroplast. Anaphase is unusual in that chromosome‐to‐spindle pole distance remains constant even though the 2 groups of chromosomes become widely separated. When anaphase is half completed, a vacuole forms in the interzonal region and appears to be involved in further separation of the chromosomes. Vacuolar development is also involved with events of early interphase. The cytology of K. flaccidum is compared to those of Ulothrix fimbriata and Stigeoclonium helveticum. The comparison, does not support the present classification of the 3 species, and indicates the value of comparative fine structural studies in the classification of ulotrichalean algae.

MITOSIS AND CYTOKINESIS IN PLATYMONAS SUBCORDIFORMIS, A SCALY GREEN MONAD1

Scaly green monads are often placed in a separate class, Prasinophyceae, and have been considered to be among the most, primitive of green algae. Platymonas possesses rhizoplasts which resemble sarcomeric structures. At prophase, extranuclear spindle micro‐tubules emanate from a granular region which appears to arise through dissolution or dispersion of the rhizoplasts. It is probable that the rhizoplasts are largely consumed during the formation of the spindle and only small fragments are left at metaphase. The rhizoplasts can be seen again at telophase but are short at this stage. The basal bodies are not at the spindle poles but remain at their interphase position. The interzonal spindle collapses early at telophase, and shortly thereafter cleavage microtubules appear. These microtubules extend from the region of the basal bodies to the posterior of the cell. The events of cell division are compared with these events in other green algae and in Ochromonas. The functional and phylogenetic significance of the observations is discussed.

The comparative aspects of cell wall chemistry in the green algae (chlorophyta)

SummaryThe origin of a cell wall was an event of fundamental importance in the evolution of plants. In the green algae, cell walls apparently had independent origins in at least three lines of evolution. In this paper, the components of the cell wall were determined and compared in four filamentous green algae representing the charophycean, chlorophycean and ulvacean evolutionary lines. The walls of all four have hydroxyproline-containing proteins which separate into five or six bands upon SDS gel electrophoresis. Variation does exist, with the charophyte possessing fast moving electrophoretic bands and high hydroxyproline content, the chlorophytes having intermediate movement of bands and lower hydroxyproline content, and the ulvacean representative possessing slow moving bands and a very low, if not questionable, hydroxyproline and saccharide content. Qualitative and quantitative estimates of wall proteins and sugars have been determined and compared. A hypothetical scheme of cell wall evolution based on these data, those of previous analyses, and recent phylogenetic schemes is presented. Although sound conclusions cannot be made until more information is available, the scheme might help to emphasize the areas most in need of additional research.

COMPARATIVE CYTOLOGY OF ULOTHRIX AND STIGEOCLONIUM1

This investigation describes the cytology of the ulotrichalean genera Ulothrix and Stigeoclonium. Cellular organization is similar to the degree that interphase cells of the 2 genera cannot be distinguished with certainly. In Stigeoclonium, the nuclear envelope becomes disrupted at the end of prophase, and centrioles enter the nucleoplasm. At metaphase the nuclear envelope is again intact, and some of the spindle tubules appear to be contiguous with the nuclear envelope. The spindle in Ulothrix is essentially open with, no attachment of spindle tubules to the nuclear envelope and with, centrioles on the spindle‐cytoplasm interface at the spindle poles. Spindle poles are blunt in Stigeoclonium and pointed in Ulothrix. Cytokinesis is by cell plate formation in both genera, but there is no phragmoplast.

THE FLAGELLAR APPARATUS OF CHILOMONAS PARAMECIUM (CRYPTOPHYCEAE) AND ITS COMPARISON WITH CERTAIN ZOOFLAGELLATES1

The major components of the internal flagellar apparatus of Chilomonas paramecium Ehr. are two large microtubular roots and a striated root paralleled by three microtubules. The two microtubular roots overlap at the basal bodies. One microtubular root follows a curved path in the anterior of the cell, and the other extends straight to the posterior passing through a groove in the nucleus. The striated root extends laterally from the basal bodies. Except that it is smaller, the posteriorly directed root bears a strong resemblance to the axostyle of oxymonads. The overall arrangement and structure of the flagellar roots is similar to the pelta, axostyle and costa of trichomonads and the pelta and axostyle of oxymonads, groups of mitochondrion‐less, largely parasitic or symbiotic protozoans. An affinity between cryptomonads and oxymonads or trichomonads would have many phylogenetic implications, some of which are discussed.

COMPARATIVE CYTOLOGY AND TAXONOMY OF THE ULVAPHYCEAE. I. THE ZOOSPORE OF ULOTHRIX ZONATA (CHLOROPHYTA)1

This fine structural study of the quadriflagellate zoospore of Ulothrix zonata (Weber & Mohr) Kützing, with special attention to the flagellar root system, demonstrates that it is very similar to the zoospore of Ulva lactuca L. in several aspects. Common features include the presence of a cruciate root system (4‐2‐4‐2 type), a non‐striated band that connects basal bodies, a so‐called terminal cap, and system I and system II striated root components. Only slight differences exist, i.e. in the shape of the terminal cap, and in the number and position of the system II root components. It is concluded that the taxonomic affinities of U. zonata lie with the Ulvaphyceae sensu Stewart and Mattox rather than with the Chlorophyceae. Additional support for this conclusion is the discovery of tiny, flat body scales on the zoospore of U. zonata. A summary of the distinctive characteristics of the Chlorophyceae, Charophyceae and Ulvaphyceae reflecting the current state of knowledge is given.

The novel light-harvesting pigment-protein complex ofMantoniella squamata (Chlorophyta): Phylogenetic implications

SummaryA light-harvesting pigment-protein complex has been isolated fromMantoniella squamata (Micromonadophyceae, Chlorophyta) by nondenaturing polyacrylamide-gel electrophoresis. The complex runs as two bands of molecular weights 54,000 and 55,000. There are two constituent polypeptides of molecular weights 20,500 and 22,000. Antibodies were raised to the 20,500-dalton polypeptides from this complex and to the 24,500-dalton polypeptide from the analogous complex ofPedinomonas minor (Micromonadophyceae). The antibodies to theM. squamata polypeptide are specific for both polypeptides of theM. squamata light-harvesting complex, as well as for a 27,000-dalton polypeptide of undetermined function. The antibodies to theP. minor polypeptide are specific for polypeptide components of the light-harvesting complex of that alga. The antibodies specific for theM. squamata light-harvesting complex polypeptides do not cross react with any polypeptides ofP. minor thylakoid membranes, as demonstrated by crossed immunoelectrophoresis. Similarly, no polypeptides ofM. squamata thylakoids cross react with the antibodies specific forP. minor light-harvesting complex polypeptides. These results indicate that the light-harvesting complex ofM. squamata is structurally very different from that ofP. minor. In a survey of several land plants and green algae, including representatives of all classes of green algae, a light-harvesting complex homologous to that ofM. squamata was found only inMicromonas pusilla. All other organisms tested possessed a lightharvesting complex homologous to that ofP. minor. The evolutionary and taxonomic implications of the novelM. squamata light-harvesting complex are discussed.

The flagellar apparatus ofMesostigma viride (Prasinophyceae): Multilayered structures in a scaly green flagellate

Mesostigma virideLauterborn (Prasinophyceae) is the first green flagellate found to have multilayered structures (MLS) in its flagellar apparatus. MLSs were previously known from green algae only in charophycean swarmers, linking theCharophyceae to the origin of land plants, whose male gametes (when flagellated) also possess an MLS.M. viride is, therefore, probably more closely related to the origin of theCharophyceae than any other green flagellate that has been thoroughly studied so far. The occurrence of MLSs in green flagellates and apparently in other algae and protozoans suggests that an MLS occurred in an ancient group of flagellates and has survived in various protistan lines, including the line of green algae related to land plants. The occurrence of a synistosome inM. viride and other of its characteristics suggest that it is more closely related toPyramimonas than to other genera of scaly green flagellates.