PHYLOGENETIC SYSTEMATICS OF THE ULVACEAE (ULVALES,ULVOPHYCEAE) USING CHLOROPLAST AND NUCLEAR DNA SEQUENCES1

Systematic hypotheses for the Ulvaceae were tested using phylogenetic analysis of sequences for the gene encoding the large subunit of RUBISCO, small subunit rDNA and a combined data matrix. Representatives of eight putative ulvaceous genera and twelve additional taxa from the Ulvophyceae and Trebouxiophyceae were included in analyses using maximum parsimony and maximum likelihood criteria. Molecular data supported hypotheses for the Ulvaceae that are based on the early development of vegetative thalli and motile cell ultrastructure. Ulvaceae sensu Floyd and O'Kelly, including Percursaria Bory de Saint‐Vincent, Ulvaria Ruprecht and a complex of closely related species of Chloropelta Tanner, Enteromorpha Link and Ulva L. was supported; however, monophyly of Enteromorpha and Ulva was not supported. The Ulvales and Ulotrichales sensu Floyd and O'Kelly were monophyletic. Blidingia Kylin and Kornmannia Bliding were allied with the former and Capsosiphon Gobi with the latter, although relationships among these and other taxa in these orders remain uncertain. The Ulvales are characterized by an isomorphic life history pattern, gametangia and sporangia that are identical in structure and development, motile cells with bilobed terminal caps and proximal sheaths consisting of two equal subunits. Method of motile cell release and the gross morphology of vegetative thalli are not systematically reliable characters.     

A RIBOSOMAL DNA PHYLOGENY SUPPORTS THE CLOSE EVOLUTIONARY RELATIONSHIPS AMONG THE SPOROCHNALES,DESMARESTIALES, AND LAMINARIALES (PHAEOPHYCEAE)1

We report six complete 18S ribosomal DNA (rDNA) sequences representing five brown algal orders: Sporochnus comosus C. A. Agardh (Sporochnales), Chorda tomentosa Lyngbye (Chordaceae, Laminariales), Saccorhiza polyschides (Lightfoot) Batters (Phyllariaceae, Laminariales), Desmarestia ligulata (Lightfoot) Lamouroux (Desmarestiales), Ectocarpus siliculosus (Dillwyn) Lyngbye (Ectocarpales), and Scytosiphon lomentaria (Lyngbye) J. G. Agardh (Scytosiphonales). These sequences were compared with published laminarialean (Alaria marginata Postel et Ruprecht [Alariaceae] and Macrocystis integrifolia Bory [Lessoniaceae]) and fucalean (Fucus gardneri Silva) rDNA sequences for phylogeny inference using both the distance-matrix and parsimony methods. The inferred 18S phylogenies clustered Sporochnus, Desmarestia, Chorda, Saccorhiza, Alaria, and Macrocystis in an assemblage. This Sporochnales–Desmarestiales–Laminariales (S-D-L) complex was consistently separated from the Ectocarpales, Scytosiphonales, and Fucales by bootstrap analyses. The inferred phylogenies are consistent with several possible evolutionary processes leading to this S-D-L complex. Members in this assemblage lack eyespots in their sperm, and their sperm have the atypical brown algal flagellation: shorter anterior and longer posterior flagella. In addition, they are oogamous with a heteromorphic alternation of generations between a microscopic gametophyte and a macroscopic sporophyte. Members of the S-D-L complex can be separated into different phylogenetic lines based on the presence/absence of eyespots in their meiospores. Our findings support the contention that the Sporochnales, Desmarestiales, and Laminariales are closely related. In addition, our rDNA tree suggests that the Laminariales is paraphyletic.     

NUCLEAR HISTONE PROTEINS OF GAMETES IN AN OOGAMOUS AND TWO ISOGAMOUS BROWN ALGAE1

Nuclear basic proteins (histones) were studied in male and female gametes of the isogamous brown algae, Colpomenia bullosa (Saunders) Yamada and Analipus japonicus (Harvey) Wynne and sperm of the oogamous Cystoseira hakodatensis (Yendo) Fensholt by using SDS‐ and AUT‐PAGE. Four major core histones and several linker histone H1s were detected by electrophoresis. Each of the core histones was identified by amino acid sequence analysis and peptide mapping. Electrophoresis patterns of histones were the same in male and female gametes and quite similar between the two species. The composition of histone H1s in conspicuously condensed sperm nuclei of C. hakodatensis was different from that in isogamous gametes. Electrophoresis after micrococcal nuclease digestion of chromatin in male and female gamete nuclei of C. bullosa and A. japonicus and sperm of C. hakodatensis resulted in regular ladder patterns of DNA fragments (ca. 200 base pair). The chromatin of the brown algal gametes thus has the typical nucleosome structure. These results showed that chromatin condensation in sperm nuclei of C. hakodatensis was associated with a modification of linker histone H1 but not by change of core histones, replacement by other basic proteins, changes of repeating patterns, or disappearance of nucleosomes.     

DISCONTINUOUS MITOCHONDRIAL AND CHLOROPLAST LARGE SUBUNIT RIBOSOMAL RNAs AMONG GREEN ALGAE: PHYLOGENETIC IMPLICATIONS1

To provide insights into the occurrence, evolution, and phylogenetic distribution of discontinuous mitochondrial and chloroplast large subunit ribosomal RNAs (LSU rRNAs) among green algae, we surveyed 12 taxa representing three classes of green algae: the Chlorophyceae, Pleurastrophyceae, and Micromonadophyceae (sensu Mattox and Stewart 1984). We present evidence that discontinuous mitochondrial and chloroplast LSU rRNAs are quite widespread among green algae. Mitochondrial LSU rRNAs appear discontinuous in zoosporic chlorophycean lineages displaying a clockwise or directly opposed configuration in their flagellar apparatus, as well as in chlorococcalean autosporic taxa phylogenetically related to them, but are continuous among zoosporic green algal lineages with a counterclockwise flagellar apparatus configuration, as well as among chlorococcalean autosporic taxa phylogenetically related to them. Chloroplast LSU rRNAs appear discontinuous in all of the lineages investigated. Discontinuous mitochondrial LSU rRNA represents a molecular trait that might have originated at or near the base of Chlorophyceae, whereas discontinuous chloroplast LSU rRNA might have developed very early in the evolutionary history of the green algal group itself. We suggest, therefore, that the presence of discontinuous mitochondrial but not chloroplast LSU rRNA can be used as an additional character in assessing phylogenetic affiliations among green algae.     

EFFECT OF TAXON SAMPLING,CHARACTER WEIGHTING,AND COMBINED DATA ON THE INTERPRETATION OF RELATIONSHIPS AMONG THE HETEROKONT ALGAE1

Nuclear ribosomal small subunit and chloroplast rbcL sequence data for heterokont algae and potential outgroup taxa were analyzed separately and together using maximum parsimony. A series of taxon sampling and character weighting experiments was performed. Traditional classes (e.g. diatoms, Phaeophyceae, etc.) were monophyletic in most analyses of either data set and in analyses of combined data. Relationships among classes and of heterokont algae to outgroup taxa were sensitive to taxon sampling. Bootstrap (BS) values were not always predictive of stability of nodes in taxon sampling experiments or between analyses of different data sets. Reweighting sites by the rescaled consistency index artificially inflates BS values in the analysis of rbcL data. Inclusion of the third codon position from rbcL enhanced signal despite the superficial appearance of mutational saturation. Incongruence between data sets was largely due to placement of a few problematic taxa, and so data were combined. BS values for the combined analysis were much higher than for analyses of each data set alone, although combining data did not improve support for heterokont monophyly.     

ANALYSIS OF CLONAL CULTURES OF THE BROWN TIDE ALGAE AUREOCOCCUS AND AUREOUMBRA (PELAGOPHYCEAE) USING 18S rRNA, rbcL, AND RUBISCO SPACER SEQUENCES

Variability among clonal cultures of the brown tide algae Aureococcus anophagefferens Hargraves et Sieburth and Aureoumbra lagunensis Stockwell, DeYoe, Hargraves et Johnson was examined by DNA sequence comparisons. Nuclear-encoded 18S rRNA and plastid-encoded rbc L gene sequences were determined for six Aureococcus strains. RUBISCO spacer sequences were determined for 14 strains of Aureococcus. No differences among Aureococcus strains were found in the DNA regions examined. The rbc L and RUBISCO spacer sequences for three Aureoumbra strains were identical but differed from those of Aureococcus. These data indicate that blooms of these species are comprised of cells that are very similar and also imply that Aureococcus and Aureoumbra do not contain varieties or cryptic species. Separate and combined phylogenetic analyses of the 18S rRNA and rbc L gene sequences were performed. Results confirm that the brown-tide-causing algae of Long Island Sound, New York ( Aureococcus ), and Laguna Madre, Texas ( Aureoumbra ), are best classified in separate genera within the Pelagophyceae. Phylogenetic trees place Aureococcus and Aureoumbra within the Pelagomonadales and Sarcinochrysidales, respectively.     

THE DNA POLYMERASE GENE OF A BROWN ALGAL VIRUS: STRUCTURE AND PHYLOGENY

We have reported the complete sequence of the DNA polymerase gene from the virus that infected a filamentous brown alga, Feldmannia sp. (FsV). The DNA polymerase gene from FsV encoded 986 amino acids and contained all the conserved motifs of 3'-5' exonuclease domains and catalytic domains found in B-family (α-like) DNA polymerases. The codons for the FsV DNA polymerase appeared to have some bias toward guanine/cytosine (G/C) in the third position. The phylogenetic analysis of the FsV DNA polymerase gene and other viral DNA polymerase genes indicated that FsV belongs to a family of algal viruses recently defined as Phycodnaviridae.     

A REASSESSMENT OF PHYLOGENETIC RELATIONSHIPS WITHIN THE PHAEOPHYCEAE BASED ON RUBISCO LARGE SUBUNIT AND RIBOSOMAL DNA SEQUENCES

To better assess the current state of phaeophycean phylogeny, we compiled all currently available rbc L, 18S, and 26S rDNA sequences from the EMBL/GenBank database and added 21 new rbc L sequences of our own. We then developed three new alignments designed to maximize taxon sampling while minimizing information loss due to partial sequences. Phylogenetic analyses were performed on separate and combined data sets (with and without taxa from the sister classes Tribophyceae and Phaeothamniophyceae as outgroups) using a variety of assumption sets, tree-drawing algorithms (parsimony, neighbor joining, and likelihood), and resampling methods (bootstrap, decay, jackknife). Partition homogeneity testing (PHT) by codon position within rbc L showed that all positions could be used despite mild third position saturation. PHT by gene and domain within rDNA showed that the 26S D1 and D2 regions do not enhance phylogenetic signal even when combined with the 18S. The rbc L and rDNA (excluding the 26S D1 and D2) could be combined under PHT. The topology of the combined tree was the same as that of the rbc L tree alone, but bootstrap support was consistently higher in the combined analysis, applied to more branches, and enabled the establishment of sister group relationships among six orders. Although the taxon sampling for the combination tree was lower ( n = 22) than for individual gene analyses ( n = 58 for rbc L and n = 59 for rDNA), results show that the Laminariales (previously reported) and Sphacelariales (new) are both paraphyletic. Choristocarpus tenellus (Kützing) Zanardini is the most basal phaeophyte and the Dictyotales the most basal order. In contrast, the Laminariales sensu stricto ( s.s. ) and Ectocarpales sensu lato ( s.l. ) are the most derived. For phylogenetic studies in the Phaeophyceae, rbc L has more resolving power than rDNA, though the reason for this is unclear based on the fact that both genes are highly conserved.     

ASSESSING THE RELATIONSHIPS OF AUTOSPORIC AND ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE WITH 18S rDNA SEQUENCE DATA1

We examined the relationships of autosporic and zoosporic taxa in the Chlorococcales by analyzing available complete nuclear-encoded small-subunit (18S) rRNA gene sequences along with two new sequences from Hydrodictyon reticulatum (L.) Lagerh. and Neochloris vigenis Archibald. Some autosporic taxa grouped with the coenobial hydrodictyacean algae and related unicellular organisms having directly opposed basal bodies. These include Scenedesmus obliquus (Turp.) Kütz. and Chlorella fusca var. vacuolata Shihira et Krauss. Other autosporic organisms, including Chlorella kessleri Fott et Novakova, C. minutissima Fott et Novakova, C. pro-tothecoides Krug., C. vulgaris Beij., Nanochlorum eucaryotum Wilhelm, Eisenbeis, Wild, et Zahn, and Prototheca wickerhamii Soneda et Tubaki, form a separate group. Of the zoosporic taxa examined, this group would appear to have the greatest affinity to organisms having a counterclockwise displacement of basal bodies, the Pleurastrophyceae. Beyond the fact that Ankistrodesmus stipitatus (=A. falcatus var. stipitatus (Chodat) Lemm.) does not group with the latter organisms, its position remains in doubt. None of the autosporic taxa appear to be closely related to chlorophycean organisms possessing a clockwise basal body displacement.     

A FLAVIN-LIKE AUTOFLUORESCENT SUBSTANCE IN THE POSTERIOR FLAGELLUM OF GOLDEN AND BROWN ALGAE1

An autofluorescent substance occurs in the flagella of flagellate cells of the golden and brown algae. It is localized only in the posterior (short) flagellum and could not be detected in the anterior (long) one. It showed maximum fluorescence emission at 515–520 nm upon excitation of 440 nm; therefore, it is considered to be a flavin. This substance is distributed widely among flagellate cells of golden and brown algae irrespective of their nature (vegetative cells, zoospores, gametes, or sperm). It is absent, however, in some brown algal zoospores and sperm which lack an eyespot and flagellar swelling and are considered to lack phototaxis. Because the flagellar swelling in the posterior flagellum is a presumptive photoreceptor for phototaxis in these groups, it is suggested that the flavin located in the posterior flagellum acts as a photoreceptor pigment in phototaxis.     

PHYLOGENY OF THE CONJUGATING GREEN ALGAE BASED ON CHLOROPLAST AND MITOCHONDRIAL NUCLEOTIDE SEQUENCE DATA1

The conjugating green algae represent a lineage of charophyte green algae known for their structural diversity and unusual mode of sexual reproduction, conjugation. These algae are ubiquitous in freshwater environments, where they are often important primary producers, but few studies have investigated evolutionary relationships in a molecular systematic context. A 109‐taxon data set consisting of three gene fragments (two from the chloroplast and one from the mitochondrial genome) was used to estimate the phylogeny of the genera of the conjugating green algae. Maximum likelihood (ML), maximum parsimony (MP), and Bayesian inference (BI) were used to estimate relationships from the 4,047 alignable nucleotides. This study confirmed the polyphyly of the Zygnemataceae and Mesotaeniaceae with respect to one another. The Peniaceae were determined to be paraphyletic, and two genera traditionally classified among the Zygnematales appear to belong to the lineage that gave rise to the Desmidiales. Six genera, Euastrum, Cosmarium, Cylindrocystis, Mesotaenium, Spondylosium, and Staurodesmus, were polyphyletic in this analysis. These findings have important implications for the evolution of structural characteristics in the group and will require some taxonomic changes. More work will be required to delineate lineages of Zygnematales in particular and to identify structural synapomorphies for some of the newly identified clades.     

PHYLOGENY OF THE EUGLENOID LORICATE GENERA TRACHELOMONAS AND STROMBOMONAS (EUGLENOPHYTA) INFERRED FROM NUCLEAR SSU AND LSU rDNA1

Previous studies using the nuclear SSU rDNA and partial LSU rDNA have demonstrated that the euglenoid loricate taxa form a monophyletic clade within the photosynthetic euglenoid lineage. It was unclear, however, whether the loricate genera Trachelomonas and Strombomonas were monophyletic. In order to determine the relationships among the loricate taxa, SSU and LSU nuclear rDNA sequences were obtained for eight Strombomonas and 25 Trachelomonas strains and combined in a multigene phylogenetic analysis. Conserved regions of the aligned data set were used to generate maximum‐likelihood (ML) and Bayesian phylogenies. Both methods recovered a strongly supported monophyletic loricate clade with Strombomonas and Trachelomonas species separated into two sister clades. Taxa in the genus Strombomonas sorted into three subclades. Within the genus Trachelomonas, five strongly supported subclades were recovered in all analyses. Key morphological features could be attributed to each of the subclades, with the major separation being that all of the spine‐bearing taxa were located in two sister subclades, while the more rounded, spineless taxa formed the remaining three subclades. The separation of genera and subclades was supported by 42 distinct molecular signatures (33 in Trachelomonas and nine in Strombomonas). The morphological and molecular data supported the retention of Trachelomonas and Strombomonas as separate loricate genera.     

PCR AMPLIFICATION OF NUCLEAR AND PLASTID GENES FROM ALGAL HERBARIUM SPECIMENS AND ALGAL SPORES1

Plastid and nuclear ribosomal genes were amplified from an 11-year-old herbarium specimen using simple, rapid, nontoxic, and inexpensive methods. Gonimoblast tissue, isolated from either dried or fresh red algal cystocarps, was ground using the polyvalent, metal chelating resin Chelax 100. After boiling and centrifuging, the supernatant yielding enough DNA for 20 or more polymerase chain reactions. Using these methods, we also amplified plastid and nuclear genes from as few as two red algal spores. These methods should facilitate future studies of algal systematics, evolutionary biogeography, and phylogeny as well as studies of algal dispersal patterns and population biology.     

THE OCCURRENCE OF CHLOROPHYLL C1 AND C2 IN ALGAE1

Forty-two species of chlorophyll c-containing algae (diatoms, dinoflagellates, chrysomonads, haptophytes, cryptomonads and xanthophytes) were examined for their content of chlorophyll c₁ and c₂. This work, and recent studies on c₁/c₂ distribution in the literature (total 86 species), show that chlorophyll c₂ is universal to all algae examined. Chlorophyll c₁ occurs in addition to c₂ in brown seaweeds, diatoms, chrysomonads, haptophytes (coccolithophorids) xanthophytes and the, fucoxanthin-containing dinoflagellates; c₂ only occurs in dinoflagellates and cryptomonads. Two exceptions to the generalizations are one dinoflagellate and one cryptomonad containing c₁ in addition to c₂ No explanation can be offered on present knowledge for these exceptions. No alga was found containing only chlorophyll c₁. Chlorophyll c, far from being a minor accessory chlorophyll, occurred in amounts almost equal to chlorophyll a(some diatoms and dinoflagellates) or ranged from 50 to 20% of the chlorophyll a (diatoms, dinoflagellates, chrysomonads, cryptomonads, browns). Xanthophytes, however, contained only trace amounts of chlorophyll c with ratios of chlorophyll a:c ranging from 55:1 to 116:1 on a weight basis. In those algae with both chlorophyll c components, c₁ and c₂, occurred either in equal amounts, or chlorophyll c₂was twice the c₁ content.     

MOLECULAR SYSTEMATICS OF THE FLORIDEOPHYCEAE (RHODOPHYTA) USING NUCLEAR LARGE AND SMALL SUBUNIT rDNA SEQUENCE DATA

Sequence data are presented for approximately 85% of the nuclear large subunit (LSU) rDNA gene for one member of the Bangiophyceae and 47 members of the Florideophyceae, the latter representing all but one of the currently recognized florideophyte orders. Distance, parsimony, and maximum likelihood analyses of these data were used to generate phylogenetic trees, and bootstrap resampling was implemented to infer robustness for distance and parsimony results. LSU phylogenies were congruent with published nuclear small subunit (SSU) rDNA results in that four higher level florideophyte lineages were resolved: lineage 1, containing the order Hildenbrandiales; lineage 2, recovered only under distance analysis, composed of the orders Acrochaetiales, Balliales, Batrachospermales, Corallinales, Nemaliales, Palmariales, and Rhodogorgonales; lineage 3, containing the Ahnfeltiales; and lineage 4, composed of the orders Bonnemaisoniales, Ceramiales, Gelidiales, Gigartinales, Gracilariales, Halymeniales, Plocamiales, and Rhodymeniales. Analyses were also performed on a combined LSU–SSU data set and an SSU-only data set to account for differences in taxon sampling relative to published studies using this latter gene. Combined LSU–SSU analyses resulted in phylogenetic trees of similar topology and support to those obtained from LSU-only analyses. Phylogenetic trees produced from SSU-only analyses differed somewhat in particulars of branching within lineages 2 and 4 but overall were congruent with the LSU-only and combined LSU–SSU results. We close with a discussion of the phylogenetic potential that the LSU has displayed thus far for resolving relationships within the Florideophyceae.     

COORDINATNE NUCLEAR AND CHLOROPLAST DIVISION IN UNILOCULAR SPORANGIA OF LAMINARIA ANGUSTATA (LAMINARIALES,PHAEOPHYCEAE)1

Changes in the number of nuclei and chloroplasts were examined during the process of unispore formation in unilocular sporangia of Laminaria angustata. Just before meiosis, eight chloroplasts were always present in unilocular sporangial mother cells. The number of chloroplasts remained constant through meiosis. After the resulting four nuclei divided again (third nuclear division), a close association between a nucleus and a chloroplast developed among each of the eight nuclei and eight chloroplasts. The eight chloroplasts divided ahost synchronously before the synchronous division of the eight nuclei. Following the 16 nucleate stage with 16 chloroplasts and the final 32 nucleate stage with 32 chloroplasts, 32 unispores, each with a nucleus and a chloroplast, were fomd in unilocular sporangza of L. angustata. Immunofluorescence microscopy using an anti-centrin antibody showed that two anticentrin-stained structures (as future mitotic poles) occurred adjacent to each of the premitotic four nuclei, and each spot was located near a chloroplast. Therefore, after the third division, each of the eight nuclei established close contact with a chloroplast presumably mediated by the centrosomes.     

PHYLOGENETIC RELATIONSHIPS OF THE BROWN ALGAL ORDERS ECTOCARPALES, CHORDARIALES, DICTYOSIPHONALES, AND TILOPTERIDALES (PHAEOPHYCEAE) BASED ON RUBISCO LARGE SUBUNIT AND SPACER SEQUENCES

Phylogenetic relationships among 23 species of morphologically simple brown algae belonging to the Ectocarpales sensu stricto , Chordariales, Dictyosiphonales, and Tilopteridales sensu stricto , Phaeophyceae (Fucophyceae), were analyzed using chloroplast-encoded RUBISCO large subunit gene sequences ( rbc L) and the associated RUBISCO spacer sequences. Comparison of the observed and expected sequence divergence at the three codon positions of rbc L showed that the level of mutational saturation within the brown algae is minor. Thus, rbc L is well suited for phylogenetic studies in this group. Unweighted parsimony analyses and a neighbor-joining distance analysis were performed using unambiguously aligned rbc L sequences from the above four orders, one marine raphidophyte and two Tribophyceae (Xantophyceae). Polyphyly of Tilopteridales sensu lato (i.e. including Dictyosiphonales) is verified; we therefore recommend the use of Tilopteridales in the strict sense. The Ectocarpales, Chordariales, and Dictyosiphonales are paraphyletic with respect to each other, forming a highly interwoven clade. A separate parsimony analysis of the RUBISCO spacer as well as a combined rbc L and spacer analysis supported the close relationship among the latter three orders, adding to the evidence that they should be subsumed into the Ectocarpales sensu lato.     

MOLECULAR PHYLOGENY AND REVISION OF THE GENUS NETRIUM (ZYGNEMATOPHYCEAE,STREPTOPHYTA): NUCLEOTAENIUM GEN. NOV.1

Nuclear‐encoded SSU rDNA, chloroplast LSU rDNA, and rbcL genes were sequenced from 53 strains of conjugating green algae (Zygnematophyceae, Streptophyta) and used to analyze phylogenetic relationships in the traditional order Zygnematales. Analyses of a concatenated data set (5,220 nt) established 12 well‐supported clades in the order; seven of these constituted a superclade, termed “Zygnemataceae.” Together with genera (Zygnema, Mougeotia) traditionally placed in the family Zygnemataceae, the “Zygnemataceae” also included representatives of the genera Cylindrocystis and Mesotaenium, traditionally placed in the family Mesotaeniaceae. A synapomorphic amino acid replacement (codon 192, cysteine replaced by valine) in the LSU of RUBISCO characterized this superclade. The traditional genera Netrium, Cylindrocystis, and Mesotaenium were shown to be para‐ or polyphyletic, highlighting the inadequacy of phenotypic traits used to define these genera. Species of the traditional genus Netrium were resolved as three well‐supported clades each distinct in the number of chloroplasts per cell, their surface morphology (structure and arrangement of lamellae) and the position of the nucleus or nuclear behavior during cell division. Based on molecular phylogenetic analyses and synapomorphic phenotypic traits, the genus Netrium has been revised, and a new genus, Nucleotaenium gen. nov., was established. The genus Planotaenium, also formerly a part of Netrium, was identified as the sister group of the derived Roya/Desmidiales clade and thus occupies a key position in the evolutionary radiation leading to the most species‐rich group of streptophyte green algae.     

IMMUNOLOCALIZATION OF CENTER IN THE FLAGELLAR APPARATUS OF MALE GAMETES OF ECTOCARPUS SILICULOSUS (PHAEOPHYCEAE) AND OTHER BROWN ALGAL MOTILE CELLS1

Centrin or a centrin homologue was localized using immunofluorescence in the flagellar basal body region in zoids of five brown algal species: Ectocarpus siliculosus (Dillw.) Lyngb., Scytosiphon lomentaria (Lyngb.) Link, Laminaria digitata (Huds.) Lamour., Sphacelaria rigidula (Kütz.) Prud'homme van Reine, and Fucus serratus L. The antigen is restricted to short rods extending along the basal body(ies) and towards the nucleus, which always remains firmly linked to the flagellar apparatus in isolated cytoskeletons. To identify these antigenic sites, pre- and postembedding immunogold electron microscopy was applied to male gametes of E. siliculosus. At least three different structures associated with the basal bodies were antigenic: a fibrous structure connecting the proximal end of the posterior basal body to the nucleus (nucleus-basal body connector), a striated band that links the two basal bodies to each other and is located in the angel formed by them, and amorphous material interconnecting the basal bodies in their most proximal regions. In addiction, specific labeling occurs along the external surface and within the lumen of both basal bodies and in the flagellar transitional region. The possible function of these centrin-containing structures is discussed.