SPECIES DELIMITATION,TAXONOMY, AND BIOGEOGRAPHY OF DICTYOTA IN EUROPE (DICTYOTALES,PHAEOPHYCEAE)1

Taxonomy of the brown algal genus Dictyota has a long and troubled history. Our inability to distinguish morphological plasticity from fixed diagnostic traits that separate the various species has severely confounded species delineation. From continental Europe, more than 60 species and intraspecific taxa have been described over the last two centuries. Using a molecular approach, we addressed the diversity of the genus in European waters and made necessary taxonomic changes. A densely sampled DNA data set demonstrated the presence of six evolutionarily significant units (ESUs): Dictyota dichotoma (Huds.) J. V. Lamour., D. fasciola (Roth) J. V. Lamour., D. implexa J. V. Lamour., D. mediterranea (Schiffn.) G. Furnari, D. spiralis Mont., and the newly described D. cyanoloma sp. nov., which was previously reported as D. ciliolata from the Mediterranean Sea. Species distributions, based on DNA‐confirmed occurrence records, indicate that all species are geographically confined to the NE Atlantic Ocean with the exception of D. dichotoma and D. implexa, which also occur in South Africa and Bermuda, respectively. To investigate potential hybridization between D. dichotoma and D. implexa, which were previously shown to be sexually compatible in culture, we compiled and analyzed sets of mitochondrial, plastid, and nuclear markers to detect putative hybrids or introgression in natural populations. Failure to detect natural hybrids indicates that effective pre‐ and postzygotic isolation mechanisms are at play in natural populations and supports the by‐product hypothesis of reproductive isolation.     

Effect of solar ultraviolet radiation on growth in the marine macroalga Dictyota dichotoma (Phaeophyceae) at Helgoland and its ecological consequences

At Helgoland, in the North Sea, growth of the high sublittoral brown macroalga Dictyota dichotoma (Hudson) Lamoroux was examined in October (the time of tetraspore release) in an outdoor tank by exposing 2-day-old germlings to four solar radiation treatments achieved with different filter materials or an additional artificial light source: photosynthetically active radiation (PAR; 395–700 nm), PAR plus ultraviolet (UV)-A (320–700 nm), full solar spectrum, or solar spectrum plus artificial UV radiation (UVR). Based on length measurements over a period of 3 weeks, the growth rate in germlings strongly decreased in conditions with UVR compared to PAR: by 14% under PAR+UV-A, by 31% under the full solar spectrum and by 65% with additional UVR. Although growth rates of germlings under UVR were reduced mainly in the first week, the plants did not regain the size of the untreated plants even after 9 weeks. Regardless of the exposure, no defects in morphology or anatomy including the exposed apical meristem were detected, except for a reduction in cell division rates perhaps due to additional cost for photoprotective or repair mechanisms. Depending on the actual position of D. dichotoma plants in the natural habitat, individuals in high positions receive substantial amounts of the more harmful UV-B while those lower down might only receive UV-A during part of the day, thus the effect of UV-B on the growth of D. dichotoma will depend on its position in the field. The effects of tidal variation of the light climate and the implications of our results for the zonation of D. dichotoma are discussed. Received in revised form: 6 July 2000 Electronic Publication     

OVERWINTERING OF DICTYOTA DICHOTOMA (PHAEOPHYCEAE) NEAR ITS NORTHERN DISTRIBUTION LIMIT ON THE EAST COAST OF NORTH AMERICA1

The mechanism of yearly repopulation of Dictyota dichotoma (Hudson) Lamouroux in the inshore waters of North Carolina was studied in the field and in laboratory experiments. It was demonstrated that D. dichotoma is maintained throughout the year at this location and does not require yearly immigrations. A young germling stage was shown to function as the overwintering structure. Although release of aplanospores was unaffected by temperature and photoperiod, subsequent germination and establishment required warm conditions. If germlings were allowed to grow to the 7–9 cell stage under summer conditions, they could survive 21 wk of winter conditions. Transfer of 21 wk old winterized germlings to summer conditions resulted in the rapid production of erect blades. It therefore appears that D. dichotoma maintains its populations near its northern distribution limit on the East Coast of North America by undergoing dormancy after germling establishment.     

FATTY ACIDS,AMINO ACIDS,MINERAL CONTENTS,AND PROXIMATE COMPOSITION OF SOME BROWN SEAWEEDS1

This study was conducted to create a nutritional database on brown seaweeds and to popularize their consumption and utilization in Iran. The fatty acid contents, amino acids profiles, and certain mineral elements composition of some brown seaweeds, Padina pavonica (L.) Thivy, Dictyota dichotoma (Huds.) J. V. Lamour., and Colpomenia sinuosa (Mert. ex Roth) Derbés et Solier were determined. Total lipid content ranged from 1.46 ± 0.38 to 2.94 ± 0.94 g · 100 g^?1dry weight (dwt), and the most abundant fatty acids were C16:0, C18:1, C20:4 ω6, and C20:5 ω3. The unsaturated fatty acids predominated in all species and had balanced sources of ω3 and ω6 acids. Highest total polyunsaturated fatty acid (PUFA) levels occurred in C. sinuosa. The protein content of D. dichotoma was 17.73 ± 0.29 g · 100 g^?1dwt, significantly higher than the other seaweeds examined. Among amino acids essential to human nutrition, methionine (Met; in D. dichotoma and P. pavonica) and lysine (Lys; in C. sinuosa) were present in high concentrations. The crude fiber content varied by 9.5 ± 11.6 g · 100 g^?1dwt in all species. Chemical analysis indicated that ash content was between 27.02 ± 0.6 and 39.28 ± 0.7 g · 100 g^?1dwt, and that these seaweeds contained higher amounts of both macrominerals (7,308–9,160 mg · 100 g^?1dwt; Na, K, Ca) and trace elements (263–1,594 mg · 100 g^?1dwt; Fe, Ni, Mn, Cu, Co) than have been reported for edible land plants. C. sinuosa had the highest amount of Ca, Fe, and a considerable content of Na was measured in P. pavonica.     

Towards a universal barcode of oomycetes – a comparison of the cox1 and cox2 loci

Oomycetes are a diverse group of eukaryotes in terrestrial, limnic and marine habitats worldwide and include several devastating plant pathogens, for example Phytophthora infestans (potato late blight). The cytochrome c oxidase subunit 2 gene (cox2) has been widely used for identification, taxonomy and phylogeny of various oomycete groups. However, recently the cox1 gene was proposed as a DNA barcode marker instead, together with ITS rDNA. The cox1 locus has been used in some studies of Pythium and Phytophthora, but has rarely been used for other oomycetes, as amplification success of cox1 varies with different lineages and sample ages. To determine which out of cox1 or cox2 is best suited as a universal oomycete barcode, we compared these two genes in terms of (i) PCR efficiency for 31 representative genera, as well as for historic herbarium specimens, and (ii) sequence polymorphism, intra‐ and interspecific divergence. The primer sets for cox2 successfully amplified all oomycete genera tested, while cox1 failed to amplify three genera. In addition, cox2 exhibited higher PCR efficiency for historic herbarium specimens, providing easier access to barcoding‐type material. Sequence data for several historic type specimens exist for cox2, but there are none for cox1. In addition, cox2 yielded higher species identification success, with higher interspecific and lower intraspecific divergences than cox1. Therefore, cox2 is suggested as a partner DNA barcode along with ITS rDNA instead of cox1. The cox2‐1 spacer could be a useful marker below species level. Improved protocols and universal primers are presented for all genes to facilitate future barcoding efforts.     

PATTERNS OF INTERSPECIFIC INTERACTIONS IN THE ULVA‐DOMINATED INTERTIDAL COMMUNITY IN A SOUTHERN COAST OF KOREA

The reproductive success of marine species with external fertilization depends on environmental conditions during gamete release. There is special interest presently in whether water motion causes sperm limitation under natural conditions. We investigated gamete release of Fucus vesiculosus from an exposed shore to ascertain: 1) when gametes are released during the tidal cycle, 2) when fertilization occurs, and 3) what the natural sperm:egg ratios are. Water samples were collected and concentrated over five minutes every half hour off Pemaquid Point, ME from three replicate sites within each of two locations using a pump‐filter device. Immunofluorescence microscopy revealed that gamete release occurred only on the two calmest spring tides. Sperm became present in the water column at the same time as oogonia (30 min^?1 h prior to high tide [HT]) and reached peak concentration at exactly HT. The sperm:egg ratio was 76:1 on 8 Oct 1999 and 21:1 on 8 Nov 1999 at exactly 30 min prior to HT and dropped sharply after HT. Gametes continued to be collected for several hours after HT but analysis of pronuclear position in aceto‐iron‐hematoxylin stained eggs revealed that all fertilization occurred at approximately HT. We modelled the total number of days when reproduction was possible using these results and wind and wave data from the National Data Buoy Center. Our research provides evidence that gamete release by F. vesiculosus occurs at slack HT on calm days and that sperm are not a limiting factor in fertilization for this species.     

Dictyota cyanoloma (Dictyotales,Phaeophyceae), a Newly Introduced Brown Algal Species in California

Here, we report for the first time the presence of Dictyota cyanoloma in southern California. Dictyota cyanoloma is conspicuous in harbors and bays by its distinctive bright blue‐iridescent margins. This species was originally described from Europe, but subsequent studies have revealed that it represented an introduction from Australia. The current distribution of D. cyanoloma comprises southern Australia and the North East Atlantic, including the Mediterranean Sea and the Macaronesian islands. The presence of D. cyanoloma in southern California is supported by molecular cox1 and psbA gene sequences. A reconstruction of the invasive history based on nine polymorphic microsatellite markers reveals a close affinity of the Californian specimens with European populations. Dictyota cyanoloma in the United States appears to be (so far) restricted to the Californian coast from San Diego Bay in the south to Santa Catalina Island and Long Beach Harbor in the north. A correlative species distribution model suggests gradually declining habitat suitability north of the Southern Californian Bight and high suitability in Baja California, including the Gulf of California. Finally, its widespread abundance in bays and harbors suggests shipping is a likely transport mechanism.     

Phylogeography of the freshwater red alga B atrachospermum viride‐brasiliense (Rhodophyta,Batrachospermales)

Phylogeography of B atrachospermum viride‐brasiliense was investigated using two mitochondrial regions: the cox2‐3 spacer and the barcode region of cox1 gene. Eighty‐seven individuals were analyzed from nine stream segments throughout its distribution in Brazil. Ten cox2‐3 spacer and nine cox1 haplotypes were observed among the individuals studied (87 vs. 43, respectively). Divergences among haplotypes were relatively low (≤2.4% for cox2‐3 and ≤1.8% for cox1). Most locations have a single haplotype, whereas only two locations had two haplotypes for both markers. The haplotype network for cox2‐3 showed a phylogeographic trend from the south towards the southeast with haplotypes from the southeast more closely related. For cox1 a trend from the southeast spreading towards the south and north was revealed, with the southern haplotypes more closely associated. Results clearly indicated that B . viride‐brasiliense represents a single species and the phylogeographic pattern consisted of a closely connected group of haplotypes from southern and southeastern Brazil. Levels of intra‐ and inter‐population variation were similar for the two markers with slightly higher values for cox2‐3. The trend observed in this study is similar to that in other members of Batrachospermales with little variation within a stream segment (one or two haplotypes) and more distant haplotypes showing higher divergences. This pattern could be attributed to the fact that colonization of a site might be rare by a single event with subsequent proliferation of the population. The geographic distribution of B . viride‐brasiliense was interpreted according to the biogeographic models proposed for South America being limited to three morpho‐climatic domains or biogeographic provinces: tropical Atlantic rainforest, sub‐tropical rainforest and cerrado (Brazilian savannah).     

MITOCHONDRIAL DNA PHYLOGENY OF THE SYMBIOTIC DINOFLAGELLATES (SYMBIODINIUM,DINOPHYTA)1

Symbiotic dinoflagellates belonging to the genus Symbiodinium (Freudenthal) are found worldwide in association with shallow‐water tropical and subtropical marine invertebrates. Most phylogenetic studies of Symbiodinium have used nuclear rRNA (nrDNA) genes to infer relationships among members of the genus. In this report, we present the first phylogeny of Symbiodinium based on DNA sequences from a mitochondrial protein‐coding gene (cytochrome oxidase subunit I [cox1]). Two principal groups, one comprised of Symbiodinium clade A and the second encompassing Symbiodinium clades B/C/D/E/F, are strongly supported in the cox1 phylogeny. Relationships within Symbiodinium clades B/C/D/E/F, however, are less well resolved compared with phylogenies inferred from nrDNA and chloroplast large subunit (cp23S)‐rDNA genes. Statistical tests between alternative tree topologies verified, with an exception being the position of one controversial member of Symbiodinium clade D, that relationships inferred from cox1 are congruent with those inferred from nrDNA and cp23S‐rDNA. Taken together, the relationships between the major Symbiodinium clades are robust, and there appears to be no evidence of hybridization or differential introgression of nuclear and plastid genomes between clades.     

蕨类植物碳氮磷化学计量特征及其与土壤养分的关系

为探讨蕨类植物碳氮磷化学计量特征与土壤养分的关系,对福建省亚热带森林林下芒萁和乌毛蕨地上部分和地下部分的碳、氮、磷(C、N、P)含量和0~10 cm和10~20 cm两个土层的养分含量进行了测定。结果表明,无论是芒萁还是乌毛蕨,地上部分的N、P含量均高于地下部分,而C含量则无显著差异,导致地上部分的C∶N和C∶P均低于地下部分。与乌毛蕨相比,芒萁地上部分的N、P含量更低,地上和地下部分的C含量、C∶N和C∶P以及N、P含量的变异系数和表型可塑性指数则更高,表明芒萁采取了较高的养分利用效率和"表现最大化"的策略,而乌毛蕨则选择了较低的养分利用效率和"表现维持"的方式。两种蕨类植物地上和地下部分的N含量与土壤N含量(0~20 cm)均无显著相关。芒萁两个部位的P含量则均与土壤P含量(0~10 cm和10~20 cm)呈显著正相关,乌毛蕨P含量总体上与土壤P含量的相关性不显著(除地下部分的P含量与10~20 cm土层的P含量呈弱的正相关外)。这表明芒萁具有作为亚热带森林土壤P库指示植物的潜力。     

Ligulate Desmarestia (Desmarestiales,Phaeophyceae) revisited: D. japonica sp. nov. and D. dudresnayi differ from D. ligulata

The phylogeny of ligulate and sulfuric‐acid containing species of Desmarestia, occurring worldwide from polar to temperate regions, was revised using a multigenic and polyphasic approach. Sequence data, gametophyte characteristics, and sporophyte morphology support reducing a total of 16 taxa to four different species. (1) D. herbacea, containing broad‐bladed and highly branched forms, has dioecious gametophytes. The three other species have monoecious gametophytes: (2) D. ligulata which is profusely branched and, except for one subspecies, narrow‐bladed, (3) Japanese ligulate Desmarestia, here described as D. japonica sp. nov., which is morphologically similar to D. ligulata but genetically distant from all other ligulate taxa. This species may have conserved the morphology of original ligulate Desmarestia. (4) D. dudresnayi, including unbranched or little branched broad‐bladed taxa. A figure of the holotype of D. dudresnayi, which was lost for decades, was relocated. The taxonomy is complemented by a comparison of internal transcribed spacer and cytochrome c oxidase subunit I (cox1) as potential barcode loci, with cox1 offering good resolution, reflecting species delimitations within the genus Desmarestia.     

Phylogeography of the freshwater red alga Sirodotia (Batrachospermales,Rhodophyta) in Brazil

Considering the lack of knowledge on genetic variation on members of the freshwater red algal of the order Batrachospermales in tropical regions, phylogeographic patterns in Sirodotia populations were investigated using two mitochondrial regions: the cox2‐3 spacer and partial cox1 gene (barcode). Individuals identified as Sirodotia delicatula were analyzed from 14 stream segments across its distribution in Brazil. Phylogenetic analyses based on the ribulose‐1,5‐bisphosphate carboxylase/oxygenase large sub‐unit gene showed three clades, one representing S. delicatula, from all locations in southeastern Brazil and other regions from Brazil. The remaining samples formed two clades, which were highly divergent and distantly positioned from those of S. delicatula: 2.5–2.7% and 3.4–3.7%. This level of variation would warrant the species split of these taxa from mid‐western Brazil. A total of eight cox2‐3 spacer and nine cox1 haplotypes were observed among the 122 individuals studied. One location had two cox2‐3 haplotypes and three locations had two cox1 haplotypes; all others had a single dominant haplotype each. The existence of high intraspecific genetic variation among individuals of distinct locations (several haplotypes), but little variation within a location seems to be a pattern for the Batrachospermales. Haplotype networks showed low variation among the haplotypes from southeastern Brazil (10 locations with divergence of 0.3–1.1% for cox2‐3, 0.1–0.3% for cox1) and high variation among the haplotypes from the mid‐west region (four locations, 4.0–9.3% for cox2‐3, 6.2–8.4% for cox1). Thus, the present data clearly suggest the existence of cryptic species in Sirodotia in Brazil.     

The plastome of a brown alga,Dictyota dichotoma

Summary Plastids of the brown algaDictyota dichotoma contain a single homogeneous DNA species which bands at a buoyant density of 1.693 g/cm³ in neutral CsCl equilibrium density gradients. The corresponding nuclear DNA has a density of 1.715 g/cm³. The molecular size of the plastid DNA is 123 kbp as calculated by both electron microscopy of spread intact circular molecules and gel electrophoresis following single and double digestions with various restriction enzymes. A restriction map has been constructed using the endonucleases Sal I, Bam HI, and Bgl II which cleave theDictyota plastome into 6, 12, and 17 fragments, respectively. No large repeated regions, as found in chlorophycean andEuglena plastid DNAs, were detected.Dictyota dichotoma is the first member from the chlorophyll c-line of the algal pedigree for which a physical map of plastid DNA has been established. Dedicated to Professor Dr. W. Stubbe on the occasion of his 65th birthday.     

GRACILARIA VERMICULOPHYLLA (RHODOPHYTA,GRACILARIALES) IN THE VIRGINIA COASTAL BAYS,USA: COX1 ANALYSIS REVEALS HIGH GENETIC RICHNESS OF AN INTRODUCED MACROALGA

Gracilaria vermiculophylla (Ohmi) Papenfuss is an invasive alga that is native to Southeast Asia and has invaded many estuaries in North America and Europe. It is difficult to differentiate G. vermiculophylla from native forms using morphology and therefore molecular techniques are needed. In this study, we used three molecular markers (rbcL, cox2‐cox3 spacer, cox1) to identify G. vermiculophylla at several locations in the western Atlantic. RbcL and cox2‐cox3 spacer markers confirmed the presence of G. vermiculophylla on the east coast of the USA from Massachusetts to South Carolina. We used a 507 base pair region of cox1 mtDNA to (i) verify the widespread distribution of G. vermiculophylla in the Virginia (VA) coastal bays and (ii) determine the intraspecific diversity of these algae. Cox1 haplotype richness in the VA coastal bays was much higher than that previously found in other invaded locations, as well as some native locations. This difference is likely attributed to the more intensive sampling design used in this study, which was able to detect richness created by multiple, diverse introductions. On the basis of our results, we recommend that future studies take differences in sampling design into account when comparing haplotype richness and diversity between native and non‐native studies in the literature.     

A TAXONOMIC STUDY OF THE GENUS PADINA (DICTYOTALES,PHAEOPHYCEAE) INCLUDING THE DESCRIPTIONS OF FOUR NEW SPECIES FROM JAPAN,HAWAII, AND THE ANDAMAN SEA1

A taxonomic study of the genus Padina from Japan, Southeast Asia, and Hawaii based on morphology and gene sequence data (rbcL and cox3) resulted in the recognition of four new species, that is, Padina macrophylla and Padina ishigakiensis from Ryukyu Islands, Japan; Padina maroensis from Hawaii; and Padina usoehtunii from Myanmar and Thailand. All species are bistratose and morphologically different from one another as well as from any known taxa by a combination of characters relating to degree of calcification; the structure, position, and arrangement of hairlines (HLs) and reproductive sori; and the presence or absence of rhizoid‐like groups of hairs and an indusium. Molecular phylogenetic analyses demonstrated a close relationship between P. ishigakiensis, P. macrophylla, P. maroensis, and Padina australis Hauck. The position of P. usoehtunii, however, was not fully resolved, being either sister to a clade comprising the other three new species and P. australis in the rbcL tree or more closely related to a clade comprising several other recently described species in the cox3 tree. The finding of the four new species demonstrates high species diversity particularly in southern Japan. The following characters were first recognized here to be useful for species delimitation: the presence or absence of small rhizoid‐like groups of hairs on the thallus surface, structure and arrangement of HLs on both surfaces either alternate or irregular, and arrangement of the alternating HLs between both surfaces in equal or unequal distance. The evolutionary trajectory of these and six other morphological characters used in species delineation was traced on the phylogenetic tree.     

Delimitation of cryptic species of the Scytosiphon lomentaria complex (Scytosiphonaceae,Phaeophyceae) in Japan,based on mitochondrial and nuclear molecular markers

Scytosiphon lomentaria (Scytosiphonaceae, Ectocarpales) is believed to include some cryptic species, particularly in the Pacific. We attempted to delimit these species in Japan using mitochondrial cox1 and cox3 and nuclear ITS2 and the second intron of the centrin gene (cetn‐int2). Fifty‐three cox1+cox3 mitotypes, 26 ITS2 ribotypes and 45 cetn‐int2 haplotypes were found in 107 samples collected from 33 localities in Japan. Based on phylogenetic analyses, similar sequence types were grouped into ten mitogroups, eight ribogroups and six cetn‐int2 haplogroups (sequence‐type groups). From the molecular trees and combinations of the mito‐, ribo‐ and haplogroups, three cryptic species were apparent (Groups I–III). Group I, widely distributed on Pacific coasts, was highly supported by all molecular trees, whereas Groups II (North Pacific) and III (Northwestern Pacific and Australasia) were more closely related to each other. However, sequence‐type‐group combinations that would be characteristic of hybrids between Groups II and III were not detected, suggesting no gene flow between the two Groups. Further investigations of an additional 127 sympatrically growing plants supported the absence of gene flow between Groups II and III. Four samples did not belong to any of the Groups I–III and possibly represent additional species.     

GAMETOGENESIS AND GAMETE RELEASE OF ULVA MUTABILIS AND ULVA LACTUCA (CHLOROPHYTA): REGULATORY EFFECTS AND CHEMICAL CHARACTERIZATION OF THE “SWARMING INHIBITOR”1

Gametophytes of Ulva mutabilis Føyn and Ulva lactuca L. were artificially induced to form gametangia by removal of sporulation inhibitors. After this treatment, U. mutabilis gametes were ready for swarming on the third morning after induction, while U. lactuca gametangia needed 1–2 d longer for maturation. Release of gametes of U. lactuca was dependent solely upon exposure to the first light in the morning. Gametangia of U. mutabilis, however, also required sufficient dilution of the swarming inhibitor (SWI). SWI was excreted transiently by both Ulva species early during gametogenesis. While the SWI concentration in U. mutabilis medium remained above the inhibitory concentration until the gametangia were mature, the concentration of U. lactuca‐SWI dropped rapidly below this level. In the presence of sufficient SWI, mature gametes of U. mutabilis remained motionless within the gametangia despite light and open exit pores. However, using SEM, an additional seal was detected within these pores, which probably prevented premature swarming until dilution of SWI and exposure to light. Observations by time lapse microscopy and experiments with the myosin kinase inhibitor BDM suggest that the gametes may be either extruded by the gametangium or leave the exit pore by active gliding motion, driven by a myosin‐like motor protein. The SWIs were purified from both Ulva species, and mass spectral analysis showed their molecular masses (292 Da) were identical.     

Utility of mitochondrial‐encoded cytochrome c oxidase I gene for phylogenetic analysis and species identification of the planktonic diatom genus Skeletonema

Small subunit (SSU) and large subunit (LSU) rDNA sequences have been commonly used to delineate the taxonomy and biogeography of the planktonic diatom genus Skeletonema, but the genes occur as multiple copies and are therefore not suitable for barcoding purposes. Here, we analyzed phylogenetic relationships of Skeletonema using the mitochondrial‐encoded cytochrome c oxidase I gene (cox1), as well as partial LSU rDNA (D1–D3) and SSU rDNA, to identify the factors that define species and to evaluate the utility of these three markers for this taxon. Twelve Skeletonema species were divided into six clades, I–VI, each of which comprised the same species by the three markers: clades I (S. japonicum, S. grethae, S. pseudocostatum, and S. tropicum), II (S. menzelii), III (S. dohrnii and S. marinoi), IV (S. costatum, S. potamos, and S. subsalsum), V (S. grevillei), and VI (S. ardens). However, the branching order among these clades was incongruent among the markers. In clade III, six S. marinoi strains had identical cox1 sequences. These S. marinoi strains branched along with S. dohrnii, except for strains from the Gulf of Naples, with high support in cox1. Species delimitation between S. dohrnii and S. marinoi was therefore not supported. In clade IV, S. costatum and S. subsalsum were robustly clustered, with S. potamos as a sister clade in the cox1 tree, not in the LSU and SSU trees. In clade II, cox1 also confirmed that S. menzelii includes three subclades potentially distinguishable from each other by morphological features. Cox1 proved to be the most useful marker for the identification of Skeletonema species because it gave a tree with highly supported clades, has sufficient variation within and among species, encodes a protein in a single copy, and requires relatively few primers.     

Polysaccharides composition from tropical brown seaweeds

Polysaccharides composition of the tropical brown seaweeds Turbinaria turbinata, Sargassum filipendula, Dictyota caribaea and Padina perindusiata collected at Yucatan Peninsula (Mexico) was determined in this study. Crude fucoidan extracted with HCl and alginate extracted with a hot alkali solution were characterized in terms of their molecular weight, sulfate content, uronic acid, total carbohydrate and neutral sugar components. Low molecular weight sulfated‐fucoidan was the major component in all species studied. Fucoidan from T. turbinata and from D. caribaea were characterized as a homofucan, with fucose as the neutral sugar. Fucoidan from S. filipendula was composed of a galactofucan, and fucoidan from P. perindusiata was characterized as a heterofucan consisting of fucose, glucose and galactose. The Fourier transform infrared (FT‐IR) spectra of fucoidan extracted from species studied indicated that the majority of sulfate groups are located at C‐4 and to a lesser extent at C‐2 and/or C‐3 of the fucopyranose residues. This could be advantageous since several therapeutic effects have been reported for fucoidans with similar characteristics. FT‐IR spectra from D. caribaea and P. perindusiata revealed the presence of O‐acetyl groups in crude fucoidan, which could be potentially utilized as an immune stimulant. Molecular weight of alginate varied between 595 and 1301 kDa with similar uronic acid content in all species. Alginate M : G ratio inferred from FT‐IR spectra suggests a high content of G‐block in all species. Potential applications of these polysaccharides are discussed.     

网地藻多糖清除DPPH·自由基活性的动力学研究

该研究通过超声辅助并采用醇沉、脱蛋白、脱色、干燥的方法,分别检测低(0.1 mg·mL~(-1))、中(0.25mg·mL~(-1))、高(0.5 mg·mL~(-1))三种浓度下的网地藻多糖对DPPH·自由基的清除能力,探讨质量浓度和反应时间对网地藻多糖清除DPPH·自由基活性的变化规律。按照一级反应动力学方程和二级反应动力学方程分别建立反应动力学模型。结果表明:不同的质量浓度和反应时间对网地藻多糖清除DPPH·自由基活性均有影响,网地藻多糖质量浓度提高,其清除DPPH·自由基的能力逐渐加强,当网地藻多糖浓度为0.5 mg·mL~(-1)时,反应20 min,网地藻多糖清除DPPH·自由基的清除率最高为86.06%,其清除DPPH·自由基活性半数清除率(IC_(50))为0.25 mg·mL~(-1)。准一级动力学模型拟合的线性相关性较差,相关系数R~2的范围分别为0.848~0.891;准二级动力学模型拟合的相关系数R~2的范围为0.902~0.967,因此采用二级动力学拟合方程能较好地描述网地藻多糖对DPPH·自由基的清除能力。网地藻多糖在低(0.1 mg·mL~(-1))、中(0.25 mg·mL~(-1))、高(0.5 mg·mL~(-1))三种浓度时对DPPH·的二级反应的清除速率常数(k_2)分别为0.011、0.054、0.421。这说明网地藻多糖随着反应浓度逐渐升高其清除DPPH·自由基的速度越来越快,清除自由基能力也越来越强,结合IC_(50)值来共同评价抗氧化能力,IC_(50)值越小,反应速率值越大,表明其抗氧化活性越好,这与实验得出的数据一致。