Fucus ‘lignin’: A reassessment

A ‘lignin’ fraction isolated by the Björkman method from the marine brown alga Fucus vesiculosus has been examined by ¹³C NMR and degradative analysis, and shown to consist of polyphloroglucinols identical to those characterized earlier from Fucus. No evidence for the presence of lignin in F. vesiculosus could be found.     

Phylogenetic relationships within the genus Sargassum (Fucales, Phaeophyceae), inferred from ITS-2 nrDNA, with an emphasis on the taxonomic subdivision of the genus

Sequences from the ribosomal DNA internal transcribed spacer‐2 (ITS‐2) were compared among species of Sargassaceae including the genera Sargassum and Hizikia. Species of different subgenera and sections of Sargassum were used to assess the taxonomic relationships within the genus, especially the subdivisions of the subgenus Bactrophycus. Sequences were aligned in accordance with their common secondary structure. Phylogenetic trees were constructed using neighbor‐joining, maximum likelihood and maximum parsimony methods with three species of Turbinaria as outgroups. The resulting phylogenetic trees showed that the genus Sargassum is divided into three clades corresponding to the subgenera Phyllotrichia, Sargassum and Bactrophycus. This last subgenus is further divided into four distinct groups: a Spongocarpus clade, a Teretia clade, a Hizikia clade, and a Halochloa/ Repentia clade. The position of the section Phyllo‐cystae, excluded from the subgenus Bactrophycus and included within the subgenus Sargassum is once again confirmed by the present study. Current results strongly support the assignation of Hizikia fusiformis to the genus Sargassum. Based on morphological differences and a distinct position in the molecular trees, Hizikia should be recognized as a section in the subgenus Bactrophycus so that Hizikia (Okamura) Yoshida, stat. nov. is proposed. A remarkably low divergence of ITS‐2 sequences was observed for the species in the sections Repentia and Halochloa, suggesting very recent radiation of these species. The subgenus Sargassum is divided into three clades corresponding to the three known sections: Acanthocarpicae, Malacocarpicae and Zygocarpicae, previously recognized by the morphology of receptacles. The position of Sargassum duplicatum, S. carpophyllum, S.yendoi, S. piluliferum and S. patens within the subgenus Sargassum is discussed.     

Effect of laminaran accumulation on maturation in sporophyte fragments from Ecklonia cava (Phaeophyceae,Laminariales) under various laboratory light and temperature conditions

Fragments of Ecklonia cava Kjellman were cultured under controlled laboratory conditions of light irradiance, water temperature, and photoperiod. To clarify the relationship between the maturation of E. cava and the photosynthetic products, laminaran, the content in the fragments was measured with the progress of maturation. The culture conditions ranged from 12.5 to 100 µmol m^?2 s^?1, 10–25°C, and 14 : 10 h LD (light : dark) to 10 : 14 h LD. In the case of low light conditions, despite an optimum temperature for maturation, the fragments did not form sori and laminaran was not accumulated during the culture period. In the case of sufficient light and non‐optimum temperature conditions, the fragments did not form sori, but laminaran was accumulated. When the fragments were cultured under optimum light and temperature conditions for maturation, laminaran was accumulated in the early stage of maturation, just before or after cortex of the bladelets thickened, and decreased with the progress of maturation, and all fragments matured regardless of the length of the photoperiod. So, these results support the idea that laminaran is used as the main respiratory substrate in the maturation of E. cava.     

Phylogeography of Padina boryana (Dictyotales,Phaeophyceae) around the Thai-Malay Peninsula

The Indo-Pacific Ocean is a biodiversity hotspot for marine organisms. In this area, most of the research has focused on marine animals, such as reef fish, molluscs and other associated coral fauna, but very little has been done on macroalgae. The Thai-Malay Peninsula is an important north–south barrier in this area, which faces two different oceans – the Indian Ocean and the Pacific Ocean. This study aims to investigate genetic distribution patterns of Padina boryana Thivy around the Thai-Malay Peninsula, where it is common. Three DNA marker regions, the mitochondrion-encoded cytochrome c oxidase subunit 3 gene (cox3); the plastid rbcL, and the nuclear internal transcribed spacer 2 (ITS2) were used to evaluate genetic diversity and the relationships within and between populations. Samples were collected from both the Andaman Sea and Gulf of Thailand sides of the peninsula. Parsimony networks and maximum likelihood and Bayesian analyses showed clearly that there are two separated P. boryana lineages, one restricted to the Gulf of Thailand and the other to the Andaman Sea and other areas of the Indo-Pacific. The effect of different ocean currents along the Andaman Sea and Gulf of Thailand may have shaped these populations of P. boryana. This phylogeographic separation, based on persistent currents in the area, may affect other marine organisms along the Thai peninsula.     

ISOLATION AND CHARACTERIZATION OF SIX cDNAs INVOLVED IN CARBON METABOLISM IN LAMINARIA DIGITATA (PHAEOPHYCEAE)

An expressed sequence tag (EST) approach was used to retrieve cDNA clones involved in carbon metabolism in Laminaria digitata Lamouroux. Six partial open reading frames were identified, respectively encoding an α-type carbonic anhydrase (CA), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), phosphoglycerate kinase (PGK), glycolate oxidase (GLO), and GDP-4-keto-6-d-mannose-3,5-epimerase-4-reductase, also known as fucose synthase (FS). These enzymes were further characterized through Southern blot analyses, amino acid sequence comparisons, and patterns of expression. In contrast to the other genes, which are expressed in both the gametophytic and sporophytic generations of L. digitata, the α-type carbonic anhydrase messenger RNA was shown by RT-PCR and northern blot analyses to be present in the gametophytes only. The evolutionary relationships of these genes and their interest as molecular tools for investigating carbon fluxes in brown algae are discussed.     

Infection experiments reveal broad host ranges of Eurychasma dicksonii (Oomycota) and Chytridium polysiphoniae (Chytridiomycota), two eukaryotic parasites in marine brown algae (Phaeophyceae)

Unialgal cultures of the brown alga Pylaiella littoralis (L.) Kjellman infected by either Eurychasma dicksonii (Wright) Magnus (Oomycota) or Chytridium polysiphoniae (Cohn) H. E. Petersen (Chytridiomycota) were used to elaborate the host ranges of these pathogens. Infection experiments with 48 host species covering 13 orders of the Phaeophyceae showed that 45 species were susceptible to attack by Eurychasma and 23 to Chytridium. The two pathogens showed host-specific differences in generation times: while in Pylaiella the shortest cycles were 16 days for Eurychasma and 6 days for Chytridium, one and five days more, respectively, were required in Acinetospora. Heavy parasite attack on the microscopic stages of host species with heteromorphic life histories, like kelps (Laminariales), is documented and discussed as a potential regulatory factor for the population dynamics of macroalgae.     

Sphondylothamnion multifidum (Huds.) Näg. in western Europe

The lipid composition of 140 clonal isolates of brown algae, covering 16 species of the genera Ectocarpus, Feldmannia and Hincksia, was analysed. All taxa contained the glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulphoquinovosyldiacylglycerol, and the phospholipids phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and an unidentified PX. Presence of the betaine lipid diacylglycerylhydroxymethyltrimethyl-β-alanine (DGTA) was strongly correlated with certain species in the genera Hincksia and Ectocarpus. While seven species of Hincksia contained DGTA, this lipid was absent in H. granulosa and in an unidentified Hincksia species. Due to heteromorphy of generations, species assignments in the genus Ectocarpus were made only for isolates for which the complete life history was known. We found that E. fasciculatus contains DGTA, while this lipid is absent in E. siliculosus. A collection of 40 non-sexual Ectocarpus strains included representatives with and without DGTA. The value of DGTA as a taxonomic marker in Ectocarpus and Hincksia is discussed.     

SEASONAL PATTERNS OF PHOTOSYNTHESIS AND LIGHT-INDEPENDENT CARBON FIXATION IN MARINE MACROPHYTES1

The contribution of light-independent carbon fixation (LICF) to the overall carbon gain and the seasonal patterns of maximum photosynthesis (P_max and LICF were characterized in a broad taxonomic range of macrophytes from Monterey Bay, California. P_max and LICF rates (nmol C.g filtered seawater^?1.min^?1) varied among species and taxonomic groups examined, and as a function of tissue type in the phaeophyte Laminaria setchellii Silva (Phaeophyceae). On average, P_max values were higher in the Rhodophyta, whereas LICF rates were greater in the Phaeophyceae. LICF rates were generally less than 5% of P_max in the marine macrophytes studied and, as a consequence, cannot fully compensate for respiratory carbon losses, which usually are greater than 10% of P_max. All species studied possessed the highest P_max and LICF rates when irradiance levels were highest and decreased during periods of low incident irradiance. Seasonal patterns of P_max and LICF in most of the macrophytes from the stenothermal environment of Monterey Bay were strongly correlated with photosynthetic photon flux rather than seawater temperature. The concomitant decrease of LICF and P_max rates in all species examined argues against LICF playing a major role in carbon acquisition under light-limiting conditions as suggested previously. Rather, the strong positive correlation of P_max and LICF indicates the direct coupling of photosynthate (e.g. 3-phosphoglyceric acid) generation with production of substrates for LICF reactions. Our results also suggest that LICF might be a useful indicator of photosynthetic metabolism in marine macrophytes.     

Measurements of diatom adhesion and their relationship with movement

Adhesive and tractive forces of diatoms have been measured by the bending of a glass fibre. The results show that motility depends on attachment to the substrate. Movement on girdle bands occurs when the raphe acts against lumps of trail substance. Resistance to shear stress in laminar flow through a capillary tube is found to be particularly high in large epipsammic spp., e.g. Amphora ovalis, and is related to strong adhesion.

The mechanism of movement is discussed in relation to the physical properties of the raphe and trail.     

Incorporation of14C-radioactivity into various lipid classes at different growth-stages of culturedLaminaria japonica

A study is reported on the incorporation of¹⁴C-acetate into lipid classes from three different growth stages ofLaminaria japonica, a species long used for food in Japan. This was done because of the possible utilization of its lipids.Radioactivity incorporated into whole lipids in the three growth stages under the same experimental conditions (10 °C, 500 lux) increased with maturity of the thalli. The radioactivity was found mainly in PC, TG and 1,2-DG and subsequently distributed into other lipid classes (PG,PI,PE,MGDG,SQDG and DGDG) to a lesser extent. The incorporation patterns of the former group were similar at all stages, but those of the latter group differed slightly according to growth stage.In juvenile thalli,¹⁴C was incorporated to a much higher extent into PG, MGDG, PI and fucosterol than PE, SQDG, DGDG and MG, while the¹⁴C-incorporation into MG, SQDG, DGDG and PS in the mature growth stage was higher than into the other lipid classes. The absolute level of incorporation was higher for all these compounds in mature thalli than the thalli of other growth stages.