SIGNIFICANCE OF PHYLOGENETIC SYSTEMATICS FOR THE BIOGEOGRAPHY OF THE MARINE RED ALGAE

Hovencamp (1997) recommends that geographical information can be extracted from cladistic analyses of phylogenetic data in which the Earth's history is resolved in terms of vicariance events that established barriers to migration. Nodes in a cladogram that specify two sister groups which do not overlap in their distributions are taken as evidence for a vicariance event and the sequential order of cladogram nodes leads to a procedure whereby the sequence of vicariance events can be reconstructed. For red algae, two such events are the persistence of the northward extension of the eastern end of Gondwanaland across a cool to warm temperature gradient with the formation of present‐day Australasia, and the opening of the Tethyan Ocean followed by closure of the Tethyan Seaway between Africa and Eurasia. Phylogenetic hypotheses related to the first of these events are seen among genera belonging to the Bonnemaisoniaceae, Gracilariaceae, Kallymeniaceae, Gigartinaceae, and Delesseriaceae. A Tethyan origin and distribution is exemplified in part by families that comprise the Solieriaceae complex. Orders such as the Rhodymeniales, Halymeniales and the families Ceramiaceae and Rhodomelaceae contain taxa that fall partly into the first and partly into the second category. Phylogenies are constructed from rbcL sequence data and compared to the morphological evidence. The biogeographical speculations resulting from these observations are preliminary in nature and can only be confirmed or refuted with addtional data and more refined analytical techniques.     

CAROTENOID COMPOSITION OF MARINE RED ALGAE1

Photosynthetic organisms possess carotenoids that function either as accessory, photoprotective, or structural pigments. Therefore, the carotenoid profile provides information about certain photoacclimation and photoprotection responses. Carotenoids are also important chemosystematic markers because specific enzymes mediate each step of carotenoid biosynthesis. For red algae, diverse and often contradictory carotenoid compositions have been reported. As a consequence, it is difficult to infer the physiological importance of carotenoids in Rhodophyta. To characterize the relationship between carotenoid composition, rhodophycean phylogeny, and the presence of potentially photoprotective pigments, we analyzed the carotenoid composition of 65 subtropical species from 12 orders and 18 rhodophyte families. Our results showed that red algae do not present a unique carotenoid profile. However, a common profile was observed up to the level of order, with exception of the Ceramiales and the Corallinales. The main difference between profiles is related to the xanthophyll that represents the major carotenoid. In some species lutein is the major carotenoid while in others it is substituted by zeaxanthin or antheraxanthin. The presence of this epoxy carotenoid together with the presence of violaxanthin that are xanthophyll cycle (XC)‐related pigments was found in four of the 12 analyzed orders. The carotenoid pigment profiles are discussed in relation to Rhodophyta phylogeny, and it is suggested that the xanthophyll cycle‐related pigments appeared early in the evolution of eukaryotic phototrophs.     

TOXICITY OF SUBTROPICAL MARINE ALGAE USING FISH MORTALITY AND RED BLOOD CELL HEMOLYSIS FOR BIOASSAYS1

Two bioassays (fish mortality and fish erythrocyte hemolysis) were used to survey for the presence of toxic principles in aqueous extracts of 19 species of marine macro-algae found in south Florida coastal waters. Extracts from six species (Chlorophyta—Anadyomene stellata (Wulfen) C. Ag., Caulerpa prolifera (Forsskål) Lamour., Penicillus capitatus Lamarck: Rhodophyta—Centroceras clavulatum (C. Ag.) Montague, Laurencia papillosa (Forsskål) Grev., L. poitel (Lamour.) Howe) showed lethal toxicity to the spotfin mojarra, Euconistomus argenteus Baird & Girard. Extracts from three species (Chlorophyta—A. stellata: Phaeophyta—Dictyota dichotoma (Hudson) Lamour.: Rhodophyta—Wrangelia penicillata C. Ag.) lysed erythrocytes of sea bream, Archosargus rhomboidalis (L.).     

BIOGEOGRAPHY AND ECOLOGY OF THE KELP/RED ALGAL SYMBIOSIS

A kelp/red algal symbiosis is described from nature based on extensive collections from the San Juan Islands, Washington. Kelp gametophytes were found as endophytes in the cell walls of seventeen species of red algae in three different kelp communities. Host red algae were mostly filamentous (e.g., Pleonosporium vancouverianum) or polysiphonous (e.g. Polysiphonia paniculata). The kelp gametophytes completed vegetative and reproductive development in the hosts with gametangia formed at the host surface and with sporophytes up to several mm in height being produced while still attached to the host. To date, none of the kelp gametophytes from nature have been identified to genus or species, although the gametophyte of Nereocystis luetkeana is a potential candidate for the symbiosis. Preliminary observations from Nova Scotia and the Isle of Man have not found the association in the Atlantic Ocean. Laboratory studies in Korea successfully reconstructed the symbiosis in the red alga Aglaothamnion oosumiense using zoospores of Undaria pinnatifida but not Laminaria religiosa. Here we outline the development of the symbiosis and discuss the potential adaptive significance of the kelp/red algal interaction.     

海洋红藻龙须菜对2种逆境温度胁迫的应激生理响应

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钙质红藻化石的主要类群特征及演化

钙质红藻是指可以发生生物钙化作用在其细胞壁上沉淀碳酸钙的红藻。钙质红藻可以保存为化石,是红藻古生物研究中的重要类群,具有重要的生态意义,但以往的研究对钙质红藻类群的系统分类及地史分布缺乏清晰认识。本文详细综述了钙质红藻化石的系统分类,归属于红藻门(Rhodophyta)红藻纲(Rhodophyceae)的4个目7个科,分别为珊瑚藻亚纲(Corallinophycidae)珊瑚藻目(Corallinales)的珊瑚藻科(Corallinaceae)、石叶藻科(Lithophyllaceae)、宽珊藻科(Mastophoraceae)和管孔藻科(Solenoporaceae),混石藻目(Hapalidiales)的混石藻科(Hapalidiaceae),孢石藻目(Sporolithales)的孢石藻科(Sporolithaceae)以及真红藻亚纲(Florideophycidae)耳壳藻目(Peyssonneliales)的耳壳藻科(Peyssonneliaceae)。最早的钙质红藻为管孔藻科,出现于中奥陶世,于中新世灭绝。珊瑚藻科最早出现于晚志留世并于白垩纪辐射演化至今,其他科均于白垩纪...     

TRANSFER OF PRODUCTS BETWEEN EPIPHYTIC MARINE ALGAE AND HOST PLANTS1,2

The red alga Smithora naiadum is normally found only as an epiphyle on the sea grasses Phyllospadix scouleri and Zostera marina. I used ³²P and ¹⁴CO₂ to examine the chemical communication between host and alga. Both ³²P and the product of ¹⁴CO₂ light fixation moved from the host to the alga. Reverse movement between host and epiphyte was also demonstrated. Part of this transfer occurred through the plant and part occurred by leakage from the host into the medium and subsequent uptake by the alga. Although plants were initially labeled in the light, transfer of ¹⁴C was light independent. Transfer of ¹⁴C-labeled products between host and epiphyte was also shown for Punctaria orbiculata and Z. marina; for Microdadia coulteri on Grateloupia doryphora, and between Gonimophyllum skottsbergii and Botryoglossum ruprechtiana. Epiphyte-host associations do not require a penetrating rhizoid for an exchange of the isotopes tested. By their proximity alone, epiphytic flora are apparently capable l exchanging products before these are diluted by the sea.     

EFFECT OF LIGHT QUALITY ON POLYSACCHARIDE YIELD AND COMPOSITION OF TWO RED ALGAE

Porphyra perforata is a common seaweed inhabiting the upper intertidal zone, and as a consequence it experiences great fluctuations in tissue temperature and desiccation. The objective of this work was to evaluate the effect of ambient temperature and the tissue desiccation status on the photosynthetic performance of P. perforata. Photosynthetic performance was evaluated polarographically after the temperature or desiccation treatments. Maximum photosynthesis (P_max) occurred between 25 and 30° C and decreased at higher and lower temperatures, however, no significant differences were observed in the initial slope of photosynthesis (α) from 10 to 30° C. This suggests that the photosynthetic efficiency of this species does not decrease as a result of fluctuating temperatures during tidal emergence/submergence. P_max and α were relatively constant in tissue of P. perforata with 5 to 100% relative water content. This also suggests that natural desiccation rates during low tides do not decrease photosynthetic rates in this species. Variations in the synthesis of specific proteins as a result of fluctuations in temperature and relative water content in the tissue of P. perforata are being studied.     

THE EVOLUTION OF PARASITISM IN RED ALGAE: CELLULAR INTERACTIONS OF ADELPHOPARASITES AND THEIR HOSTS1

In the initial stages of cell–cell interactions (spore germination and host penetration), the adelphoparasites Gardneriella tuberifera Kyl. and Gracilariophila oryzoides Setch. & Wilson form infection rhizoids that fuse directly with underlying host epidermal or cortical cells. In so doing, parasite nuclei and other organelles enter the cytoplasm of the host. The resulting heterokaryon may fuse with adjacent host cells either directly, via secondary pit connections, or by the dissolution or dislodgment of pit plugs from existing pit connections. The cell fusion events result in a heterokaryotic syncytium in which parasite nuclei replicate. In Gardneriella, formation of the syncytium induces surrounding host tissues to divide to form a photosynthetic callus. The internalized syncytium forms conjunctor and rhizoidal cells that fuse with host callus, eventually transforming the host callus into cells containing parasite nuclei. Gracilariophila does not induce surrounding host tissue to divide. Rather, division of the initial heterokaryotic tissue gives rise to the colorless mantle that protrudes from the host and forms reproductive structures. The heterokaryotic tissue also fuses with underlying host cells, thereby spreading parasite nuclei throughout adjacent host cells. In both these adelphoparasites, transformation of host cells by parasite nuclear invasion results in plastid dedifferentiation, an increase in mitochondria, autolysis of organelles, and accumulation of large amounts of floridean starch. The development and physiology of these parasites is similar to normal post-fertilization processes in the hosts that give rise to carposporophytes and suggests that these adelphoparasites may have originated from perturbations of developmental pathways involved in their host's post-fertilization development.