大型绿藻浒苔藻段及组织块的生长和发育特征

通过将浒苔叶状体分为基部、中部和顶端三部分分别进行切段和切碎处理,在实验室条件下,用液体浅层培养的方法,系统地研究了其组织和细胞的生长和发育特性。显微观察的结果显示：切段培养条件下,基部和中部的藻段均可在其形态学下端形成假根,在形态学上端产生类似叶状体的突起。藻段的发育具极性,但是其极性并不绝对的,在1.0 mm的基部藻段两端都观察到了假根的形成。虽然顶端的藻段和组织块全都形成和释放了孢子,未见明显的营养生长,但是在培养早期,其下端仍然具有形成假根的能力。浒苔各部位藻段和组织块释放的和滞留于孢子囊内的孢子都可以立即萌发成苗。快速生长的中基部藻段形成了气囊,致使其漂浮于培养基上。有很多藻段和组织块形成和释放了生殖细胞,释放到外界以及滞留于孢子囊内的孢子均可立即附着萌发。数据分析表明：藻段的生长具有极性,不同部位相同长度的藻段生长率差异明显,基部藻段的生长率高于中部藻段,顶部藻段无明显的营养生长。藻段的生长与其原始长度和在藻体中所处的位置有密切关系;藻段和组织块的再生与藻体的完整性及其在藻体中所处的位置有关。     

Nitrate uptake and storage in the seaweed Ulva rigida C. Agardh in relation to nitrate availability and thallus nitrate content in a eutrophic coastal lagoon (Sacca di Goro, Po River Delta, Italy)

The seasonal cycle of biomass and tissue composition of Ulva rigida C. Agardh, in relation to nitrogen availability in the water column, was studied in 1991-1992 in the Sacca di Goro, a highly eutrophic lagoon in the Po River Delta (Italy). Nitrate uptake rates and storage capacity were also determined in laboratory experiments. The seasonal growth of U. rigida was related to the seasonal trend of nitrogen concentration in the water column. U. rigida biomass increased exponentially during spring and attained peaks of about 300-400 g dry mass (DM) m⁻² in June. As biomass increased, U. rigida depleted nitrate in the water column. Thallus nitrate reserves also declined from 100 μmol N (g DM)⁻¹ to almost undetectable levels, and total thallus nitrogen declined from 4% to 2.5% DM and 1.25% DM in 1991 and 1992, respectively. During summer, U. rigida decomposition increased, and organic nitrogen concentrations in the water column increased. The uptake experiments demonstrated an inverse relationship between thallus nitrate content and nitrate uptake rates. A modified Michaelis-Menten equation that accounts for thallus nitrate fit the uptake data well. U. rigida can accumulate up to about 400-500 μmol nitrate (g DM)⁻¹ in cellular reserves. U. rigida in the Sacca di Goro has higher K_m and lower V_max/K_m ratios for nitrate uptake than other chlorophycean species, indicating a low efficiency of uptake at low nitrate concentrations. This low uptake efficiency, and the ability to exploit N availability by storing cellular nitrate pools in excess of immediate growth needs, may represent a physiological response to an eutrophic environment where nitrate is in large supply for most of the year.     

Research note: Identity of the Qingdao algal bloom

In early July 2008, news agencies worldwide reported on a vast algal bloom that was threatening the upcoming Olympic sailing events in Qingdao, China. The identity of the culpable alga, however, remained undiscussed. We have identified the alga that caused the bloom by means of morphological and molecular data, including sequence data of the plastid encoded large subunit ribulose 1,5-bisphosphate carboxylase gene ( rbc L) and the nuclear encoded rDNA internal transcribed spacer (ITS) region. The bloom-forming alga falls within the morphological limits of the green seaweed Ulva prolifera O.F. Müller (' Enteromorpha prolifera (O.F. Müller) J. Agardh') but our phylogenetic analyses show that it forms a clade with representatives of the Ulva linza-procera-prolifera (LPP) complex. The Chinese rbc L sequences are identical to those of specimens collected from Japan, New Zealand, Finland and Portugal, suggesting that the taxon is widely distributed. rDNA ITS sequences showed a close affinity with Japanese isolates of the species complex. The Qingdao bloom is a typical illustration of a green tide, which occurs increasingly along several coasts worldwide.     

Ecological studies on Ulva lactuca L. from Veraval,India

Ulva lactuca L., at Veraval (20° 54N and 70° 22E) on the western coast of India, grows in the intertidal belt from June to late February. During the summer months of March, April and May, the species dries up, leaving rhizoidal fragments for perennation. High values of density, phytomass, frequency, weight, and volume have been recorded during September and January. Accumulation of phytomass appears to be chiefly density dependent. High dissolved oxygen content and low temperatures of the surface sea water favoured enhanced growth and, consequently, more phytomass.     

INVESTIGATIONS INTO SOUTHERN AUSTRALIAN ULVA (ULVOPHYCEAE,CHLOROPHYTA) TAXONOMY AND MOLECULAR PHYLOGENY INDICATE BOTH COSMOPOLITANISM AND ENDEMIC CRYPTIC SPECIES1

Appreciation of the true species diversity of the genus Ulva in Australian waters has been blinkered by the unproved assumption that its representatives there are largely cosmopolitan. As species of Ulva are some of the longest‐standing and most widely reported taxa of macroalgae, the presumption that they are worldwide in distribution has led to most Australian members being equated with species originally described from extra‐Australian type localities. Ulva species can be notoriously difficult to identify due to the few and often variable characters on which classical taxonomic studies focus so that names of specimens in hand, as well as names appearing in historical distribution records, are frequently difficult or impossible to verify. The combination of morphological and molecular analyses, the latter involving both nuclear (internal transcribed spacer [ITS]) and plastid (rbcL) markers, is critically important in taxonomic studies of the genus and has here been applied to selected Ulva populations from mostly cool‐temperate southern Australian localities. It has been determined that habit‐ and anatomy‐based keys of standard taxonomic literature are largely adequate for assigning species names based on classical concepts, but they often obscure a number of cryptic and pseudocryptic species that do not conform to extra‐Australian populations of the same designation, as indicated by the corresponding molecular data. Here, we present six species (Ulva australis Aresch., U. compressa Forssk., U. fasciata Delile, U. intestinalis L., U. laetevirens Aresch., U. tanneri H. S. Hayden et J. R. Waaland) for which anatomical and molecular data were congruent with both classical concepts and GenBank accession data and confirm these as cosmopolitan taxa in Australia. We also present six putative species designations based on anatomy [U. clathrata (Roth) C. Agardh, U. flexuosa Wulfen, U. linza L., U. prolifera O. F. Müll., U. stenophylla Setch. et N. L. Gardner, U. brisbanensis sp. nov.] that are inconsistent with molecular data, suggesting novel or cryptic taxa not represented in GenBank.     

CHLOROPHYLL A:B RATIOS IN SOME SIPHONOUS GREEN ALGAE IN RELATION TO SPECIES AND ENVIRONMENT1

The chlorophyll a:b ratios measured in several species of Caulerpa and in Bryopsia plumosa (Hudson) C. Ag. gave values close to 2.00 or below. Values obtained for Ulva lactuca L. taken from the same site gave a higher value of 2.44, and the sea-grass Heterozostera tasmanica (Martens ex Aschers) den Hartog a value of 2.98. Although there were changes in a:b ratios observed when Caulerpa plants were, stored for up to 10 days in dim light, the values did not suggest that chlorophyll a:b ratios were directly controlled by light intensity. It is conducted that the a:b ratios described in this paper, are a characteristic of the species themselves and are not a result of their growth in extremely shaded situations.     

Engineered antifouling microtopographies: mapping preferential and inhibitory microenvironments for zoospore attachment

An algorithm was developed and implemented to map the locations of attached spores of Ulva linza on patterned surfaces. Using this mapping algorithm, spore preference among regions within a pattern can be detected and quantified. Settlement maps of spores on patterned topographies from several assays showed clear preferences in spore settlement. Over 94% of the spores attached within the depressed regions on the surfaces, including a surface containing pits instead of protruding features. The spores attached primarily at the intersections of several features, with over half and up to 96% of spores settling in these regions. The highest spore densities occurred at intersections where the features were most dissimilar. In contrast, the location of attached beads on the surfaces was nearly uniform across the surface. Identification of preferential attachment locations allows for the study of localized properties that influence cell behavior and aids in the development of new surfaces to control cell–surface interactions.     

Requisite Morphologic Interaction for Attachment between Ulva pertusa (Chlorophyta) and Symbiotic Bacteria

In order to understand the morphogenesis-inducing mechanism of Ulva pertusa by symbiotic bacteria, we observed the requisite conditions of bacteria for attachment to U. pertusa for algal morphogenesis. Non-morphogenesis-inducing bacterial mutants derived by ultraviolet irradiation did not attach onto the surface of this alga. Scanning electron microscopic observation during the process of morphogenesis in U. pertusa revealed a network-like structure formed on the algal surface within 1 week after application of bacteria. The bacteria attached onto the alga after 2 weeks of incubation. After this attachment process the morphologic change was observed in U. pertusa. Received August 7, 1997; accepted July 24, 1998.     

Holographic microscopy provides new insights into the settlement of zoospores of the green alga Ulva linza on cationic oligopeptide surfaces

Interaction of zoospores of Ulva linza with cationic, arginine-rich oligopeptide self-assembled monolayers (SAMs) is characterized by rapid settlement. Some spores settle (ie permanently attach) in a ‘normal’ manner involving the secretion of a permanent adhesive, retraction of the flagella and cell wall formation, whilst others undergo ‘pseudosettlement’ whereby motile spores are trapped (attached) on the SAM surface without undergoing the normal metamorphosis into a settled spore. Holographic microscopy was used to record videos of swimming zoospores in the vicinity of surfaces with different cationic oligopeptide concentrations to provide time-resolved insights into processes associated with attachment of spores. The data reveal that spore attachment rate increases with increasing cationic peptide content. Accordingly, the decrease in swimming activity in the volume of seawater above the surface accelerated with increasing surface charge. Three-dimensional trajectories of individual swimming spores showed a ‘hit and stick’ motion pattern, exclusively observed for the arginine-rich peptide SAMs, whereby spores were immediately trapped upon contact with the surface.