Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earth's surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are examined in detail. These interactions are central to interpretation of field measurements of photoinhibition under natural solar radiation conditions. Potential strategies and mechanisms for repair of UVBR damage are discussed. Before the long-term effects of UVBR on macroalgal production and community structure can be determined, a greater knowledge of the specific targets of UVBR in macrophytes and the mechanisms of protection and repair must be determined. The ability of macrophytes to acclimate to higher UVBR and the interaction of UVBR with other stresses, such as high PAR, temperature and desiccation, must be assessed. Studies are needed which encompass effects on all stages of the macrophyte life cycle, from recruitment to maturity.

Plasmodesmata in photosynthetic eukaryotes are found in all embryophytes, in many members of the Chlorophyta, and in the Phaeophyceae. The Phaeophyceae and the Chlorophyta clearly developed cell walls and multicellularity independently, so that (in the absence of lateral gene transfer) plasmodesmata evolved independently in these groups. The minimum number of independent origins of plasmodesmata in the Chlorophyta based on molecular phylogenies is two (Chlorophyceae sensu lato, Charophyceae sensu lato). Other intercellular connections in members of the Chlorophyta (Ctenocladus, Smithsoniella, Volvox) are structurally very different from true plasmodesmata. Recently published taxonomies of the Chlorophyta have five classes (Chlorophyceae, Oedegoniophyceae, Trentepohliophyceae, Klebsormidiophyceae and Charophyceae sensu stricto) with plasmodesmata out of a total of thirteen. However, it is by no means clear that these classes all acquired plasmodesmata independently.

This article considers molecular biological to global environment work on inorganic carbon acquisition processes in the algae sensu lato (i.e. including the cyanobacteria).

At least 95% of the organic C in photolithotrophic algae has been fixed by RUBISCO, while the remaining 5% or so has involved a range of anaplerotic carboxylases. The catalytic characteristics of RUBISCO show substantial phylogenetic variation; for some algal RUBISCOs (those from cyanobacteria and, possibly, Dinophyta) the kinetics of the carboxylase and oxygenase activity are such that net photosynthetic CO2 fixation could not occur with diffusive CO2 entry from air-equilibrium solution. In many other algae the kinetics of inorganic C assimilation are at variance with in vitro RUBISCO kinetics, and, as in cyanobacteria and Dinophyta, a CO2-concentrating mechanism is hypothesized. In many cases, the operation of such a mechanism can be demonstrated as a higher internal than external CO2 level during photosynthesis. In cases where such a CO2 concentration difference cannot be demonstrated, mechanisms may produce CO2 from HCO3− in an extracellular or intracellular compartment maintained at a lower pH than the cytosol and stroma but, with the exception of the acid zones on the surface of certain characeans, such mechanisms have not been experimentally verified. Reactions downstream of RUBISCO include the polyphyletic metabolic processes which deal with the products of RUBISCO oxygenase activity subsequent to phosphoglycolate phosphatase; even when a CO2-concentrating mechanism is present there is a minor C flux through phosphoglycolate. There are important consequences for bioenergetics, for the allocation among solutes of the low intracellular osmolarity of some freshwater algae, and of the occurrence of CO2-concentrating mechanisms or of diffusive CO2 entry. Some algae today are inorganic C-limited for photosynthesis in their natural environment under otherwise optimal conditions; even in these organisms it is not clear that they are C-limited in nature. The chances of C limitation in the past would have been greater with the low CO2 concentrations of the last glacial maximum 18,000 years ago, but would have been less likely to be C limited in the pre-pleistocene past, and in the anthropogenically CO2-enriched future, than at present. The evaluation of inorganic C acquisition mechanisms must be viewed against the general decrease in CO2, and increase in O2, over the almost 4 billion years since RUBISCO-based CO2 fixation evolved. It is not yet clear whether (polypheletic) CO2 concentrating mechanisms or (polyphyletic) mechanisms of glycolate metabolism evolved first.

This is the fourth birthday of the European Journal of Phycology, and also the beginning of my fourth year as editor-in-chief. I would like to take this opportunity to thank the previous editor, Dr Roger Jones, for setting up the present structure of the journal and for initiating the present happy relationship with our publishers, Cambridge University Press. The first term of office for the Associate Editors has now ended, and many thanks are due to all of them for their contributions to the journal. We are very fortunate in that most of the Associate Editors have been able to continue in their posts, and that those retiring have been replaced by distinguished new editors. The important work done by editorial board members, new, retired and continuing, is also much appreciated. Communication between the editorial team and authors is being facilitated by wider use of e-mail and the journal now includes e-mail addresses for authors who supply them. Current instructions to authors are now available on the CUP world wide web site (see address inside journal back cover), and the contents of each issue will appear on the web site two weeks before publication.

The past decade has seen substantial breakthroughs in understanding the biochemistry, molecular biology and regulation of nitrate reductases (NR) in higher plants and green algae. In contrast, although there has been considerable interest in using various measurements of NR to provide ecophysiological information, comparable knowledge of NR is largely lacking in algal groups other than chlorophytes. Applying information about NR from chlorophytes and higher plants to other algae may be difficult. There is evidence that non-chlorophyte forms of NR are diverse and distinct in terms of biochemical characteristics and regulatory features. Key areas to be pursued in non-chlorophyte algae include the identification and adoption of model organisms for NR research in different algal groups; the creation of selected and engineered mutants; the purification, biochemical characterization and production of antibodies to different algal forms of NR; the identification of NR genes; and the undertaking of coordinated research on nitrate uptake proteins and other enzymes in pathways of nitrate assimilation.

Nostoc punctiforme is the microsymbiont of the unique fungal endocyanosis Geosiphon pyriforme. During the establishment of this endosymbiosis fungal hyphae incorporate a specific stage of the N. punctiforme life cycle, formed during differentiation from the motile hormogonium to the non-motile primordium stage. The life cycle of N. punctiforme was synchronized by first inducing hormogonium differentiation by red light illumination for 36 h, followed by applying light/dark cycles for 96 h. Different developmental stages of N. punctiforme including hormogonia, primordia and vegetative colonies were analysed by fluorescein isothiocyanate (FITC)-conjugated lectins with sugar specificity to α-D-mannose/α-D-glucose, N-acetyl-β-D-glucosamine oligomers, α-L-fucose, β-D-galactose, α-D-galactose, N-acetyl-α-D-galactosamine and sialic acid. Lectin binding properties indicate that the slime produced by the motile hormogonia contains β-D-galactosyl and α-L-fucosyl residues, which disappear during further development. There is a clear correlation between the transition from the hormogonium to the non-motile primordium stage and the appearance of a large amount of α-D-mannosyl (or α-D-glucosyl) residues in the extracellular slime. This strongly Concanavalin A (Con A)-positive compound is lost in part during later differentiation into vegetative colonies. Consequently these significant changes in the Nostoc slime, occurring at the developmental stage involved in the establishment of the Geosiphon symbiosis, could play a role in the specific recognition between the symbiosis partners.

The total DNA of ten isolates of different chlorophycean algal genera was extracted according to a protocol for the extraction of fungal DNA. Algal DNA was digested with up to ten different restriction endonucleases. In Southern hybridizations, DNA was probed with a digoxigenin-labelled 440 base pair (bp) fragment of bacteriophage M13 containing a repetitive sequence with a 15 bp core repeat. Stringency conditions for the detection of banding patterns in algae of different genera are described. The stability of DNA fingerprints of subcultures of the same isolate was investigated. DNA fingerprints of isolates of the genera Chlorella, Klebsormidium and Stichococcus were compared. The results show that the M13 minisatellite probe can be used to detect DNA fingerprints in chlorophyte algae of different genera and to differentiate isolates of the same species.

Effects of UVA and UVB radiation were evaluated on two cyanobacterial strains (Phormidium murrayi and Oscillatoria priestleyi) isolated from the McMurdo Ice Shelf, Antarctica. The two isolates showed some similarities, but also major differences in their qualitative and quantitative responses to ultraviolet radiation (UVR). Growth decreased with increasing UVR, but with a 5-fold (UVA) or 10-fold (UVB) greater effect on O. priestleyi than P. murrayi. In both isolates, cellular concentrations of phycobiliproteins (measured by in vivo absorbance), and to a lesser extent chlorophyll a, diminished with increasing UVR exposure. Spectral scans of methanol extracts indicated the presence of UVR-screening compounds in O. priestleyi but not P. murrayi; however, the absorbance per unit dry weight was low, and similar in cultures with and without UVR. Carotenoid pigments increased up to a threshold UVB flux and thereafter decreased. In both isolates, moderate UVA lessened the effect of growth inhibition by UVB, consistent with a UVA-activated repair mechanism. Comparative motility tests showed that O. priestleyi is a fast gliding species that can rapidly relocate in response to changes in ambient light, while P. murrayi is non-motile. The ability of O. priestleyi to escape UVR by gliding, and the greater ability of P. murrayi to tolerate UVA and UVB exposure, illustrate the differences in UVR survival strategies even between closely related species of cyanobacteria.

Nucleotide gene sequences for both the nuclear-encoded small-subunit RNA (SSU) and plastid-encoded large subunit of RuBisCO (rbcL) were determined for 16 species classified in the red algal order Gelidiales. Sequence comparisons indicate that rbcL is evolving at a faster rate than SSU in these species and that there is a more even distribution of changes across the length of the rbcL gene compared with that observed for the SSU gene. The rbcL sequences also showed a marked anti-GC bias at synonymous third-codon base positions. Parsimony and maximum-likelihood analyses were used to generate phylogenetic trees from both separate and combined analyses of the two sequence data sets. Relationships among most taxa are resolved robustly; however, the relative order of branching for the Capreolia and Ptilophora clades remains uncertain. The molecular data provide unambiguous, independent support for recognition of the newly established genus Pterocladiella. Although the position of Pterocladiella within the Gelidiales was not resolved clearly by the rbcL data alone, analyses of both the SSU and combined data matrices indicate that this genus is one of the three earliest-diverging lineages within the order. These data also suggest that Gelidium as currently circumscribed is not monophyletic. Molecular and morphological evidence suggests that the origin and, perhaps, diversification of the major lineages of gelidialean algae is correlated with distinct, independently evolved nutritional strategies for the developing carposporophyte.

Batch culture experime nts were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11·3–23·7 °C and from 10 to 40 psu.Maximum division rates of more than 0·3 di visions d−1took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at differ ent temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11·3–23·7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting c ysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When st ained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal fl agellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.

The ultrastructure of male gametes of Ectocarpus siliculosus is described and discussed in relation to the information available on other brown algal zoids. In general, the fine structure and the organelle associations agree with those of other brown algal cells. In particular, the male gametes typically contain a single chloroplast with a pyrenoid and a prominent concave eyespot, into which the swelling of the posterior flagellum (the photoreceptor) fits. The continuity of the chloroplast endoplasmic reticulum and nuclear membrane, as well as the presence of a perinuclear Golgi consisting of several dictyosomes, is shown. The fine structure of microbodies, lipid bodies and different types of vesicles, including physodes and coated vesicles, is also discussed. Several specializations of cellular elements and their interactions are unique and have not been reported before. These features include the connection between the nuclear envelope, the Golgi and the flagellar bases mediated by fibres resembling intermediate filaments, and the organization of the Golgi as well as the association of mitochondria and a microtubular flagellar root.

During the last two decades, more than 100 cattle deaths have been reported from 11 alpine sites in south-eastern Switzerland. Pathological findings and the histological examination of their organs strongly indicated acute hepatotoxicosis. Clinical symptoms suggestive of neurotoxicity were also observed in some cases. To elucidate the etiology of these poisonings, different water bodies in one of the affected alpine pastures were investigated for cyanobacterial toxins. The waters were highly oligotrophic, cold and turbid, and the ice-free period was limited to 3–4 months. The algal community in these waters consisted mostly of benthic cyanobacteria forming dense mats on the surface of sediments and on submerged rocks. Oscillatoria limosa and Phormidium konstantinosum (=Oscillatoria tenuis) dominated these populations, but occasionally other species of Oscillatoria, Phormidium, Tychonema and Pseudanabaena also occurred in the mats. Samples from the cyanobacterial mats yielded positive results in a protein phosphatase inhibition assay, reacted with antibodies against microcystins in an enzyme-linked immunosorbent assay and were hepatotoxic in a mouse bioassay. The same cyanobacterial material also included neurological effects in mice. High-performance liquid chromatography was used to identify a microcystin, in these cyanobacterial samples as well as in the corresponding lake water. To our knowledge, this is the first documented example of hepatotoxicity associated with benthic cyanobacteria, and the first report of toxic cyanobacteria from the remote, oligotrophic alpine environment.

After 60 years of receiving treated sewage effluent from the city of Lahti, Lake Vesijärvi had become very eutrophic. Diversion of the effluent in 1976 resulted in a slow recovery of the water quality. In 1989–93, biomanipulation removed 380 kg of coarse fish per hectare from Enonselkä, the most polluted basin of the lake. Since then cyanobacterial blooms have decreased and water transparency has increased. Paleolimnological analysis of deep water sediments was used to reconstruct the changes in the diatom community, with varved sediment structure providing a year-by-year chronology. During the biomanipulation period the following diatom species increased in Enonselkä: Asterionella formosa, Fragilaria crotonensis, Stephanodiscus heterostylus and Tabellaria spp. In contrast, diatom species commonly considered to be indicators of eutrophication, such as Aulacoseira islandica, Diatoma elongatum and Stephanodiscus parvus, have decreased since the end of the 1980s reflecting the recovery of the Enonselkä basin. The changes in the diatom plankton recorded in the less polluted basin of Laitialanselkä were much less marked than those recorded from the sediments of the Enonselkä basin. In 1990 a diatom species, Actinocyclus normanii f. subsalsa, appeared for the first time in Lake Vesijärvi and since then it has been one of the dominant diatoms in the plankton of the Enonselkä basin. Two years later it was also present in small numbers in the plankton of Laitialanselkä, the least polluted basin of the lake. The appearance of A. normanii f. subsalsa was concomitant with the dredging of the boat harbour of Lahti city in the late summer of 1990. It was therefore apparently not directly affected by biomanipulation but benefited indirectly from the collapse of cyanobacterial populations that led to improved light and nutrient availability in the water column.

The effect of low pH on growth and photosynthesis was compared in two strains of Chlorella isolated from symbiosis with Paramecium bursaria. One, 3N813A, releases large amounts of maltose at low pH; the other, NC64A, does not release maltose in culture. Maltose synthesis at low pH appeared to have a greater effect on cell growth than pH by itself. Growth of maltose-releasing 3N813A showed a direct relationship with pH; growth of non-maltose-releasing NC64A was reduced only as pH fell from 7·0 to 5·5. At pH 5·0, net photosynthetic capacity of 3N813A cells was reduced to 76% of controls at pH 7·0, but the specific growth constant (k) was reduced to 22%, and at pH 4·0 growth and nitrate uptake were inhibited. In 3N813A cells at pH 5·0, carbon (C) was diverted from cell growth, net chlorophyll synthesis, assimilation of nitrogen (N), and synthesis of protein and starch to maltose release, but C[ratio ]N ratios were unchanged. In NC54A cells, starch but not protein synthesis was inhibited at pH 5·0, and a reduction in accumulation of N led to an increase in C[ratio ]N ratios. Unlike N starvation, growth of 3N813A cells at pH 5·0 did not reduce chlorophyll content. When measured at pH 7·0 with excess bicarbonate, photosynthetic parameters of both 3N813A and NC64A cells grown at pH 5·0 were similar to those of cells grown at pH 7·0; however, net photosynthesis of 3N813A cells N starved at pH 7·0 was 22% of that of N-sufficient controls. In symbiosis, release of excess photosynthate as maltose may inhibit cell growth by inhibiting assimilation of inorganic N, but because C[ratio ]N ratios are unchanged, photosynthetic capacity of cells is not affected.

The fine structure of the flagellar apparatus of male gametes of Ectocarpus siliculosus has been studied in negatively stained whole-mount preparations of isolated flagellar apparatuses and by transmission electron microscopy of embedded whole cells and flagellar apparatuses. Reconstructions from serial sections revealed a single absolute configuration and new structural details of the flagellar apparatus. A set of 5 microtubular roots is associated with the 2 flagellar basal bodies: the major anterior root consisting of 9 microtubules originates at the anterior basal body and loops through the anterior part of the cell. Cytoplasmic microtubules originate from this root at the apex of the cell and splay out in a posterior direction through the cell, thus determining cell shape. A broad microtubular band composed of a 9-membered bypassing root and a 3-membered major posterior root runs across the basal bodies. Two additional flagellar roots, the minor anterior and minor posterior rootlets, consist of a single microtubule each. The proximal end of the posterior basal body is laterally connected to the anterior basal body by a cross-striated connective (deltoid band). The basal bodies are connected to the nucleus by a small rhizoplast, and several other fibrous structures are associated with the basal bodies. The results are discussed in relation to earlier observations on flagellar apparatus organization in brown algae.

A new diatom genus and species, Australodiscus peruvianus Porguen et Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The valve outline is stellate with ocelli and rimoportulae situated singly on alternate points of the star. The rimoportulae are winged and situated on a secondary marginal ridge. Three types of spines are present; two of these are also winged. Our new form appears to be best placed for the present in the centric family Triceratiaceae (Schütt) Lemmermann, being most closely related to the type genus Triceratium Ehrenberg and Grovea A. Schmidt.

A comparative study of fertile gametophytes has been carried out on six species of the Dictyotales from Australia. Patterns of gametangial distribution and structure are similar in Zonaria angustata, Zonaria diesingiana, Zonaria spiralis and Zonaria turneriana, but there are some marked differences apparent between both Homoeostrichus olsenii and Homoeostrichus sinclairii and the Zonaria species. Sterile cortical cells and mucilage between the cylindrical oogonia are characteristic of the indusiate female sori of Zonaria, which differ markedly from the comparable structures of H. olsenii, in which all cortical cells have been transformed into oogonia and the walls of adjacent oogonia are contiguous. In contrast, the large spherical oogonia of H. sinclairii are unique in the Dictyotales, lacking a stalk cell and occurring among brown paraphyses in a large non-indusiate sorus on each terminal branch segment. Antheridial sori of the six species exhibit far less structural variation than the oogonial sori. Male sori are surrounded by undifferentiated cortical cells in H. olsenii, by tall brown paraphyses and short paraphyses in H. sinclairii and by sterile cells in Zonaria spp. Short paraphyses form only around the male sori of H. sinclairii in the Dictyotales; they differ in structure from the brown paraphyses but are similar to the antheridia, from which they may have been derived. Gametangial characters have proved invaluable in defining the genus Zonaria and in separating H. olsenii from H. sinclairii, but they cannot be used to delimit the species of Zonaria. Furthermore, the differences observed in the gametangia have provided new characters for phylogenetic analyses, as well as providing further supporting evidence for the recognition of Zonaria and Homoeostrichus as distinct entities.

Gelidium maggsiae sp. nov. is described from plants found in shallow subtidal maërl beds off the west coast of Ireland, where it attaches to detached coralline algae by peg-like rhizoids. Rhizines are more abundant in the medullary region than in the cortex and erect axes display a prominent central row formed by the axial and periaxial filaments. Gametophytes are bisexual and protandrous and were found only in culture. Post-fertilization and cystocarp development are similar to that of G. pteridifolium and cystocarps are biloculate. Tetrasporophytes are morphologically similar to gametophytes; tetrasporangia are irregularly arranged in pod-shaped terminally inserted stichidia, borne on erect axes and arranged unilaterally. Gametangial plants reproduced under short-day (8[ratio ]16 h) conditions at 20–25°C in enriched media, but gametangial formation was independent of photoperiod when plants were kept in unenriched medium. No tetrasporophytic plants were produced from germinated carpospores, but plants originally collected in a vegetative state formed tetraspongia at 20°C, 16[ratio ]8 h. The validity of several characters previously used in species delimitation within the Gelidiales is discussed, and only cystocarp structure and the bisexual nature of the gametophyte are considered to be reliable characters.

The effect of copper on carbohydrate production in the diatom Cylindrotheca fusiformis and in the dinoflagellate Gymnodinium sp. was examined in batch cultures. Copper was shown to inhibit the growth of the two species to different extents: in particular the dinoflagellate was highly sensitive to the metal when metal chelators were absent. Analysis of the carbohydrate content showed that C. fusiformis produced a much higher total amount than Gymnodinium sp. and cells of the diatom which were exposed to toxic copper concentrations displayed a higher carbohydrate production which paralleled the increase in copper concentrations. The increased production could be attributed to extracellular rather than to intracellular carbohydrate and it occurred after 12 and 16 days of growth, respectively, for cells exposed to 0·2 and 0·5 mg l−1 Cu. The response of carbohydrate production by Gymnodinium sp. to the presence of copper was much smaller and occurred only in late stationary phase of growth (21st day). An analysis of the copper content showed that the amount of metal accumulated by Gymnodinium sp. was similar to that absorbed by C. fusiformis, but it was a larger fraction of the quantity supplied. The results presented indicate that carbohydrate extrusion is one of the mechanisms which may prevent toxic effects due to the presence of copper in the culture medium.

Photoinhibition of photosynthesis in the red alga Chondrus crispus from different shore levels was investigated under laboratory and field conditions. The underwater light climate at Roscoff (French Atlantic coast), characterized by transmittance spectra, was shown to be intermediate between Jerlov coastal type 1 and oceanic type III. Chondrus crispus thalli were collected at four depths (3·5–8·5 m below high tide level) and exposed to daily courses of artificial and natural light. Filters were used to discriminate between the effects of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) under the photoinhibitory treatments. In the presence of natural UVR, photoinhibition at midday was increased by up to 60%. Recovery from photoinhibition was measured at different times throughout the light stress. Recovery kinetics differed between morning and early afternoon in all treatments, and were dependent on the light dose. Whereas biphasic kinetics were observed in all treatments in the morning, the recovery in early afternoon was significantly slower. The influence of UVR on recovery was apparent after exposure to higher light doses. In all investigations, sensitivity to photoinhibition corresponded to zonation of the algae, with deeper-growing algae showing a greater depression of fluorescence yield, and slower recovery (indicating acclimation to the growth irradiance). An increase in the phycoerythrin content and increasing photosynthetic efficiency with increasing growth depth were observed.