Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1·3 optical depths (KPAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4·6 optical depths) was 17·4%, with 14% due to UVAR and an additional 3·4% due to UVBR. Lake Titicaca phytoplankton had a threshold for inhibition of photosynthesis at about 0·3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7 °C±0·73 (SD) to 21 °C±1·19. Monthly mean biomass in 25×25 cm quadrats (n = 3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27 °C. Tetrasporangia, gametangia and cystocarps were formed at 19 °C and above, but not at 13 or 16 °C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21 °C) yet only three plants with tetrasporangial branches were found in the field. In September the biomass of C. okamurae declined sharply following severe storm damage. Thus, the absence of reproductive organs in field populations of C. okamurae may occur because they inhabit a seasonally stressful habitat, in which typhoon damage removes branches before the water temperature becomes favourable for reproduction.

Phenotypic variation of Fucus spiralis was examined in terms of morphology and chemical composition, as determined by pyrolysis mass spectrometry (PyMS). After discriminant analysis both techniques revealed the existence of two morphotypes which were subsequently designated as F. spiralis and F. spiralis forma nanus. The nanus plants differed from the nominate spiralis in that they were shorter, narrower and had fewer branches, but had more units of growth from a single holdfast. F. spiralis f. nanus was consistently higher on the shore than F. spiralis, but the two morphotypes overlapped in terms of shore exposure level. We suggest that the formae exist within a mosaic of stable phenotypes representing populations specifically adapted to the local environment. PyMS data were in agreement with morphological descriptions showing that gross morphology can be correlated with chemical composition.

The stimulating effect of blue light on the carbon-concentrating mechanism of Ectocarpus siliculosus was investigated by measuring the intracellular pools of inorganic carbon (Ci) in red light (low photosynthetic rates) and in red light plus blue light (high photosynthetic rates). Ci accumulated in red light to about twice the levels found in the presence of blue light, but the permeability of the cell membranes for Ci, measured as the rate of influx of tracer carbon, was similar in both light conditions. This was also true after the seawater pH was adjusted to pH 9·5, when bicarbonate should be the only inorganic carbon species to enter the cells. Activation of photosynthesis after prolonged red light caused the accumulated Ci to decline to levels similar to those observed in blue light. The time course of this decline was rapid and coincided with the time course that was expected for the emptying of a carbon pool whose existence had been demonstrated earlier in measurements of photosynthetic oxygen evolution in the absence of external carbon. The accumulation of Ci in red light required active photosynthesis, but it also occurred in the presence of inhibitors of carbonic anhydrase activity. It is suggested that blue light mobilizes the Ci pool by causing changes in intracellular pH and that the size of the pool depends on the activity of metabolic CO2-sink activities that are also under the control of blue light.

Different stages of the automortality in phytoplankton have been studied applying flow cytometry. These stages are, in order of expression: (1) compromised cell membranes, (2) degradation of the photosynthetic pigments and reduction of the photosynthetic activity, (3) fragmentation of the genomic DNA. The integrity test of the cell membranes is based on the inability of the DNA-specific stain SYTOX Green to pass into cells with intact plasma membranes. The reduction in photosynthetic activity was examined by sorting 14C-labelled phytoplankton cells differing in viability. Finally, DNA fragmentation was traced by measuring changes in genomic DNA. The different phytoplankton species tested showed a great variety in response when grown under the same conditions, but there was also considerable intraspecific variation. Unstained cells, fully stained cells (equivalent to full staining of genomic DNA in fixed cells) and cells with intermediate fluorescence signal occurred together within the same culture. The photosynthetic activity in cells with a reduced viability dropped by as much as 60% relative to that of the viable cells. In the subsequent stage, when photosynthetic pigments were fully degraded, this value dropped further to around 10%. Cells in this stage also showed subdiploidy as a result of genome fragmentation. Field tests using samples of phytoplankton collected in the North Atlantic Ocean (40° N, 23° W) during spring showed staining properties similar to those found in cultures grown at suboptimal growth conditions. The percentage of non-viable cells varied considerably (ranging from 5% to 60%) between the various phytoplankton groups present. The lowest value was observed for Synechococcus, but some pico-eukaryotes showed percentages as high as 60%. Moreover, the viability varied with depth (light level) and over a light–dark cycle. The present findings suggest the existence of a (genetically based) uniform process of automortality in phytoplankton. Non-viable cells are a substantial component of the oceanic phytoplankton, affecting the food-web structure and species succession.

Marked seasonal reproduction is a widespread phenomenon in seaweeds in temperate waters strongly influenced by seasonal variations. In the Baltic Sea, however, the perennial brown alga Fucus vesiculosus exhibits two periods of reproduction: early summer (May–June) or late autumn (September–November). In this study, we compared the geographical distribution, the reproductive biology and the recruitment success for F. vesiculosus that reproduce during either of these two periods on the east coast of Sweden. Both monocultures and mixed populations of summer- and autumn-reproducing F. vesiculosus occurred along the mainland coast from the southern parts of the Stockholm archipelago to the southernmost part of Sweden. F. vesiculosus reproduced only during summer around the coasts of the large islands of Öland and Gotland. After reproduction, in July and January respectively, plants that reproduced in summer abscised their receptacles and part of their branches, while plants reproducing in autumn abscised only their receptacles. In laboratory experiments, short-day treatments (light:dark 8:16 h) were shown to initiate receptacles in summer-reproducing plants, whereas plants reproducing in autumn initiated receptacles independently of short- or long-day (light:dark 16:8 h) treatment. Plants reproducing during summer produced more eggs (21·0×104 eggs/g−1 frond mass) of smaller size (0·067 mm) than plants reproducing during autumn (8·9×104 eggs/g−1 frond mass, egg size 0·070 mm). However, recruitment success in the field was similar irrespective of the period of reproduction. The differences in the photoperiodic response, the differences in reproductive output and egg size between summer and autumn plants, and the observation that a single individual kept the same pattern of reproduction over a period of at least three reproductive seasons, may indicate that the two strategies of reproduction in F. vesiculosus are expressions of two distinct genotypes.

Gene expression in Fucus vesiculosus L. from the Ria Formosa, Faro, Portugal was investigated by screening a cDNA library generated by suppression subtractive hybridization (SSH) for algae undergoing mild desiccation stress (60–70% tissue water content). The subtractive library was constructed from small amounts (1 μg) of total RNA using PCR-based techniques. Screening by reverse Northern analysis (cDNA Southerns) revealed that between 60% and 70% of clones randomly selected from the library were differentially regulated in desiccated and hydrated algae. Most genes could not be directly identified based on sequence homology with known gene sequences. However, several cDNAs for chloroplast-encoded transcripts were identified and shown to be up-regulated or differentially regulated in desiccated algae relative to hydrated controls. These included partial sequences for ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco; rbcL/rbcS), chloroplast coupling factor ATPase (atpH/atpI) and a photosystem I P700 chlorophyll a binding protein (psaA). The usefulness of reverse Northern analysis was confirmed with conventional Northern analysis of transcript abundance for Rubisco, which varied rapidly in response to light and the hydration status of the algae. These results show that SSH is a useful technique for analysing the responses of gene expression to environmental stress, and as a starting point for the subsequent identification of stress-responsive genes in macroalgae.

Lagynion delicatulum Skuja is a first record for New Zealand freshwaters. Individual vegetative cells in nature and culture were sessile, aflagellate, and surrounded by a hyaline lorica lacking mineral deposits. Cells were uninucleate, had one or two chloroplasts with girdle lamellae and ring nucleoids, several mitochondria, and two to four basal-body-like centrioles. Cell division was followed by the release of one or both progeny from the parent lorica as biflagellate zoospores without eyespots. The anterior flagellum bore a tomentum of fine fibrils and two balanced rows of tripartite tubular hairs. The posterior flagellum was short, scarcely visible with light microscopy. A paraflagellar rod and paraflagellar vanes were associated with its axoneme. The flagellar apparatus consisted of two basal bodies and three microtubular roots. The coplanar basal bodies diverged from each other at an angle of approximately 130°. Simple transitional helices were present. No root that could be identified with the R3 root of other stramenopiles was present. Settling zoospores produced a few long pseudopods, and lost flagella by abscission. Cells forming loricas had a circumferential array of numerous short pseudopodia. Similarities in morphology and reproduction suggest that at least those Stylococcaceae with apparently uniflagellate swarmers form a monophyletic group. Flagellar apparatus similarities between Lagynion and Hibberdia suggest a relationship, but this is not supported by previously-published phylogenies reconstructed from molecular sequences. Convergent evolution of flagellar apparatus architecture is a possibility.

Modern chemical residues from water pollution (such as herbicides, antibiotics and even chemical substances of military use) are a challenge to survival of microalgal populations. Adaptation of three microalgal species – Pseudanabaena planctonica (Cyanophyceae), Dunaliella tertiolecta (Polyblepharidaceae, Chlorophyceae) and Scenedesmus sp. (Chlorophyceae) – to growth and survival in the presence of erythromycin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and 2,4,6-trinitrotoluene was analysed as an experimental model. Growth of these species was restricted even by micromolar concentrations of such xenobiotics. When such contaminants are added to a dense microalgal culture, the cell density will be reduced after a few days due to the death of sensitive cells. However, after further incubation for several days, the culture will sometimes increase in density again due to the growth of a cell variant which is resistant to the contaminants. A Luria–Delbrück fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutation and resistant cells arising from other mechanisms of adaptation. In all cases, the contaminant-resistant cells arise randomly by rare spontaneous mutation during replication of cells prior to the addition of the contaminant (pre-selective mutations). Since wild-type microalgal genotypes are unable to survive in the presence of such contaminants, spontaneous pre-selective mutation (i.e. mutation from herbicide sensitivity to herbicide resistance) offers insights into the evolutionary capabilities of microalgal populations in contaminated environments. The rate of spontaneous mutation from sensitivity to resistance ranged from 2·0×10−6 mutants per cell division for erythromycin sensitive [xrarr ] erythromycinresistantP. planctonica to 8·2×10−6 mutants per cell division for TNTsensitive [xrarr ] TNTresistantScenedesmus sp. Since contaminant-resistant mutants have a diminished fitness, the resistant variants are maintained in the absence of the contaminants as the result of balance between new resistant cells arising from spontaneous mutation and resistant cells eliminated by natural selection. Thus recurrence of rare spontaneous pre-selective mutations ensures the survival of microalgal population in suddenly polluted environments.

Carotenoid contents of terrestrial cyanobacteria sampled from rock surfaces with different exposure to sunlight were studied in the Guyana-shield region of Venezuela. At the collecting locations of two table mountains Roraima-tepui (2700 m), Auyan-tepui (2000 m) and an inselberg near Puerto Ayacucho (80 m), the most frequent species were Stigonema ocellatum, Stigonema hormoides and Scytonema crassum, respectively. Usually, these species were associated with the unicellular cyanobacterium Gloeocapsa sanguinea. Their carotenoid and chlorophyll a contents were determined by high-performance liquid chromatography. In general, carotenoids consisted almost equally of myxolglycosides and of β-carotene derivatives, such as β-carotene, echinenone and canthaxanthin. On a chlorophyll a basis, myxolglycoside content increased in full exposure to solar irradiation. The relative proportions of the different β-carotene derivatives appeared to be even more strongly influenced by irradiance. Whereas their total amount was increased at full exposure, the content of β-carotene decreased and that of canthaxanthin increased. Maximal ratios of canthaxanthin/β-carotene of around 5 were observed in the most sun-exposed samples. We conclude that acclimation of the carotenoid content to irradiance, especially the adjustment of the ratio canthaxanthin/β-carotene, is a response found in many different terrestrial cyanobacterial species. However, when a natural population was artificially shaded for 6 days, short-term acclimation in pigment content was not detected. The results support a photoprotective function of canthaxanthin in terrestrial cyanobacteria under natural environmental conditions.

The hypothesis that carbon acquisition in phaeophytes of lower organization is controlled by a blue-light-regulated C4 mechanism was tested by various approaches with the filamentous species Ectocarpus siliculosus. Here we report analyses at the enzymatic level. Enzymes potentially participating in a C4 cycle were assayed in extracts, and activities of a phosphoenolpyruvate carboxykinase (PEPCK), of NAD- and NADP-malate dehydrogenases, and of a NADP-malic enzyme were detected. No activity could be measured of phosphoenolpyruvate carboxylase or of pyruvate-Pi-dikinase, which is essential to complete the cycle by regenerating phosphoenolpyruvate from pyruvate. The kinetic properties of all enzymes were determined. Malic enzyme and PEPCK were purified to homogeneity, as tested by gel filtration. The molecular mass of native malic enzyme was determined to be 440 kDa. In SDS gel electrophoreses it produced a single band with a relative molecular mass of 53 kDa, which suggested that the native molecule might be a homo-octamer. The molecular mass of PEPCK was 90 kDa and separation on SDS gels produced two major bands, one of 56 kDa and one of 18 kDa, which appeared not to be a degradation product of the larger polypeptide. The composition of the native enzyme is unclear. In extracts, the activities of malic enzyme and PEPCK followed a circadian rhythm, but none of the enzymes tested was found to be blue-light-dependent. The above results neither prove nor dismiss the possibility that a C4 mechanism operates in Ectocarpus.

The only eukaryotes found in highly acidic environments (pH 0·5–3) with elevated temperatures (up to 56 °C) are three species of unicellular red algae: Cyanidioschyzon merolae, Cyanidium caldarium and Galdieria sulphuraria. These habitats are scattered all over the world and are usually very small. Because all three species are strictly acidophilic and will not tolerate desiccation, distribution by wind or water seems very unlikely. The populations in the various habitats might have been isolated for very long times, providing a unique opportunity to observe a significant degree of independent evolution under strong selective pressure. We investigated the biogeography of 18 isolates of these red algae by comparison of partial sequences of the 18S rRNA. A gene tree based on 18S rRNA assigns 15 strains to one branch with high bootstrap values. These isolates share the feature of facultative heterotrophy, whether or not they were originally placed in the genus Galdieria. The remaining three strains – Galdieria maxima, C. merolae and C. caldarium – form a sister clade to this group. The exact position of these two groups in relation to other red algae remains unresolved. The evolutionary distance between individual Galdieria strains is high, indicating that within this genus several races have developed significantly altered 18S sequences. Our comparison of 18S sequences from thermo-acidophilic red algae indicates that even within a seemingly homogeneous group of eukaryotic organisms the limits of phylogenetic analysis may be reached.

The reproductive structures in Actinotrichia fragilis (Forsskål) Børgesen are described, including the first report of the structure and development of the carpogonial branch and cystocarp for the genus. Tetrasporangia usually arise in a terminal position on assimilatory filaments; occasionally they are formed laterally and in a secund manner. In male thalli, conceptacles are initiated from the apical pit of a thallus branch. Filaments bearing spermatangia issue from the inner face of the conceptacle wall. In female thalli, a carpogonial branch consists of a carpogonium, hypogynous cell and basal cell. Carpogonial branches may arise in two ways, either replacing a vegetative branch or rarely as a third branch between vegetative dichotomous branches. Before fertilization, the hypogynous cell divides to produce four cells. Subsequently, the basal cell produces branched filaments that eventually form the pericarp, which envelops the carpogonial branch and developing gonimoblast. After fertilization, the carpogonium divides transversely into two cells. The upper progeny cell retains its cytoplasmic connection to the trichogyne. The lower cell produces a lateral gonimoblast initial. Primary gonimoblast filaments form a compact pseudoparenchymatous mass at the base of the carposporophyte. Carposporangia are produced singly from the tips of the secondary gonimoblast filaments, which develop from the primary gonimoblast mass. Many simple or little-branched sterile paraphyses issue from the inner face of the pericarp and grow into the cavity. A comparison of the reproductive structures of Actinotrichia with those of the other genera of the Galaxauraceae suggests that the genus is closely related to Tricleocarpa Huisman et Borowitzka and Galaxaura Lamouroux.

Blue light stimulates photosynthesis in brown algae by activating a mechanism for carbon acquisition. As this is connected with liberation of CO2 from an internal pool, it had previously been suggested that a C4 pathway might operate, with CO2 mobilization from an intermediate mediated by the action of blue light. The possibility that such a C4 mechanism functions was tested in Ectocarpus siliculosus by investigating metabolite pools and carbon fixation products. Extracts were analysed by HPLC with an ion exchange column. With the exception of citrate/isocitrate all metabolite levels were far too low to serve as the intermediate pool. No changes in the concentrations of any of the metabolites were found after activation by blue light following red light pre-irradiation. During short-term incubations with 14C inorganic carbon, the major label was found in phosphoglycerate. There was also clear labelling of peaks containing malate plus pyruvate and in citrate/isocitrate. In addition, glycerate contained high levels of radioactivity in some culture strains of Ectocarpus siliculosus. In chase experiments, the radioactivity of all metabolites continued to increase, indicating the presence of considerable amounts of intracellular inorganic carbon. Transient labelling was not observed for any of the fixation products. When Ectocarpus was pre-irradiated with red light and then stimulated by blue light, fixation rates increased with a time course that correlated with the activation of oxygen evolution. Photosynthetic oxygen evolution was investigated in vivo after the addition of possible intermediates to carbon-free seawater. Most of the exogenous applied substrates did not enhance photosynthesis, either in red light or after blue light stimulation. A strong enhancement seen after the addition of oxaloacetate was most likely due to release of CO2 during the breakdown of the metabolite in the medium. Taken together, the data argue strongly against the operation of a C4 pathway in Ectocarpus. It is suggested that the internal pool mobilized by blue light contains inorganic carbon.

In a recently published examination of the newly re-discovered holotype of Leptophytum (Lithophyllum) laeve, the characters of the holotype specimen were judged to be taxonomically inadequate. Consequently, an epitype was selected which was determined to belong to Phymatolithon lenormandii, rendering Leptophytum and its type L. laeve junior synonyms of Phymatolithon and P. lenormandii, respectively. We have re-studied the holotype specimen in Stockholm, and in this paper we demonstrate that it is consistent with the protologue and exhibits features that are fully consistent with the modern circumscription of Leptophytum laeve, based on population studies. Our results demonstrate that the holotype specimen is taxonomically adequate and that the selection of an epitype was not necessary. Accordingly, we propose the re-instatement of Leptophytum Adey 1966, based on its type L. laeve (Foslie) Adey (basionym: Lithophyllum lenormandii f. laeve Foslie 1891). The genera Leptophytum and Phymatolithon Foslie are similar in some anatomical respects (such as in having diminutive sub-epithallial initials, i.e. meristem cells, a polystromatic non-coaxial hypothallium, and roundish to flattened epithallial cells in transverse section). The genera differ somewhat in morphology and markedly in most reproductive features (such as spermatangial systems, origin of gonimoblasts, position of conceptacle primordia, and the presence or absence of distinct asexual conceptacle pore cells). The taxonomic, ecological and biogeographic characteristics of the two genera lead us to conclude that the similarities between Phymatolithon and Leptophytum have very likely resulted from parallel evolution.

A mechanism of bicarbonate uptake with a high sensitivity to the putative anion-exchange inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid (DIDS) has been previously reported in green algae. In this study, DIDS inhibited net oxygen evolution by Dunaliella tertiolecta by up to 22 %, but internal pH regulation, intracellular CO2 accumulation, carbon fixation and affinity for dissolved inorganic carbon (DIC) in Dunaliella tertiolecta showed low or insignificant sensitivity to DIDS. However, in cells grown and tested at pH 9·5, treatment with DIDS elevated the k0·5(HCO3-), suggesting there may be a minor role for a DIDS-sensitive anion-exchange-type HCO3- transporter in DIC acquisition by D. tertiolecta at high pH. In contrast, significant external carbonic anhydrase (CAext) activity and up to 70 % inhibition of DIC-dependent O2 evolution by acetozolamide (AZ) suggest that CAext has an important role in DIC acquisition in D. tertiolecta, in normal seawater conditions and at elevated pH. Furthermore, the rate of DIC-dependent photosynthesis at high pH, in the presence of AZ, was 12 times higher than the calculated uncatalysed rate of CO2 supply from HCO3-. This requires some system for direct HCO3- uptake by D. tertiolecta, which may include a DIDS-insensitive mechanism. The effects of DIDS upon indirect measures of DIC acquisition should be interpreted cautiously as DIDS may have non-specific effects upon whole cell function, and affect ion transport processes not directly related to HCO3- uptake.

Over the course of nearly a year, counts were made of the algae present in the samples from a Burkard-type volumetric aerobiological trap which sampled continuously the atmosphere of the city of Badajoz (SW Spain), yielding hourly and daily results. The method permits only the major taxa of algae to be distinguished. Most of the algae found belong to the Chlorococcales (Chlorophyceae) and small centric diatoms (most of them Cyclotella). Some filamentous algae were also found and even Pediastrum coenobia as well as lichen soredia. Up to 12 Chlorococcales coenobia per cubic metre were found. The mean number of cells in the coenobia was more than 10, although some coenobia with more than 100 cells were observed. Their greatest concentration was during the months of May and June. The mean daily concentration of diatoms was highly variable, with maximal concentrations of more than 70 cells m−3 in June. The maximum daily concentration of lichen soredia was 5 m−3, with the concentration being fairly constant throughout the year but particularly high in spring and early summer. The hourly distribution showed maxima during the day and minima during the night. Significant positive correlations were found with temperature, and negative correlations with relative humidity in the three groups studied. The wind speed seemed to have a positive influence on the concentration of diatoms and Chlorococcales coenobia, although the direction of the wind also had an effect.