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.

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.

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.

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.

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.

A Crypthecodinium cohnii-like dinoflagellate was found to prey on the unicellular red alga Porphyridium sp. The cytoplasm of the prey is ingested by myzocytosis within 10–30 s, and the contents of up to 20 Porphyridium cells can be taken up by one dinoflagellate. The feeding tube is retracted after each uptake process. Cytochalasin D disturbs the suction and the retraction of the feeding tube. Feeding behaviour depends on the light–dark regime: the dinoflagellates prey preferentially in the dark period and finish the trophic phase at the beginning of the light period. They then assemble and encyst, and digestion takes place in the light period. Cell division is restricted to the encysted stage. At the end of the light period excystment takes place, combined with defecation. Isogamy as well as anisogamy and nuclear cyclosis were observed. The trophonts have very thin thecal plates and a microtubular basket with two kinds of elongate vesicles. The microtubules of the tubular basket are also found in young cysts, formed after the end of the feeding period. The fine structure of the digestion vacuoles and of the faecal bodies is described.

Polypeptides of 21, 36 and 37 kDa are induced in the unicellular green alga Chlamydomonas reinhardtii when cells are transferred from high (5%) to low (0·03%) CO2 concentrations. The synthesis of these polypeptides is correlated with the induction of the CO2-concentrating mechanism. Interaction between the induction of low-CO2-inducible polypeptides, the CO2-concentrating mechanism and photorespiration has been studied in wild-type C. reinhardtii with the aim of clarifying whether the glycolate pathway is involved in algal acclimation to limiting CO2 conditions. Our results showed that the induction of the 37 kDa periplasmic carbonic anhydrase and 21 kDa polypeptide under low-CO2 conditions was not observed in the presence of aminooxyacetate, an inhibitor which completely blocks glycolate metabolism. However, the induction of the 36 kDa polypeptide was not affected by this inhibitor. The presence of aminooxyacetate during the acclimation to low CO2 conditions also inhibited the increase in the photosynthetic affinity for inorganic carbon shown by low-CO2-acclimated Chlamydomonas cells without the inhibitor. Our results suggest that the induction of the CO2-concentrating mechanism may require the function of the glycolate pathway. In addition, our results also indicate that there is differential regulation of the induction of these three low-CO2-inducible polypeptides in Chlamydomonas reinhardtii.

Monoecious, bisexual and unisexual clones of Achnanthes longipes were isolated from the Black Sea and studied in laboratory culture. Clones differed in their growth characteristics: in monoecious clones the cells formed tufted aggregations while in other clones they were more dispersed. Bisexual and unisexual clones exhibited intraclonal (monoecious) reproduction, but only at a very low frequency and usually within a more restricted size range than in monoecious clones. Interclonal crosses were made in all possible pairwise combinations. Abundant auxosporulation took place in all crosses, except where unisexual clones of the same sex were incubated together. Auxosporulation was more vigorous and occurred over a wider size range in interclonal crosses than during monoecious reproduction. Sexual reproduction is isogamous. In the commonest pattern of auxosporulation, two paired gametangia each produce two gametes, which fuse to give two auxospores. More rarely (9% of pairs), the gametangia produce only one gamete apiece, and hence only one auxospore. In addition, very small cells can enlarge vegetatively, although genetic or cytological damage sometimes compromises their long-term viability.

Single coccoliths of Emiliania huxleyi grown in mesocosm enclosures (60°16′N, 05°14′E, May–June 1991) under different N[ratio ]P regimes were analysed in a scanning electron microscope. The results indicate that only E. huxleyi with Type A coccoliths was present in the enclosures. Approximately 80–90% of the total coccolith assemblages had developed normally, whilst the remainder were malformed, incompletely grown or dissolved. Severely under-calcified specimens were rare and dissolution and breakage less than 5%. The coccoliths were of larger size than normal, as has been found previously in fjords of southwestern Norway, supporting the conclusion that a local population of E. huxleyi has developed, specific to these waters. Both phosphorus and nitrogen stress caused significant changes in coccolith size and evidence of malformation was clear, particularly in the low-phosphate enclosure. Although the observations presented here concern only Type A coccoliths and it is not known how nutrient stress may affect the coccoliths of the other types of E. huxleyi, they do serve to stress the fact that environmental conditions may possibly obscure genetically determined features. Following our observations on coccolith morphology in relation to nutrient status in enclosures, it will be of interest to test whether a similar correlation can be detected in the natural environment.

In Porphyra umbilicalis, circadian rhythms of nuclear division and growth activity persisted for at least 7 cycles in continuous white fluorescent light, with a period of 21 h for the free-running growth rhythm at 15 μmol m−2 s−1 and 10°C. Growth rhythmicity was lost at irradiances above 20 μmol m−2 s−1. The growth and mitotic rhythms seem to be driven in parallel by circadian rhythmicity, and the details of growth kinetics must be due mainly to the growth behaviour of non-dividing cells. This was inferred from the finding that individual cells continued to grow from one cell division to the next, with generation times of 2–6 days. Transfer from continuous light to 12[ratio ]12 h light[ratio ]dark synchronized the free-running growth rhythm, with a high growth peak appearing every 24 h at the start of the light phase and an increase in growth rate during the dark phase. The ascending portion of the free-running growth curve was thus shifted into the night phase of the diurnal regime and the descending portion into the light phase. This behaviour of decreasing growth activity after the morning hours, previously found in a brown and a green marine macroalga, ensures that cell activity is available primarily for photosynthesis during the day.

Fine structure of vegetative cells, development and morphology of sporangia and general morphology of zoospores were studied for the first time in the genus Endophyton Gardner. Vegetative cells contained one parietal perforate chloroplast with 2–4 ulvophycean pyrenoids and transverse cell walls without plasmodesmata. Sporangial walls were formed by two distinct electron-dense and fuzzy layers which contained a contiguous electron-translucent, fibrillar material. Zoospores were naked, with an anterior dense aggregation of vesicles and a cup-shaped chloroplast with one eyespot. The flagellar apparatus showed 180° rotational symmetry and counterclockwise absolute orientation of its components. Microtubular roots had a cruciate pattern, in which d=2 and s=4 with 3/1 arrangement. Electron-dense bilobed terminal caps covered the proximal end of each basal body. These observations support the suggested close relationship of Endophyton to the allied genus Entocladia and other ulvalean algae, and reinforce the criteria for including the genus in the class Ulvophyceae, order Ulvales, family Ulvellaceae.

In both field samples and cultures the total amount of sugar and of carbon in colonies of Phaeocystis globosa was correlated with colony surface area, suggesting a hollow structure. A conceptual model based on biochemical data and on the assumption that the mucus occurs as a layer of a fixed thickness, irrespective of colony size, predicts that the thickness of the layer is 7 μm. A confocal laser scanning microscope image of fluorescently labelled mucus confirmed this view of the colony structure. The measured contents of carbon and sugar per cell (including mucus) were constant for all colony sizes. Cells in laboratory cultures contained 122 pg C, which is twice the value for cells obtained at a field station in the North Sea (57 pg). In contrast, sugar per cell was higher in the field than in exponentially growing cultures. Therefore the percentage of sugar carbon relative to total carbon of colonies in the field was higher (19–35%) than that in cultures (10%). Highest values were found at low ambient nutrient concentrations, probably due to the presence of storage glucans in the cells that are produced under nutrient limitation. The functional role of Phaeocystis colonies in the pelagic system has to be re-evaluated because (i) biomass estimates have previously often been based on the assumption of a colony filled with mucus while in reality it is a hollow structure with an aqueous lumen, and (ii) in contrast to earlier reports it is shown that only a small amount of carbohydrate is needed to build the colony structure.

Morphological characters and growth rates of Ascophyllum nodosum were compared on fronds collected from different shore levels at one site in Strangford Lough, Northern Ireland. Both the bladders and axes of thallus tips were smaller and less variable on the upper shore than on the middle and lower shores, and the proportion of biomass invested in the production of bladders was smaller. The axes of upper shore plants were wider and flatter than on the lower shore, and the bladders were also relatively flat on the upper shore but more rounded on the lower shore. The maximum age of unbroken fronds, as estimated from the number of air bladders, was 6 years on the upper shore and 17 years on the lower shore, indicating the higher probability of breakage of plants caused by stress on the upper shore. In situ growth rates of individually marked plants along a vertical shore transect were monitored at 2- to 4-week intervals for 31 months. Length increase was highest (16 cm yr−1) in the middle of the Ascophyllum nodosum zone, and lowest (10 cm yr−1) on the upper shore. Growth was strongly seasonal with low (but not zero) growth rates during November and December, and highest growth rates in late spring and early summer. A decline in growth in mid-summer was observed at all shore levels. Growth was positively correlated with sunshine hours and total solar irradiance in winter and spring but there was no correlation with these factors during summer months. Maximum daily temperatures had a positive influence on growth in late spring, but no effect in the rest of the year. In transplantation experiments conducted in summer and winter, 80% of plants moved from the lower to the upper shore died within 3 months, whereas all transplants from the upper to the lower shore and all controls survived. Growth rates of surviving transplants at both shore levels were similar to those of control plants at the same shore level in the summer experiment. The pigment content and photosynthetic capacity of surviving plants acclimated to ambient conditions and, after 3 months, were not significantly different from those of control plants at the same shore level. It is suggested that the phenotypic acclimation of physiological characteristics and the genetic adaptation of morphological features contribute to the ability of this species to dominate such a wide band in the intertidal zone of sheltered rocky shores in the North Atlantic.