Dimorphism in cryptophytes-The case of Teleaulax amphioxeia/Plagioselmis prolonga and its ecological implications.

Growing evidence suggests that sexual reproduction might be common in unicellular organisms, but observations are sparse. Limited knowledge of sexual reproduction constrains understanding of protist ecology. Although Teleaulax amphioxeia and Plagioselmis prolonga are common marine cryptophytes worldwide, and are also important plastid donors for some kleptoplastic ciliates and dinoflagellates, the ecology and development of these protists are poorly known. We demonstrate that P. prolonga is the haploid form of the diploid T. amphioxeia and describe the seasonal dynamics of these two life stages. The diploid T. amphioxeia dominates during periods of high dissolved inorganic nitrogen (DIN) and low irradiance, temperature, and grazing (winter and early spring), whereas the haploid P. prolonga becomes more abundant during the summer, when DIN is low and irradiance, temperature, and grazing are high. Dimorphic sexual life cycles might explain the success of this species by fostering high genetic diversity and enabling endurance in adverse conditions.

Detection of an anatoxin-a(s)-like anticholinesterase in natural blooms and cultures of cyanobacteria/blue-green algae from Danish lakes and in the stomach contents of poisoned birds.

Ten natural bloom samples of cyanobacteria from the Danish lakes Knud sø (5), Ravn sø (4), and Salten Langsø (1) collected during 1993-1995 were assayed for toxicity by mouse bioassay, for acetylcholinesterase inhibiting activity by a colorimetric method, and for microcystins by enzyme-linked immunosorbent assay. In the mouse bioassay, seven samples were neurotoxic, two were non-toxic and one gave a protracted toxic response. One of the non-toxic and the single protracted toxic sample both contained anticholinesterase activity equivalent to 4 micrograms anatoxin-a(s) g-1. The neurotoxic samples contained equivalents to 20-3300 micrograms anatoxin-a(s) g-1. The highest anticholinesterase activities (equivalent to 2300 and 3300 micrograms anatoxin-a(s) g-1, respectively) were found in samples collected from Lake Knud sø in connection with bird-kills in 1993 and 1994. Small amounts of microcystins (0.1-0.9 microgram g-1) were detected in all samples but one. All Lake Knud sø and Lake Ravn sø samples were dominated by Anabaena lemmermannii, and the Lake Salten Langsø sample by several species of Anabaena. Gel filtration profiles indicated similarity between the toxic component from the Lake Knud sø 1994 bloom with registered bird-kills and anatoxin-a(s) isolated from Anabaena flos-aquae NRC-525-17. Anticholinesterase-producing cultures of A. lemmermannii were isolated from the Lake Knud sø 1993 bloom. These laboratory cultures produced anatoxin-a(s) equivalents of 29-743 micrograms g-1. Other cultures of A. lemmermannii isolated from Lake Knud sø and Lake Ravn sø were hepatotoxic or non-toxic. Dead birds collected from Lake Knud sø during the neurotoxic 1993 Anabaena bloom possibly died from cyanobacterial toxicosis. The stomach contents contained colonies and single trichomes of Anabaena, and anticholinesterase activities equivalent to 2.1-89.7 micrograms anatoxin-a(s) kg-1 body weight and microcystins (53-95 ng kg-1) were also detected.

Seasonal variations in microcystin contents of Danish cyanobacteria.

One hundred ninety-eight of 296 phytoplankton net samples, collected from Danish fresh waters during 1993-1995, contained microcystins when analyzed by high-performance liquid chromatography (HPLC), and the seasonal variations in microcystin contents were examined. Three genera, Anabaena, Microcystis, and Planktothrix, with microcystin-production potential were found. The highest percentage of the samples dominated by Anabaena and Microcystis was found in June-July and July-November, respectively, and those by Planktothrix in May and October-November. The highest microcystin contents were found in samples collected in July and September. When pooling all samples by month of collection, no major differences in mean toxin contents were seen in samples collected from May through November, with the exception of slightly higher microcystin contents in September and October. The frequency of samples (all samples grouped by month of collection) with detected microcystins ranged from 62% in July (n = 116) to 86% in May (n = 7). Variations in toxin profiles were found between 5 lakes sampled several times during 1993-1995, and in addition, quantitative and qualitative seasonal changes in microcystin content accompanied species composition changes in 3 of these lakes. Consistent blooms dominated by single species were characterized by more or less constant toxin profiles but variable toxin concentrations. Analysis of 6 samples from Lake Bryrup Langsø 1995 by enzyme linked immunoabsorbent assay and HPLC revealed 1-70 and 0-737 micrograms microcystins/g dry wt, respectively. The discrepancy between the two detection methods may be attributed to the types of microcystin variants present, emphasizing the possible influence of seasonal variations in toxin profiles on the quantification of microcystins.

Fine structure of Pyramimonas cyclotreta sp. nov. (Prasinophyceae) from Northern Foxe Basin, Arctic Canada, with some observations on growth rates.

An undescribed species of Pyramimonas, P. cyclotreta from Northern Foxe Basin (Arctic Canada) has been examined by light and electron microscopy of cultured material. Particular emphasis is given to the fine structure of the cell and the periplast. Pyramimonas cyclotreta is a typical member of the subgenus Vestigifera but differs in scale structure. It possesses a type of footprint scales not encountered before in the genus. Pyramimonas cyclotreta also differs in certain cytoplasmic features such as the structure of the posterior end of the cell and the very distinct connection between the flagellar apparatus and the microbody system. The response of growth to different temperatures reveals P. cyclotreta as cold stenothermal. Pyramimonas cyclotreta shows some morphological similarity to P. torta, a species from Belgian waters.

Studies on scale morphogenesis in the Golgi apparatus of Pyramimonas tetrarhynchus (Prasinophyceae).

Ultrastructural investigations of scale formation in the cisternae of the Golgi apparatus have been carried out on the prasinophycean flagellate Pyramimonas tetrarhynchus, whose cell surfaces are covered with 6 different scale types, 3 on the flagella and 3 on the cell body. Our results suggest that at least 4 and probably all 6 scale types can be formed together within the same cisterna and that there is some degree of intracisternal differentiation, since the formation of 2 scale types (the small underlayer scales on cell body and flagella) is restricted to the cisternal peripheries, whereas the remaining scale types are formed in the more central portions. Detailed studies of morphogenesis of the larger body scales reveal the earliest identifiable stages as 8-armed figures, with 8 thin arms in the intermediate body scales (IBS), and 4 thick and 4 thin arms in the outer body scales (OBS). From these incipients structures that bear little resemblance to the finished products, the complex, 3-dimensional mature body scales are elaborated in each of the cell's 4 distyosomes, and maintain throughout their different developmental sequences a close relationship to the inner surfaces of the cisternal membranes, as well as a particular orientation within the dictyosomes. Preliminary calculations of total numbers of scales that cover cell and flagellar surfaces are included. The small, underlayer scales, which on the flagella are shown to be arranged in 24 rows, number about 350000; larger scales of more complex construction number about 20 000.

The fine structure of mature spermatozoids of Chara corallina, with special reference to microtubules and scales.

New features recorded here for the first time include demonstration of the presence of a covering of tiny diamond shaped scales all over the body of the helical cell of the mature spermatozoids of Chara corallina Klein ex Willd. as well as a covering of slightly larger diamond shaped scales over the surfaces of the two flagella which has previously been seen by other authors in spermatozoids of both Chara and Nitella.The arrangement of microtubules in the anterior end of the spermatozoid, as a layer completely surrounding the anterior row of mitochondria resembles that of Chara fibrosa described by Pickett-Heaps 1968 and differs from that described for Nitella missouriensis by Turner 1968; these details are therefore perhaps phyletically significant.Other features such as the partial degeneration of the anteriorly placed flagellar bases are similar to those previously described for these two species although the distance between the bases and the point of emergence of the flagella from the body surface seems to differ somewhat from species to species.The investigation includes observations on the dehiscence of the antheridia and on the emergence of living cells from the spermatogenous filaments.The possible phyletic significance of some of these observations is discussed in a preliminary way.