The role of Ca(2+) in stimulated bioluminescence of the dinoflagellate Lingulodinium polyedrum. (65/633)

Many marine dinoflagellates emit bright discrete flashes of light nearly instantaneously in response to either laminar or turbulent flows as well as to direct mechanical stimulation. The flash involves a unique pH-dependent luciferase and a proton-mediated action potential across the vacuole membrane. The mechanotransduction process initiating this action potential is unknown. The present study investigated the role of Ca(2+) in the mechanotransduction process regulating bioluminescence in the dinoflagellate Lingulodinium polyedrum. Calcium ionophores and digitonin stimulated luminescence in a Ca(2+)-dependent manner in the absence of mechanical stimulation. Mechanically sensitive luminescence was strongly inhibited by the intracellular Ca(2+) chelator BAPTA-AM [1,2-bis(o-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid acetoxymethyl ester]; there was only a partial and irreversible dependence on extracellular Ca(2+). Ruthenium Red, a blocker of intracellular Ca(2+) release channels, inhibited mechanically sensitive luminescence. Luminescence was also stimulated by increasing K(+), even in the absence of extracellular Ca(2+); K(+) stimulation was inhibited both by BAPTA-AM and Ruthenium Red. These results support the hypothesis that Ca(2+) mediates stimulated bioluminescence and also indicate the involvement of intracellular Ca(2+) stores. Rapid coupling between mechanical stimulation and mobilization of intracellular Ca(2+) stores might occur through a mechanism similar to excitation-contraction coupling in skeletal muscle.  (+info)

Mimosine, the Allelochemical from the leguminous tree Leucaena leucocephala, selectively enhances cell proliferation in dinoflagellates. (66/633)

Mimosine, the allelochemical from the leguminous tree Leucaena leucocephala, is toxic to most terrestrial animals and plants. We report here that while mimosine inhibits major phytoplankton groups, it enhances cell proliferation in dinoflagellates. On addition to coastal seawater samples, mimosine is able to confer a growth advantage to dinoflagellates. The use of mimosine will promote the isolation and culture of this group of phytoplankton.  (+info)

Chemosensory responses of a protozoan are modified by antitubulins. (67/633)

Modification of a behavioral response of a marine dinoflagellate to chemical cues is described. Negative response to choline was modified by the antitubulins vincristine, vinblastine, griseofulvin, and trifluralin, but not by colchicine. Positive responses to 3,4-dihydroxyphenylalanine were unaffected by these drugs.  (+info)

Dinoflagellate-cyanobacterium communication may determine the composition of phytoplankton assemblage in a mesotrophic lake. (68/633)

The reasons for annual variability in the composition of phytoplankton assemblages are poorly understood but may include competition for resources and allelopathic interactions. We show that domination by the patch-forming dinoflagellate, Peridinium gatunense, or, alternatively, a bloom of a toxic cyanobacterium, Microcystis sp., in the Sea of Galilee may be accounted for by mutual density-dependent allelopathic interactions. Over the last 11 years, the abundance of these species in the lake displayed strong negative correlation. Laboratory experiments showed reciprocal, density-dependent, but nutrient-independent, inhibition of growth. Application of spent P. gatunense medium induced sedimentation and, subsequently, massive lysis of Microcystis cells within 24 hr, and sedimentation and lysis were concomitant with a large rise in the level of McyB, which is involved in toxin biosynthesis by Microcystis. P. gatunense responded to the presence of Microcystis by a species-specific pathway that involved a biphasic oxidative burst and activation of certain protein kinases. Blocking this recognition by MAP-kinase inhibitors abolished the biphasic oxidative burst and affected the fate (death or cell division) of the P. gatunense cells. We propose that patchy growth habits may confer enhanced defense capabilities, providing ecological advantages that compensate for the aggravated limitation of resources in the patch. Cross-talk via allelochemicals may explain the phytoplankton assemblage in the Sea of Galilee.  (+info)

Isolation and characterization of dinochrome A and B, anti-carcinogenic active carotenoids from the fresh Water red tide Peridinium bipes. (69/633)

Two epimeric carotenoids, named dinochromes A (2) and B (3), were isolated from the fresh water red tide Peridinium bipes, as anti-carcinogenic compounds. The stereostructure of dinochrome A and B were characterized to be (3S,5R,6R,3'S,5'R,8'R)- and (3S,5R,6R,3'S,5'R,8'S)-5',8'-epoxy-6,7-didehydro-5,6,5',8'-tetrahydro-beta,beta-c arotene-3,5,3'-triol 3-O-acetate, respectively by (1)H- and (13)C-NMR, and circular dichroism (CD) data. Dinochromes A (2) and B (3) inhibit 12-O-tetradecanoyl phorbol 13-acetate (TPA)-stimulated (32)P-incorporation into the phosholipids of HeLa cells. Furthermore, dinochrome A was found to inhibit the proliferation of human malignant tumor cells, such as GOTO, OST and HeLa cells.  (+info)

Effect of associated bacteria on the growth and toxicity of Alexandrium catenella. (70/633)

Saprophytic bacteria in cultures of the marine dinoflagellate Alexandrium catenella were removed to assess their effect on growth and paralytic shellfish poisoning toxin production of this dinoflagellate. The actual axenic status was demonstrated by the lack of observable bacteria both immediately after treatment and following extended incubation in the absence of antibiotics. Bacteria were measured by counting CFU and also by epifluorescence microscopy and PCR amplification of bacterial 16S-23S spacer ribosomal DNA to detect noncultivable bacteria. Removal of bacteria did not have any effect on the growth of the dinoflagellate except for the inhibition of A. catenella disintegration after reaching the stationary phase. Toxicity was determined in dinoflagellate cell extracts by different methods: high-performance liquid chromatography (HPLC); an electrophysiological test called the Electrotest, which measures the inhibition of saxitoxin-sensitive Na(+) channels expressed in a cell line; and a mouse bioassay, which measures the toxic effect on the whole mammal neuromuscular system. A lower toxicity of the dinoflagellates in axenic culture was observed by these three methods, though the difference was significant only by the mouse bioassay and HPLC methods. Altogether the results indicate that axenic cultures of A. catenella are able to produce toxin, though the total toxicity is probably diminished to about one-fifth of that in nonaxenic cultures.  (+info)

Detection of the parasitic dinoflagellate Hematodinium in the Norway lobster Nephrops norvegicus by ELISA. (71/633)

Norway lobsters Nephrops norvegicus from the coastal waters of Scotland are seasonally infected by a parasitic dinoflagellate of the genus Hematodinium. An enzyme-linked immunosorbent assay (ELISA) has been developed for the detection of the parasite in the haemolymph of N. norvegicus. The ELISA is simple to perform with a detection limit of 5 x 10(4) parasites ml(-1) haemolymph. The ELISA is currently being used to study the prevalence and seasonality of Hematodinium infection in N. norvegicus and other crustacean hosts.  (+info)

Host site of activity and cytological effects of histone-like proteins on the parasitic dinoflagellate Amyloodinium ocellatum. (72/633)

Histone-like proteins (HLPs) are broad-spectrum, endogenously produced antibiotics which we have isolated from tissues of rainbow trout Oncorhynchus mykiss and hybrid striped bass (Morone saxatilis male x M. chrysops female). Here, we show that HLP-1, which has high sequence homology to histone H2B, equally inhibited both young and mature trophonts of the important ectoparasite Amyloodinium ocellatum. In addition to direct killing of Amyloodinium trophonts, there was evidence that HLP-1 from both rainbow trout and hybrid striped bass caused severe developmental abnormalities, including delayed development, in both the parasitic trophont stage as well as the reproductive tomont stage. The deleterious effects of HLP-1 also were manifested in what appeared to be 'delayed mortality', where parasites of normal appearance would die later in development. Similar serious damage was also seen with calf histone H2B and the unrelated peptide antibiotic magainin 2. A comparison of the antibiotic activity in mucus versus epidermis compartments of the skin of hybrid striped bass suggested that the majority of antibiotic (including HLP-1) activity resided in the epidermis, although some activity was present in the mucus. These data suggest that normal, nonimmune fish skin contains potent defenses against protozoan ectoparasites and that the effects of these defenses may extend beyond their transient interactions with the parasites, which has important implications for this host-parasite relationship.  (+info)