The effects of major environmental factors and nutrient limitation on growth and encystment of planktonic dinoflagellate Akashiwo sanguinea

The bloom-forming dinoflagellate Akashiwo sanguinea is commonly observed in estuarine and coastal waters around the world. Annually recurrent blooms of this species have been observed in the coastal waters of China, particularly in the Sishili Bay, Yantai since 2004. However, limited studies have been conducted on the recurrence mechanism of A. sanguinea other than periodical monitoring of its population dynamics and associated environmental variables. Thus, to further explore the bloom and succession mechanisms of A. sanguinea in the field, we studied the effects of major nutritional components on the growth and encystment of A. sanguinea, as well as the effects of key environmental factors on the growth of A. sanguinea through a series of laboratory trials. Our results indicated that A. sanguinea was able to grow well within the temperature range of 20–25 °C, salinity range of 20 - 30, with the maximum laboratory irradiance of 78.14 μE m⁻² s⁻¹, and was able to survive and grow in low nutrient. However, lower concentrations of nutrients (e.g., nitrate, phosphate) and higher ammonium exerted different degrees of limiting effects on the growth of A. sanguinea, and induced 2.3–21.24% of vegetative cells to form resting cysts simultaneously in laboratory cultures. On the other hand, very limited or no cyst formation was observed in nutrient-replete or extremely low nutrient cultures, indicating the threshold effect of nutritional stress on the encystment of A. sanguinea. The physiological strategy of encystment of A. sanguinea in nutrient-limiting environment facilitates the survival and succession of A. sanguinea species in fluctuating seawaters, and provides seed sources for reoccurring algal blooms under favorable environmental conditions.     

Distribution of anionic sites in gut tissue: an electron-microscopical study

Summary A new one-step incubation method using cationic gold colloid was applied to reveal anionic moieties in rat colonic mucosa. Gold particles were detected in all cellular nuclei, basement membranes, mast cell granules and collagen fibres, while the luminal surfaces of all vascular endothelial cells were devoid of gold label. Application of the method for detection of anionic domains under various conditions is discussed.     

A light and electron microscope study on oogenesis in the freshwater pulmonate snail Biomphalaria glabrata

In the freshwater snail Biomphalaria glabrata the formation and composition of yolk granules and the role of the follicle cells were studied by histochemical and electron microscopical techniques. The rough endoplasmic reticulum and the Golgi apparatus appeared to be involved in yolk formation, which is a continuous process throughout oogenesis. From the very beginning of yolk formation two main types of yolk granules were distinguished morphologically. However, with histochemical and enzyme cytochemical methods no differences were observed between these types. The granules acquire lysosomal enzymes after oviposition, indicating that their main function is probably digestion of perivitelline fluid, which contains nutrients for the developing embryo.Yolk formation and the activity of the follicle cells were studied in successive stages of oogenesis by quantitative electron microscopy. The data strongly suggest that the follicle cells are involved in the formation of the follicular cavity and hence in the ovulation process.     

Electrophoretic and immunological study of myosin light chains from freshwater teleost fishes

White muscle myosin light chains from nine freshwater teleosts show a qualitative and quantitative variability on PAGE without phylogenetic correlation. They look different from their higher vertebrate counterparts mainly with regard to electric charge and relative amounts of alkali light chains corresponding to various contents of isoenzymic forms of white muscle myosin. Antibodies against carp white myosin LC1 recognize almost entirely white muscle LC1 from the other fishes and to a lesser degree LC1 from other muscles and vertebrates. The primary structure of this light chain is thus relatively constant. LC2 from carp cardiac muscle and mammalian slow and cardiac muscle do not react at all.     

A chemical and autoradiographic study of cellulose synthesis during the encystment of Acanthamoeba castellanii

When cells of Acanthamoeba castellanii are placed in a non-nutrient medium, they differentiate into cysts which possess cellulosic walls. In the present study, the source of the glucosyl unit for cyst wall cellulose was investigated by following the encystment of trophozoites grown in the presence of ¹⁴C-labeled fatty acids (uniformly labeled palmitate or oleate) or [3-³H]glucose. Cells were fractionated at the beginning and after 30 hr of encystment using a modified Schmidt-Tannhauser procedure. In cells grown on fatty acids, 90% of the labeled material was in the lipid fractions both before and after encystment with the total amount of label/cell changing very little. Both partial and complete acid hydrolysis of the glycogen of the acidsoluble fraction and the alkali-insoluble residue of the cyst wall indicated that the glucose of both fractions was not radioactive, although Acanthamoeba is known to have a functional glyoxylate pathway.Fractionation data of cells grown on [³H]glucose indicated a sevenfold increase in radioactivity in the wall insoluble fraction and a fivefold decrease in the acid-soluble fraction with the cpm/cell of the other fractions changing very little after 30 hr of encystment. Approximately 70% of the ³H-labeled material was recovered as glucose from the 30-hr wall insoluble fraction following complete acid hydrolysis. The specific radioactivity of glucose in the cyst wall insoluble fraction was the same as that of glycogen glucose isolated from the acid soluble fraction of trophozoites. Electron microscopic autoradiography showed that the majority of nonlipid radioactivity was due to glycogen in trophozoites. Autoradiograms failed to reveal Golgi bodies or any particular region of the cell as being the specialized site of cellulose synthesis. The results of the fractionation and autoradiographic studies are consistent with the concept that glycogen is a precursor of cyst wall cellulose, and that glucosyl units of glycogen and/or other glucose derivatives are converted to cellulose without significant dilution under the experimental conditions used.     

A cytophotometric and electron-microscopical study on catalase activity in serial cryostat sections of rat liver

Summary The validity of the histochemical procedure for demonstrating catalase activity in cryostat sections of rat liver at the light-and electron-microscopical level was studied cytophotometrically. Incubations in the presence of 5 mm diaminobenzidine, 44 mm hydrogen peroxide and 2% polyvinyl alcohol performed on fixed cryostat sections resulted in the highest amounts of final reaction product precipitated in a fine granular form which was specific for catalase activity. Serial sections processed for electron microscopy indicated that the osmiophilic final reaction product was exclusively localized in the matrix and core of peroxisomes. The relationship between incubation time and the amounts of final reaction product generated by catalase activity as measured at 460 nm in mid-zonal areas of liver lobules showed non-linearity for the test-minus-control reaction because first-order inactivation of the enzyme occurred during incubation. Linearity of the test-minus-control reaction and section thickness was observed up to 8 m. Catalase in rat liver showed a K_m value of 2.0 mm for its substrate hydrogen peroxide when the diaminobenzidine concentration was 5 mm. It is concluded that the procedure for demonstrating catalase activity in serial cryostat sections of rat liver at the light- and electron-microscopical level is specific and can be applied to quantitative purposes. This approach may be useful in pathology, when only small biopsies are available, when the tissue is heterogeneous, and when other histochemical markers also need to be studied in the same material.     

The fifth base: A natural feature of dinoflagellate DNA

The presence of 5-Hydroxymethyluracil which replaces important fractions of thymine in Dinoflagellate DNA is analyzed according to different procaryotic models of biosynthesis. The detection of HOMeU inAmphidinum carterae cells suggests an incorporation of this 5th base during polymerisation of DNA chains rather than a post-synthetic modification of thymines. A relationship between HOMeU and the permanent repair-like DNA synthesis observed inA. carterae is discussed.     

Deposition of amyloid in the liver of hamsters: an enzyme-histochemical and electron-microscopical study.

In induced amyloidosis the amyloid was first deposited in the portal areas, then in the centre of the lobule and disseminated through it in the spaces of Disse. No intracellular amyloid was found in the predeposit phase. In the hepatic lobule both mononuclear phagocytes and hepatocytes showed a topographic relationship to the first deposits of amyloid. Some macrophages showed invaginations or vacuoles containing amyloid fibrils. Between the microvilli of hepatocytes, parallel amyloid fibrils occurred. Between the amyloid fibrils were 30-50 nm membrane-bounded spherical particles which may have been lipoprotein aggregates. There was no large-scale phagocytosis of amyloid during the induction period or after survival without casein treatment up to 18 weeks. Lysosomal enzyme activity was seen in the deposits of extracellular amyloid.     

The phased division of the freshwater dinoflagellate Ceratium hirundinella and its use as a method of assessing growth in natural populations

SUMMARY. The nocturnal phasing and partial synchrony of cell division in Ceratium hirundinella was investigated on four occasions for dense planktonic populations in a small productive lake (Esthwaite Water). The population growth rates deduced from the proportion of cells dividing per day are compared with the rates of increase of cell density in the lake. The maximum proportion of Ceratium cells found dividing at any time was 5.8 ± 1.0%, and the time of optimum division was 03.00 hours G.M.T. The daily rate of division during the main phase of population increases was similar to that deduced from the overall population increments at that time, although during the week of collection the increase had apparently ceased temporarily. On the other three occasions, either increase of cell numbers had ceased or the population was declining, but a continued low rate of division ( c . 3% day⁻¹) was found.
The nocturnal division of Ceratium in Esthwaite Water is compared with the division phasing of dinaflagellates described from elsewhere. Some general problems associated with the derivation of estimates of population growth rate from division frequency are also considered.     

Vertical migration, entrainment and photosynthesis of the freshwater dinoflagellate Peridinium cinctum in a shallow urban lake

Vertical migration, entrainment and photosynthesis of Peridiniumcinctum were investigated in the Torrens Lake, South Australia.Cell distribution was a function of swimming speed, shear velocityand the surface mixed layer depth. During the morning, whenthe wind speed was low, cells migrated upwards, at a velocityof 2.35 x10^-4 m s^-1 and accumulated at 0.7 m (827 µmolm^-2 s^-1 at 13:00 h). After 13:00 h, cells migrated downwardsto 3.3–3.6 m at 1.85 x 10^-4 m s^-1. As wind speed increasedin the afternoon, the shear velocity of the surface mixed layerexceeded the swimming speed, leading to a homogeneous cell distributionwithin the surface mixed layer. Below the surface mixed layer,a deep chlorophyll maximum persisted. The observations werefound to fit in an entrainment function (), where if > 1,cells are disentrained, and if < 1, cells are entrained.The maximum effective quantum yield of photosystem II (F'_v/F'_m)was used as an index to monitor the photosynthetic performanceof P. cinctum and the ratio of bottle (fixed depth) to lakeF'_v/F'_m indicated whether or not migration or mixing was enhancingphotosynthesis or preventing photoinhibition. A small (0.1–0.2units) but significant depression in F'_v/F'_m was observed inP. cinctum in bottle and lake surface samples during stratifiedconditions. However, this recovered to initial values laterin the day. The ratio of bottle to lake F'_v/F'_m was consistentwith P. cinctum migration patterns. A comparison between modelleddaily photosynthetic rates of the observed migrating and a theoreticalhomogeneous population revealed that migration would not increasephotosynthetic rates within the Torrens Lake. The net ratesof O₂ production in the water column from dawn to dusk for themigrating and evenly distributed cell populations were 2574and 3120 mg m^-2, respectively.     

The mouse vomeronasal glands: a light and electron microscopical study

The glands of adult mouse vomeronasal organ (VNO) were studiedwith light- and electro-microscopical techniques. The vomeronasalglands (VN-Gs) consist of several individual glandular complexesdistributed along the long axis of the VNO. The secretory productsreleased from VN-G cells enter into the lumen of the VNO inthe region of transition between the neuroepithelium and thereceptor-free epithelium. The acini show the typical morphologicalfeatures of serous glands. The secretory cells of these aciniare characterized by a round to oval nucleus and a well-developed,rough endoplasmic reticulum, both preferentially located inthe basal part of the cell. The supranuclear region is occupiedby the Golgi apparatus and secretory granules varying in sizeand electron density. They accumulate towards the apical partof the cell. Secretory cells are connected by tight junctions,desmosomes and membrane interdigitations, moreover, they arealso coupled by gap junctions. Axonal terminals containing clearvesicles and dense-cored vesicles are frequently seen betweenthe secretory cells. Secretory cells are directly related tothe thin basal lamina of the acinus; myoepithelial cells arenot present. In the lamina propria, numerous smooth muscle cells,blood vessels and nerve bundles containing both myelinated andunmyelinated axons can be observed. An automatic regulationof the activity of the VN-Gs is discussed in relation to thevomeronasal pump.     

Microspectrophotometric study and kinetics of autogamy during encystment of Tetrahymena rostrata

The process of autogamy that accompanies encystment in Tetrahymena rostrata was divided into five stages; A: first meiotic division, B: second meiotic division. C: post-meiotic division and fusion of the pronuclei, D: first and second synkaryon's mitosis and E: macronuclear-polyploidization. In this communication the kinetics of these phases is reported. The degeneration of the old-macronucleus begins about the second meiotic division (stage-B), and the development of the new-macronucleus progressively rises during about 15h.     

Effect of a salt water intrusion on a freshwater chironomidae community: A paleolimnological study

Examination of two 90 cm sediment cores from Front Lake, a shallow (1 m) eutrophic habitat, revealed a chironomid community consisting of at least 24 species prior to the destruction of the fauna by an intrusion of salt water resulting from the high tides associated with the Saxby Gale of 1869. With the withdrawal of the salt water and a return to freshwater conditions, 23 species recolonized the lake. Of these, 22 were also found in the preintrusion community. The three species not common to both freshwater periods constituted only 2.3% of the head capsules recovered. Consequently, the chironomid community established in Front Lake both before and after the salt water intrusion had essentially identical species compositions, relative abundances of each species, and species diversity indices.     

A role for a galactose lectin and its ligands during encystment of Entamoeba

In the life cycle of Entamoeba parasites alternate between the colon-dwelling trophozoite and the infectious cyst forms. The physiologic stimuli that trigger differentiation of trophozoites into cysts remain undefined. On the surface of the human-infecting Entamoeba, parasites express a galactose/N-acetylgatactosamine (gal/galNAc)-binding lectin, which plays demonstrated roles in contact-dependent lysis of target cells and resistance to host complement. Using a reptilian parasite, Entamoeba invadens, to study cyst formation in vitro, we found that efficient encystation was dependent on the presence of gal-terminated ligands in the induction medium. Precise concentration ranges of several gal-terminated ligands, such as asialofetuin, gal-bovine serum albumin (gal-BSA), and mucin, functioned in encystation medium to stimulate differentiation. Greater than 10 mM levels of free gal inhibited the amoeba aggregation that precedes encystation and prevented formation of mature cysts. Inhibitory levels of gal also prevented the up-regulation of genes which normally occurs at 24 h of encystation. The surface of Entamoeba invadens was found to express a gal lectin which has a heterodimeric structure similar to that of Entamoeba histolytica. The 30 kDa light subunit (LGL) of the E. invadens lectin is similar in overall size and sequence to the LGL of E. histolytica. The heavy subunits, however, differ in size, have an identical spacing of cysteines in their extracellular domains, and have highly conserved C-terminal transmembrane and cytoplasmic domains. These results suggest a new role for the Entamoeba gal lectins in monitoring the concentrations of gal ligands in the colon and contributing to stimuli that induce encystment.     

Role of intestinal mucus in crystal biogenesis: an electron-microscopical,diffraction and X-ray microanalytical study

Summary In the posterior intestine of the sea-water eel, mucus plays an important role in biocrystallization of calcium ions. By means of transmission and scanning electron microscopy associated with X-ray microanalysis and X-ray diffraction it has been possible to determine the role of mucous fibers as nucleation sites. Biocrystallization occurs in 2 steps: (1) Calcification of mucus. As soon as mucus is excreted in the intestinal lumen, it is loaded with calcium, as shown by lanthanum affinity and X-ray microanalysis on freeze-dried tissues. (2) Genesis of crystals. Needleshaped crystallites build up in coalescent spherites in the intestinal lumen near the microvilli. Genesis occurs as follows: (a) crystallite mineralization by nucleation in an organic matrix composed of glycoproteinaceous mucous fibers, followed by the appearance of spherites; (b) coalescence in spherites and association of spherites in rhombohedra; (c) extrusion of organic material during the final step of crystallization.     

The aggregation behaviour of protein-coated particles: a light scattering study

The different mechanisms involved in the aggregation of spherical latex particles coated with bovine serum albumin (BSA) have been studied using static and dynamic light scattering. These techniques assess the fractal dimension of the aggregates and their mean hydrodynamic radius. Particles with different degrees of surface coverage have been prepared. The net charge of the covered particles has been modified by varying the pH of the aqueous phase. The aggregation rate was measured and used to determine the importance of the different aggregation mechanisms that are responsible for these types of flocculation processes. At low and intermediate degrees of surface coverage, bridging flocculation is the principal aggregation mechanism irrespective of the electrical state of the protein-particle complexes. At high degree of surface coverage, however, weak flocculation is important only when the BSA molecules are at their isoelectric point.