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1.
Shunto Sakurada Shoko Fujiwara Michio Suzuki Toshihiro Kogure Tatsuya Uchida Tomonari Umemura Mikio Tsuzuki 《Marine biotechnology (New York, N.Y.)》2018,20(3):304-312
Coccolithophorids, unicellular marine microalgae, have calcified scales with elaborate structures, called coccoliths, on the cell surface. Coccoliths generally comprise a base plate, CaCO3, and a crystal coat consisting of acidic polysaccharides. In this study, the in vitro calcification conditions on the base plate of Pleurochrysis haptonemofera were examined to determine the functions of the base plate and acidic polysaccharides (Ph-PS-1, -2, and -3). When EDTA-treated coccoliths (acidic polysaccharide-free base plates) or low pH-treated coccoliths (whole acidic polysaccharide-containing base plates) were used, mineralization was not detected on the base plate. In contrast, in the case of coccoliths which were decalcified by lowering of the pH and then treated with urea (Ph-PS-2-containing base plates), distinct aggregates, probably containing CaCO3, were observed only on the rim of the base plates. Energy dispersive X-ray spectroscopy (EDS) confirmed that the aggregates contained Ca and O, although X-ray diffraction analysis did not reveal any evidence of crystalline materials. Also, in vitro mineralization experiments performed on EDTA-treated coccoliths using isolated acidic polysaccharides demonstrated that the Ca-containing aggregates were markedly formed only in the presence of Ph-PS-2. Furthermore, in vitro mineralization experiments conducted on protein-extracted base plates suggested that the coccolith-associated protein(s) are involved in the Ca deposition. These findings suggest that Ph-PS-2 associated with the protein(s) on the base plate rim initiates Ca2+ binding at the beginning of coccolith formation, and some other factors are required for subsequent calcite formation. 相似文献
2.
Mary E. Marsh 《Protoplasma》1994,177(3-4):108-122
Summary Immunolocalization of two highly acidic polysaccharides (PS-1 and PS-2) in a calcifying algaPleurochrysis carterae is described throughout the mineralization process, from before crystal nucleation through the cessation of crystal growth. This unicellular coccolithophorid alga is a useful model for mineralization because it produces calcified scales known as coccoliths in homogeneous cell culture. PS-1 and PS-2 were localized in the crystal coats of mature coccoliths and in electron dense Golgi particles. The polyanions are synthesized in medial Golgi cisternae and co-aggregate with calcium ions into discrete 25 nm particles. Particle-laden vesicles bud from cisternal margins and fuse with a coccolith-forming saccule containing an organic oval-shaped scale which forms the base of the future coccolith. The particles are localized on the base before the onset of mineral deposition and are present in the coccolith saccule throughout the period of crystal (CaCO3) nucleation and growth. During the final phase of coccolith formation, the particles disappear, and the mature crystals acquire an amorphous coat containing PS-1 and PS-2 polysaccharides which remain with the mineral phase after the coccoliths are extruded from the cell. Postulated mechanisms of polyanion-mediated mineralization are reviewed and their relevance to the calcification of coccoliths is addressed.Abbreviations PS-1
polysaccharide one
- PS-2
polysaccharide two
- BSA
bovine serum albumin
- SDS
sodium dodecyl sulfate
- MES
2-(N-morpholino)-ethanesulfonic acid
- EDTA
ethylenediaminetetraacetic acid
- DHA
3-deoxy-lyxo-2-heptulosaric acid
- TCA
trichloroacetic acid 相似文献
3.
Fumio Katagiri Yukiko Takatsuka Shoko Fujiwara Mikio Tsuzuki 《Marine biotechnology (New York, N.Y.)》2010,12(1):42-51
The effects of Ca2+ and Mg2+ on cellular growth and calcification in Pleurochrysis haptonemofera were investigated. In the presence of a normal concentration of Mg2+, coccolith-bearing cells (C-cells) required more than 0.5 mM Ca2+ for growth, while naked cells could grow even with 0.5 mM Ca2+. The calcification rate of C-cells, which was determined using decalcified cells, was significantly repressed with less than
or equal to 0.5 mM Ca2+. Although the calcification rate did not change so much with 5–30 mM Ca2+, it decreased with higher concentrations of Ca2+, as well as C-cell-specific growth repression. Under these conditions, Ca2+ affected the rate of coccolith formation, but neither the coccolith morphology nor total amounts and ratios of divalent cations
and acidic polysaccharides (Ph-PS-1, -2, and -3) were included in coccoliths. These findings suggest that sufficient calcification
is required for the division of C-cells. Under low Ca2+ and high Mg2+ conditions, coccoliths with an abnormal morphology, having immature shield elements, were synthesized. Composition analysis
of the coccoliths revealed high Mg/Ca and low Ph-PS-2/(Ph-PS-1 and -3) ratios, as compared with those under low Ca2+ and normal Mg2+ conditions, suggesting that the abnormal morphology is due to a change in the crystal type and/or acidic polysaccharide composition. 相似文献
4.
Takahashi J Fujiwara S Kikyo M Hirokawa Y Tsuzuki M 《Marine biotechnology (New York, N.Y.)》2002,4(1):94-101
We investigated the extent of calcification on the cell surface of the coccolithophorid Pleurochrysis haptonemofera using flow cytometry. Side scattering (SSC) by coccolith-bearing cells was higher than that by naked cells, suggesting the
difference was due to scattering of the laser beam by the coccoliths. SSC of coccolith-bearing cells under acidic conditions
corresponded well to the extracellular Ca content, although SSC could not be used to detect a delicate change in the coccolith
thickness. The increase in SSC during the reproduction of coccoliths after decalcification was consistent with the increase
in the number of coccoliths on the cell surface. The fluorescence after fluorescein-isothiocyanate-labeled lectin staining
suggests that α-d-mannose, α-d-glucose, d-galactose, d-N-acetylgalactosamine, or derivatives of them are included in the coccoliths. Measurement of SSC and fluorescence after fluorescein-isothiocyanate-labeled
lectin staining enabled rapid and quantitative determination of the status on the cell surface and isolation of desirable
cells for physiological studies by cell sorting.
Received May 22, 2001; accepted July 30, 2001. 相似文献
5.
Takayanagi T Hirokawa Y Yamamoto M Ohki T Fujiwara S Tsuzuki M 《Marine biotechnology (New York, N.Y.)》2007,9(1):56-65
Both coccolith-bearing cells (C-cells) and naked cells (N-cells) of the coccolithophorid Pleurochrysis haptonemofera can grow in salinities of more than 7‰ (about 20% of a “normal” sea water salinity [35‰]), with the highest growth rates
in salinities of more than 14‰. Microscopic observations of cells suspended in 100 mM NaCl (7‰) showed that, while N-cells
were swelling uniformly all over the cell surface, C-cells were bulging the plasma membrane from the hole of the coccosphere
at the apical (flagellar) pole of the cell. Effects of several cations and anions on the morphological change of C-cells under
hypoosmotic pressure were investigated. When 100 mM K+ was used, protoplasts were released from the coccosphere completely in almost all the cells. This phenomenon was shown with
K+ most effectively. The protoplasts could grow in the fresh medium and form the first coccolith within 9 h. 相似文献
6.
Hiroyuki Takano Jaekuk Jeon J. Grant Burgess Eichi Manabe Yoshito Izumi Megumi Okazaki Tadashi Matsunaga 《Applied microbiology and biotechnology》1994,40(6):946-950
A new procedure for the production of ultrafine calcite particles by the marine coccolithophorid alga Pleurochrysis carterae is reported. During continuous culture, calcite particles (coccoliths) were detached from the cell surface by optimized air-bubbling, which greatly reduced the damage associated with previous sonication methods. Detached calcite particles could be continuously recovered directly from the culture medium using a nylon mesh membrane filtration module. Cells remained viable and continued to produce coccoliths during culture. The optimum productivity of ultrafine calcite particles was 18 mg/l per day. These results demonstrate the potential for a continuous system for the photosynthetically driven removal of CO2 and its fixation into ultrafine inorganic calcite particles.
Correspondence to: T. Matsunaga 相似文献
7.
Ozaki N Sakuda S Nagasawa H 《Biochemical and biophysical research communications》2007,357(4):1172-1176
Coccolith, a calcified scale with species-specific fine structure produced by marine unicellular coccolithophorid algae, consists of calcium carbonate (CaCO(3)) crystals and a small amount of organic matrices. A novel polysaccharide named coccolith matrix acidic polysaccharide (CMAP) was isolated from the coccolith of a coccolithophorid alga, Pleurochrysis haptonemofera. The structure of CMAP was determined by chemical analysis and NMR spectroscopy including COSY, TOCSY, HMQC, and HMBC to be a polysaccharide composed of the following unit: -->4) l-iduronic acid (alpha1-->2) meso-tartaric acid (3-->1) glyoxylic acid (1-->. It has four carboxyl groups per a disaccharide unit as observed in another polysaccharide PS-2 characterized previously in Pleurochrysis carterae. CMAP showed a strong inhibitory activity on CaCO(3) precipitation. These results suggest that CMAP serves as a regulator in the calcification of the coccolith. 相似文献
8.
The long-term culture of the coccolithophore Pleurochrysis carterae (Haptophyta) in outdoor raceway ponds 总被引:2,自引:0,他引:2
The calcareous marine haptophyte algae, the coccolithophorids, are of global environmental significance because of the impact of their blooms on the carbon cycle. The coccolithophorid, Pleurochrysis carterae was grown semi-continuously in paddlewheel-driven outdoor raceway ponds over a period of 13 months in Perth, Western Australia. The mean total dry weight productivity of P. carterae was 0.19 g.L−1.d−1 with cell lipid and CaCO3 contents of up to 33% and 10% of dry weight respectively, equivalent to an annual total biomass productivity of about 60 t.ha−1.y−1 and 21.9 t.ha−1.y−1 total lipid and 5.5 t.ha−1.y−1 total calcium carbonate production. Throughout the culture period there was little protozoan contamination or contamination by other algae. The pH of the growth medium increased to pH 11 during the day and was found to be a useful variable for monitoring the state of the culture. A comparison of the growth of P. carterae and Dunaliella salina in the raceway ponds showed no significant differences between these two species with regard to areal total dry weight productivity and lipid content. 相似文献
9.
The effects of changes in CO2 and pH on biomass productivity and carbon uptake of Pleurochrysis carterae and Emiliania huxleyi in open raceway ponds and a plate photobioreactor were studied. The pH of P. carterae cultures increased during day and decreased at night, whereas the pH of E. huxleyi cultures showed no significant diurnal changes. P. carterae coccolith production occurs during the dark period, whereas in E. huxleyi, coccolith production is mainly during the day. Addition of CO2 at constant pH (pH-stat) resulted in an increase in P. carterae biomass and coccolith productivity, while CO2 addition lowered E. huxleyi biomass and coccolith production. Neither of these algae could grow at less than pH 7.5. Species-specific diurnal pH and
pCO2 variations could be indicative of significant differences in carbon uptake between these two species. While E. huxleyi has been suggested to be predominantly a bicarbonate user, our results indicate that P. carterae may be using CO2 as the main C source for photosynthesis and calcification. 相似文献
10.
Fujiwara S Hirokawa Y Takatsuka Y Suda K Asamizu E Takayanagi T Shibata D Tabata S Tsuzuki M 《Marine biotechnology (New York, N.Y.)》2007,9(5):550-560
Pleurochrysis haptonemofera is a unicellular marine coccolithophorid that has calcified scales, coccoliths, on the cell surface. Some coccolithophorids
including P. haptonemofera have a coccolith-bearing stage and a naked stage in their life cycles. To characterize genes involved in the coccolithogenesis,
we generated a total of 9550 expressed sequence tags (EST) from a normalized cDNA library that was prepared using both coccolith-bearing
cells (C-cells) and naked cells (N-cells), constructed a cDNA macroarray using the EST clones, and then analyzed the gene
expression specificity in C-cells and N-cells. When cDNA clones whose expression ratio exceeded 3-fold were selected, as many
as 180 clones were identified as C-cell-specific ones, while only 12 were found to be N-cell-specific ones. These clones were
sequenced, assembled, and homology-searched against a public nonredundant protein database. As a result, they were grouped
into 54 C-cell-specific and 6 N-cell-specific genes, and 59% and 50% of these genes exhibited significant similarity to those
of other known proteins, respectively. To assess mRNA expression further, Northern hybridization was performed for 12 of the
C-cell-specific genes and one of the N-cell-specific ones. These clones, together with the new cDNA macroarray, will provide
a powerful tool for the future genome-wide functional analysis of uncharacterized genes related to the regulation of the calcification
and life cycle of coccolithophorids.
Shoko Fujiwara and Yasutaka Hirokawa contributed equally to this work. 相似文献
11.
Summary A serial reconstruction of the chondriome ofPleurochrysis carterae (Braarudet Fagerland) Christensen has revealed a single, reticulated mitochondrion branching throughout the cell. The occurrence of a single mitochondrion in unicellular algae is briefly reviewed and its phylogenetic significance is discussed. 相似文献
12.
Marsh ME 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》2003,136(4):743-754
Coccolithophores impact the ocean carbon cycle principally through the generation of CO2 during CaCO3 production. Coccolithophore biomineralization has been examined most extensively in Pleurochrysis carterae and Emiliania huxleyi both of which produce mineralized scales—coccoliths—composed of elaborate calcite crystals attached to an underlying organic base plate. Calcification of preformed base plates is mediated by acidic polysaccharides and occurs in Golgi-derived structures known as mineralizing vesicles. In Pleurochrysis a high capacity calcium-binding polysaccharide PS2 is required for efficient nucleation of calcitic protocrystals. A galacturonomannan PS3 is required for the growth and transformation of the protocrystals into a massive double disc of calcite. The genes that regulate expression of the glycans have not yet been identified. In addition to the coccolith-bearing diploid phases, Pleurochrysis and Emiliania possess both haploid and diploid non-calcifying stages, which are self-perpetuating via binary fission. One non-calcifying Pleurochrysis phase fails to synthesis PS2 and spontaneously reverts to the mineralizing morphotype in laboratory cultures. As yet, there is little information on environmental factors that effect the expression or silencing of calcifying genes or favor the growth of calcifying over non-calcifying phases. These issues will need extensive investigation, if we are to appreciate the role of coccolithophores in the regulation of atmospheric CO2 levels. 相似文献
13.
Paul van der Wal. Johannes P. M. de Vrind Elisabeth W. de Vrind-de Jong Anton H. Borman 《Journal of phycology》1987,23(1):218-221
Pleurochrysis carterae is a marine biflagellate that produces calcified structures called coccoliths. The coccoliths are formed inside the cells and released from the latter after formation. The light dependence of calcium incorporation in this species was studied using45Ca as a tracer. Cells exposed to a repeating cycle of 16 h of light and 8 h of darkness incorporated calcium in extracellular coccoliths at a more or less constant rate throughout a cycle. The cells divided during the dark periods with a concomitant decrease in size. Their size increased during the light periods Coccolith formation in cells incubated in continuous darkness was greatly reduced and finally ceased. These cells did not divide and did not increase in size. Removal of extracellular coccoliths prior to the calcium incorporation experiments stimulated coccolith formation both in dark-incubated cells and in cells exposed to a repeating light-dark cycle. Cells in the stationary phase of growth ceased producing coccoliths. Calcification could be induced in these cells by removal of the extracellular coccoliths. Based on these findings we suggest that cells of Pleurochrysis carterae tend to produce a complete cover of coccoliths and that the available cell surface is a factor controlling coccolith formation. 相似文献
14.
Moheimani NR Isdepsky A Lisec J Raes E Borowitzka MA 《Biotechnology and bioengineering》2011,108(9):2078-2087
The feasibility of growth, calcium carbonate and lipid production of the coccolithophorid algae (Prymnesiophyceae), Pleurochrysis carterae, Emiliania huxleyi, and Gephyrocapsa oceanica, was investigated in plate, carboy, airlift, and tubular photobioreactors. The plate photobioreactor was the most promising closed cultivation system. All species could be grown in the carboy photobioreactor. However, P. carterae was the only species which grew in an airlift photobioreactor. Despite several attempts to grow these coccolithophorid species in the tubular photobioreactor (Biocoil), including modification of the airlift and sparger design, no net growth could be achieved. The shear produced by turbulence and bubble effects are the most likely reasons for this failure to grow in the Biocoil. The highest total dry weight, lipid and calcium carbonate productivities achieved by P. carterae in the plate photobioreactors were 0.54, 0.12, and 0.06 g L−1 day−1 respectively. Irrespective of the type of photobioreactor, the productivities were P. carterae > E. huxleyi > G. oceanica. Pleurochrysis carterae lipid (20–25% of dry weight) and calcium carbonate (11–12% of dry weight) contents were also the highest of all species tested. Biotechnol. Bioeng. 2011;108:2078–2087. © 2011 Wiley Periodicals, Inc. 相似文献
15.
Marine coccolithophorids (Haptophyceae) produce calcified scales “coccoliths” which are composed of CaCO3 and coccolith polysaccharides (CP) in the coccolith vesicles. CP was previously reported to be composed of uronic acids and
sulfated residues, etc. attached to the polymannose main chain. Although anionic polymers are generally known to play key
roles in biomineralization process, there is no experimental data how CP contributes to calcite crystal formation in the coccolithophorids.
CP used was isolated from the most abundant coccolithophorid, Emiliania huxleyi. CaCO3 crystallization experiment was performed on agar template layered onto a plastic plate that was dipped in the CaCO3 crystallization solution. The typical rhombohedral calcite crystals were formed in the absence of CP. CaCO3 crystals formed on the naked plastic plate were obviously changed to stick-like shapes when CP was present in the solution.
EBSD analysis proved that the crystal is calcite of which c-axis was elongated. CP in the solution stimulated the formation of tabular crystals with flat edge in the agarose gel. SEM
and FIB-TEM observations showed that the calcite crystals were formed in the gel. The formation of crystals without flat edge
was stimulated when CP was preliminarily added in the gel. These observations suggest that CP has two functions: namely, one
is to elongate the calcite crystal along c-axis and another is to induce tabular calcite crystal formation in the agarose gel. Thus, CP may function for the formation
of highly elaborate species-specific structures of coccoliths in coccolithophorids. 相似文献
16.
M. E. Marsh 《Protoplasma》1996,190(3-4):181-188
Summary Polyanions are postulated intermediates in biomineralization because they sequester large numbers of calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. In this study mineral ion and polyanion metabolism was examined inPleurochrysis carterae to determine whether polyanions function as intermediate calcium-carriers during coccolith (mineralized scale) formation. In this organism mineralization occurs intracellularly in coccolith-forming saccules, and mature coccoliths are extruded through the plasma membrane into the coccosphere. The polyanions (acidic polysaccharides known as PS-1 and PS-2) are synthesized in medial Golgi cisternae and transported to the coccolith-forming saccule prior to the onset of mineral deposition; they also cover the mineral surface of mature coccoliths. Pulse-chase experiments with45Ca2+ and14CO3
– show the calcium uptake into the coccolith-forming saccule is much slower than carbonate uptake. The extended intracellular half-life of calcium ions destined for the coccosphere suggests that calcium is initially sequestered in more distal Golgi elements (perhaps in association with the polyanions) and enters the coccolith-forming saccule only after passage through the endomembrane system. This is consistent with previous cytochemical studies showing that the polyanions are complexed with calcium prior to mineral deposition. It has been suggested that polyanions may be degraded at the mineralization front in order to free calcium ions for precipitation with available carbonate or phosphate ions. However, this study demonstrates that the polyanions are not degraded; essentially all PS-1 and PS-2 are eventually secreted with the mineral phase into the coccosphere. The kinetics of mineral ion and polyanion secretion are consistent with a polyanion-mediated calcium transport; however, the manner in which calcium might be sequestered by and freed from the polyanions is still obscure.Abbreviations PS-1/2/3
polysaccharide 1/2/3
- EDTA
ethylenediaminetetraacetic acid
- TCA
trichloroacetic acid 相似文献
17.
Cells of Coccolithus huxleyi which fail to deposit CaCO3 and form coccoliths often occur as unwanted components in cultures used for studies of calcification. Non-calcified cells generally cannot be made to recalcify, but they can be removed from cultures by treatment at elevated pH or by a method based on faster sinking of calcified cells. Lowering the concentrations of nitrate, phosphate, or trace metals in the medium did not restore calcifying ability of non-calcified cells. However, addition of strontium did promote recalcification of decalcified Cricosphaera carterae grown under calcium limitation. Strontium seemed to promote coccolith attachment to cells rather than to affect calcium uptake or coccolith formation itself. 相似文献
18.
The relationship between calcification and photosynthesis in the coccolithophorid Pleurochrysis carterae
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Coccolithophorids are one of the dominant groups of marine phytoplankton. They are found in large numbers throughout the surface euphotic zone of the ocean, and are able to form large-scale blooms that persist for long periods of time. Coccolithophorid cells are covered by species-specific calcium carbonate crystals of various structures. In the process of calcification in coccolithophorids, Ca2+ is absorbed into cells from the culture medium, and a coccolith unit is formed inside the cell. Then, the coccolith unit extrudes to the cell surface where it is constructed into crystal layers. The formation of these crystals is regulated by cellular metabolism under different environmental conditions. The carbon biogeochemical cycle in the coccolithophorids involves both photosynthetic and calcification processes, which not only play an important role in population dynamics, but also in the global carbon cycle and climate change. However, one important question remains, namely, whether the relationship between photosynthesis and calcification is species-dependent. Previous studies have yielded controversial results, even in the same species. In this paper, we selected Pleurochrysis carterae, a coccolithophore species that frequently blooms in coastal areas, to study the relationship between calcification and photosynthesis. First, we studied population growth in a batch culture over several days. For batch cultures, P. carterae was inoculated into a 10 L bioreactor at an initial cell density of approximately 5 × 104 cells mL-1. The culture conditions were optimal for cell growth. Dissolved oxygen (DO) was detected during all the culture period, and the rate of photosynthetic oxygen evolution was calculated according the DO changes during the 12-h illumination period. Algal samples (10 mL) were collected during the population growth phases. The calcium carbonate content on the cell surface was determined each day by chemical titration. Next, we studied the relationship between photosynthesis and calcification at the cellular level by observing patterns of recalcification during a 12-h period. In this study, non-calcified cells were obtained by decalcifying calcified cells collected during the exponential growth period in MES-NaOH buffer solution (pH 5.5). The non-calcified cells were inoculated into culture media containing different concentrations of Ca2+ (0, 5, 20, 40, 50, or 100 mg L-1). The rate of recalcification was determined by microscopic analyses in which the number of recalcified cells per 100 cells was counted at 0, 3, 6, 9, and 12 h of culture. Ca2+ absorbed into the cell was detected by measuring the fluorescence intensity of Fluo-3/AM labeled Ca2+. The rate of photosynthetic oxygen evolution in the non-calcified cell cultures was detected by measuring the changes in dissolved oxygen during the 12-h illumination period. The results showed that during the population growth period, the rate of photosynthetic oxygen evolution was inversely related to the calcium carbonate content per cell. When the amount of calcium carbonate on the cell surface increased, the relative photosynthetic ability (the rate of photosynthetic oxygen evolution) decreased, and vice versa. Both recalcification rates and photosynthetic oxygen evolution were affected by the extracellular calcium concentration. Non-calcified cells showed different recalcification abilities at different extracellular Ca2+ concentrations. The recalcification rate of non-calcified cells was positively correlated with the extracellular calcium concentration when [Ca2+] in the medium ranged from 0 to 100 mg L-1. However, photosynthetic oxygen evolution was suppressed at higher cell calcification rates, especially when extracellular [Ca2+] was 50–100 mg L-1. Our analyses of the population growth process and the cell recalcification process confirmed that photosynthesis is inversely related to calcification in P. carterae. 相似文献
19.
Anton H. Barman Elisabeth W. de Jong Remi Thierry Peter Westbroek Leendert Bosch Marijke Gruter Johannes P. Kamerling 《Journal of phycology》1987,23(1):118-123
Coccoliths of Emiliania huxleyi (Lohmann) Hay and Mohler, a unicellular calcifying alga, consist of calcite closely associated with an acidic, Ca2+-binding polysaccharide. This polysaccharide is thought to play a regulatory role in coccolith synthesis by interfering with CaCO3 crystallization. Here we show that the polysaccharides from three different strains, A 92, L and 92 D, all inhibit the precipitation of CaCO3 in vitro to the same extent. The monosaccharide compositions of the A 92 and L polysaccharide are similar. The 92 D material, however, deviates from the other two: it contains significantly lower amounts of methylated sugars and ribose, and elevated levels of rhamnose and galactose. It also contains antigenic determinants not detected in the A 92 and L polysaccharides. In contrast to the latter two macromolecules the 92 D polysaccharide migrates as two bands upon polyacrylamide gel electrophoresis, possibly resulting from complexing with small amounts of protein. The coccolith polysaccharide from L cells, cultured at an elevated growth rate, also migrates as two bands. This phenomenon is due to an increase in molecular size distribution. The results suggest that certain properties of the molecule may be subject to variation without interfering with its function. 相似文献
20.
SYNOPSIS. A careful re-examination with refined technics of the ultrastructure of the formation of calcified scales (coccoliths) in the marine unicellular alga Hymenomonas carterae has yielded new and more detailed information about the structure and morphogenesis of these unique and complex Golgi-elaborated organelles. The coccolith rim is formed from 2 distinct, alternating, anvil-shaped elements, 13–16 each, fitted together with a “right-handed” asymmetry. The coccolith is assembled in Golgi cisternae from 2 precursors, a single, scale-like base and multiple granular elements called coccolithosomes. The association of scales and coccolithosomes and subsequent development to the mature coccolith occur in a characteristic sequential fashion within what is one of the better examples of a polarized Golgi. Morphogenesis involves a special cisternal membrane association with the base of the coccolith, the contribution of granular material by coccolithosomes to form the outer rim matrix, and the subsequent filling of the area enclosed by the matrix with an electron-dense material, presumably CaCO3. A “microenvironment” model system for species specific shape-determination of calcified elements is proposed. 相似文献