Occurrence of jasmonic acid in Dunaliella (Dunaliellales, Chlorophyta)

The occurrence of jasmonic acid and related compounds in Dunaliella species was investigated using gas-liquid chromatography/mass spectroscopy (GCY MS). Jasmonic acid was identified in the ethyl acetate soluble-acidic fraction of Dunaliella tertiolecta and Dunaliella salina (Dunal) Teodoresco, The concentration of jasmonic acid in D. salina. which is extremely halophilic, was much higher than that in D. tertiolecta Butcher, These results indicate that jasmonic acid might play an important role in salt-tolerance in Dunaliella.     

THE UPTAKE OF IODATE BY MARINE PHYTOPLANKTON1

Several studies have suggested that phytoplankton play a role in the iodine cycle. Using a short-term incubation technique for determining the uptake of iodate by phytoplankton, cultures of Thalassiosira oceanica Hasle, Skeletonema costatum (Greville) Cleve, Emiliania huxleyi (Lohmann) Hay and Mohler, and Dunaliella tertiolecta Butcher were found to be capable of assimilating iodate at rates ranging from 0.003 to 0.24 nmol IO₃^?·μg chlorophyll a^?1·h^?1. The kinetics for the uptake of iodate can be modeled, and the similarity between the model and experimental results suggests that there is a steady state between iodate uptake and release of dissolved iodine from the cells, presumably in the form of iodide. Two experiments were conducted in the Sand Shoal Inlet of the Cobb Bay estuary (37°15′N, 75°50′W). The uptake of iodate was 0.26 and 0.08 nmol IO₃^?·μg chlorophyll a^?1·h^?1 during high and low tide, respectively. Using field estimates based on measured levels of iodate in the estuary, we estimate that phytoplankton can take up as much as 3% of the ambient pool of iodate on a daily basis and the entire pool in about 1 month. Thus, phytoplankton can be a significant component of the global iodine cycle by mediating changes in the speciation of iodine in the marine environment.     

EFFECTS OF TEMPERATURE ON GROWTH,LIGHT ABSORPTION,AND QUANTUM YIELD IN DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE)1

The effects of growth temperature on the marine chlorophyte Dunaliella tertiolecta Butcher were studied to provide a more mechanistic understanding of the role of environmental factors in regulating bio-optical properties of phytoplankton. Specific attention was focused on quantities that are relevant for modeling of growth and photosynthesis. Characteristics including chlorophyll a (chl z)-specific light absorption (a*_ph(λ)), C:chl a ratio, and quantum yield for growth (φ_μ) varied as functions of temperature under conditions of excess light and nutrients. As temperature increased over the range examined (12°-28°C), intracellular concentrations of chl a increased by a factor of 2 and a*_ph(λ) values decreased by more than 50% at blue to green wavelengths. The lower values of a*_ph(λ) were due to both a decrease in the abundance of accessory pigments relative to chl a and an increase in pigment package effects arising from higher intracellular pigment concentrations. Intracellular pigment concentration increased as a consequence of higher cellular pigment quotas combined with lower cell volume. At high growth temperatures, slightly more light was absorbed on a per-cell-C basis, but the dramatic increases in growth rate from μ= 0.5 d^?1 at 12° C to μ= 2.2 d^?1 at 28°C were primarily due to an increase in φ_μ (0.015–0.041 mol C (mol quanta)^?1). By comparison with previous work on this species, we conclude the effects of temperature on a*_ph(λ) and φ_μ are comparable to those observed for light and nutrient limitation. Patterns of variability in a*_ph(λ)and φ_μ as a function of growth rate at different temperatures are similar to those previously documented for this species grown at the same irradiance but under a range of nitrogen-limited conditions. These results are discussed in the context of implications for bio-optical modeling of aquatic primary production by phytoplankton.     

Isolation and characterisation of components of the <Emphasis Type="Italic">Dunaliella tertiolecta</Emphasis> chloroplast genome

Three chloroplast genes, psbA, psbB and rbcL, of the microalgae Dunaliella tertiolecta were targeted with the view to using these components in the construction of a chloroplast transformation vector. The three genes and surrounding genomic regions were isolated by screening libraries and using degenerate primers to amplify by PCR conserved coding regions and unknown flanking sequences. The putative Dunaliella psbA, psbB and rbcL proteins show high levels of sequence conservation sharing approximately 87, 92 and 97% similarity to the homologues of Chlamydomonas reinhardtii. Interestingly, four of the five introns of the psbA gene contain long open-reading frames which have sequence similarity to the H-N-H and GIY-YIG site-specific homing endonucleases suggesting that, like other microalgae, the Dunaliella gene contains group I introns. Putative promoter regions of the psbB and rbcL genes were isolated and found to contain the required signals necessary for gene expression.     

Glycerol cycle enzymes and intermediates during adaption of Dunaliella teriolecta cells to hyperosmotic stress

Abstract Dunaliella tertiolecta cells subjected to a hyperosmotic shock of 0.930 osmol kg^?1 start almost immediately to synthesize glycerol at a rate of some 100 nmol min^?1 mg protein^?1. Glycerol synthesis was equally fast in both light and darkness, and was not affected by the nature but only by the concentration of solutes. During the period of rapid glycerol synthesis, which lasted about 1h, the concentration of glycerol-3-phosphate transiently increased. During the same period, ATP, fructose 1-6-bisphosphate, and triosephosphate content decreased markedly, especially when 0.1 kmol m^?3 NaCl-grown cells were used. The content of hexose-6-phosphates, nicotinamide coenzymes, and phosphate underwent no dramatic changes. Since no in vitro activity changes of the glycerol cycle enzymes could be detected during the adaptation period, the activity of glycerol-3-phosphate dehydrogenase in vivo is probably increased by a change in concentration of its effectors such as ATP.     

INDUCTION OF SPECIFIC PROTEINS IN EUKARYOTIC ALGAE GROWN UNDER IRON-, PHOSPHORUS-, OR NITROGEN-DEFICIENT CONDITIONS1

What limits phytoplankton growth in nature? The answer is elusive because of methodological problems associated with bottle incubations and nutrient addition experiments. We are investigating the possibility that antibodies to proteins repressed by a specific nutrient can be used as probes to indicate which nutrient limits photosynthetic carbon fixation in the ocean. The diatom Phaeodactylum tricornutum Bohlin and the chlorophyte Dunaliella tertiolecta Butcher were grown in batch cultures in artificial seawater and f/2 nutrient lacking either phosphorus, iron, or nitrogen. Chlorosis was induced by nutrient limitation in both species with the exception of phosphorus-limited D. tertiolecta. The synthesis and appearance of specific proteins were followed by labeling with ¹⁴C-bicarbonate. Nutrient limitation in general leads to a decrease in the quantum efficiency of photosystem II, suggesting that deficiency of any nutrient affects the photosynthetic apparatus to some degree: however, the effect of nitrogen and iron limitation on quantum efficiency is more severe than that of phosphorus. A crude fractionation of the soluble and membrane proteins demonstrated that the large proteins induced under limitation by phosphorus and iron were associated with the membranes. However, small iron-repressible proteins were located in the soluble fraction. Isolation with anion-exchange chromatography and N-terminal sequencing of iron-repressible, 23-kDa Proteins from D. tertiolecta, P. tricornutum, and Chaetoceros gracilis revealed that these small soluble proteins have strong homology with the N-terminal sequence of flavodoxins from Azotobacter and Clostridium. The identity of the flavodoxin from D. tertiolecta was confirmed by immunodetection using antiflavodoxin raised against Chlorella. Flavodoxin was detected only under iron deprivation and was absent from nitrogen-and phosphorus-limited algae. Flavodoxin is a prime candidate for a molecular probe of iron limitation in the ocean. The requirements to confirm its utility in nature are discussed.     

Ultrastructural study of the epidermis in two free-living Platyhelminthes, Mesostoma viaregginum and M. productum (Rhabdocoela, Typhloplanida)

Abstract. The epidermis of the free-living typhloplanids Mesostoma viaregginum and M. productum (Mesostominae) is described. In both species, the epidermis has polarized cells with nuclei located at the basal part of the cell, whereas mitochondria are in the apical one. The epidermis is entirely covered by microvilli and locomotory cilia anchored in the cytoplasm by vertical and horizontal rootlets. Rootlets exhibit distinct length and periodic structure in the two species. Furthermore, in each species vertical and horizontal rootlets possess different periodic structure. The pattern of termination of microtubules in epidermal cilia is described for the first time in the Typhloplanida; central microtubules shift along one axonemal side, doublets 1 and 6–9 lose their microtubule B, and gradually peripheral doublets become singlets. Finally, an electron-dense material caps the tip of the cilia. This pattern of termination closely resembles that of Temnocephalida, Kalytorhynchia, and Dalyelliida examined so far, but differences exist.     

Growth of Collagen Fibril Seeds from Embryonic Tendon: Fractured Fibril Ends Nucleate New Tip Growth

Collagen fibrils are the principal tensile element of vertebrate tissues where they occur in the extracellular matrix as spatially organised arrays. A major challenge is to understand how the mechanisms of nucleation, growth and remodelling yield fibrils of tissue-specific diameter and length. Here we have developed a seeding system whereby collagen fibrils were isolated from avian embryonic tendon and added to purified collagen solution, in order to characterise fibril surface nucleation and growth mechanisms. Fragmentation of tendon in liquid nitrogen followed by Dounce homogenisation generated fibril length fragments. Most (> 94%) of the fractured ends of fibrils, which show an abrupt square profile, were found to act as nucleation sites for further growth by molecular accretion. The mechanism of this nucleation and growth process was investigated by transmission electron microscopy, atomic force microscopy and scanning transmission electron microscopy mass mapping. Typically, a single growth spur occurred on the N-terminal end of seed fibrils whilst twin spurs frequently formed on the C-terminal end before merging into a single tip projection. The surface nucleation and growth process generated a smoothly tapered tip that achieved maximum diameter when the axial extension reached ∼ 13 μm. Lateral growth also occurred along the entire length of all seed fibrils that contained tip projections. The data support a model of collagen fibril growth in which the broken ends of fibrils are nucleation sites for propagation in opposite axial directions. The observed fibril growth behaviour has direct relevance to tendon matrix remodelling and repair processes that might involve rupture of collagen fibrils.     

Accumulation,localisation, and toxic effects of cadmium in the liverwort Lunularia cruciata

Summary. Accumulation, tissue and intracellular localisation, and toxic effects of cadmium were investigated in the liverwort Lunularia cruciata. The results of analyses carried out by atomic absorption spectrometry on single plants showed that the cadmium accumulation was dose- and time-dependent. Cadmium localisation was assessed by X-ray scanning electron microscopy microanalysis in gemmalings and in the different tissues of the thallus and by X-ray transmission electron microscopy microanalysis at the cellular level. The metal preferentially accumulated in the hyaline parenchyma and at the base of the gemma cups. Inside the cell, cadmium accumulated in the vacuoles and the cell wall. Metal accumulation was accompanied by a concomitant increase in sulphur content within the vacuoles of stressed cells. Gel-permeation chromatography showed that most of the cadmium was associated with a low-molecular-mass fraction eluting at a ratio of elution volume to void volume corresponding to that of phytochelatins. The excess of sulphur deposited in the vacuoles may well have been caused by the stress-induced synthesis of phytochelatins. At the ultrastructural level, sublethal concentrations of cadmium caused alterations of the fine structure of the cells, inducing marked alterations of the chloroplast structure. Cadmium also induced a dose-dependent inhibition of apical thallus growth and gemma germination.Correspondence and reprints: Department of Plant Biology, University Federico 11, via Foria 223, 80132 Naples, Italy.     

Alpha-synuclein,especially the Parkinson's disease-associated mutants,forms pore-like annular and tubular protofibrils

Two mutations in the alpha-synuclein gene (A30P and A53T) have been linked to autosomal dominant early-onset Parkinson's disease (PD). Both mutations promote the formation of transient protofibrils (prefibrillar oligomers), suggesting that protofibrils are linked to cytotoxicity. In this work, the effect of these mutations on the structure of alpha-synuclein oligomers was investigated using electron microscopy and digital image processing. The PD-linked mutations (A30P and A53T) were observed to affect both the morphology and the size distribution of alpha-synuclein protofibrils (measured by analytical ultracentrifugation and scanning transmission electron microscopy). The A30P variant was observed to promote the formation of annular, pore-like protofibrils, whereas A53T promotes formation of annular and tubular protofibrillar structures. Wild-type alpha-synuclein also formed annular protofibrils, but only after extended incubation. The formation of pore-like oligomeric structures may explain the membrane permeabilization activity of alpha-synuclein protofibrils. These structures may contribute to the pathogenesis of PD.     

不同温度下黄曲霉菌菌丝超微形态的比较研究

为探究黄曲霉菌的毒素合成是否影响菌丝超微形态,本研究结合扫描和透射电镜技术比较观察产毒(28℃和30℃)和不产毒(37℃和40℃)温度下培养的不同发育阶段的黄曲霉菌菌丝形态和超微结构.扫描电镜结果显示:28℃下,在24h和44h菌丝体表面有丝状粘性分泌物附着,48-72h之间菌丝体逐渐出现皱缩、塌陷和扭曲现象,而37℃...     

Purification and characterization of an algal (Dunaliella tertiolecta) protein cross-reacting with an anti-Ga-common antibody

A 26-kDa and a 36-kDa protein that cross-reacted with anti-G_a-common and anti-G_β antibodies, respectively, were detected in Dunaliella cells. The 26-kDa protein was solubilized from a crude membrane fraction with deoxycholate and purified to homogeneity by DE52 and hydroxylapatite chromatography and DEAE-5PW high performance liquid chromatography (HPLC). The hydroxylapatite-purified preparation had GTPγS binding and GTPase activities, but the homogeneous 26-kDa protein had none. The sequence of the 28 N-terminal amino acids of the 26-kDa protein had no homology to any GTP binding protein thus far reported.