Microbodies of the alga Chara

Chara fragilis possesses microbodies with a remarkably large size of up to 2 µm in diameter . Many of the organelles contain huge nucleoids of amorphous material or paracrystalline inclusions. After isolation of the organelles by gradient centrifugation the specific density of the microbodies was determined to be 1.25 g cm⁻³. Catalase, glycolate oxidase and hydroxypyruvate reductase as well as enzymes of the fatty acid β -oxidation pathway were demonstrated to be constituents of the microbodies in Chara indicating that they are similar to those in green leaves. The data obtained are in agreement with the view that the Charophyceae and especially the algae in the subgroup of Charales are very closely related to the land plants.     

Scale-invariant pattern in the alga Micrasterias

Spatial structures arise in a variety of different physical, chemical and biological systems. A striking example is found during morphogenesis in the single-celled alga Micrasterias, where cell extensions called lobes branch repeatedly to produce a highly regular, apparently self-similar pattern. Lobe outgrowth in Micrasterias is thought to be controlled by the local accumulation of growth determinants at the lobe tips. These tip-growth sites undergo successive spatial bifurcations, leading to the recursively branched, final cell form. I have tested for scale invariance of this form, by measuring the distribution of tips as a function of position along the cell perimeter in mature Micrasterias cells of four different species. This tip distribution should reflect the steady-state distribution of growth determinants at the end of the spatial bifurcation process. For each cell measured, the distribution of tips resembled a Cantor set with three levels of constant, nested scaling. Significantly, roughly the same scale factor (3.0) was found at each scaling level in individual cells, and among different cells in each of the four species measured. These data suggest that scaling by this factor is intrinsic to the pattern formation process in Micrasterias.     

褐藻多糖

褐藻多糖主要包括褐藻胶、褐藻糖胶和褐藻淀粉。近年来研究表明,褐藻多糖有一定的抗癌、抗HIV-1作用。详细介绍了褐藻多糖的来源、类型、结构及性质;分离、提纯方法以及它们的生理活性和相关的构效关系研究。     

Sesquiterpenes from the red alga Laurencia tristicha

Phytochemical investigation on Laurencia tristicha afforded eleven cuparane-derived sesquiterpenes, including ten monomers and one dimer, and their structures were elucidated by a combination of spectroscopic analysis and comparison with those reported in literature. Four compounds, laurinterol acetate, debromolaurinterol acetate, aplysinal, and (−)-α-bromocuparene were obtained from L. tristicha for the first time. Additionally, the chemotaxonomic significance of these cuparane-derived sesquiterpenes, as well as their plausible biogenetic pathway, was also discussed.     

Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and the mesophilic alga Chlorella sorokiniana

Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K. antarctica NR has a native molecular mass of 367 kDa. NR from K. antarctica used both NADPH and NADH, whereas NR from C. sorokiniana used NADH only. Both NRs used reduced methyl viologen (MVH) or benzyl viologen (BVH). In crude extracts, maximal NADH and MVH-dependent activities of cryophilic NR were found at 15 and 35 degrees C, respectively, and retained 77 and 62% of maximal activity, respectively, at 10 degrees C. Maximal NADH and MVH-dependent activities of mesophilic NR, however, were found at 25 and 45 degrees C, respectively, with only 33 and 23% of maximal activities being retained at 10 degrees C. In presence of 2 microM flavin adenine dinucleotide (FAD), activities of cryophilic NADH:NR and mesophilic NADH:NR were stable up to 25 and 35 degrees C, respectively. Arrhenius plots constructed with cryophilic and mesophilic MVH:NR rate constants, in both presence or absence of FAD, showed break points at 15 and 25 degrees C, respectively. Essentially, similar results were obtained for purified enzymes and for activities measured in crude extracts. Factors by which the rate increases by raising temperature 10 degrees C (Q10) and apparent activation energy (E(a)) values for NADH and MVH activities measured in enzyme preparations without added FAD differed slightly from those measured with FAD. Overall thermal features of the NADH and MVH activities of the cryophilic NR, including optimal temperatures, heat inactivation (with/without added FAD) and break-point temperature in Arrhenius plots, are all shifted by about 10 degrees C towards lower temperatures than those of the mesophilic enzyme. Transfer of electrons from NADH to nitrate occurs via all three redox centres within NR molecule, whereas transfer from MVH requires Mo-pterin prosthetic group only; therefore, our results strongly suggest that structural modification(s) for cold adaptation affect thermodynamic properties of each of the functional domains within NR holoenzyme in equal measure.     

Lipids from the brown alga Cystoseira barbata

Two new diunsaturated lipids, related to palmitic acid, were isolated from the brown alga Cystoseira barbata, one of which is toxic to mice during P388 lymphocytic leukemia tests.     

Development of the insect pathogenic alga Helicosporidium

This study examined the morphogenesis and replication dynamics of the different life stages (cysts, filamentous cells, vegetative cells) of Helicosporidium sp., a non-photosynthetic, entomopathogenic alga. The isolate (SjHe) used originated from an infected black fly larva. Filamentous cell transformation into vegetative cells and autosporulation during vegetative cell replication were observed under controlled in vitro conditions. The transformation process was initiated by a partial swelling of the filamentous cell along with the reorganization of the nuclear material. Two subsequent nuclear and cell divisions resulted in the release of 4 rod-shaped daughter cells, which divided into oval to spherical vegetative cells. These underwent several cycles of autosporogenic cell division. Multiple-passaged vegetative cell cultures formed non-motile, adherent cell clusters (palmelloid colonies). Vegetative replication dynamics were also observed in 2 experimental noctuid hosts, Spodoptera exigua and Helicoverpa zea. The average density of helicosporidial cells produced per microliter hemolymph exceeded cell concentrations obtained in vitro by 15- and 46-fold in S. exigua and H. zea, respectively. Cyst morphogenesis was only observed in the hemolymph, whereas no cysts differentiated at various in vitro conditions.     

Polysaccharide of the red alga rissoella verruculosa

The Mediterranean red alga, Rissoella verruculosa, contains a K-like carrageenan. ¹³CNMR studies indicate that the polysaccharide contains neocarrabiose sulphate units alternating with non-sulphated neocarrabiose residues.     

Ribosomes from the blue-green alga Anabaena variabilis

Summary Extracts from the blue-green alga Anabaena variabilis were prepared by ultrasonic disintegration or by extrusion through a French pressure cell; examination by sucrose density gradient centrifugation and analytical ultracentrifugation indicated the existence of a procaryotic (70S) ribosome. However both the ribosomes and their sub-units were found to be relatively unstable after isolation and examination in tris buffer pH 7.4 but not in 10^-3 m-sodium phosphate buffer pH 7.0 containing 10^-1 m-potassium chloride. Experiments with ³²P and ³⁵S isotopes indicated that this instability was associated with the loss of ³⁵S labelled material, presumably therefore protein rather than nucleic acid. A comparison of behaviour with that of bacterial ribosomes is presented and the existence of certain similarities to ribosome preparations from chloroplasts of several plant species discussed.     

Trihydroxyphlorethols from the brown alga Carpophyllum angustifolium

The structural elucidation of four phloroglucinol derivatives isolated from the ethanolic extract of the brown alga Carpophyllum angustifolium after peracetylation is described. Three of them, trihydroxyheptaphlorethol-A octadecaacetate, trihydroxyoctaphlorethol-A eicosaacetate and trihydroxyoctaphlorethol-B eicosaacetate, are described for the first time. Characterized by three additional hydroxyl groups and two 1,2-diphenoxylated 3,4,5-triacetoxybenzene rings directly linked by an ether bond they are called trihydroxyphlorethols as a novel group of phlorotannins. The structural elucidation was carried out on the basis of spectral data.     

Tetraprenyltoluquinols from the brown alga Cystoseira stricta

Four novel metabolites of mixed biogenesis have been isolated from the brown alga Cystoseira stricta and their structures determined by chemical and spectral methods.     

Diterpenes from the brown alga Dictyota mertensii

Here we report the variation of diterpenes from three populations of the brown alga Dictyota mertensii. The populations were analyzed by ¹H NMR and GC-MS techniques. Both chemical GC-MS and ¹H NMR profiles of D. mertensii presented diterpenes as major constituents. In all populations, we detected the prenylated guaiane diterpenes, dictyoxide, pachydictyol A, isopachydictyol A, dictyol B and its acetate, and dictyol C. Although dictyol H has been described as a taxonomic marker, this diterpene was found in only two of the three studied populations. This result reinforces the need for studies of temporal and geographic variation for the establishment of the taxonomic limits of the species chemical patterns. It was also possible to observe mass spectra fragmentation and proton chemical shift in the NMR spectra characteristic from xeniane diterpenes, for the first time in this species, which led to the detection of dictyodial, suggesting that D. mertensii belongs to the chemotaxonomic group of species D. ciliolata, D. jamaicensis, and D. menstrualis, all of which are producers of diterpene from chemical groups I and III.     

Tetraprenyltoluquinols from the brown alga Cystophora fibrosa

Six cyclised tetraprenyltoluquinols and five stereoisomers with the previously reported amentol skeleton have been isolated from the lipophilic extract of the South African brown alga Cystophora fibrosa. Structures and relative stereochemistry were determined using spectrometric techniques, particularly 1D and 2D NMR, and molecular modelling experiments. The compounds isolated appear to be enantiomeric to compounds with the same skeleton isolated from brown algae of the genus Cystoseira collected in northern Africa and the Mediterranean Sea. The isolation of tetraprenyltoluquinols with the amentol skeleton from this alga suggests that C. fibrosa should be moved from the genus Cystophora into the Cystoseira.     

Sterols of the brown alga Sargassum fluitans

The sterol composition of the warm-water brown alga Sargassum fluitans Børgesen of the Gulf of Mexico was determined by TLC, GLC and IR measurements. The presence of over ten sterols was suggested, of which four (fucosterol, cholesterol, 24-methylenecholesterol, and trans- 22-dehydrocholesterol) were identified and four (a 24-methylcholesterol, a 24-ethylcholesterol, a 24-methyl-trans-22-dehydrocholestero 1 and a 24-ethyl-trans-22-dehydrocholesterol) were recognized but not definitively identified. Saringosterol and 24-ketocholesterol were not found. The crude sterol mixture from S. fluitans was oxidized by osmium tetroxide to 24-ketocholesterol in poor yield.     

A bromophenol in the red alga Halopitys incurvus

A new dibromophenol has been isolated from the acidified ethanolic extracts of the red alga Halopitys incurvus, and is shown to be 2,6-dibromo-3,5-dihydroxyphenylacetic acid, probably derived from a disulfate dipotassium salt.     

Sterols of the senegalese brown alga Padina vickersiae

Contrary to all the brown algae already studied for sterol content the Senegalese Padina vickersiae contains a great amount of cholesterol, chiefly in the later stages of growth. The seasonal variation of the sterols is studied and compared to other Phaeophyceae belonging to the genus Cystoseira.