Chloroplasts Of Algae Research Articles

TmRDB (tmRNA database).

The tmRNA database (tmRDB) is maintained at the University of Texas Health Science Center at Tyler, Texas, and accessible on the World Wide Web at the URL http://psyche.uthct.edu/dbs/tmRDB/tmRDB.++ +html. Mirror sites are located at Auburn University, Auburn, Alabama (http://www.ag.auburn.edu/mirror/tmRDB/) and the Institute of Biological Sciences, Aarhus, Denmark (http://www.bioinf.au. dk/tmRDB/). The tmRDB provides information and citation links about tmRNA, a molecule that combines functions of tRNA and mRNA in trans-translation. tmRNA is likely to be present in all bacteria and has been found in algae chloroplasts, the cyanelle of Cyanophora paradoxa and the mitochondrion of the flagellate Reclinomonas americana. This release adds 26 new sequences and corresponding predicted tmRNA-encoded tag peptides for a total of 86 tmRNAs, ordered alphabetically and phylogenetically. Secondary structures and three-dimensional models in PDB format for representative molecules are being made available. tmRNA alignments prove individual base pairs and are generated manually assisted by computational tools. The alignments with their corresponding structural annotation can be obtained in various formats, including a new column format designed to improve and simplify computational usability of the data.

Biosynthesis of carotenoids in the chloroplasts of algae and higher plants.

Physiological, biochemical, and genetic aspects of carotenoid biosynthesis in the chloroplast membranes of green algae and higher plants are discussed starting from the earliest stages of biosynthesis of key C5-isoprene units. The latter are synthesized either from acetate (C2) to mevalonic acid (C6) or from glucose (C6) by forming glyceraldehyde 3-phosphate (C3) and pyruvate decarboxylation product (C2) through intermediate compounds to isopentenyl diphosphate (C5). In all organisms, the further carotenoid synthesis from isopentenyl diphosphate and its isomer dimethylallyl diphosphate (C5) proceeds through their transformation into geranyl diphosphate (C10), farnesyl diphosphate (C15), geranylgeranyl diphosphate (C20) and phytoene (C40). Phytoene desaturation (dehydrogenation) to carotene, neurosporene, and lycopene, and all steps of their cyclization to α, β and e carotenes are discussed in detail. The synthesis of xanthophylls in chloroplasts is presented as the sequential formation of hydroxy-, epoxy- and oxo- groups. Genetic control of biosynthesis, as well as the localization and functional role of carotenoids in the chloroplast membranes of plants and algae are briefly discussed.

An unspliced group I intron in 23S rRNA links Chlamydiales, chloroplasts, and mitochondria.

Chlamydia was the only genus in the order Chlamydiales until the recent characterization of Simkania negevensis Z(T) and Parachlamydia acanthamoebae strains. The present study of Chlamydiales 23S ribosomal DNA (rDNA) focuses on a naturally occurring group I intron in the I-CpaI target site of 23S rDNA from S. negevensis. The intron, SnLSU. 1, belonged to the IB4 structural subgroup and was most closely related to large ribosomal subunit introns that express single-motif, LAGLIDADG endonucleases in chloroplasts of algae and in mitochondria of amoebae. RT-PCR and electrophoresis of in vivo rRNA indicated that the intron was not spliced out of the 23S rRNA. The unspliced 658-nt intron is the first group I intron to be found in bacterial rDNA or rRNA, and it may delay the S. negevensis developmental replication cycle by affecting ribosomal function.

L- myo-Inositol 1-phosphate synthase from Entamoeba histolytica

l- myo-Inositol 1-phosphate synthase (I-1-P synthase) catalyses the primary reaction for the synthesis of inositol in a variety of prokaryotes, eukaryotes and in the chloroplasts of algae and higher plants. Inositol is a precursor of essential macromolecules like membrane phospholipids, GPI anchor proteins and lipophosphoglycans, which play a determinant role in the pathogenesis of protozoan parasites such as Leishmania and Entamoeba. However, there is no report of I-1-P synthase or its gene from these organisms. The gene INO1 coding for this enzyme was first cloned from Saccharomyces cerevisiae and subsequently from several plants. Using molecular cloning techniques we have isolated and characterised the INO1 gene coding for the enzyme I-1-P synthase from Entamoeba histolytica. Simultaneously, we have purified and characterised the native enzyme from E. histolytica trophozoites and the cloned gene product from Escherichia coli. The gene product and the purified enzyme were both shown to be recognised by a heterologous anti-I-1-P synthase antibody from the phytoflagellate Euglena gracilis. Phylogenetic analysis of I-1-P synthase sequences from different eukaryotes suggest that it is highly conserved across species and the origin of this enzyme precedes the evolutionary divergence of modern eukaryotes.

Symbiosis between Nitrogen-Fixing Cyanobacteria and Plants

T he cyanobacteria (blue-green algae) are a morphologically diverse group of Gram-negative prokaryotes within the domain Bacteria (Giavannoni et al. 1988). This group includes unicellular forms, filamentous forms that contain only vegetative cells, and filamentous forms that differentiate specialized cells (Castenholz and Waterbury 1989). Cyanobacteria are photoautotrophs with an oxygenevolving photosynthetic mechanism that is identical to that of chloroplasts of algae and higher plants. Indeed, molecular genetic evidence strongly supports the idea that a recent ancestor(s) in the cyanobacterial evolutionary line gave rise to chloroplasts (Douglas 1994). Many cyanobacteria fix atmospheric nitrogen, which is an oxygen-sensitive process; they fix nitrogen either under low-oxygen growth conditions or, when in air, in specialized cells called heterocysts (Fay 1992). As a group, oxygenic photoautotrophic cyanobacteria, especially those species that fix nitrogen, are the most nutritionally independent organisms in the biosphere. Because of this nutritional independence, as well as their tolerance to physicochemical extremes,

A ribosomal protein in Acanthamoeba polyphaga is conserved in eukaryotic nuclei, organelles and bacteria.

An EcoRI fragment from the mitochondrial DNA of Acanthamoeba polyphaga was cloned and partly sequenced, and the conceptual translation product of the open reading frame (partial sequence) was found to have similarities with rp114, a ribosomal protein. Phylogenetic analysis based on the amino acid (aa) sequences of this conserved protein resolved four branches that consisted of: (1) eubacteria and the chloroplasts of algae and higher plants, (2) ciliate mitochondria, (3) Acanthamoeba, and (4) archaebacteria and the nuclei of eukaryotes. The groupings based on the rp114 aa sequences were consistent with the phylogenies derived by rRNA analysis of these organisms.

δ-Aminolevulinic acid biosynthesis in Escherichia coli and Bacillus subtilis involves formation of glutamyl-tRNA

Cell-free extracts of Escherichia coli and Bacillus subtilis catalyzed the tRNA-dependent, RNase A-sensitive formation of delta-aminolevulinic acid (ALA) from glutamate. Cell extracts prepared from cultures of E. coli grown under aerobic or anaerobic conditions had similar levels of ALA biosynthetic activity. Both the tRNA-stimulated conversion of glutamate to ALA and the conversion of glutamate-1-semialdehyde to ALA were inhibited by gabaculin. However, gabaculin had no effect on the growth of either E. coli or B. subtilis. The tRNA-dependent transformation of glutamate to ALA in E. coli and B. subtilis thus appears to be very similar to the pathway found in cyanobacteria, certain obligate anaerobic eubacteria, archaebacteria and in the chloroplasts of algae and higher plant species.

δ-Aminolevulinic acid biosynthesis inEscherichia coliandBacillus subtilisinvolves formation of glutamyl-tRNA

Cell-free extracts of Escherichia coli and Bacillus subtilis catalyzed the tRNA-dependent, RNase A-sensitive formation of delta-aminolevulinic acid (ALA) from glutamate. Cell extracts prepared from cultures of E. coli grown under aerobic or anaerobic conditions had similar levels of ALA biosynthetic activity. Both the tRNA-stimulated conversion of glutamate to ALA and the conversion of glutamate-1-semialdehyde to ALA were inhibited by gabaculin. However, gabaculin had no effect on the growth of either E. coli or B. subtilis. The tRNA-dependent transformation of glutamate to ALA in E. coli and B. subtilis thus appears to be very similar to the pathway found in cyanobacteria, certain obligate anaerobic eubacteria, archaebacteria and in the chloroplasts of algae and higher plant species.

The route of entry of cytoplasmic ally synthesized proteins into: Chloroplasts of algae possessing chloroplast ER

In 8 classes of algae, namely the Cryptophyceae, Raphidophyceae, Haptophyceae, Chrysophyceae, Bacillariophyceae, Xanthophyceae, Eustigmatophyceae and Phaeophyceae, the chloroplasts, in addition to being surrounded by a double-membraned chloroplast envelope, are also enclosed by a cisterna of endoplasmic reticulum called the chloroplast ER. Often this ER cisterna is continuous with the outher membrane of the nuclear envelope in such a manner that the nuclear envelope forms a part of the ER sac enclosing the chloroplast. In all these classes of algae except the Cryptophyceae, a regular network of tubules and vesicles, named the periplastidal reticulum, is present at a specific location between the chloroplast envelope and the chloroplast ER. In the Cryptophyceae, scattered vesicles are found between the chloroplast envelope and the chloroplast ER. Ribosomes which have been shown to be arranged to polysomes are found on the outer membrane of the chloroplast ER. It is proposed that nuclear-coded proteins which are destined for the chloroplast are synthesized on these polysomes, passing during synthesis into the lumen of the ER cisterna. Vesicles containing these proteins then pinch off the chloroplast ER and form the periplastidal reticulum. Vesicles containing these proteins then pinch off the chloroplast ER and form the periplastidal reticulum. Vesicles then fuse with the outer membrane of the chloroplast envelope thereby delivering their contents to the lumen of the chloroplast envelope. Proteins then cross the inner membrane of the chloroplast envelope in an as yet unknown manner. Experimental evidence for this hypothesis comes from studies on Ochromonas danica using chloramphenicol and spectinomycin, which inhibit protein synthesis on plastid ribosomes, and cycloheximide, which inhibits protein synthesis on cytoplasmic ribosomes. In cells of Ochromonas exposed to chloramphenicol or spectinomycin, the periplastidal reticulum proliferates markedly becoming several layers thick. Presumably this build up of periplastidal reticulum occurs because the transport of cytoplasmically synthesized plastid proteins is slowed down when protein synthesis in the chloroplast is inhibited. Conversely, when cells of Ochromonas are treated with cycloheximide, there is a reduction in the amount of periplastidal reticulum presumably because there are no cytoplasmically synthesized proteins to be transported into the chloroplast.

HETEROGENEITY OF THE PHOTOCHEMICAL CENTERS IN SYSTEM II OF CHLOROPLASTS*

Abstract— In 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas.Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a‐component, and a relatively slow β‐component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.

Deoxyribonucleic acid-dependent incorporation of amino acids into the proteins of chloroplasts isolated from anucleate Acetabularia fragments

Isolated chloroplasts from anucleate fragments of Acetabularia actively incorporate a mixture of radioactive amino acids into proteins. This incorporation is inhibited by chloramphenicol and puromycin but appears to be relatively insensitive to streptomycin, ribonuclease (EC 2.7.7.16) and deoxyribonuclease (EC 3.1.4.5). Actinomycin D, at a concentration of 166 μg/ml, totally inhibits the incorporation of amino acids by chloroplasts of algae enucleated 11 days previously. It is concluded that, at this time, the synthesis of chloroplastic proteins is dependent on chloroplastic deoxyribonucleic acid.

The ultrastructure of the chloroplasts of algae

The ultrastructure of the chloroplasts of 13 species of algae belonging to seven divisions is described. The chloroplasts of all the species studied are limited by a narrow double membrane and contain a granular matrix material made up of dense particles 90–150 A in diameter. Scattered lipidlike globules are present in the chloroplasts of all species. Starch grains are present only in the chloroplasts of green algae. The lamellar structures in all these chloroplasts are membrane-enclosed discs or flattened sacs. In the Rhodophyta the discs occur singly; in all the other divisions they are stacked together into bands. In the Cryptophyta, bands of two discs predominate; in the Chrysophyta, Pyrrophyta, and Phaeophyta, bands of three discs predominate. In the Chlorophyta and Euglenophyta, the number of discs per band is more variable, but is most commonly between two and six. In the Chrysophyta and Pyrrophyta, the bands are usually very compressed; the discs are narrower than in other groups and are very tightly appressed. In the Cryptophyta and Phaeophyta, the discs are loosely associated and have a distinct 20–30 A space between them. When cells of Ochromonas danica are fixed in potassium permanganate in order to resolve unit membrane structure, the chloroplast discs are seen to be collapsed internally as well as appressed together externally.