Chloroplasts Of Algae Research Articles

Structure, biogenesis, and evolution of thylakoid membranes.

Cyanobacteria and chloroplasts of algae and plants harbor specialized thylakoid membranes (TMs) that convert sunlight into chemical energy. These membranes house PSII and I, the vital protein-pigment complexes that drive oxygenic photosynthesis. In the course of their evolution, TMs have diversified in structure. However, the core machinery for photosynthetic electron transport remained largely unchanged, with adaptations occurring primarily in the light-harvesting antenna systems. Whereas TMs in cyanobacteria are relatively simple, they become more complex in algae and plants. The chloroplasts of vascular plants contain intricate networks of stacked grana and unstacked stroma thylakoids. This review provides an in-depth view of TM architectures in phototrophs and the determinants that shape their forms, as well as presenting recent insights into the spatial organization of their biogenesis and maintenance. Its overall goal is to define the underlying principles that have guided the evolution of these bioenergetic membranes.

Food shaped photosynthesis: Photophysiology of the sea slug Elysia viridis fed with two alternative chloroplast donors.

Some Sacoglossa sea slugs steal and integrate chloroplasts derived from the algae they feed on into their cells where they continue to function photosynthetically, a process termed kleptoplasty. The stolen chloroplasts - kleptoplasts - can maintain their functionality up to several months and support animal metabolism. However, chloroplast longevity can vary depending on sea slug species and algal donor. In this study, we focused on Elysia viridis, a polyphagous species that is mostly found associated with the macroalga Codium tomentosum, but that was reported to eat other macroalgae, including Chaetomorpha sp. We have investigated the changes in E. viridis physiology when provided with the two different food sources to evaluate to which extent the photosynthetic and photoprotective mechanisms of the algae chloroplasts matched those of the plastids once in the animal cells. To perform the study, we rely on the evaluation of chlorophyll a variable fluorescence to study the photophysiological state of the integrated kleptoplasts and high-performance liquid chromatography (HPLC) to study variations in the photosynthetic pigments. We observed that the photosynthetic efficiency of E. viridis is lower when fed with Chaetomorpha. Also, significant differences were observed in the non-photochemical quenching (NPQ) abilities of the sea slugs. While sea slugs fed with C. tomentosum react similarly to high-light stress as the alga, E. viridis hosting Chaetomorpha chloroplasts were unable to properly recover from photoinhibition or perform a functional xanthophyll cycle (XC). Our results showed that, even if the sea slugs fed with the two algae show photosynthetic activities like the respective algal donors, not all the photoprotective mechanisms present in Chaetomorpha can be maintained in E. viridis. This indicates that the functionality of the kleptoplasts does not depend solely on their origin but also on the degree of compatibility with the animal species integrating them.

Structure and function of the Si3 insertion integrated into the trigger loop/helix of cyanobacterial RNA polymerase

Cyanobacteria and evolutionarily related chloroplasts of algae and plants possess unique RNA polymerases (RNAPs) with characteristics that distinguish them from canonical bacterial RNAPs. The largest subunit of cyanobacterial RNAP (cyRNAP) is divided into two polypeptides, β'1 and β'2, and contains the largest known lineage-specific insertion domain, Si3, located in the middle of the trigger loop and spanning approximately half of the β'2 subunit. In this study, we present the X-ray crystal structure of Si3 and the cryo-EM structures of the cyRNAP transcription elongation complex plus the NusG factor with and without incoming nucleoside triphosphate (iNTP) bound at the active site. Si3 has a well-ordered and elongated shape that exceeds the length of the main body of cyRNAP, fits into cavities of cyRNAP in the absence of iNTP bound at the active site and shields the binding site of secondary channel-binding proteins such as Gre and DksA. A small transition from the trigger loop to the trigger helix upon iNTP binding results in a large swing motion of Si3; however, this transition does not affect the catalytic activity of cyRNAP due to its minimal contact with cyRNAP, NusG, or DNA. This study provides a structural framework for understanding the evolutionary significance of these features unique to cyRNAP and chloroplast RNAP and may provide insights into the molecular mechanism of transcription in specific environment of photosynthetic organisms and organelle.

Food shaped photosynthesis: Photophysiology of the sea slug Elysia viridis fed with two alternative chloroplast donors

Background: Some Sacoglossa sea slugs integrate intracellular chloroplasts derived from the algae they feed on, a process termed kleptoplasty. The stolen chloroplasts – kleptoplasts – can maintain their functionality up to several months and support animal metabolism. However, chloroplast longevity can vary depending on sea slug species and algal donor. In this study, we focus our attention on Elysia viridis, a polyphagous species that is mostly found associated to the macroalga Codium tomentosum, but that was reported to eat other macroalgae, including Chaetomorpha sp. Methods: We have investigated the changes in E. viridis physiology when provided with the two different food sources to evaluate to which extent the photosynthetic and photoprotective mechanisms of the algae chloroplasts matched those of the plastids once in the animal cells. To perform the study, we rely on the evaluation of chlorophyll a variable fluorescence to study the photophysiologic state of the integrated kleptoplasts and the high-performance liquid chromatography (HPLC) to study variations in the photosynthetic pigments. Results: We observed that the photosynthetic efficiency of E. viridis specimens is similar to the one of the respective algal donor but specimens fed with Chaetomorpha tend to have lower performances. Significant differences appear in the non-photochemical quenching (NPQ) abilities. While sea slugs fed with C. tomentosum react to high-light stress as the algae, E. viridis hosting Chaetomorpha chloroplasts are unable to properly recover from photoinhibition or perform a functional xanthophyll cycle (XC). Conclusions: Our results showed that, even if the sea slugs fed with the two algae show photosynthetic activities like the respective algal donors, not all the photoprotective mechanisms present in Chaetomorpha can be maintained in E. viridis. This indicates that the functionality of the kleptoplasts does not depend solely on their origin but also on the degree of compatibility with the animal species integrating them.

Photodynamic control of harmful algal blooms by an ultra-efficient and degradable AIEgen-based photosensitizer

Harmful algal blooms (HABs) have a severe impact on human health, aquatic ecosystems, and the economy. There is still a lack of effective means to control algal blooms. Herein, TVP-A, a positively charged photosensitizer with aggregation-induced emission (AIE) characteristics is introduced as a super-efficient, cost-effective, and eco-friendly agent for the governance of HABs. TVP-A efficiently harvests white light to generate reactive oxygen species (ROS). Due to its positive surface charge, TVP-A has good water solubility and quickly adsorbs onto algal cells floating on the surface of water, triggering algal cell death through oxidative destruction of the nuclei and chloroplasts of algae. TVP-A is effective at low concentrations and requires sunlight irradiation periods of only a few minutes to destroy algal blooms, making it applicable for large scale algal bloom control under most weather conditions. Further, TVP-A is non-toxic to fish, mice or mammalian cells. The slow self-degradation of TVP-A during the photodynamic control of algal blooms prevents environmental accumulation or secondary pollution to ecological systems. TVP-A therefore serves as an excellent candidate for the green governance of HABs.

Reduction of nickel content from the model solution by consortium of fungal pellets and green algae

The accumulation of Ni from the model aqueous solution (100 mg/L) by pellets of Aspergillus niger (A. niger) together with the green algae Chlorella sp., as a microbial consortium, during five days was compared. In the experiment, already formed pellets were used (5 mL A. niger conidia in Sabouraud Dextrose Broth, shaked with 200 rpm for 5 days). The experiment was carried out under static and also dynamic conditions at 25 °C. Oxidation-Reduction-Potential (ORP) and pH were measured as well in the first, third and fifth days. Microbial consortium (A. niger with Chlorella sp.) was found always more effective – reduction of the Ni content was higher 48.95 mg/L (under static conditions) and 56.45 mg/L (dynamic conditions), pH values were medium acidic (5.84 static conditions), to weak acid (6.52 dynamic conditions). Monitored ORP values were significantly reduced in the range of -309 mV up to - 385 mV in the Ni model aqueous solution, when the both microorganisms were present. This reduction was attributed to the anoxic conditions occurred when the Reactive Oxygen Species (ROS) radicals were produced by the photoactive pigments in the algae chloroplasts.

Pyrenoid functions revealed by proteomics in Chlamydomonas reinhardtii.

Organelles are intracellular compartments which are themselves compartmentalized. Biogenic and metabolic processes are localized to specialized domains or microcompartments to enhance their efficiency and suppress deleterious side reactions. An example of intra-organellar compartmentalization is the pyrenoid in the chloroplasts of algae and hornworts. This microcompartment enhances the photosynthetic CO2-fixing activity of the Calvin-Benson cycle enzyme Rubisco, suppresses an energetically wasteful oxygenase activity of Rubisco, and mitigates limiting CO2 availability in aquatic environments. Hence, the pyrenoid is functionally analogous to the carboxysomes in cyanobacteria. However, a comprehensive analysis of pyrenoid functions based on its protein composition is lacking. Here we report a proteomic characterization of the pyrenoid in the green alga Chlamydomonas reinhardtii. Pyrenoid-enriched fractions were analyzed by quantitative mass spectrometry. Contaminant proteins were identified by parallel analyses of pyrenoid-deficient mutants. This pyrenoid proteome contains 190 proteins, many of which function in processes that are known or proposed to occur in pyrenoids: e.g. the carbon concentrating mechanism, starch metabolism or RNA metabolism and translation. Using radioisotope pulse labeling experiments, we show that pyrenoid-associated ribosomes could be engaged in the localized synthesis of the large subunit of Rubisco. New pyrenoid functions are supported by proteins in tetrapyrrole and chlorophyll synthesis, carotenoid metabolism or amino acid metabolism. Hence, our results support the long-standing hypothesis that the pyrenoid is a hub for metabolism. The 81 proteins of unknown function reveal candidates for new participants in these processes. Our results provide biochemical evidence of pyrenoid functions and a resource for future research on pyrenoids and their use to enhance agricultural plant productivity. Data are available via ProteomeXchange with identifier PXD004509.

Roles of Lipids in Photosynthesis.

Thylakoid membranes in cyanobacterial cells and chloroplasts of algae and higher plants are the sites of oxygenic photosynthesis. The lipid composition of the thylakoid membrane is unique and highly conserved among oxygenic photosynthetic organisms. Major lipids in thylakoid membranes are glycolipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol, and the phospholipid, phosphatidylglycerol. The identification of almost all genes involved in the biosynthesis of each lipid class over the past decade has allowed the generation and isolation of mutants of various photosynthetic organisms incapable of synthesizing specific lipids. Numerous studies using such mutants have revealed that these lipids play important roles not only in the formation of the lipid bilayers of thylakoid membranes but also in the folding and assembly of the protein subunits in photosynthetic complexes. In addition to the studies with the mutants, recent X-ray crystallography studies of photosynthetic complexes in thylakoid membranes have also provided critical information on the association of lipids with photosynthetic complexes and their activities. In this chapter, we summarize our current understanding about the structural and functional involvement of thylakoid lipids in oxygenic photosynthesis.

Improvement of chlorophyll identification in foodstuffs by MALDI ToF/ToF mass spectrometry using 1,5-diaminonaphthalene electron transfer secondary reaction matrix

Chlorophylls (Chls) are important pigments responsible for the characteristic green color of chloroplasts in algae and plants. In this study, 1,5-diaminonaphthalene (DAN) was introduced as an electron transfer secondary reaction matrix for the identification of intact chlorophylls and their derivatives, by matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS). DAN was proved to drastically outperform conventional matrices such as α-cyano-4-hydroxycinnnamic acid, dithranol, antracene, and even terthiophene, since loss of the metal ion and fragmentation of the phytol-ester linkage are negligible. Absence of significant fragmentation of radical cations of Chls a and b at m/z 892.529 and 906.513, respectively, makes MALDI MS capable of following natural degradation of intact porphyrin-based pigments whose initial steps are just represented by demetalation and dephytylation. Chl by-products, such as pyropheophytins, have been identified in dried tea leaves showing the potential of MALDI MS to follow chlorophyll biotransformation occurring in processed foodstuffs. Finally, preliminary results show the potential of MALDI MS to detect illegal vegetable oil re-greening practices.

The Primitive Thylakoid-Less Cyanobacterium Gloeobacter Is a Common Rock-Dwelling Organism.

Cyanobacteria are an ancient group of photosynthetic prokaryotes, which are significant in biogeochemical cycles. The most primitive among living cyanobacteria, Gloeobacter violaceus, shows a unique ancestral cell organization with a complete absence of inner membranes (thylakoids) and an uncommon structure of the photosynthetic apparatus. Numerous phylogenetic papers proved its basal position among all of the organisms and organelles capable of plant-like photosynthesis (i.e., cyanobacteria, chloroplasts of algae and plants). Hence, G. violaceus has become one of the key species in evolutionary study of photosynthetic life. It also numbers among the most widely used organisms in experimental photosynthesis research. Except for a few related culture isolates, there has been little data on the actual biology of Gloeobacter, being relegated to an “evolutionary curiosity” with an enigmatic identity. Here we show that members of the genus Gloeobacter probably are common rock-dwelling cyanobacteria. On the basis of morphological, ultrastructural, pigment, and phylogenetic comparisons of available Gloeobacter strains, as well as on the basis of three new independent isolates and historical type specimen, we have produced strong evidence as to the close relationship of Gloeobacter to a long known rock-dwelling cyanobacterial morphospecies Aphanothece caldariorum. Our results bring new clues to solving the 40 year old puzzle of the true biological identity of Gloeobacter violaceus, a model organism with a high value in several biological disciplines. A probable broader distribution of Gloeobacter in common wet-rock habitats worldwide is suggested by our data, and its ecological meaning is discussed taking into consideration the background of cyanobacterial evolution. We provide observations of previously unknown genetic variability and phenotypic plasticity, which we expect to be utilized by experimental and evolutionary researchers worldwide.

How to build functional thylakoid membranes: from plastid transcription to protein complex assembly.

Chloroplasts are the endosymbiotic descendants of cyanobacterium-like prokaryotes. Present genomes of plant and green algae chloroplasts (plastomes) contain ~100 genes mainly encoding for their transcription-/translation-machinery, subunits of the thylakoid membrane complexes (photosystems II and I, cytochrome b 6 f, ATP synthase), and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Nevertheless, proteomic studies have identified several thousand proteins in chloroplasts indicating that the majority of the plastid proteome is not encoded by the plastome. Indeed, plastid and host cell genomes have been massively rearranged in the course of their co-evolution, mainly through gene loss, horizontal gene transfer from the cyanobacterium/chloroplast to the nucleus of the host cell, and the emergence of new nuclear genes. Besides structural components of thylakoid membrane complexes and other (enzymatic) complexes, the nucleus provides essential factors that are involved in a variety of processes inside the chloroplast, like gene expression (transcription, RNA-maturation and translation), complex assembly, and protein import. Here, we provide an overview on regulatory factors that have been described and characterized in the past years, putting emphasis on mechanisms regulating the expression and assembly of the photosynthetic thylakoid membrane complexes.

Microbial Community Compositional Shifts in Bleached Colonies of the Brazilian Reef-Building Coral Siderastrea stellata

The association of metazoan, protist, and microbial communities with Scleractinian corals forms the basis of the coral holobiont. Coral bleaching events have been occurring around the world, introducing changes in the delicate balance of the holobiont symbiotic interactions. In this study, Archaea, bacteria, and eukaryotic phototrophic plastids of bleached colonies of the Brazilian coral Siderastrea stellata were analyzed for the first time, using 16S rRNA gene libraries. Prokaryotic communities were slightly more diverse in healthy than in bleached corals. However, the eukaryotic phototrophic plastids community was more diverse in bleached corals. Archaea phylogenetic analyses revealed a high percentage of Crenarchaeota sequences, mainly related to Nitrosopumilus maritimus and Cenarchaeum symbiosum. Dramatic changes in bacterial community composition were observed in this bleaching episode. The dominant bacterial group was Alphaproteobacteria followed by Gammaproteobacteria in bleached and Betaproteobacteria in healthy samples. Plastid operational taxonomic units (OTUs) from both coral samples were mainly related to red algae chloroplasts (Florideophycea), but we also observed some OTUs related to green algae chloroplasts (Chlorophyta). There seems to be a strong relationship between the Bacillariophyta phylum and our bleached coral samples as clones related to members of the diatom genera Amphora and Nitzschia were detected. The present study reveals information from a poorly investigated coral species and improves the knowledge of coral microbial community shifts that could occur during bleaching episodes.

Photosynthetic pigment localization and thylakoid membrane morphology are altered in Synechocystis 6803 phycobilisome mutants.

Cyanobacteria are oxygenic photosynthetic prokaryotes that are the progenitors of the chloroplasts of algae and plants. These organisms harvest light using large membrane-extrinsic phycobilisome antenna in addition to membrane-bound chlorophyll-containing proteins. Similar to eukaryotic photosynthetic organisms, cyanobacteria possess thylakoid membranes that house photosystem (PS) I and PSII, which drive the oxidation of water and the reduction of NADP+, respectively. While thylakoid morphology has been studied in some strains of cyanobacteria, the global distribution of PSI and PSII within the thylakoid membrane and the corresponding location of the light-harvesting phycobilisomes are not known in detail, and such information is required to understand the functioning of cyanobacterial photosynthesis on a larger scale. Here, we have addressed this question using a combination of electron microscopy and hyperspectral confocal fluorescence microscopy in wild-type Synechocystis species PCC 6803 and a series of mutants in which phycobilisomes are progressively truncated. We show that as the phycobilisome antenna is diminished, large-scale changes in thylakoid morphology are observed, accompanied by increased physical segregation of the two photosystems. Finally, we quantified the emission intensities originating from the two photosystems in vivo on a per cell basis to show that the PSI:PSII ratio is progressively decreased in the mutants. This results from both an increase in the amount of photosystem II and a decrease in the photosystem I concentration. We propose that these changes are an adaptive strategy that allows cells to balance the light absorption capabilities of photosystems I and II under light-limiting conditions.

The combined effect of anthracene and cadmium on photosynthetic activity of three Desmodesmus (Chlorophyta) species

Individual toxicity of heavy metals (HM) and polycyclic aromatic hydrocarbons (PAH) to plants living in water bodies is well-documented. In view of frequent joint occurrence of these compounds in the environment, plants are subjected to damage from their combined action. Cadmium and anthracene can generate production of reactive oxygen species (ROS). We have recently detected elevated activity of Fe- and Mn-SOD isoforms, indicating chloroplast and mitochondrion as the main sites of combined toxicity of HM and PAH. In the present paper, short-term (1–24h) experiments on the mechanism of combined toxicity of anthracene and cadmium to the photosynthesis of three Desmodesmus species are reported. Inhibition, stimulation or no effect on the oxygen evolution was observed following the treatment with the contaminants when applied either separately or jointly. The response pattern was both strongly species- and time-dependent. In contrast, the photosynthetic activity of cells, expressed by chlorophyll fluorescence parameters, was substantially unaffected, since no effect or, in several cases, a slight stimulation of PS II quantum efficiency (Φ PS II) were noted. A characteristic relationship between the SOD activity and the qN values was observed. The treatment of Desmodesmus cells with anthracene or cadmium had either no effect or slightly enhanced either the SOD activity or the qN value, whereas the mixture of the contaminants resulted in a multifold increase in both the SOD activity and the qN values. The results suggest that chloroplasts of algae are well protected against the combined action of the two contaminants the toxicity of which should be attributed to nucleocytoplasmic compartments and reproductive processes of the cell cycle.

A microbiotic survey of lichen-associated bacteria reveals a new lineage from the Rhizobiales

This study uses a set of PCR-based methods to examine the putative microbiota associated with lichen thalli. In initial experiments, generalized oligonucleotide-primers for the 16S rRNA gene resulted in amplicon pools populated almost exclusively with fragments derived from lichen photobionts (i.e., Cyanobacteria or chloroplasts of algae). This effectively masked the presence of other lichen-associated prokaryotes. In order to facilitate the study of the lichen microbiota, 16S ribosomal oligonucleotide-primers were developed to target Bacteria, but exclude sequences derived from chloroplasts and Cyanobacteria. A preliminary microbiotic survey of lichen thalli using these new primers has revealed the identity of several bacterial associates, including representatives of the extremophilic Acidobacteria, bacteria in the families Acetobacteraceae and Brucellaceae, strains belonging to the genus Methylobacterium, and members of an undescribed lineage in the Rhizobiales. This new lineage was investigated and characterized through molecular cloning, and was found to be present in all examined lichens that are associated with green algae. There is evidence to suggest that members of this lineage may both account for a large proportion of the lichen-associated bacterial community and assist in providing the lichen thallus with crucial nutrients such as fixed nitrogen.

Community composition of the marine bacterioplankton in Kongsfjorden (Spitsbergen) as revealed by 16S rRNA gene analysis

Phylogenetic diversity of the marine bacterioplankton in Kongsfjorden (Spitsbergen) was investigated by 16S rRNA gene analysis. Community fingerprint analysis by PCR-denaturing gradient gel electrophoresis revealed that there was no apparent difference of bacterioplankton community composition between sampling locations in the fjord. A higher biodiversity was observed in bottom water of station 3 in the central part of the fjord. By 16S rRNA gene clone library analysis, sequences detected both in surface and bottom water of station 3 fell into eight putative divisions, including Proteobacteria (Alpha, Beta, Gamma and Delta), Bacteroidetes, Actinobacteria, Verrucomicrobia and unidentified bacteria, in addition to chloroplasts of algae. Sequences representing Planctomycetes were only observed in bottom water. Compared to the preponderance of clones representing Gammaproteobacteria (36.5%) and Alphaproteobacteria (29.4%) in bottom water, Alphaproteobacteria (43.6%) and algae (27.7%) constituted two dominant fractions in surface water. Cloned sequences showed 82.1–100% similarity to those described sequences. It suggests that, attributing to the influence of ocean currents as well as freshwater input in the summer, the bacterial community in Kongsfjorden may consist of a mixture of cosmopolitan and uniquely endemic phylotypes.

Not so simple after all

Biologists have long thought that the internal workings of prokaryotes—the smallest and simplest organisms, including bacteria—are well understood, and have accordingly considered eukaryotic organisms and their cells to be more fascinating objects for study. During the past decade, however, the focus of some research has begun to turn back to prokaryotes—particularly because genomic analyses have shown the enormous flexibility and adaptability of these seemingly simple organisms. Moreover, recent structural research has shown that the cell components of prokaryotes might also be more complex than previously thought. It has long been held that prokaryotic cells lack the internal structure and organization of eukaryotic cells, which have various membrane‐bound organelles, such as mitochondria, chloroplasts and the nucleus. Indeed, prokaryotes are assumed to be the predecessors of some eukaryotic organelles—permanently captured after a period of endosymbiosis. > …there is no rule that says an organelle must be enclosed by a membrane The view that bacterial cells are structurally simpler than those of ‘higher’ organisms is reflected in many text books and web sites with comments such as: “the ribosome is the only prokaryotic organelle”—if, indeed, this highly complex and sophisticated protein‐synthesizing machinery is an organelle in its own right. These types of statement are correct in the sense that prokaryotes contain no membrane‐bound organelles; but there is no rule that says an organelle must be enclosed by a membrane. Many eukaryotic ribosomes are freely suspended in the cytoplasm where they manufacture cytosolic proteins. Furthermore, the word ‘organelle’ itself is being replaced by the terms ‘functional unit’ or ‘compartment’, which are increasingly used to describe coherent structures within a cell that perform clearly defined sets of tasks—such as mitochondria, which create energy by aerobic respiration, or chloroplasts, which do so by photosynthesis. By using this definition, a series of recent discoveries show that prokaryotes also …

TRANSLATION REGULATION OF INTRON-CONTAINING GENES IN CHLOROPLASTS

The paper provides a short description of the originally developed algorithm for searching of the conservative protein-RNA binding sites. The algorithm is applied to analyze chloroplast genes. The candidate protein-RNA binding sites were detected upstream of atpF, petB, clpP, psaA, psbA, and psbB genes in many chloroplasts of algae and plants. We suggest that some of these sites are involved in suppressing translation until splicing is completed.

Translation of some chloroplast genes is checked to allow for splicing and editing

The expression of some genes in the chloroplasts of algae and plants is regulated by the binding of nuclear-coded proteins to the mRNA. Previously, we have found and studied the candidate sites for protein binding to the 5′-untranslated regions (UTRs) of atpF, petB, clpP, psaA, psbA, and psbB genes in algal and plant chloroplasts, and traced the evolution of these sites. It was suggested that some of these sites are involved in a mechanism suppressing translation until the gene splicing is completed. These sites in the 5′-UTRs of petB, clpP, psaA, and psbA genes include a conserved helix, while those of the two remaining sites consist of several boxes devoid of this helix. This paper considers the assumption that long hairpins in the 5′-UTR near the ribosome-binding site are involved in translation suppression until the completion of editing the accD and atpH gene transcripts in the chloroplast of plant genera Adiantum and Anthoceros.

Comparison of Fatty Acid Composition of Cell Homogenates and Isolated Chloroplasts in Acetabularia crenulata (Lamouroux)

Algal preparations from Acetabularia crenulata were analyzed for their fatty acid composition to establish the suitability of this alga as a model to study fatty acid oxidation and oxylipin biosynthesis. The work was based on two goals. The first goal of this study was to determine the contribution of fatty acids from contaminating bacteria and how this influenced the total fatty acid composition of cell homogenates of A. crenulata collected in the wild as compared to specimens cultured in sterile conditions. The major fatty acids detected for both specimens were palmitic (C16:0), palmitoleic (C16:1n-7), oleic (C18:1n-9), linoleic (C18:2n-6), linolenic (C18:3n-3), and octadecatetraenoic acid (C18:4n-3). Significant amounts of odd-chain fatty acids common to bacteria were not detected in either sample. Furthermore, branched-chain fatty acids, typical bacterial biomarkers, were not detected in either sample. Data suggest that bacteria do not greatly contribute to the total fatty acid pool of A. crenulata. The second goal was to compare the fatty acid composition of cell homogenates with that of isolated chloroplasts. Comparatively speaking palmitoleic and octadecatetraenoic acid were found at significantly lower concentrations in the chloroplast whereas oleic and linolenic acid were found at significantly higher amounts in this organelle. Furthermore, the amount of hexadecatrienoic acid (C16:3), a fatty acid commonly esterified to monogalactosyldiacylglycerol (MGDG; lipid present at high concentrations inside the chloroplasts of algae), was present at very low concentrations in these plastids (0.7%). Typically green algal follow the "prokaryotic pathway" for MGDG biosynthesis where C18:3 is esterified at the sn-1 position of the glycerol backbone and C18:3 or C16:3 at the sn-2 position, making C16:3 a major fatty acid inside chloroplasts. Interestingly, our results suggest that chloroplasts of A. crenulata appear to follow the "eukaryotic pathway" for MGDG biosynthesis where C18:3 is both at the sn-1 and sn-2 position of MGDG. Taking into account the exceptions noted, the fatty acid composition for A. crenulata is similar to that reported for most chlorophytes.