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PubMed1985

Enzymic ribonucleoside reduction at the non-phosphorylated level in Acetabularia.

The occurrence of an enzyme that catalyses the conversion of cytidine into deoxycytidine was demonstrated in homogenates of Acetabularia. Cytidine was identified as the substrate by comparing cytidine, cytidine 5'-monophosphate, cytidine 5'-diphosphate and cytidine 5'-triphosphate as potential substrates. Experiments with ATP analogues whose inhibitory effect on kinase reactions is well established, supplied evidence that the nucleoside is reduced without a phosphorylation step before the reduction. Further evidence in this line came from incubations with cytidine in the presence of phosphatase and from trap-type experiments in which the effects of excess non-labelled cytidine 5'-phosphate and deoxycytidine, respectively, on the formation of deoxycytidine phosphates from cytidine were studied.

Acetabularia↗
PubMed1988

Magnetic resonance imaging approaching microscopic scale: maturation stages of Acetabularia mediterranea reproductive caps.

The reproductive cap of the giant single-celled alga Acetabularia mediterranea (or A. acetabulum) has rays tapering from a width of about 400 microns at the circumference of the cap to about 30 microns at their junction with the stalk of the cell. This is ideal geometry for testing the current limits of spatial resolution of proton magnetic resonance imaging. In this work, resolution of features down to 40 microns is achieved. Maturation of the cap rays involves a major cytoplasmic reorganization, from continuous cytoplasm and a central vacuole in each ray to bundles of cysts surrounded by aqueous solution. This work shows that an intermediate stage in the change can be highlighted in images by relaxation time (T1) contrasting.

Acetabularia↗
PubMed1994

[Roles of anions in cells: studies on a Cl(-)-translocating ATPase and sulfate uptake system in Acetabularia acetabulum].

Biochemical and molecular biological approaches to two anion translocators, a Cl(-)-translocating ATPase and sulfate permease were described for Acetabularia acetabulum, a unicellular marine alga. The primary structures of an almost complete cDNA clone of the 50 kDa subunit and a partial cDNA clone of the 54 kDa subunit of the Cl(-)-ATPase were highly similar to the beta and alpha subunits of the F type ATPase, respectively. A partial cDNA clone encoding the alpha subunit of chloroplast ATPase, and partial cDNA clones coding for the beta subunits of chloroplast and mitochondrial ATPases were also obtained from A. acetabulum. The presence of a small multigene family for the F type ATPases with different ion specificities was strongly suggested for the organism. Sulfate uptake system in this organism was also studied and partial cDNA clones encoding CysA and sulfate binding proteins were obtained. ca. 1.7 kb RNA for cysA gene and 1.55 kb for sbp gene were detected by Northern analysis, respectively. A putative malK gene was also partially cloned.

Acetabularia↗
PubMed1994

Chloroplast ATPase in Acetabularia acetabulum: purification and characterization of chloroplast F1-ATPase.

ATPases were isolated from chloroplasts of the unicellular marine alga Acetabularia acetabulum. Two preparations of ATPase, a chloroplast-enriched fraction and an alpha beta gamma-complex were compared. The alpha beta gamma-complex was released into an EDTA solution and purified by anion-exchange chromatography, hydrophobic chromatography, and gel permeation chromatography. The subunit composition of this enzyme appeared to be 52-53 (alpha), 51 (beta), and 40 (gamma) kDa from SDS-PAGE. ATPase activity was enriched about 260-fold to a specific activity of approximate 4.1 U.mg protein-1. The catalytic properties of the alpha beta gamma-complex were as follows: pH optimum at 7.5; substrate specificity, ATP > ITP, GTP > UTP = CTP (Km for ATP 0.2 mM); divalent cation requirement, Mg2+ = Mn2+ = Co2+ > Zn2+ > Ni2+ > Ca2+; ATPase activity was inhibited by monovalent anions (NO3-, SCN-), while monovalent cations had neither inhibitory nor stimulatory effect. Orthovanadate had no inhibitory effect on the enzyme activity of alpha beta gamma-complex. Azide was the most effective inhibitor of the alpha beta gamma-complex. N-Terminal amino acid sequences of the alpha and beta subunits were not obtained and appeared to be blocked. The gamma subunit gave a sequence of AGLKEMKD-XIGSVXNTKKI, which showed 60% similarity to the gamma subunits of spinach and Chlamydomonas reinhardtii CF1-ATPase and EF1-ATPase.

Acetabularia↗
PubMedDate not supplied

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.

Acetabularia↗
PubMed1994

High-resolution measurement of circadian periodicities in Acetabularia.

Well-expressed endogenous circadian rhythms in Acetabularia acetabulum were spectrally analyzed and recorded in time-period distributions. The stability of the circadian periods under constant conditions and their changes could be monitored continually in step sizes close to the circadian period length. The resolution of period estimates of the circadian component was increased by a factor of approximately 4-10 by adapting analyzed interval lengths to full period sizes of the corresponding main component. Methodological aspects of the applied algorithms are discussed by means of examples that measure the temperature dependency of the circadian period.

Acetabularia↗
PubMed1996

Decreasing period-length of the endogenous circadian rhythm of oxygen evolution in Acetabularia and its possible relation to aging.

Endogenous circadian rhythms observed under constant conditions normally show period length variations. However, a general trend is difficult to identify when cells or organisms are entrained with the usual 24-h-period light/dark cycles. Therefore, these variations in time have been considered as fluctuations. In order to gain more insight into this phenomenon, individual Acetabularia cells were exposed to light/dark cycles of 16 h (LD 8:8) and 33.6 h (LD 16.8:16.8), respectively, i.e., periods which lie distinctly outside the range of the normal circadian entrainment. Employing a high-resolution procedure for data analysis, decreasing period lengths could consistently be detected when cells were kept under constant conditions for several weeks. Possible causes of this decrease are discussed.

Acetabularia↗
PubMed1976

[Ultrathin structure of normally growing and regenerating cells of Acetabularia mediterranea].

The ultrastructure of nucleus and cytoplasm in regenerating cells of Acetabularia mediterranea differs from that in normally growing ones: the nucleus of regenerating cells form numerous outgrowths; the cortical layer of nucleolus disintegrates markedly; the emission of nucleolar material in the nucleoplasm is observed. In the cytoplasm the portion of active chloroplasts increases and a great number of tubular fibrils appears. In the cytoplasm of regenerating cells the Golgi dictyosomes occur more frequently and the vesicles at their ends are larger than in that of normally growing cells. The changes of macromolecular organization of the nucleus and cytoplasm in question observed at the earlier stages of regeneration (2--12 hrs) suggest the increase of metabolic activity of cells.

Acetabularia↗
PubMed1976

[Species specificity of morphogenetic factors of Acetabularia, localized in the cytoplasmic zone adjacent to the cell membrane].

The species specificity of the factors controlling the cap development was established in the experiments with the transplantation of both the intact and centrifuged in the basal direction apical regions of Acetabularia meditteranea on nuclear basal regions of A. crenulata. These factors are found at the stage of 72 hrs of regeneration primarily in the cytoplasmic zone adjacent to the cell membrane which is not displaced during centrifugation. Using direct measurements and radiochemical method, we have shown that the accumulation of proteins proceeded in this zone due, mainly, to their transition from the cytoplasmic zone displaced during centrifugation.

Acetabularia↗
PubMed1975

[Role of the cell nucleus in the mechanism of the effect of auxin on Acetabularia mediterranea].

The effect of an auxin, naphthyl acetic acid (NAA), upon nuclear and anuclear fragments of adult Acetabularia cells was studied. In the darkness, NAA stimulated the release from the nucleus to the cytoplasm of informational agents programming the formation of caps and exerted no marked effect upon the anuclear fragments. NAA activated RNA synthesis and accelerated the decrease of its content in the nucleus. A suggestion is put forward to the effect that NAA influences the morphogenesis (cap regeneration) while strengthening the synthesis and passage from the nucleus to the cytoplasm of agents, apparently, of ribonucleic nature responsible for the formation of caps.

Acetabularia↗
PubMed1975

[Polar distribution of RNA in the cytoplasm of Acetabularia mediterranea].

The distribution of total RNA and its individual fractions in two regions of Acetabularia mediterranea stem during regeneration was investigated. During regeneration of both the nuclear and enucleated cells, RNA concentration increases in the cytoplasm of growth zone whereas it changes insignificantly in the central stem region. A study of the qualitative RNA composition in the same stem regions has shown that during regeneration high molecular weight RNA fractions (main peaks - 0,56-10(6) and 1.04-10(6) Dalton) are found in the growth zone and are practically absent from the central cell region. Low molecular weight RNA (supposedly, tRNA and products of RNA destruction) are present in both the cell regions under study.

Acetabularia↗
PubMed1975

[Photic induction of polar growth in enucleated fragments of Acetabularia mediterranea].

The process of induction of polarity in enucleated fragments (EF) of Acetabularia mediterranea has been studied by the method of local illumination. A device is described which allows to illuminate one part of EF at 2, 500 lx and another at 5 lx. The local illumination of a part of EF during 10-24 hrs was shown to polarize with a high probability the subsequent growth and formation of caps at the subsequent uniform illumination. Using the method of successive illumination and darkening of apical and basal portions of EF, it was shown that the initial stages of induction were partially reversible and the complete determination of polarity took place after the initiation of the cap anlage. After the short-term induction by light (2500 lx), the darkening of the growth zone inhibits completely the process of cap initiation, but already at 100 lx the EF previously induced at 2 500 lx are initiated and grow. While using the local illumination of grafts of EF from two species, A. crenulata and A. mediterranea, with their subsequent fragmentation and the analysis of cap morphology, it was shown that the induction of polar growth did not provide the directed transport of the factors controlling morphogenesis to the future growth zone.

Acetabularia↗
PubMed2003

Oscillations in ultraweak photon emission of Acetabularia acetabulum (L.).

Ultraweak photon emission of dark-incubated A. acetabulum cells were measured with the use of a sensitive electronphotomultiplier of the Hamamatsu 550 type. The photon count series were subjected to Fourier analysis for 2-1020 sec period range. The average level of photon emission in samples containing 50 cells was approximately. 40% above background. Cell cultures were prepared at least 24 hr before the photon emission measurements and kept un-disturbed ("established cultures"). This paper reports results of Fourier analysis of a number of samples of Acetabularia cells. In a single population cells periodicity of light emission was not defined directly from Fourier transformation. A large number of analyses, however, if they are combined and compared with background data, reveal a cell-culture specific frequency pattern. The results suggest the idea that established cell-cultures are characterized by higher intensities of long period (minutes) oscillations occurs, while a relative decrease was observed in the short period (few seconds) range. The long period oscillations were not detected in cell cultures that were prepared within 1 hr before the photon emission measurements. It is concluded that Fourier analysis of ultraweak photon emission, even with relatively low signals, appears to be possible. It may serve as a non-invasive tool for monitoring the physiological state of cells, or for studying the control of intercellular dynamics.

Acetabularia↗
PubMed1977

[Some pathways of biosynthesis and degradation of polyphosphates from green algae Acetabularia mediterranea].

The activity of ATP: polyphosphate phosphotransferase was detected in free-cellular extracts of Acetabularia mediterranea. The enzyme activity in cells originally deficient in phosphorus and subsequently transferred into the phosphate-containing medium increases 5-10-fold as compared to normal. Polyphosphate degradation in A. mediterranea is probably produced by polyphosphatase, which was also detected in the free-cellular extract. It was shown that the polyphosphatase activity has two pH optima, i.e. 4.5 and 7.5, and is considerably increased when the cells are transferred into the phosphate-free medium. It is assumed that high-molecular polyphosphates involved in A. Mediterranea metabolism are responsible for regulation of orthophosphate and ATP level in the cells by ATP: polyphosphate phosphotransferase and polyphosphatase.

Acetabularia↗
PubMed1977

[Isoenzyme makeup of the malate dehydrogenase in 2 species of Acetabularia].

The isozymes of malate dehydrogenase (MDH) were studied by means of electrophoresis in polyacrilamide gel in Acetabularia crenulata and A. mediterranea. The isozyme profile of MDH was shown to be variable in different parts of the plant. Distinct differences in isozyme profiles of MDH between A. crenulata and A. mediteranea were found when studying the cell fractions which consisted mainly of chloroplasts. The chloroplast fraction of A. mediterranea contained 8 isozymes which form 2 groups with different electrophoretic mobility. The chloroplast fraction of A. crenulata contained 9 isozymes. All the isozymes of the first group were common for both the species under study.

Acetabularia↗
PubMed1988

Role of the cytochrome b6.f complex in the redox-controlled activity of Acetabularia thylakoid protein kinase.

The regulation of the protein kinase activity responsible for the phosphorylation of the light-harvesting complex of photosystem II (LHCII) 27-kDa polypeptide involved in the State I-State II transitions in Acetabularia thylakoids was investigated. The LHCII kinase of isolated thylakoids retains its activity in absence of light-driven electron flow or reductants added in the dark. However, the kinase is reversibly inactivated by addition of oxidants in vitro or by far red (710 nm) light in vivo. Inhibitors of the quinol oxidase site of the cytochrome b6.f complex inactivate the LHCII kinase in the dark, and also in the light, or in presence of duroquinol when the plastoquinone pool is reduced. Inhibitors of the quinone reductase site of the b6.f complex have practically no effect in the dark and stimulate the kinase activity in the light. Based on these data and on our previous report, showing specific loss of LHCII kinase activity in a Lemna mutant lacking the cytochrome b6.f complex (Gal, A., Shahak, Y., Schuster, G., and Ohad, I. (1987) FEBS Lett. 221, 205-210), we propose that the activity of the LHCII kinase is regulated by the redox state of a cytochrome b6.f complex component(s) which responds to the balance of electron flow from photosystem II via the plastoquinone pool to photosystem I.

Acetabularia↗
PubMed1974

[Morphogenesis of reconstructed enucleated Acetabularia cells].

Survival and morphogenesis of the enucleated fragments of Acetabularia has been studied after their reconstruction from the cell membrane and the endoplasm. Membranes and endoplasms of different species as well as of the same species but from plants in different functional states and with different regenerative abilities were combined. It was shown that inability of plants for growth and morphogenesis was due to the membrane state. When reconstructing anuclear fragments from membranes and endoplasms of different species or the same species but from plants in different functional states, a phenomenon of membrane-endoplasm incompatibility was found.

Acetabularia↗