Photosynthetic Activity during the Division Cycle in Synchronized Euglena gracilis

Axenic populations of the photosynthetic protozoan Euglena gracilis, grown with autotrophic nutrition, were synchronized with respect to cell division by culture on an alternating light-dark cycle. No cell divisions occurred in the light periods; approximately 100% of the cells divided in the dark periods. In such cultures, the synthesis of photosynthetic pigments and accumulation of polysaccharide were confined to the light periods. The capacity for photosynthesis, however, increased continuously over the entire light-dark cycle, and is thus not directly correlated with pigment content. A correlation was seen between photosynthetic capacity and protein content, suggesting that enzymatic mechanisms of the photosynthetic apparatus might be the limiting factor. Estimates of total photosynthetic activity indicate that about 5 x 10(-6) calories are required for the synthesis of a new cell.     

Growth in Volume of Euglena gracilis During the Division Cycle

The distribution of volumes of Euglena gracilis cells was measured conductimetrically. The volume spectrum of cultures in balanced growth was analyzed by the method of Collins and Richmond. The kinetics of volume increase of Euglena is neither linear nor exponential; the growth rate of small and large cells is low, but intermediate size cells show the largest growth rate.     

Interactions between the Nucleus and Cytoplasmic Organelles during the Cell Cycle of Euglena gracilis in Synchronized Cultures: II. Associations between the Nucleus and Chloroplasts at an Early Stage of the Cell Cycle under Photoautotrophic Conditions

Chloroplast-nucleus interactions were examined in cells of Euglenagracilis Z synchronized under photoautotrophic conditions. Thechloroplasts were localized near the cell periphery. At an earlystage of the cell cycle, however, some chloroplasts were transientlylocated in the inner space close to the nucleus. Electron microscopyusing serial cell sections revealed that the chloroplast formedprotrusions at several sites, which became associated with thenucleus. The outer membrane of the chloroplast envelope wasin contact, or at least continuous in part, with the outer membraneof the nuclear envelope at the sites of association, and densematerial was present in the chloroplast membrane. A chromosomewas close to each site of the association between these twoorganelles. Most of the chloroplasts including those in associationwith the nucleus were connected by fine bridges. The 4',6-diamidino-2-phenylindole-stainednucleoids in the chloroplast associated with the nucleus appearedto have a thread-like shape. There was another type of chloroplast-nucleusconnection, in which an intervening membranous body was in contactwith the outer part of the nuclear envelope on one side andwith the chloroplast envelope on the other side. ¹ This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan, Kyoto, October, 1983. (Received June 5, 1984; Accepted November 20, 1984)     

Effects of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea on the Cell Cycle in Euglena gracilis

The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G₂/M. The specificity of this response and its relationship to photosynthesis was studied by looking at the effect of DCMU on dark grown wild-type cells, and on two bleached variants of Euglena (W₃BUL and W₁₀BSmL) that lack chloroplasts. The drug does block G₂/M in these cells, but not entrance into the cell cycle. Our studies show that entrance of cells into the cell cycle from a quiescent state does not require active photosynthesis, and that DCMU has effects on G₂/M transit that are independent of the photosynthetic capacity of the cells.     

Interactions between the Nucleus and Cytoplasmic Organelles during the Cell Cycle of Euglena gracilis in Synchronized Cultures III. Association between the Nucleus and Chloroplasts at an Early Stage in the Cell Cycle under Photoorganotrophic Conditions (Part II)

Three-dimensional models of chloroplasts before and during theirassociation with the nucleus in Euglena gracilis Z were constructedbased on serial sections of cells taken during an early phaseof the cell cycle in synchronized cultures under photoorganotrophiccondition. Before association, the cell contained two to threechloroplasts which were composed of elongated tubular bodiesextending in different directions toward the cell periphery.These tubular arms of chloroplasts were drawn toward the nucleus,and folded, with concurrent coalescence, into a single giantbody surrounding the nucleus. A DAPI-fluorescence photomicrographof a giant chloroplast revealed that the chloroplast-nucleoidswere in the form of a continuous strand lying throughout thechloroplast body, and that some protuberances from the nucleoidstrand were in especially close proximity to the nuclear periphery. A new mode of the chloroplast-nucleus connection was observed.The nucleus had conspicuous protrusions, whose distal ends wereconnected with the chloroplast. The outer membrane of the nuclearenvelope was continuous with the outer chloroplast membrane,and at some sites, an open space was formed between the innernuclear membrane and the inner chloroplast membrane. ¹ This work was reported at the 48th Annual Meeting of the BotanicalSociety of Japan, held in Kyoto, in October, 1983. For PartI see Ehara et al. (1984).     

Large-Scale Temperature-Induced Synchrony of Cell Division in Euglena gracilis*

SYNOPSIS. Temperature-induced patterns of synchronous cell division and cell size were obtained with Euglena gracilis. The alga was cultured in a glutamate-sucrose medium in 6-liter quantities. Synchrony was induced by non-lethal shifts of temperature between 14.5 and 28.5 C. Three liters of cells containing 2 × 10⁶ cells/ml were harvested in each 24-hour cycle.     

The light-harvesting system of Euglena gracilis during the cell cycle

The apoproteins of the light-harvesting chlorophyll-protein complexes LHCI and CP29 (apparent molecular weights of 27 kDa and 29 kDa, respectively) of Euglena gracilis were identified immunologically. Both complexes are present in the thylakoids of autotrophically cultured Euglena cells during the whole cell cycle. The relative amount of each apoprotein tends to increase towards the end of the cell cycle. The light-harvesting chlorophyll-protein complex of photosystem II, LHCII, of E. gracilis contains chlorophyll a, chlorophyll b, neoxanthin, diadinoxanthin and beta-carotene. Its chlorophyll a/b ratio is about 1.7 during the whole cell cycle. About 9 h after cell division the ratio of diadinoxanthin to chlorophyll a is doubled for a time of 3–4 h. The relevance of this increase during one developmental stage is discussed in relation to the insertion and-or assembly of newly synthesized LHCII.Abbreviations LHCP light-harvesting chlorophyll-protein complex - PS photosystem This research was partly supported by the Deutsche Forschungsge meinschaft.     

Influence of Cell Division on the Degree of Streptomycin Bleaching of Euglena gracilis

SYNOPSIS. Streptomycin (SM) inhibition of greening of Euglena gracilis , strain z, was studied. The antibiotic was most effective if present during cell division in the absence of light. The next most effective condition was that which allowed cell division in the light, and the least effective conditions were those that allowed only minimal cell division in the dark or light (i.e., under "resting" conditions). In the dark, 20–200 times higher concentrations of SM were required for the same degree of inhibition under resting conditions as under growing conditions. The observation of Kirk ( Biochim. Biophys. Acta , 1962, 56 , 139–51)-that the pH of the resting medium influenced the degree of inhibition–was confirmed.     

Graviperception in the flagellate Euglena gracilis during a shuttle space flight

During a recent space flight, gravitaxis of the unicellular photosynthetic flagellate, Euglena gracilis, was studied on board of the American shuttle Columbia. Accelerations were varied between 0 and 1.5 x g using a slow rotating centrifuge microscope (NIZEMI). The cells showed a sigmoidal response curve for the dependence of the precision of gravitaxis on acceleration which is indicative of the involvement of an active, physiological gravireceptor with a threshold at g-values < or = 0.16 x g and a saturation at g-values > or = 1 x g. No adaptation to microgravity was found during the prolonged space mission. After return the cells showed a normal gravitactic behavior at 1 x g. Since the cells are heavier than water, their swimming velocity is affected by sedimentation. The velocity distribution at different accelerations closely follows Stokes' law for sedimentation indicating that, in contrast to the ciliate Paramecium, E. gracilis, does not show any gravikinesis.     

Erythromycin-Induced Bleaching of Euglena gracilis

SYNOPSIS. Erythromycin bleaches Euglena gracilis in a manner resembling that of streptomycin. Erythromycin-bleached substrains have been cultivated 16 months in light on erythro-mycin-free media without greening. Bleached substrains were obtained only if erythromycin was added to actively growing cultures: erythromycin did not bleach if added during the stationary phase of growth of green cultures.     

Ultrastructure of the pellicle of Euglena gracilis

Deep-etching technique was used to investigate the organization of the pellicle complex of Euglena gracilis. The interpretation of the images was further supported by SEM and TEM investigations. Our results mainly validate data obtained by previous freeze-fracture studies on the E and P faces of the outer cortical membrane. At the level of the ridges, the outer E fracture face is highly organized in a regular striated pattern, whereas the P inner face shows a particulate structure. However, our images reveal that this particulate organization of the P face is not limited to the ridges, but it is displayed also by the grooves. Moreover, this face shows two distinct layers, a particulate layer facing the cytoplasm and a striated layer facing the E face; these layers represent different true fracture levels of the same P face.     

Differential Inhibition of Cell Division in Euglena gracilis by Cysteamine and Cystamine

Cysteamine (2-aminoethanethiol) inhibited cell division in synchronously dividing cultures of Euglena gracilis at relatively low concentrations (0.005 M), Cystamine (2,2′-dithiobis(ethylamine). however, was only partially inhibitory at high concentrations (0.1 M). This differential inhibition may reflect certain unique features of nuclear division in euglenoid flagellates.     

Mitomycins and the bleaching of Euglena gracilis

Summary The effects of some mitomycin antibiotics on the chloroplast system of Euglena gracilis were studied. Only those derivatives which contained an alkyl group on the aziridine nitrogen were effective bleaching agents. Thus, only N-methyl-mitomycin, porfiromycin, and mitomycin B caused a highly significant loss of chloroplasts. This sensitivity of the Euglena chloroplast to small structural differences in the active centers of antibiotics demonstrates the usefulness of this organism in the study of relationships between biological activity and chemical structure of antibiotics.