[Influence of DCMU on the formation of lipids and fatty acids, and on the ultrastructure of Euglena gracilis (author's transl)]

Euglena gracilis Klebs (strain Z) was grown heterotrophically in the dark for 6 days. Subsequently, the cells were grown photoautotrophically under white fluorescent light with varying amounts of 3-(3,4-dichlorophenyl)-1,1 dimethyl urea (DCMU) (1.7X10(-9)--1.0X10(-5)mol/l) added to the nutrient medium. Under non-photosynthetic conditions (addition of 10(-6)--10(-5)mol DCMU/l), the cells still produced chloroplast structures and a considerable percentage of compounds typical for chloroplasts, such as galactolipids (40-50%), chlorophylls (40%), and polyunsaturated C16 and C18 fatty acids (16:2, 16:3, 16:4, 18:2, 18:3) (65%). The results indicate that under these conditions the above compounds are synthesized from carbon sources outside the chloroplasts.

Ferredoxin biosynthesis in Euglena gracilis

Analysis of ferredoxin content in cultures of Euglena gracilis grown in the presence of selective antibiotic inhibitors of protein synthesis resulted in the following conclusions: 1. Ferredoxin is synthesized from cytoplasmic (80s-type) ribosomes; cycloheximide, a potent inhibitor of 80s translation completely abolished the synthesis, while the inhibitors of 70s translation chloramphenicol and erythromycin were not effective. In addition, ferredoxin was detected in a streptomycin-bleached mutant that lacks the chloroplast structure and chloroplast DNA. 2. Ferredoxin's transcript is presumably of nuclear origin; rifampicin, an inhibitor of chloroplast DNA-dependent RNA polymerase did not inhibit synthesis, while the streptomycin-bleached mutant continued to synthesize ferredoxin without chloroplast DNA.

Deoxyribonucleoside triphosphate pools in vitamin B-12-deficient Euglenagracilis

The size of the deoxyribonucleoside triphosphate pools of vitamin B-12-deficient cells of Euglena gracilis, and of vitamin B-12-deficient cells repleted with the vitamin, were measured. We found that the pools were very small, if they exist at all, in deficient cells but expand rapidly with the addition of the vitamin. The sizes of the pools decrease when DNA synthesis is completed, and are very small when the cells begin to divide.

The coupling effects of some thiol and other sulfur-containing compounds on the circadian rhythm of cell division in photosynthetic mutants of Euglena

Previous work has demonstrated a persisting, free-running, circadian rhythm of cell division in the P4ZUL photosynthetic mutant of the alga Euglena gracilis Klebs (Strain Z) Pringsheim grown organotrophically in continuous light or darkness at 19 degrees C following prior synchronization by a repetitive LD:10,14 light cycle. A similar circadian rhythmicity has been recently discovered in the W6ZHL heat-bleached and the Y9ZNalL naladixic acid-induced mutants of Euglena grown under comparable conditions. Over extended timespans, however, these mutants appear to gradually lose first their ability to display persisting overt rhythms, and then even their capability of being entrained by imposed LD cycles. These properties can be restored by the addition of certain sulfur-containing compounds to the medium including cysteine, methionine, dithiothreital, sodium monosulfide, sodium sulfite, and sodium thiosulfate, as well as thioglycolic [mercaptoacetic] acid. The implications of these findings toward biological clock mechanisms are discussed: It appears that some sort of coupling process is operating as opposed to the initiation of an underlying oscillation.

Mutagenic action of nitrofurans on Euglena gracilis and Mycobacterium phlei

There is a pronounced difference between the action of antibiotics and nitrofurans on Euglena gracilis. Those antibiotics that induce hereditary loss of chloroplasts do so only when they affect dividing cells. On the other hand, nitrofurans induce a mass mutation in both dividing and nondividing cells (under conditions of continuous illumination of cultures). It was found that a breakdown product, 5-nitro-2-furaldehyde, is liberated from furadantin and furoxone. This intermediate is responsible for the observed specific mutagenicity of 5-nitrofuran drugs. The mutagenic action of 5-nitro-2-furaldehyde is very similar to that of nitrosoguanidine. Both compounds induce bleached mutants of E. gracilis when acting on growing or resting cells, regardless of the dark or light conditions. Similarly, both compounds induce reverse mutations in auxotrophic strains of Mycobacterium phlei.

A reinvestigation of the sites of transcription and translation of Euglena chloroplastic phenylalanyl-tRNA synthetase

An attempt was made to determine the sites of chloroplast phenylalanyl-tRNA synthetase transcription and translation. Inhibitors of bacterial RNA and protein synthesis were added to logarithmic and stationary phase cultures of Euglena gracilis wild-type B. Logarithmic phase cultures were sensitive to both types of inhibitors. In stationary phase cultures plastid synthetase was reduced by RNA but not by protein synthesis inhibitors. The effect of the antibiotics on the mitochondrial enzyme was also noted. Several possible explanations of these resuults are discussed.

Synthesis and translation site of light-induced mRNAs in etiolated Euglena gracilis

Poly(a)-mRNA synthesis has been studied in etiolated Euglena gracilis exposed to 1 or 2 h of illumination. 1. Labeling kinetics of mRNAs containing poly(A) sequences, during illumination or after return to darkness, reach a plateau in 10 or 20 min according to nutritional conditions. When the cultures are returned to darkness, the mRNA synthesis decreases rapidly. Thus, the synthesis of these mRNAs (light-induced mRNAs) is dependent on light and their half-life can be evaluated. 2. Cycloheximide induces accumulation of label in poly(A)-containing mRNA; such an accumulation is not observed after addition of lincomycin. Labeling during illumination of mRNA in a chloroplast mutant is similar to that in the wild type strain. These data suggest that the poly(A)-mRNAs synthesized in the two first hours of illumination are translated on cytoplasmic polyribosomes.

ATPase activity in flagella from Euglena gracilis. Localization of the enzyme and effects of detergents

The biochemical effects of some detergents on the ATPase activity of isolated flagella from Euglena gracilis are related to morphologic obliterations induced by those detergents. Enzymic activity can be localized by electron microscopy along the microtubules and also on the paraflagellar rod. The nonionic detergent digitonin solubilizes the enzyme linked to dyneinic arms, whereas the activity linked to residual structures appears enhanced. These results support the hypothesis that the paraflagellar rod may be a structure activity related to the motility of this type of flagellum.

DNA distribution in the cell cycle of Euglena gracilis. Cytofluorometry of zinc deficient cells

Analysis of DNA content of intact cells by laser induced cytofluorometry permits dynamic studies of the cell cycle in the synchronously dividing eukaryote Euglena gracilis. In this manner, the effects of zinc deficiency and cadmium toxicity on in situ DNA synthesis and cell division of this organism have been studied. In the G-1 hase of the cell cycle, prior to initiation of DNA synthesis, the DNA content of synchronously growing E. gracilis is characteristic of cells with an ureplicated genome. In S phase there is a progressive increase in DNA content which leads to genome duplication as the cells enter G2. In the subsequent mitosis all cells divide. Cytofluorometric definition of DNA content serves as a standard of reference to study variables which alter or block each stage of the cell cycle. Growth in zinc dificient media inhibits cell division. The DNA content of such zinc dificnet cells is characteristic of a population of cells blocked in S/G2 with a small fraction in G1. Moreover, cells synchronized in G1 and placed in zinc deficient media do not progress into S phase. Cadmium also inhibits cell division, and the DNA content of these blocked cells is three to four times greater than that of cells in G1. Zinc is essential for the biochemical events of the premitotic state which include initiation of DNA synthesis, DNA synthesis, and progression from G-2 to mitosis. Cadminum-induced derangements of the cell cycle include alterations in regulation cellular DNA content.

Induction potential for glyoxylate cycle enzymes during the cell cycle of Euglena gracilis

In light/dark synchronized cultures of Euglena gracilis Klebs Z the enzymes malate synthase, isocitrate lyase and acetate thiokinase were induced upon addition of acetate at all stages of the cell cycle. Cycloheximide and p-fluorophenylalanine inhibited the development of enzyme activity, showing that induction was dependent on protein synthesis. The maximum rate of induction for all three enzymes was constant for much of the cell cycle but doubles in a single step during the period of DNA replication. Although these data indicate that enzyme potential was regulated by gene dosage and that the structural gene for each enzyme was continuously available for transcription during the cell-cycle it was not possible by using inhibitors of RNA synthesis, to demonstrate concurrent transcription during enzyme induction.

Chloroplast and cytoplasmic ribosomes of Euglena: selective binding of dihydrostreptomycin to chloroplast ribosomes

Dihydrostreptomycin binds preferentially to chloroplast ribosomes of wild-type Euglena gracilis Klebs var. bacillaris Pringsheim. The K(diss) for the wild-type chloroplast ribosome-dihydrostreptomycin complex is 2 x 10(-7) M, a value comparable with that found for the Escherichia coli ribosome-dihydrostreptomycin complex. Chloroplast ribosomes isolated from the streptomycin-resistant mutant Sm(1) (r)BNgL and cytoplasmic ribosomes from wild-type have a much lower affinity for the antibiotic. The K(diss) for the chloroplast ribosome-dihydrostreptomycin complex of Sm(1) (r) is 387 x 10(-7) M, and the value for the cytoplasmic ribosome-dihydrostreptomycin complex of the wild type is 1,400 x 10(-7) M. Streptomycin competes with dihydrostreptomycin for the chloroplast ribosome binding site, and preincubation of streptomycin with hydroxylamine prevents the binding of streptomycin to the chloroplast ribosome. These results indicate that the inhibition of chloroplast development and replication in Euglena by streptomycin and dihydrostreptomycin is related to the specific inhibition of protein synthesis on the chloroplast ribosomes of Euglena.

Effects of Ethidium Bromide on Growth, Chlorophyll Synthesis, Ultrastructure and Mitochondrial Dna in Green and Bleached Mutant Euglena Gracilis

Green Euglena cells were grown with 1, 5, 20, 50 and 100 µg/ml ethidium bromide (EB), a DNA-intercalating dye and cytoplasmic mutagen. Treatment with 50 µg EB/ml for 3 days in growing medium, pH 3.3 (heterotrophic growth) was maximally effective and inhibited cell division by 70% and chlorophyll formation by 60%. Similar results were obtained in Cramer Meyers medium, pH 6.8 without acetate (autotrophic growth). When dark-grown cells were shifted from heterotrophic to autotrophic medium and exposed to light and 20 or 50 µg EB/ml for 3 days, the cells barely divided and chlorophyll formation (greening) was inhibited by 30 and 60% with 20 and 50 µg EB/ml, respectively. Greening was similarly inhibited in heterotrophic medium. The ultrastructure of chloroplasts appeared normal in all conditions, but mitochondria of EB-treated cells had fewer cristae than control cells and frequently concentrically arranged cristae. Dark-grown cells were treated with 5, 20, 50, 100 and 150 µg EB/ml for 24 h, transferred to resting medium, pH 4.5, and exposed to EB and light for 3 days. Chlorophyll synthesis was significantly inhibited even with 5 µg EB/ml. The ultrastructure of chloroplasts and mitochondria appeared normal.

Bleached mutant Euglena were treated with 1, 5, 10 and 20 µg EB/ml in growing medium. Cell division was inhibited by 70% after 7 days of culture with 20 µg EB/ml. Inhibition was greater in the light than in the dark. The ultrastructure of mitochondria was strikingly changed even with 1 or 5 µg EB/ml for 5 days, and there were 2 types: mitochondrial profiles with few and/or concentrically arranged cristae and electron-lucid matrix, and fused sheets of mitochondrial membranes encircling the periphery of the cell. Cytochrome oxidase activity was partially inhibited. The ultrastructural changes in mitochondria after growth of bleached Euglena in 1, 5 and 10 µg EB/ml for 10 days were reversed (partially in some cells) when cells were transferred to EB-free medium for another 20 days. There was a 10-15 day lag in the recovery of cell division rate. Re-exposure of reversed cells to 20 µg EB/ml showed a progressively greater resistance to the drug directly proportional to the original concentration of EB.

The yield of mitochondrial DNA after exposure to EB was slightly lowered after 3 days, and after 8 days was reduced from 1.84 µg M-DNA/mg M-protein (control) to 1.69 and 0.98 (with 1 and 5 µg EB/ml, respectively). Mitochondrial DNA synthesis, as reflected by the incorporation of [3H]guanine and [3H]adenine into DNA, was unaffected after 3 days of growth in 1 and 5 µg EB/ml, but was inhibited by 70% after 8 days. Nuclear DNA synthesis was not significantly inhibited. The specific activities of circular satellite DNA were lowered by 50%.

The results demonstrate that EB inhibits cell division in both strains of Euglena, that ultra-structure is changed only in mitochondria of growing cells, not in chloroplasts, and that some chloroplast but mainly mitochondrial functions are inhibited under suitable conditions. The results also indicate that resistance to the drug can be developed.

Vitamin B 12 and the macromolecular composition of Euglena. II. Recovery from unbalanced growth induced by Vitamin B 12 deficiency

When vitamin B(12) is added to B(12)-deficient cultures of Euglena gracilis, the cells undergo two relatively synchronous cell divisions within a shorter than usual period of time, apparently as a result of a transitory shortening of the cell cycle. The first cell division pulse, occurring 4.5 h after addition of B(12), is preceded by the completion of DNA duplication, but appears to involve no net synthesis of RNA or protein. Before the second round of cell division at about 11 h, a significant amount of DNA synthesis is observed. This time it is accompanied by a minor increase in the RNA and protein content of the culture. The cellular contents of RNA and protein were observed to decrease steadily after the resumption of cell division in B(12)-depleted cultures receiving the vitamin. Ultimately all three macromolecules returned to their nondeficient, plateau stage levels; by this time, cell division had ceased.

A possible ribosomal-directed regulatory system in Euglena gracilis. Chlorophyll synthesis

Cycloheximide at concentrations of 0.1-100mum stimulated chlorophyll synthesis when dark-grown cells of Euglena were illuminated. Chloramphenicol (1-4mm) inhibited chlorophyll synthesis. The effect of cycloheximide on the incorporation of [(14)C]leucine into material insoluble in trichloroacetic acid, and its failure to affect the incorporation of [(32)P]orthophosphate into such material in short incubations, are interpreted as evidence that cycloheximide specifically inhibits protein synthesis by 80S ribosomes. Since the inhibitory effect of chloramphenicol on chlorophyll synthesis is counteracted by the presence of cycloheximide, it is suggested that chlorophyll synthesis is subject to control by a cytoplasmic repressor synthesized on 80S ribosomes, and to a de-repressor synthesized on 70S ribosomes.

A possible ribosomal-directed regulatory system in Euglena gracilis. Carbon dioxide fixation

It was shown that cycloheximide inhibits CO(2) fixation in Euglena cells in the dark, but no effect of chloramphenicol was found. The light-dependent CO(2) fixation was inhibited by chloramphenicol and by large amounts of cycloheximide, but was stimulated by small amounts of cycloheximide. The presence of the stimulatory concentration of cycloheximide abolished the inhibition effect of high concentrations of chloramphenicol. The results indicate that the light-dependent CO(2) fixation is controlled by a repression-derepression regulatory system, which seems to be independent of chlorophyll synthesis.