Studies of Chloroplast Development in Euglena: XV. Factors Influencing the Decay of Photoreactivability of Green Colony Formation

When UV-treated cells of Euglena gracilis var. bacillaris are incubated in the dark in a nutrient medium which permits cell division, they lose the ability to be photoreactivated. The rate of this loss increases with the UV dose. For any given UV dose, the rate of decay increases with increasing growth rate. The same phenomena are observed in light-grown and in dark-grown cells, although the sensitivity to UV of the light-grown cells is smaller by a factor of 1.7. The kinetics of photoreactivation (PR) change during the decay of photoreactivability only if the cells are incubated in growth medium. A UV-inactivation curve for cells photoreactivated only after appreciable PR shows the same slope as that for untreated cells (number of UV-sensitive targets). These results are discussed from the point of view of possible models.     

A Model for Ultraviolet and Photoreactivating Light Effects in Euglena

A unified mathematical model is presented of the reversible effects of ultraviolet (UV) and photoreactivating (PR) light on the chloroplast-forming ability of dark-grown Euglena gracilis (var. bacillaris). This model is an extension of several aspects of target theory and also of a model for the decay of photoreactivability in Euglena proposed by Schiff et al. The data presented in several earlier papers are compared with the predictions of the proposed unified model and reasonably good agreement is found.     

Studies of Chloroplast Development in Euglena: XIII. Variation of Ultraviolet Sensitivity with Extent of Chloroplast Development

Ultraviolet (UV) inactivation of green colony-forming ability of several different types of Euglena gracilis var. bacillaris was studied. The observed target numbers are not widely different, while the doses required to produce a single inactivation event (D(o)) vary with the type of cell used. In dark-grown cells adapting to the light in resting medium and in an X-ray-induced mutant, D(o) is proportional to the chlorophyll content of the cells. However, in hyperdeveloped cells which contain abnormally high amounts of chlorophyll, the correlation does not hold, suggesting that it is not chlorophyll per se which is responsible for the differences observed. D(o)'s of colony-forming ability (viability) of light-grown and dark-grown cells are found to differ by the same factor as those of green colony-forming ability. Stationary phase and exponential phase cells show a small difference in D(o) with no obvious difference in target multiplicity. The multiplicity of the various target curves has been re-evaluated by computer and found to be between 30 and 40.     

Studies on Chloroplast Development and Replication in Euglena: III. A Study of the Site of Synthesis of Alkaline Deoxyribonuclease Induced during Chloroplast Development in Euglena gracilis

During chloroplast development in Euglena, the activity of a specific DNase, Euglena alkaline DNase, increases in a manner similar to that of chlorophyll synthesis, but without the lag customarily associated with the early hours of chlorophyll synthesis. The increase in Euglena alkaline DNase activity is not inhibited by chloramphenicol or by streptomycin, but is inhibited by cycloheximide. Euglena alkaline DNase activity is present in a group of aplastidic substrains which contain carotenoids. These results are interpreted to mean that this chloroplast-related DNase is synthesized in the cytoplasm, and that the genetic information for this enzyme is probably nuclear.     

Ultraviolet Inactivation of Euglena Chloroplasts: I. Effect of Light Intensity of Culture

Target numbers for ultraviolet (UV) inactivation of chloroplast replication in Euglena gracilis were about 45 when cells were grown in the dark and about 150 when grown in the light (700 or 1200 foot-candles [ft-cd]). Total cell DNA was about 25% greater in the light-grown cells.     

Action of Nitrofuran Derivatives on the Chloroplast System of Euglena gracilis: Effect of Light

SYNOPSIS. When cultures of Euglena are exposed to nitro-furantoin in the light, there is extensive bleaching and, at higher concentrations, killing. In the dark the same concentrations have essentially no effect. The enhanced activity in light is a consequence of the rapid photolysis of nitrofurantoin to yield 5-nitro-2-furaldehyde which is, in turn, destroyed by light. Nitrofuraldehyde and several other nitrofuran derivatives bleach at low concentrations in the dark.
Of 14 nitrofuran derivatives tested, only 4 Schiff's bases which were readily decomposed to nitrofuraldehyde in light were more active in the light than in the dark.     

Interactions Between Light and Gas Vacuoles in Halobacterium salinarium Strain 5: Effect of Ultraviolet Light

The potential light shielding by intracellular gas vacuoles in Halobacterium salinarium strain 5 was examined by looking at the ultraviolet light inactivation curves of both wild-type cells and mutants which are defective in the production of gas vacuoles. Whereas strains defective in gas vacuole production were slightly more sensitive to ultraviolet inactivation, no significant differences in ultraviolet sensitivity were seen, indicating that these subcellular inclusion bodies are not effective as light-shielding organelles. In addition, it was shown that ultraviolet light acts as a plasmid-curing agent in Halobacterium.     

Sensitivity of Chloroplast Development in Euglena to Acridine Orange: Bleaching and Recovery from Damage

Treatment of light-grown Euglena cells with acridine orange(AO) at non-lethal concentrations resulted in the permanentloss of their ability to form chloroplasts. However, dark-growncells were insensitive to AO. Starvation of the cells underlight culture or the addition of chloramphenicol (CM) deformedthe chloroplasts and made them less AO sensitive. Cells withmature chloroplasts seemed to show the most sensitivity to AO.Illumination with intense visible light of the AO-treated cells,whether they had been light- or dark-grown, made a greater proportionof them liable to be bleached or to be killed. The photosensitizationwas evident over the range of wavelengths of 450–500 nm,where the absorption maximum of AO is located. When light-grown cells, after AO treatment, were held in darknessin a nongrowth medium for 24 hr, the bleaching effect was reduced.However, if held under a light of 620–670 nm, where cellswere not photosensitized but were able to form chloroplasts,the AO-damage was not reversed. The possibility of repair afterAO-treatment is discussed. (Received May 15, 1981; Accepted October 8, 1981)     

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.     

The Chloroplast and Cytoplasmic Ribosomes of Euglena: II. Characterization of Ribosomal Proteins

Cytoplasmic and chloroplast ribosomal proteins were isolated from Euglena gracilis and analyzed on polyacrylamide gels. Cytoplasmic ribosomes appear to contain 75 to 100 proteins ranging in molecular weight from 10,200 to 104,000, while chloroplast ribosomes appear to contain 35 to 42 proteins with molecular weights ranging from 9,700 to 57,900. This indicates that the cytoplasmic ribosomes are similar in composition to other eucaryotic ribosomes, while chloroplast ribosomes have a protein composition similar to the 70S procaryotic ribosome. The kinetics of light-induced labeling of cytoplasmic ribosomal proteins during chloroplast development has been determined, and the results are compared with the kinetics of ribosomal RNA synthesis.     

Chlorophyll-Protein Complexes and other Thylakoid Components at the Low Intensity Threshold in Euglena Chloroplast Development

The plastids of dark-grown resting cells of Euglena gracilisKlebs var. bacillaris Cori undergo only limited developmentwhen illuminated at the developmental threshold for light intensity7 foot-candles (ft-c) (27 µW/cm²). In the present work,we have found that these low intensity cells have substantialamounts of electron transport components such as ferredoxin-NADPreductase and Cyt c-552 but only trace amounts of the majorantenna components such as the light-harvesting Chl-proteincomplex (LHCP), the LHCP oligomer, CP la, Chi b and the 26.5kDa apo-LHCP; CP I and CPa are at levels comparable to the electrontransport components. Exposure of the low intensity cells tonormal light intensity causes large increases in major antennacomponents and small increases in electron transport components.The kinetics of accumulation of the antenna components Chi band apo-LHCP during greening of dark-grown resting cells atnormal intensities are the same as for Chi a. The low intensitywild-type cells strongly resemble mutants of Euglena low inChi b grown at normal intensities in lacking major antenna components. (Received April 7, 1987; Accepted June 19, 1987)     

Comparative Studies on Plastoquinones: V. Changes in Lipophilic Chloroplast Quinones during Development

Changes of lipophilic chloroplast quinones in corn, oats, peas, and Vicia faba are reported after 0, 4, 8, 12, 16, 20, 24, 48, 72, or 96 hours of exposure to light. There is a pronounced increase in plastoquinone A and chlorophyll levels and slight increase, in plastoquinone C_1-6, vitamin K₁, and α-tocopherylquinone content. Coenzyme Q levels, on the other hand, show little change upon exposure to light.     

Interaction between Green and Far-Red Light on the Low Fluence Rate Chloroplast Orientation in Mougeotia

Continuous irradiation of Mougeotia with linearly polarized green light (550 nanometers, 0.2 watt per square meter) induces a change in the orientation of its chloroplast from profile to face position, if the electrical vector of the green light is vibrating normal to the cell axis. This change is complete within 25 minutes of the onset of irradiation. In contrast, if the electrical vector of the green light is parallel to the cell axis, no chloroplast reorientation is induced, even with a fluence rate as high as 3 watts per square meter. Furthermore, unpolarized far-red light (727 nanometers, 2 watts per square meter) given alone has no effect on chloroplast reorientation. Simultaneous and continuous irradiation with polarized green light, regardless of its plane of polarization, together with unpolarized far-red light, however, does lead to chloroplast reorientation. These data indicate that, in addition to the red-absorbing form of phytochrome, there exists in Mougeotia another sensory pigment absorbing green light.