Dependence of chloroplast pigment synthesis on protein synthesis: effect of actidione.

Experiments have been carried out to determine the basis for the dependence of chloroplast pigment synthesis on protein synthesis in dark-grown cells of Euglena gracilis greening in the light. The complete inhibition of chlorophyll synthesis brought about by actidione (10 μg/ml) when added half way through the greening process was not relieved, even to the slightest extent, when 0.01 M δ-aminolaevulinic acid (ALA) was also present. The much smaller inhibition of chlorophyll synthesis brought about by chloramphenicol (2 mg/ml) was also relieved little, if at all, by the addition of ALA. It is concluded that the inhibition of chlorophyll synthesis by actidione can not be solely or primarily due to lack of ALA resulting from the decay of possibly labile enzymes of ALA synthesis, but could be due to inhibition of synthesis of the thylakoid structural protein. The results obtained with chloramphenicol are difficult to interpret because of the possibility that the drug, at high concentration, directly inhibits processes other than protein synthesis.Chlorophyll and carotenoid synthesis by E. gracilis were both markedly stimulated by the addition of ALA. It is suggested that the rate of chlorophyll synthesis in the greening cells is limited by the rate of formation of ALA. The stimulation of formation of carotenoids as well as chlorophyll may indicate that the cells have a mechanism for ensuring that the rate of carotenoid synthesis does not fall below a certain proportion of the rate of chlorophyll synthesis.A nomogram has been devised from which the concentrations of chlorophylls a and b, and total chlorophyll can be read off once the absorbances of an 80% acetone extract at 663 and 645 mμ have been determined.

Studies on the dependence of chlorophyll synthesis on protein synthesis in Euglena gracilis , together with a nomogram for determination of chlorophyll concentration

Mode of action of antibiotics. II. Drugs affecting nucleic acid and protein synthesis.

Members of the family Trichomonadidae, mainly Trichomonas gallinae and Tetratrichomonas gallinarum, represent important parasites in birds with worldwide presence, since being reported in the 19th century. Especially Columbiformes, Falconiformes and Strigiformes can be severely affected by trichomonads, whereas the majority of infections in Galliformes and Anatiformes are subclinical although severe infections are occasionally reported. With the recent appearance of deadly infections in wild Passeriformes the protozoan parasite T. gallinae obtained greater attention which will be addressed in this review. Although light microscopy remains the method of choice to confirm the presence of trichomonads molecular studies were introduced in recent years, in order to characterize the parasites and to establish relationships between isolates. Isolation of trichomonads is a prerequisite for detailed in vitro and in vivo studies and different media are reported to obtain suitable material. The limited information about virulence factors will be reviewed in context with the pathogenicity of trichomonads which varies greatly, indicating certain strain heterogeneity of the parasites. Options for treatment characterized by the leading role of imidazoles whose activity is sometimes hampered by resistant parasites remains a challenge for the future. Introducing more standardized genetic studies and investigations concentrating on the host-pathogen interaction should be helpful to elucidate virulence factors which might lead to new concepts of treatment.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0031182013002096

Trichomonads in birds--a review.

Publisher Summary Chloroplasts are self-reproducing semiautonomous structures that possess their own independent genetic system. In many respects, chloroplasts resemble certain blue–green algae in their structure, biochemistry, and genetic behavior. It is suggested that chloroplasts originated through an association between a colorless host organism and a blue green alga like symbiont similar in form and function to those known to exist today. The assertion of these symbiotic origins may be found in situations in which isolated chloroplasts are known to exist endosymbiotically in the cells of invertebrates. The capacity for self-replication that chloroplasts seem to exhibit in most situations implies that some extranuclear mechanism of control exists within the chloroplast itself. Similarly, observations on the hereditary behavior of chloroplasts suggest that this control is genetic in character and may be expected to be associated in some way with either DNA or RNA. A great deal of research is needed before the idea that chloroplasts are symbiotic organelles can be asserted with any great degree of confidence.

J.T.O. Kirk

Papers

Effect of streptomycin on greening and biosynthesis in Euglena gracilis.

Effect of streptomycin on [14C]leucine incorporation in Euglena gracilis