Comparative studies on mitochondrial development in yeasts. II. Mitochondrial ribosomes from Saccharomyces cerevisiae.
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Acrylamides↗
Biomedical subjects
R Poulson
Publications and source records attributed to R Poulson.
Protein Synthesis in Cotyledons of Pisum sativum L: I. Changes in Cell-Free Amino Acid Incorporation Capacity during Seed Development and Maturation.
The changes in protein content of pea cotyledons have been followed during the period from 9 to 33 days after flowering. Initially protein content increased gradually with a rapid period of deposition occurring between days 21 and 27 after flowering. After the 28th day the rate of accumulation of protein declined as the seed dehydrated and matured. At maturity the pea cotyledon contained approximately 25% protein which was divided into albumins and globulins in the ratio of 1:1.4.Analytical data and the incorporation of exogenously supplied (14)C-leucine indicated that albumins were synthesized early in cotyledon development whereas globulin synthesis predominated with increasing maturity.Ribosomal preparations extracted from seeds during the period of rapid protein synthesis contained a high percentage of polysomes. Preparations from older cotyledons with a declining capacity for protein synthesis had few polysomes and an abundance of monosomes. The amino acid-incorporating capacity of ribosomal preparations from cotyledons of varying age was related to the polysomic content. The phenylalanine-incorporating capacity of ribosomal preparations from mature pea seed could be stimulated by the addition of polyuridylic acid. The distribution of polysomes and the in vitro incorporation data suggested that protein synthesis could be partially restricted by the availability of messenger RNA at maturity.However, reciprocal mixing experiments of supernatant and ribosomal fractions from cotyledons of different developmental age indicated that the supernatant fractions have varying capacities to stimulate in vitro amino acid incorporation. Thus the possibility of the regulation of protein synthesis at the translational level was not precluded.
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The Influence of Axis Removal on Protein Metabolism in Cotyledons of Pisum sativum L.
The protein metabolism of cotyledons attached to the embryonic axis has been compared with that in cotyledons removed from the axis at the initiation of a 6-day imbibition. Total protein declined in the attached but not in the detached cotyledons. Concurrent with the decline in protein level in the intact cotyledons there was an increased capacity to incorporate exogenously supplied leucine into protein. In contrast, detached cotyledons showed a restricted capacity for protein synthesis. It was demonstrated that ribosomal preparations from cotyledons of intact seedlings contained an increasing proportion of polyribosomes as germination progressed and such ribosomes were active in in vitro amino acid incorporation. Ribosomal preparations from detached cotyledons contained few polyribosomes and had a restricted capacity to incorporate amino acids in vitro. The in vitro incorporation of phenylalanine was stimulated by polyuridylic acid with the stimulation being greatest in ribosomal preparations from detached cotyledons. The results suggest that an axis component may regulate the availability of messenger RNA in the cotyledons during germination.
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Nucleic Acid Metabolism during Greening and Unrolling of Barley Leaf Segments.
Barley (Hordeum vulgare) leaf segments unroll and green when illuminated. Illuminated segments also have an increased capacity for RNA synthesis. Part of this increased RNA synthesis may be attributed to an increased RNA polymerase activity. In addition, following illumination there is an increased formation of polysomes.Analyses of RNA synthesized during illumination showed that the radioactive RNA which accumulated was predominantly associated with cytoplasmic ribosomal RNAs. It appears that the early phases of greening are achieved without chloroplast RNA synthesis. Following extended illumination there was evidence of chloroplast ribosomal RNA synthesis; however, this occurred after appreciable chlorophyll synthesis. Actinomycin D, which effectively inhibits RNA synthesis and leaf unrolling, restricts chlorophyll synthesis only during the later stages of illumination. 5-Fluorouracil inhibits the bulk of RNA synthesis but not greening, unrolling, or polysome formation. Studies with inhibitors of protein synthesis have demonstrated a requirement for protein synthesis concomitant with chlorophyll production and leaf unrolling.
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Effects of light and growth regulators on leaf unrolling in barley.
The influence of light, gibberellic acid, and abscisic acid on unrolling of etiolated barley leaf segments was investigated. Gibberellic acid stimulated unrolling of both illuminated and nonilluminated leaf segments. In contrast, abscisic acid prevented light-stimulated unrolling and abolished the slight unrolling of segments maintained in the dark.Analysis of the time course of photoinduced unrolling showed a lag period of 6 hours before the onset of rapid leaf unrolling. The application of gibberellic acid to illuminated segments shortened this lag phase. Also, incubating the segments in buffer in darkness prior to illumination eliminated the lag period. Inhibitors of RNA and protein synthesis prevented light- and gibberellic acid induced unrolling, indicating a requirement for macromolecular synthesis. The possibilities that the lag period of unrolling following illumination represents the time required for the removal of endogeneous inhibitor or the synthesis of essential macromolecules are discussed.
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Effects of growth regulators on ribonucleic acid metabolism of barley leaf segments.
Illumination or gibberellic acid treatment of etiolated barley leaf segments stimulates unrolling and results in an increased level of RNA. In contrast, segments treated with abscisic acid do not unroll and have a lower content of RNA. Gibberellic acid treatment enhanced the capacity of segments to incorporate radioactivity from (32)P-orthophosphate into all the RNA components detected by gel electrophoresis; abscisic acid greatly restricted the incorporation of precursors into all the RNA fractions. In conjunction with a changed capacity for RNA synthesis it was observed that abscisic acid-treated segments had a lowered soluble DNA-dependent RNA polymerase level in comparison to gibberellic acid-treated or illuminated segments. However, the influence of growth regulators on RNA polymerase content of the segments was associated with general effects on protein level rather than a specific effect on the synthesis of polymerase enzyme. Ribosomal preparations from gibberellic acid-treated segments had a greater percentage of polysomes and a greater capacity for amino acid incorporation in vitro into proteins than similar preparations from abscisic acid-treated segments.
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