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 ³²P-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.     

Synthesis of ribonucleic acids during the germination of Rhizopus stolonifer sporangiospores

A number of ribonucleic acids initiated synthesis during the first 15 min of germination of Rhizopus stolonifer sporangiospores. They included ribosomal, 5S, and transfer RNA, and a heterogeneously-sedimenting fraction that composed about 5% of the total cellular RNA; this fraction was unmethylated, did not compete with ribosomal RNA for hybridization to DNA, and was bound to poly dT-cellulose in a manner characteristic of RNAs containing polyadenylate segments. The nearly simultaneous onset of synthesis of the various RNAs with germination contrasts with the sequential onset of RNA synthesis reported for other fungal spores.     

Ribonucleic Acid Synthesis by Cucumber Chromatin: Developmental and Hormone-induced Changes

When intact etiolated 2-day cucumber (Cucumis sativus) embryos were treated with indoleacetic acid (IAA), gibberellin A₇ (GA₇), or kinetin, chromatin derived from the embryonic axes exhibited an increased capacity to support RNA synthesis in either the presence or the absence of bacterial RNA polymerase. An IAA effect on cucumber RNA polymerase activity was evident after 4 hours of hormone treatment; the IAA effect on DNA template activity (bacterial RNA polymerase added) occurred after longer treatments (12 hours). GA₇ also promoted template activity, but again only after a prior stimulation of endogenous chromatin activity. After 12 hours of kinetin treatment, both endogenous chromatin and DNA template activities were substantially above control values, but longer kinetin treatments caused these activities to decline in magnitude. When chromatin was prepared from hypocotyl segments that were floated on a GA₇ solution, a GA-induced increase in endogenous chromatin activity occurred, but only if cotyledon tissue was left attached to the segments during the period of hormone treatment.     

Butachlor influence on selected metabolic processes of plant cells and tissues

Time- and concentration-course studies were conducted to determine the effects of butachlor (N-[butoxymethyl]-2-chloro-2′,6′-diethylacetanilide) on photosynthesis, protein synthesis, RNA synthesis, and lipid synthesis using isolated leaf cells of red kidney bean (Phaseolus vulgaris L.). At the 2-h incubation period, butachlor inhibited photosynthesis, protein synthesis, RNA synthesis, and lipid synthesis 99, 99, 96, and 81% respectively at 100 μM, and 0, 19, 17, and 40% respectively at 10 μM. At 100 μM and 15-, 30-, and 60-min incubations, RNA synthesis was inhibited 20, 76 and 90% respectively, and lipid synthesis 35, 48, and 62% respectively; photosynthesis and protein synthesis were inhibited over 90% at all of these time periods. The effects of 50 μM butachlor on protein and RNA synthesis in rice (Oryza sativa L.) and barnyardgrass (Echinochloa crusgalli L.) root and shoot segments were also investigated. Protein synthesis was inhibited in both species and to a greater degree in roots (81–90%) than in shoots (55–65%). RNA synthesis was inhibited 33% in barn-yardgrass roots but not significantly in barnyardgrass shoots or either organ of rice.     

Biochemical responses of pea root tissue to cytokinin: enhanced rates of RNA synthesis

Rates of RNA synthesis were studied in cultured pea (Pisum sativum) root segments and cortical explants which require the hormone cytokinin for DNA replication and cell proliferation. Rate calculations were based on the specific radioactivity of the extracted RNA and the specific radioactivity of the extracted ATP pool after a pulse with ³H-adenosine. The kinetics of RNA synthesis was studied after 24 hours of culture with or without kinetin. We found that kinetin stimulated a 2- to 4-fold enhancement in the rate of RNA synthesis after 24 hours of culture as compared to controls. A similar order of magnitude of stimulation of RNA synthesis was found when RNA was isolated by cesium chloride centrifugation. Pulses during the first 24 hours indicate that kinetin stimulates the rate of RNA synthesis as early as 9 hours after treatment has begun. During the first 24 hours of culture, kinetin did not affect the specific radioactivity of the ATP pool. The ATP pool equilibrated slowly with the exogenous label (³H-adenosine) in the presence or absence of kinetin. After 3 days in culture, we found kinetin to cause an expansion of the extractable ATP pool and a corresponding reduction in the ATP pool specific radioactivity. We interpret these results to indicate a stimulation in the rate of RNA synthesis due to kinetin treatment prior to any other known response.     

Massive synthesis of ribonucleic Acid and cellulase in the pea epicotyl in response to indoleacetic Acid, with and without concurrent cell division

Measurements were made over a 4-day period of the effect of added indoleacetic acid (IAA), puromycin, actinomycin D and 5-fluorodeoxyuridine (FUdR) on growth and the levels of total DNA, RNA, protein and cellulase in segments of tissue at the apex of decapitated etiolated epicotyls of Pisum sativum, L. var. Alaska.

The hormone induced swelling of parenchyma cells and cell division. By 3 days after IAA application, the amounts of DNA and protein were approximately double, RNA triple and cellulase 12 to 16 times the levels in controls. All of these changes were prevented by both puromycin and actinomycin D. FUdR prevented DNA synthesis and cell division but not swelling or synthesis of RNA, protein and cellulase.

It is concluded that IAA-induced RNA synthesis is required for cellulase synthesis and lateral cell expansion, whether or not cell division takes place.

     

Selective activation of RNA polymerase I in fat body nuclei of Sarcophaga peregrina larvae by beta-ecdysone.

RNA synthesis in fat body nuclei of Sarcophaga peregrina larvae was temporarily activated after injection of β-ecdysone: increased synthesis was detectable 2 hr after injecting the hormone and lasted for at least 2 hr. This increased RNA synthesis was insensitive to α-amanitin and was observed in KCl-free reaction mixture, indicating that β-ecdysone activated RNA polymerase I but not RNA polymerase II. No activation was observed when protein synthesis was inhibited by cycloheximide, suggesting that protein synthesis was essential for the activation of the nuclei.     

Regulation of vitellogenin synthesis by juvenile hormone analogue in Coccinella septempunctata

Vitellogenesis in the lady beetle, Coccinella septempunctata, is controlled by juvenile hormone (JH). When immature females were reared on an artificial diet, they were characterized by hypertrophy of the fat bodies and slow development of the ovaries. Vitellogenin (Vg) synthesis in the fat body remained at a very low level throughout adult development. RNA synthesis also stayed at a relatively low level. Treatment with hydroprene induced vitellogenesis in these non-fecund females. Stimulation in Vg synthesis in hormone-treated females was demonstrated both in vivo and in fat body culture. Synthesis of fat body RNA also increased after hormone treatment. Fat body RNA from hormone-treated females directed the synthesis of Vg polypeptides both in Xenopus oocytes and in a reticulocyte lysate. Thus the induction of Vg synthesis by JH involves an increase in the level of translatable Vg mRNA.     

Morphogenetic pathway of bacteriophage φ6: A flow analysis of subviral and viral particles in infected cells

Three types of virus-specific particles of double-stranded RNA bacteriophage φ6 were isolated and characterized by pulse-label and pulse-chase experiments on φ6-infected Pseudomonas phaseolicola. The first particle was “previrion I”, which consisted of early proteins P1, P2, P4 and P7, and had no RNA. It was detected immediately after labeling of proteins and the radioactivity was chased into the second structure, designated previrion II, after ten minutes. Previrion II contained three segments of double-stranded RNA in addition to the component of previrion I, and had RNA polymerase activity that produced messenger RNA species coding for late proteins. The RNA polymerase activity in the cell extract emerged nearly in parallel with the synthesis of late proteins, and this activity of previrion II was supposed to be responsible for late protein synthesis in infected cells. Via previrions I and II, the third radioactive particle was observed in infected cells after late protein synthesis started. This particle was identified as the intact virion, because it had infectivity as well as all of the viral components, including lipids. This intact virion was accumulated in the infected cell before bursting the cell.     

The relationships among RNA synthesis,RNA polymerase synthesis and guanosine tetraphosphate levels in Escherichia coli during nutritional shift-up

The relationships among the rate of RNA synthesis, RNA polymerase synthesis and activity, and guanosine tetraphosphate levels were investigated following nutritional shift-up in Escherichia coli. RNA synthesis continues at the preshift rate for 1.5 min after which an increase is observed that reaches a new steady-state rate at between 2 and 2.5 min. RNA polymerase activity measured in crude extracts increases immediately and by 10 min has increased 50%. RNA polymerase synthesis as measured by the synthesis of the β and β′ subunits lags for 2.5 min and then increases 75% by 10 min. Guanosine tetraphosphate levels decrease 50% by 3 min to levels characteristic of steady-state post-shift-up cells. The significance of these data to the regulation of RNA synthesis during shift-up is discussed.     

Myosin-Va-Dependent Cell-To-Cell Transfer of RNA from Schwann Cells to Axons

To better understand the role of protein synthesis in axons, we have identified the source of a portion of axonal RNA. We show that proximal segments of transected sciatic nerves accumulate newly-synthesized RNA in axons. This RNA is synthesized in Schwann cells because the RNA was labeled in the complete absence of neuronal cell bodies both in vitro and in vivo. We also demonstrate that the transfer is prevented by disruption of actin and that it fails to occur in the absence of myosin-Va. Our results demonstrate cell-to-cell transfer of RNA and identify part of the mechanism required for transfer. The induction of cell-to-cell RNA transfer by injury suggests that interventions following injury or degeneration, particularly gene therapy, may be accomplished by applying them to nearby glial cells (or implanted stem cells) at the site of injury to promote regeneration.     

Macromolecular events following refeeding of starved Tetrahymena

Tetrahymena were starved in inorganic buffer for 24 h and then refed with enriched nutrient medium. An early increase of protein synthesis which is correlated with the rapid reformation of polysomes occurs prior to the onset of increased RNA synthesis. Inhibition of RNA synthesis with actinomycin D during refeeding did not stop the initiation of increased protein synthesis nor did it stop the reformation of polysomes. The occurrence of increased protein synthesis prior to increased RNA synthesis is a different sequence than has occurred in other studies on this cell and indicates that unlike in bacteria the macromolecular response of this cell to a new environment is not fixed but is dependent upon the cell's previous environmental history.