Activation of protein synthesis by microsomes from aging beet disks

Ethylene regulation of wound-induced ribonuclease in turnip root tissue

Exogenous ethylene enhances the synthesis of wound-induced ribonuclease (RNase) (EC2.7.7.16) in tissue discs of white turnip (Brassica rapa L. var. rapa (L.) Tell.). The half-maximal concentration is <0.01 μl/l ehtylene. Maximal response was obtained with either continuous ethylene treatment, or a 90-min pulse of ethylene followed by flushing with 1500 cm(3) of air/min at standard pressure or 500 cm(3)/min at hypobaric pressure for the remainder of the experiments. Addition of ethylene at 60-75 min after cutting had no effect on RNase activity. Also the effect of ethylene in enhancing RNase decreased about linearly when addition of ethylene was delayed for tissue discs. Since actinomycin-D inhibition of RNase synthesis, observed earlier, is also limited to the initial 45-60 min after cutting, these results are consistent with the view that ethylene is acting at transcription.

Evidence from inhibitor studies that the endophyte synthesises nitrogenase in the root nodules of Alnus glutinosa L. Gaertn

Nitrogenase activity (acetylene reduction assay) in the nodulated non-leguminous angiosperm Alnus glutinosa is inhibited within minutes when plants are exposed to a gas phase containing 90% oxygen On returning the plants to air, nitrogenase activity recovers within a few hours, both in the presence of cycloheximide, which inhibits protein synthesis on 80 S (eukaryotic) ribosomes, and in the absence of inhibitor. When chloramphenicol, which inhibits protein synthesis on 70 S (prokaryotic) ribosomes, is added instead of cycloheximide, recovery from oxygen inhibition does not occur, or occurs only slowly. The effects of chloramphenicol are specific to the D-threo-isomer which indicates a direct inhibition of protein synthesis. Erythromycin has a similar effect to chloramphenicol. Protein biosynthesis in non-nodulated roots is inhibited by cycloheximide but not by chloramphenicol. The results are interpreted as evidence that the nitrogenase within Alnus glutinosa root nodules is synthesised by the microbial symbiont.

Activation of Protein Synthesis upon Dilution of an Arachis Cell Culture from the Stationary Phase

When a stationary phase cell culture of Arachis hypogaea L. is diluted into fresh media, there occurs a 10-fold increase in the rate of protein synthesis. The kinetics of the activation of amino acid-incorporating capacity show a lag of 10 to 15 minutes with maximal activity reached at 2 hours after dilution. The activation of protein synthesis is oxygen-dependent and is accompanied by a 2- to 4-fold increase in polyribosome content, as well as by a 3- to 4-fold increase in the rate of mRNA synthesis. Ribosomal function, as ascertained by determination of ribosomal transit time, is about 2.5 times more efficient in 2-hour diluted cultures as in cells immediately after dilution. These observations indicate that a very early response in the transition of plant cell cultures from the stationary state is an increased capacity for protein synthesis. At a molecular level, this increase in protein synthetic capacity is due in part to an increased mobilization of mRNA into polyribosomes and in part to a more efficient ribosomal translational capacity.

The effect of salt on protein synthesis in the halophyte Suaeda maritima

An amino acid-incorporating microsomal fraction has been isolated from the leaves of the halophyte Suaeda maritima and the characteristics of the incorporation described. There were no differences in the properties of the microsomes isolated from plants grown in saline and non-saline conditions. The incorporation was severely inhibited by high concentrations of sodium or potassium ions. The results are discussed in relation to the mechanism of salt tolerance in halophytes and the localization of salt in the cells.

Effects of cycloheximide, D-threo-chloramphenicol, erythromycin and actinomycin D on De-novo synthesis of cytoplasmic and mitochondrial proteins in the cotyledons of germinating pea seeds

Inhibitors of, and radioactive substrates for, protein synthesis were introduced into germinating pea (Pisum sativum L.) seeds, and protein synthesis was allowed to proceed in vivo. Subsequent analyses of subcellular fractions showed the following: Cycloheximide strongly inhibited the incorporation of [(14)C]leucine into both mitochondrial and cytoplasmic proteins. D-Threo-chloramphenicol and erythromycin did not affect cytoplasmic protein synthesis, but partially inhibited mitochondrial protein synthesis. These results suggest that most of the new mitochondrial proteins were originally synthesized in the cytoplasm. Actinomycin D did not appreciably affect the initial incorporation of [(14)C]leucine into either mitochondrial or cytoplasmic proteins, suggesting that information (mRNA) concerning the initially synthesized proteins may be present in the quiescent seeds. The lack of appreciable incorporation of [(3)H]thymidine into mitochondrial DNA supported our previons report that mitochondria may not be synthesized de novo in pea cotyledons.

Adenosine triphosphatase of bean plastids: its properties and site of formation

Extracts of bean (Phaseolus vulgaris L.) etioplasts and chloroplasts contain a dithiothreitol-activated Ca(2+)-dependent adenosine triphosphatase which is inhibited by Dio-9. The chloroplast and etioplast enzymes have identical R(F) values upon disc gel electrophoresis. Optimum extraction of the enzyme from either plastid preparation is accomplished with 1 mm ethylenediamine tetraacetic acid. Photophosphorylation capacity can be partially restored to depleted chloroplast preparations by addition of either the chloroplast or etioplast extract. These results suggest that the adenosine triphosphatase from etioplasts and chloroplasts represents a modified coupling factor for photophosphorylation.The specific activity of the adenosine triphosphatase in the extracts of plastids increases upon greening of etiolated plants due to protein synthesis. This light-induced increase is inhibited by both chloramphenicol and cycloheximide, specific inhibitors of chloroplastic and cytoplasmic protein synthesis. There is no accumulation of adenosine triphosphatase in postribosomal supernatants of cycloheximide or chloramphenicol treated leaves. The results indicate that both the chloroplastic and the cytoplasmic ribosomal systems are required for the formation of the chloroplast adenosine triphosphatase.

Effects of gamma irradiation on chromatin activity of sugar beet tissue

Chromatin-associated RNA polymerase activity increases during washing of sugar beet tissue to a maximum by 20 hours. This increase was inhibited by dosages of gamma irradiation between 50 and 400 krad. Template availability, as measured by saturating levels of added Escherichia coli RNA polymerase, also increased with washing and was inhibited, although to a lesser extent, by the above irradiation dosages. Neither endogenous polymerase activity nor template availability was affected by high dosages (300 krad) in unwashed tissue. Exposure of tissue to irradiation (300 krad) at different times during a 20-hour washing period severely inhibited the development of RNA polymerase activity during the early stages of washing. The inhibition of template availability, however, was independent of time of irradiation. The data presented are discussed in relation to the mechanisms involved in the inhibitory effects of gamma irradiation on RNA production and subsequent protein synthesis.

Further similarities between chloroplast and bacterial ribosomes

Protein synthesis by chloroplasts isolated under aseptic conditions from Phaseolus vulgaris leaves is inhibited by the bacterial antibiotics spectinomycin, lincomycin, and erythromycin; that by chloroplasts from Nicotiana tabacum leaves is inhibited by spectinomycin and lincomycin but not by erythromycin. Protein synthesis by cytoplasmic ribosomes from plants and animals is not inhibited by these compounds, nor is amino acid activation by the soluble fraction from bean chloroplasts. These results suggest that chloroplast ribosomes possess sites which bind several unrelated bacterial antibiotics and support the idea that chloroplasts originated from prokaryotic cells. These antibiotics may be useful in studying the process of chloroplast formation in intact cells.

A multiple origin for plastids and mitochondria

The impressive homologies between mitochondria and plastids, on the one hand, and procaryotic organisms, on the other, make it almost certain that these important cellular organelles had their origin as independent organisms. The vast number of symbiotic relationships of all degrees of evolutionary antiquity which have been found in contemporary organisms point to the ease with which such relationships can be established.

Specificity of cycloheximide in higher plant systems

Although cycloheximide is extremely inhibitory to protein synthesis in vivo in higher plants, the reported insensitivity of some plant ribosomes suggests that it may not invariably act at the ribosomal level. This suggestion is reinforced by results obtained with red beet storage tissue disks, the respiration of which is stimulated by cycloheximide at 1 microgram per milliliter. Inorganic ion uptake by these disks is inhibited by cycloheximide at 1 microgram per milliliter while the uptake of organic compounds, by comparison, is unaffected. Ion uptake by all nongreen tissues tested is inhibited by cycloheximide, but leaf tissue is unaffected, indicating that the ion absorption mechanism in the leaf may differ fundamentally from that in the root. It is concluded that cycloheximide can affect cellular metabolism other than by inhibiting protein synthesis and that the inhibition of ion uptake may be due to disruption of the energy supply.

Influence of calcium on sodium and potassium absorption by fresh and aged bean stem slices

The influence of Ca on the aging processes of bean stem (Phaseolus vulgaris) slices and on the absorption of K and Na by fresh and aged slices was investigated. In the presence of Ca, fresh tissue showed a preferential Na uptake. The preference for Na over K resulted from a differential depressive effect of Ca on absorption of these two ions. In aged tissue Na uptake was also depressed, but K absorption was accelerated, with a net result of a much greater absorption of K than Na.The presence of Ca in the aging medium promoted the development of K-absorbing capacity as well as an increase in the rate of respiration but did not influence the loss of capacity to absorb Na as tissue aged. This, along with the demonstration that protein synthesis is involved in the development of K-absorbing capacity by aging tissue, suggests that Ca may have an effect on basic physiological processes concerned with development of ion absorption by aging tissue. The influences that Ca may have on the physical and physiological aspects of ion transport are discussed.

The induction of phosphatase activity in thin slices of Jerusalem artichoke tissue by treatment with indole acetic acid

Prolonged washing of thin slices of Jerusalem artichoke (Helianthus tuberosus) did not result in any apparent increase in the activity of the phosphatase enzymes, although the washing process is known to stimulate the activity of many other enzymes. However, treatment of the tissue in either 3×10(-5)M 2,4-dichlorophenoxyacetic acid or 10(-4)M indole acetic acid resulted in a 3-fold increase in the phosphatase activity. Significant stimulations of activity were detectable one hour after placing the tissue in the auxin. Treatment of the tissue in either kinetin or gibberellic acid failed to stimulate the activity of the enzyme. The enhancement of phosphatase activity caused by auxins could not be prevented by adding cycloheximide to the treatment solution an it is concluded that the stimulation occurred as the result of the activation of enzyme already present in the tissue rather than by the de novo synthesis of new enzyme protein.

The influence of microbial contamination of fresh and washed beetroot disks on their capacity to absorb phosphate

When plant storage tissue is cut into thin disks it rapidly develops a high capacity to absorb phosphate from dilute solutions. The recent trend has been to attribute the development of this ability to the increased metabolic activity of bacteria known to be containing the tissue. Data presented in this paper shows that bacterial contamination of the tissue does contribute to the apparent uptake of phosphate by the disks. However, during the ageing process the number of bacteria decrease and therefore contribute less to the total uptake in the aged tissue. If the tissue is prepared and maintained in a sterile condition it is still able to develop a high capacity for phosphate absorption during ageing.

[Chloroplast ribosomes: stereospecificity of inhibition by chloramphenicol]

Chloroplast ribosomes from tobacco leaves show the same stereospecificity of inhibition by chloramphenicol as bacterial ribosomes do. Cytoplasmic ribosomes from the same leaves are unaffected by chloramphenicol. These results remove doubts raised by nonstereospecific effects of chloramphenicol on higher plant cells and support the concept that chloroplasts have evolved from prokaryotes.

Photoinduction of phenylalanine deaminase in gherkin seedlings : III. Effects of excision and irradiation on enzyme development in hypocotyl segments

1. If hypocotyl segments from gherkin seedlings are floated on water the level of the enzyme phenylalanine deaminase (PADAse) increases for about 30 hours (25°) and then remains constant. The pattern of these changes differs from that of the photoinduced changes in the PADAse level in intact seedlings, where an initial increase in enzyme level is followed by a decline that starts at 25° about 3 hours after the beginning of irradiation. 2. The development of PADAse in the segments is inhibited by cycloheximide and puromycin, inhibitors of protein synthesis, and by the end products of its reaction, namely, cinnamic acid and p-coumaric acid. Repression due to the accumulation of p-coumaric acid is the likely reason why the irradiation gradually loses its effect on the induction of PADAse in intact seedlings whereas the derepressing effect of excision could be explained by the disappearance of p-coumaric acid from the segments. 3. Application of cinnamic acid or p-coumaric acid to the segments 16 hours after excision results in a drop in the PADAse level. Cycloheximide prevents this decline. These findings indicate the induction of a PADAse inactivating system requiring de novo protein synthesis, probably the same system found to be responsible for the drop in enzyme level in intact seedlings. 4. Irradiation of the segments with blue light stimulates the PADAse synthesis, and so does the addition of glutathione to the incubation medium. These agents must have different sites of action, since irradiation antagonizes the repressing effect of cinnamic acid, whereas glutathione does not.

Characterisation of amino acid incorporation by subcellular fractions from sterile beet disks

The optimum concentrations of leucine, ATP, GTP and Mg(2+) ion for the incorporation of leucine into protein by the microsomal fraction isolated from sterile disks of red beetroot are 0.06 mM, 5 mM, 0.5 mM, and 12 mM respectively. Incorporated (14)C-leucine does not exchange with an excess of soluble-(12)C-leucine. Incorporation into protein is partly dependent on the addition of a high speed supernatant fraction which incorporates leucine into a product with the properties of aminoacyl RNA. Addition of polyuridylic acid to microsomes isolated from fresh disks stimulates the incorporation of phenylalanine into protein nine-fold but has no effect on leucine incorporation. Polyuridylic acid - stimulated incorporation is not inhibited by chloramphenicol. Preincubation of fresh microsomes with trypsin does not increase their activity. These results suggest that the low activity of fresh microsomes may be due to a lack of messenger RNA. The mitochondrial fraction shows a rise and fall in leucine-incorporating ability during aging similar to that shown by the microsomal fraction. Studies with inhibitors suggest that about 25% of this incorporation is due to the mitochondria themselves, the rest being attributable to large microsomes. Fractions isolated from disks aged under non-sterile conditions show large incorporations of leucine which are not dependent on an added energy source. This result confirms the importance of using aseptic techniques when studying the aging of storage tissue disks.

Further evidence of oxygen diffusion as the determining factor in the relation between disk thickness and respiration of potato tissue

The effect of oxygen tension above atmospheric pO(2) on the development of respiratory capacity in potato disks has been examined. Raising the oxygen tension of the aqueous environment to 40% during the aging of 2.0 mm or 3.0 mm thick disks at 25 degrees progressively increased the respiration rate of the tissue as shown by subsequent assay in 100% oxygen. Disks 3.0 mm thick showed a greater response to increased pO(2) than did 2.0 mm disks. A comparison of center 1.0 mm sections excised from 3.0 mm disks after aging, showed that the respiration rate of internal tissue from disks aged in high pO(2) was approximately 40% greater than such tissue aged with atmospheric pO(2). The characteristic inverse relationship between respiration rate and thickness in aged disks can be modified from a concave-downwards curve to a convex-downwards curve by pretreating the tissue with increased pO(2), thus indicating that raising the pO(2) during aging can increase the thickness threshold at which the transition from tissue manifesting the respiratory characteristics of thin disks to that manifesting the characteristics of thick disks, occurs. Similarly increased pO(2) during aging can modify the hyperbolic relationship obtaining between pretreatment temperature in the range 10 degrees to 25 degrees and respiratory capacity of aged 3.0 mm disks, to approximate to the linear relationship observed with 0.75 mm disks. It is concluded that the development of respiratory capacity in disks between 0.75 mm and 3.0 mm thick is restricted by oxygen dificiency and that the characteristic inverse relationship between respiration rate and thickness in aged disks is largely attributable to this factor, the influence of which is discernible both on the development of respiratory capacity and on its subsequent assay.