The Influence of Syringomycin on Ribonucleic Acid Synthesis

Syringomycin, a wide-spectrum antibiotic produced by strains of Pseudomonas syringae which cause bacterial canker of peach, was able to bind to salmon sperm and calf thymus deoxyribonucleic acid but not to calf thymus histone; it also inhibited ribonucleic acid polymerase activity. These abilities to bind to deoxyribonucleic acid and to inhibit ribonucleic acid polymerase were inactivated when the phytotoxic and antibiotic properties of syringomycin were inactivated.     

Developmental Changes in Multiple Forms of Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase in Soybean Hypocotyl

The relative levels of multiple RNA polymerases were determined in soybean (Glycine max L. var. Wayne) hypocotyl during various stages of development. The meristematic region of the hypocotyl contains more total polymerase activity per gram fresh weight and a greater proportion of polymerase I relative to II than the differentiated regions. The fully elongated tissue comprising the lower half of the hypocotyl contains mainly RNA polymerase II. The hook region contains a polymerase activity peak which is completely sensitive to alpha-amanitin and partially sensitive to rifamycin SV. This peak is not detectable in other regions of the hypocotyl. Polymerase I is reproducibly separated into a major and a minor component, both being resistant to alpha-amanitin. The two components elute at salt concentrations of 0.2 m and 0.23 m KCl, respectively, while the alpha-amanitin-sensitive polymerase (II) elutes at 0.3 m KCl. The polymerase activity peak which is detectable only in the hook region elutes at approximately 0.5 m KCl. Polymerase levels were also determined in water-stressed tissue and in tissue which was harvested after three days of growth instead of the usual four days.     

Increased Activity of Chromatin-bound Ribonucleic Acid Polymerase from Soybean Hypocotyl with Spermidine and High Ionic Strength

Optimal activity of chromatin-bound RNA polymerase from soybeans is obtained with 1 mm Mn²⁻, but only when high ionic strength or polyamines are included in the medium. Such inclusion does not increase the Mg²⁺ activation of the polymerase, but it does lower the concentration needed for optimum activity from 10 mm to 1 mm. Mg²⁻ activation is inhibited by added Mn²⁺, and the inhibition is relieved by high ionic strength or spermidine. The RNA polymerase with either cation is almost entirely polymerase I at low and high ionic strength as evidenced by insensitivity to α-amanitin. Treatment of soybean seedlings with 2,4-dichlorophenoxyacetic acid does not change these characteristics; although the activity rises 3- to 4-fold.     

Stimulation of Auxin Induced Ethylene Production in Mung Bean Hypocotyl Segments by 5,5' -Dithiobis-2-nitrobenzoic Acid

The non-permeant protein inhibitor 5,5'-dithiobis-2-nitrobenzoicacid (DTNB) was tested for its effects on auxin induced ethyleneproduction. There was a stimulation in the rate of auxin inducedethylene production at all concentrations of DTNB tested (1,2, 5, and 10 mM). The 5 mM DTNB treatment promoted the maximumstimulation of ethylene production with no further enhancementat the 10 mM concentration. After 12 hr ethylene productionplateaued with 0.1 mM indoleacetic acid (IAA) alone and in combinationwith 1 and 2 mM DTNB. Although the DTNB treatments plateauedit was at a higher level than IAA alone. Both the 5 and 10 mMtreatments of DTNB plus IAA did not show this leveling responseeven after 22 hr at which time these treatments were between90 and 100% higher than the control. There was no stimulationof ethylene production by DTNB in the absence of IAA. Segmentstreated with 10^–4 M rß-naphthaleneacetic acid(NAA) produced significantly higher levels of ethylene thanIAA at the same concentration. Stimulation of ethylene productionby DTNB was greatest at lower concentrations of IAA and NAA.The uptake of ¹⁴C-NAA by mung bean segments was 6-fold greaterin the presence of DTNB than in its absence. Ca^SS was requiredin the incubating media for DTNB to be effective. In the presenceof Ca^SS there was a highly significant increase in ethyleneproduction while in its absence there was no significant effect.The stimulation of IAA induced ethylene production appearedto have a pH optima of 4.6, at higher pH values this responsewas not shown. ¹ Approved for publication May 28, 1981 as paper number 6243in the journal series of the Pennyslvania Agricultural ExperimentStation. (Received June 10, 1981; Accepted January 5, 1982)     

The Isolation and Characterization of Adenosine Monophosphate-rich Polynucleotides Synthesized by Soybean Hypocotyl Cells: Their Relation to Messenger Ribonucleic Acid

Plant ribonucleic acids which have high adenosine monophosphate concentrations were studied. Purified deoxyribonucleic acid-like ribonucleic acid and tenaciously bound ribonucleic acid fractions both contained poly-adenosine monophosphate sequences (those from the latter being longer than those from the former); without these poly-adenosine monophosphate sequences their base compositions were the same. The average poly-adenosine monophosphate sequence from purified tenaciously bound ribonucleic acid was 160 residues long, as measured by gel electrophoresis. However, base hydrolysis and chromatography indicated one 3′-nucleoside (adenosine) per 71 nucleotides, giving a chain length of 72 residues. The dominant species in the cytoplasm, as measured by radioactive precursor incorporation, was tenaciously bound ribonucleic acid, whereas deoxyribonucleic acid-like ribonucleic acid was present in greater amounts in the nucleus. This work provides evidence that deoxyribonucleic acid-like ribonucleic acid and tenaciously bound ribonucleic acid represent forms of messenger ribonucleic acid in soybean, with deoxyribonucleic acid-like ribonucleic acid residing in the nucleus, perhaps as the messenger ribonucleic acid precursor, and tenaciously bound ribonucleic acid residing, as the active messenger ribonucleic acid, in the cytoplasm.     

生长素、乙烯和一氧化氮对拟南芥下胚轴插条形成不定根的调节

研究生长素、乙烯和一氧化氮（NO）对拟南芥下胚轴插条形成不定根的调节,以及生长素和乙烯信号转导成员在IAA促进不定根形成中的作用的结果表明：拟南芥切条以IAA和硝普钠（N0供体）单独处理7d后的不定根形成均受到促进,其中以50μmol·L^-1 IAAμmol·L^-1 SNP的促进作用为最强,乙烯的促进作用不明显;生长素运输和信号转导以及乙烯信号转导相关突变体对IAA促进生根作用的敏感性比野生型有所下降,特别是IAA14功能获得型的突变体。IAA和NO在促进不定根形成中有协同效应。     

Auxin Has No Effect on Modification of External pH by Soybean Hypocotyl Cells

The cellular adjustment of the pH of the external environment of soybean (Glycine max) hypocotyl elongating cells, frequently assumed to be hydrogen ion secretion when the pH is lowered, is unaffected by auxin. These elongating cells actively adjust the external hydrogen ion concentration (from any pH in the range of 4-8) to pH 5.4 + 0.2. This pH adjustment occurs in a medium which does not contain potassium. Growth-optimum auxin concentrations have no effect on cellular pH adjustment of the external medium, whether added at the beginning of the experiment or after the equilibrium pH is attained. The pH adjustment by the cells occurs rapidly and in spite of the presence of a cuticle.     

Cell Elongation and Microtubule Behavior in the Arabidopsis Hypocotyl: Responses to Ethylene and Auxin

During elongation of the Arabidopsis hypocotyl, each cell reacts to light and hormones in a time- and position-dependent manner. Growth in darkness results in the maximal length a wild-type cell can reach. Elongation starts at the base and proceeds in the acropetal direction. Cells in the upper half of the hypocotyl can become the longest of the whole organ. Light strongly inhibits cell elongation all along the hypocotyl, but proportionally more in the upper half. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is known to stimulate hypocotyl elongation in the light. Here we show that this stimulation only occurs in cells of the apical half of the hypocotyl. Moreover, ACC application can partially overcome light inhibition, whereas indole-3-acetic acid (IAA) cannot. On low-nutrient medium (LNM) in the light, elongation is severely reduced as compared to growth on rich medium, and both ACC and IAA can stimulate elongation to the levels reached on a nutrient-rich medium. Furthermore, microtubule orientation was studied in vivo. During elongation in darkness, transverse and longitudinal patterns are clearly related with rates of elongation. In other conditions, except for the association of longitudinally orientated microtubules with growth arrest, microtubule orientation is merely an indicator of developmental age, not of elongation activity. A hypothesis on the relation between microtubules and elongation rate is discussed.     

Ribonucleic Acid Polymerase Catalyzing Synthesis of Double-stranded Arbovirus Ribonucleic Acid

The large-particle fraction from the cytoplasm of chick embryo fibroblasts infected with Semliki Forest virus was found to catalyze the incorporation of the 5'-triphosphates of guanosine, adenine, cytidine, and uridine into an acid-insoluble alkali-labile product. The conditions affecting the preparation and assay of this enzyme were investigated. The ribonucleic acid (RNA) polymerase was not present in uninfected cells, and it appeared in infected cells at the time of rapid viral RNA synthesis. The polymerase was found to catalyze the synthesis of a species of RNA which was resistant to ribonuclease and which exhibited the sedimentation properties, buoyant density, and thermal transition temperature of the double-stranded RNA found in vivo in chick cells infected with Semliki forest virus. Attempts to demonstrate that the reaction product of this enzyme also included single-stranded viral RNA were not successful. Although other interpretations are possible, these results give some support to the suggestion that more than one enzyme may be involved in the replication of viral RNA.     

Inhibition of Auxin-induced Deoxyribonucleic Acid Synthesis and Chromatin Activity by 5-Fluorodeoxyuridine in Soybean Hypocotyl

Rootless soybean (Glycine max) seedlings were used as a test system to examine the action of auxin on chromatin-directed RNA synthesis. Chromatin from the basal tissue of rootless seedlings (both control and auxin-treated) had RNA synthetic capacity similar to that of chromatin from comparably treated intact seedlings. When DNA synthesis normally induced in the basal tissue by auxin was blocked in the rootless seedlings by 5-fluorodeoxyuridine, the auxin enhancement of chromatin activity was inhibited 70%. This level was still three times the control level, indicating that auxin influenced the synthetic activity of existing DNA template. Experiments with Escherichia coli RNA polymerase revealed that chromatin from both auxin- and auxin plus 5-fluorodeoxyuridine-treated tissue saturated at higher levels than chromatin from control tissue.     

The Structural Organization of Ribonucleic Acid Associated with Soybean Microsomes

The microsomal fraction of soybean (Glycine max) hypocotylswas characterized using analytical and electron microscope techniques.Two microsomal sub-fractions (smooth and rough vesicles) wereseparated by untracentrifugation. Analysis showed that the ribonucleicacid (RNA) of the microsomal fraction cannot be completely accountedfor by the ribosomes, and that some of the RNA is associatedwith the membranes in a non-ribosomal form. A similar conclusionwas reached by using ethylenediaminetetra-acetic acid (EDTA)to disperse the ribosomal material. Although no visible robosomesremained after the treatment with EDTA, the microsomal fractionretained a quarter of its RNA. Ribonuclease removed all themocrosomal RNA without visibly altering the membrane structureexamined in cross section. When hypocotyl tissue sections wereincubated with ¹⁴C amino-acids, the microsomes incorporatedthe radioactive label more rapidly than any other subcellularfraction. This was especially true in the rapidly growing zoneof the hypocotyl. Smooth microsomes were 75 per cent as activeas rough microsomes. These observations are discussed with referenceto the structural organization of the microsomal RNA and itsrole in protein synthesis.     

Influence of Gibberellic Acid on Growth and Endogenous Auxin Level in Epicotyl and Hypocotyl Tissues of Normal and Dwarf Bean Plants

Application of gibberellic acid to the apex of dwarf bean plants (cv. Alabaster) stimulated the elongation growth of epicotyl and hypocotyl but showed no significant effect on elongation growth in a normal cultivar (‘Blue Lake’). Gibberellin-treatment of dwarf plants was characterized by about twofold increase in the level of endogenous auxin. Maximum increase in IAA level was observed after 48 h of GA treatment. There was less increase in IAA content in normal bean plants. — Gibberellin treatment to excised epicotyl and hypocotyl sections of either dwarf or normal cultivar showed no effect on elongation growth. However, a considerable increase in the auxin level was observed in the sections of the dwarf cultivar. The maximum effect occurred with only 1 h incubation in basal medium containing gibberellin. — The indolo-α-pyrone spectro-fluoremetric method for IAA determination was used.     

Role of Isoleucyl-Transfer Ribonucleic Acid Synthetase in Ribonucleic Acid Synthesis and Enzyme Repression in Yeast

Temperature-sensitive mutations in the isoleucyl-transfer ribonucleic acid (tRNA) synthetase of yeast, ilS(-)1-1 and ilS(-)1-2, were used to examine the role of aminoacyl-tRNA synthetase enzymes in the regulation of ribonucleic acid (RNA) synthesis and enzyme synthesis in a eucaryotic organism. At the permissive temperature, 70 to 100% of the intracellular isoleucyl-tRNA was charged in mutants carrying these mutations; at growth-limiting temperatures, less than 10% was charged with isoleucine. Other aminoacyl-tRNA molecules remained essentially fully charged under both conditions. Net protein and RNA syntheses were rapidly inhibited when the mutant was shifted from the permissive to the restrictive temperature. Most of the ribosomes remained in polyribosome structures at the restrictive temperature even though protein synthesis was strongly inhibited. Two of the enzymes of isoleucine biosynthesis, threonine deaminase and acetohydroxyacid synthetase, were derepressed about twofold during slow growth of the mutants at a growth-limiting temperature. This is about the same degree of derepression that is achieved by growth of an auxotroph on limiting isoleucine. We conclude that charged aminoacyl-tRNA is essential for RNA synthesis and for the multivalent repression of the isoleucine biosynthetic enzymes. Aminoacyl tRNA synthetase enzymes appear to play important regulatory roles in the cell physiology of eucaryotic organisms.     

Abscisic Acid, Auxin, and Ethylene in Explant Abscission

Experiments with explants of Phaseolus vulgaris L., cv. CanadianWonder, show that abscission and the associated rise in oarboxymethyl-cellulaseactivity in the separation zone are initiated by a peak in ethyleneproduction during senescence of pulvinar tissue distal to thezone. Distal applications of abscisic acid (ABA) induce an earlierpeak in ethylene production, increase cellulase activity, andpromote abscission. ABA is more effective in these ways if treatmentis delayed from 0 to 24 h after excision. With increasing concentrations of ABA the maximum rate of ethylene production is achievedsooner. Indol-3yl-acetic acid (IAA) and ABA are antagonisticin this system and have opposing effects. IAA retards the timeof peak ethylene-production and delays abscission. Explantsmay be retained for long periods without abscinding if incubatedin an ethylene-free atmosphere: the addition of ethylene forany one 24-h period (except the first 24 h after excision) willinduce abscission. The initial period of insensitivity to ethyleneis extended by distal applications of IAA. Ethylene-inducedabscission can be inhibited by IAA applied up to 72 h afterexcision provided the ethylene is not applied first. It is proposedthat abscission in the explant is controlled at two levels:(1) an auxin-dependent stage determining the duration of insensitivityto ethylene; (2) the timing of a rise in ethylene productionin senescing tissue distal to the separation zone. An auxin-ethylenebalance-mechanism at the separation zone is discussed.     

Ribonucleic Acid Regulation in Permeabilized Cells of Escherichia coli Capable of Ribonucleic Acid and Protein Synthesis

A cell permeabilization procedure is described that reduces viability less than 10% and does not significantly reduce the rates of ribonucleic acid and protein synthesis when appropriately supplemented. Permeabilization abolishes the normal stringent coupling of protein and ribonucleic acid synthesis.     

生长素与乙烯信号途径及其相互关系研究进展

长期的研究表明,生长素在调节植物生长发育的各种生理活动中起关键作用,但对它如何调控这些生理活动却缺乏系统和深入的了解。最近,细胞核内生长素信号途径的发现为揭示其作用机制带来了曙光。乙烯参与果实成熟及植物对逆境的反应等生理活动,其信号途径也已得到部分阐明。越来越多的证据表明,乙烯的作用与生长素对植物生长发育的调控之间有密切的联系。该文概述了生长素与乙烯信号途径的研究进展及其相互关系,讨论了生长素在植物三重反应中的作用;并对生长素与乙烯相互关系研究中存在的问题及研究前景进行了探讨。     

生长素与乙烯信号途径及其相互关系研究进展

长期的研究表明, 生长素在调节植物生长发育的各种生理活动中起关键作用, 但对它如何调控这些生理活动却缺乏系统和深入的了解。最近, 细胞核内生长素信号途径的发现为揭示其作用机制带来了曙光。乙烯参与果实成熟及植物对逆境的反应等生理活动, 其信号途径也已得到部分阐明。越来越多的证据表明, 乙烯的作用与生长素对植物生长发育的调控之间有密切的联系。该文概述了生长素与乙烯信号途径的研究进展及其相互关系, 讨论了生长素在植物三重反应中的作用; 并对生长素与乙烯相互关系研究中存在的问题及研究前景进行了探讨。     

Inhibitors of Ribonucleic Acid Synthesis in Saccharomyces cerevisiae: Decay Rate of Messenger Ribonucleic Acid

Daunomycin and ethidium bromide, two deoxyribonucleic acid-intercalating drugs, inhibit ribonucleic acid (RNA) and protein synthesis in Saccharomyces cerevisiae. Both agents rapidly curtail uptake of radioactive adenine, whereas the kinetics of radioactive leucine uptake after drug addition are consistent with translation of a pool of exponentially decaying messenger RNA. Messenger RNA half-life determinations from these experiments gave identical results over a range of drug concentrations; this value is 21 +/- 4 min at 30 C. In a temperature-sensitive mutant in which RNA synthesis is curtailed at the nonpermissive temperature, a similar half-life for messenger RNA decay is found both in the absence and in the presence of either drug. This indicates that at the concentrations used in this study, neither daunomycin nor ethidium bromide has an appreciable direct effect on translation and do not increase the lability of messenger RNA.