Avena coleoptile elongation: stimulation by fluorophenylalanine

A 100 to 150% stimulation of Avena coleoptile segment elongation by the amino acid analogue p-fluorophenylalanine (FPA) has been observed. The effect is reversed by phenylalanine and is not seen with comparable concentrations of sodium fluoride. FPA does not alter elongation of red-irradiated segments. Stimulation by FPA occurs only when the apex is intact and the segments are incubated in the absence of exogenous auxin. In the presence of FPA, ¹⁴C-leucine uptake by coleoptile segments is reduced by 34% and protein synthesis by 42%. When pre-incubated on labeled media and subsequently transferred to unlabeled media, segments fail to incorporate into the protein fraction any of the previously absorbed label. It is therefore difficult to ascertain whether FPA results in a genuine inhibition of protein synthesis in apical coleoptile segments. Possible mechanisms for the action of FPA and its relationship to light dependent elongation are considered.     

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.     

Regulation by auxin of carbohydrate metabolism involved in cell wall synthesis by pea stem tissue

Promotion of cell wall synthesis (from glucose) in pea (Pisum sativum) stem segments by indoleacetic acid (IAA) develops over a period of 1 to 2 hours and is comprised of a promotion of glucose uptake plus a promotion of the utilization of absorbed glucose. The effect of IAA resembles, in these and other respects, its effect on cell wall synthesis in oat coleoptile segments, but the pea system differs in not being inhibited by galactose or mannose, in involving considerably more isotope dilution by endogenous substrates, and in certain other respects.     

Stochastic continuous time neurite branching models with tree and segment dependent rates

In this paper we introduce a continuous time stochastic neurite branching model closely related to the discrete time stochastic BES-model. The discrete time BES-model is underlying current attempts to simulate cortical development, but is difficult to analyze. The new continuous time formulation facilitates analytical treatment thus allowing us to examine the structure of the model more closely. We derive explicit expressions for the time dependent probabilities p(γ,t) for finding a tree γ at time t, valid for arbitrary continuous time branching models with tree and segment dependent branching rates. We show, for the specific case of the continuous time BES-model, that as expected from our model formulation, the sums needed to evaluate expectation values of functions of the terminal segment number μ(f(n),t) do not depend on the distribution of the total branching probability over the terminal segments. In addition, we derive a system of differential equations for the probabilities p(n,t) of finding n terminal segments at time t. For the continuous BES-model, this system of differential equations gives direct numerical access to functions only depending on the number of terminal segments, and we use this to evaluate the development of the mean and standard deviation of the number of terminal segments at a time t. For comparison we discuss two cases where mean and variance of the number of terminal segments are exactly solvable. Then we discuss the numerical evaluation of the S-dependence of the solutions for the continuous time BES-model. The numerical results show clearly that higher S values, i.e. values such that more proximal terminal segments have higher branching rates than more distal terminal segments, lead to more symmetrical trees as measured by three tree symmetry indicators.     

Synthesis of individual ribosomal proteins in Escherichia coli B/r

The differential synthesis rates of individual ribosomal proteins (r-proteins) were measured in Escherichia coli B/r during the transition period following a nutritional shift-up from succinate minimal to glucose/ammo acids medium. These rates were observed to respond sequentially to the shift-up; the differential synthesis rate of protein L28 begins to increase within 0.1 of a minute following the shift-up, while the protein L29 synthesis rate begins to increase only after a lag of 2.5 minutes. The onset of induction of the remaining r-proteins occurs within this 2.5-minute interval. Furthermore, there was a twofold variation in the acceleration of the differential synthesis rates of individual r-proteins. Within the initial two to ten-minute period following the shift-up the differential synthesis rates of most r-proteins reached values ranging from 2.2 to 3.0-fold higher than the pre-shift rates, before declining to the post-shift steady-state values. It is suggested that the increases in the differential synthesis rates of r-proteins result in part from increases in the translational efficiency of messenger RNA in the post-shift growth medium and in part from increases in the amount of r-protein mRNA that is present.     

Regulation of glucose metabolism and cell wall synthesis in Avena stem segments by gibberellic Acid

Gibberellic acid (GA) stimulated both the elongation of Avena sativa stem segments and increased synthesis of cell wall material. The effects of GA on glucose metabolism, as related to cell wall synthesis, have been investigated in order to find specific events regulated by GA. GA caused a decline in the levels of glucose, glucose 6-phosphate, and fructose 6-phosphate if exogenous sugar was not supplied to the segments, whereas the hormone caused no change in the levels of glucose 6-phosphate, fructose 6-phosphate, UDP-glucose, or the adenylate energy charge if the segments were incubated in 0.1 m glucose. No GA-induced change could be demonstrated in the activities of hexokinase, phosphoglucomutase, UDP-glucose pyrophosphorylase, or polysaccharide synthetases using UDP-glucose, UDP-galactose, UDP-xylose, and UDP-arabinose as substrates. GA stimulated the activity of GDP-glucose-dependent β-glucan synthetase by 2- to 4-fold over the control. When glucan synthetase was assayed using UDP-glucose as substrate, only β-1,3-linked glucan was synthesized in vitro, whereas with GDP-glucose, only β-1,4-linked glucan was synthesized. These results suggest that one part of the mechanism by which GA stimulates cell wall synthesis concurrently with elongation in Avena stem segments may be through a stimulation of cell wall polysaccharide synthetase activity.     

CHROMOSOMAL DNA SYNTHESIS IN DROSOPHILA MELANOGASTER

Analysis of labeling patterns in three chromosome segments of Drosophila melanogaster has shown that the replicative activity within chromosomes is temporally ordered. Moreover, specific labeling patterns on one chromosome occur with specific patterns on another chromosome with a very high degree of correlation. This circumstance leads to the conclusion that DNA synthesis among all the regions in the three chromosome segments studied is coordinated. The various labeling patterns observed in any one chromosome and the combinations of labeling patterns observed in all three chromosome segments can be arranged in ordered arrays, if one assumes that the DNA synthesis in each chromosome region will go to completion without stopping once it has started. Such arrays can serve as models for the temporal order of DNA synthesis among chromosome regions. They predict that in any one chromosome DNA replication begins and ends at very few loci and that synthesis at a larger number of points occurs at an intermediate time.     

Early biochemical events during adventitious root initiation in the hypocotyl of Phaseolus vulgaris

Indole butyric acid (IBA) initiates roots in the hypocotyl tissue of Phaseolus vulgaris (French bean). The response is dependent on the concentration of IBA and the duration of exposure to the hormone. IBA enhances the rate of total protein synthesis in ca 30 min after exposure of the hypocotyl segments to the hormone. There is no detectable change in total or poly(A)-containing RNA synthesis in this period although significant increases are seen 2 hr after hormone pre-treatment. The early IBA-mediated increase in protein synthesis (30 min) is not sensitive to Actinomycin D but the antibiotic blocks the increase manifested 2 hr after hormone pre-treatment. Inhibition of early protein synthesis by cycloheximide depresses and delays root initiation. Cytosol prepared from IBA-treated hypocotyl tissue stimulates protein synthesis in vitro to a greater extent than that of the control.     

Rapid Production of Auxin-induced Ethylene

The time course of auxin-induced ethylene production was determined in mesocotyl segments of etiolated sorghum (Sorghum bicolor L. Moench) seedlings. The latent period between addition of auxin and a detectable rise in ethylene release was 15 to 20 minutes in four different genotypes. This may indicate that the initial effect of auxin on ethylene production is too rapid to involve synthesis of an ethylene-producing enzyme. The technique devised for these experiments involves placing tissue segments end to end in a glass tube, and it allows simultaneous determination of growth and ethylene production.     

Polymer-supported biopolymer synthesis: 1. High load solid (gel) phase strategy for peptide synthesis with a phenolic poly(acryloylmorpholine)-based support

An efficient, low-cost, reaction strategy for the solid (gel) phase synthesis of peptides and protected peptide segments has been developed. The strategy involves the use of a new poly(acryloylmorpholine)-based phenolic support matrix, Koch-Light Peptide Resin A. Illustrative syntheses of N-terminal Boc- and Z-protected[Leu]- enkephalin derivatives, including C-terminal acid hydrazides and esters, are described. The strategy, which is effective for the synthesis of peptides at high matrix loadings, is adopted readily for large-scale application.     

Differential inhibition of coliphage MS2 protein synthesis by ribosome-directed antibiotics

Of thirteen ribosome-directed antibiotics surveyed for their inhibitory effect on viral protein synthesis in Escherichia coli infected with coliphage MS2, three antibiotics, kasugamycin, tetracycline and chloramphenicol, were found to exert differential inhibition, with synthesis of maturation protein being more sensitive than coat protein synthesis. Differential effects of kasugamycin and tetracycline were also observed in vitro. Such differential inhibition might reflect the presence of cistron-speciflc ribosomes or the induction of functional ribosomal heterogeneity by these antibiotic ligands.     

Mating variation by DNA inversions of shufflon in plasmid R64

Gene organization of the 54-kb transfer region of IncI1 plasmid R64 was deduced from the DNA sequence. Forty-eight ORFs were found in this region. A unique DNA rearrangement designated shufflon is located at the downstream region of an operon responsible for synthesis of thin pilus. The shufflon of R64 consists of four DNA segments, designated as A, B, C, and D, which are flanked and separated by seven 19-bp repeat sequences. Site-specific recombination mediated by the product of the rci gene between any two inverted repeats results in a complex DNA rearrangement. An analysis of open reading frames revealed that the shufflon is a biological switch to select one of seven C-terminal segments of the pilV genes. The products of pilV genes were shown to be components of thin pilus which was required for liquid mating.Seven R64 derivatives where the pilV genes were fixed in the seven C-terminal segments were constructed and their transfer frequencies in liquid mating were measured using various bacterial strains as recipients. Transfer frequencies of R64 in liquid mating strongly depended on the combination of C-terminal segments of the pilV genes in donor cells and bacterial strains of recipient cells, suggesting that the shufflon determines the recipient specificity in liquid mating of plasmid R64.     

The interaction of cholesterol with bilayers of phosphatidylethanolamine

The interaction of cholesterol with the glycerol backbone segments of phospholipids was studied in bilayers of phosphatidylethanolamine containing equimolar amounts of cholesterol. Glycerol selectively deuterated at various positions was supplied to the growth medium of Escherichia coli strain 131 GP which is defective in endogeneous glycerol synthesis. The procedure enables the stereospecific labeling of the three glycerol backbone segments of the membrane phospholipids. Phosphatidylethanolamine with wild-type fatty acid composition was purified from E. coli cells and deuterium magnetic resonance spectra were obtained either from dispersions of pure phosphatidylethanolamine or from equimolar mixtures of phosphatidylethanolamine with cholesterol. For comparative purposes 1,2-di[9,10-²H₂]elaidoyl-sn-glycero-3-phosphoethanolamine and [3-α-²H]cholesterol were synthesized in order to monitor the behavior of the fatty acyl chains and of the cholesterol molecule itself. For all deuterated segments the deuterium quadrupole splittings as well as the deuterium spin-lattice (T₁) relaxation times were measured as a function of temperature. The glycerol backbone was found to be a remarkably stable structural element of the phospholipid molecule. The quadrupole splittings of the backbone segments changed only by at most 2 kHz upon incorporation of 50 mol % cholesterol. This was in contrast to the fatty acyl chains where the same amount of cholesterol increased the quadrupole splitting by more than 20 kHz. The glycerol segments exhibited the shortest T₁ relaxation times of all CH₂ segments indicating that the glycerol backbone is the slowest motional moiety of the lipid molecule. Addition of cholesterol has no effect on the backbone motion but the fast reorientation rate of the trans-double bonds in 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine is increased dramatically.     

Preliminary characterization of the temperature-sensitive defect in DNA replication in a mutant mouse L cell

Temperature-sensitive ts A1S9 mouse L cells synthesize DNA apparently normally for 6–8 hr upon incubation at 38.5°C. Thereafter, these cells are able to perform limited polydeoxyribonucleotide chain synthesis at the high temperature, but are unable to convert newly replicated small single-strand segments of DNA (of the order of molecular weight 10⁶ daltons) to large molecular weight chromosomal DNA. Data obtained are compatible with a model which suggests that ts A1S9 cells are able to carry out most individual reactions of DNA synthesis at the high temperature, but are temperature-sensitive in a protein which participates in the joining of small DNA segments to make chromosomal DNA strands. When cells are reincubated at a permissive temperature, after the temperature-sensitive lesion has been established, they recover the latter capability several hours before they are able once again to synthesize DNA at normal rates.     

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.     

Occurrence and metabolism of sphagnum acid in the cell walls of bryophytes

Sphagnum acid was detected in all 30 Sphagnum species investigated. The content declines in older stem segments. Investigations have so far failed to detect this cinnamic acid derivative outside the Sphagnales. In all the Sphagnum species analysed, a second, conspicuous substance was detected, apparently identical with a degradation product of sphagnum acid produced by enzymatic reaction with peroxidase in vitro. A casual correlation between the sphagnum acid content and peroxidase activity in vivo is discussed. Glyphosate (0.5 mM) inhibits the synthesis of sphagnum acid and shikimate accumulates. Exogenously supplied phenylalanine is able to produce up to 65% reversal of the glyphosate-mediated inhibition of sphagnum acid synthesis. A mixed effect of glyphosate was found on amino acid levels. The content of sphagnum acid is also reduced by daily application of 0.1 mM l-α-aminooxy-β-phenylpropionic acid.