Reduction In Rate Of Elongation Research Articles

A wheat/rye polymorphism affects seminal root length and yield across different irrigation regimes.

The introgression of a small segment of wheat (Triticum aestivum L.) chromosome arm 1BS in the distal region of the rye (Secale cereale L.) 1RS.1BL arm translocation in wheat (henceforth 1RSRW) was previously associated with reduced grain yield, carbon isotope discrimination, and stomatal conductance, suggesting reduced access to soil moisture. Here we show that lines with the normal 1RS arm have longer roots than lines with the 1RSRW arm in both field and hydroponic experiments. In the 1RSRW lines, differences in seminal root length were associated with a developmentally regulated arrest of the root apical meristem (RAM). Approximately 10 d after germination, the seminal roots of the 1RSRW plants showed a gradual reduction in elongation rate, and stopped growing a week later. Seventeen days after germination, the roots of the 1RSRW plants showed altered gradients of reactive oxygen species and emergence of lateral roots close to the RAM, suggesting changes in the root meristem. The 1RSRW lines also showed reduced biomass (estimated by the normalized difference vegetation index) and grain yield relative to the 1RS lines, with larger differences under reduced or excessive irrigation than under normal irrigation. These results suggest that this genetic variation could be useful to modulate root architecture.

Wide-ranging and unexpected consequences of altered Pol II catalytic activity in vivo.

Here we employ a set of RNA Polymerase II (Pol II) activity mutants to determine the consequences of increased or decreased Pol II catalysis on gene expression in Saccharomyces cerevisiae. We find that alteration of Pol II catalytic rate, either fast or slow, leads to decreased Pol II occupancy and apparent reduction in elongation rate in vivo. However, we also find that determination of elongation rate in vivo by chromatin immunoprecipitation can be confounded by the kinetics and conditions of transcriptional shutoff in the assay. We identify promoter and template-specific effects on severity of gene expression defects for both fast and slow Pol II mutants. We show that mRNA half-lives for a reporter gene are increased in both fast and slow Pol II mutant strains and the magnitude of half-life changes correlate both with mutants’ growth and reporter expression defects. Finally, we tested a model that altered Pol II activity sensitizes cells to nucleotide depletion. In contrast to model predictions, mutated Pol II retains normal sensitivity to altered nucleotide levels. Our experiments establish a framework for understanding the diversity of transcription defects derived from altered Pol II activity mutants, essential for their use as probes of transcription mechanisms.

Divergence of a conserved elongation factor and transcription regulation in budding and fission yeast.

Complex regulation of gene expression in mammals has evolved from simpler eukaryotic systems, yet the mechanistic features of this evolution remain elusive. Here, we compared the transcriptional landscapes of the distantly related budding and fission yeast. We adapted the Precision Run-On sequencing (PRO-seq) approach to map the positions of RNA polymerase active sites genome-wide in Schizosaccharomyces pombe and Saccharomyces cerevisiae. Additionally, we mapped preferred sites of transcription initiation in each organism using PRO-cap. Unexpectedly, we identify a pause in early elongation, specific to S. pombe, that requires the conserved elongation factor subunit Spt4 and resembles promoter-proximal pausing in metazoans. PRO-seq profiles in strains lacking Spt4 reveal globally elevated levels of transcribing RNA Polymerase II (Pol II) within genes in both species. Messenger RNA abundance, however, does not reflect the increases in Pol II density, indicating a global reduction in elongation rate. Together, our results provide the first base-pair resolution map of transcription elongation in S. pombe and identify divergent roles for Spt4 in controlling elongation in budding and fission yeast.

Effects of MgO whiskers on mechanical properties and crystallization behavior of PLLA/MgO composites

In this study, composites of stearic acid-modified magnesium oxide whiskers (Sa-w-MgO)/poly-l-lactic acid (PLLA) were prepared through solution casting, and the properties of the composites with different whisker contents were investigated in terms of crystallization, mechanical properties, water absorption, and hydrophilicity. The results showed that, in comparison to PLLA, the composites exhibited better mechanical properties and greatly improved crystallization behavior. At a whisker content of 1wt.%, Sa-w-MgO increased Young's modulus and tensile strength of PLLA by 78% and 17%, respectively, without a reduction of elongation rate at break. Meanwhile, the crystallinity of composites was also increased remarkably, which was 77% higher than that of PLLA at a whisker content of 1wt.%. Furthermore, the hydrophilicity of the composites was notably improved, which was beneficial to the cell affinity of the material, and an obvious decline in the water absorption rate was detected in the composites, which was helpful in inhibiting water infiltration from the matrix and maintaining the mechanical properties at the initial degradation stage in vivo.

Elongation rates and endogenous indoleacetic acid levels in roots of pea mutants differing in internode length

Growth of the primary root of 12 genotypes of peas (Pisum sativum) differing in their stem height was recorded for 14 days. The growth rate of roots of wild‐type tall, gibberellin (GA)‐deficient le dwarf or slender mutants (with la crys) was similar (3 cm day−1); that of severely GA‐deficient nana (na‐1) plants was 50% of wild‐type but elongation ceased after 8 days; moderately severe dwarf GA‐deficient lines ls‐1 and lh‐1 had a 15% reduction in elongation rate but displayed no time‐dependent slowing of the growth rate and brassinosteroid‐insensitive and ‐deficient dwarfs lka and lkb showed slightly decreased root elongation. GA (levels reported in Yaxley et al. 2001) is not substantially limiting to root growth until it is severely deficient. The terminal 3 cm of roots of tall plants contained about 25 or 35 ng g−1 fresh weight indole‐3‐acetic acid (IAA), depending on the genetic background, and le‐1 dwarfs were similar. Nana (na‐1) had less than 50% the level of IAA of tall, all the moderately severe dwarfs had reductions of about 30% and the slender plants had about 40% more IAA than the corresponding wild‐type. With the exception of slender plants, IAA level in the root tips correlated with root elongation. Root growth seems to be promoted by IAA within the range of the internal concentrations detected. Nana plants had a reduced amount of IAA and a lower root‐growth rate. Whereas external application of IAA always inhibits root growth, even at very low concentrations, root growth is not similarly inhibited by internal IAA as slender plants had the highest IAA level and growth rate similar to wild‐type, regardless of the shoot GA content.

Numerical Analysis of Elongation Behavior of Melt Flow in Contraction Channels with Cylindrical Barriers

The flow of polymer melt in contraction channels with cylindrical barriers was numerically simulated. A commercial LDPE melt was considered, and the rheological property of the melt was represented using the Extended Pom-Pom model (XPP). The simulation was performed with various barrier configurations, and the effects of the barriers were investigated extensively in relation to the efforts to clarify the phenomenon of melt fracture mitigation by the addition of filter or porous medium. It can be observed that the addition of barriers modifies significantly the flow fields in the region near the contraction. Investigation of the elongation stress shows that the addition of barriers increases the stress in the region near the contraction, but decreases the elongation rate and elongation stress in the region at the upstream of the contraction and induces the undershoots of elongation rate and elongation stress in the region at the downstream of the contraction. With the increase in Weissenberg numbers, these effects are more significant for the channels with two barriers as compared to that with single barrier. The reduction of elongation rate and elongation stress should play an important role in the mitigation of the upstream instability, which in turn mitigates the gross melt fracture.

Growth and morphological responses to different UV wavebands in cucumber (Cucumis sativum) and other dicotyledonous seedlings

We examined the influence of short-term exposure of different UV wavebands on the fine-scale kinetics of hypocotyl growth of dim red light-grown cucumbers (Cucumis sativus L.) and other selected dicotyledonous seedlings to evaluate: (1) whether responses induced by UV-B radiation (280-320 nm) are qualitatively different from those induced by UV-A (320-400 nm) radiation, and (2) whether different wavebands within the UV-B elicit different responses. Responses to brief (30 min) irradiations with 3 different UV wavebands all included transient inhibition of elongation during irradiation followed by wavelength specific responses. Irradiations with proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm) induced inhibition of hypocotyl elongation within 20 min of onset of irradiation, while UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation with a lag of 1-2 h. The response to short wavelength UV-B was persistent for at least 24 h, while the response to long wavelength UV-B lasted only 2-3 h. The UV-A treatment induced reductions in elongation rates of approximately 6-9 h following exposure followed by a continued decline in rates for the following 15-18 h. Short wavelength UV-B also induced positive phototropic curvature in both cucumber and Arabidopsis seedlings, and this response was present in nph-1 mutant Arabidopsis seedlings defective in normal blue light phototropism. Reciprocity was not found for the response to short wavelength UV-B. The short wavelength and long wavelength UV-B responses differed in dose-response relationships and both short wavelength responses (phototropic curvature and elongation inhibition) increased sharply at wavelengths below 300 nm. These results indicate that different photosensory processes are involved in mediating growth and morphological responses to short wavelength UV-B (280-300 nm), long wavelength UV-B (essentially 300-320 nm) and UV-A. The existence of two separate types of hypocotyl inhibition responses to UV-B, with one that depends on the intensity of the light source, provides alternate interpretations to findings in other studies of UV-B induced photomorphogenesis and may explain inconsistencies between action spectra for inhibition of stem growth.

Silk Elongation in Maize

In maize (Zea mays L.), the gradient in floret development and silk length along the ear at silking determines a time lag between early‐ and late‐appearing silks, which results in pollination asynchrony between them. This asynchrony is partially responsible of reduced kernel set at the ear tip, and hybrids differ in this trait. The objective of this work was to analyze the pattern of floret and silk differentiation and elongation at different spikelet positions (Sn) along the apical ear of two hybrids of contrasting ear size (DEA ≅ 500 spikelets ear−1; DK696 ≅ 800 spikelets ear−1). At silking, both hybrids had reached approximately the same proportion of final ear length (about 44%), but DK696 had differentiated a greater number of spikelets row−1 (46 spikelets) than DEA (33 spikelets). Silk initiation rate was always faster than spikelet initiation rate, and silk extension dynamics was similar for all spikelet positions. Silks from the base of the ear were always longer than those from the tip (S25 in DEA or S35 in DK696). Before pollination, silks experienced an early phase of exponential elongation followed by a phase of linear growth. A drastic reduction in elongation rate followed silk emergence, which did not occur when ears were bagged and pollination was prevented. Convergence in silking among spikelets along the ear could be attained by (i) synchronous silk initiation among spikelet positions, followed by a similar pattern of silk elongation in all florets (hybrid DEA), or (ii) increased silk elongation rate in apical florets (hybrid DK696).

Using Impedance for Mechanical Conditioning of Tomato Transplants to Control Excessive Stem Elongation

Mechanical stimulation is known to control excessive stem elongation in high-density tomato (Lycopersicon esculentum Mill.) transplants. Mechanical stimulation using physical impedance provided height control equivalent to that obtained using brushing. Low-cost materials can be used to apply the impedance. Mylar film in a plastic frame was equivalent to expensive acrylic sheets in its effect on plant height (40 mm shorter than nontreated, a 40% reduction in the elongation rate during the treatment period), stem diameter (18% thicker), and biomass (14% lighter) when they applied a pressure of 66 N·m-2. Stem elongation was not reduced if less pressure was applied (25 or 50 N·m-2). Height control was equally effective with a solid material (mylar film) and a permeable material (fiberglass insect screen), indicating that restricting air movement is not an important mechanism for the growth response. Overnight treatments resulted in the desired growth response (27 mm shorter than nontreated, a 30% reduction in elongation rate), but 0.5-h treatments had insufficient effect for commercial use (11 mm shorter, 10% reduction in elongation rate). These experiments demonstrate that impedance can be used in commercial production conditions to control tomato transplant height with inexpensive materials. However, satisfactory height control requires a large applied force and a long daily treatment period.

RpoB8, a rifampicin-resistant termination-proficient RNA polymerase, has an increased Km for purine nucleotides during transcription elongation

The rpoB8 allele of Escherichia coli maps to the beta-subunit of RNA polymerase and confers rifampicin resistance as well as increased termination at both intrinsic and rho-dependent terminators in vivo. This phenotype suggests that the mutant is defective in an enzymatic property of RNA polymerase important for all termination events. We analyzed the in vitro transcription properties of this enzyme to determine the nature of the defect. As compared with the wild-type enzyme, RpoB8 exhibits enhanced pausing and a significant reduction in rate of elongation on natural templates. In addition, RpoB8 RNA polymerase has a 3-5-fold higher Km for purine nucleotides during elongation on synthetic templates. In contrast, both the mutant and wild-type enzyme have the same initiation Km for ATP. Kinetic analysis indicates that RpoB8 is likely to be defective in nucleotide binding during elongation, suggesting that the mutational alteration affects the binding site. We show that our data are consistent with the idea that the altered Km underlies the altered pausing and elongation properties of the enzyme, and we discuss the implication of these results for the termination proficiency of the mutant strain.

Effects of solar radiation on growth of cassava (Manihot esculenta crantz.). II. Fibrous root length

Effects of solar radiation on the growth of fibrous roots of cassava cv. M Aus 7 were examined by growing plants without shading (control) and under shade cloths which reduced input to 78% and 32% respectively of full solar radiation. Plants were at two different stages of growth when shading treatments were imposed. The experimental results indicate that cassava can develop fibrous root systems rapidly and extensively. Within 50 days of planting, root length density in the 0-20 cm soil layer was 1.6 cm cm-3 and by 84 days it had increased to 3.6 cm cm-3. Maximum root depth also increased from 60-80 cm at 29 days after planting to 100-120 cm by day 50 and beyond 120 cm by day 72. Estimated total fibrous root length per m2 ground area to a depth of 120 cm was 32 km m-2 and 23 km m-2 at the end of the experiment for the two crops, 133 days old and 84 days old, respectively. Shading the plants for 35 days reduced the rate of increase in root length density and hence decreased total root length in the two crops. Reduction in solar input to 32% resulted in a 50% reduction in elongation rate of fibrous roots. Reduction to 78% resulted in a similar reduction in elongation rate when plants were at tuber bulking stage, but much less reduction when plants were at the tuber initiation stage. The results indicate that under limited carbohydrate supply shoot was a stronger sink than both fibrous roots and tubers. At tuber initiation stage tuber was a weaker sink than fibrous roots, but at bulking stage it was about equal to fibrous roots.

Polypeptide elongation factor 1 and the control of elongation rate in rat liver in vivo.

THE development of rapid kinetic methods for measurement of elongation rate in protein synthesis in vivo, independent of initiation rate, has made possible the study of the control of elongation in relation to changes in overall protein synthesis1–4. In rat liver a 40% reduction in elongation rate (from about six to four amino acid residues per ribosome) is associated with thyroparathyroidectomy2,4; the normal rate is restored by triiodothyronine injections2. The work reported here concerns the role of polypeptide elongation factor 1 (EF1), the factor responsible for aminoacyl-tRNA binding to ribosomes, in the control of elongation rate in this system. Several studies have suggested that EF1 may have regulatory significance in eukaryotic systems5,8; however no direct correlation between EF1 activity and elongation rate in vivo has previously been described.

Experimental Control of Soil Water Content in the Vicinity of Root Hairs

AbstractA technique for controlling water content in the root hair zone of growing plants has been developed which involves growing plants on a fine screen placed over soil in such a way that only root hairs can extend through the screen into soil beneath. Gamma‐ray attenuation is used to monitor the supply of water in the root hair zone. By means of controlling either the length of a hanging water column or the rate of water supply, the rate of water flow to the soil lamina beneath the screen can be so adjusted as to just offset the loss due to transpiration. A predetermined soil water content can be maintained to within 0.015 cm3/cm3 in the root hair zone of a growing plant.Plant growth was affected by soil water potential. Reduction in elongation rate of corn (Zea mays L.) leaves was observed at matric potentials higher than −1 bars. Elongation essentially ceased at matric potentials of about −22 to −30 bars within the root hair zone. A large water content gradient existed adjacent to the root hair zone and extended to a depth greater than 10 mm.

Effect of Soil Overburden Pressure on Penetration of Fine Metal Probes

The interactive effect of overburden pressure and root confinement on root elongation in a fine-structured loam soil has been examined using fine-metal probes to simulate a plant root. Substantial increases in probe resistance with simulated overburden pressure were found only at high soil bulk densities and high ratios of probe to soil volumes. These findings suggest that for low root to soil volumes (root density) and the maximum soil density used, 1.63 g cm⁻³, the elongation rate of plant roots at a depth of 150 cm would be only 4% less than in the surface layer. For root densities in excess of 0.01 and the same bulk density and depth of overburden, the model predicts a 30% reduction in elongation rate.

THE EFFECT OF ABSCISIC ACID ON STEM ELONGATION AND CORRELATIVE INHIBITION

SummaryThe mature length of the second internode (which was undergoing rapid vacuolation at the time of treatment with ABA) was not appreciably affected by doses of ABA below 20 μg per plant although the rate of elongation was depressed for the first 2 days after treatment, the depression being as much as 50% in tall varieties. Doses of ABA in excess of 20 μg not only depressed elongation rate immediately, but resulted in shorter internode length at maturity. Etiolated seedlings showed a stimulation of elongation rate and mature length in the dwarf ‘Meteor’, hut no statistically significant differences in the tall variety ‘The Pilot’ with doses below 20 μg ABA. Higher doses of ABA caused immediate cessation of elongation in vacuolating internodes, but only postponed the onset of vacuolation in younger internodes. Lighted plants also showed this postponement of the onset of vacuolation in the younger internodes at higher doses; in both lighted and etiolated seedlings the normal growth rate was resumed after a delay of between 3 and 7 days.Decapitation reduced elongation rate during the subsequent 48 hours either with or without ABA. In the absence of ABA there was a subsequent recovery in growth rate of the dwarf variety so that the final length of the second internode was the same for both intact and decapitated plants. But decapitation of the tall variety produced a marked reduction in mature length of the second internode, as it did in all ABA treated plants both dwarf and tall, intact and decapitated. The only significant interaction between decapitation and ABA on elongation rate occurred in the tall variety: during the first 24 hours all doses of ABA produced approximately the same big reduction in elongation rate in intact plants but had no statistically significant effect on decapitated plants; during the second day only the higher doses of ABA reduced the elongation rate of intact plants while all three levels produced the same big reduction in elongation rate of the decapitated plants. In the dwarf variety there was no significant interaction between the decapitation and ABA effects. Lateral bud outgrowth in decapitated plants was inhibited by ABA, and 100 μg per plant achieved inhibition comparable to that produced by the apex in intact plants. Hence ABA may possibly be the inhibitory substance demonstrated to be responsible for the phenomena of correlative inhibition.

Cotton Seedling Taproot Elongation as Affected by Soil Strength Changes Induced by Slurrying and Water Extraction

Elongation rates of cotton seedling taproots (Gossypium hirsutum) were evaluated in loose nonslurried and in slurried soils Soil strength increases were caused by slurrying and by increasing soil water suction from 1/5 to 1/3 or 2/3 bar. All of the resulttant penetrometer resistances, which varied from almost zero to 11 bars, frequently are found in arable soils. These soil strength increases caused large reductions in elongation rates. Consequently, soil strength should be considered as a prime factor affecting root growth rather than a condition limiting root growth only in unusual situations.