Varying Growth Conditions Research Articles

Evaluation of the tetracycline promoter system for regulated gene expression inKluyveromyces marxianus

A tetracycline repressible promoter system designed for Saccharomyces cerevisiae was evaluated for use in Kluyveromyces marxianus. A plasmid was constructed containing the Escherichia coli beta-glucuronidase (gus) gene cloned downstream of the yeast tet-off promoter, the tetR-VP16 activator protein gene, and the URA3 gene for selection. The tet-off promoter-gus construct was integrated into the chromosomal DNA and tested under varying growth conditions in complex medium. The repressors tetracycline and doxycycline were both found to be effective for inhibiting gene expression. Doxycycline levels of 0.5 microg/mL or greater were sufficient to nearly completely suppress Gus synthesis. For most transformants, the induction ratio was approximately 2,000-fold. The tet-off promoter was effective at 30, 37, and 42 degrees C, although the overall Gus activity was highest at 37 degrees C. During exponential growth, little product was formed; expression increased dramatically in late exponential and early stationary phase. The promoter thus shows promise for protein synthesis following cell growth. No inducer is required and the repressor is only needed to prevent expression during the seed culture.

Growth Chemistry of Nanocrystalline Si:H Films

AbstractWe report on the growth of nanocrystalline Si:H films using both plasma CVD and remote hot wire deposition under systematically varied growth conditions. The films were grown from mixtures of silane and hydrogen. It was found that when the films were grown under low pressure VHF plasma growth conditions, the orientation of the film changed as the pressure increased. At the lowest pressures, the films were mainly <111> oriented, but changed to <220> orientation as the pressure increased. The grain size increased as the growth temperature increased. When the films were grown using remote hot wire deposition, the orientation depended upon both hydrogen dilution and growth temperature. As the hydrogen dilution increased, the <220> grain size became smaller. Grain size as large as 36 nm was obtained by controlling the growth conditions in hot wire deposition. As the growth temperature increased, the size of <220> grains increased. Growth rates also increased with increasing temperature. The data can be explained by invoking a growth model which recognizes that the natural growth direction for Si is <220>, since the surface energy is highest for (220) plane. Random nucleation leads to <220> grains. Bonded H is believed to inhibit the growth of <220> grains.

Photoluminescence characteristics of ZnGa 2O 4− xM x:Mn 2+ (M=S, Se) thin film phosphors grown by pulsed laser ablation

Mn-doped ZnGa 2O 4− x M x (M=S, Se) thin film phosphors have been grown using a pulsed laser deposition technique at varying growth conditions. The structural characterization carried out on a series of ZnGa 2O 4− x M x :Mn 2+ (M=S, Se) films grown on MgO (100) substrates using Zn-rich ceramic targets. Oxygen pressure was varied from 50 to 200 mTorr and substrate temperatures were varied from 500 to 700 °C. The lattice constants of the ZnGa 2O 4− x M x :Mn 2+ (M=S, Se) thin film decrease with the substitution of sulfur and selenium for the oxygen in the ZnGa 2O 4. Measurements of photoluminescence (PL) properties of ZnGa 2O 4− x M x :Mn 2+ (M=S, Se) thin films have indicated that MgO (100) is a promising substrate for the growth of high quality ZnGa 2O 4− x M x :Mn 2+ (M=S, Se) thin films. In particular, a remarkable increase of green emission intensity was observed with ZnGa 2O 3.925Se 0.075:Mn 2+ and ZnGa 2O 3.925S 0.075:Mn 2+ films, whose brightness was increased by a factor of 3.1 and 1.4 in comparison with that of ZnGa 2O 4:Mn 2+ films, respectively. Improved PL brightness with Se or S doping is suggested to result not only from improved crystallinity, but also from reduced internal reflections caused by rougher surfaces. The PL intensity and root mean square (rms) roughness behave similarly as a function of oxygen pressure. These phosphors maybe promising for application to the flat panel displays.

The effect of breeding on allometry and phenotypic plasticity in four varieties of oat ( Avena sativa L.)

New directions in crop improvement via alteration of plant responsiveness to variation in growth conditions are being actively debated. It appears, however, that little is known about the impact of previous breeding on the phenotypic plasticity of plants, which results from correlated responses to selection on high yield. We used four oat ( Avena sativa) varieties, originating from 1930, 1952, 1980 and 1999, to examine the effects of long-term breeding on the patterns of autecological phenotypic responses to variation in light and nutrient supply. The modern variety showed the least plasticity in stem elongation in response to variation in light conditions. As a by-product of decreased sensitivity to light availability, the modern oat variety appeared to be more susceptible to low light levels compared to other varieties. The patterns of plastic response in leaf area and root biomass were similar in all varieties. Changes in allocation to panicles in response to resource variation were completely attributable to passive plasticity, i.e. the proportion of biomass invested into reproduction varied as a function of total plant size. Interestingly, variation in specific leaf mass, the trait considered to be important in adaptive shade-avoidance responses, was only partially attributable to ontogenetic plasticity (environmentally induced adjustments of ontogeny). Our results support the idea that it can be more advantageous in the breeding of crop plants to select for a fixed pattern of allocation to different tissues, dependent on developmental stage, than to select for the ability to adjust the whole ontogeny to particular environmental conditions. Uniform high-nutrient conditions and completely predictable changes in light environment during ontogeny are common for crop plants, and are known to enhance genetic differentiation, not plasticity. Obviously, it is not possible to lose ontogenetic plasticity, as such, entirely: plants will have to adjust their development in response to stressful conditions if the allocational pattern of underdeveloped plants is not consistent with optimal foraging behaviour. On the other hand, the similar patterns of plastic responses in the studied varieties imply that further development of more plastic varieties can be precluded by homogenizing selection on optimal reaction norm (greater plasticity can be associated with excessively high costs and can outweigh possible advantages).

Growth Increment Patterns in the Roots of Two Alpine Forbs Growing in the Center and at the Periphery of a Snowbank

Snowbanks are characteristic for many alpine areas and add considerably to the great variability of growth conditions in high mountain systems. We studied the long-term (5- to 9-yr) growth response of two alpine forbs, Pedicularis recutita and Cirsium spinosissimum, to the environmental conditions in the center and at the periphery of a snowbank in the Swiss Alps. For that we analyzed the growth increments (annual rings) in the roots or rhizomes of the plants. While for both species there were no considerable size differences (number of shoots) between individuals growing in the center of the snowbank and those at the periphery, the growth patterns differed depending on species, temporal variations in growth conditions, and growth position. There were synchronous fluctuations in the width of the annual growth increments that were more pronounced in C. spinosissimum than in P. recutita and were restricted to plants growing in the center of the snowbank. These were apparently related to interannual variations in climatic conditions. In addition, C. spinosissimum plants growing at the periphery of the snowbank showed initially wide but strongly declining growth increments whereas plants growing in the center of the snowbank showed initially narrower but relatively stable growth increments. These patterns were only weakly reflected in P. recutita. Our results suggest that effects of climatic fluctuations on plant growth can be amplified in snowbanks and that there may be favorable growth conditions initially at the periphery of the snowbank that are compensated for in the center of the snowbank, in the long run, by continuously low-competition growth conditions.

Degradation of the Gluconeogenic Enzymes Fructose-1,6-bisphosphatase and Malate Dehydrogenase Is Mediated by Distinct Proteolytic Pathways and Signaling Events

The key gluconeogenic enzyme fructose-1,6-bisphosphatase (FBPase) is subjected to catabolite inactivation and degradation when glucose-starved cells are replenished with fresh glucose. In various studies, the proteasome and the vacuole have each been reported to be the major site of FBPase degradation. Because different growth conditions were used in these studies, we examined whether variations in growth conditions could alter the site of FBPase degradation. Here, we demonstrated that FBPase was degraded outside the vacuole (most likely in the proteasome), when glucose was added to cells that were grown in low glucose media for a short period of time. By contrast, cells that were grown in the same low glucose media for longer periods of time degraded FBPase in the vacuole in response to glucose. Another gluconeogenic enzyme malate dehydrogenase (MDH2) showed the same degradation characteristics as FBPase in that the short term starvation of cells led to a non-vacuolar degradation, whereas long term starvation resulted in the vacuolar degradation of this protein. The N-terminal proline is required for the degradation of FBPase and MDH2 for both the vacuolar and non-vacuolar proteolytic pathways. The cAMP signaling pathway and the phosphorylation of glucose were needed for the vacuolar-dependent degradation of FBPase and MDH2. By contrast, the cAMP-dependent signaling pathway was not involved in the non-vacuolar degradation of these proteins, although the phosphorylation of glucose was required.

The potential of enhanced germplasm for mungbean (Vigna radiata (L.) Wilczek) improvement

AbstractMungbean (Vigna radiata (L.) Wilczek), also known as greengram, is the most widely cultivated Asian Vigna species. Improved mungbean cultivars have a narrow genetic base that limits yield potential and they are poorly adapted to varying growth conditions in different agro-ecological conditions. The genetic potential of landrace germplasm accessions in gene- banks therefore needs to be better exploited. Germplasm core collections are made of a reduced set of representative accessions from the entire diversity maintained by genebanks. This subset of accessions can be used for testing general combining ability with local germplasm in the search for yield enhancement. Core collections also help breeders in selecting parental material that could maximize potential genetic gain from derived hybrid populations. At the National Bureau of Plant Genetic Resources (NBPGR), India, genetic enhancement/pre- breeding studies in mungbean have been initiated involving diverse parents mainly from the cultivated gene pool, using the Bureau's core collection as starting material. Germplasm enhancement aims at widening the genetic base of breeding materials by transferring desired genes from unimproved germplasm into enhanced varieties. Mild and decentralized selected material was maintained in target sites across the country. A total of 102 progenies were advanced to F5 for further selection and use by the breeders in Delhi. The genetic potential of a few selected enhanced progenies with desired plant types and better yield-related traits is presented in this paper. The study clearly demonstrates the potential of germplasm accessions conserved in genebanks for use in large-scale base-broadening efforts in mungbean.

Growth of ferromagnetic MnAs 1− xSb x films and MnSb/MnAs/MnAs 1− xSb x multilayers on GaAs ( [formula omitted]) by molecular beam epitaxy

We investigated ternary MnAs 1- x Sb x thin films on GaAs ( 0 0 1 ) substrates by low-temperature molecular beam epitaxy under varying growth conditions, studying their crystal structures and magnetic properties. It was found that MnAs 1- x Sb x film with x=0.2 seems to be lattice-matched to GaAs ( 0 0 1 ) substrates and is suitable for the growth of magnetic multilayers. We explored the possibility of growing magnetic MnSb/MnAs/MnAs 1- x Sb x multilayers on GaAs ( 0 0 1 ), and successfully prepared this kind of magnetic multilayer. We also report herein preliminary results regarding the magnetotransport properties of MnAs 1- x Sb x films in relation to the Sb content.

Influences of biaxial strains on the vibrational and exciton energies in ZnO

We have investigated the structural, optical, and vibrational properties of strained heteroepitaxial ZnO layers by high resolution x-ray diffraction, reflectivity, and Raman measurements. The ZnO layers were grown by metalorganic vapor phase epitaxy on sapphire substrates under varying growth conditions. A Poisson number of μ=0.303 and phonon deformation-potential parameters of a=−690 cm−1, b=−940 cm−1 for the high-energy E2 optical phonon mode have been determined. The shift of the excitonic resonances due to the strain in the layers agrees well with the experimentally determined Poisson ratio using the deformation-potentials D1–D4 determined by Wrzesinski and Fröhlich [Phys. Rev. B 56, 13087 (1997)].

Enhanced luminescence in ZnGa2O4-xSx:Mn2+ thin-film phosphors grown on MgO(100) substrate

Mn-doped ZnGa2O4-xSx thin-film phosphors have been grown using a pulsed laser deposition technique at varying growth conditions. Structural characterization was carried out on a series of ZnGa2O4-xSx:Mn2+ films grown on MgO(100) substrates using Zn-rich ceramic targets. Oxygen pressure was fixed at 100 mTorr and substrate temperatures were varied from 500 to 700 °C. The results of X-ray-diffraction patterns showed that the lattice constants of the ZnGa2O3.95S0.05:Mn2+ thin films decrease with the substitution of sulfur for the oxygen in ZnGa2O4. Measurements of photoluminescence (PL) properties of ZnGa2O4-xSx:Mn2+ thin films have indicated that MgO(100) is one of the most promising substrates for the growth of high-quality ZnGa2O4-xSx:Mn2+ thin films. In particular, the incorporation of sulfur into the ZnGa2O4 lattice could induce a remarkable increase of PL. The highest green-emission intensity was observed with ZnGa2O3.95S0.05:Mn2+ films, whose brightness was increased by a factor of 3.5 in comparison with that of ZnGa2O4:Mn2+ films. This phosphor may be promising for application to flat-panel displays.

Primary production, new production, and growth rate in the equatorial Pacific: Changes from mesotrophic to oligotrophic regime

Under an apparent monotony characterized by low phytoplankton biomass and production, the Pacific equatorial system may hide great latitudinal differences in plankton dynamics. On the basis of 13 experiments conducted along the 180° meridian (8°S–8°N) from upwelled to oligotrophic waters, primary production was strongly correlated to chlorophyll a (chl a), and the productivity index PI (chl a‐normalized production rate) varied independently of macronutrient concentrations. Rates of total (14C uptake) and new (15N‐NO3 uptake) primary production were measured in situ at 3°S in nutrient‐rich advected waters and at 0° where the upwelling velocity was expected to be maximal. Primary production was slightly higher at the equator, but productivity index profiles were identical. Despite similar NO3 concentrations, new production rates were 2.6 times higher at 0° than at 3°S, in agreement with much higher concentrations of biogenic particulate silica and silicic acid uptake rates (32Si method) at the equator. Furthermore, phytoplankton carbon concentrations from flow cytometric and microscopical analyses were used with pigment and production values to assess C:chl a ratios and instantaneous growth rates (μ). Growth rates in the water column were significantly higher, and C:chl a ratios lower at 0° than at 3°S, which is consistent with the more proximate position of the equatorial station to the source of new iron upwelling into the euphotic zone. For the transect as a whole, compensatory (inverse) changes of C:chl a and μ in response to varying growth conditions appear to maintain a high and relatively invariant PI throughout the equatorial region, from high‐nutrient to oligotrophic waters.

Growth of Carbon Nanotubes: A Combinatorial Method To Study the Effects of Catalysts and Underlayers

With their interesting electrical, structural, and physical properties, carbon nanotubes (CNTs) are envisioned to impact future nanoelectronics, nanosensors, and nanophotonics. Current research and development efforts in the growth of CNTs rely on the time-consuming one-parameter-at-a-time approach, whereby marginal variations in growth conditions from run-to-run experiments could result in substantially different outcomes. Here we report a highly efficient combinatorial approach to study the effects of catalysts and underlying metals for the generation of a comprehensive discovery library of CNTs. Shadow masking and sequential ion-beam deposition are used to construct an ensemble of catalysts and underlying metals on a generic addressable platform, whereby upon chemical vapor deposition, the CNT library can be assayed efficiently and conveniently to reveal a host of interesting phenomena. The approach could, in principle, be adapted and used for combinatorial investigations of other nanostructures.

The LP-MOCVD of CdS/Bi 2S 3 bilayers using single-molecule precursors

The single-molecule precursors [Cd(S 2CNMe n-Hex) 2] and [Bi(S 2CNMe n-Hex) 3] (Me=methyl; n-Hex= n-hexyl) were used to prepare CdS/Bi 2S 3 layers by low-pressure metal organic chemical vapour deposition (LP-MOCVD). The bilayers were deposited onto glass substrates at 400–450 °C for varying growth conditions. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical measurements. The results were compared with those obtained for the single phases.

Atomic structure of InAs and InGaAs quantum dots determined by cross-sectional scanning tunneling microscopy

In this work we present a comparative cross-sectional scanning tunneling microscopy study of different InAs and InGaAs quantum dot structures grown by metalorganic vapor phase epitaxy. The varying growth conditions lead to completely different spatial structures, as distinctive quantum dots, intermixed layers, and intermixed dots. Especially the overgrowth procedure and the arrangement of growth interruptions are responsible for segregation of the InAs material.

Spatio-temporal dynamics of expansion growth in roots: automatic quantification of diurnal course and temperature response by digital image sequence processing.

A newly developed technique based on image sequence analysis allows automatic and precise quantification of the dynamics of the growth velocity of the root tip, the distribution of expansion growth rates along the entire growth zone and the oscillation frequencies of the root tip during growth without the need of artificial landmarks. These three major parameters characterizing expansion growth of primary roots can be analysed over several days with high spatial (20 microm) and temporal resolution (several minutes) as the camera follows the growing root by an image-controlled root tracking device. In combination with a rhizotron set up for hydroponic plant cultivation the impact of rapid changes of environmental factors can be assessed. First applications of this new system proved the absence of diurnal variation of root growth in Zea mays under constant temperature conditions. The distribution profile of relative elemental growth rate (REGR) showed two maxima under constant and varying growth conditions. Lateral oscillatory movements of growing root tips were present even under constant environmental conditions. Dynamic changes in velocity- and REGR-distribution within 1 h could be quantified after a step change in temperature from 21 degrees C to 26 degrees C. Most prominent growth responses were found in the zone of maximal root elongation.

Effect of Growth Conditions on the Morphology and Structural Perfection of Vapor-Grown PbI2 Crystals

Data are presented on the morphology and structural perfection of PbI2 crystals grown from the vapor phase in a closed system. By varying growth conditions, platelike, ribbon, needle, twinned, and dendritic crystals were prepared, as well as combinations and intergrowths of these habits.

Growth and characterization of MnAs/ZnSe ferromagnet/semiconductor hybrid heterostructures

We report a detailed study of the molecular beam epitaxy of MnAs/ZnSe heterostructures on GaAs (100) substrates under varying growth conditions. As with the MnAs/GaAs system, these MnAs/ZnSe epilayers show ferromagnetism at room temperature, although with different structural and magnetic characteristics. We study the impact of parameters such as the As/Mn beam equivalent pressure ratio, substrate temperature, templating, and substrate misorientation on the MnAs/ZnSe heterostructures utilizing in situ reflectance high energy electron diffraction, as well as ex situ x-ray diffraction and atomic force microscopy. This structural information is correlated with magnetic properties obtained from magneto-optical Kerr effect and superconducting quantum interference device magnetometry. Finally, we discuss preliminary studies on the properties of MnAs/ZnSe/MnAs trilayers for spin-valve type applications.

Magneto-optical response of isolated and embedded Fe nanoparticles

The magneto-optical response of nanometric Fe particles with varying size and shape has been studied, both in sputtered single layers and pulsed laser deposited nanocomposite films. The shape of Fe nanoparticles was controlled by varying growth conditions. An effective medium theory for arbitrary particle shapes has been derived and used to simulate the experimentally measured magneto-optical transverse Kerr spectra. The simulations show that the transverse Kerr magneto-optical spectra depend on the particles shape and correlate well with the experimentally determined spectra. From this result, it is deduced that Fe nanoparticles with dimensions down to 3-4 nm keep their bulk magneto-optical constants. On the other hand, large magneto-optical signals are reported in multilayered structures due to interferential effects.

Pasteurella multocida gene expression in response to iron limitation.

Pasteurella multocida is the causative agent of a wide range of diseases in avian and mammalian hosts. Gene expression in response to low iron conditions was analyzed in P. multocida using whole-genome microarrays. The analysis shows that the expression of genes involved in energy metabolism and electron transport generally decreased 2.1- to 6-fold while that of genes used for iron binding and transport increased 2.1- to 7.7-fold in P. multocida during the first 2 h of growth under iron-limiting conditions compared with controls. Notably, 27% of the genes with significantly altered expression had no known function, illustrating the limitations of using publicly available databases to identify genes involved in microbial metabolism and pathogenesis. Taken together, the results of our investigations demonstrate the utility of whole-genome microarray analyses for the identification of genes with altered expression profiles during varying growth conditions and provide a framework for the detailed analysis of the molecular mechanisms of iron acquisition and metabolism in P. multocida and other gram-negative bacteria.

CRP Modulates fis Transcription by Alternate Formation of Activating and Repressing Nucleoprotein Complexes

The DNA architectural proteins FIS and CRP are global regulators of transcription in Escherichia coli involved in the adjustment of cellular metabolism to varying growth conditions. We have previously demonstrated that FIS modulates the expression of the crp gene by functioning as its transcriptional repressor. Here we show that in turn, CRP is required to maintain the growth phase pattern of fis expression. We demonstrate the existence of a divergent promoter in the fis regulatory region, which reduces transcription of the fis promoter. In the absence of FIS, CRP activates fis transcription, thereby displacing the polymerase from the divergent promoter, whereas together FIS and CRP synergistically repress fis gene expression. These results provide evidence for a direct cross-talk between global regulators of cellular transcription during the growth phase. This cross-talk is manifested in alternate formation of functional nucleoprotein complexes exerting either activating or repressing effects on transcription.