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Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that laser-excited muon pump–probe spin spectroscopy (photo-μSR) can temporally and spatially map these processes with a spatial resolution at the single-carbon level in a molecule with a pentacene backbone. The observed time-dependent light-induced changes of an avoided level crossing resonance demonstrate that the photochemical reactivity of a specific carbon atom is modified as a result of the presence of the excited state wavefunction. This demonstrates the sensitivity and potential of this technique in probing molecular excitations and photochemistry.

The study of the G-mode pressure coefficients of carbon nanotubes, reflecting the stiff sp2bond pressure dependence, is essential to the understanding of their extraordinary mechanical properties as well as fundamental mechanics. However, it is hindered by the availability of carbon nanotubes samples only as bundles or isolated with surfactants. Octadecylamine-functionalized carbon nanotubes are mostly of a single diameter and can be stably dispersed in 1,2-dichloroethane and chloroform without surfactants. Here we perform high-pressure Raman spectroscopy on these tubes and obtain their experimental G-mode pressure coefficients for individual tubes and bundles. The G+pressure coefficient for bundles is only about half of that for individual tubes in 1,2-dichloroethane and is about two-thirds in chloroform. The G–pressure coefficient for bundles is about one-third of G+in 1,2-dichloroethane and about the same in chloroform. These results for the first time provide unambiguous experimental evidence of the significant effect of bundling on carbon nanotubes’ G-mode pressure coefficients, identifying it as one of the major reasons for the lack of consensus on what the values should be in the literature.

We have investigated the exciton spin dynamics in strained InxGa1-xAs/GaAs (x ≤ 0.2) quantum wells. The variation of the initial polarization with the excitation energy is well correlated with the increasing mixing of the valence band states. The time behavior of the depolarization curves clearly demonstrates the prime importance of the hole and exciton spin relaxation processes.

We report measurements of the transition energies of the ground and excited state excitons in 100Å quantum wells of In0.15Ga0.85As and In0.18Ga0.82As as a function of hydrostatic pressure by photoconductivity excitation spectroscopy and absorption spectroscopy in a diamond anvil cell. The pressure coefficients of the E1HH1 and E2HH2 transitions agrees well with eight-band k.p theory provided the pressure coefficient of bulk strained InGaAs is given the anomalously low value reported previously [Wilkinson et al., Phys. Rev. B46, 3113 (1989)]. This result shows that the anomaly is an intrinsic property of the bulk strained crystal and is not associated with defects.

It has long been controversial as to whether small volumes of material are, or should be, more resistant to plastic deformation than is implied by the yield strength of bulk material. We generalize the established theory of critical thickness for strained layers to show that there is an increase in the initial yield stress for geometrical reasons wherever there is a strain gradient. The theory is in quantitative agreement, without free fitting parameters, with the classic experimental data on the torsion of thin wires and on the bending of thin beams.

The relative pressure coefficients across the (AlxGa1–x)0.5In0.5P alloy range are accurately reported for the first time as a function of the aluminium content. Low temperature continuous-wave photoluminescence (CWPL) at hydrostatic pressures up to 30 kbar was used on a specially designed sample.

The values given in the literature for the third-order elastic constants cIJK of the standard semiconductors have long been suspect. We have applied modern statistical analysis to the raw data from which the databook cIJK were obtained, and we give revised values with reliable error estimates for Si, Ge and GaAs. The databook cIJK are appropriate for an expansion of the elastic energy of a body as a Taylor series in Lagrangian strain ηIJ, but there are formidable mathematical difficulties in using Lagrangian strain in the analysis of physical problems. To facilitate such analysis, we introduce effective second-order elastic constants for materials under finite strain. From these, strain, stress and pressure derivatives are readily calculated. The pressure derivatives are given for Si, Ge and GaAs. Using the stress derivatives, the relationships between physical observables such as acoustic velocities and the databook cIJK can be obtained by simple algebra.

The diffusion of polystyrene latex particles in solutions of a poly(acrylic acid-co-acrylamide) polyelectrolyte as a function of both polyelectrolyte concentration and solution ionic strength has been investigated using dynamic light scattering. Two apparent diffusion coefficients were measured for the latex probe particles in the polyelectrolyte solutions. Designated as Dfast and Dslow, the fast diffusional mode increases to a maximum as a function of polyelectrolyte concentration, with the maximum increasing in magnitude as the ionic strength increases. Dslow decreases as a function of polyelectrolyte concentration in low ionic strength solutions. However, Dslow shows a slight increase with polyelectrolyte concentration in the higher ionic strength solutions. The results are discussed with reference to calculated correlation lengths for the polyelectrolyte solutions and are compared with the data obtained from polymer solutions measured using dynamic light scattering where similar trends have been observed. The latex spheres appear to probe the single chain motion, cooperative diffusion, and the macroscopic diffusional motions, self-diffusion, of the polyelectrolyte molecules.

The local viscosity experienced by the chain backbone of fluorescein-labeled hydroxypropylguar (HPG) in aqueous solution has been studied using time-resolved and steady-state fluorescence polarization spectroscopy. These measurements have been undertaken over a range of HPG concentrations and in a series of glycerol/water solutions of varying Newtonian viscosity. The results indicate that despite the bulk viscosities varying over several orders of magnitude as a function of HPG concentration, the rotational dynamics of the fluorophore attached to the backbone are only measurably affected at concentrations of ~10 wt %. Samples of the HPG at concentrations as high as 10 wt % therefore contain regions with viscosity similar to the aqueous phase as sensed by the probe molecule. Intermolecular interaction between the chains introduces a slow rotational mode at concentrations approaching 10 wt %. The rotational correlation time of the probe attached to the HPG backbone shows a square root dependence on the solvent viscosity in the glycerol/water mixtures. This may be attributed to the restricted motion of the probe molecule around the central axis in two dimensions.

Photon correlation spectroscopy has been used to determine the degree and sizes of PEGylated-liposome aggregation. The aggregation of the liposomes has been induced by NeutrAvidin−biotin adsorbed to the surfaces of the vesicles. None of the liposome preparations described herein exhibited aggregation before the introduction of NeutrAvidin. The critical ratios of the NeutrAvidin−biotin required to induce vesicle aggregation have been measured and are reported in this work. The aggregation is found to be dependent upon the ratio of NeutrAvidin to exposed biotinylated lipid and also the exposed biotinylated lipid fraction.

Much work on semiconductors, soft solids and biological materials does not require the megabar capability of the diamond anvil cell; a few accurate kbar being all that may be required. Work in this range poses its own challenges, to make the experiments routine, safe and reliable, and well-calibrated. We contrast diamond anvil cells working at what for them is very low pressure, with traditional bombs working at what for them is dangerously high pressure. We describe our preferred solution, a single-diamond cell, and demonstrate its use with Raman data from ethanol under low pressure. Negative hydrostatic pressure cannot be obtained by traditional methods. However, we present data showing the Raman spectrum of ethanol apparently at the negative pressure of m 3 kbar.

Solutions of xanthan gum form a strong gel in the presence of metal ions. The gelation process of a low concentration xanthan solution in the presence of aqueous aluminum ions (Al(III)) was followed as a function of temperature. Thermal gelation was observed at 44 ± 2 °C by the onset of heterodyne and nonergodic behavior and by the divergence of the observed fast motion. The paper deals extensively with the main problem of light scattering from systems where long relaxation processes are occurring and the time average no longer coincides with the ensemble average. The two approaches suggested in the literature, i.e., the heterodyne and the nonergodic approach, developed by Geissler and Pusey, respectively, are tested. Two modes of motion are observed in the solution state as well as in the gel. The fast motions can be assigned to the collective diffusion of the gel modes. The relaxation time passes through a sharp maximum at the gel point and then decreases. The slow motions arise from clusters or heterogeneities. In the gel state the collective diffusion is superimposed by marked internal network fluctuations.

Raman spectroscopy was used to compare the structural effects on single-walled carbon nanotubes of pressures due to the cohesive energy of liquid media with the effects of an externally applied macroscopic pressure. Results were very similar, showing that the interpretation of the cohesive energy density as an internal pressure is physically realistic.

The diffusion coefficients of polystyrene latex spheres in both Newtonian and elastic liquids have been measured using dynamic light scattering. The diffusion coefficients of the latex particles measured in glycerol/water (Newtonian) solutions obey Stokes−Einstein behavior over a range of solvent viscosity and temperature. Two apparent diffusion coefficients for the particles are measured in viscoelastic polyacrylamide solutions and are designated Dfast and Dslow. The apparent fast diffusion coefficients measured in the polyacrylamide solutions show an increase to a maximum, above that measured in the solvent water, with increasing polyacrylamide concentration. The apparent fast diffusion coefficient is seen to increase to twice that measured in the water solvent. At higher polyacrylamide concentrations the observed Dfast values decrease below the value obtained in the solvent water. Dfast increases with the scattering vector (q) while Dslow is independent of q.

Atomic force microscopy (AFM) is used to image hydroxypropylguar gel structures formed under quiescent conditions as well as gels formed under varying levels of steady shear. Hydroxypropylguar (HPG) in aqueous solution is representative of a high molecular weight, flexible polysaccharide. HPG readily cross-links with borate ions to form a gel network. The steady-state rheological properties of borate cross-linked HPG gels are shown to be dependent on the shear rate applied during the gelation reaction. The storage modulus is used as an indication of the gel strength. The gel strength is shown to be enhanced under moderate shear conditions and is seen to decrease under high shear during gelation. AFM images show an aligned, ordered structure is present in the high gel strength material (low preshear rate), with a random network structure present in the gel formed under quiescent conditions. A material composed of globular structures is apparent in the gel formed under high shear. The variation in the observed microstructure and rheological data with preshear rate is discussed in relation to alignment of polymer molecules in shear fields.

The microstructural changes induced by shear in dilute suspensions of colloidal Fe2O3 rods (aspect ratio = 8.4) have been studied using a novel rheo-optic technique. The large extinction coefficient for the hematite system at the wavelength used (λ = 392 nm) enables rheo-optic experiments on truly dilute suspensions to be undertaken. The elimination of any particle−particle interactions ensures that the measurements obtained can be directly related to the induced physical changes of the isolated particles. Optical absorbance spectra have been measured over a range of shear rates and angle of light polarization relative to the shear direction. The measured absorbance changes can be directly attributed to the shear-induced anisotropy in the suspension due to particle alignment. The results indicate that the hematite particles align with the direction of shear. The transition in the particle orientation is observed from a random Brownian-dominated system at Pe < 3, to a more ordered system under shear at Pe > 60. Plateau values in the measured spectra are observed at high Peclet numbers, indicating that a limiting degree of particle orientation occurs. Convergence of the observed extinction coefficients to zero at a polarization angle of ~55° is seen at high Peclet numbers.

The electrophoretic mobilities of hemoglobin and lysozyme were measured through polycarbonate track‐etched membranes of different pore sizes. Together with the zeta potential of the protein‐fouled membranes, and measurements of the free‐solution mobilities, protein sizes, and membrane pore sizes, the theory of Ennis et al. was tested. The presence of the membrane offered little hindrance to protein transfer when the membrane pore size was large in comparison with the protein size and the thickness of the electrical double layers. Under some solution conditions, protein agglomeration was significant and the interactions between the larger particles, and the membrane pore walls caused a more pronounced reduction in the protein mobility from its free‐solution value. Good agreement with the theoretical model was found only for cases where the solution remained as a monodispersed suspension of protein monomers.

High hydrostatic pressures were applied to single-wall carbon nanotubes by means of a diamond anvil cell (DAC), and micro-Raman spectroscopy was simultaneously used to monitor the pressure-induced shift of various nanotube bands. The data confirm recent results independently obtained from internal pressure experiments with various liquids, where the peak shifts were considered to arise from compressive forces imposed by the liquids on the nanotubes. It is also shown that the nanotube peak at 1580 cm^-1 (the G band) shifts linearly with pressure up to 20 000 atm and deviates from linearity at higher pressure. This deviation is found to be coincident with a drop in Raman intensity for the disorder-induced peak at 2610 cm^-1 (the overtone of the D* band), possibly corresponding to the occurrence of reversible flattening of the nanotubes. The independent results presented here confirm the potential of nanotubes as molecular sensors.

The electron beam of a scanning electron microscope causes carrier generation in a semiconductor and these carriers are the probe for various types of image. In particular, the electron‐beam‐induced current mode gives images which reveal electrically active near‐surface defects in a semiconductor sample. Since semiconductor multilayer structures are now very common, one needs to know how the multilayer structure modifies the shape of the generation volume. The Monte Carlo technique for modelling beam electron trajectories inside the sample is used and gives a detailed insight into the shape of such a generated carrier generation distribution. Additionally, a simpler analytical method is developed for constructing a one‐dimensional depth distribution for multilayer structures, starting from known depth dose distributions for bulk materials. The analytical method is validated by comparison with Monte Carlo results.

Single-crystal semiconductor layers can be grown with large coherency strains. This review covers their standard elasticity theory and methods of measuring the strain. High-quality strained layers are thermodynamically stable up to a critical thickness, and both theoretical and experimental determinations of critical thickness are considered. Above critical thickness there is a metastable regime, with thicknesses of a few tens of nanometres for a typical misfit ε0∼1%. A relaxation critical thickness is identified, above which compressive strain produces plastic relaxation so the strain in a layer is less than its misfit (tensile layers commonly experience cracking instead of plastic relaxation). Relaxing layers may have a misfit ε0∼1%, and thicknesses of a few hundred nanometres. In the high-mismatch regime, any strain severely perturbs the crystal growth; this occurs typically for misfits of 2% upwards. The review concludes with some unresolved questions about multilayer structures.

Abstract Both somatic and excised zygotic embryos of interior spruce (Picea glauca engelmannii complex) required exogenous sucrose in the medium for germination in vitro. Over a period of 29 days on sucrose-containing medium germinants with roots and epicotyls developed from both kinds of embryo, and their content of linolenic acid (9,12,15-18:3) increased about six- to eightfold. Without added sucrose, embryos showed retarded growth or were necrotic, and the content of linolenic acid was barely detectable in their fatty acid profiles. Through ¹⁴C-sucrose uptake studies, it was determined that germinants consumed only 25% of the sucrose available in a 1% (wt/vol) sucrose-containing medium. Since no radiolabelled fatty acids were detected, it appears that externally supplied sucrose was not used in the synthesis of lipids. Although sucrose was present during plantlet development, 72% of the initial lipids were consumed. To some extent, the plantlets appeared to be obligate storage lipid utilizers.

The kinetics of competitive tunnelling recombination paths are treated theoretically, and solutions are obtained for tunnelling radiative and non-radiative recombination mechanisms. A general solution is given in the form of a non-linear integral equation that can readily be solved numerically. Results are compared with a Monte Carlo solution and with experimental data for GaP : N and for a-Si : H from the literature. The mechanism of non-radiative recombination in a-Si : H is discussed.

The kinetics of the recombination of separately trapped electrons and holes are treated theoretically, and the results are compared with the low-temperature 1·4 eV luminescence of a-Si: H. The carriers are assumed to be distributed at random spatially, and the recombination transition rate is assumed to depend exponentially on the electron-hole separation. We obtain an exact solution, in the form of a non-linear integral equation, for the case of luminescence decay following a single excitation pulse; and we give approximate solutions for repetitively pulsed excitation (as in time-resolved spectroscopy) and for continuous excitation. Good agreement is found between the experimentally observed behaviour of a-Si: H and the predictions of the distant-pair model, without any adjustable parameters. In particular, the model predicts that the decay curve will be independent of the excitation pulse intensity when the pulse creates fewer than ∼ 1018 cm-3 carriers. We show, therefore, that frequency-response spectroscopy is necessary for the unambiguous identification of the recombination kinetics of a distant-pair system.

A class of models of plastic relaxation is identified, in which relaxation is due to a function of state of strained layers which can be summed over a multilayer heterostructure. It is shown that in these models relaxation occurs at a single plane which can move upwards (away from the substrate) but not downwards through the structure. These results permit a simple algorithm to predict strain relaxation in heterostructures, and also demonstrate that there are conditions under which a relaxed buffer layer may be made stable with respect to the growth of further strained layers or device structures on top.

The spectroelectrochemical response of small silver particles was studied in aqueous solution using an optically transparent, thin layer electrode. The position of the surface plasmon band of the colloidal silver was found to depend on the applied electrode potential. It varied from 400 nm in air, corresponding to a redox potential of +0.15 V vs Ag/AgCl, to about 392 nm at −0.6 V vs Ag/AgCl. A value of 80 ± 10 μF cm^-2 for the double-layer capacitance of the silver−water interface was obtained on the basis of the spectroelectrochemical shift. The equilibration kinetics of the particles with the electrode obeyed the Cottrell equation. However, the number of electrons transferred at each particle−electrode encounter was found to be potential dependent and reached 1600 ± 300 at potentials more negative than −0.4 V vs Ag/AgCl. The evidence suggests that this particle charging current occurs via electron tunneling across the particle and electrode double layers and not by contact electrification. Changes in the redox potential of the particles due to added chemical reductants could also be directly monitored by laser doppler electrophoresis.

This work describes a rheooptical experiment with the ability to distinguish between orientation and deformation of polymers while quantifying the degree of deformation in shear using a polymeric chromophore. The chromophore used is poly(4-butoxycarbonylmethylurethane)diacetylene, referred to as 4BCMU, which is known to display varying optical properties that are attributed to conformational changes in the polymer backbone. The orientation may be measured by changes in the extinction coefficient both perpendicular and parallel to the shear field. The results obtained for dilute solutions of 4BCMU under shear are explained by an ellipsoidal random coil polymer in the quiescent state orientating in the shear field. In apparent contradiction to earlier theoretical models, no deformation of the polymer is observed within the range of shear fields used in this work. Extant theories have attributed the rheological behavior of polymer solutions to deformation of the spherical random polymer coils under shear.

Summary Cells of the scutellum of immature embryos ofSorghum bicolor plated onto an agar medium containing 2,4-D give rise to shoots and embryo-like structures and to some callus. Some of the embryo-like structures later develop into typical sorghum embryos complete with scutellum, coleoptile and coleorhiza. The results of anatomical studies of the development of these secondary growth forms by light and scanning electron microscopy suggest that shoots and embryo-like structures can arise directly from cells of the primary scutellum without an intervening callus phase. In some cases it appears that the scutellum of the secondary embryos arises by folding of the scutellum of the sexual embryo and does not arisede novo. In other cases the structures arise from single cells. No evidence was found to indicate that organized structures arose from proliferating callus cells. The unorganized callus which arises initially is not capable of growth through continuous subculture; it produces a purple-black pigment and rapidly becomes necrotic. The significance of these observations is discussed in relation to present views on morphogenesis in cereal cell cultures and their implications forin vitro cell genetics.

Theoretical models and experimental data on plastic relaxation are reviewed. It is concluded that neither equilibrium nor kinetic effects are responsible for the relaxation observed under conditions of high growth quality in III-V epitaxy; instead dislocation multiplication mechanisms and the space they require to operate constitute the determining factor. Residual strain is then given by ?(h)= (0·8;± 0·1 nm)/h for a layer of thickness h. Deviationsfrom this rule are indicative of poor crystallinity. Silicon–germanium and II-VI materials are briefly discussed.MST/3328

The study of recombination lifetimes and kinetics is an essential part of the analysis of recombination mechanisms in semiconductors. In recent years, time-resolved spectroscopy (TRS) has become the standard method of obtaining such experimental data, using a pulsed excitation source and gated detection. In this paper is discussed an alternative experimental approach which overcomes some of the limitations inherent in the TRS method by working in the frequency domain. The application of this method, which we call frequency-resolved spectroscopy (FRS), is described and illustrated with several examples from both crystalline and amorphous semiconductor spectroscopy.

The Matthews-Blakeslee equilibrium theory provides predictions of the critical thickness of a strained heteroepitaxial layer as a function of misfit strain and material constants. At low strains the prediction is double valued with one value producing a physically reasonable result for the critical thickness. At higher strains, no prediction is provided at all. It is shown that these features arise from a particular approximation which increases in importance for larger strains and hence for reduced critical layer thickness. A correction is proposed which lessens the influence of this approximation and which provides a single-valued prediction for all layer thicknesses, thus extending the useful range of applicability of the Matthews-Blakeslee theory.

Somatic embryo cultures of Picea mariana and the species complex P. glauca-engelmannii were each grown in 7.5-l-capacity mechanically-stirred bioreactors containing 61 medium (LP, von Arnold and Eriksson) with 30 mm sucrose. Growth of both species occurred with no observable signs of shear stress due to mechanical agitation. Growth kinetics were analysed using an array of parameters (settled culture volume, packed culture volume, osmolarity, conductivity, pH). These were compared with fresh weight, dry weight, and somatic embryo number in order to determine what parameters were highly correlated with growth and embryo number. Increasing the sucrose concentration from 30 mm to 60 mm resulted in an increase in biomass and total number of somatic embryos. For P. mariana a maximum dry weight of 6.3 gl-1 and 3076 embryos ml-1 occurred in LP medium with 60 mm sucrose after 10–12 days of culture. For P. glauca-engelmannii a maximum dry weight of 4.3 gl-1 and 2278 embryos ml-1 occurred in LP medium with 60 mm sucrose after 6–8 days culture. For all sucrose concentrations, fresh weight, dry weight and embryo number were closely correlated with packed culture volume and conductivity for P. mariana, and settled culture volume, packed culture volume and conductivity for P. glauca-engelmannii.

Abstract: InxGa1-xAs quantum wells grown pseudomorphically in GaAs and AlGaAs with values ofx up to 0.25 have been studied by photoluminescence under high hydrostatic pressure. We concentrate here on the pressure range where the emissions quench and take on the characteristics of theX-minima. In the InGaAs/GaAs structures, these transitions display an unexpected pressure coefficient, -2.6 meV/kbar, twice that of theX minima in GaAs. We assign these transitions to theX minima in the wells, and therefore make a direct measurement of the strainedX positions as a function of composition. In the InGaAs/AIGaAs structures the crossovers occur against theX-minima in the barriers and these crossovers yield an accurate value for the band offset ratio for InGaAs/GaAs heterojunctions which is found to be 60:40 (CB:VB).

The buckling of a compression member of finite and of infinite length is analysed in the case of continuous elastic support. The effective spring constant of the support can vary with the buckling wavelength, and we find the conditions under which the infinite elastically supported structure buckles at a finite load and a finite buckling wavelength. The results are applied to two cases of interest in solid-state physics and the following conclusions reached: a biaxially compressed layer on a semi-infinite substrate with the same elastic constants, such as a pseudomorphic epitaxial strained layer, will not buckle. An idealized cross-sectional transmission electron microscopy sample made from such a layer is stable up to a finite critical strain, which is proportional to the wedge angle of the thinned edge.

Summary Protoplasts from suspension cultures of somatic embryos of white spruce (Picea glauca Moench Voss) were electroporated with plasmids containing the chimeric genes for chloramphenicol acetyl transferase (CAT) or ß-glucuronidase (GUS), under control of one of three promoters. Transient CAT gene expression of approximately equal magnitude resulted when the CAT gene was fused to either the cauliflower mosaic virus (CaMV) 35S promoter or the nopaline synthase (NOS) promoter. When the CAT gene was fused to a tandem repeat CaMV 35S promoter (pPBI-363), CAT enzyme activity compared to NOS or 35S promoters increased up to eightfold (cell line WS-34), and were up to 100-fold greater than control (electroporated without plasmid). Comparatively, protoplasts of black spruce (Picea mariana Mill) and jack pine (Pinus banksiana Lamb.), electroporated with pPBI-363, produced increases in CAT activity compared to control of 90-fold and 70-fold, respectively. White spruce (WS-34) protoplasts were subsequently electroporated with the GUS gene fused to the tandem repeat CaMV 35S promoter. Comparatively, GUS enzyme activity increased up to tenfold compared to GUS fused to a CaMV 35S promoter. The results indicated that transient expression of the CAT and GUS genes was influenced by the type of promoter and cell line used, as well as by electroporation conditions.

Methods were developed for transient gene expression in protoplasts of black spruce (Picea mariana) and jack pine (Pinus banksiana). Protoplasts were isolated from embryogenic suspension cultures of black spruce and from non-embryogenic suspensions of jack pine. Using electroporation, transient expression of the chloramphenicol acetyltransferase (CAT) gene was assayed and shown to be affected by the cell line used, by voltage, temperature, and by the plasmid concentration and conformation. Increasing the plasmid DNA concentration (0–150µg ml-1) resulted in higher levels of transient CAT expression. In jack pine, linearized plasmid gave 2.5 times higher levels of CAT enzyme activity than circular. Optimal voltage varied for each cell line of the two species within the range 200–350 V cm-1 (960 µF). A heat shock treatment of protoplasts for 5 min at 45 °C resulted in enhanced CAT gene expression for both species.

Summary: Embryogenic cell cultures ofPicea mariana (black spruce) and the species complexPicea glauca-engelmannii (interior spruce) were maintained either as suspensions in liquid medium in 250 or 500-ml-capacity shake-flasks, 7-liter-capacity airlift or mechanically stirred bioreactors, or on agar-solidified medium. Cultures from each of the maintenance conditions were subsequently transferred to agar-solidified LP medium containing 40M () -abscisic acid for maturation into cotyledonary stage embryos. For both species, the highest maturation frequency resulted from cultures grown in the airlift bioreactor. With black spruce cells grown in the airlift bioreactor containing LP medium with 60 mM sucrose, a maximum of 7.1 gliter−1 dry weight and 2892 embryosml−1 were obtained after 15 days. For interior spruce cells, a maximum dry weight of 5.9 gliter−1 and 2698 embryosml−1 were obtained after 21 to 30 days. During culture over 2 wk, ammonia was almost completely utilized by both species, wherease nitrate was depleted to 40% of the initial concentration. Sucrose was rapidly hydrolyzed to glucose and fructose by both species. Black spruce cultures preferentially metabolized glucose, whereas interior spruce preferentially metabolized fructose. Improved growth of interior spruce cells in mechanically stirred bioreactors occurred when cultured in LP medium with 60 mM fructose as the sole carbon source.

Summary The organization of microtubules during interphase and prophase in embryogenic cultures of black spruce (Picea mariana) was investigated by indirect immunofluorescence. Somatic embryos of black spruce possessed an extensively branched and interconnecting network of fine interphase cortical microtubules. The development of pre-prophase bands (PPBs) in embryogenic black spruce cultures was compared with that in non-embryogenic cell cultures of jack pine (Pinus banksiana). PPBs in both species were initially arranged as a very broad array of microtubules, later (early to mid-prophase) becoming narrower and more intensely fluorescent. The occurrence of pre-prophase bands in relation to the number of phragmoplasts (i.e. PPB index) of black spruce somatic embryos was significantly higher (p<0.01) than that found for jack pine cells.

Regeneration of white spruce (Picea glauca) somatic embryos from protoplasts derived from an embryogenic suspension culture was accomplished using a culture medium containing 2 mgl-1 2,4-D and 1 mgl-1 6-BAP. Divisions within 2 days led to plating efficiencies in the order of 24% after 9 days. A reduction in the osmoticum, necessary for sustained growth, was carried out gradually over 30 days. Embedding in agarose and culture in 5 cm petri dishes prior to transfer of agarose blocks to a bead type culture, led to the formation of somatic embryos as early as 23 days after isolation and yielded plating efficiencies in the order of 5–10% after 35 days culture.

The hydrostatic pressure dependence of the photoluminescence (PL) intensity from hydrogenated amorphous silicon has been measured in a diamond anvil cell at 80 K. The PL intensity is not quenched significantly by pressures up to ∼90 kbar, but in the pressure range ∼90-130 kbar quenching is observed. The luminescence displays a red shift of 1.9±0.1 meV kbar-1, with a hysteresis of ∼35meV at the highest pressures.