GD 552: a cataclysmic variable with a brown dwarf companion?

GD 552 is a high proper motion star with the strong, double-peaked emission lines characteristic of the dwarf nova class of cataclysmic variable (CV) star, and yet no outburst has been detected during the past 12yr of monitoring. We present spectroscopy taken with the aim of detecting emission from the mass donor in this system. We fail to do so at a level which allows us to rule out the presence of a near-main-sequence star donor. Given GD 552's orbital period of 103 min, this suggests that it is either a system that has evolved through the ~80-minute orbital period minimum of CV stars and now has a brown dwarf mass donor, or that has formed with a brown dwarf donor in the first place. This model explains the low observed orbital velocity of the white dwarf and GD 552's low luminosity. It is also consistent with the absence of outbursts from the system.

The effect of the magnetic field of the secondary star in dwarf novae

We investigate the effect of a secondary star magnetic field on the accretion disc dynamics of dwarf novae. Simulations have been carried out with a particle code and a dipolar magnetic field structure. The magnetic field acts to remove angular momentum from the disc material, increasing the inward mass flow. This makes the accretion disc more centrally condensed, causing a reduction in the recurrence time for dwarf nova outbursts. We have produced Doppler tomograms and light curves which may be compared with observations. These tomograms are significantly different from those produced in the absence of a magnetic field on the secondary. We derive an upper limit to the magnetic moment of the secondary star in UGem of mu_2<2x10^32 A m^2. The magnetic truncation of the accretion disc produces resonance phenomena similar to those seen in the superoutbursts of SUUMa systems. While these have not been observed for systems like UGem, observations of the SUUMa systems provide us with a useful diagnostic of the disc-field interaction. We are able to place an upper limit on the magnetic moment of the secondary in ZCha of mu_2<1x10^30 A m^2.

A two-armed pattern in flickering maps of the nova-like variable UU aquarii

We report the analysis of a uniform sample of 31 light curves of the nova-like variable UU Aqr with eclipse-mapping techniques. The data were combined to derive eclipse maps of the average steady-light component, the long-term brightness changes, and the low- and high-frequency flickering components. The long-term variability responsible for the ""low-brightness`` and ""high-brightness`` states is explained in terms of the response of a viscous disk to changes of 20%-50% in the mass transfer rate from the donor star. Low- and high-frequency flickering maps are dominated by emission from two asymmetric arcs reminiscent of those seen in the outbursting dwarf nova IP Peg, and they are similarly interpreted as manifestations of a tidally induced spiral shock wave in the outer regions of a large accretion disk. The asymmetric arcs are also seen in the map of the steady light aside from the broad brightness distribution of a roughly steady-state disk. The arcs account for 25% of the steady-light flux and are a long-lasting feature in the accretion disk of UU Aqr. We infer an opening angle of 10 degrees +/- 3 degrees for the spiral arcs. The results suggest that the flickering in UU Aqr is caused by turbulence generated after the collision of disk gas with the density-enhanced spiral wave in the accretion disk.

Roche tomography of cataclysmic variables - V. A high-latitude star-spot on RU Pegasi

We present Roche tomograms of the secondary star in the dwarf nova system RU Pegasi derived from blue and red arm ISIS data taken on the 4.2-m William Herschel Telescope. We have applied the entropy landscape technique to determine the system parameters and obtained component masses of M1 = 1.06 Msun, M2 = 0.96 Msun, an orbital inclination angle of i = 43 degrees, and an optimal systemic velocity of gamma = 7 km/s. These are in good agreement with previously published values. Our Roche tomograms of the secondary star show prominent irradiation of the inner Lagrangian point due to illumination by the disc and/or bright spot, which may have been enhanced as RU Peg was in outburst at the time of our observations.We find that this irradiation pattern is axi-symmetric and confined to regions of the star which have a direct view of the accretion regions. This is in contrast to previous attempts to map RU Peg which suggested that the irradiation pattern was non-symmetric and extended beyond the terminator. We also detect additional inhomogeneities in the surface distribution of stellar atomic absorption that we ascribe to the presence of a large star-spot. This spot is centred at a latitude of about 82 degrees and covers approximately 4 per cent of the total surface area of the secondary. In keeping with the high latitude spots mapped on the cataclysmic variables AE Aqr and BV Cen, the spot on RU Peg also appears slightly shifted towards the trailing hemisphere of the star. Finally, we speculate that early mapping attempts which indicated non-symmetric irradiation patterns which extended beyond the terminator of CV donors could possibly be explained by a superposition of symmetric heating and a large spot.

RU Peg and AE Aqr: two contrasting CVs with one thing in common

Roche tomography is a powerful tool for imaging the surfaces of stars. We have applied it to two contrasting systems, a normal dwarf nova, RU Peg, and the peculiar intermediate polar AE Aqr. Despite these differences, the Roche tomograms of the cool stars in the two systems are remarkably similar. We compare them with tomograms of two other stars, and discuss the differences and similarities. The rotation speed may be critical in determining the surface appearance, and it is strongly recommended that a Roche tomogram be obtained for the bright CV SS Cygni, which would be the fastest-rotating secondary to be studied. In addition, V426 Oph should be re-observed.

The impact of accretion disc winds on the optical spectra of cataclysmic variables

Many high-state non-magnetic cataclysmic variables (CVs) exhibit blueshifted absorption or P-Cygni profiles associated with ultraviolet (UV) resonance lines. These features imply the existence of powerful accretion disc winds in CVs. Here, we use our Monte Carlo ionization and radiative transfer code to investigate whether disc wind models that produce realistic UV line profiles are also likely to generate observationally significant recombination line and continuum emission in the optical waveband. We also test whether outflows may be responsible for the single-peaked emission line profiles often seen in high-state CVs and for the weakness of the Balmer absorption edge (relative to simple models of optically thick accretion discs). We find that a standard disc wind model that is successful in reproducing the UV spectra of CVs also leaves a noticeable imprint on the optical spectrum, particularly for systems viewed at high inclination. The strongest optical wind-formed recombination lines are H alpha and He ii lambda 4686. We demonstrate that a higher density outflow model produces all the expected H and He lines and produces a recombination continuum that can fill in the Balmer jump at high inclinations. This model displays reasonable verisimilitude with the optical spectrum of RW Trianguli. No single-peaked emission is seen, although we observe a narrowing of the double-peaked emission lines from the base of the wind. Finally, we show that even denser models can produce a single-peaked H alpha line. On the basis of our results, we suggest that winds can modify, and perhaps even dominate, the line and continuum emission from CVs.

Rapid Keck Spectroscopy of Cataclysmic Variables

We present an analysis of Rapid Keck Spectroscopy of the CVs AM Her (polar) and SS Cyg (dwarf nova). We decompose the spectra into constant and variable components and identify different types of variability in AM Her with different characteristic timescales. The variable flickering component of the accretion disc flux and the observational characteristics of a small flare in SS Cyg are isolated.

The Unusually Luminous Extragalactic Nova SN 2010U

We present observations of the unusual optical transient SN 2010U, including spectra taken 1.03 days to 15.3 days after maximum light that identify it as a fast and luminous Fe II type nova. Our multi-band light curve traces the fast decline (t 2 = 3.5 ± 0.3 days) from maximum light (MV = -10.2 ± 0.1 mag), placing SN 2010U in the top 0.5% of the most luminous novae ever observed. We find typical ejecta velocities of ≈1100 km s-1 and that SN 2010U shares many spectral and photometric characteristics with two other fast and luminous Fe II type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme luminosity of this nova, the maximum magnitude versus rate of decline relationship indicates a massive white dwarf (WD) progenitor with a low pre-outburst accretion rate. However, this prediction is in conflict with emerging theories of nova populations, which predict that luminous novae from massive WDs should preferentially exhibit an alternate spectral type (He/N) near maximum light.

XMM-Newton EPIC and OM observation of Nova Centauri 1986 (V842 Cen)

We report the results from the temporal and spectral analysis of an XMMNewton observation of Nova Centauri 1986 (V842 Cen). We detect a period at 3.51 +/- 0.4 h in the EPIC data and at 4.0 +/- 0.8 h in the Optical Monitor (OM) data. The X-ray spectrum is consistent with the emission from an absorbed thin thermal plasma with a temperature distribution given by an isobaric cooling flow. The maximum temperature of the cooling flow model is keV. Such a high temperature can be reached in a shocked region and, given the periodicity detected, most likely arises in a magnetically channelled accretion flow characteristic of intermediate polars. The pulsed fraction of the 3.51-h modulation decreases with energy as observed in the X-ray light curves of magnetic cataclysmic variables, possibly due either to occultation of the accretion column by the white dwarf body or phase-dependent to absorption. We do not find the 57-s white dwarf spin period, with a pulse amplitude of 4 mmag, reported by Woudt et al. in either the OM data, which are sensitive to pulse amplitudes ?0.03 mag, or the EPIC data, sensitive to pulse fractions p? 14 +/- 2 per cent.

Recombinant protein production using a Tobacco yellow dwarf virus-based episomal expression vector : control of Rep activity

Over the past decade, plants have been used as expression hosts for the production of pharmaceutically important and commercially valuable proteins. Plants offer many advantages over other expression systems such as lower production costs, rapid scale up of production, similar post-translational modification as animals and the low likelihood of contamination with animal pathogens, microbial toxins or oncogenic sequences. However, improving recombinant protein yield remains one of the greatest challenges to molecular farming. In-Plant Activation (InPAct) is a newly developed technology that offers activatable and high-level expression of heterologous proteins in plants. InPAct vectors contain the geminivirus cis elements essential for rolling circle replication (RCR) and are arranged such that the gene of interest is only expressed in the presence of the cognate viral replication-associated protein (Rep). The expression of Rep in planta may be controlled by a tissue-specific, developmentally regulated or chemically inducible promoter such that heterologous protein accumulation can be spatially and temporally controlled. One of the challenges for the successful exploitation of InPAct technology is the control of Rep expression as even very low levels of this protein can reduce transformation efficiency, cause abnormal phenotypes and premature activation of the InPAct vector in regenerated plants. Tight regulation over transgene expression is also essential if expressing cytotoxic products. Unfortunately, many tissue-specific and inducible promoters are unsuitable for controlling expression of Rep due to low basal activity in the absence of inducer or in tissues other than the target tissue. This PhD aimed to control Rep activity through the production of single chain variable fragments (scFvs) specific to the motif III of Tobacco yellow dwarf virus (TbYDV) Rep. Due to the important role played by the conserved motif III in the RCR, it was postulated that such scFvs can be used to neutralise the activity of the low amount of Rep expressed from a “leaky” inducible promoter, thus preventing activation of the TbYDV-based InPAct vector until intentional induction. Such scFvs could also offer the potential to confer partial or complete resistance to TbYDV, and possibly heterologous viruses as motif III is conserved between geminiviruses. Studies were first undertaken to determine the levels of TbYDV Rep and TbYDV replication-associated protein A (RepA) required for optimal transgene expression from a TbYDV-based InPAct vector. Transient assays in a non-regenerable Nicotiana tabacum (NT-1) cell line were undertaken using a TbYDV-based InPAct vector containing the uidA reporter gene (encoding GUS) in combination with TbYDV Rep and RepA under the control of promoters with high (CaMV 35S) or low (Banana bunchy top virus DNA-R, BT1) activity. The replication enhancer protein of Tomato leaf curl begomovirus (ToLCV), REn, was also used in some co-bombardment experiments to examine whether RepA could be substituted by a replication enhancer from another geminivirus genus. GUS expression was observed both quantitatively and qualitatively by fluorometric and histochemical assays, respectively. GUS expression from the TbYDV-based InPAct vector was found to be greater when Rep was expected to be expressed at low levels (BT1 promoter) rather than high levels (35S promoter). GUS expression was further enhanced when Rep and RepA were co-bombarded with a low ratio of Rep to RepA. Substituting TbYDV RepA with ToLCV REn also enhanced GUS expression but more importantly highest GUS expression was observed when cells were co-transformed with expression vectors directing low levels of Rep and high levels of RepA irrespective of the level of REn. In this case, GUS expression was approximately 74-fold higher than that from a non-replicating vector. The use of different terminators, namely CaMV 35S and Nos terminators, in InPAct vectors was found to influence GUS expression. In the presence of Rep, GUS expression was greater using pInPActGUS-Nos rather than pInPActGUS-35S. The only instance of GUS expression being greater from vectors containing the 35S terminator was when comparing expression from cells transformed with Rep, RepA and REnexpressing vectors and either non-replicating vectors, p35SGS-Nos or p35SGS-35S. This difference was most likely caused by an interaction of viral replication proteins with each other and the terminators. These results indicated that (i) the level of replication associated proteins is critical to high transgene expression, (ii) the choice of terminator within the InPAct vector may affect expression levels and (iii) very low levels of Rep can activate InPAct vectors hence controlling its activity is critical. Prior to generating recombinant scFvs, a recombinant TbYDV Rep was produced in E. coli to act as a control to enable the screening for Rep-specific antibodies. A bacterial expression vector was constructed to express recombinant TbYDV Rep with an Nterminal His-tag (N-His-Rep). Despite investigating several purification techniques including Ni-NTA, anion exchange, hydrophobic interaction and size exclusion chromatography, N-His-Rep could only be partially purified using a Ni-NTA column under native conditions. Although it was not certain that this recombinant N-His-Rep had the same conformation as the native TbYDV Rep and was functional, results from an electromobility shift assay (EMSA) showed that N-His-Rep was able to interact with the TbYDV LIR and was, therefore, possibly functional. Two hybridoma cell lines from mice, immunised with a synthetic peptide containing the TbYDV Rep motif III amino acid sequence, were generated by GenScript (USA). Monoclonal antibodies secreted by the two hybridoma cell lines were first screened against denatured N-His-Rep in Western analysis. After demonstrating their ability to bind N-His-Rep, two scFvs (scFv1 and scFv2) were generated using a PCR-based approach. Whereas the variable heavy chain (VH) from both cell lines could be amplified, only the variable light chain (VL) from cell line 2 was amplified. As a result, scFv1 contained VH and VL from cell line 1, whereas scFv2 contained VH from cell line 2 and VL from cell line 1. Both scFvs were first expressed in E. coli in order to evaluate their affinity to the recombinant TbYDV N-His-Rep. The preliminary results demonstrated that both scFvs were able to bind to the denatured N-His-Rep. However, EMSAs revealed that only scFv2 was able to bind to native N-His-Rep and prevent it from interacting with the TbYDV LIR. Each scFv was cloned into plant expression vectors and co-bombarded into NT-1 cells with the TbYDV-based InPAct GUS expression vector and pBT1-Rep to examine whether the scFvs could prevent Rep from mediating RCR. Although it was expected that the addition of the scFvs would result in decreased GUS expression, GUS expression was found to slightly increase. This increase was even more pronounced when the scFvs were targeted to the cell nucleus by the inclusion of the Simian virus 40 large T antigen (SV40) nuclear localisation signal (NLS). It was postulated that the scFvs were binding to a proportion of Rep, leaving a small amount available to mediate RCR. The outcomes of this project provide evidence that very high levels of recombinant protein can theoretically be expressed using InPAct vectors with judicious selection and control of viral replication proteins. However, the question of whether the scFvs generated in this project have sufficient affinity for TbYDV Rep to prevent its activity in a stably transformed plant remains unknown. It may be that other scFvs with different combinations of VH and VL may have greater affinity for TbYDV Rep. Such scFvs, when expressed at high levels in planta, might also confer resistance to TbYDV and possibly heterologous geminiviruses.

Vectors and alternative hosts of tobacco yellow dwarf virus in southeastern Australia

Factors that determine the epidemiology of Tobacco yellow dwarf virus (TbYDV), including alternative host plants and insect vector(s), were assessed over three consecutive growing seasons at four field sites in Northeastern Victoria in commercial tobacco growing properties. In addition, these factors were assessed for one growing season at three bean growing properties. Overall, 23 leafhopper species were identified at the 7 sites, with Orosius orientalis as the predominant leafhopper. Of the leafhoppers collected, only O. orientalis and Anzygina zealandica tested positive for TbYDV by polymerase chain reaction (PCR). The population dynamics of O. orientalis was assessed using sweep net sampling over three growing seasons and a trimodal distribution was observed. Despite large numbers of O. orientalis occurring early in the growing season (September–October), TbYDV was only detected in these leafhoppers between late November and end of January. The peaks in the detection of TbYDV in O. orientalis correlated with the observation of disease symptoms in tobacco and bean and were associated with warmer temperatures and lower rainfall. Spatial and temporal distribution of vegetation at selected sites was determined using quadrat sampling. Of the 40 plant species identified, TbYDV was detected only in four dicotyledonous species, Amaranthus retroflexus, Phaseolus vulgaris, Nicotiana tabacum and Raphanus raphanistrum. The proportion of host and non-host availability for leafhoppers was associated with climatic conditions.

Characterisation of the tritrophic interactions between tobacco yellow dwarf virus, its vector and host-plants

Tobacco yellow dwarf virus (TbYDV, family Geminiviridae, genus Mastrevirus) is an economically important pathogen causing summer death and yellow dwarf disease in bean (Phaseolus vulgaris L.) and tobacco (Nicotiana tabacum L.), respectively. Prior to the commencement of this project, little was known about the epidemiology of TbYDV, its vector and host-plant range. As a result, disease control strategies have been restricted to regular poorly timed insecticide applications which are largely ineffective, environmentally hazardous and expensive. In an effort to address this problem, this PhD project was carried out in order to better understand the epidemiology of TbYDV, to identify its host-plant and vectors as well as to characterise the population dynamics and feeding physiology of the main insect vector and other possible vectors. The host-plants and possible leafhopper vectors of TbYDV were assessed over three consecutive growing seasons at seven field sites in the Ovens Valley, Northeastern Victoria, in commercial tobacco and bean growing properties. Leafhoppers and plants were collected and tested for the presence of TbYDV by PCR. Using sweep nets, twenty-three leafhopper species were identified at the seven sites with Orosius orientalis the predominant leafhopper. Of the 23 leafhopper species screened for TbYDV, only Orosius orientalis and Anzygina zealandica tested positive. Forty-two different plant species were also identified at the seven sites and tested. Of these, TbYDV was only detected in four dicotyledonous species, Amaranthus retroflexus, Phaseolus vulgaris, Nicotiana tabacum and Raphanus raphanistrum. Using a quadrat survey, the temporal distribution and diversity of vegetation at four of the field sites was monitored in order to assess the presence of, and changes in, potential host-plants for the leafhopper vector(s) and the virus. These surveys showed that plant composition and the climatic conditions at each site were the major influences on vector numbers, virus presence and the subsequent occurrence of tobacco yellow dwarf and bean summer death diseases. Forty-two plant species were identified from all sites and it was found that sites with the lowest incidence of disease had the highest proportion of monocotyledonous plants that are non hosts for both vector and the virus. In contrast, the sites with the highest disease incidence had more host-plant species for both vector and virus, and experienced higher temperatures and less rainfall. It is likely that these climatic conditions forced the leafhopper to move into the irrigated commercial tobacco and bean crop resulting in disease. In an attempt to understand leafhopper species diversity and abundance, in and around the field borders of commercially grown tobacco crops, leafhoppers were collected from four field sites using three different sampling techniques, namely pan trap, sticky trap and sweep net. Over 51000 leafhopper samples were collected, which comprised 57 species from 11 subfamilies and 19 tribes. Twentythree leafhopper species were recorded for the first time in Victoria in addition to several economically important pest species of crops other than tobacco and bean. The highest number and greatest diversity of leafhoppers were collected in yellow pan traps follow by sticky trap and sweep nets. Orosius orientalis was found to be the most abundant leafhopper collected from all sites with greatest numbers of this leafhopper also caught using the yellow pan trap. Using the three sampling methods mentioned above, the seasonal distribution and population dynamics of O. orientalis was studied at four field sites over three successive growing seasons. The population dynamics of the leafhopper was characterised by trimodal peaks of activity, occurring in the spring and summer months. Although O. orientalis was present in large numbers early in the growing season (September-October), TbYDV was only detected in these leafhoppers between late November and the end of January. The peak in the detection of TbYDV in O. orientalis correlated with the observation of disease symptoms in tobacco and bean and was also associated with warmer temperatures and lower rainfall. To understand the feeding requirements of Orosius orientalis and to enable screening of potential control agents, a chemically-defined artificial diet (designated PT-07) and feeding system was developed. This novel diet formulation allowed survival for O. orientalis for up to 46 days including complete development from first instar through to adulthood. The effect of three selected plant derived proteins, cowpea trypsin inhibitor (CpTi), Galanthus nivalis agglutinin (GNA) and wheat germ agglutinin (WGA), on leafhopper survival and development was assessed. Both GNA and WGA were shown to reduce leafhopper survival and development significantly when incorporated at a 0.1% (w/v) concentration. In contrast, CpTi at the same concentration did not exhibit significant antimetabolic properties. Based on these results, GNA and WGA are potentially useful antimetabolic agents for expression in genetically modified crops to improve the management of O. orientalis, TbYDV and the other pathogens it vectors. Finally, an electrical penetration graph (EPG) was used to study the feeding behaviour of O. orientalis to provide insights into TbYDV acquisition and transmission. Waveforms representing different feeding activity were acquired by EPG from adult O. orientalis feeding on two plant species, Phaseolus vulgaris and Nicotiana tabacum and a simple sucrose-based artificial diet. Five waveforms (designated O1-O5) were observed when O. orientalis fed on P. vulgaris, while only four (O1-O4) and three (O1-O3) waveforms were observed during feeding on N. tabacum and the artificial diet, respectively. The mean duration of each waveform and the waveform type differed markedly depending on the food source. This is the first detailed study on the tritrophic interactions between TbYDV, its leafhopper vector, O. orientalis, and host-plants. The results of this research have provided important fundamental information which can be used to develop more effective control strategies not only for O. orientalis, but also for TbYDV and other pathogens vectored by the leafhopper.

Situation Review of Barley Yellow Dwarf Virus in West Asia and North Africa

Symptoms of barley yellow dwarf (BYD) have been observed on cereals in nearly all countries of West Asia and North Africa. Its incidence. however, has varied during the last 15 years. Observations from field surveys are summarized. Since symptoms of barley yellow dwarf virus (BYDV) are of low diagnostic value, especially in wheat (Triticum aestivum L.), more precise qualitative and quantitative detection was derived by vector transmission and serology. In 1985 and 1986. preliminary surveys by enzyme-linked immunosorbent assay (ELlS A) indicated that BYDV incidence in the regions surveyed in Syria, Morocco, and Tunisia was around 7. 22. and 24%. respectively. By vector transmission PAV-, RPV-, and RMV-like isolates ofBYDV were identified in Morocco and the PAV-like isolate in Syria. By serology PAV-like isolates were identified in Ethiopia, Lebanon. Morocco. Syria. and Tunisia. and MA V-like isolates were identified from Morocco and Tunisia. The PAV-like type was the most common in all countries surveyed. Screening for BYDV resistance by natural infection has been carried out in a number of countries of the region during the last few years. Screening for resistance by aphid inoculation was initiated in Syria in 1986 at the International Center for Agricultural Research in the Dry Areas (ICARDA). Such screening is expected to follow in other countries of the region soon.

Survey of Spring Oats for Barley Yellow Dwarf Viruses in Illinois

During the spring of 1987, 1,215 samples of spring oats (Avena sativa L.) were collected in Madison, Champaign, Woodford, Warren, and DeKalb counties, Illinois. At each site on each of three sampling dates, 45 samples were collected (regardless of symptoms) in a W pattern in I ha and tested for the PAY, MAV, RPV, and RMV serotypes of barley yellow dwarf virus (BYDV) by direct doubleantibody sandwich enzyme-linked immunosorbent assay (ELISA). RMV was not detected at any location. PAY and RPV were detected at all locations, as early as 17 April in Champaign County. The incidences of P A V and RPV from all plants sampled ranged from 2 to 64% and from 2 to 88%, respectively. Highest incidences of both strains were in May samples [rom Woodford County. MAV was detected in lower incidences (2-16%) only in samples from the central region of the state (Champaign, Woodford, and Warren counties). The presence of MA V serotypes was confirmed in triple-antibody sandwich ELISA with the MA V -specific MAFF2 monoclonal antibody from L. Torrance. In the last previous survey for BYDV in Illinois during 1967-1968 (1), about 75% of the isolates were PAY and about 20% were RPV; single isolates of RMV and MAV were found. Twenty years later, 55% were PAY, 39% were RPV, and 6% were MAV.

Growth-hormone-stimulated dentinogenesis in Lewis dwarf rat molars

In dentinogenesis, certain growth factors, matrix proteoglycans, and proteins are directly or indirectly dependent on growth hormone. The hypothesis that growth hormone up-regulates the expression of enzymes, sialoproteins, and other extracellular matrix proteins implicated in the formation and mineralization of tooth and bone matrices was tested by the treatment of Lewis dwarf rats with growth hormone over 5 days. The molar teeth were processed for immunohistochemical demonstration of bone-alkaline phosphatase, bone morphogenetic proteins-2 and -4, osteocalcin, osteopontin, bone sialoprotein, and E11 protein. Odontoblasts responded to growth hormone by more cells expressing bone morphogenetic protein, alkaline phosphatase, osteocalcin, and osteopontin. No changes were found in bone sialoprotein or E11 protein expression. Thus, growth hormone may stimulate odontoblasts to express several growth factors and matrix proteins associated with dentin matrix biosynthesis in mature rat molars.