Innate immunity in plants

Studies of receptors and signal-transduction components that play a role in plant disease resistance have revealed remarkable similarities with innate immunity pathways in insects and mammals. In plants, specific receptors encoded by disease-resistance genes interact with products of microbial effector genes to activate defence responses. Resistance proteins have been found to have motifs in common with components of immune response pathways in mammals and invertebrates, and to rely on similar downstream signalling components. In the future, the sharing of ideas among plant and animal biologists is likely to broaden our understanding of defence responses in diverse organisms.

Arabidopsis genome sequence as a tool for functional genomics in tomato

Tomato is a well-established model organism for studying many biological processes including resistance and susceptibility to pathogens and the development and ripening of fleshy fruits. The availability of the complete Arabidopsis genome sequence will expedite map-based cloning in tomato on the basis of chromosomal synteny between the two species, and will facilitate the functional analysis of tomato genes.

The pseudomonas AvrPto protein is differentially recognized by tomato and tobacco and is localized to the plant plasma membrane

The avrPto gene of Pseudomonas syringae pv tomato triggers race-specific resistance in tomato plants carrying Pto, a resistance gene encoding a protein kinase. When introduced into P. s. tabaci, avrPto triggers resistance in tobacco W38 plants that carry the corresponding R gene. The AvrPto protein is believed to be secreted into host cells through the bacterial type III secretion pathway, where it activates disease resistance in tomato by interacting with Pto. We report here the identification of two distinct regions in AvrPto that determine the recognition specificity of this protein in tomato and tobacco. Point mutations in the central region disrupted the avirulence activity in tomato but not in tobacco. Conversely, point mutations in the C-terminal region abolished the avirulence in tobacco but not in tomato. We further report that AvrPto was localized to the plasma membrane of plant cells. Disrupting the membrane association by mutating a putative myristoylation motif of AvrPto abolished the avirulence activity in both tomato and tobacco. These findings demonstrate that AvrPto is recognized differently by the R genes in tomato and tobacco and that the recognition of AvrPto probably is associated with the plasma membrane.

Signal recognition and transduction mediated by the tomato Pto kinase: a paradigm of innate immunity in plants

Plant disease resistance is the result of an innate host defense mechanism, which relies on the ability of the plant to recognize pathogen invasion and to efficiently mount defense responses. In tomato, resistance to the pathogen Pseudomonas syringae is mediated by the specific interaction between the plant serine/threonine kinase Pto and the bacterial protein AvrPto. This article reviews molecular and biochemical properties that confer to Pto the capability to function as an intracellular receptor and to activate a signaling cascade leading to the induction of defense responses.

Determinants of the annual pattern of reproduction in mature male merino and Suffolk sheep: modification of endogenous rhythms by photoperiod

In mediterranean environments, pastures are very poor during the autumn and consequently small ruminants, such as sheep, would have been losing body mass for many months so, during mating, gamete production would be depressed in both sexes. Effectively, the nutritive requirements for a photoperiod-driven, annual reproductive cycle are out of phase with seasonal changes in food availability. The problem could be overcome through more flexible timing of reproduction, perhaps explaining variations in seasonality between breeds that originate from differing latitudes. To study these concepts and the mechanisms involved, the endogenous rhythms and responses to photoperiod were compared in rams of 'mediterranean origin' (Merino) and 'temperate origin' (Suffolk). Groups of 16 rams of each breed were given a constant food supply and subjected to 16 months of constant equinoctial photoperiod (12L : 12D) or simulated 'mediterranean' changes in daylength (from 14L : 10D to 14D : 10L). With nutritional and photoperiodic inputs held constant, Merino and Suffolk rams showed similar endogenous rhythms in reproductive activity. Under constant nutritional inputs and a mediterranean photoperiodic cycle, the endogenous rhythms were modified differently in the two breeds, with the Merinos starting and finishing their seasons about 2 months earlier than the Suffolks. These observations partially explain the patterns observed in rams kept under field conditions. It is now necessary to test whether the rhythms of reproduction in these breeds are also modified by changes in nutrition and social cues.

Metabolic factors affecting the reproductive axis in male sheep

Changes in food intake affect the reproductive axis in both sexes, and the nutritional signals involved and the sites that receive those signals are now beginning to be unravelled. Our studies have focussed on the mature male sheep, a model in which high food intake stimulates GnRH-LH pulse frequency for only 10-20 days but continues to promote testicular growth over several months. Different signals and different target organs seem to be responsible for these short- and long-term responses. Short-term dietary treatments lead to changes in blood concentrations of glucose, fatty acids, insulin and leptin, and concentrations of glucose, insulin, leptin and some amino acids in cerebrospinal fluid. It seems unlikely that amino acids affect GnRH-LH secretion directly in sheep. Intracerebroventricular infusions of insulin specifically increase LH pulse frequency, but intravenous, intra-abomasal or intracerebroventricular infusions of glucose have no effect, despite their effects on cerebrospinal fluid insulin concentrations. The addition of fatty acids to the diet also increases LH pulse frequency, but does not affect the concentrations of insulin or leptin in the cerebrospinal fluid. It appears that acute responses to changes in nutrition involve a range of alternative pathways, possibly including interactions among insulin, leptin and energy substrates. Effects of long-term dietary treatments on testicular size are only partly dependent on the GnRH-LH system (that is, on brain control) and so must also depend on other, as yet unknown, pathways. Concepts of 'metabolic sensing and integration' are being developed from the basis of existing knowledge of the central control of appetite and reproduction.

Metabolic factors affecting the reproductive axis in male sheep

Changes in food intake affect the reproductive axis in both sexes, and the nutritional signals involved and the sites that receive those signals are now beginning to be unravelled. Our studies have focussed on the mature male sheep, a model in which high food intake stimulates GnRH-LH pulse frequency for only 10-20 days but continues to promote testicular growth over several months. Different signals and different target organs seem to be responsible for these short- and long-term responses. Short-term dietary treatments lead to changes in blood concentrations of glucose, fatty acids, insulin and leptin, and concentrations of glucose, insulin, leptin and some amino acids in cerebrospinal fluid. It seems unlikely that amino acids affect GnRH-LH secretion directly in sheep. Intracerebroventricular infusions of insulin specifically increase LH pulse frequency, but intravenous, intra-abomasal or intracerebroventricular infusions of glucose have no effect, despite their effects on cerebrospinal fluid insulin concentrations. The addition of fatty acids to the diet also increases LH pulse frequency, but does not affect the concentrations of insulin or leptin in the cerebrospinal fluid. It appears that acute responses to changes in nutrition involve a range of alternative pathways, possibly including interactions among insulin, leptin and energy substrates. Effects of long-term dietary treatments on testicular size are only partly dependent on the GnRH-LH system (that is, on brain control) and so must also depend on other, as yet unknown, pathways. Concepts of 'metabolic sensing and integration' are being developed from the basis of existing knowledge of the central control of appetite and reproduction.

Role of peripheral and central aromatization in the control of gonadotrophin secretion in the male sheep

Both testosterone and its aromatized metabolite, oestradiol-17beta, are known to act centrally on the secretion of GnRH, but the major site of aromatization is not clear as aromatase activities are found in numerous tissues including brain and testis. Here, we tested the importance of central aromatization of testosterone using a non-steroidal aromatase inhibitor, fadrozole. To distinguish between testicular and non-testicular sites, five intact and five testosterone-infused castrated rams (600 microg kg(-1) per 24 h for 3 days) were given four injections of fadrozole (i.m.; 500 microg kg(-1)) at 48, 52, 64 and 68 h relative to the start of testosterone infusion. Control rams (n = 5) received vehicle only. Fadrozole treatment decreased plasma oestradiol-17beta concentrations and increased the LH pulse frequency in both intact rams and testosterone-treated castrates, suggesting that non-testicular sites of aromatization are important in the control of pulsatile LH secretion. To test the importance of central aromatization, intact rams (n = 5) were infused into the third ventricle with vehicle (artificial cerebrospinal fluid) or with fadrozole (20 and 200 microg kg(-1) per day). After two weeks, the same two doses of fadrozole were infused intravenously instead of intracerebrally. Central infusion of fadrozole did not affect plasma oestradiol concentrations but increased LH pulse frequency. Only the highest dose increased LH pulse frequency when infused intravenously. In conclusion, central aromatization is involved in the control of pulsatile LH secretion in male sheep.

AvrPto-dependent Pto-interacting proteins and AvrPto-interacting proteins in tomato

The plant-intracellular interaction of the avirulence protein AvrPto of Pseudomonas syringae pathovar tomato, the agent of bacterial speck disease, and the corresponding tomato resistance protein Pto triggers responses leading to disease resistance. Pto, a serine/threonine protein kinase, also interacts with a putative downstream kinase, Pto-interactor 1, as well as with members of a family of transcription factors Pto-interactors 4, 5, and 6. These proteins are likely involved, respectively, in a phosphorylation cascade resulting in hypersensitive cell death, and in defense gene activation. The mechanism by which the interaction of AvrPto and Pto initiates defense response signaling is not known. To pursue the hypothesis that tertiary interactions are involved, we modified the yeast two-hybrid protein interaction trap and conducted a search for tomato proteins that interact with Pto only in the presence of AvrPto. Five classes of AvrPto-dependent Pto interactors were isolated, and their interaction specificity confirmed. Also, to shed light on a recently demonstrated virulence activity of AvrPto, we conducted a standard two-hybrid screen for tomato proteins in addition to Pto that interact with AvrPto: i.e., potential virulence targets or modifiers of AvrPto. By constructing an N-terminal rather than a C-terminal fusion of AvrPto to the LexA DNA binding domain, we were able to overcome autoactivation by AvrPto and identify four classes of specific AvrPto-interacting proteins.

Level of nutrition affects leptin concentrations in plasma and cerebrospinal fluid in sheep

In mature male sheep, the level of nutrition acutely influences the secretion of reproductive hormones. The mechanism involved is not fully understood but findings in humans and laboratory rodents would suggest a major role for leptin that is secreted from adipose tissue and then travels via the circulation to the central nervous system. Before we can begin to test this hypothesis, we need to be able to measure leptin concentrations in blood plasma and cerebrospinal fluid. We have therefore developed a radioimmunoassay using antibodies raised against biologically active recombinant bovine-ovine leptin. Using this assay, we found that plasma concentrations of leptin were highly correlated to back-fat thickness and to the ratio of back-fat thickness to liveweight, in female and castrated male sheep. Plasma concentrations of leptin were higher in female sheep than in castrated or intact male sheep. Serial samples (every 5 min) suggested that the secretion of leptin in male sheep is episodic but it does not appear to show clear pulsatility, increases post-prandially, or a diurnal rhythm. Leptin concentrations in both plasma and cerebrospinal fluid increased within 5 days in male sheep fed a diet with a high content of energy and protein that also stimulates the secretion of LH pulses. These data suggest that in sheep, as in other species, leptin production is correlated with the mass of adipose tissue and that the hormone passes from the circulation to the cerebrospinal fluid and then to hypothalamic sites. There, it may affect appetite and perhaps GnRH secretion. The role of leptin in the link between nutrition and reproduction needs further investigation.

Thr38 and Ser198 are Pto autophosphorylation sites required for the AvrPto-Pto-mediated hypersensitive response

The tomato Pto kinase confers resistance to Pseudomonas syringae pv. tomato expressing the AvrPto protein. To elucidate the role of Pto autophosphorylation in disease resistance, eight sites autophosphorylated by Pto in vitro were identified by a combination of HPLC purification of tryptic phosphopeptides, MALDI-TOF/MS analysis and Edman degradation. Mutational analysis of the autophosphorylation sites revealed that Pto residues Thr38 and Ser198 are required for AvrPto-Pto- mediated elicitation of a hypersensitive response in the plant. Thr38, which is the main Pto autophosporylation site and is located outside the kinase catalytic domain, was also required for Pto kinase activity and its physical interaction with AvrPto, the Pti1 kinase and the transcription factor Pti4. Ser198, located in the Pto activation domain, was dispensable for kinase activity and for interaction with AvrPto. However, a mutation at this site resulted in altered Pto interactions with the Pti1 kinase and the Pto interactors of unknown function Pti3 and Pti10. These results suggest that autophosphorylation events at Pto Thr38 and Ser198 are required for signal transduction by Pto and participate in distinct molecular mechanisms.

Pti4 is induced by ethylene and salicylic acid, and its product is phosphorylated by the Pto kinase

The tomato Pti4 gene encodes a transcription factor that was identified on the basis of its specific interaction with the product of the Pto disease resistance gene in a yeast two-hybrid system. We show here that the Pti4 protein specifically binds the GCC-box cis element, which is present in the promoter region of many pathogenesis-related (PR) genes. Expression of the Pti4 gene in tomato leaves was rapidly induced by ethylene and by infection with Pseudomonas syringae pv tomato, and this induction preceded expression of GCC-box-containing PR genes. Although salicylic acid also induced Pti4 gene expression, it did not induce GCC-box PR genes. Rather, salicylic acid antagonized ethylene-mediated expression of GCC-box PR genes. We demonstrate that the Pti4 protein is specifically phosphorylated by the Pto kinase and that this phosphorylation enhances binding of Pti4 to the GCC box. In addition, induced overexpression of Pto and Pti4 in tomato leaves resulted in a concomitant increase in GCC-box PR genes. Our results support a model in which phosphorylation of the Pti4 protein by the Pto kinase enhances the ability of Pti4 to activate expression of GCC-box PR genes in tomato.

Pti4 is induced by ethylene and salicylic acid, and its product is phosphorylated by the Pto kinase

The tomato Pti4 gene encodes a transcription factor that was identified on the basis of its specific interaction with the product of the Pto disease resistance gene in a yeast two-hybrid system. We show here that the Pti4 protein specifically binds the GCC-box cis element, which is present in the promoter region of many pathogenesis-related (PR) genes. Expression of the Pti4 gene in tomato leaves was rapidly induced by ethylene and by infection with Pseudomonas syringae pv tomato, and this induction preceded expression of GCC-box-containing PR genes. Although salicylic acid also induced Pti4 gene expression, it did not induce GCC-box PR genes. Rather, salicylic acid antagonized ethylene-mediated expression of GCC-box PR genes. We demonstrate that the Pti4 protein is specifically phosphorylated by the Pto kinase and that this phosphorylation enhances binding of Pti4 to the GCC box. In addition, induced overexpression of Pto and Pti4 in tomato leaves resulted in a concomitant increase in GCC-box PR genes. Our results support a model in which phosphorylation of the Pti4 protein by the Pto kinase enhances the ability of Pti4 to activate expression of GCC-box PR genes in tomato.

Long-term alterations in adiposity affect the expression of melanin-concentrating hormone and enkephalin but not proopiomelanocortin in the hypothalamus of ovariectomized ewes

We have developed a ruminant model to study long-term alterations in adiposity on the expression of appetite-regulating peptides in the hypothalamus. In this model endocrine and metabolic status are fully defined as well as body composition. The current study sought to define the effects of altered adiposity on the expression of genes for neuropeptide Y (NPY), POMC, enkephalin (ENK), and melanin-concentrating hormone (MCH). Ovariectomized ewes with high (60 +/- 1 kg) (FAT) or low (37 +/- 3 kg) body weights (THIN) were blood sampled every 10 min for 8 h to determine metabolic and endocrine status. The animals were then killed and the brains perfused for in situ hybridization. Body composition analysis was performed on the carcass using dual energy x-ray absorptiometry; this indicated that the FAT animals were 36 +/- 1% fat, whereas the THIN animals were 15 +/- 2% fat. The LH interpulse interval was lower and mean GH concentrations were higher in the THIN animals; cortisol and TSH levels were not different between the two groups but free T4 and free T3 levels were lower; the FT3:FT4 ratio was higher in THIN ewes. Levels of insulin, lactate, and nonesterified fatty acids were lower in the THIN group, and plasma glucose and urea concentrations were similar in THIN and FAT animals. Levels of gene expression of NPY and MCH were higher in THIN ewes. POMC expression was similar in the two groups. In the THIN animals, ENK expression was lower in the paraventricular and ventromedial nuclei but higher in the periventricular region. In conclusion, we have shown that alterations in adiposity influence the expression of appetite-regulating peptides in the absence of ovarian steroids. The appetite stimulators, NPY and MCH, appear to be involved in the metabolic response to altered adiposity, whereas ENK in the periventricular region may be linked to the secretion of GH and possibly LH. Our results suggest that altered expression of appetite- regulating peptides can be linked with the endocrine and metabolic adaptations that occur with long-term changes in adiposity.

Role of male-female interaction in regulating reproduction in sheep and goats

The induction of synchronous ovulatory activity in anovulatory sheep and goats after the introduction of males, the 'male effect', has probably been used to advantage since these species were domesticated and the underlying physiological and behavioural mechanisms have been progressively elucidated over the past 50 years. Less well understood is the analogous effect of oestrous females on males. This review examines the nature and importance of these male-female interactions in sheep and goats, and describes the most important internal and external factors influencing the reproductive outcomes of such interactions. It is proposed that the male and female effects are both components of a self-reinforcing cycle of stimulation that, under ideal conditions, culminates in the synchronous very rapid onset (within days) of fertile reproductive activity. However, precisely because of the speed of this response, it is suggested that mechanisms have evolved to limit its efficacy, and thus prevent conception at inappropriate times. The complexity of these factors and the interactions between them are highlighted, and a broad conceptual framework for understanding them is proposed based upon an appreciation of variation in both the responsiveness of the target animal and the quality of the signal from the signalling animal.

The major site of the pti1 kinase phosphorylated by the pto kinase is located in the activation domain and is required for pto-pti1 physical interaction

The Pto and Pti1 serine/threonine protein kinases are key components of the signaling pathway leading to speck disease resistance in tomato. The two kinases physically interact in the yeast two-hybrid system, and Pto specifically phosphorylates Pti1 in vitro. In this study, we identified and characterized the major Pti1 site phosphorylated by Pto. Pto was expressed in Escherichia coli as a maltose-binding fusion protein (MBP-Pto), and used to phosphorylate in vitro a kinase deficient Pti1 protein fused to glutathione S-transferase (GST-Pti1[K96N]). The major phosphopeptide derived from trypsin digestion of phosphorylated GST-Pti1(K96N) was partially purified by reverse-phase HPLC and analyzed by matrix assisted laser desorption/ionization mass spectrometry. Its mass corresponded to phosphopeptide LHSTR, which lies in the Pti1 kinase activation domain at amino acid position 230-234. By phosphoamino acid analysis, Thr233 was determined to be the phosphorylation site of peptide LHSTR. Mutations of Thr233 reduced dramatically Pti1 phosphorylation by MBP-Pto and Pti1 autophosphorylation, providing evidence that the same Pti1 site is involved in the two reactions. Moreover, phosphorylation of Thr233 appeared to be required for Pto-Pti1 physical interaction, as a mutation of this site to alanine, but not to aspartate, abolished the interaction between Pto and Pti1 in the yeast two-hybrid system.

Day length affects feeding behaviour and food intake in adult male emus (Dromaius novaehollandiae)

1. In south-western Australia, male and female emus decrease their food intake when they start breeding in early winter and increase their intake during spring and summer when the breeding season and egg incubation are finished. 2. This annual feeding cycle seems to be under the influence of several environmental factors. Here, we tested the importance of photoperiod using male emus kept in light-controlled rooms with ad libitum access to food and water. 3. Long days increased food intake whereas short days decreased it. Emus fed only during the light hours. 4. Frequency of meals was similar under the 2-day lengths but meal duration was shorter when the emus were on short days than when they were on long days. Thus, day length seemed to affect appetite but not interest in food. 5. Further investigations are needed to test whether these changes in feeding behaviour are a direct consequence of day length or if they are secondary to photoperiod-driven changes in sexual activity.

Pseudomonas syringae pv tomato induces the expression of tomato EREBP-like genes pti4 and pti5 independent of ethylene, salicylate and jasmonate

The tomato genes Pti4 and Pti5 encode ethylene-responsive element binding protein-like transcription factors that bind to the GCC box, a conserved cis-element in many defense-related genes. The Pti proteins have previously been shown to interact with the tomato disease resistance protein Pto. Here we report that the expression of both Pti4 and Pti5 are induced by a virulent strain of Pseudomonas syringae pv tomato. The expression of Pti5 is further enhanced by the interaction of the Pto gene in tomato and the corresponding avrPto gene in the bacterium. The enhancement of Pti5 expression by Pto-avrPto interaction requires a functional Prf gene in the plant. Pti5 appears to be expressed specifically during biotic stresses, suggesting a specific role in plant defense. Pti4 and several EREBP-like genes are induced by ethylene, salicylate and wounding. However, the Pseudomonas bacterium induced a wild-type level of Pti4 and Pti5 transcripts in tomato plants carrying the nahG transgene, the Nr mutation, or the def1 mutation. In addition, the ethylene action inhibitor norbornadiene did not inhibit the induction of Pti4 and Pti5 either in the compatible or incompatible interactions. The results suggest that the Pseudomonas bacterium induces Pti4 and Pti5 expression through a pathway independent of salicylic acid, ethylene and jasmonic acid.

Functional analysis of plant disease resistance genes and their downstream effectors

Plant disease resistance (R) genes encode proteins that both determine recognition of specific pathogen-derived avirulence (Avr) proteins and initiate signal transduction pathways leading to complex defense responses. Recent developments suggest that recognition specificity of R proteins is determined by either a protein kinase domain or by a region consisting of leucine-rich repeats. R genes conferring resistance to bacterial, viral, and fungal pathogens appear to use multiple signaling pathways, some of which involve distinct proteins and others which converge upon common downstream effectors. Manipulation of R genes and their signaling pathways by transgenic expression is a promising strategy to improve disease resistance in plants.

Rapid transcript accumulation of pathogenesis-related genes during an incompatible interaction in bacterial speck disease-resistant tomato plants

In the yeast two-hybrid system, the Pto kinase interacts with three putative transcription factors Pti4, Pti5 and Pti6. The Pti4/5/6 proteins contain a DNA binding domain that recognizes and binds a DNA sequence (5'-AGCCGCC3'; the 'PR box') present in the promoter region of a large number of genes encoding 'pathogenesis-related' (PR) proteins. We have now investigated the pathogen-induced expression of PR box-containing genes in tomato. We isolated a tomato osmotin gene that contains two PR boxes in its promoter region and demonstrated that the abundance of the osmotin transcript rapidly increases during an incompatible interaction involving Pro-containing tomato plants and the bacterial pathogen Pseudomonas syringae pv. tomato expressing the avrPto gene. In addition, we found that transcripts of two other tomato PR genes (encoding endochitinase and beta-1,3-glucanase B) and at least one ACC oxidase gene, all of which contain PR boxes in their promoter regions, rapidly accumulate in the incompatible interaction. These data support the hypothesis that the tomato Pto kinase regulates the expression of certain defense genes in tomato by interaction with transcription factors that bind the PR box.

Overexpression of Pto activates defense responses and confers broad resistance

The tomato disease resistance (R) gene Pto specifies race-specific resistance to the bacterial pathogen Pseudomonas syringae pv tomato carrying the avrPto gene. Pto encodes a serine/threonine protein kinase that is postulated to be activated by a physical interaction with the AvrPto protein. Here, we report that overexpression of Pto in tomato activates defense responses in the absence of the Pto-AvrPto interaction. Leaves of three transgenic tomato lines carrying the cauliflower mosaic virus 35S::Pto transgene exhibited microscopic cell death, salicylic acid accumulation, and increased expression of pathogenesis-related genes. Cell death in these plants was limited to palisade mesophyll cells and required light for induction. Mesophyll cells of 35S::Pto plants showed the accumulation of autofluorescent compounds, callose deposition, and lignification. When inoculated with P. s. tomato without avrPto, all three 35S::Pto lines displayed significant resistance and supported less bacterial growth than did nontransgenic lines. Similarly, the 35S::Pto lines also were more resistant to Xanthomonas campestris pv vesicatoria and Cladosporium fulvum. These results demonstrate that defense responses and general resistance can be activated by the overexpression of an R gene.

A nitrilase-like protein interacts with GCC box DNA-binding proteins involved in ethylene and defense responses

Ethylene-responsive element-binding proteins (EREBPs) of tobacco (Nicotiana tabacum L.) bind to the GCC box of many pathogenesis-related (PR) gene promoters, including osmotin (PR-5). The two GCC boxes on the osmotin promoter are known to be required, but not sufficient, for maximal ethylene responsiveness. EREBPs participate in the signal transduction pathway leading from exogenous ethylene application and pathogen infection to PR gene induction. In this study EREBP3 was used as bait in a yeast two-hybrid interaction trap with a tobacco cDNA library as prey to isolate signal transduction pathway intermediates that interact with EREBPs. One of the strongest interactors was found to encode a nitrilase-like protein (NLP). Nitrilase is an enzyme involved in auxin biosynthesis. NLP interacted with other EREBP family members, namely tobacco EREBP2 and tomato (Lycopersicon esculentum L.) Pti4/5/6. The EREBP2-EREBP3 interaction with NLP required part of the DNA-binding domain. The specificity of interaction was further confirmed by protein-binding studies in solution. We propose that the EREBP-NLP interaction serves to regulate PR gene expression by sequestration of EREBPs in the cytoplasm.

Endocrine and testicular changes in a short-day seasonally breeding bird, the emu (Dromaius novaehollandiae), in southwestern Australia

Seasonal changes in testicular morphology and blood plasma concentrations of LH, testosterone, and prolactin are described for captive male emus in southwestern Australia. Testicular mass and testicular testosterone did not differ between the non-breeding (spring-summer) and the breeding (autumn-winter) seasons. Nevertheless, the testes obtained in the breeding season (May and August) were nearly two fold greater in mass than those collected in the non-breeding season (October and February). The highest testicular concentrations of testosterone were observed in February and lowest in October, while the values during the breeding season were intermediate. The patterns of histological changes in the testes also indicate that emus breed over the autumn-winter months. Tubule diameter was larger in the breeding season than in the non-breeding season, whereas the relative volume of the interstitium was larger in the non-breeding and smaller in the breeding season. Moreover, during the autumn and winter months, plasma LH and testosterone concentrations were high. Outside this period, in spring and summer, the concentrations of these hormones were low. Prolactin concentrations rose around the winter solstice, after the initial increases in plasma LH and testosterone. The end of the breeding season, in early spring, was marked by a gradual decrease in plasma LH concentrations but a rapid fall in testosterone concentrations. Prolactin concentrations continued to increase and peaked near the spring equinox, several weeks after the breeding season ended, and then decreased to reach baseline values by mid-summer. These testicular and endocrine changes are consistent with observations that the emu is a short-day breeder in southwestern Australia. Reproductive activity in the male begins soon after the summer solstice, well in advance of the development of suitable breeding conditions, and is then terminated in spring before food resources become limited by the onset of the dry season.

Molecular mechanisms involved in bacterial speck disease resistance of tomato

An important recent advance in the field of plant–microbe interactions has been the cloning of genes that confer resistance to specific viruses, bacteria, fungi or nematodes. Disease resistance ( R ) genes encode proteins with predicted structural motifs consistent with them having roles in signal recognition and transduction. The future challenge is to understand how R gene products specifically perceive defence–eliciting signals from the pathogen and transduce those signals to pathways that lead to the activation of plant defence responses. In tomatoes, the Pto kinase (product of the Pto R gene) confers resistance to strains of the bacterial speck pathogen, Pseudomonas syringae pv. tomato , that carry the corresponding avirulence gene avrPto . Resistance to bacterial speck disease is initiated by a mechanism involving the physical interaction of the Pto kinase and the AvrPto protein. This recognition event initiates signalling events that lead to defence responses including an oxidative burst, the hypersensitive response and expression of pathogenesis–related genes. Pto–interacting (Pti) proteins have been identified that appear to act downstream of the Pto kinase and our current studies are directed at elucidating the roles of these components.

Recognition specificity for the bacterial avirulence protein AvrPto is determined by Thr-204 in the activation loop of the tomato Pto kinase

The Pto kinase confers resistance in tomato to P. syringae pv. tomato strains expressing the AvrPto protein. Physical interaction of the Pto kinase and AvrPto protein in the plant cell initiates host defense responses. The recognition event between these two proteins is very specific; AvrPto does not interact with other closely related kinases, including the Fen kinase, which shares 80% amino acid identity with Pto. By using Pto-Fen chimeric proteins and site-directed mutagenesis, we found that Thr-204 is required for Pto interaction with AvrPto in a yeast two-hybrid system and for recognition specificity in a tobacco leaf transient assay. Substitution of Thr-204 into the Fen kinase allowed that kinase to interact with AvrPto and to confer an AvrPto-specific defense response in tobacco leaves. Thus, simple mutations appear capable of giving rise to new resistance gene specificities.

Hypothalamic dopamine D1 receptors are involved in the stimulation of prolactin secretion by high environmental temperature in the female sheep

Recent evidence suggests that dopamine, acting via its D1 receptors, may function as a neurotransmitter in intrahypothalamic pathways involved in the stimulation of prolactin secretion. Functional dopamine D1 receptors are present in the ventromedial hypothalamic nucleus (VMH) and we hypothesized that they might be part of a prolactin-stimulatory pathway activated by stress. We tested this hypothesis in a series of experiments on sheep involving two different forms of stressors, audiovisual (barking dog) and high environmental temperature. We attempted to block the stimulation of prolactin secretion by infusion into the VMH of an antagonist specific for the D1 receptor. Ovariectomised, oestradiol-implanted merino ewes were surgically implanted with bilateral guide tubes directed at the VMH. After a 180 min pretreatment period, the ewes either were or were not exposed to a stressor (30 min of barking dog or 120 min at 35 degrees C, 65% relative humidity). D1 receptor antagonist, SCH23390 or vehicle (0.9% saline) was infused into the VMH (1.7 microliters/h, 120 nmol/h) for 60 min prior to and during the stressor period. Blood was sampled every 15 min via jugular cannulae and the plasma was assayed for prolactin, cortisol and growth hormone (GH). Both stressors significantly increased prolactin concentrations over control levels. SCH23390 infusion significantly attenuated the prolactin response to high environmental temperature, but had no effect on the prolactin response to audiovisual stress. Cortisol concentrations were significantly increased by audiovisual stress only and were not affected by SCH23390. GH concentrations were not changed by either stressor or infusion. Drug infusion alone did not affect the concentration of the hormones. The data suggest that the VMH D1 receptors are involved in a prolactin stimulatory pathway in response to high environmental temperature. The inability of the D1 antagonist to affect the response to the barking dog indicates that this pathway is stress-specific, implying that there is more than one mechanism or pathway involved in the prolactin response to different stressors.

[Metabolism-reproduction interactions in domestic animals]

In farm animals as in human, reproduction is affected by changes in the level of energetic balance. The main factors that link metabolism and reproduction, like insulin, IGFs, glucose, FFA, leptin and NPY, act on hypothalamo-pituitary axis as well as on gonads by directly altering gametogenesis.

Morphometric and endocrine analyses of the effects of nutrition on the testis of mature Merino rams

The effects of nutrition on the testis were investigated in groups of five mature Merino rams that were fed either a sub-maintenance (low) diet or a supra-maintenance (high) diet for 69 days. Testosterone, oestradiol and inhibin were measured in blood plasma sampled simultaneously from jugular and testicular veins after an i.v. injection of 200 ng ovine LH kg-1. Plasma concentrations of testosterone, inhibin and oestradiol were higher in testicular than in jugular vein plasma for both diets (P < 0.01). After the LH injection, jugular plasma testosterone increased more rapidly (P < 0.01) in rams fed the high diet than in rams fed the low diet. This was not seen in the testicular vein. Oestradiol concentrations were higher in rams on the high diet than in those on the low diet, in both the testicular (P < 0.0001) and the jugular vein (P < 0.02). Diet did not affect inhibin concentrations. Testes were surgically removed and processed for light microscopy. Testicular mass and seminiferous tubule length and diameter were higher with the high diet than the low diet (P < 0.01). The number of Sertoli cell nuclei per testis was also affected (high diet: 120 +/- 6 x 10(8); low diet: 77 +/- 7 x 10(8); P < 0.001), whereas the proportion of testis occupied by Sertoli cell nuclei was not affected. The number of Leydig cells per testis was not affected by diet, but Leydig cells occupied a greater volume of testis in rams on the high diet than in those on the low diet (P < 0.001). The effects of nutrition on Leydig and Sertoli cells are consistent with changes in the endocrine and exocrine functions of the testis. The finding that Sertoli cell population was altered in adult rams may be explained by the GnRH-independent effects of nutrition.

Biochemical properties of two protein kinases involved in disease resistance signaling in tomato

In tomato plants, resistance to bacterial speck disease is mediated by a phosphorylation cascade, which is triggered by the specific recognition between the plant serine/threonine protein kinase Pto and the bacterial AvrPto protein. In the present study, we investigated in vitro biochemical properties of Pto, which appears to function as an intracellular receptor for the AvrPto signal molecule. Pto and its downstream effector Pti1, which is also a serine/threonine protein kinase, were expressed in Escherichia coli as maltose-binding protein and glutathione S-transferase fusion proteins, respectively. The two kinases each autophosphorylated at multiple sites as determined by phosphopeptide mapping. In addition, Pto and Pti1 autophosphorylation occurred via an intramolecular mechanism, as their specific activity was not affected by their molar concentration in the assay. Moreover, an active glutathione S-transferase-Pto fusion failed to phosphorylate an inactive maltose-binding protein-Pto(K69Q) fusion excluding an intermolecular mechanism of phosphorylation for Pto. Pti1 phosphorylation by Pto was also characterized and found to occur with a Km of 4.1 microM at sites similar to those autophosphorylated by Pti1. Pto and the product of the recessive allele pto phosphorylated Pti1 at similar sites, as observed by phosphopeptide mapping. This suggests that the inability of the kinase pto to confer resistance to bacterial speck disease in tomato is not caused by altered recognition specificity for Pti1 phosphorylation sites.

The myristylation motif of Pto is not required for disease resistance

The tomato Pto kinase confers resistance to bacterial speck disease caused by strains of Pseudomonas syringae pv. tomato that express the avirulence gene avrPto. Pto contains a putative myristylation site at its amino terminus that was hypothesized to play a role in localizing Pto in the plant cell. Site-directed mutagenesis was used to change the invariant glycine residue in the myristylation motif to an alanine. Transgenes encoding the mutant Pto(G2A) and wild-type Pto were placed behind the cauliflower mosaic virus 35S promoter and transformed into tomato plants that are susceptible to bacterial speck disease. Both the mutant and wild-type forms of Pto conferred resistance to a strain of P. syringae pv. tomato expressing avrPto. These results indicate that the myristylation motif of Pto is not required for bacterial speck disease resistance.

Signal recognition and transduction involved in plant disease resistance

Gene-for-gene relationships, in which plant disease resistance involves a single resistance (R) gene in the plant which responds specifically to a single avirulence (avr) gene in the pathogen, have been described in numerous plant-pathogen interactions. R genes encode proteins that appear to be involved in both recognition of the pathogen and in signal transduction. Physical interaction of R gene products and Avr proteins provides an explanation for the molecular basis of some gene-for-gene interactions. Multiple signalling pathways lie downstream of R gene products and lead to the hypersensitive response and activation of specific defence-related genes. Plants use diverse mechanisms to defend themselves from pathogens including the generation of active oxygen species, cell wall strengthening, production of defence-related proteins and localized cell death.

Central metabolic messengers and the effects of nutrition on gonadotrophin secretion in sheep

Nutrition influences the reproductive axis via alteration of gonadotrophin secretion. However, a link between nutrition and the secretion of GnRH, which drives the axis, has yet to be established. The aim of the present study was to measure the change in the concentrations of metabolic substances in the cerebrospinal fluid of adult male sheep offered a diet designed to maintain constant gonadotrophin secretion (Group M; n = 6), or a diet known to increase gonadotrophin secretion (Group M + L; n = 6). On days 1, 3 and 10 of the dietary treatments, cerebrospinal fluid and jugular blood were sampled and analysed for metabolic fuels (glucose, amino acids and free fatty acids) and metabolic hormones (insulin, insulin-like growth factor I, GH, prolactin, cortisol and the thyroid hormones). On day 11 of the dietary treatment, LH pulse frequency and mean FSH concentrations in Group M + L had increased relative to Group M and to day 0. Plasma concentrations of prolactin and insulin on days 3 and 10, and glucose and insulin-like growth factor I on day 10, were higher in Group M + L than in Group M, but only cerebrospinal fluid concentrations of insulin, glucose and certain amino acids were affected by the dietary treatments on days 3 and 10. Cerebrospinal fluid, but not plasma, concentrations of aspartate, tyrosine, cystine, phenylalanine and arginine on day 3, and glutamine, gamma-aminobutyric acid, threonine, alanine on days 3 and 10, were higher in Group M + L relative to Group M. On day 10, plasma and cerebrospinal fluid concentrations of arginine, phenylalaine, proline, tyrosine, methionine and phosphoserine, but only the plasma concentrations of linoleic acid, aspartate and serine, were higher in Group M + L than in Group M. Concentrations of triiodothyronine, thyroxine, and cortisol in plasma and cerebrospinal fluid were not affected. These results show that the nutritional stimulation of gonadotrophin secretion is accompanied primarily by fluctuations in plasma and cerebrospinal fluid concentrations of insulin and certain amino acids, which suggests that, when nutritional status is improved, insulin, amino acids and possibly glucose interact to modulate GnRH secretion.

Emergency department cardiopulmonary bypass in the treatment of human cardiac arrest

OBJECTIVE

To study the use of emergency department (ED) femoro-femoral cardiopulmonary bypass (CPB) in the resuscitation of medical cardiac arrest patients.

DESIGN

Prospective, uncontrolled trial.

SETTING

Urban academic ED staffed with board-certified emergency physicians (EPs).

PARTICIPANTS

Ten patients with medical cardiac arrest unresponsive to standard therapy.

INTERVENTIONS

Femoro-femoral CPB instituted by EPs.

RESULTS

The time of cardiac arrest prior to CPB (mean+/-SD) was 32.0+/-13.6 min. The cardiac output while on CPB was 4.09+/-1.03 L/min with an average of 229+/-111 min on bypass. All 10 patients had resumption of spontaneous cardiac activity while on CPB. Seven of these were weaned from CPB with intrinsic spontaneous circulation. Of these, six patients were transferred from the ED to the operating room for cannula removal and vessel repair while the other patient died in the ED soon after discontinuing CPB. Mean survival was 47.8+/-44.7 h in the six patients leaving the ED. Although these patients had successful hemodynamic resuscitation, there were no long-term survivors.

CONCLUSION

CPB instituted by EPs is feasible and effective for the hemodynamic resuscitation of cardiac arrest patients unresponsive to advanced cardiac life support therapy. Future efforts need to focus on improving long-term outcome.

Physiological limits to further improvement in the efficiency of oestrous synchronization in goats

The variability between animals in the timing of oestrus after administration of a synchronization treatment seems to explain the low rate of fertility in goats inseminated at a predetermined time after progesterone withdrawal. Two experiments were performed during the breeding season to test whether the variation was due to the exogenous hormone regime or to the endogenous physiology of the animals. Twenty-one goats were given a synchronization treatment consisting of a vaginal sponge impregnated with 45 mg of fluorogestone acetate (FGA) for 11 days associated with intramuscular injection of 400 I.U. of equine chorionic gonadotrophin (eCG) and 50 microg of cloprostenol 48 h before sponge removal. Progesterone concentrations were measured during the subsequent cycle and the patterns were modelled to allow precise determination of the onset of luteolysis. Oestrus and the luteinizing hormone (LH) surge began 33.0+/-6.8 h and 76.0+/-33.0 h after sponge withdrawal, v. 43.4+/-5.7 h and 90.0+/-36.0 h after natural luteolysis. For both observations, the between-goat variability was larger during the natural than during the synchronized oestrus (P < 0.05). The duration of the oestrous cycle was independent of the number of corpora lutea (CL), whereas the duration of luteal phase was shorter in goats with 2-3 CL (16.4+/-0.9 day than in those with 1 CL: 17.7+/-1.3 day; P < 0.05). In the second experiment, 20 goats were ovariectomized and given a vaginal sponge as described above. Sixteen h after sponge removal, they were injected with 50 microg of oestradiol benzoate (ODB). This treatment was repeated with the second sponge being inserted 1-2 days after observation of oestrus. Oestrus and LH surge were observed: 32.8+/-6 8 h v. 27.8+/-7.8 h after the first ODB injection, and 36.6+/-7.3 h v. 34.3+/-4.8 h after the second ODB injection. No relationship was observed between data of the two experiments. In both cases, the variability in the occurrence of oestrus and LH surge was of the same order as observed in the first experiment. This study shows that the timing of oestrus and LH surge is less variable after progestagen treatment than during a natural oestrous cycle. Moreover, a significant proportion of variability is inherent in the delays following the oestradiol peak, suggesting that further improvement in the synchronizing capacity of treatment based on progestagen administration is unlikely.

Role of glucose, fatty acids and protein in regulation of testicular growth and secretion of gonadotrophin, prolactin, somatotrophin and insulin in the mature ram

This study tested whether the effects of nutrition on gonadotrophin secretion and testicular growth in mature rams are due to increases in the supply of glucose, fatty acids (FA) or amino acids. Responses to protein (casein) and glucose, alone or in combination, were compared with responses to lupin grain and responses to a combination of protein, glucose and FA (acetate, propionate and vegetable oil). Glucose and casein were infused intra-abomasally whereas lupins and FA were added to the diet. Lupin feeding decreased blood growth hormone (GH) concentrations, but increased pulsatile luteinizing hormone (LH) secretion and increased the concentrations of follicle-stimulating hormone (FSH), prolactin, glucose and insulin. These effects were associated with testicular growth. Glucose or casein increased insulin concentrations and decreased GH concentrations, but did not affect gonadotrophins or testicular growth. There was no synergism between casein and glucose. Responses elicited by adding FA to the glucose+casein treatment were similar to those observed with lupins. In conclusion, the reproductive axis does not seem to be closely linked with dietary intakes of amino acids or with circulating concentrations of glucose, insulin or GH. However, the energetic components of the diet, particularly the fatty acids, appear to play a key role in the reproductive responses to changes in nutrition.

Administration of fatty acids and gonadotrophin secretion in the mature ram

The addition of lupin grain to a maintenance diet increases circulating concentrations of volatile fatty acids and gonadotrophin secretion in mature rams. The experiments reported in this paper tested whether these responses were linked causally. The first experiment used 24 rams, of which 16 had two intra-ruminal cannulae inserted each, one for infusion of buffer and the other for infusion of volatile fatty acids. The treated rams (n = 8) were infused for 10 h each day with 1 litre of a solution of volatile fatty acids containing 1.93 moles acetate, 1.89 moles propionate and 0.68 moles butyrate, and 2 litres of a buffer solution containing 14.78 moles sodium bicarbonate, 6.39 moles potassium bicarbonate and 2.06 moles sodium chloride. The eight negative control rams were fed to maintenance and four of them were infused intra-ruminally each day with 3 litres of buffer containing the same mass of salts as the treated rams were given. The eight positive control rams were fed the maintenance diet plus a daily supplement of 900 g lupin grain and four of them were also infused with buffer salts. Blood was sampled before treatment, on Day 3 and at the end of the treatment period (Day 10) for measurement of the plasma concentrations of gonadotrophins (LH and FSH), glucose, insulin and cortisol. In the second experiment, another 24 mature rams were fed to maintain constant live weight and, for 12 of them, sodium acetate (127 g), sodium propionate (64 g) and vegetable oil (60 g) were added to the diet every day for 11 days. Blood was sampled before, and at the end of the treatment period for measurement of the plasma concentrations of gonadotrophins, inhibin, glucose and insulin. In Experiment 1, intraruminal infusion of buffer alone did not affect any of the endocrine variables measured. The infusion of fatty acids and buffer did not alter gonadotrophin secretion, but depressed food intake and increased the plasma concentrations of glucose, insulin and cortisol. When the fatty acids were added to the diet (Experiment 2), the pulsatile secretion of LH was stimulated and FSH and inhibin concentrations were increased. Lupin feeding increased LH pulse frequency on Days 5 and 10, but did not affect FSH concentrations. There were no changes in the circulating concentrations of glucose or insulin. The effects of intra-ruminal infusion of fatty acids on cortisol concentrations and appetite, which were completely absent when similar amounts of fatty acids were fed, suggest that such infusions have undesirable, perhaps stressful, side-effects that prevent expression of the reproductive endocrine responses. On the other hand, the stimulation of gonadotrophin secretion following addition of fatty acids to the diet possibly suggests that changes in the plane of nutrition or rams, for example with lupin supplements, stimulates the reproductive centres of the brain via pathways associated with the synthesis or utilisation of fatty acids. These pathways do not seem to involve changes in glucose homeostasis.

GnRH secretion into CSF in rams treated with a GnRH antagonist

The equilibrium of the brain-pituitary-testicular axis is controlled by negative feedback exerted primarily through changes in the circulating concentrations of gonadal steroids. This is usually studied in gonadectomised animals treated with single large doses or constant low levels of exogenous steroid. However, the feedback system probably also contains dynamic components, perhaps expressed as delays to changes in GnRH secretion following a change in steroid concentration. These delays must be measured without interference from surgical procedures, including anaesthesia, bias associated with changes in pituitary responsiveness (which affect the efficiency of pulse detection), and chronic side-effects of gonadectomy. We used a GnRH antagonist ['Antarelix': Ac-D-Nal, D-Cpa, D-Pal, Ser, Tyr, D-Hci, Leu, Lys-(iPr), Pro, D-Ala-NH2] to transiently block LH and steroid secretion (in effect, inducing and reversing castration) in mature male sheep, and measured GnRH secretion into cerebrospinal fluid (CSF) in the third cerebral ventricle. The CSF was withdrawn with a peristaltic pump at a rate of 2 ml/h and pooled every 20 min. Jugular plasma was sampled every 20 min and analysed for testosterone and LH pulses. The antagonist (500 microg i.v.) was injected after 6 h of baseline sampling and the study continued for a further 24 h. The pulses of LH and testosterone disappeared shortly after antagonist injection, with delays of 20 +/- 12 min for LH and 80 +/- 29 min for testosterone. This led to an increase in GnRH pulse frequency, starting 300 +/- 54 min after antagonist injection. Secretion of LH and testosterone pulses resumed at 553 +/- 38 and 530 +/- 30 min (after antagonist injection), and GnRH pulse frequency returned to baseline values after 170 +/- 42 min (relative to LH) and 117 +/- 35 min (relative to testosterone). The consistent nature of these responses across the group of animals suggests that this can be used to test the effects of exteroceptive factors on the dynamics of negative feedback.

Stimulation of LH secretion in sheep by central administration of corticotrophin-releasing hormone

Corticotrophin-releasing hormone (CRH) has been proposed as a mediator of the antireproductive effects of stress through an action within the hypothalamus to inhibit GnRH secretion. This hypothesis was tested in sheep by studying the responses to central administration of CRH in both sexes and in both seasons. Sexually mature, Ile-de-France ewes and Romanov rams that had been gonadectomized and implanted with a permanent guide cannula into the third cerebral ventricle were used. Ewes were studied in the presence and absence of exogenous oestradiol plus progesterone, in both the breeding and anoestrous seasons. All rams were treated with testosterone and were studied only during the breeding season. Each observation involved serial samples (every 10 min) of jugular blood for 5 h before (control) and 5 h after an intracerebroventricular (i.c.v.) injection of either saline (vehicle) or 5 nmoles CRH in 20 microliters vehicle. The saline injections did not affect any of the endocrine variables measured; however, CRH always increased cortisol concentrations in jugular plasma. In the absence of treatment with replacement sex steroids, icv injection of CRH had no effect on pulsatile LH secretion in females either during the breeding season or during anoestrus. However, LH pulse frequency and mean LH concentrations increased significantly on every occasion on which animals were treated with sex steroids. Treatment with CRH also increased LH secretion in the testosterone-treated rams. It is concluded that, contrary to the hypothesized role of CRH as an inhibitor of reproductive activity, this neuropeptide stimulates pulsatile LH (and thus GnRH) secretion, at least in this species. The fact that gonadal steroids seem to be obligatory for the expression of this effect suggests that the protocols used in past studies need to be reassessed.

Involvement of insulin-like growth factors in the interactions between nutrition and reproduction in female mammals

The effects of nutrition on the reproductive system of female mammals are discussed in an attempt to determine the importance of the role of the insulin-like growth factor (IGF) system of proteins in the physiological mechanisms. The IGF system comprises IGF-I, IGF-II, their receptors and binding proteins. For this review, insulin and its receptors have been included in this system. The reproductive responses have been separated into two classes, based on fundamental differences in the reproductive biology and physiological mechanisms underlying them. The first involves the effects of nutrition on the induction of ovulation, at puberty or postpartum. In this case, the question is whether or not the animal will reproduce. The second class of response, changes in ovulation rate, involves consideration of reproductive efficiency in animals in which ovulation is inevitable.

Gonadotrophin and prolactin secretion in castrated male sheep following subcutaneous or intracranial treatment with testicular hormones

Interactions between testosterone, estradiol, and inhibin in the control of gonadotrophin secretion in males are poorly understood. Castrated rams were treated with steroid-free bovine follicular fluid (bFF), testosterone, or estradiol and for 7 d (2 x 2 x 2 factorial design). Given independently, none of the exogenous hormones affected follicle-stimulating hormone (FSH) concentrations, but the combination of one or both steroids with bFF reduced FSH secretion. Testosterone and estradiol reduced luteinizing hormone (LH) pulse frequency (there was no synergism), and bFF had no effect. Plasma prolactin concentrations were not affected by any treatment. To locate the central sites of steroid action, castrated rams were bilaterally implanted in the preoptic area (POA), ventromedial nucleus (VMH), or arcuate nucleus (ARC). These implants did not affect FSH or prolactin concentrations, or LH pulse amplitude. The frequency of the LH pulses was not affected by testosterone in any site. Estradiol located in the ARC, but not the POA or VMH, decreased LH pulse frequency. In summary, FSH secretion is controlled by synergistic interactions between inhibin and estradiol or testosterone, whereas GnRH/LH pulse frequency is controlled by testicular steroids. Estradiol acts partly, at least, in the ARC, but the central site of action, testosterone remains unknown.

Phytoestrogens reduce bone loss and bone resorption in oophorectomized rats

To examine a potential role for phytoestrogens in postmenopausal bone loss, the oophorectomized (OOX) rat model has been used in three studies to investigate the effects of the phytoestrogens coumestrol, zearalanol and a mixture of isoflavones on estrogen-dependent bone loss. In the studies of coumestrol and zearalanol, the rats were allocated to a control group, a phytoestrogen-treated group (1.5 micromol coumestrol or 3.1 mmol zearalanol twice per week, intramuscular) or, in the coumestrol study, an estrogen-treated group (28.1 nmol, intramuscular). In the isoflavone study, the rats were allocated to a control group, an estrogen treated group or a treatment group that received 131.25 mg of phytoestrogens per week incorporated into the nonpurified rat diet. Bone mineral density was measured globally and at the spine and femur at base line and 6 wk post-oophorectomy. In the coumestrol study, blood and urine samples were collected. Compared with the control group, rats receiving coumestrol and zearalanol had significantly reduced bone loss at all sites measured. The estrogen-treated group had significantly greater bone density than the control and the coumestrol-treated groups in the spine and global measurements. Coumestrol reduced urine calcium excretion and the bone resorption markers pyridinoline and deoxypyridinoline after 1 wk of treatment. Oral isoflavone phytoestrogens had no effect on oophorectomized rats including bone loss at the dose used. Thus, for the first time, the bioactivity of coumestrol and zearalanol in preventing bone loss has been demonstrated in a well-recognized model of postmenopausal bone loss.

Vasopressin can increase coronary perfusion pressure during human cardiopulmonary resuscitation

OBJECTIVES

To determine the hemodynamic effect of vasopressin on coronary perfusion pressure (CPP) in prolonged human cardiac arrest.

METHODS

A prospective, open-label clinical trial of vasopressin during cardiac resuscitation was performed. Ten patients presenting in cardiac arrest initially received resuscitative measures by emergency physicians according to Advanced Cardiac Life Support (ACLS) guidelines. A central venous catheter for fluid and drug administration and a femoral artery catheter for measurement of CPP (aortic minus right atrial relaxation phase pressures) were placed. When each patient was deemed nonsalvageable, 1.0 mg epinephrine was given and CPP was measured for 5 minutes, followed by a dose of vasopressin (1.0 U/kg). CPP measurements were continued for another 5 minutes.

RESULTS

The mean duration of cardiac arrest (out-of-hospital interval plus duration of ED ACLS) was 39.6 +/- 16.5 min. There was no improvement in CPP after 1.0 mg of epinephrine. Vasopressin administration resulted in a significant increase of CPP in 4 of the 10 patients. Patients responding to vasopressin had a mean increase in CPP of 28.2 +/- 16.4 mm Hg (range: 10-51.5), with these peak increases occurring at 15 seconds to 4 minutes after administration. The increases in the vasopressin levels after administration did not differ between the responders and nonresponders.

CONCLUSIONS

In this human model of prolonged cardiac arrest, 40% of the patients receiving vasopressin had a significant increase in CPP. This pilot study suggests that investigation of earlier use of vasopressin as a therapeutic alternative in the treatment of cardiac arrest is warranted.

Effects of nutrition on testicular growth in mature Merino rams actively immunized against GnRH

Nutrition-induced changes in testicular size in Merino rams appear to involve both GnRH-dependent and -independent pathways. This hypothesis was tested by feeding mature Merino rams that had been actively immunized against BSA or GnRH conjugated to BSA a diet that maintained initial body weight or the same diet supplemented daily with 1.5 kg of lupin grain. Blood was sampled every 20 min for 24 h on days-1, 19 and 70 relative to the change in diet. The plasma was used to assess the effects of treatments on changes in LH, FSH and testosterone concentrations. In the group immunized against BSA, FSH increased in lupin-supplemented rams compared with maintenance-fed rams, while LH and testosterone were not affected by diet. In comparison, the concentrations of LH, FSH and testosterone were significantly lower in the group immunized against GnRH than in rams immunized against BSA, but none of these endocrine variables was affected by nutrition. With both immunization treatments, the testes were significantly larger in lupin-supplemented than in maintenance-fed rams. In the group immunized against BSA, this difference was caused by testicular growth in lupin-supplemented rams, whereas in the group immunized against GnRH, lupin supplementation effectively maintained testicular mass, rather than allowed the regression observed in maintenance-fed rams. In conclusion, differences in testicular growth that were induced by dietary treatments in rams immunized against GnRH were not associated with changes in gonadotrophin or testosterone secretion. This supports the hypothesis that part of the effect of nutrition on testicular growth is independent of changes in GnRH secretion. The differences in testicular size observed in control rams were of similar magnitude to those observed in treated rams, but associated with large differences in plasma FSH concentrations, suggesting that this hormone plays an important role in this effect.

The Pto kinase conferring resistance to tomato bacterial speck disease interacts with proteins that bind a cis-element of pathogenesis-related genes

In tomato, the Pto kinase confers resistance to bacterial speck disease by recognizing the expression of a corresponding avirulence gene, avrPto, in the pathogen Pseudomonas syringae pv. tomato. Using the yeast two-hybrid system, we have identified three genes, Pti4, Pti5 and Pti6, that encode proteins that physically interact with the Pto kinase. Pti4/5/6 each encode a protein with characteristics that are typical of transcription factors and are similar to the tobacco ethylene-responsive element-binding proteins (EREBPs). Using a gel mobility-shift assay, we demonstrate that, similarly to EREBPs, Pti4/5/6 specifically recognize and bind to a DNA sequence that is present in the promoter region of a large number of genes encoding 'pathogenesis-related' (PR) proteins. Expression of several PR genes and a tobacco EREBP gene is specifically enhanced upon Pto-avrPto recognition in tobacco. These observations establish a direct connection between a disease resistance gene and the specific activation of plant defense genes.

Level of nutrition modulates the dynamics of oestradiol feedback on plasma FSH in ovariectomized ewes

The frequency of multiple ovulations in mature, cyclic ewes is strongly influenced by the level of nutrition, but it is difficult to demonstrate concurrent changes in plasma concentrations of gonadotropins. The failure to do so might be a consequence of rapid compensation by the homeostatic feedback mechanism linking secretion by the hypothalamus/pituitary gland and ovarian hormones. Most experimental models have examined the components of the homeostatic feedback system after steady state relationships had been established. We hypothesised that the effects of nutrition might be observed more readily if the system were disrupted and then examined while equilibrium was being re-established. This hypothesis was tested in three experiments in Merino ewes by allowing gonadotropin secretion to escape feedback for 5 days after ovariectomy and then replacing ovarian hormones and examining effects of feeding regimen on the return of plasma concentrations of FSH to baseline values. In all three experiments, oestrogen replacement caused plasma concentrations of FSH to decline more rapidly (P < 0.05) in ewes fed at 0.5x maintenance, than in ewes fed at 1.4x maintenance, with groups fed at maintenance being intermediate. No effect of diet was observed on plasma FSH concentrations in the absence of oestradiol, and neither progesterone nor charcoal-treated bovine follicular fluid influenced the effect of nutrition. Plasma concentrations of oestradiol were 9.8% lower on average (NS) in ewes fed above maintenance than in the sheep fed below maintenance over the three experiments, suggesting that there may have been a reduced clearance of oestradiol which contributed to the result. We conclude that feeding regimen affects the secretion or clearance of gonadotropins in mature ewes, as in the mature ram, and that this is one mechanism by which ovulation rate may be affected.

Semen production by the emu (Dromaius novaehollandiae). 1. Methods for collection of semen

Two methods for collecting semen from male emus using an artificial cloaca (AC) have been developed. In the first method, the male mounts the female teaser and the collector effects erection and subsequent ejaculation using the AC. The second method takes advantage of the development of sexual behaviour directed towards the semen collector and semen is collected when the male mounts the collector's back. Eight of 11 males were successfully trained with teasers and 5 of the 7 males trained without teasers ejaculated successfully. The ease of training varied between birds. The use of a teaser was very valuable, as the crouching behavior of the teaser elicited mating attempts in every male. The training and collection of semen was done by one person. Both methods can be used for routine collection of semen, as they take advantage of natural stimulation and the voluntary ejaculation reflex to which the birds adapted readily.

Semen production by the emu (Dromaius novaehollandiae). 2. Effect of collection frequency on the production of semen and spermatozoa

This experiment tested the hypothesis that frequent collection of semen from emus would increase the total output of semen and spermatozoa over less frequent collection. Semen was collected from trained male emus using an artificial cloaca. In Experiment 1, semen was collected from males every 4th d (96-h interval), every 2nd d (48-h interval), and every day (24-h interval) for 16 d. In Experiment 2, semen was collected daily (24-h interval), twice daily (6-h interval), and three times per day (3-h interval) over 6 d. Twice-daily collections yielded twice as much volume and number of spermatozoa than daily collections. Collecting semen three times per day did not yield extra semen, as it adversely affected the libido of males. Twice-daily collections appears to yield the optimum output over the 6 d of this experiment, but longer periods of collection need to be studied.

Alleles of Pto and Fen occur in bacterial speck-susceptible and fenthion-insensitive tomato cultivars and encode active protein kinases

The Pto gene was derived originally from the wild tomato species Lycopersicon pimpinellifolium and confers resistance to Pseudomonas syringae pv tomato strains expressing the avirulence gene avrPto. The Fen gene is also derived from L. pimpinellifolium and confers sensitivity to the insecticide fenthion. We have now isolated and characterized the alleles of Pto and Fen from cultivated tomato, L. esculentum, and designated them pto and fen. High conservation of genome organization between the two tomato species allowed us to identify the pto and fen alleles from among the cluster of closely related Pto gene family members. The pto and fen alleles are transcribed and have uninterrupted open reading frames that code for predicted proteins that are 87 and 98% identical to the Pto and Fen protein kinases, respectively. In vitro autophosphorylation assays revealed that both the pto and fen alleles encode active kinases. In addition, the pto kinase phosphorylates a previously characterized substrate of Pto, the Pto-interacting Pti1 serine/threonine kinase. However, the pto kinase shows impaired interaction with Pti1 and with several previously isolated Pto-interacting proteins in the yeast two-hybrid system. The observation that pto and fen are active kinases and yet do not confer bacterial speck resistance or fenthion sensitivity suggests that the amino acid substitutions distinguishing them from Pto and Fen may interfere with recognition of the corresponding signal molecule or with protein-protein interactions involved in the Pto- and Fen-mediated signal transduction pathways.

Initiation of Plant Disease Resistance by Physical Interaction of AvrPto and Pto Kinase

Resistance to bacterial speck disease in tomato occurs when the Pto kinase in the plant responds to expression of the avirulence gene avrPto in the Pseudomonas pathogen. Transient expression of an avrPto transgene in plant cells containing Pto elicited a defense response. In the yeast two-hybrid system, the Pto kinase physically interacted with AvrPto. Alterations of AvrPto or Pto that disrupted the interaction in yeast also abolished disease resistance in plants. The physical interaction of AvrPto and Pto provides an explanation of gene-for-gene specificity in bacterial speck disease resistance.