Molecular characterization and expression of alfalfa isoliquiritigenin 2'-O-methyltransferase, an enzyme specifically involved in the biosynthesis of an inducer of Rhizobium meliloti nodulation genes

A cDNA clone encoding an O-methyltransferase (OMT) from alfalfa has been isolated, which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) to form 4,4'-dihydroxy-2'-methoxychalcone, the most potent of the nod-gene-inducing flavonoid derivatives released from alfalfa roots. The cDNA clone was identified on the basis of N-terminal sequence identity to purified S-adenosyl-L-methionine:isoliquiritigenin 2'-O-methyltransferase (chalcone OMT) and expression of enzymatically active chalcone OMT protein in Escherichia coli. The deduced amino acid sequence showed significant similarities to other OMTs. Chalcone OMT is encoded by a small gene family in alfalfa and related sequences are present in other legumes. The chalcone OMT gene is expressed primarily in alfalfa roots; transcript levels were highest during the first 2 weeks of development. The OMT transcript was also detected, to a much lesser extent, in root nodules. In contrast, chalcone isomerase (CHI), although expressed at high levels in roots, was found in all plant organs and had a somewhat different developmental expression pattern. Chalcone OMT transcripts were localized primarily to epidermal and cortical cells starting 1.5-2.0 mm behind the root tip, whereas CHI transcripts were present at approximately equal levels in epidermal, cortical and vascular tissues, both at the root tip and throughout the root. Chalcone OMT transcripts were elicitor-inducible in alfalfa cell suspension cultures, although only low levels of methoxychalcone accumulated. The implications of these results for plant-microorganism interactions are discussed.

Effect of pinealectomy and plane of nutrition on wool growth in Merino sheep

The effects of surgical pinealectomy and plane of nutrition on wool growth and plasma prolactin concentrations in young Merino wethers were investigated. In young pinealectomized wethers maintained at a low live weight under conditions of minimal stress, the decline of conditioned clean wool production on midside patches was slowed when compared to pineal-intact controls. This difference appeared to be due in part to the observed greater secondary wool follicle density in the pinealectomized wethers; mean fiber diameter was affected to a smaller extent, while staple length growth rate was not significantly altered. Circulating prolactin profiles showed a seasonal variation (high in summer, low in winter) in both pinealectomized and control wethers. There was no difference in wool production between pinealectomized and control wethers when the diet of the same wethers was subsequently supplemented with formaldehyde-treated cottonseed meal. While the role of melatonin in the regulation of wool growth remains to be determined, it is suggested that the hormone may have a transient effect on wool production in young wethers under conditions of limited nutrition, but not at higher nutritional levels, and that melatonin may be involved in partitioning of nutrients to the wool follicle.

The effects of exogenous melatonin and prolactin on wool follicle development in ovine foetal skin grafts

The fleece of the Merino sheep is composed predominantly of wool fibres grown from secondary wool follicles. This study investigates the effects of melatonin and prolactin on the development of secondarv follicles in grafted ovine foetal skin. Skin from day 85 ovine foetuses was grafted onto nude mice, developed for 40 days and then excised. Mice received either 30 8g prolactin ip mouse-1 day-1 (P), one melatonin implant (Regulin�) sc mouse -1 (M), commencing at grafting or no further treatment (C). Wool follicle density and development were assessed in grafted skin and compared with day 125 control foetal skin. Cuticle structure of graft fibres was also examined and compared with those of day 125 foetuses. Total follicle density and the rate of follicle initiation were reduced in the grafts compared with control foetal skin. Total follicle density did not vary significantly between treatments, but the number of derived secondary follicles was greater in grafts from mice receiving prolactin (group P). Follicles in grafted skin were larger, produced medullated fibres, and were not grouped, in comparison with follicles in the control foetal skin. Epidermal thickness was greater in grafts than in control foetal skin. The cuticle structure of graft fibres from all groups was similar to the control wool fibres. These findings indicate that prolactin, but not melatonin, may be involved in the regulation of derived secondary follicle development.

Effect of immunization against melatonin on seasonal fleece growth in feral goats

Four vaccination protocols were utilized to investigate the effects of immunoneutralizing circulating melatonin on the annual cashmere growth cycle and cashmere production in Australian feral goats. A fluctuating anti-melatonin antibody response, achieved by repeated booster vaccinations, resulted in an acceleration of the growth cycle in goats which exhibited a significant immune response, compared to sham-immunized controls. Responding goats showed two cycles of cashmere length growth in the first 16 months and increased annual cashmere production in the first year. However, in the second year, these effects were no longer apparent, suggesting either some form of desensitization to melatonin, or a diminished response due to declining antibody titre. The effects of immunization were observed in both sexes; the effect on cashmere length was greater in wethers than in does. Cashmere fibre growth in response to a continuously declining plane of specific antibody showed increased cycle frequency, albeit with a decreased amplitude; guard hair growth cycles were affected to a much lesser extent. Small transient peaks of specific immunity at the summer or winter solstice were without significant effect on cashmere growth. Immunization to provoke a persistent anti-melatonin antibody response at the winter solstice resulted in significantly increased greasy fleece weight, % cashmere yield, and mass of cashmere produced, but no change in fibre diameter in both sexes. Thus the timing of cashmere growth cycles in goats may be, at least transiently, altered by appropriately timed immunization against melatonin. The mechanism of pineal-mediated regulation of cashmere growth cycles may involve (i) entrainment of an endogenous rhythm by melatonin, or (ii) seasonal alteration of cashmere follicle sensitivity to the effect of melatonin.

Trigonelline and Stachydrine Released from Alfalfa Seeds Activate NodD2 Protein in Rhizobium meliloti

Spectroscopic data (nuclear magnetic resonance, mass spectrometry, ultraviolet-visible) in this study identify trigonelline and stachydrine as major components of alfalfa (Medicago sativa L.) seed rinse. Moreover, biological assays show that these natural products induce nodulation (nod) gene transcription in Rhizobium meliloti by activating the regulatory protein NodD2, but not the homologous NodD1 protein. These findings contrast with the fact that the only previously identified NodD2 activator, 4,4' -dihydroxy-2' -methoxychalcone (MCh), also activates NodD1 protein. Trigonelline and stachydrine induce nod genes only at much higher concentrations than MCh, but they are released from seeds in correspondingly greater amounts. The existence of these amphoteric, nonflavonoid nod gene inducers broadens our understanding of the biochemical processes and ecological mechanisms that a legume host uses to regulate its microbial symbiont.

Identification, purification, and characterization of S-adenosyl-L-methionine: isoliquiritigenin 2'-O-methyltransferase from alfalfa (Medicago sativa L.)

An O-methyltransferase (OMT) which methylates the 2'-hydroxyl of isoliquiritigenin (2',4,4'-trihydroxychalcone) was identified in alfalfa (Medicago sativa L.) seedlings and cell cultures. The OMT activity increased during early stages of seedling development and was predominantly located in roots. Treatment of alfalfa cell cultures with an elicitor from yeast resulted in a fivefold increase in chalcone OMT activity, whereas treatment of seedlings with CuCl2 caused a reduction in activity. The chalcone OMT was purified to near homogeneity from elicited alfalfa cell cultures. Only one form of the enzyme was found. It consisted of an active monomer of subunit Mr 43,000 which could be photoaffinity labeled with S-adenosyl-L-[methyl-3H]methionine. The purified OMT had a pH optimum of 9.0, pI of 4.7, and was highly specific for the 2'-hydroxyl of 2',4,4'-trihydroxychalcone, with essentially no activity toward narigenin chalcone, caffeic acid, or daidzein. Kinetic analysis indicated a sequential bi bi mechanism with Km values of 2.2 and 17.7 microM for 2',4,4'-trihydroxychalcone and S-adenosyl-L-methionine, respectively. S-Adenosyl-L-homocysteine was a potent inhibitor. The chalcone OMT represents the third distinct OMT isolated from alfalfa cell cultures.

Concentrations of plasma melatonin and luteinizing hormone in domestic gilts reared under artificial long or short days

Plasma melatonin concentrations were measured every 1-2 h over 24 h and plasma luteinizing hormone (LH) concentrations every 15 min over 12 h in domestic gilts reared under artificial light regimens that had previously been used to demonstrate photoperiodic effects on puberty. In Expt 1, the light regimens both commenced at 12 h light: 12 h dark (12L:12D) and either increased (long-day) or decreased (short-day) by 15 min/week until the long-day gilts were receiving 16L:8D and the short-day gilts 8L:16D at sampling. In Expt 2, both light regimens commenced at 12L:12D and either increased (long-day) or decreased (short-day) by 10 or 15 min/week to a maximum of 14.5L:9.5D or a minimum of 9.5L:14.5D before being reversed. Sampling took place when daylength had returned to 14L:10D (long-day) or 10L:14D (short-day). In immature gilts housed at 12L:12D (Expt 1) and in postpubertal (Expt 1) and prepubertal (Expt 2) gilts reared under long-day or short-day light regimens, mean plasma melatonin concentrations were basal (3.6 pg/ml) when the lights were on and increased to peak concentrations greater than 15 pg/ml within 1-2 h after dark, before declining gradually to basal concentrations at or near the end of the dark phase. In prepubertal gilts bearing subcutaneous melatonin implants and reared under long-days (Expt 2), mean plasma melatonin concentration in the 6 h before dark was 91.9 +/- 5.26 pg/ml and 125.0 +/- 6.66 pg/ml 1 h after dark, but this increase was not statistically significant. In Expt 2, the short-day gilts had fewer LH pulses (2.6 +/- 0.25 vs. 4.6 +/- 0.24; P less than 0.01) in the 12-h sampling period than the long-day gilts, but the amplitude of the pulses (2.28 +/- 0.23 vs. 1.26 +/- 0.16 ng/ml; P less than 0.01) and the area under the LH curve (78.8 +/- 5.60 vs. 47.3 +/- 6.16; P less than 0.01) was greater in the short-day gilts. In the short-day, but not in the long-day, gilts LH pulses were more frequent (2.0 +/- 0.0 vs. 0.6 +/- 0.25; P less than 0.01), but had a smaller area (61.9 +/- 7.2 vs. 120.2 +/- 23.6; P less than 0.05) in the 6 h of dark than in the 6 h of light, which together made up the 12-h sampling period.(ABSTRACT TRUNCATED AT 400 WORDS)

Seasonal inhibition of puberty in domestic gilts is overcome by melatonin administered orally, but not by implant

The ability of exogenous melatonin, applied either orally or by implant, to overcome the seasonal inhibition of puberty in domestic gilts was tested in two experiments. In Expt 1, 24 gilts received two melatonin implants at 126 days of age and again at 161 days and 196 days, while 24 gilts acted as controls. All gilts were slaughtered at a mean age of 223 days. Blood samples were collected by venepuncture from eight gilts in each treatment at 126, 144 and 178 days of age and the plasma was assayed for melatonin concentration by direct radioimmunoassay. In Expt 2A, four gilts (125 days of age) were fed either 0, 1, 2 or 4 mg of melatonin at 14:00 h on each of four consecutive days. Blood samples for melatonin assay were collected via indwelling jugular catheters every 30 or 60 min from 12:00 to 22:00 h. In Expt 2B, 27 gilts were fed 1 mg of melatonin at 15:00 h each day from 129 days of age until slaughter at 221 days, while 25 gilts acted as controls. In both experiments, the presence of morphologically normal corpora lutea at slaughter was the criterion for puberty. In Expt 1, constant-release melatonin implants had no effect on the percentage of gilts which reached puberty. Among the 24 control gilts, two (8.3%) reached puberty compared with one of the 24 (4.2%) gilts with implants. In all the samples from control gilts, and in the samples taken from treated gilts prior to implantation at 126 days of age, mean plasma melatonin concentration was below the sensitivity of the assay (3.6 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a seasonal elevation in daytime melatonin levels associated with the rut in fallow bucks (Dama dama): the effect of day length and exogenous melatonin

The timing of the seasonal reduction in voluntary food intake and hormonal changes associated with the rut were investigated in mature fallow bucks subjected to artificial long-day exposure with and without superimposed melatonin-releasing implants. Circulating testosterone profiles and the period of inappetence, signalling the onset of the period of reproductive activity in untreated bucks under natural photoperiod, were phase-advanced in both treatment groups. In the long-day treated group, these profiles were phase-advanced by 1 week, while in the long-day + melatonin group, the phase advance was 6 weeks compared to the controls. Circulating daytime melatonin, elevated in all three groups, corresponds with seasonal changes in circulating testosterone levels associated with the rut. Prolactin profiles followed ambient photoperiod, being high during natural or artificial long days and low during natural short days. Exogenous melatonin administered during long-day exposure initiated a rapid and reversible decrease in circulating prolactin levels. The elevation in plasma melatonin could not be separated temporally from the seasonal testosterone peak by exposure to long days or to exogenous melatonin. However, this daytime melatonin profile was abolished by the ablation of circulating testosterone following immunization against luteinizing hormone releasing hormone (LHRH). The presence of this endogenous melatonin during daylight was observed only during the rut, as measured in two radioimmunoassays and confirmed by mass spectrometry. It is likely that both testosterone and melatonin influence the onset of the seasonal rut in fallow bucks.

Stress Responses in Alfalfa (Medicago sativa L.): X. Molecular Cloning and Expression of S-Adenosyl-l-Methionine:Caffeic Acid 3-O-Methyltransferase, a Key Enzyme of Lignin Biosynthesis

S-Adenosyl-l-methionine:caffeic acid 3-O-methyltransferase (COMT, EC 2.1.1.6) catalyzes the conversion of caffeic acid to ferulic acid, a key step in the biosynthesis of lignin monomers. We have isolated a functionally active cDNA clone (pCOMT1) encoding alfalfa (Medicago sativa L.) COMT by immunoscreening a lambdaZAPII cDNA expression library with anti-(aspen COMT) antibodies. The derived amino acid sequence of pCOMT1 is 86% identical to that of COMT from aspen. Southern blot analysis indicates that COMT in alfalfa is encoded by at least two genes. Addition of an elicitor preparation from bakers' yeast to alfalfa cell suspension cultures resulted in a rapid accumulation of COMT transcripts, which reached a maximum level around 19 hours postelicitation. Northern blot analysis of total RNA from different organs of alfalfa plants at various developmental stages showed that COMT transcripts are most abundant in roots and stems. Transcripts encoding ATP: i-methionine-S-adenosyl transferase (AdoMet synthetase, EC 2.5.1.6), the enzyme responsible for the synthesis of the methyl donor for the COMT reaction, were coinduced with COMT transcripts in elicitor-treated cells and exhibited a similar pattern of expression to that of COMT in different organs of alfalfa plants at various stages of development.

Effects of prolonged artificial photoperiod on circulating prolactin and melatonin levels in seasonal ewes

Crossbred ewes exposed to long days for 46 months prior to photoperiod reversal showed no alteration in the duration or amplitude of the circulating melatonin peak between 24 and 46 months of continuous long day exposure. By 3 months after photoreversal to short days, both the amplitude and duration of the peak had adapted to the new scotophase. In short day treated ewes, the melatonin peak was abolished by 46 but not 24 months of short day exposure, and was not fully restored in all ewes 3 months after photoreversal. Mean prolactin levels over 24 h remained high up to 46 months of long day treatment, and declined 3 months after short day exposure. Conversely, mean prolactin levels remained low up to 46 months of short day treatment, increasing 3 months after exposure to long days. Thus: (i) depletion of the melatonin-synthesizing capability of the ovine pineal gland by prolonged exposure to long nights is not completely reversed after 3 months of continuous long day exposure, and (ii) a nocturnal melatonin peak is not essential for maintenance of plasma prolactin levels under these conditions.

Control of Bancroftian filariasis by integrating therapy with vector control using polystyrene beads in wet pit latrines

In the town of Makunduchi, Zanzibar, wet pit latrines provided breeding places for Culex quinquefasciatus and there were few other mosquito breeding places available. The adult mosquito population in bedrooms was monitored for a year and found to consist almost entirely of Cx quinquefasciatus of which 2.45% carried infective larvae of Wuchereria bancrofti. It was estimated that each person received about 24,993 bites per year, of which 612 were potentially infective. After a year of baseline data collection, polystyrene beads were expanded in boiling water and applied to form floating layers on all infested pits. Subsequently the adult mosquito population declined remarkably so that the estimated number of bites per person per year was only about 439. To retain control, surveillance for newly wet pits continued to be necessary. Initially the microfilarial rate in the human population was 49.5%, with many cases of filarial disease. The microfilarial rate was reduced to 10.3% by mass treatment with diethylcarbamazine, with no sign of resurgence a year after treatment. The infective rate among mosquitoes was reduced to 0.41% and the combined effect of the vector and microfilarial control was to reduce the number of infective bites per person per year by 99.7%.

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Alfalfa roots release three major nod-gene inducers: 4',7-dihydroxyflavanone, 4',7-dihydroxyflavone, and 4,4'-dihydroxy-2'-methoxychalcone. The objective of the present study was to define temporal relationships between synthesis and exudation for those flavonoids. Requirements for concurrent flavonoid biosynthesis were assessed by treating roots of intact alfalfa seedlings with [U-(14)C]-l-phenylalanine in the presence or absence of the phenylalanine ammonia-lyase inhibitor l-2-aminoxy-3-phenylpropionic acid (AOPP). In the absence of AOPP, each of the three flavonoids in exudates contained (14)C. In the presence of AOPP, (14)C labeling and release of all the exuded nod-gene inducers were reduced significantly. AOPP inhibited labeling and release of the strongest nod-gene inducer, methoxychalcone, by more than 90%. Experiments with excised cotyledons, hypocotyls, and roots incubated in solution showed that the flavonoids could be synthesized in and released from each organ. However, the ratio of the three flavonoids in exudates from intact plants was most similar to the ratio recently synthesized and released from excised roots. A portion of recently synthesized flavonoid aglycones was found conjugated, presumably as glycosides, in root extracts and may have been involved in the release process. Data from root extracts showed that formononetin, an isoflavonoid which does not induce nod genes, was present in conjugated and aglycone forms but was not released by normal intact roots. In contrast, roots stressed with CuCl(2) did release the aglycone formononetin. Thus, the release process responsible for exudation of nod-gene inducers appears to be specific rather than a general phenomenon such as a sloughing off of cells during root growth. The synthesis and specific concurrent release of flavonoid nod-gene inducers in this study is consistent with the physiological requirement for nodule formation of the 3-day-old seedlings used.

Effects of alfalfa nod gene-inducing flavonoids on nodABC transcription in Rhizobium meliloti strains containing different nodD genes

Transcription of the nodulation genes nodABC in Rhizobium meliloti requires a plant flavonoid signal and nodD, a family of bacterial regulatory genes (nodD1, nodD2, and nodD3). Results from this study show that all previously identified nod gene inducers released by alfalfa seeds and roots induced nodABC-lacZ transcription in R. meliloti containing extra copies of nodD1, but only 4,4'-dihydroxy-2'-methoxychalcone gave high levels of induction with extra copies of nodD2. While mixtures of the methoxychalcone and luteolin showed a positive synergism with extra NodD1 protein, they apparently competed for binding to the NodD2 protein.

Chrysoeriol and Luteolin Released from Alfalfa Seeds Induce nod Genes in Rhizobium meliloti

Flavonoid signals from alfalfa (Medicago sativa L.) seed and root exudates induce transcription of nodulation (nod) genes in Rhizobium meliloti. The flavone luteolin previously was isolated from alfalfa seeds by other workers and identified as the first nod gene inducer for R. meliloti. Our recent study of ;Moapa 69' alfalfa root exudates found no luteolin but did identify three other nod gene inducers: 4,4'-dihydroxy-2'-methoxychalcone, 4',7-dihydroxyflavone, and 4',7-dihydroxyflavanone. The goal of the current study was to identify and quantify nod gene-inducing flavonoids that may influence Rhizobium populations around a germinating alfalfa seed. Aqueous rinses of Moapa 69 alfalfa seeds were collected and assayed for induction of a nodABC-lacZ fusion in R. meliloti. During the first 4 hours of imbibition, total nod gene-inducing activity was released from seeds at 100-fold higher rates than from roots of 72-hour-old seedlings. Five flavonoids were purified and identified by spectroscopic analyses (ultraviolet/visible absorbance, proton nuclear magnetic resonance, and mass spectroscopy) and comparison with authentic standards. Two very active nod gene-inducing flavonoids, chrysoeriol (3'-methoxyluteolin) and luteolin, were identified in seed rinses. Luteolin required a higher concentration (18 nanomolar) than chrysoeriol (5 nanomolar) for half-maximum induction of nodABC-lacZ in R. meliloti, and both were less active than 4,4'-dihydroxy-2'-methoxychalcone (2 nanomolar) from root exudates. Seeds exuded three other luteolin derivatives: luteolin-7-O-glucoside, 5-methoxyluteolin, and 3',5-dimethoxyluteolin. Their combined quantities were 24-fold greater than that of luteolin plus chrysoeriol. Most nod gene-inducing activity of these luteolin derivatives apparently is associated with degradation to luteolin and chrysoeriol. However, their presence in large quantities suggests that they may contribute significantly to nod gene-inducing activity in the soil. These results indicate the importance of germinating seeds as a source of nod gene-inducing flavonoids and emphasize the quantitative and qualitative differences in those compounds around the seed and root.

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots

Alfalfa (Medicago sativa L.) seeds and roots can create complex rhizosphere effects by releasing flavonoids that induce nodulation (nod) genes in Rhizobium meliloti. Previous reports identified luteolin and 4,4'-dihydroxy-2'-methoxychalcone as strong inducers that are released from seeds and roots, respectively, and 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone as weaker inducers which are exuded by roots. As a first step toward identifying flavonoid interactions that may occur in the rhizosphere, combinations of these molecules were tested for transcriptional effects on a nodABC-lacZ fusion in R. meliloti. At low concentrations (e.g. 8.4 nanomolar), interactions of the three nod gene inducers from root exudate were additive. When the strong inducers 4,4'-dihydroxy-2'-methoxychalcone and luteolin were present separately at higher concentrations (e.g. 21 nanomolar), their effect could be decreased significantly by the weaker inducers 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone. In contrast, when low concentrations of luteolin from seed rinses and 4,4'-dihydroxy-2'-methoxychalcone from root exudate were present together, they produced synergistic increases in nod gene transcription. Tests with mixtures of the three nod gene inducers from root exudate indicated that alfalfa seedlings might easily decrease the strong inductive effect of the chalcone by releasing modest amounts of the weaker inducers. In addition, mixtures of luteolin and the nod gene inducers in root exudate suggested that interactions between nod gene inducers from seeds and roots may create a zone highly favorable to root nodule formation near the top of the primary root.

A Chalcone and Two Related Flavonoids Released from Alfalfa Roots Induce nod Genes of Rhizobium meliloti

Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Previous investigations identified the flavone luteolin as an active inducer in alfalfa seed extracts, but the nature of nod inducers released from roots has not been reported. Root exudate from 3-day-old alfalfa seedlings was purified and then assayed for biological activity with a nodABC-lacZ fusion in R. meliloti. Indentities of major nod inducers were established by spectroscopic analyses (ultraviolet/visible, proton nuclear magnetic resonance, and mass spectroscopy) and comparison with authentic standards. Major nod inducers, which were identified as 4',7-dihydroxyflavone, 4'-7-dihydroxyflavanone, and 4,4'-dihydroxy-2'-methoxychalcone, were released from seedling roots at 54, 22, and 20 picomole.plant(-1).day(-1), respectively. Luteolin was not found in these root exudates. The 4,4'-dihydroxy-2'-methoxychalcone induced nod genes at a concentration one order of magnitude lower than luteolin and is the first naturally released chalcone reported to have this function. Moderate and weak nod-inducing activity was associated, respectively, with 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone.

Seasonal modification of ovine pineal function. 2. Steroidal effects on melatonin and prolactin profiles

Pineal beta-adrenoceptor density and affinity in ewes are modified in a season-dependent manner by gonadal steroids and by the sympathetic innervation of the gland. The present study was undertaken to relate the steroidal effects on the receptors to post receptor endocrine events, and to investigate the influence of the sympathetic innervation of the pineal gland on these events. Plasma melatonin and prolactin profiles were determined during anestrus and during the normal breeding season in ewes subjected to sympathetic denervation of the pineal and/or a range of steroid-related treatments. Wherever valid comparisons could be drawn between effects of the treatments on beta-adrenoceptor variables and on circulating hormone levels, similar effects were noted. Further, ganglionectomy influenced hormone profiles similarly to estradiol under all conditions tested. It appears that gonadal steroids (estradiol) and the sympathetic neurotransmitter noradrenaline have opposing actions on prolactin levels, just as they have on pineal beta-adrenoceptor binding affinity. These findings suggest that steroid-mediated changes in receptor number and affinity are reflected in post receptor endocrine events. In addition, other factors (e.g. photoperiodic information transmitted via the sympathetic innervation) also play important roles in the regulation of the observed hormonal profiles. A steroid-mediated feedback regulation of pituitary prolactin release, partly direct and partly via pineal melatonin release, is suggested.

The use of hypothermia in surgical pinealectomy of the neonate rat

A technique is described in which rat pups (5-7 days old) are induced into a state of suspended animation by placing them in the freezing compartment of a refrigerator at -20 degrees C for 8-10 minutes. This induces cessation of respiration and heart beat for 12-15 minutes. Surgical pinealectomy is undertaken during this period. Postoperation the animal is gradually warmed and restored to its dam. The effectiveness of pinealectomy was checked after some 400 days by measurement of plasma dark cycle melatonin levels using radioimmune assay. The method is reliable, robust and the results predictable, no melatonin being detectable 400 days after surgery.

Seasonal modification of ovine pineal function. I. Interaction of gonadal steroids and sympathetic innervation on beta-adrenoceptors

The results of a seasonal study of the regulation by steroids of ovine pineal beta-adrenoceptors are reported. The effects of ovariectomy, steroid implants and superior cervical ganglionectomy were investigated in Merino ewes. The results confirm earlier observations showing a seasonal variation in the sensitivity of the receptors to modification by gonadal steroids. A marked difference in receptor density and affinity between the follicular and luteal phases of the estrous cycle is shown for the first time, a difference which can be modified by appropriate steroid-related treatments. A season-dependent antagonism between the sympathetic innervation of the gland (presumably acting via the neurotransmitter noradrenaline) and gonadal steroids in the regulation of ovine pineal beta-adrenoceptor function is also shown.

Seasonal changes in the sensitivity of ovine pineal beta-adrenoceptors to steroids

Immunoneutralization of endogenous gonadal steroids has recently been shown to modify pineal beta-adrenoceptor function in intact Merino ewes. In the current study, interactions between gonadal steroids and these receptors have been further investigated. beta-Adrenoceptor density and binding affinity both showed time-related changes in ewes; the significance of these changes requires further study. Two observations, firstly modification of beta-adrenoceptor function by androstenedione and 17 beta-estradiol in ovariectomized, but not in intact ewes, and secondly that steroid-mediated effects on receptor density and binding affinity in the pineal of ovariectomized Merino ewes could be demonstrated during anestrus, but not during the breeding season for intact ewes, indicate that gonadal steroids may regulate pineal beta-adrenoceptor variables in Merino ewes. It is suggested that gonadal steroids may regulate ovine pineal function in ewes, and that the seasonal differences in sensitivity of luteinizing hormone release to steroid feedback may be mediated in part via effects on the pineal gland.

Transport and Partitioning of CO(2) Fixed by Root Nodules of Ureide and Amide Producing Legumes

Nodulated and denodulated roots of adzuki bean (Vigna angularis), soybean (Glycine max), and alfalfa (Medicago sativa) were exposed to (14)CO(2) to investigate the contribution of nodule CO(2) fixation to assimilation and transport of fixed nitrogen. The distribution of radioactivity in xylem sap and partitioning of carbon fixed by nodules to the whole plant were measured. Radioactivity in the xylem sap of nodulated soybean and adzuki bean was located primarily (70 to 87%) in the acid fraction while the basic (amino acid) fraction contained 10 to 22%. In contrast, radioactivity in the xylem sap of nodulated alfalfa was primarily in amino acids with about 20% in organic acids. Total ureide concentration was 8.1, 4.7, and 0.0 micromoles per milliliter xylem sap for soybean, adzuki bean, and alfalfa, respectively. While the major nitrogen transport products in soybeans and adzuki beans are ureides, this class of metabolites contained less than 20% of the total radioactivity. When nodules of plants were removed, radioactivity in xylem sap decreased by 90% or more. Pulse-chase experiments indicated that CO(2) fixed by nodules was rapidly transported to shoots and incorporated into acid stable constituents. The data are consistent with a role for nodule CO(2) fixation providing carbon for the assimilation and transport of fixed nitrogen in amide-based legumes. In contrast, CO(2) fixation by nodules of ureide transporting legumes appears to contribute little to assimilation and transport of fixed nitrogen.

Response of pineal beta-adrenoceptors in different breeds of sheep to immunization against selected steroids

Active immunization of Merino and Wiltshire Horn X Merino cross-bred sheep against a range of gonadal steroids has revealed that pineal beta-adrenoceptors in both breeds are sensitive to hormonal modification by androgens, but only in the less seasonal, non-shedding Merino do these receptors appear to be sensitive to regulation by estrogens. Neither breed showed sensitivity of its pineal beta-adrenoceptors to active immunization against the pineal hormone melatonin under either normal or reversed photoperiod treatment. These results (a) suggest that pineal related seasonal differences between the breeds (i.e. wool shedding and/or reproductive function) may reside in differential sensitivity of the pineal gland to regulation by specific circulating steroid hormones, and (b) indicate an absence of end-product regulation of beta-adrenoceptor-mediated pineal melatonin biosynthesis in both seasonally shedding and non-shedding sheep.

Sheep pineal beta-adrenoceptor function--interaction with gamma-aminobutyric acid

To clarify the role and site of action of gamma-aminobutyric acid (GABA) in ovine pineal glands, we have investigated the effects of aminooxyacetic acid (AOAA), an inhibitor of GABA transaminase, on endogenous GABA content and beta-adrenoceptor mediated pineal function in Merino sheep. A significant elevation of endogenous GABA levels was noted in the glands, but no effect was observed on radioligand binding in vitro to pineal beta-adrenoceptors following in vivo administration of AOAA. Incubation of washed pineal membranes with GABA or AOAA had no effect on ligand binding to beta-adrenoceptors. Incubation of Merino pineal slices with GABA inhibited isoprenaline-stimulated but not basal serotonin N-acetyltransferase (NAT) activity. Incubation of whole pineal homogenates with GABA was without effect on either isoprenaline-stimulated or basal adenyl cyclase activity. Thus, Merino pineal glands resemble bovine pineals in that beta-adrenoceptor mediated melatonin biosynthesis in both species may be regulated in part by GABA. Our results indicate that GABA may exert its effect on Merino pineal NAT activity at a locus distal to the site of action of adenyl cyclase; however, the detailed mechanism and physiological role of this regulation remain to be elucidated.

Modification of sheep pineal beta-adrenoceptors by some gonadal steroids but not by melatonin

The effects of active immunization against a range of gonadal steroids on pineal beta-adrenoceptors were studied in cycling Merino ewes. In selected cases, the effects of exogenous steroids were also investigated. Immunization against progesterone had no detectable effect on pineal beta-adrenoceptor density or ligand binding affinity. Immunization against estrone or 17 beta-estradiol significantly increased binding affinity and decreased beta-receptor density. Testosterone immunization in ewes caused similar effects but to a lesser degree. In contrast, immunization against androstenedione resulted in a decreased affinity and an increase in receptor density in ewes. In subsequent experiments, some parameters of pineal function in intact cycling and ovariectomized ewes were compared; a significant decrease in beta-receptor density and an increase in binding affinity were noted in the ovariectomized animals. Androstenedione-releasing implants decreased beta-receptor density and increased beta-receptor affinity in pineals from intact ewes, but these implants had no effect on pineal parameters in ovariectomized ewes. Immunization of ewes against 17 beta-estradiol had no significant effects on basal or isoprenaline-stimulated N-acetyltransferase or adenyl cyclase activities. Immunization of ewes against melatonin, or in vitro incubation of pineal glands with the hormone had no effects on the pineal parameters studied. It is concluded that estrogens affect the pinealocyte beta-receptors in ewes, while specific androgens may act indirectly on these receptors to modify their interaction with estrogens.