End Of Light Period Research Articles

Light Intensity Affects the Assimilation Rate and Carbohydrates Partitioning in Spinach Grown in a Controlled Environment.

The cultivation of spinach (Spinacia oleracea L.) has been increasing during the last years in controlled environment agriculture, where light represents a key factor for controlling plant growth and development and the highest energetic costs. The aim of the experiment was to evaluate the plant's response to two light intensities, corresponding to an optimal and a reduced level, in terms of the photosynthetic process, photoassimilates partitioning, and the biosynthesis of sucrose and starch. Plants of spinach cv. 'Gigante d'Inverno' were grown in a phytotron under controlled conditions, comparing two values of photosynthetic photon flux density (PPFD), 800 μmol m-2 s-1 (800 PPFD) and 200 μmol m-2 s-1 (200 PPFD), at a 10 h light/14 h dark regime. Compared to 800 PPFD, under 200 PPFD, plants showed a reduction in biomass accumulation and a redirection of photoassimilates to leaves, determining a leaf expansion to optimize the light interception, without changes in the photosynthetic process. A shift in carbon partitioning favouring the synthesis of starch, causing an increase in the starch/sucrose ratio at the end of light period, occurred in low-light leaves. The activity of enzymes cFBAse, SPS, and AGPase, involved in the synthesis of sucrose and starch in leaves, decreased under lower light intensity, explaining the rate of accumulation of photoassimilates.

Diurnal and circadian rhythmicity of the human blood transcriptome overlaps with organ- and tissue-specific expression of a non-human primate

BackgroundTwenty-four-hour rhythmicity in mammalian tissues and organs is driven by local circadian oscillators, systemic factors, the central circadian pacemaker and light-dark cycles. At the physiological level, the neural and endocrine systems synchronise gene expression in peripheral tissues and organs to the 24-h-day cycle, and disruption of such regulation has been shown to lead to pathological conditions. Thus, monitoring rhythmicity in tissues/organs holds promise for circadian medicine; however, most tissues and organs are not easily accessible in humans and alternative approaches to quantify circadian rhythmicity are needed. We investigated the overlap between rhythmic transcripts in human blood and transcripts shown to be rhythmic in 64 tissues/organs of the baboon, how these rhythms are aligned with light-dark cycles and each other, and whether timing of tissue-specific rhythmicity can be predicted from a blood sample.ResultsWe compared rhythmicity in transcriptomic time series collected from humans and baboons using set logic, circular cross-correlation, circular clustering, functional enrichment analyses, and least squares regression. Of the 759 orthologous genes that were rhythmic in human blood, 652 (86%) were also rhythmic in at least one baboon tissue and most of these genes were associated with basic processes such as transcription and protein homeostasis. In total, 109 (17%) of the 652 overlapping rhythmic genes were reported as rhythmic in only one baboon tissue or organ and several of these genes have tissue/organ-specific functions. The timing of human and baboon rhythmic transcripts displayed prominent ‘night’ and ‘day’ clusters, with genes in the dark cluster associated with translation. Alignment between baboon rhythmic transcriptomes and the overlapping human blood transcriptome was significantly closer when light onset, rather than midpoint of light, or end of light period, was used as phase reference point. The timing of overlapping human and baboon rhythmic transcriptomes was significantly correlated in 25 tissue/organs with an average earlier timing of 3.21 h (SD 2.47 h) in human blood.ConclusionsThe human blood transcriptome contains sets of rhythmic genes that overlap with rhythmic genes of tissues/organs in baboon. The rhythmic sets vary across tissues/organs, but the timing of most rhythmic genes is similar in human blood and baboon tissues/organs. These results have implications for development of blood transcriptome-based biomarkers for circadian rhythmicity in tissues and organs.

Levels of daily light doses under changed day-night cycles regulate temporal segregation of photosynthesis and N2 Fixation in the cyanobacterium Trichodesmium erythraeum IMS101.

While the diazotrophic cyanobacterium Trichodesmium is known to display inverse diurnal performances of photosynthesis and N2 fixation, such a phenomenon has not been well documented under different day-night (L-D) cycles and different levels of light dose exposed to the cells. Here, we show differences in growth, N2 fixation and photosynthetic carbon fixation as well as photochemical performances of Trichodesmium IMS101 grown under 12L:12D, 8L:16D and 16L:8D L-D cycles at 70 μmol photons m-2 s-1 PAR (LL) and 350 μmol photons m-2 s-1 PAR (HL). The specific growth rate was the highest under LL and the lowest under HL under 16L:8D, and it increased under LL and decreased under HL with increased levels of daytime light doses exposed under the different light regimes, respectively. N2 fixation and photosynthetic carbon fixation were affected differentially by changes in the day-night regimes, with the former increasing directly under LL with increased daytime light doses and decreased under HL over growth-saturating light levels. Temporal segregation of N2 fixation from photosynthetic carbon fixation was evidenced under all day-night regimes, showing a time lag between the peak in N2 fixation and dip in carbon fixation. Elongation of light period led to higher N2 fixation rate under LL than under HL, while shortening the light exposure to 8 h delayed the N2 fixation peaking time (at the end of light period) and extended it to night period. Photosynthetic carbon fixation rates and transfer of light photons were always higher under HL than LL, regardless of the day-night cycles. Conclusively, diel performance of N2 fixation possesses functional plasticity, which was regulated by levels of light energy supplies either via changing light levels or length of light exposure.

Developmental and light-entrained expression of melatonin and its relationship to the circadian clock in the sea anemone Nematostella vectensis.

BackgroundThe primary hormone of the vertebrate pineal gland, melatonin, has been identified broadly throughout the eukaryotes. While the role for melatonin in cyclic behavior via interactions with the circadian clock has only been reported in vertebrates, comparative research has shown that the transcription-translation loops of the animal circadian clock likely date to the cnidarian-bilaterian ancestor, leaving open significant questions about the evolutionary origin of melatonin signaling in circadian behavior by interacting with the molecular clock.ResultsExpression of melatonin in adult anemones showed peak expression at the end of light period (zeitgeber time (ZT) = 12) when cultured under diel conditions, coinciding with expression of genes and enzyme activity for members of the melatonin synthesis pathway (tryptophan hydroxylase and hydroxyindol-O-methyltransferase), which also showed rhythmic expression. During embryogenesis and juvenile stages, melatonin showed cyclic oscillations in concentration, peaking in midday. Spatial (in situ hybridization) and quantitative (real-time PCR) transcription of clock genes during development of N. vectensis showed these ‘clock’ genes are expressed early in the development, prior to rhythmic oscillations, suggesting functions independent of a function in the circadian clock. Finally, time-course studies revealed that animals transferred from diel conditions to constant darkness lose circadian expression for most of the clock genes within 4 days, which can be reset by melatonin supplementation.ConclusionsOur results support an ancient role for melatonin in the circadian behavior of animals by showing cyclic expression of this hormone under diel conditions, light-dependent oscillations in genes in the melatonin synthesis pathway, and the function of melatonin in initiating expression of circadian clock genes in the cnidarian N. vectensis. The differences in expression melatonin and the circadian clock gene network in the adult stage when compared with developmental stages of N. vectensis suggests new research directions to characterize stage-specific mechanisms of circadian clock function in animals.

Timing to promote initial swimbladder inflation by surface film removal in Pacific bluefin tuna,Thunnus orientalis(Temminck and Schlegel), larvae

This study investigated the optimal timing of day to promote initial swimbladder inflation (ISI) for improved Pacific bluefin tuna (PBT), Thunnus orientalis, larval survival. Larval swimbladder inflation frequency was compared based on three experiments using different time schemes of surface film removal (SFR) from 3 to 9 days post hatch (dph). SFR was conducted from 05:00 to 19:00 hours (light period: S.5–19), 19:00 to 05:00 hours (dark period: S.19–5), 08:00 to 19:00 hours (S.8–19) and the entire day (S.24) in Experiment 1; from 08:00 to 19:00 hours (S.8–19-E2), 08:00 to 13:00 hours (S.8–13), 13:00 to 19:00 hours (S.13–19) in Experiment 2; and from 13:00 to 16:00 hours (S.13–16), 16:00 to 19:00 hours (S.16–19), 18:00–19:00 hours (S.18–19) in Experiment 3. The swimbladder inflation frequency at the experiment termination (9 dph) was significantly higher (P < 0.001) in S.24 (91.1 ± 5.7%), S.5–19 (92.2 ± 5.1%) and S.8–19 (93.3 ± 3.4%) than in S.19–5 (11.1 ± 5.1%) in Experiment 1, and remarkably higher in S.8–19-E2 (81.7%) and S.13–19 (88.3%) than in S.8–13 (0.0%) in Experiment 2, and significantly higher (P < 0.001) in S.16–19 (84.4 ± 5.1%) and S.18–19 (70.0 ± 12.0%) than in S.13–16 (7.8 ± 3.9%) in Experiment 3. These results suggest that the optimal timing to promote larval ISI by SFR is a few hours before the end of light period (16:00–19:00 hours) from 3 to 9 dph.

MicroRNA 138, let-7b, and 125a inhibitors differentially alter sleep and EEG delta-wave activity in rats

Sleep deprivation was previously reported to alter microRNA (miRNA) levels in the brain; however, the direct effects of any miRNA on sleep have only been described recently. We determined miRNA 138 (miR-138), miRNA let-7b (let-7b), and miRNA 125a-5p (miR-125a) levels in different brain areas at the transitions between light and dark. In addition, we examined the extent to which inhibiting these miRNAs affects sleep and EEG measures. We report that the levels of multiple miRNAs differ at the end of the sleep-dominant light period vs. the end of the wake-dominant dark period in cortical areas, hippocampus, and hypothalamus. For instance, in multiple regions of the cortex, miR-138, let-7b, and miR-125a expression was higher at the end of the dark period compared with the end of the light period. Intracerebroventricular injection of a specific inhibitor (antiMIR) to miR-138 suppressed sleep and nonrapid eye movement sleep (NREMS) EEG delta power. The antiMIR to let-7b did not affect time in state but decreased NREMS EEG delta power, whereas the antiMIR to miR-125a failed to affect sleep until after 3 days and did not affect EEG delta power on any day. We conclude that miRNAs are uniquely expressed at different times and in different structures in the brain and have discrete effects and varied timings on several sleep phenotypes and therefore, likely play a role in the regulation of sleep.

A chloroplast envelope membrane protein containing a putative LrgB domain related to the control of bacterial death and lysis is required for chloroplast development in Arabidopsis thaliana

• A protein encoded by At1g32080 was consistently identified in proteomic studies of Arabidopsis chloroplast envelope membranes, but its function remained unclear. The protein, designated AtLrgB, may have evolved from a gene fusion of lrgA and lrgB. In bacteria, two homologous operons, lrgAB and cidAB, participate in an emerging mechanism to control cell death and lysis. • We aim to characterize AtLrgB using reverse genetics and cell biological and biochemical analysis. • AtLrgB is expressed in leaves, but not in roots. T-DNA insertion mutation of AtLrgB produced plants with interveinal chlorotic and premature necrotic leaves. Overexpression of full-length AtLrgB (or its LrgA and LrgB domains, separately), under the control of CaMV 35S promoter, produced plants exhibiting veinal chlorosis and delayed greening. At the end of light period, the T-DNA mutant had high starch and low sucrose contents in leaves, while the 35S:AtLrgB plants had low starch and high sucrose contents. Metabolite profiling revealed that AtLrgB appeared not to directly transport triose phosphate or hexose phosphates. In yeast cells, AtLrgB could augment nystatin-induced membrane permeability. • Our work indicates that AtLrgB is a new player in chloroplast development, carbon partitioning and leaf senescence, although its molecular mechanism remains to be established.

The photoenzymatic cycle of NADPH: protochlorophyllide oxidoreductase in primary bean leaves (Phaseolus vulgaris) during the first days of photoperiodic growth

The photoenzymatic cycle of the light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) was investigated in situ during early stages of development of bean leaves under light-dark cycles (LDC). In the experimental system used in this study, prolamellar bodies developed during night periods and disappeared during light periods. This was accompanied by changes in the photoactive to non-photoactive Pchlide ratio, which was higher at the end of the light period, and tended to increase with the number of LDC's. Flash-induced absorbance changes in the Chlide absorption region (700 nm) were used in order to monitor the formation of short- and long-wavelength forms of Chlide (C670-675 and C682-694), which correspond to free Chlide and aggregated Chlide-NADPH-LPOR complexes, respectively. The ratio of long-wavelength to short-wavelength Chlides after one flash increased with the number of LDC's, and was higher in leaves collected at the end of light periods, compared to leaves collected at the end of night periods. During light periods, photoactive Pchlide regeneration and Chlide phytylation were completed within 1 min after flash-induced formation of long-wavelength Chlide. The results show for the first time that the photoenzymatic LPOR cycle proceeds through similar steps, but at much faster rates, during photoperiodic greening than in the previously studied leaves of etiolated plants. In particular, the parallel formation of two Chlide species always occurs, but the ratio of the two species depends on the ratio of photoactive to non-photoactive Pchlide and on light or dark adaptation.

Light absorption of Isochrysis galbana (Prymnesiophyceae) under a day–night cycle with ultraviolet radiation

Diel variation in chlorophyll a-specific absorption coefficients, a* ph (λ), m 2 (mg chl a) -1 , was examined to study the effect of ultraviolet radiation (UVR) on a* ph (λ) of the prymnesiophycean Isochrysis galbana (Parke). A continuous culture was exposed for 2 wk to a 12 h light: 12 h dark cycle of photosynthetically available radiation (PAR) supplemented with UVR. Photosynthetic and photoprotective pigments as well as cell density and diameter were also determined every 2 h for 2 d to confirm the periodicity of a* ph (λ). A distinct diel variation was observed, with maxima toward the end of light periods and minima toward the end of dark periods. The magnitude of diel variation in a* ph (440) and a* ph (676) was 14 and 6.6%, respectively. To reconstruct the absorption coefficient, the absorption efficiency factors Q a (λ), were determined using intracellular chl a concentration, cell diameter, and chl a-specific absorption coefficients after solubilization on Triton X, a* TX (λ). The main source of diel variation for Q a (λ) appears to be a *TX (λ). Diel variation in the absorption ratio of photoprotective pigments to chl a was observed to be more significant than that for the absorption ratio of other photosynthetic pigments to chl a. The diel variations in a* ph (λ) were primarily caused by changes in pigmentation of photoprotective pigments due to UVR.

Compensation of decreased triose phosphate/phosphate translocator activity by accelerated starch turnover and glucose transport in transgenic tobacco.

Tobacco (Nicotiana tabacum L.) plants were transformed with an antisense construct of the chloroplast triose phosphate/phosphate translocator (TPT). Three transformant lines of the T4 progeny, which showed a large decrease in the transcript level of the TPT were used for further biochemical and physiological characterisation. In all antisense lines tested, TPT transport activity was diminished by 50-70% compared with the wild type (WT). Despite this high reduction in the transport capacity, alpha TPT plants lacked any visible phenotype. Hexokinase and alpha-amylase activities were increased in alpha TPT plants compared with the WT, whereas activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and ADP-glucose pyrophosphorylase (AGPase) were not affected. At the end of a 14-h light period, leaf starch contents in alpha TPT lines were similar to those of the WT and controls, indicating that a decrease in the TPT had no effect on starch accumulation. Sucrose contents were diminished by more than 50% in alpha TPT lines compared with control plants. The time course of starch accumulation revealed a transient increase in the starch content in a selected alpha TPT line after 6 h in the light, followed by a decrease towards the end of the light period. Labelling with 14C indicated that during the dark and light (late afternoon) periods starch is mobilised at higher rates in alpha TPT lines than in the controls. Glucose/fructose ratios at the end of the dark period were increased from 1.2 in control plants to 2 in alpha TPT lines indicating increased amylolytic starch degradation. Initial rates of [14C] glucose transport in isolated chloroplasts were increased by a factor of 2-3 in alpha TPT plants compared with the WT. Rates of CO2 assimilation were substantially diminished in the alpha TPT lines in high CO2 and low O2, but remained unaffected in ambient CO2. The rate of photosynthetic electron transport during the induction of photosynthesis in saturating CO2 exhibited pronounced oscillations only in WT and control plants. Oscillations were less pronounced in alpha TPT plants, indicating that phosphate limitation of photosynthesis is lowered in alpha TPT plants compared with the WT. It is proposed that photoassimilates are more readily directed into starch biosynthesis in alpha TPT plants. This is supported by determinations of 3-phosphoglycerate levels (an activator of AGPase) during the transition from dark to light in high CO2.

Oxidative Stress and Chilling Tolerance in Tomato Seedlings

Diurnal variation in the chilling sensitivity of tomato seedlings was examined. Sensitivity to chilling in tomato seedlings is a response to light and not under the control of a circadian rhythm. Chilling sensitivity is highest in seedlings chilled at the end of the dark period, and these seedlings become more resistant to chilling injury upon exposure to the light. Diurnal variation in chilling sensitivity was associated with changes in catalase and superoxide dismutase activities. The results show an increase in catalase and superoxide dismutase activities at the end of the light period. The recovery of the net photosynthesis rate following chilling was faster in seedlings chilled at the end of the light period. It is suggested that an increase in catalase and superoxide dismutase activities at the end of light period before the chilling plays a role in the resistance to chilling stress in tomato seedlings. Forty-eight hours of 14°C acclimation or hydrogen peroxide pretreatment conferred chilling tolerance to tomato seedlings and were correlated with elevated catalase activity. Acclimated seedlings still exhibited diurnal variation in chilling sensitivity while hydrogen peroxide treated seedlings showed little evidence of a diurnal variation in chilling sensitivity. Transgenic tomato plants expressing an antisense catalase gene were generated. A several-fold decrease in total catalase has been detected in the leaf extracts of transformants. Preliminary analysis of these plants indicated that modification of reactive oxygen species scavenging in plant system can lead to change in oxidative stress tolerance.

Photosynthetic Carbon Metabolism and Translocation in Wild-Type and Starch-Deficient Mutant Nicotiana sylvestris L

A high rate of daytime export of assimilated carbon from leaves of a starch-deficient mutant tobacco (Nicotiana sylvestris L.) was found to be a key factor that enabled shoots to grow at rates comparable to those in wild-type plants under a 14-h light period. Much of the newly fixed carbon that would be used for starch synthesis in leaves of wild-type plants was used instead for sucrose synthesis in the mutant. As a result, export doubled and accumulation of sucrose and hexoses increased markedly during the day in leaves of the mutant plants. The increased rate of export to sink leaves appeared to be responsible for the increase in the proportion of their growth that occurred during the day compared to wild-type plants. Daytime growth of source leaves also increased, presumably as a result of the increased accumulation of recently assimilated soluble carbon in the leaves. Even though starch accumulation did not occur in the leaves of mutant plants, nearly all the sugar that accumulated during the day was exported in the period of decreasing irradiance at the end of the diurnal light period. Changes in carbon allocation that occurred in leaves of wild-type and mutant plants near the end of the light period appeared to result from endogenous diurnal regulation associated with the day-night transition.

Parathion (O,O-dimethyl-O-p-nitrophenyl phosphorothioate) induces pineal melatonin synthesis at night

The effects of parathion on male rat pineal N-acetyltransferase (NAT) activity, hydroxyindole-O-methyltransferase (HIOMT) activity and pineal and serum melatonin levels at the end of light period (2000 h) and at night (2300 h and 0100 h) were studied. Additionally, pineal levels of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were estimated. Parathion was administered intragastrically at total doses (over 6 days) of either 6.5 or 13 mg/kg. Control rats received vehicle (corn oil) only. During the study, the rats were exposed to light:dark cycles of 14:10 with light off at 2100 h. Pineal NAT activity was increased at 0100 h following parathion administration at both doses, but HIOMT activity was unaffected. Pineal and serum melatonin levels were increased at night (2300 h and 0100 h) after the 13 mg/kg dose of parathion while the lower dose increased pineal melatonin only at 0100 h. Also, both doses decreased 5-HTP at 2000 h while the lower dose increased it at 2300; 5-HT was significantly decreased at 2300 h and 5-HIAA levels were lower but only significantly so for the 13 mg/kg dose at 2000 h. The results indicate that parathion has significant effects on pineal melatonin synthesis by mechanisms which remain unknown.

Plasma prolactin and luteinizing hormone levels of pinealectomized and enucleated turkey hens

Plasma levels of LH and prolactin were determined in pinealectomized (PX) and/or bilateral ocular enucleated (EX) adult turkey hens maintained in either constant (24LL) or diurnal (16L:8D) lighting. Blood samples were obtained at the following times over a 24-hr period: onset, middle, and end of light period, middle and end of dark period. In experiment 1, the effects of PX alone were evaluated in photorefractory hens exposed to two different photoperiods (24LL and 16L:8D). In experiment 2, the effects of PX and EX were determined in egg-laying and photorefractory hens exposed to a 16L:8D daily photoperiod. Neither PX nor EX significantly altered LH or prolactin levels of egg laying or photorefractory hens at any of the sampling times of the day in either experiment. In experiment 1, LH levels were very similar in both 16L:8D and 24LL but prolactin levels were significantly lower in 24LL than 16L:8D. It was concluded that the pineal gland does not play an essential role in maintaining circulating LH and prolactin levels in constant light or a photoperiod of 16L:8D.

Changes in the proportion of endogenous osmotic solutes accumulated by Chlorella emersonii in the light and dark

Abstract. The type of endogenous osmotic solute accumulated by Chlorella emersonii grown at high external osmotic pressure (πext) depended on the light/dark conditions: proline accumulated to high concentrations in cells in the light, while sucrose accumulated to high concentrations in the dark. These findings were made during the alternating light dark cycles used to obtain synchronized cultures, i.e. cultures containing cells at only one stage of development at any one time. Similar decreases in proline and increases in sucrose in the dark were found for cells previously grown in continuous light to obtain non‐synchronized cultures, i.e. cultures containing cells at all stages of development.In cultures synchronized at 200 mol m −3 NaCl (πext= 1.01 MPa), recently divided ‘daughter cells’ at the beginning of the light periods contained 60 mol m−3 proline and 100mol m−3 sucrose, while mature cells towards the end of light periods contained 130 mol m proline and 20 mol m−3 sucrose. The changes in proline and sucrose which occurred in synchronized cultures were due mainly to light/dark conditions and to a much lesser extent to different stages of cell development. The proportion of proline to sucrose in daughter cells collected from non‐synchronized cultures in continuous light was not different from the proportion in heterogeneous populations of cells.Results are discussed in relation to the accumulations of two, rather than one, endogenous osmotic solute and to growth reductions of C. emersonii exposed to high external osmotic pressures.

Polyunsaturated Fatty Acid Biosynthesis in Cotyledons from Germinating and Developing Cucumis sativus L. Seedlings

Etiolated Cucumis sativus L. cotyledons preferentially catabolized exogenous [1-(14)C]oleic acid and [1-(14)C]linoleic acid with relatively little incorporation into complex lipids or desaturation of the (14)C-labeled fatty acids. Following a 16-hour exposure to light, the greening cotyledons efficiently desaturated the exogenous (14)C-labeled fatty acids. A small amount of oleate desaturation to linoleate was observed in etiolated tissue, but hardly any linoleate desaturation to alpha-linolenate was detected. Both oleate and linoleate desaturation showed diurnal variations with maxima at the end of light periods and minima at the end of dark periods. Illumination of etiolated tissue by flashing light, as opposed to continuous light, failed to stimulate either chlorophyll or alpha-linolenic acid biosynthesis, and both processes could be halted or reversed by 10 micrograms per milliliter cycloheximide. Production of polyunsaturated fatty acids from [1-(14)C]acetate, [1-(14)C]oleic acid, and [1-(14)C]linoleic acid, by greening cucumber cotyledons, was markedly affected by tissue integrity with finely chopped cotyledons having very little capacity for their synthesis and intact seedlings showing the highest rates.

Relation of Hormonal Variations to Nutritional Studies and Metabolism of Ruminants1,2

Variations in concentrations of growth hormone, insulin, glucagon, prolactin, adrenal corticoids, and thyroid hormones in blood plasma of ruminants as related to circadian rhythms, environmental factors, and nutrition are reviewed. Rhythms in prolactin concentrations are related to light and temperature. Concentrations of prolactin in plasma are higher in warm environments and during longer photoperiods. There is episodic secretion of growth hormone in cattle with frequent peaks in plasma concentrations during 24h. Marked increases in environmental temperature result in greater secretion of growth hormone for short times followed by a decline in plasma concentration with prolonged exposure. Extreme cold temperature also increases growth hormone concentrations in plasma. Secretion of thyroid hormones increases in cold and decreases in warm environments. Circadian rhythms are definite for plasma concentrations of adrenal corticoids in ruminants adjusted to their surroundings. Peaks occur late in dark periods, and lows occur during the end of light periods. Circadian patterns have not been consistent for secretion of insulin. Prolonged subjection to stresses such as noise, handling, and restraint can modify concentrations of prolactin, growth hormone, and adrenal corticoids. Changes in concentrations of insulin may occur if blood glucose is increased. After feeding, concentrations of growth hormone in plasma decrease and concentrations of insulin and glucagon increase. Relationships of these changes with metabolism are discussed.

Effect of Changing Photoperiods on the Diurnal Rhythm of Pituitary Gonadotropic Activity of Mature Male Japanese Quail

Male Japanese quail were raised under 14-hr (5:00-19:00) light per day for 4 months from the day of hatch, and their gonadotropic activities of the anterior lobes of pituitary at various times during a 24-hr period were measured using a bioassay method based on 32P-uptake by chick testes. A peak of the gonadotropic activity was found at the end of light period. When the time of onset of light was shifted from 5:00 to 17:00 and the birds were kept for 2 weeks, the peak shifted to a time close to the end of the new light period. When the length of the light period was reduced to 8 hours and the birds were kept for 16 weeks, the peak disappeared.

Daily rhythmic changes in tyrosine transaminase activity of the rat liver.

Several marnrnalian enzymes have been shown to exhibit regular variations in activity during each 24-hour period. When rats are kept in a lighting schedule of 12 hours of light alternated with 12 hours of darkness, adrenal succinic dehydrogenase activity rises 50 per cent above basal levels at the end of the daily light period.' Under similar conditions, renal traiisarninase activity in rnice is lowest toward the end of the dark period, and increases by 30 per ceit during the first 6 hours of light.2 The tryptophan pyrrolase activity of the rat liver rises toward the end of the light period, doubling within 8 hours; it then falls to basal levels, where it rernains for the better part of the day.3 The rhythmic changes in this last enzyme are abolished when the animals are adrenalectomized. 3 We have observed that the activity of tyrosine transamninase in. the rat liver varies each day over a fourfold range. This rhythm appears to be remarkably synchronous among animals maintained oii the same lighting schedule, and persists with altered phase relationships following the removal of the pituitary or the adrenals.