LL Conditions Research Articles

Circadian disruption promotes tumor growth by anabolic host metabolism; experimental evidence in a rat model

BackgroundLight at night creates a conflicting signal to the biological clock and disrupts circadian physiology. In rodents, light at night increases the risk to develop mood disorders, overweight, disrupted energy metabolism, immune dysfunction and cancer. We hypothesized that constant light (LL) in rats may facilitate tumor growth via disrupted metabolism and increased inflammatory response in the host, inducing a propitious microenvironment for tumor cells.MethodsMale Wistar rats were exposed to LL or a regular light-dark cycle (LD) for 5 weeks. Body weight gain, food consumption, triglycerides and glucose blood levels were evaluated; a glucose tolerance test was also performed. Inflammation and sickness behavior were evaluated after the administration of intravenous lipopolysaccharide. Tumors were induced by subcutaneous inoculation of glioma cells (C6). In tumor-bearing rats, the metabolic state and immune cells infiltration to the tumor was investigated by using immunohistochemistry and flow cytometry. The mRNA expression of genes involved metabolic, growth, angiogenes and inflammatory pathways was measured in the tumor microenvironment by qPCR. Tumor growth was also evaluated in animals fed with a high sugar diet.ResultsWe found that LL induced overweight, high plasma triglycerides and glucose levels as well as reduced glucose clearance. In response to an LPS challenge, LL rats responded with higher pro-inflammatory cytokines and exacerbated sickness behavior. Tumor cell inoculation resulted in increased tumor volume in LL as compared with LD rats, associated with high blood glucose levels and decreased triglycerides levels in the host. More macrophages were recruited in the LL tumor and the microenvironment was characterized by upregulation of genes involved in lipogenesis (Acaca, Fasn, and Pparγ), glucose uptake (Glut-1), and tumor growth (Vegfα, Myc, Ir) suggesting that LL tumors rely on these processes in order to support their enhanced growth. Genes related with the inflammatory state in the tumor microenvironment were not different between LL and LD conditions. In rats fed a high caloric diet tumor growth was similar to LL conditions.ConclusionsData indicates that circadian disruption by LL provides a favorable condition for tumor growth by promoting an anabolic metabolism in the host.

Food in synchrony with melatonin and corticosterone relieves constant light disturbed metabolism.

Circadian disruption is associated with metabolic disturbances such as hepatic steatosis (HS), obesity and type 2 diabetes. We hypothesized that HS, resulting from constant light (LL) exposure is due to an inconsistency between signals related to food intake and endocrine-driven suprachiasmatic nucleus (SCN) outputs. Indeed, exposing rats to LL induced locomotor, food intake and hormone arrhythmicity together with the development of HS. We investigated whether providing temporal signals such as 12-h food availability or driving a corticosterone plus melatonin rhythm could restore rhythmicity and prevent the metabolic disturbances under LL conditions in male rats. Discrete metabolic improvements under these separate treatments stimulated us to investigate whether the combination of hormone treatment together with mealtime restriction (12-h food during four weeks) could prevent the metabolic alterations. LL exposed arrhythmic rats, received daily administration of corticosterone (2.5 µg/kg) and melatonin (2.5 mg/kg) in synchrony or out of synchrony with their 12-h meal. HS and other metabolic alterations were importantly ameliorated in LL-exposed rats receiving hormonal treatment in synchrony with 12-h restricted mealtime, while treatment out of phase with meal time did not. Interestingly, liver bile acids, a major indication for HS, were only normalized when animals received hormones in synchrony with food indicating that disrupted bile acid metabolism might be an important mechanism for the HS induction under LL conditions. We conclude that food-elicited signals, as well as hormonal signals, are necessary for liver synchronization and that HS arises when there is conflict between food intake and the normal pattern of melatonin and corticosterone.

Circadian rhythm of melatonin secretion and growth-related gene expression in the tiger puffer Takifugu rubripes

Somatostatin (SS) and growth hormone-releasing hormone (GHRH) are primary factors regulating growth hormone (GH) secretion in the pituitary. To date, it remains unknown how this rhythm is controlled endogenously, although there must be coordination of circadian manners. Melatonin was the main regulator in biological rhythms, and its secretion has fluctuation by photic information. But relationship between melatonin and growth-related genes (ghrh and ss) is unclear. We investigated circadian rhythms of melatonin secretion, ghrh and ss expressions, and correlation between melatonin with growth-related genes in tiger puffer Takifugu rubripes. The melatonin secretion showed nocturnal rhythms under light and dark (LD) conditions. In constant light (LL) condition, melatonin secretion has similar patterns with LD conditions. ss1 mRNA was high during scotophase under LD conditions. But ss1 rhythms disappeared in LL conditions. Ghrh appeared opposite expression compared with melatonin levels or ss1 expression under LD and LL. In the results of the melatonin injection, ghrh and ss1 showed no significant expression compared with control groups. These results suggested that melatonin and growth-related genes have daily or circadian rhythms in the tiger puffer. Further, we need to know mechanisms of each ss and ghrh gene regulation.

Season-dependent effects of photoperiod and temperature on circadian rhythm of arylalkylamine N-acetyltransferase2 gene expression in pineal organ of an air-breathing catfish, Clarias gariepinus

Arylalkylamine N-acetyltransferase (AANAT) activity, aanat gene expression and melatonin production have been reported to exhibit prominent circadian rhythm in the pineal organ of most species of fish. Three types of aanat genes are expressed in fish, but the fish pineal organ predominantly expresses aanat2 gene. Increase and decrease in daylength is invariably associated with increase and decrease in temperature, respectively. But so far no attempt has been made to delineate the role of photoperiod and temperature in regulation of the circadian rhythm of aanat2 gene expression in the pineal organ of any fish with special reference to seasons. Therefore, we studied effects of various lighting regimes (12L-12D, 16L-8D, 8L-16D, LL and DD) at a constant temperature (25°C) and effects of different temperatures (15°, 25° and 35°C) under a common photoperiod 12L-12D on circadian rhythm of aanat2 gene expression in the pineal organ of Clarias gariepinus during summer and winter seasons. Aanat2 gene expression in fish pineal organ was studied by measuring aanat2 mRNA levels using Real-Time PCR. Our findings indicate that the pineal organ of C. gariepinus exhibits a prominent circadian rhythm of aanat2 gene expression irrespective of photoperiods, temperatures and seasons, and the circadian rhythm of aanat2 gene expression responds differently to different photoperiods and temperatures in a season-dependent manner. Existence of circadian rhythm of aanat2 gene expression in pineal organs maintained in vitro under 12L-12D and DD conditions as well as a free running rhythm of the gene expression in pineal organ of the fish maintained under LL and DD conditions suggest that the fish pineal organ possesses an endogenous circadian oscillator, which is entrained by light-dark cycle.

Effects of drop sets with resistance training on increases in muscle CSA, strength, and endurance: a pilot study

ABSTRACTTo investigate the effects of a single high-load (80% of one repetition maximum [1RM]) set with additional drop sets descending to a low-load (30% 1RM) without recovery intervals on muscle strength, endurance, and size in untrained young men. Nine untrained young men performed dumbbell curls to concentric failure 2–3 days per week for 8 weeks. Each arm was randomly assigned to one of the following three conditions: 3 sets of high-load (HL, 80% 1RM) resistance exercise, 3 sets of low-load [LL, 30% 1RM] resistance exercise, and a single high-load (SDS) set with additional drop sets descending to a low-load. The mean training time per session, including recovery intervals, was lowest in the SDS condition. Elbow flexor muscle cross-sectional area (CSA) increased similarly in all three conditions. Maximum isometric and 1RM strength of the elbow flexors increased from pre to post only in the HL and SDS conditions. Muscular endurance measured by maximum repetitions at 30% 1RM increased only in the LL and SDS conditions. A SDS resistance training program can simultaneously increase muscle CSA, strength, and endurance in untrained young men, even with lower training time compared to typical resistance exercise protocols using only high- or low-loads.

Light- and circadian-controlled genes respond to a broad light spectrum in Puffer Fish-derived Fugu eye cells

Some cell lines retain intrinsic phototransduction pathways to control the expression of light-regulated genes such as the circadian clock gene. Here we investigated the photosensitivity of a Fugu eye, a cell line established from the eye of Takifugu rubripes, to examine whether such a photosensitive nature is present. Microarray analysis identified 15 genes that showed blue light-dependent change at the transcript level. We investigated temporal profiles of the light-induced genes, as well as Cry and Per, under light-dark, constant light (LL), and constant dark (DD) conditions by quantitative RT-PCR. Transcript levels of Per1a and Per3 genes showed circadian rhythmic changes under both LL and DD conditions, while those of Cry genes were controlled by light. All genes examined, including DNA-damage response genes and photolyase genes, were upregulated not only by blue light but also green and red light, implying the contribution of multiple photopigments. The present study is the first to identify a photosensitive clock cell line originating from a marine fish. These findings may help to characterize the molecular mechanisms underlying photic synchronization of the physiological states of fishes to not only daily light-dark cycles but also to various marine environmental cycles such as the lunar or semi-lunar cycle.

Acclimation of shade-tolerant and light-resistant Tradescantia species to growth light: chlorophyll a fluorescence, electron transport, and xanthophyll content.

In this study, we have compared the photosynthetic characteristics of two contrasting species of Tradescantia plants, T. fluminensis (shade-tolerant species), and T. sillamontana (light-resistant species), grown under the low light (LL, 50-125 µmol photons m-2s-1) or high light (HL, 875-1000µmol photons m-2s-1) conditions during their entire growth period. For monitoring the functional state of photosynthetic apparatus (PSA), we measured chlorophyll (Chl) a emission fluorescence spectra and kinetics of light-induced changes in the heights of fluorescence peaks at 685 and 740nm (F 685 and F 740). We also compared the light-induced oxidation of P700 and assayed the composition of carotenoids in Tradescantia leaves grown under the LL and HL conditions. The analyses of slow induction of Chl a fluorescence (SIF) uncovered different traits in the LL- and HL-grown plants of ecologically contrasting Tradescantia species, which may have potential ecophysiological significance with respect to their tolerance to HL stress. The fluorometry and EPR studies of induction events in chloroplasts in situ demonstrated that acclimation of both Tradescantia species to HL conditions promoted faster responses of their PSA as compared to LL-grown plants. Acclimation of both species to HL also caused marked changes in the leaf anatomy and carotenoid composition (an increase in Violaxanthin + Antheraxantin + Zeaxanthin and Lutein pools), suggesting enhanced photoprotective capacity of the carotenoids in the plants grown in nature under high irradiance. Collectively, the results of the present work suggest that the mechanisms of long-term PSA photoprotection in Tradescantia are based predominantly on the light-induced remodeling of pigment-protein complexes in chloroplasts.

Proteome Analysis Reveals Extensive Light Stress-Response Reprogramming in the Seagrass Zostera muelleri (Alismatales, Zosteraceae) Metabolism.

Seagrasses are marine ecosystem engineers that are currently declining in abundance at an alarming rate due to both natural and anthropogenic disturbances in ecological niches. Despite reports on the morphological and physiological adaptations of seagrasses to extreme environments, little is known of the molecular mechanisms underlying photo-acclimation, and/or tolerance in these marine plants. This study applies the two-dimensional isoelectric focusing (2D-IEF) proteomics approach to identify photo-acclimation/tolerance proteins in the marine seagrass Zostera muelleri. For this, Z. muelleri was exposed for 10 days in laboratory mesocosms to saturating (control, 200 μmol photons m−2 s−1), super-saturating (SSL, 600 μmol photons m−2 s−1), and limited light (LL, 20 μmol photons m−2 s−1) irradiance conditions. Using LC-MS/MS analysis, 93 and 40 protein spots were differentially regulated under SSL and LL conditions, respectively, when compared to the control. In contrast to the LL condition, Z. muelleri robustly tolerated super-saturation light than control conditions, evidenced by their higher relative maximum electron transport rate and minimum saturating irradiance values. Proteomic analyses revealed up-regulation and/or appearances of proteins belonging to the Calvin-Benson and Krebs cycle, glycolysis, the glycine cleavage system of photorespiration, and the antioxidant system. These proteins, together with those from the inter-connected glutamate-proline-GABA pathway, shaped Z. muelleri photosynthesis and growth under SSL conditions. In contrast, the LL condition negatively impacted the metabolic activities of Z. muelleri by down-regulating key metabolic enzymes for photosynthesis and the metabolism of carbohydrates and amino acids, which is consistent with the observation with lower photosynthetic performance under LL condition. This study provides novel insights into the underlying molecular photo-acclimation mechanisms in Z. muelleri, in addition to identifying protein-based biomarkers that could be used as early indicators to detect acute/chronic light stress in seagrasses to monitor seagrass health.

Circadian Oscillation of the Lettuce Transcriptome under Constant Light and Light-Dark Conditions.

Although, the circadian clock is a universal biological system in plants and it orchestrates important role of plant production such as photosynthesis, floral induction and growth, there are few such studies on cultivated species. Lettuce is one major cultivated species for both open culture and plant factories and there is little information concerning its circadian clock system. In addition, most of the relevant genes have not been identified. In this study, we detected circadian oscillation in the lettuce transcriptome using time-course RNA sequencing (RNA-Seq) data. Constant light (LL) and light–dark (LD) conditions were used to detect circadian oscillation because the circadian clock has some basic properties: one is self-sustaining oscillation under constant light and another is entrainment to environmental cycles such as light and temperature. In the results, 215 contigs were detected as common oscillating contigs under both LL and LD conditions. The 215 common oscillating contigs included clock gene-like contigs CCA1 (CIRCADIAN CLOCK ASSOCIATED 1)-like, TOC1 (TIMING OF CAB EXPRESSION 1)-like and LHY (LATE ELONGATED HYPOCOTYL)-like, and their expression patterns were similar to those of Arabidopsis. Functional enrichment analysis by GO (gene ontology) Slim and GO Fat showed that the GO terms of response to light stimulus, response to stress, photosynthesis and circadian rhythms were enriched in the 215 common oscillating contigs and these terms were actually regulated by circadian clocks in plants. The 215 common oscillating contigs can be used to evaluate whether the gene expression pattern related to photosynthesis and optical response performs normally in lettuce.

Circadian Rhythmicity of Diazinon Susceptibility, Detoxifying Enzymes, and Energy Reserves in Aphis gossypii (Hemiptera: Aphididae).

The daily susceptibility rhythm of the cotton aphid, Aphis gossypii Glover, to diazinon and the corresponding changes in the activity of three xenobiotic detoxifying enzymes-cytochrome P450 monooxygenases (P450), glutathione S-transferases (GSTs), and esterases-were investigated. Bioassays were conducted to estimate the median lethal doses (LD50) of diazinon at six different zeitgeber times (ZT0, 4, 8, 12, 16, and 20) under constant light (LL) and lighting conditions of 16 h of light and 8 h of darkness (LD). The results showed that the highest susceptibility occurred at the onset of night (ZT16) and 4 h before this time point (ZT12) under the LD condition. The endogenous rhythmicity of susceptibility was ensured, as the highest susceptibility occurred at the same time under the LL condition. The circadian changes in susceptibility to diazinon were almost coincident with changes in esterase and GSTs activity, but not in P450 activity. We also found rhythmic changes in energy components of whole-body aphids, with similar patterns of circadian changes of proteins, lipids, and soluble carbohydrates, but not glycogen, under LL and LD conditions. These photoperiod conditions (LD and LL) showed different fluctuation in trends of energy resources and of course, different quantities. Our study represents the first report of circadian control of insecticide susceptibility in aphids and provides insights into more efficient control of these pests by unveiling the times of day during which aphids are more susceptible to insecticides with attention to endogenous physiological phenomena.

Pigment patterns and photoprotection of anthocyanins in the young leaves of four dominant subtropical forest tree species in two successional stages under contrasting light conditions.

Light-driven subtropical forest succession is a dynamic process in which mesophytic climax communities replace heliophytic ones. Juvenile leaves (particularly mesophytic ones) are sensitive to high irradiances. To determine the photoprotection strategy that juvenile leaves use during subtropical forest succession, anthocyanin accumulation patterns were investigated in the young leaves of two mid-successional dominant trees (i.e., Schima superba and Castanopsis fissa) and two late-successional dominant trees (i.e., Cryptocarya concinna and Acmena acuminatissima) grown in 100% (FL) and 25% (LL) of full sunlight. All four tree species produced anthocyanins in their juvenile leaves when <50% of chlorophylls and carotenoids had developed. Higher anthocyanin concentrations accumulated in the young leaves grown in FL than in those grown in LL and in late-successional than in mid-successional trees. The juvenile leaves of late-successional trees were subjected to higher light-induced photoinhibition than those of mid-successional trees, despite of the fact that the leaves of late-successional trees showed greater non-photochemical quenching than those of mid-successional trees. Under LL conditions, photosystem II excitation pressure (1 - qP) was significantly higher in the juvenile leaves of late-successional trees than those of mid-successional trees. Under either FL or LL conditions, anthocyanin concentrations in juvenile leaves were negatively related to the light compensation point in mature leaves across species. However, anthocyanin concentrations were positively related to the antioxidant capacity of juvenile leaves. These results indicate that anthocyanin accumulation in the juvenile leaves of subtropical dominant trees during forest community succession is a flexible photoprotective response to ambient irradiances according to leaf sensitivity to light.

Evidence for age-related changes in the circadian activity rhythm of the diurnal primate Callithrix jacchus: a case report

Many cross-sectional studies have shown that circadian rhythms change with age, but such age-related modifications are gradual and may be insufficiently described by cross-sectional studies. In this case study, circadian activity rhythm (CAR) was evaluated longitudinally, in both LD (12:12) and LL conditions, on two occasions in a single male marmoset: when ‘adult’ (3 y.o.) and when ‘old’ (9 y.o.). When adult, the CAR synchronized with positive phase angles for the onset and offset of activity. In LL, the rhythm free-ran with τ < 24 h. When old, the animal showed a significant phase delay of its activity rhythm with respect to the LD cycle (t-test, p < 0.01) and a reduction on total daily activity (t-test, p < 0.01), with signs of lesser stability, greater fragmentation and some loss of photic synchronization. In LL, the period free-ran with τ > 24 h. We conclude that aging is associated with attenuation of photic synchronization and expression of CAR in LL in the marmoset. Further studies with a larger number of individuals are needed to confirm these findings.

Chlorophyll a fluorescence of typical desert plant Alhagi sparsifolia Shap. at two light levels

Alhagi sparsifolia Shap. is exposed to a high-irradiance environment as the main vegetation found in the forelands of the Taklamakan Desert. We investigated chlorophyll a fluorescence emission of A. sparsifolia seedlings grown under ambient (HL) and shade (LL) conditions. Our results indicated that the fluorescence intensity in the leaves was significantly higher for LL-grown plants than that under HL. High values of the maximum quantum yield of PSII for primary photochemistry (φPo) and the quantum yield that an electron moves further than QA - (φEo) in the plants under LL conditions suggested that the electron flow from QA - (primary quinone electron acceptors of PSII) to QB (secondary quinone acceptor of PSII) or QB - was enhanced at LL compared to natural HL conditions. The efficiency/probability with which an electron from the intersystem electron carriers was transferred to reduce end electron acceptors at the PSI acceptor side and the quantum yield for the reduction of end electron acceptors at the PSI acceptor side were opposite to φPo, and φEo. Thus, we concluded that the electron transport on the donor side of PSII was blocked under LL conditions, while acceptor side was inhibited at the HL conditions. The PSII activity of electron transport in the plants grown in shade was enhanced, while the energy transport from PSII to PSI was blocked compared to the plants grown at HL conditions. Furthermore, PSII activity under HL was seriously affected in midday, while the plants grown in shade enhanced their energy transport.

Impairment of Circadian Rhythms in Peripheral Clocks by Constant Light Is Partially Reversed by Scheduled Feeding or Exercise.

In mammals, circadian rhythms in peripheral organs are impaired when animals are maintained in abnormal environmental light-dark cycles such as constant light (LL). This conclusion is based on averaged data from groups of experimental animals sacrificed at each time point. To investigate the effect of LL housing on the peripheral clocks of individual mice, an in vivo imaging system was used to observe the circadian bioluminescence rhythm in peripheral tissues of the liver, kidney, and submandibular salivary gland in PER2::LUCIFERASE knock-in mice. Using this technique, we demonstrated that the majority of individual peripheral tissues still had rhythmic oscillations of their circadian clocks in LL conditions. However, LL housing caused decreased amplitudes and a broad distribution of peak phases in PER2::LUCIFERASE oscillations irrespective of the state of the animals' behavioral rhythmicity. Because both scheduled feeding and scheduled exercise are effective recovery stimuli for circadian clock deficits, we examined whether scheduled feeding or scheduled exercise could reverse this impairment. The results showed that scheduled feeding or exercise could not restore the amplitude of peripheral clocks in LL. On the other hand, the LL-induced broad phase distribution was reversed, and peak phases were entrained to a specific time point by scheduled feeding but only slightly by scheduled exercise. The present results demonstrate that LL housing impairs peripheral circadian clock oscillations by altering both amplitude and phase in individual mice. The broad distribution of clock phases was clearly reversed by scheduled feeding, suggesting the importance of scheduled feeding as an entraining stimulus for impaired peripheral clocks.

Effects of Low- vs. High-Load Resistance Training on Muscle Strength and Hypertrophy in Well-Trained Men.

The purpose of this study was to compare the effect of low- versus high-load resistance training (RT) on muscular adaptations in well-trained subjects. Eighteen young men experienced in RT were matched according to baseline strength and then randomly assigned to 1 of 2 experimental groups: a low-load RT routine (LL) where 25-35 repetitions were performed per set per exercise (n = 9) or a high-load RT routine (HL) where 8-12 repetitions were performed per set per exercise (n = 9). During each session, subjects in both groups performed 3 sets of 7 different exercises representing all major muscles. Training was performed 3 times per week on nonconsecutive days, for a total of 8 weeks. Both HL and LL conditions produced significant increases in thickness of the elbow flexors (5.3 vs. 8.6%, respectively), elbow extensors (6.0 vs. 5.2%, respectively), and quadriceps femoris (9.3 vs. 9.5%, respectively), with no significant differences noted between groups. Improvements in back squat strength were significantly greater for HL compared with LL (19.6 vs. 8.8%, respectively), and there was a trend for greater increases in 1 repetition maximum (1RM) bench press (6.5 vs. 2.0%, respectively). Upper body muscle endurance (assessed by the bench press at 50% 1RM to failure) improved to a greater extent in LL compared with HL (16.6 vs. -1.2%, respectively). These findings indicate that both HL and LL training to failure can elicit significant increases in muscle hypertrophy among well-trained young men; however, HL training is superior for maximizing strength adaptations.

Genome-wide identification of CCA1 targets uncovers an expanded clock network in Arabidopsis

The circadian clock in Arabidopsis exerts a critical role in timing multiple biological processes and stress responses through the regulation of up to 80% of the transcriptome. As a key component of the clock, the Myb-like transcription factor CIRCADIAN CLOCK ASSOCIATED1 (CCA1) is able to initiate and set the phase of clock-controlled rhythms and has been shown to regulate gene expression by binding directly to the evening element (EE) motif found in target gene promoters. However, the precise molecular mechanisms underlying clock regulation of the rhythmic transcriptome, specifically how clock components connect to clock output pathways, is poorly understood. In this study, using ChIP followed by deep sequencing of CCA1 in constant light (LL) and diel (LD) conditions, more than 1,000 genomic regions occupied by CCA1 were identified. CCA1 targets are enriched for a myriad of biological processes and stress responses, providing direct links to clock-controlled pathways and suggesting that CCA1 plays an important role in regulating a large subset of the rhythmic transcriptome. Although many of these target genes are evening expressed and contain the EE motif, a significant subset is morning phased and enriched for previously unrecognized motifs associated with CCA1 function. Furthermore, this work revealed several CCA1 targets that do not cycle in either LL or LD conditions. Together, our results emphasize an expanded role for the clock in regulating a diverse category of genes and key pathways in Arabidopsis and provide a comprehensive resource for future functional studies.

Existence of a photoinducible phase for ovarian development and photoperiod-related alteration of clock gene expression in a damselfish

The sapphire devil, Chrysiptera cyanea, is a reef-associated damselfish and their ovarian development can be induced by a long photoperiod. In this study, we demonstrated the existence of a photoinducible phase for the photoperiodic ovarian development in the sapphire devil. Induction of ovarian development under night-interruption light schedules and Nanda–Hamner cycles revealed that the photoinducible phase appeared in a circadian manner between ZT12 and ZT13. To characterize the effect of photoperiod on clock gene expression in the brain of this species, we determined the expression levels of the sdPer1, sdPer2, sdCry1, and sdCry2 clock genes under constant light and dark conditions (LL and DD) and photoperiodic (short and long photoperiods). The expression of sdPer1 exhibited clear circadian oscillation under both LL and DD conditions, while sdPer2 and sdCry1 expression levels were lower under DD than under LL conditions and sdCry2 expression was lower under LL than under DD conditions. These results suggest a key role for sdPer1 in circadian clock cycling and that sdPer2, sdCry1, and sdCry2 are light-responsive clock genes in the sapphire devil. After 1week under a long photoperiod, we observed photoperiod-related changes in sdPer1, sdPer2, and sdCry2 expression, but not in sdCry1 expression. These results suggest that the expression patterns of some clock genes exhibit seasonal variation according to seasonal changes in day length and that such seasonal alteration of clock gene expression may contribute to seasonal recognition by the sapphire devil.

Coupling of Cellular Processes and Their Coordinated Oscillations under Continuous Light in Cyanothece sp. ATCC 51142, a Diazotrophic Unicellular Cyanobacterium.

Unicellular diazotrophic cyanobacteria such as Cyanothece sp. ATCC 51142 (henceforth Cyanothece), temporally separate the oxygen sensitive nitrogen fixation from oxygen evolving photosynthesis not only under diurnal cycles (LD) but also in continuous light (LL). However, recent reports demonstrate that the oscillations in LL occur with a shorter cycle time of ~11 h. We find that indeed, majority of the genes oscillate in LL with this cycle time. Genes that are upregulated at a particular time of day under diurnal cycle also get upregulated at an equivalent metabolic phase under LL suggesting tight coupling of various cellular events with each other and with the cell’s metabolic status. A number of metabolic processes get upregulated in a coordinated fashion during the respiratory phase under LL including glycogen degradation, glycolysis, oxidative pentose phosphate pathway, and tricarboxylic acid cycle. These precede nitrogen fixation apparently to ensure sufficient energy and anoxic environment needed for the nitrogenase enzyme. Photosynthetic phase sees upregulation of photosystem II, carbonate transport, carbon concentrating mechanism, RuBisCO, glycogen synthesis and light harvesting antenna pigment biosynthesis. In Synechococcus elongates PCC 7942, a non-nitrogen fixing cyanobacteria, expression of a relatively smaller fraction of genes oscillates under LL condition with the major periodicity being 24 h. In contrast, the entire cellular machinery of Cyanothece orchestrates coordinated oscillation in anticipation of the ensuing metabolic phase in both LD and LL. These results may have important implications in understanding the timing of various cellular events and in engineering cyanobacteria for biofuel production.

High Light Intensity Increases the CAM Expression in “MD-2” Micro-Propagated Pineapple Plants at the End of the Acclimatization Stage

This work describes the evaluation of morpho-physiological and biochemical changes in “MD-2” micro-propagated pineapple plants (Ananas comosus (L.) Merr.) grown after 30 days under low light intensity (LL, greenhouse light conditions at 250 μmol·m-2·s-1) or high light intensity (HL, field light conditions at 800 μmol·m-2·s-1). Gas exchange, leaf pH, protein content and superoxide dismutase activity (SOD) (EC 1.15.1.1) were measured every 3 h during one day. Chlorophylls content and succulence index (SI) were determined at 9 h. Results showed significant differences in CO2 exchange rates, with a maximum occurring at 6 h (3.00 and 8.25 μmol CO2 m-2·s-1 for leaves under LL and HL conditions respectively). Plants under HL conditions had higher CO2 uptake and lower pH values between 0 h and 6 h respective to LL plants. The maximum pH value was attained 3 h before in HL plants. Leaf SI was increased and chlorophyll content decreased by HL conditions. SOD activity was higher in plants under HL conditions, near doubling those of LL plants at 18 h (2.8 versus 1.5 U·mg-1 Protein respectively). Both groups showed a typical CAM phenotype, but it was stronger in HL conditions, which may confer these plants with a better acclimation to transfer to the field.

Social interaction with rat exposed to constant light during lactation prevents depressive-like behavior induced by constant light in adulthood

Circadian rhythm disruptions are often observed in depressed patients, and changes in the light/dark cycle promote depressive-like behavior in animal models. Prolonged exposure to constant light (LL) is known to lead to arrhythmicity of circadian locomotor activity and depressive-like behavior in rats. Interestingly, neonatal exposure to LL prevents both arrhythmicity and depressive behavior in adulthood. Arrhythmic rats under LL conditions that cohabitate with a rhythmic rat exhibit improvement in circadian rhythms. We tested whether such cohabitation also protects against LL-induced depressive-like behavior. Wistar rats were assigned to conditions of either neonatal constant light (neonatal-LL) on postnatal days 10–22 or a regular light/dark cycle (neonatal-LD). On day 45, the animals were assigned to three possible pair combinations. After a baseline sucrose preference test, half of the pairs were placed under LL conditions. Weekly sucrose preference tests were conducted to evaluate depressive-like behavior. The animals were isolated by an aluminum wall on the test day. At week 2 of LL, sucrose preference was reduced in neonatal-LD/neonatal-LD pairs of animals. At week 5, neonatal-LD/neonatal-LD pairs exhibited anhedonic-like behavior, but the pairs with at least one neonatal-LL rat did not. The LL cycle was returned to an LD cycle, and the neonatal-LD/neonatal-LD pairs exhibited a restoration of sucrose preference 2 weeks later. We conclude that social interaction can prevent depressive-like behavior induced by circadian rhythm disruption as long as one of the animals is more prone to present a strong rhythm.