Continuous Dark Conditions Research Articles

Spatiotemporal dynamics of circadian clock in lettuce

Abstract Plant circadian clock controls many physiological events by synchronization with environmental changes. The clock can be controlled artificially by imposing various light conditions in a closed system for plant cultivation in plant factory. The plant circadian rhythm is formed by enormous self-sustained cellular circadian oscillators, so that the synchronization of circadian oscillators is of great importance to the formation of individual circadian rhythms. Therefore, the study of synchronization phenomena is important for precise control of the circadian rhythm. In this study, we have investigated the spatiotemporal dynamics of circadian oscillators in lettuce (Lactuca sativa L.). Bioluminescence of transgenic lettuce carrying a CCA1::LUC construct as a reporter of a circadian gene expression was measured in the leaf and root. We observed phase wave propagation in the leaf with a phase delay in the region of the primary vein, with the primary vein region showing lower amplitude than the other regions. Wave propagation occurred from the edge of the leaf inward. In addition, a striped wave traveled from the base to the tip along the roots, which were grown under continuous dark or light conditions. The features observed in the lettuce plants could be explained by phase oscillator models established in the study of Arabidopsis thaliana. The results of this study show the possibility of applying circadian clock control in a model plant for plant production.

Use of Linear and Weibull Functions to Model Ascorbic Acid Degradation in Chinese Winter Jujube during Postharvest Storage in Light and Dark Conditions

Degradation of ascorbic acid (AA) in Zhanhua winter jujube stored at selected temperatures under continuous light and darkness conditions was described by first-order kinetics and Weibull distribution function, and the temperature dependence of AA loss was studied by the Arrhenius equation. The high correlation coefficients (R 2 > 0.99) indicated the acceptability of Weibull model for predicting the degradation of AA. Activation energy was determined to be 10.586 and 11.868 kcal/mol under continuous light condition and 12.636 and 13.190 kcal/ mol under continuous darkness condition according to first-order and Weibull models, respectively. This study revealed that the loss of AA in continuous darkness was more temperature-dependent than the other samples. In continuous light, AA degradation may be favored even if at low temperatures. Therefore, a low temperature and continuous darkness condition is recommended to preserve AA content in jujube fruits during postharvest storage.

Neurons of the Paraventricular Hypothalamic Nucleus Under Normal and Modified Illumination Conditions: Immunohistochemical and Morphometric Parallels

Using an immunohistochemical technique and densitometric analysis in experiments on rats, we examined the expression of an early-response protein, c-Fos, in the medial parvicellular subnucleus of the hypothalamic paraventricular nucleus (mpcPVN). During 7 days, the animals were kept under conditions of (i) normal photoperiod (group LD), (ii) continuous illumination (group LL), and (iii) continuous darkness (light deprivation, group DD). It was found that both normal photoperiodicity and artificial modifications of the latter result in significant changes of c-Fos immunopositivity in the nuclei of mpcPVN neurons (cells that synthesize corticotropin-releasing factor). Changes in the indices of concentration and amount of c-Fos in mpcPVN neurons were, from some aspects, similar to those observed under analogous experimental conditions in neurons of a leading pacemaker of the circadian periodicity, the suprachiasmatic nuclei (SChNs) of the hypothalamus [10], but, at the same time, demonstrated noticeable specificity from other aspects. In all experimental groups, the concentration and amount of c-Fos in mpcPVN neurons were greater during daytime than at night. Dramatic increases in the above parameters observed at daytime in rats subjected to light deprivation were the most significant effect of modifications of the photoperiod. Both continuous illumination and light deprivation resulted in some increase of the number (density) of c-Fos-immunopositive units in the mpcPVN. The nuclei of neurons of this structure demonstrated the phenomenon found earlier in SChN neuron; geometrical dimensions of the cell nuclei of these structures depended noticeably on both illumination conditions and periodicity. Probable mechanisms of the dependence of c-Fos expression in the hypothalamic nuclei on the photoperiod and its modifications, interdependence of such changes observed in the circadian pacemaker (SChN) and an important component of the system controlling the stress reactions (mpcPVN), and the relation of the above phenomena to the level of melatonin produced by the epiphysis cerebri (main neuroendocrine intermediator organizing the above-mentioned periodicity) are discussed.

Modulation of fungicidal potential of Anabaena strains by light and temperature

The regulation of fungicidal and hydrolytic enzyme activity was investigated in a set of cyanobacterial strains belonging to the genus Anabaena (Anabaena laxa RPAN8, Anabaena iyengarii RPAN9, Anabaena variabilis RPAN59 and Anabaena oscillarioides RPAN69), with A. variabilis RPAN16 serving as negative control. Time course studies undertaken with cultures incubated under different light and temperature conditions revealed enhancement in growth and fungicidal activity under continuous light (CL) and light dark (LD, 16:8) conditions and temperature of 30 °C and 40 °C. A significant increase of 3-18 % in chitosanase activity was recorded in all the 4-week-old cultures under CL condition and at 40 °C. Endoglucanase activity of RPAN8 and 9 was twofolds higher than the other strains under all light/dark conditions and temperature in the 4-week-old cultures, while continuous dark (CD) enhanced CMCase activity in RPAN69. This study provided useful information regarding the most suitable conditions of light and temperature for maximizing hydrolytic enzyme activity and fungicidal activity, as a prelude to their effective use as biocontrol agents.

In vitro Propagation of Stemona tuberosa Lour. - A Rare Medicinal Plant through High Frequency Shoot Multiplication using Nodal Explants

Nodal segments of Stemona tuberosa Lour. were found to proliferated without any differentiation on to MS supplemented with 3.0 mg/l BAP and 0.5 mg/l NAA under continuous dark condition. After 20 days of inoculation under dark condition the cultures were transferred to a daily cycle of 16/8 hrs light/dark photoperiod and there the proliferated nodal segments underwent direct organogenesis producing huge number of shoot buds (25.87/culture). The shoot buds underwent rapid elongation on a range of BAP (0.1 - 1.5 mg/l) and IBA (0.1 - 1.0 mg/l) supplemented MS. Rooting of elongated shoot buds was successfully achieved (90%) in half strength MS with 1.0 mg/l NAA. The plantlets were finally established in outside environment through a successive phase of acclima-tization. Key words: Nodal explant, Stemona tuberose, Rare medicinal plant, Direct organogenesis D. O. I. 10.3329/ptcb.v21i2.10238 Plant Tissue Cult. & Biotech. 21(2): 151-159, 2011 (December)

Photoperiod-modulated instar-specific clock-shifting in the circadian protein and amino acid rhythms in the larval segmental muscle of Bombyx mori

The photoperiod-modulated clock-shifting in the circadian protein rhythm was studied in the segmental muscle of Bombyx mori. The analysis of phase response curves of the fourth instar rhythm revealed that the muscle tissue completes six protein synthetic cycles (PS cycles) under normal 12 hr light and 12 hr dark cycle (LD), 8 cycles each under continuous light (LL) and continuous dark (DD) conditions. The fifth instar protein rhythm showed seven PS cycles each under LD and DD conditions, but only six under LL. The protein rhythm gets clock-shifted in instarspecific and photoperiod-specific fashions. In the fourth instar, both LL and DD conditions advanced the 24 hr free running time of the rhythm by six hours and set it at 18 hr, but in the fifth instar it is delayed by 4 hr and set at ~28 hr under LL, but remained unchanged under DD. Comparative analysis of protein and amino acid profiles shows that the photoperiod modulates the protein rhythm by altering the rate of amino acid mobilization.

Effect of environmental factors on seed germination and seedling emergence of invasive Ceratocarpus arenarius

Ebrahimi E & Eslami SV (2011). Effect of environmental factors on seed germination and seedling emergence of invasive Ceratocarpus arenarius. Weed Research 52, 50–59.SummaryCeratocarpus arenarius is a problematic and noxious weed of dryland farming in North Khorasan, Iran. Experiments were conducted to investigate the mechanism of seed dormancy, as well as the effect of environmental factors on germination and emergence of this species. Results showed that the pericarp is the major obstacle to seed germination; seeds without an intact pericarp had germination rates exceeding 90%. Ceratocarpus arenarius had identical germination rates in either light/dark and continuous dark conditions, indicating that this weed species is non‐photoblastic. Germination was >35% over a range of alternating light/dark temperatures (10/5, 20/10, 25/15, 30/20 and 35/25°C), with maximum germination (96%) at 25/15°C. Ceratocarpus arenarius seeds germinated at rates >20% in high levels of salinity (800 mm) and osmotic potential (−1 MPa), indicating that this species is tolerant to saline conditions and drought stress during germination and early seedling growth. Maximum germination of C. arenarius seeds occurred at a pH range of 7–9. Seedlings emerged from burial depths ranging from 0 (without covering with filter paper) to 6 cm, and the maximum emergence (94%) was observed in seeds placed on the soil surface covered with three layers of filter paper. This suggests that minimum‐ and no‐till systems would increase seedling emergence of this species through maintaining crop residues and seeds on the soil surface. These attributes, coupled with tolerance to salinity and drought stress during germination, should be taken into account when managing C. arenarius.

Dormancy and germination in Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee seeds: Effects of short-time moist chilling and plant growth regulators

We investigated the germination requirements of the species Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee (Lamiaceae). We studied the effects of scarification, short-time moist chilling (+4 °C) for 15 and 30 days, and various doses of gibberellic acid (GA 3; 0, 100, 150 and 250 ppm), Kinetin (KIN; 50 ppm) and a combination of 250 ppm GA 3 and 50 ppm KIN. The hormone and moist chilling treatments were carried out under both continuous darkness (20 °C) and photoperiodic (20/10 °C; 12/12 h, respectively) conditions. Seeds failed to germinate in response to short-time moist chilling treatments with distilled water under both continuous darkness and photoperiodic conditions. Seeds were found to have dormancy. Treatments with GA 3 or a combination of GA 3 and KIN were successful at breaking seed dormancy. A maximum of 37% of the seeds germinated after GA 3 application in all series. When only KIN was applied at a 50 ppm concentration, germination (12%) was found only with moist chilling for 30 days under continuous darkness. The highest germination rates were found in seeds treated with combination of 250 ppm GA 3 and 50 ppm KIN. In the combination treatments, while the moist chilling treatments for 15 days resulted in 68 and 73% germination, respectively, these rates were up to 95% in the moist chilling treatments for 30 days under continuous darkness and photoperiodic conditions. Mean germination time (MGT) in GA 3 and KIN combinations was lower than in other treatments. Scarification with 80% sulphuric acid did not promote germination. The characteristics of physiological dormancy of S. germanica ssp. bithynica seeds are consistent with conditions of existence in the in alpine habitat of this species.

Circadian transcriptional regulation by the posttranslational oscillator without de novo clock gene expression in Synechococcus

Circadian rhythms are a fundamental property of most organisms, from cyanobacteria to humans. In the unicellular obligately photoautotrophic cyanobacterium Synechococcus elongatus PCC 7942, essentially all promoter activities are controlled by the KaiABC-based clock under continuous light conditions. When Synechococcus cells are transferred from the light to continuous dark (DD) conditions, the expression of most genes, including the clock genes kaiA and kaiBC, is rapidly down-regulated, whereas the KaiC phosphorylation cycle persists. Therefore, we speculated that the posttranslational oscillator might not drive the transcriptional circadian output without de novo expression of the kai genes. Here we show that the cyanobacterial clock regulates the transcriptional output even in the dark. The expression of a subset of genes in the genomes of cells grown in the dark was dramatically affected by kaiABC nullification, and the magnitude of dark induction was dependent on the time at which the cells were transferred from the light to the dark. Moreover, under DD conditions, the expression of some dark-induced gene transcripts exhibited temperature-compensated damped oscillations, which were nullified in kaiABC-null strains and were affected by a kaiC period mutation. These results indicate that the Kai protein-based posttranslational oscillator can drive the circadian transcriptional output even without the de novo expression of the clock genes.

Effects of photoperiod on daily activity rhythm of juvenile sea cucumber, Apostichopus japonicus (Selenka)

In nature, Apostichopus japonicus exhibits a behavioral characteristic of emerging at night and sheltering during the day. Hence, it was commonly believed that longer and darker light conditions are better for a population of A. japonicus. In aquaculture situations therefore, animals have commonly been cultured without lighting, especially during juvenile-hatching culture. However, how the length of darkness each day affects A. japonicus and what the mechanism is of behavioral response of A. japonicus to different photoperiods remain unclear, and are specifically addressed in this study. We applied nine photoperiod treatments (light:dark (LD) cycles at 0:24, 3:21, 6:18, 9:15, 12:12, 15:9, 18:6, 21:3, and 24:0 under 500 lx) to 60 individuals (29.73 ± 0.23 g) per treatment (with 3 replicates). The environmental conditions were set as: water temperature = 16.9 ± 0.3°C, dissolved oxygen>6.0 mg/L, ammonia<0.3 mg/L, pH = 7.8–8.2, and salinity = 30–32. Under experimental conditions of continuous darkness as well as continuous light, cyclic nocturnal activity patterns of A. japonicus (viz. the animals emerged and fed at night and sheltered during the day) were observed. However, they spent more and less time, respectively, moving and feeding under continuous darkness and continuous light, than those under a natural light cycle. Under photoperiods with 6–12 h of light, the animals showed one sheltering behavior transition and two emerging behavior transitions. These behavior transitions appeared to be governed by some internal physiological factors and induced by daily light variation. The behavior of the animals was significantly affected by different photoperiods, and the distribution rate (DR) of the animals emerging at “daytime” increased with lengthening “light time” (except for the LD 3:21 cycle). We also found that there was no significant difference in mean DR per day under LD cycles of 6:18, 9:15, 15:9, and 12:12. Mean DRs per day were significantly lower for these photoperiods, than for those under LD cycles of 0:24 and 3:21, and significantly higher than for those under LD cycles of 18:6, 21:3 and 24:0. These results imply that 6–15 h light per day were the similar photoperiods to natural sunlight. From the viewpoint of activity and feeding behaviors, these might be the optimal photoperiods for rearing A. japonicus.

A putative flowering-time-related Dof transcription factor gene, JcDof3, is controlled by the circadian clock in Jatropha curcas

Plant-specific DNA-binding transcription factors with one finger (Dof) perform important roles in several biological processes. A yeast one-hybrid cDNA library of Jatropha curcas was used to identify Dof-type transcription factors. JcDof3, isolated from the library as a full-length cDNA, encoded a protein of 518 amino acids and contained a highly conserved Dof domain. Yeast one-hybrid systems and subcellular localization assays confirmed that JcDof3 was a typical transcription factor. In contrast to arrhythmic expression at basal level in etiolated cotyledons under continuous dark conditions, the circadian oscillations of JcDof3 transcripts were observed under long day, short day or continuous light regimes. A phylogenetic analysis showed that JcDof3 was clustered into the same clade with CYCLING DOF FACTOR (CDF), which interacts with F-box protein to regulate photoperiodic flowering. Moreover, a yeast two-hybrid assay showed that JcDof3 also interacted with F-box proteins. Our results suggest that JcDof3 is a circadian clock regulated gene, and might be involved in the flowering time regulation of J. curcas.

High Survival Rates of Sutchi Catfish, Pangasianodon hypophthalmus, Larvae Reared under Dark Conditions

The sutchi catfish, Pangasianodon hypophthalmus is an important species for aquaculture in Southeast Asia. However, the larvae demonstrate a low survival rate due to their strong cannibalism during rearing. The aim of the present study was to reduce their cannibalism and improve larval rearing methods. Larval rearing experiments were conducted under normal light conditions (following a diel rhythm) and continuous dark conditions with larval densities of 10, 20 and 40 individuals L-1 from hatching day to 20 days old. The trial with 10 individuals L-1 under dark conditions had the highest survival rate. The dark conditions with lower individual densities tended to produce higher survival rates than the light conditions with higher individual densities. Fish body weight on the final day of larval rearing showed that rearing larvae under dark conditions resulted in steady growth similar to growth under light conditions. It seemed that the feeding behavior of sutchi catfish depended on chemo-sense rather than visual sense. This study showed that the cannibalism of sutchi catfish larvae can be reduced by rearing under dark conditions at low densities with adequate access to food. Therefore, it was concluded that rearing under dark conditions is a method for reducing cannibalism and increasing survival rates. © 2011 Academic Journals Inc.

Larval Rearing and Feeding Behavior of African Catfish, Clarias gariepinus under Dark Conditions

The present study was conducted to elucidate the relationship between the larval feeding behavior of African catfish, Clarias gariepinus and their sensory organs. We also sought to reduce the cannibalism and improve larval rearing methods for this species. The feeding behavior of intact and streptomycin-treated larvae was examined under light and dark conditions using Artemia nauplii. The ingestion rates under light versus dark conditions did not vary significantly; furthermore, no difference was observed between intact and streptomycin-treated larvae. These results showed that the feeding behavior of C. gariepinus depends on chemo-sensory senses rather than visual or mechanical senses. In addition, the larvae were reared under normal light conditions (following a diurnal cycle) and continuous dark conditions from the hatching day until they were 20 days old. Although, there was no significant difference, the trials under continuous dark conditions tended to have higher survival rates than those under light conditions. Moreover, the larvae reared under dark conditions showed the same growth rate as those under light conditions. The observations of larval behavior in the present study showed that larval activity increased under dim light conditions; the number of fish resting on the bottom of the aquaria decreased and fewer larvae were bitten by other individuals than under light conditions. The results of this study suggest that higher activity of C. gariepinus under dark conditions reduced the rate of cannibalism and resulted in higher rates of survival compared to light conditions. This study suggests that the survival rate of C. gariepinus larvae can be improved under dark or dim light conditions with low larval densities and adequate access to food. © 2011 Academic Journals Inc.

Constitutive expression of the GIGANTEA Ortholog Affects Circadian Rhythms and Suppresses One-shot Induction of Flowering in Pharbitis nil, a Typical Short-day Plant

GIGANTEA (GI) is a key regulator of flowering time, which is closely related to the circadian clock function in Arabidopsis. Mutations in the GI gene cause photoperiod-insensitive flowering and altered circadian rhythms. We isolated the GI ortholog PnGI from Pharbitis (Ipomoea) nil, an absolute short-day (SD) plant. PnGI mRNA expression showed diurnal rhythms that peaked at dusk under SD and long-day (LD) conditions, and also showed robust circadian rhythms under continuous dark (DD) and continuous light (LL) conditions. Short irradiation with red light during the flower-inductive dark period did not change PnGI expression levels, suggesting that such a night break does not abolish flowering by affecting the expression of PnGI. In Pharbitis, although a single dusk signal is sufficient to induce expression of the ortholog of FLOWERING LOCUS T (PnFT1), PnGI mRNA expression was not reset by single lights-off signals. Constitutive expression of PnGI (PnGI-OX) in transgenic plants altered period length in leaf-movement rhythms under LL and affected circadian rhythms of PnFT mRNA expression under DD. PnGI-OX plants formed fewer flower buds than the wild type when one-shot darkness was given. In PnGI-OX plants, expression of PnFT1 was down-regulated, suggesting that PnGI functions as a suppressor of flowering, possibly in part through down-regulation of PnFT1.

CHANGES IN ENDOGENOUS CYTOKININ CONCENTRATIONS IN CHLORELLA (CHLOROPHYCEAE) IN RELATION TO LIGHT AND THE CELL CYCLE(1).

Endogenous cytokinins were quantified in synchronized Chlorella minutissima Fott et Novákova (MACC 361) and Chlorella sp. (MACC 458) grown in a 14:10 light:dark (L:D) photoperiod. In 24 h experiments, cell division occurred during the dark period, and cells increased in size during the light period. Cytokinin profiles were similar in both strains, consisting of five cis-zeatin (cZ) and three N(6) -(2-isopentenyl)adenine (iP) derivatives. Cytokinin concentrations were low during the dark period and increased during the light period. In 48 h experiments using synchronized C. minutissima (MACC 361), half the cultures were maintained in continuous dark conditions for the second photoperiod. Cell division occurred during both dark periods, and cells increased in size during the light periods. Cultures kept in continuous dark did not increase in size following cell division. DNA analysis confirmed these results, with cultures grown in light having increased DNA concentrations prior to cell division, while cultures maintained in continuous dark had less DNA. Cytokinins (cZ and iP derivatives) were detected in all samples with concentrations increasing over the first 24 h. This increase was followed by a large increase, especially during the second light period where cytokinin concentrations increased 4-fold. Cytokinin concentrations did not increase in cultures maintained in continuous dark conditions. In vivo deuterium-labeling technology was used to measure cytokinin biosynthetic rates during the dark and light periods in C. minutissima with highest biosynthetic rates measured during the light period. These results show that there is a relationship between light, cell division, and cytokinins.

Cultural Characteristics of Ophiocordyceps heteropoda Collected from Korea

Isolates of Ophiocordyceps heteropoda (Kobayasi) collected from Mt. Halla on Jeju-do, Korea were tested for mycelial growth on different agar media and in the presence of different carbon and nitrogen sources. Similarly, isolates were also incubated at different temperatures as well as under continuous light and dark conditions. Growth was better on Hamada agar, basal medium, and malt-yeast agar, but poor on Czapek-Dox agar. Different carbon sources such as dextrin, saccharose, starch, lactose, maltose, fructose, and dextrose resulted in better growth. Complex organic nitrogen sources such as yeast extract and peptone revealed the most effective growth. Mycelial growth was best at 25°C. The growth rate was faster in the dark than the light, but mycelial density was less compact in the dark.

Proteomic identification of rhythmic proteins in rice seedlings

Many aspects of plant metabolism that are involved in plant growth and development are influenced by light-regulated diurnal rhythms as well as endogenous clock-regulated circadian rhythms. To identify the rhythmic proteins in rice, periodically grown (12 h light/12 h dark cycle) seedlings were harvested for three days at six-hour intervals. Continuous dark-adapted plants were also harvested for two days. Among approximately 3000 reproducible protein spots on each gel, proteomic analysis ascertained 354 spots (~ 12%) as light-regulated rhythmic proteins, in which 53 spots showed prolonged rhythm under continuous dark conditions. Of these 354 ascertained rhythmic protein spots, 74 diurnal spots and 10 prolonged rhythmic spots under continuous dark were identified by MALDI-TOF MS analysis. The rhythmic proteins were functionally classified into photosynthesis, central metabolism, protein synthesis, nitrogen metabolism, stress resistance, signal transduction and unknown. Comparative analysis of our proteomic data with the public microarray database (the Plant DIURNAL Project) and RT-PCR analysis of rhythmic proteins showed differences in rhythmic expression phases between mRNA and protein, suggesting that the clock-regulated proteins in rice are modulated by not only transcriptional but also post-transcriptional, translational, and/or post-translational processes.

Immunoreactive intensity of FXPRL amide neuropeptides in response to environmental conditions in the silkworm, Bombyx mori

In the silkworm Bombyx mori, the diapause hormone-pheromone biosynthesis activating neuropeptide gene, DH-PBAN, is a neuropeptide gene that encodes a polypeptide precursor consisting in five Phe-X-Pro-Arg-Leu-NH(2) (FXPRL) amide (FXPRLa) neuropeptides; DH (diapause hormone), PBAN (pheromone-biosynthesis-activating neuropeptide) and α-, β- and γ-SGNPs (subesophageal ganglion neuropeptides). These neuropeptides are synthesized in DH-PBAN-producing neurosecretory cells contained within three neuromeres, four mandibular cells, six maxillary cells, two labial cells (SLb) and four lateral cells of the subesophageal ganglion. DH is solely responsible, among the FXPRLa peptide family, for embryonic diapause. Functional differentiation has been previously suggested to occur at each neuromere, with the SLb cells releasing DH through brain innervation in order to induce embryonic diapause. We have investigated the immunoreactive intensity of DH in the SLb when thermal (25°C or 15°C) and light (continuous illumination or darkness) conditions are altered and following brain surgery that induces diapause or non-diapause eggs in the progeny. We have also examined the immunoreactivity of the other FXPRLa peptides by using anti-β-SGNP and anti-PBAN antibodies. Pupal SLb somata immunoreactivities seem to be affected by both thermal and light conditions during embryogenesis. Thus, we have been able to identify a close correlation between the immunoreactive intensity of neuropeptides and environmental conditions relating to the determination of embryonic diapause in B. mori.

Factors influencing adult emergence from soil and the vertical distribution of burrowing scarab beetles Dasylepida ishigakiensis

The present study investigates the emergence of adult white grub beetles Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scrabaeidae) from soil as well as their burrowing behaviours. ‘Standby behaviour’ (i.e. adults come to the soil surface where they expose their heads) is shown in the field and, along with emergence behaviour, is entrained by LD photocycles. These 24-h rhythms persist after transfer to continuous light conditions for 2 days. By contrast, beetles transferred from LD photocycles to continuous dark conditions fail to show standby behaviour; thus, it appears to be manifested only in the presence of illumination. Under dark conditions, beetles emerge completely from the soil directly at the time when standby behaviour is otherwise expected to occur. Emerged adults then burrow back into the soil before dawn. Virgin and mated males, as well as virgin females, which are expected to emerge from the soil for mating on later evenings, burrow to a relatively shallow depth (<2 cm), whereas mated females burrow deeper (2–10 cm). Soil properties such as moisture, grain size, topography and temperature influence the burrowing behaviour and the depths that the beetles reach.

Photoperiodic modulation of circadian rhythms in the silk gland protein profiles of Bombyx mori and its influence on the silk productivity and quality

Circadian rhythms in the silk gland protein profiles of Bombyx mori were analyzed under 12 h light and 12 h dark cycle (LD), continuous light (LL) and continuous dark (DD) conditions. The phase response curves of protein rhythms indicate the prevalence of a series of silk cycles, each comprising three phases; transcription, translation and consolidation of silk proteins. In the 24h- protein rhythm, the silk cycle repeats every 3h, 42 m under LD, 2h, 36m under LL and 3h under DD. The light and dark conditions advanced the rhythm of each silk cycle by 48m and 24m respectively. As a result the silk gland completes 7 rounds of protein synthesis under LD, 9 rounds under LL and 8 rounds under DD during the 24h-free running time of the rhythm. The light-induced clock-shift in the protein rhythm caused significant gains in economic parameters of sericulture with positive signals for enhancing silk productivity and quality.