Effect of light pulses in early scotophase on resetting of the night-measuring diapause clock of the Indian meal moth, Plodia interpunctella

Abstract.  The Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae) may enter diapause in the last larval instar in response to the photoperiod during the preceding instars. An hourglass-type photoperiodic clock may measure night length for this purpose. The present study describes the resetting of the hourglass by light pulse(s) in the early scotophase and by scanning the subsequent clock phase by another light pulse (P). When the lights-off time of a first light pulse is fixed at 4 h after dusk under LD 4 : 20 h and LD 6 : 18 h photoperiods and its duration is increased from 1 to 3 h, the critical night length (CNL) from dawn is decreased, but that from dusk to P increases. A 3-h first light pulse efficiently resets the time measuring system. If this 3-h light pulse is split into two 1-h light pulses (L₁ and L₂) by 1 h of darkness, the dark-time measuring function appears to be impeded and CNL from P to dawn disappears, but that from L₂ to P is expressed. This indicates that the receptivity to light pulses varies among individual insects.     

Geographic variation and genetic aspects of reproductive diapause in Drosophila triauraria and D. quadraria

ABSTRACT. Geographic variation and genetic aspect of reproductive diapause were studied in Drosophila triauraria Bock & Wheeler and D. quadraria Bock & Wheeler, in relation to their quantitative response to photoperiods. D. quadraria from the subtropical region had no photoperiodic diapause. In D. triauraria strains, diapause was induced under LD 10:14 or 12:12, but not under LD 14:10 or longer photoperiods. Their diapause was induced more effectively and maintained longer by LD 10:14 than by LD 12:12. The duration of diapause was longer in a northern strain, but the diapause inducing process varied little among different geographical strains. Diapause incidence was 50% or lower in F₁ hybrids between D. triauraria and D. quadraria and backcross progenies between F₁ and D. quadraria , and about 70% in backcross progenies between F₁ and D. triauraria under LD 10:14, but very low under LD 12:12. The lower incidence of diapause in these F; and backcross progenies is assumed to be due to the less efficient induction of diapause, since once diapause was induced in them, it was maintained for a long time, especially in the backcross progenies between F₁ and D. triauraria. These experiments suggest that diapause induction and maintenance are different physiological processes controlled by different genetic systems.     

Protein Kinase C Activation Potentiates the Rapid Secretion of the Amyloid Precursor Protein from Rat Cortical Synaptosomes

Abstract : In this study we have used the presynaptic-rich rat cerebrocortical synaptosomal preparation to investigate the proteolytic cleavage of the amyloid precursor protein (AβPP) by the α-secretase pathway within the βA4 domain to generate a soluble secreted N-terminal fragment (AβPP_s). AβPP was detected in crude cortical synaptosomal membranes, although at a lower density than that observed in whole-tissue homogenates. Protein kinase C (PKC) activation induced a translocation of the conventional PKC isoform β1 and novel PKCε from cytosol to membrane fractions, but there was no alteration in the proportion of AβPP associated with the Tritonsoluble and -insoluble fractions. AβPP_s was constitutively secreted from cortical synaptosomes, with this secretion being enhanced significantly by the direct activation of PKC with phorbol ester. The PKC-induced secretion of AβPP_s was only partially blocked by the PKC inhibitor GF109203X (2.5 μ M ), whereas the phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein was significantly inhibited by GF109203X. The differential sensitivities of the MARCKS phosphorylation and AβPP_s secretion to GF109203X may imply that different PKC isoforms are involved in these two events in the synaptosomal system. These findings strongly suggest that the α-secretase activity leading to the secretion of AβPP_s can occur at the level of the presynaptic terminal.     

Light-quality effects on Arabidopsis development. Red, blue and far-red regulation of flowering and morphology

Arabidopsis thaliana (L.) Heynh. race Columbia plants were grown in red. blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m⁻² s⁻¹) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P_fr/P_tot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P_fr/P_tot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.     

The effect of brief light pulses on the photoperiodic reaction in the Djungarian hamsterPhodopus sungorus

Summary The effects of brief light pulses on photoperiodic reaction were examined in male Djungarian hamsters (Phodopus sungorus). Half of the animals came from long photoperiods and, accordingly, were in physiological summer state with large and functional testes. The other half had lived in short natural photoperiods before and was in physiological winter condition with involuted testes. These animals were exposed to long (LD 168) or to short (LD 816) photoperiods, or to short photoperiods in which the 16 h of darktime were interrupted by 1 min of light each night, either 4, 8 or 12 h after light off.Light pulses at midnight had the same effect as long photoperiods, they maintained gonadal size and activity or caused rapid recrudescence. If the light pulses were applied 4 or 12 h after light-off, however, a marked difference in effect ensued, depending on previous state and light regime. In animals coming from long photoperiods, these schedules induced regression, while in hamsters coming from short photoperiods the same schedules stimulated recrudescence, though significantly less than full long photoperiods or schedules with light-interruptions at midnight. Changes in body weight and pelage colour closely paralleled the changes in gonadal state.     

Oxygen evolution and respiration of the cyanobacterium Synechocystis sp. PCC 6803 under two different light regimes applying light/dark intervals in the time scale of minutes

The photosynthetic performance of the cyanobacterium Synechocystis sp. PCC 6803 exposed to intermittent light was studied by measuring oxygen evolution, respiration and the fluorescence parameters for maximum efficiency of excitation energy capture by photosystem II (PSII) reaction centres ( F _v/ F _m), PSII quantum yield (ΔF/ F _m ¹) and non-photochemical quenching (NPQ). Cultures were pre-acclimated to constant light conditions. Block and sinusoidal light regimes were tested using four photon-flux densities (PFDs) applied in light/dark intervals of 1:1, 5:5 and 10:10 min. Light use was higher under the sinusoidal light regime compared with the block regime. The accumulated gross photosynthesis of the cyanobacterium was lower under intermittent light conditions compared with predictions from the photosynthesis-irradiance curve (PI curve). The respiration rates were similar for all light/dark intervals tested. However, the respiration slightly increased with increasing oxygen production for both block and sinusoidal light regime. NPQ, ΔF/ F _m' and F _v/ F _m depended on the PFD rather than on the duration of the light/dark intervals tested, and there was no detected influence of the two applied light regimes.     

Analysis of entrainment of circadian oscillators by skeleton photoperiods using phase transition curves

A skeleton photoperiod consists of two short pulses which are applied on the circadian oscillator at times corresponding to the beginning and to the end of a continuous light stimulus. To study several problems in entrainment of circadian rhythms by skeleton photoperiods, we develop a simple diagrammatic solution of the steady state entrainment making use of phase transition curves which are directly gotten from phase response curves. The graphical method is simple and systematic to study entrainment by light cycles with various day lengths. As the method is also intuitive, we can easily examine three problems. (1) In Drosophila the phase relation (ψ) between rhythm and light cycle is a continuous function of day length of skeleton photoperiods up to about 12 h, but a marked discontinuity (ψ-jump) sets in between 13 and 14h. By the diagrammatic method we find that ψ-jump is mathematically a bifurcation phenomenon. (2) The action of photoperiods up to about 12 h is fully simulated by two 15-min skeleton pulses. Do 3-min skeleton pulses imitate the complete photoperiods? We find that pulse width is arbitrary to some extent. (3) Why skeleton photoperiods up to about 12 h are good models of complete photoperiods? The reason is the small amplitude and the nearly symmetrical form of phase response curves in the subjective day.     

Hourglass and oscillator expressions of photoperiodic diapause response in the cabbage moth Mamestra brassicae

Abstract. Both oscillator and hourglass features are found in the photoperiodic response that controls the pupal winter diapause of Mamestra brassicae. The expression of oscillatory response to extended long-night cycles is temperature dependent, i.e. circadian resonance appears at 23 and 25^oC but not at 20 and 28^oC. At 20^oC, scanning of extended scotophases by a short light pulse does not reveal any clear circadian rhythmicity. However, a circadian feature of the photoperiodic response is indicated even at 20^oC by a bistability phenomenon, i.e. either one of the two dark periods in symmetrical skeleton photoperiods determines the diapause response depending on the phase angle with the preceding (entraining) light-dark cycles. At 20 and 25^oC, the incidence of diapause increases as a function of the number of light–dark cycles regardless of the cycle length (T) , if T is 24 h or 2 X 24h (with a 12 h light period). A non-diel cycle (r=36h) is less effective, suggesting that disturbance of the circadian organization partly impairs the diapause-inducing function. The inductive effect of a long night is largely affected by temperature, and becomes saturated with eight cycles at 20^oC and 14 cycles at 25^oC. Presumably, an hourglass mechanism measures the dark time, and a circadian component involved in some later sequence of the photoperiodic response may or may not be expressed depending on the mode of interaction between them.     

Factors Mediating the Vitamin B12 Requirement of Euglena

SYNOPSIS. Deprived of vitamin B₁₂, Euglena gracilis strain Z ceases to divide which we believe to be a function of the light regime: division inhibition occurs more quickly in continuous light than in alternating (6L : 6D) light and not at all in total darkness. This phenomenon is dependent on the carbon source; cells grown in glutamate-malate medium do not divide regardless of the culture conditions while dl -lactate as carbon source permits growth in darkness in the absence of B₁₂. Conditions which lead to an increased O₂ or decreased CO₂ tension in the medium, such as agitation in darkness or incubation in red or white light, result in inhibition of division. This inhibition can be reversed by re-transferring the cells to still culture in the dark or, in the case of light-induced blockage, by the addition of DCMU.     

Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods

Short photoperiod induces growth cessation in seedlings of Norway spruce ( Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA₉ and GA₂₀ can not induce growth. In contrast application of GA, and GA₄ induced shoot elongation. The results indicate that 3β-hydroxylation of GA₉ to GA₄ and of GA₂₀ to GA₁ is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA₁, GA₃, GA₄, GA₇, GA₉, GA₁₂, GA₁₅, GA₁₅, GA₂₀, GA₂₉, GA₃₄ and GA₅₁ were identified by combined gas chromatography-mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and ¹⁴C-labelled GAs as intermal standards. In short days, the amounts of GA₉, GA₄ and GA₁ are less than in plants grown in continuous light. There is no significant difference in the amounts of GA₃, GA₁₂, and GA₂₀ between the different photoperiods. The lack of accumulation of GA₉ and GA₂₀ under short days is discussed.     

Nocturnal activity in a diurnal rodent (Arvicanthis niloticus): the importance of masking

It is known that day-active Nile grass rats, Arvicanthis niloticus, increase the amount of activity in the night relative to that in the day when provided with running wheels. This was confirmed in the present study. Animals without a wheel displayed 69.0% of their general activity in the L phase of a 12:12 h light-dark cycle; animals provided with wheels had only 48.6% of their wheel revolutions in the light. The contribution of direct (masking) responses to light to the increased nocturnality of animals with wheels was examined in two experiments. In experiment 1, masking was tested by exposing the animals to repeated cycles of 30 min of entraining light and 30 min of a different, usually dimmer light, during the L phase of a 12:12 h light-dark cycle. For animals with wheels, there was more running during the 30-min pulses of dim light or darkness than during the 30-min periods of entraining light. In contrast, for animals without wheels, there was more general activity during the 30-min periods of entraining light than during the 30-min pulses of dim light or darkness. In experiment 2, the animals were first exposed to a 12:12 h light-dark cycle and then put on a 1:10:1:12 h LDLD skeleton photoperiod. Animals with wheels increased their running during the subjective day of the skeleton photoperiod compared to that in the actual day of the 12:12 h light-dark cycle. Animals without wheels showed similar levels of general activity during the subjective day of the skeleton photoperiod and the actual day of the 12:12 h cycle. These experiments demonstrate that when Nile rats have running wheels, their increased nocturnal activity is associated with an increased suppression of locomotion in direct response to light. It is possible that changes in masking responses to light may be an essential and integral component of switching between diurnal and nocturnal activity profiles.     

Thermoperiod-photoperiod interactions in the determination of diapause in Ostrinia nubilalis

Photoperiodic determination of larval diapause in Ostrinia nubilalis is shown to be strongly influenced by superimposed thermoperiods, here termed “thermophotoperiods.” Thermoperiodic cryophase temperatures (0–25°C) exert effects that are markedly different from responses evoked by thermophotoperiodic cryoscotophases of the same temperatures. The differences are attributed to the presence or absence of light (thermophotophase or thermophase). Perturbations of 12 h dark: 12 h light and 10 h dark: 14 h light photoperiods by low-temperature pulses of 4 h duration demonstrated that the biological clock reactions associated with both the scotophase and photophase are sensitive to temperature. Statistically significant thermoperiod-photoperiod interactions have been demonstrated.     

Demographic parameters of cotton aphid, Aphis gossypii Glover （Homoptera： Aphididae） on five cotton cultivars

Life table parameters of the cotton aphid, Aphis gossypii Glover, were estimated on five cotton cultivars （‘ Sealand＇ ,‘Siokra＇ ,＇ Vararnin＇ ,‘ Bakhtegan＇ and ‘ Sahel＇ ）. Demographic parameters of the cotton aphid were assessed at 27.5 ± 1 ℃, 65% ＋ 10% RH and a photoperiod of 14：10 （L： D）h. The shortest developmental time for the nymphal stages was 5.5 days on ‘Siokra＇ and the longest was 6.1 days on‘ Sealand＇. The highest offspring per female was 29.6 on ‘Sahel＇ and the lowest was 15.3 on ‘Sealand＇. The rm values varied from 0.272 on ‘Sealand＇ to 0.382 （day^-1） on ‘Varamin＇. Jackknife estimates of the A. gossypii parameters on these cultivars indicated the greatest developmental rate and fecundity on ‘ Varamin＇ and the poorest on ‘ Sealand＇ cultivar.     

Regulation of the loss of frost hardiness in Pinus radiata by photoperiod and temperature

Abstract. In controlled environments, the interactive effects of warm (16: 8°C, day: night) and cool (12: 4°C, day: night) temperatures and long (13.5 h) and short (10 h) photoperiods on the dehardening of seedlings of Pinus radiata D. Don were investigated. In another experiment, the effect of four photoperiods from 9 to 14 h was examined. In a third, dehardening at constant temperatures from 5 to 17°C was followed. There was no evidence for an interaction between photoperiod and temperature. Dehardening was temporarily delayed by photoperiods below about 10 h, but there was no other quantitative effect of photoperiod. At constant temperatures, the rate of dehardening was initially constant but declined as the minimum summer frost hardiness was reached. In the initial phase the rate of dehardening was a linear function of temperature, increasing from 0.05°C day⁻¹ at 8°C to 0.30 °C day⁻¹ at 17°C. Temperature controlled the loss of frost hardiness by regulating the rate of dehardening.     

The adult eclosion rhythm in Hyphantria cunea (Lepidoptera: Arctiidae): Endogenous and exogenous light effects

Abstract

Endogenous and exogenous effects of light on adult eclosion in Hyphantria cunea were tested by exposure to various light regimes. Regression analysis showed that the position of the eclosion peak after lights on was proportional to the length of the photophase, and that the peak was influenced by the timing of both lights‐on and lights‐off. Under photoperiods of 2–12 hours LD cycle, the eclosion peak was situated after lights‐off, but moved into the light phase as the photophase increased to 22 hours. Pupae were exposed to 3 “skeleton”; photoperiods of LDLD2:2:6:14, 4:2:4:14 and 6:2:2:14. Under the first of these, most adults emerged at the start or just before the longest dark period. Under the second and third skeleton regimes, 20% and 70% respectively of pupae emerged during the shorter dark period. When the compound eyes of the pharate adults were covered, adults smerged 1–4 hours before lights‐off under LD10:14, compared to a control group which emerged just after lights‐off. When pupae were transferred from LD to LL or DD conditions, the eclosion peak occurred approximately every 24 hours after the last LD peak. Results suggest that light received by the compound eyes influences the eclosion rhythm, either through an exogenous masking effect, or by altering the phase of the pacemaker controlling eclosion.     

Entrainment Properties of the Locomotor Activity Rhythm of Drosophila melanogaster Under Different Photoperiodic Regimens

In this paper we report the results of an experiment to assess how closely repeated brief light pulses (LPs) mimic the effects of 12:12 h light/dark (LD) cycles (PPc). The locomotor activity rhythm of individual fruit flies from a laboratory population of Drosophila melanogaster was monitored under four different photoperiodic regimens, created using 12 h of light and 12 h of darkness or brief light pulses (LPs). The phase relationship (Ψ) and the stability (precision) of the locomotor activity rhythm during entrainment were estimated in order to compare the state of the circadian clocks under the four different photoperiodic regimens. The flies (n = 72) were subjected to four different LD cycles: (i) 12 h of light and 12 h of darkness (complete photoperiod, PPc); (ii) a single brief LP of 15 min duration presented close to the onset of activity (SLP-1); (iii) a single brief LP of 15 min duration administered close to the offset of activity (SLP-2); and (iv) two brief LPs administered 12 h apart (skeleton photoperiod, PPs). The locomotor activity rhythm of the flies was first monitored under constant darkness (DD) for about 10 days and then under the four different photoperiodic regimens for about 10 days, and finally in DD for the remainder of the experiment. The Ψ of the locomotor activity rhythm and its precision under PPc and PPs did not differ significantly, but they were significantly different from the SLP-1 and SLP-2 conditions. The results provide interesting insights into photoentrainment mechanisms of circadian clocks in D. melanogaster, and suggest that skeleton photoperiods, but not single brief LPs, mimic the actions of complete photoperiods.     

Capacity of cytochrome and alternative path in coupled and uncoupled root respiration of Pisum and Plantago

A critical duration of darkness must be exceeded for the photoperiodic induction of flowering in short-day plants. This requires detection of the light/dark transition at dusk and the coupling of this information to a time-measuring system.
Lowering the P_fr/P_tot, ratio photochemically at the end of the day did not accelerate the onset of dark timing in Pharbitis nil Choisy cv. Violet. Time-measurement was initiated when, with no change in spectral quality, the irradiance fell below a threshold value. Thus, if the light/dark transition at dusk is sensed by a reduction in P_fr, this reduction can be achieved as rapidly through thermal reactions as through photochemical ones. When given at hourly intervals during a 6-h extension of a 24-h main light period in white light, pulses of red light were as effective as continuous red light in delaying the onset of timing; pulses every 2 or 3 h were less effective. The effectiveness of intermittent red light indicates that phytochrome is the photoreceptor and the requirement for frequent exposures suggests that P_fr is lost rapidly in the dark. However, the red light pulses could not be reversed by far-red light, which argues against this hypothesis. An alternative explanation is that the perception of light as being continuous occurs only when "new" P_fr is regenerated sufficiently frequently.
The nature of the coupling of the dusk signal to the time-measuring system is discussed and it is suggested that the effect of each red light pulse is to delay the phase of the photoperiodic rhythm by 1–3 h.     

Entrainment of 2 subjective nights by daily light:dark:light:dark cycles in 3 rodent species

Recent work with exotic 24-h light:dark:light:dark (LDLD) cycles indicates surprising flexibility in the entrainment patterns of Syrian hamsters. Following exposure to an LDLD cycle, hamsters may adopt a form of rhythm splitting in which markers of subjective night (e.g., activity, melatonin) are expressed in each of the twice daily scotophases. This pattern contrasts markedly with that of conventionally entrained hamsters in which markers of subjective night are expressed once daily in only 1 of the 2 dark periods. The "split" entrainment pattern was examined further here in Syrian and Siberian hamsters and in mice exposed to LDLD 7:5:7:5, a condition that reliably induces split activity rhythms in all 3 species. The phase angle of entrainment and activity duration were generally similar comparing the 2 daily activity bouts in each species. The stability of this split entrainment state was assessed by deletions of photophases on individual days, by exposure to skeleton photoperiods, and by transfer to constant darkness. As in Syrian hamsters, the one-time substitution of darkness for one 7-h photophase did not grossly alter activity patterns of Siberian hamsters but acutely disrupted the split rhythms of mice. Skeleton light pulses of progressively shorter duration did not significantly alter split entrainment patterns of either Syrian or Siberian hamsters. Both species continued to exhibit stable entrainment with activity expressed in alternate scotophases of an LD 1:5 cycle presented 4 times daily. In contrast, the split activity rhythms of mice were not maintained under skeleton pulses. In constant darkness, rhythms of Siberian hamsters remained distinctly split for a minimum of 2 cycles. Split entrainment to these novel LDLD and 4-pulse skeleton lighting regimes demonstrates a marked degree of plasticity common to the circadian systems of several rodent species and identifies novel entrainment patterns that may be reliably elicited with simple environmental manipulations. Inter- and intraspecific differences in the stability of split activity rhythms likely reflect differences in coupling interactions between the component circadian oscillators, which, adopting separate phase relations to these novel LD cycles, yield a split entrainment pattern.     

Photoperiodic control of circadian activity rhythms in diurnal rodents

The responses of red squirrels(Tamiasciurus hudsonicus) and eastern chipmunks(Tamias striatus) to complete and skeleton light-dark (LD) cycles were compared. The skeletons, comprised of two 1-h pulses of light per day, effectively simulated the complete photoperiods in the squirrels, but not the chipmunks. Skeleton photoperiods greater than 12-h caused the chipmunks to shift activity from the longer to the shorter of the two intervals between the pulses. To interpret the mechanism of phase control, squirrels and chipmunks were kept in continuous darkness and exposed to 1-h light pulses every 10 days. The time-course of entrainment was also quantified. Both techniques produced light-response curves. The data suggest that the parametric and non-parametric contributions to entrainment are different in these two rodent species.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Effect of temperature and photoperiod on the calling behaviour of a migratory insect, the oriental armyworm Mythimna separata

Abstract The pre-calling period (PCP), between emergence and first release of pheromone, determines the number of nights over which female Mythimna separata (Walker) (Lepidoptera: Noctuidae) can express their migratory potential. In its seasonal migrations in eastern Asia, this armyworm penetrates to latitudes at which it is unable to over-winter but at which reliable photoperiodic and temperature cues anticipate the deterioration of conditions. The effect of these environmental factors on PCP was examined in moths descended from samples collected in Nanjing (32^oN) during the summer migration. Under LD 14:10h, a reduction in temperature, from 23^oC during larval development to 18^oC from 24 h after pupation, resulted in a twofold increase in PCP compared with insects held at 23^oC. At 23^oC, short days (LD 12:12 h) extended PCP but the magnitude of the response was increased under a regime of decreasing photoperiod, from LD 15:9h, to LD 12:12 h through larval, pupal and adult development. Further experiments demonstrated that the response depended on a decrease in photoperiod from pre-pupal stage to adult emergence (the pupal period is spent below ground). A reduction of 50–60min over the 13–15 day pupal period at 23^oC was effective. The significance of decreasing photoperiods, irrespective of absolute levels, as a cue for species whose migrations traverse substantial ranges of latitude is considered and the results are discussed in relation to the genetic determination of PCP in M.separata and to its seasonal migrations in eastern China.