Seasonal and daily rhythms of body temperature in the European hamster (Cricetus cricetus) under semi-natural conditions

Body temperature of five European hamsters exposed to semi-natural environmental conditions at 47° N in Southern Germany was recorded over a 1.5-year period using intraperitoneal temperature-sensitive radio transmitters. The animals showed pronounced seasonal changes in body weight and reproductive status. Euthermic body temperature changed significantly throughout the year reaching its maximum of 37.9±0.2°C in April and its minimum of 36.1±0.4°C in December. Between November and March the hamsters showed regular bouts of hibernation and a few bouts of shallow torpor. During hibernation body temperature correlated with ambient temperature. Monthly means of body temperature during hibernation were highest in November (7.9±0.8°C) and March (8.2±0.5°C) and lowest in January (4.4±0.7°C). Using periodogram analysis methods, a clear diurnal rhythm of euthermic body temperature could be detected between March and August, whereas no such rhythm could be found during fall and winter. During hibernation bouts, no circadian rhythmicity was evident for body temperature apart from body temperature following ambient temperature with a time lag of 3–5 h. On average, hibernation bouts lasted 104.2±23.8 h with body temperature falling to 6.0±1.7°C. When entering hibernation the animals cooled at a rate of -0.8±0.2°C·h^-1; when arousing from hibernation they warmed at a rate of 9.9±2.4°C·h^-1. Warming rates were significantly lower in November and December than in January and February, and correlated with ambient temperature (r=-0.46, P<0.01) and hibernating body temperature (r=-0.47, P<0.01). Entry into hibrnation occured mostly in the middle of the night (mean time of day 0148 hours ±3.4 h), while spontaneous arousals were widely scattered across day and night. For all animals regression analysis revealed free-running circadian rhythms for the timing of arousal. These results suggest that entry into hibernation is either induced by environmental effects or by a circadian clock with a period of 24 h, whereas arousal from hibernation is controlled by an endogenous rhythm with a period different from 24 h.Abbreviations bw body weight - CET central European time - T _a ambient temperature - T _b body temperature - TTL transistor-transistor logic     

Maintenance of biological rhythms during hibernation in Eastern woodchucks (<Emphasis Type="Italic">Marmota monax</Emphasis>)

We undertook a study to determine presence of circadian rhythms during woodchuck hibernation using continuously monitored body temperatures. Males had shorter torpor and longer euthermic periods than females. Circular statistics revealed a significant mean vector for males entering into torpor (10:21 h), but not for females. No significant mean vector was found for male or female arousal from torpor. A contingency test was applied to the torpor bout durations. All 7 males tested had significant τ’s between 24 and 26 h, while 6 of the 13 females tested had significant τ’s with a range of 22–27 h. These results implicate a free-running circadian clock during torpor bouts. Overall, the data support the existence of biological rhythms during hibernation in woodchucks, especially for males during arousals. Since entries into torpor appear to be synchronized for males, arousal periods may be used to resynchronize their circadian system. The persistence of biological rhythms during hibernation may help to insure successful mating in the spring after emergence.     

Timing of torpor bouts during hibernation in European hamsters (Cricetus cricetus L.)

Body temperature (T _b) of seven European hamsters maintained at constant ambient temperature (T _a = 8 °C) and constant photoperiod (LD 8:16) was recorded throughout the hibernating season using intraperitoneal temperature-sensitive HF transmitters. The animals spent about 30% of the hibernation season in hypothermia and 70% in inter-bout normothermy. Three types of hypothermia, namely deep hibernation bouts (DHBs), short hibernation bouts (SHBs), and short and shallow hibernation bouts (SSHBs), were distinguished by differences in bout duration and minimal body temperature (T _m). A gradual development of SSHBs from the diel minimum of T _b during normothermy could be seen in individual hamsters, suggesting a stepwise decrease of the homeostatic setpoint of T _b regulation during the early hibernation season. Entry into hibernation followed a 24-h rhythm occurring at preferred times of the day in all three types of hypothermia. DHBs and SHBs were initiated approximately 4 h before SSHBs, indicating a general difference in the physiological initiation of SSHBs on the one hand and DHBs and SHBs on the other. Arousals from SHBs and SSHBs also followed a 24-h rhythm, whereas spontaneous arousals from DHBs were widely scattered across day and night. Statistical analyses of bout length and the interval between arousals revealed evidence for a free-running circadian rhythm underlying the timing of arousals. The results clearly demonstrate that entries into hypothermia are linked to the light/dark-cycle. However, the role of the circadian system in the timing of arousals from DHBs remains unclear. Accepted: 11 December 1996     

Energy-dependent phases of the circadian clock and the clock-controlled leaf movement in Phaseolus coccineus L.

The energy requirements of the various phases of the circadian clock in the laminar pulvini cells of primary leaves of Phaseolus coccineus L. were investigated using 4-h pulses of NaCN (5 mM) and NaN₃ (1 mM). The induced phase shifts were calculated from the timing of the subjective night position during the third cycle after the treatment. Both inhibitors produce advances during phases which are correlated with the upward movement of the leaf (ca. 0–12 h after the maximum of the subjective night position) and during phases which are correlated with the downward movement of the leaf (ca. 20–28 h after the maximum of the subjective night position). Maximal advances are induced during the phase which is correlated with the maximum of the subjective night position (hour 0), whereas during phases which are correlated with the subjective day position (ca. 12–20 h after the maximum of the subjective night position) the inhibitors have no effect or induce only small advances. These results demonstrate that the part of the circadian cycle which, according to Bünning's tension-relaxation model of the circadian clock, is characterized by features of relaxation, represents a sequence of phases with decreasing energy requirement, whereas the tension part of the circadian cycle represents a sequence of phases with increasing energy requirement. The energy requirement for changing and maintaining the leaf positions was investigated by continuously offering NaCN, NaN₃, and dinitrophenol (DNP) to leaves with intact and half (flexor cut away) pulvini. The substances inhibit in both pulvini the upward movement or induce a downward movement, depending on the leaf position, when the transfer to the inhibitor solution takes place. These results give evidence that the movement of intact pulvini reflects the turgor (volume) state of the extensor cells and that the increase of turgor (volume) and high turgor (volume) state requires more energy than the decrease of turgor (volume) or low turgor (small volume) state. Therefore, the time course of the energy requirements of the circadian clock and the clock-controlled turgor (volume states or leaf movement) is out of phase during a circadian cycle. Consequently the reaction of the clock-controlled leaf movement to the reduced energy supply can mask the clock behavior in pulse and step experiments. The phase response curves towards CN^- and N ₃ ^- reflect the time course of the CN^--induced membrane depolarizations (the energy requirement of the electrogenic pump) in extensor cells of the pulvinus (Freudling et al. (1980), Plant Physiol. 65, 966–968), and both are out of phase with the time course of the energy requirement of the turgor. Consequently it is hypothesized that in Phaseolus advances are due to membrane depolarization and that at least in this organism electric properties of the plasmalemma are essentially involved in the mechanism of the circadian clock.Abbreviations LD light-dark cycle - LL continuous light - DNP dinitrophenol This paper is dedicated to Professor Erwin Bünning on the occasion of his 75th birthdayIn this paper zero corresponds to the second maximum of the subjective night position of the leaves after transfer to constant conditions. Zero to twelve hours corresponds approximately to the upward movement of the leaves, 12–20 h to the elevated (subjective day) position, and 20–28 h to the downward movement of the leaves. In other circadian systems Pittendrigh's CT (circadian time) convention is used. CT 00 is the time of dawn after a 12-h light/12-h dark cycle. Since in Phaseolus the plants are raised in a LD cycle different from 12:12 and since the phases at dawn differ considerably from leaf to leaf and are furthermore not precisely determinable (whereas the subjective night position of the leaves is a well-defined and recognizable phase) this convention is not followed in Phaseolus. Phase zero in Phaseolus corresponds to approximately CT 18 in other systems     

Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Erinaceus europaeus

Summary Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (T _b ) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of T _b were collected. The hedgehogs were exposed to natural environmental conditions at 57°N in NE Scotland. Hedgehogs showed seasonal changes in mean daily euthermic T _b ,with a July maximum of 35.9±0.2°C, a September minimum of 34.7±0.9°C, and a marked circadian T _b cycle that correlates closely with photoperiod. Maximal T _b occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum T _b was most marked between April and September. The circadian T _b cycle was least correlated with photoperiod during winter. Hibernal T _b during winter correlated with ambient temperature (T _a ),it was maximal in September (17.7±1.0°C) and minimal in December (5.2±0.9°C). Apart from the tracking of T _a and T _b during hibernal bouts, with a time-lag of 4–6 h, circadian rhythmicity of hibernal T _b was not evident. However, the T _b of hibernating hedgehogs rose significantly when T _a fell below — 5°C, although the animals did not neccessarily arouse. Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45±5.1 h GMT while the mean time of the start of spontaneous arousal from hibernation was 11:53±4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night, when euthermic hedgehogs have maximalT _b ,or in deep hibernation around midday, when euthermic hedgehogs have minimal T _b .Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T _b falling to 25.8±3.1 °C. Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with T _a or body mass. TST bouts started at 06:51±4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear, but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4°C·h^-1, and when entering hibernation cooled at 7.9±1.9°C·h^-1. Warming rates were slightly higher during mid-winter when T _b and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31°N. These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.Abbreviations T _a ambient temperature - T _b body temperature - CSD circular standard deviation - SWS slow wave sleep - TST transient shallow torpor     

Temporal organisation of hibernation in wild-type and tau mutant Syrian hamsters

The temporal pattern of hibernation was studied in three genotypes of Syrian hamsters with different circadian periodicity to assess a potential circadian control of alternating torpor and euthermy. We recorded the pattern of hibernation by measuring activity in continuous dim light and constant environmental temperature (6 +/- 1 degrees C). In spite of differences in the endogenous circadian period of three genotypes (tau +/+: approximately equals 24 h, tau +/-: approximately equals 22 h, and tau -/-: approximately equals 20 h) torpor bout duration was statistically indistinguishable (tau +/+: 86.9+/-5.3 h; tau +/-: 94.2+/-3.3 h; tau -/-: 88.8+/-6.2 h). The time between two consecutive arousals from torpor showed unimodal distributions not significantly different between genotypes. The first entry into torpor occurred within the active phase of the circadian cycle in all genotypes whereas the first arousal from torpor appeared to be timed randomly with respect to the prior circadian cycle. The amplitude of the activity rhythm was lower after hibernation compared with the amplitude before hibernation. The results suggest that in the Syrian hamster the circadian system does not control periodicity of torpor and arousal onsets in prolonged hibernation at 6 degrees C.     

Identification of a Circadian Clock-Controlled Neural Pathway in the Rabbit Retina

Background

Although the circadian clock in the mammalian retina regulates many physiological processes in the retina, it is not known whether and how the clock controls the neuronal pathways involved in visual processing.

Methodology/Principal Findings

By recording the light responses of rabbit axonless (A-type) horizontal cells under dark-adapted conditions in both the day and night, we found that rod input to these cells was substantially increased at night under control conditions and following selective blockade of dopamine D₂, but not D₁, receptors during the day, so that the horizontal cells responded to very dim light at night but not in the day. Using neurobiotin tracer labeling, we also found that the extent of tracer coupling between rabbit rods and cones was more extensive during the night, compared to the day, and more extensive in the day following D₂ receptor blockade. Because A-type horizontal cells make synaptic contact exclusively with cones, these observations indicate that the circadian clock in the mammalian retina substantially increases rod input to A-type horizontal cells at night by enhancing rod-cone coupling. Moreover, the clock-induced increase in D₂ receptor activation during the day decreases rod-cone coupling so that rod input to A-type horizontal cells is minimal.

Conclusions/Significance

Considered together, these results identify the rod-cone gap junction as a key site in mammals through which the retinal clock, using dopamine activation of D₂ receptors, controls signal flow in the day and night from rods into the cone system.     

Optimal and central-place foraging theory applied to a desert harvester ant,Pogonomyrmex californicus

Summary Certain predictions of optimal- and central place-foraging theory were tested on the desert harvester ant, Pogonomyrmex californicus. Colonies were offered three different sizes of oat seed and found to maximize net energy intake (ei) over time (t _i ) by harvesting the seed sizes with the highest e _i /t _i rank. Two aspects of t _i were measured that were assumed constant in previous studies. The handling components of t _i (time required to manipulate the seed and travel time back to the colony with the food) were measured and found to be positively correlated with seed size. The manipulation success rate (the percentage of handled seeds successfully picked up) decreased with increased seed size. These results point out how important it is to measure all parameters of e _i /t _i rather than to assume constancy with both prey type and foraging distance. The relative abundance of less preferred food types was important in determining the proportion of preferred types in the diet. The food supply of eight colonies was manipulated experimentally over a 25-day period. Four deprived colonies were constrained within aluminum enclosures to prevented foraging. The remaining four satiated colonies were given food ad libitum. The niche breadths of the treated colonies were then compared to controls, but found not to differ significantly. Seed baits were offered at three distances from the colony to test whether selectivity increased with disance. Contrary to theoretical predictions, all colonies harcested about the same proportion of each seed size at each distance.     

Effect of T3 administration on electrophysiological properties of lizard ventricular muscle fibres

We investigated the effects on the electrophysiological properties of ventricular muscle fibres from lizards kept at 20 °C of mild and severe hyperthyroidism. The hyperthyroidism was induced by a 4-day treatment with either 0.025 or 1.0 g triiodothyronine g^-1 body weight, documented by increased serum levels of thyroid hormone. Triiodothyronine treatment did not modify the duration of the action potential recorded in vitro at 25 °C from ventricular muscles stimulated at 1 Hz. Recordings at higher temperatures were associated with a faster repolarization phase and a decrease of action potential duration in both euthyroid and hyperthyroid animals. However, in lizards treated with 1.0 g triiodothyronine · g^-1 body weight, the 90% repolarization recovery times at 30 and 35 °C (95.6±14.9 ms and 53.0±6.0 ms, respectively), were significantly shorter than normal (177.6±29.2 and 107.2±18.1 ms, respectively). Action potential duration was also dependent on stimulation frequency of the preparations. Increased frequency led to significant decrease of the duration of action potentials recorded at 25 °C. In euthyroid preparations the reductions in 90% repolarization recovery time, owing to increases in stimulation frequency to 2.5 and 5 Hz, were 19.3±1.7 and 35.6±2.0 ms, respectively. In hyperthyroid preparations, the reductions in the 90% recovery time due to stimulus frequency increases varied from 35.4±1.9 and 58.1±2.1 ms at low hormone doses to 38.9±2.0 and 58.2±2.1 ms at high hormone doses. As a result of these differences, the action potential durations recorded from the two hyperthyroid preparations at high stimulation rates were shorter than from euthyroid preparations. The results obtained suggest that lizard cardiac tissue is responsive to hormone action at low environmental temperature, but the effects of such action become evident when the temperature and heart rate increase.Abbreviations A _20% integrated area above 20% depolarization - bw body weight - hw heart weight - FT ₃ free triiodothyronine - RT ₄₀ RT ₅₀ RT ₇₀ and RT ₉₀ recovery time at 40, 50, 70, and 90% of repolarization, respectively - T ₃ triiodothyronine - TT ₃ Total triiodothyronine     

Function of the Shaw potassium channel within the Drosophila circadian clock

Background

In addition to the molecular feedback loops, electrical activity has been shown to be important for the function of networks of clock neurons in generating rhythmic behavior. Most studies have used over-expression of foreign channels or pharmacological manipulations that alter membrane excitability. In order to determine the cellular mechanisms that regulate resting membrane potential (RMP) in the native clock of Drosophila we modulated the function of Shaw, a widely expressed neuronal potassium (K⁺) channel known to regulate RMP in Drosophila central neurons.

Methodology/Principal Findings

We show that Shaw is endogenously expressed in clock neurons. Differential use of clock gene promoters was employed to express a range of transgenes that either increase or decrease Shaw function in different clusters of clock neurons. Under LD conditions, increasing Shaw levels in all clock neurons (LNv, LNd, DN₁, DN₂ and DN₃), or in subsets of clock neurons (LNd and DNs or DNs alone) increases locomotor activity at night. In free-running conditions these manipulations result in arrhythmic locomotor activity without disruption of the molecular clock. Reducing Shaw in the DN alone caused a dramatic lengthening of the behavioral period. Changing Shaw levels in all clock neurons also disrupts the rhythmic accumulation and levels of Pigment Dispersing Factor (PDF) in the dorsal projections of LNv neurons. However, changing Shaw levels solely in LNv neurons had little effect on locomotor activity or rhythmic accumulation of PDF.

Conclusions/Significance

Based on our results it is likely that Shaw modulates pacemaker and output neuronal electrical activity that controls circadian locomotor behavior by affecting rhythmic release of PDF. The results support an important role of the DN clock neurons in Shaw-mediated control of circadian behavior. In conclusion, we have demonstrated a central role of Shaw for coordinated and rhythmic output from clock neurons.     

Correlation between circadian periods and cellular activities in Paramecium bursaria

Paramecium bursaria shows a circadian rhythm of photoaccumulation: photoaccumulation is stronger during the day than at night. We obtained five strains of P. bursaria having different circadian periods under continuous light conditions, ranging from 20.9 to 27.9 h. Various physiological activities were compared in the cells of these strains. The periods of contractile vacuole contraction were in the range 10–15 s, which was almost proportional to the periods of the circadian rhythm in each strain. Swimming velocities were inversely proportional to the circadian period; i.e. swimming velocities were high in strains whose circadian periods were short. Resting membrane potential was more depolarized in strains with longer circadian periods. Finally, the membrane resistance of the resting state was reduced in proportion to the increase of the circadian period. Such correlation between the cellular properties and the circadian period suggests that the circadian clock mechanism is associated with various physiological activities of the cell.     

Daily and circadian rhythms of locomotor activity in the American lobster, Homarus americanus

It is widely accepted that American lobsters, Homarus americanus (Milne-Edwards), are nocturnally active. However, the degree to which this rhythm is expressed by different individuals and the underlying causes of lobster activity rhythms, are poorly understood. In order to address these issues we recorded daily patterns of lobster locomotion using two novel techniques. In the first, reed switch assemblies were used to monitor the distance traveled by freely moving lobsters (n=43), each fitted with a small magnet, as they walked around a 1 m diameter racetrack. The advantages of this technique included: (1) lobsters were freely moving; (2) the system could be deployed in laboratory tanks or in the field and; (3) actual distances moved were measured, not just relative activity. The second technique involved placing individual lobsters (n=10) into custom-designed running wheels. This allowed for continuous monitoring of locomotor activity for extended durations (>45 days) under normal light/dark (L/D) cycles, as well as in constant darkness (D/D) and constant light (L/L).Under ambient light conditions lobsters in the racetracks moved an average of 60.1±6.5 m/day in flow-through seawater tanks. Overall, lobsters were significantly more active at night, moving 4.1±0.4 m/h in the dark vs. 1.0±0.2 m/h in the light. However, many of the lobsters moved as much during the day as during the night.Lobsters in the running wheels moved an average of 36.6±11.7 m/day and 80% expressed clear daily rhythms of activity, with a mean periodicity of 24.0±0.1 h under L/D conditions. Under D/D conditions 90% of the animals expressed free-running circadian rhythms with a mean periodicity of 24.2±0.3 h, indicating that this species possesses endogenous rhythmicity. While the running wheel results show that the nocturnal pattern of locomotor activity for this species is strongly influenced by an endogenous circadian clock, the results from the racetracks show that there is remarkable variability in the extent to which they express this pattern under natural conditions.     

The action potential of Dionaea muscipula Ellis

The intention of this investigation was to acquire more concise information about the nature of the action potential of Dionaea muscipula Ellis and the different types of cells generating and conducting it. It is shown by microelectrode measurements that, besides the sensory cells, all the major tissues of the trap lobes are excitable, firing action potentials with pronounced after-hyperpolarizations. The action potentials are strictly dependent on Ca²⁺. Their peak depolarizations are shifted 25–27 mV in a positive direction after a tenfold increase in external Ca²⁺ concentration. Perfusions with 1 mM ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA) or 1 mM LaCl₃ completely inhibit excitability. Magnesium ions only slightly affect the peak depolarizations but considerably prolong action potentials. Sodium azide and 2,4-dinitrophenol also abolish excitation, probably by reducing the intracellular ATP concentration. Furthermore, it is tested whether the sensory cells can be distinguished from the other cells of the trap by their electrical behaviour. The resting potentials of sensory cells (-161±7 mV) and mesophyll cells (-155±8 mV) are of the same magnitude. Changes in external ion concentrations affect resting and action potentials in both cell types in a similar way. Additional freeze-fracture studies of both cell types reveal similar numbers and distributions of intramembrane particles on the fracture faces of the plasma membrane, which is most likely the mechanosensor. These findings stress the view that the high mechanosensitivity of the sensory hair results from its anatomy and not from a specialized perception mechanism. It is proposed that trap closure is triggered by a rise in the cytoplasmic concentration of Ca²⁺ or a Ca²⁺-activated regulatory complex, which must exceed a threshold concentration. Since the Ca²⁺ influx during a single action potential does not suffice to reach this threshold, at least two stimulations of the trap are necessary to elicit movement.Abbreviations DNP 2,4-dinitrophenol - EF exoplasmic fracture face - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - E_m membrane potential - E_m,r resting potential - PF protoplasmic fracture face Dedicated to Professor Karl-Ernst Wohlfarth-Bottermann on the occasion of his 65th birthdayA preliminary report was presented at the 14th International Botanical Congress, Berlin, July 1987. This work is part of the dissertation (D5) of D.H.     

Phase shifts of the adult locomotor activity rhythm in Calliphora vicina induced by non-steroidal ecdysteroid agonist RH 5849

RH 5849, a non-steroidal ecdysteroid mimic, was found to cause consistent phase shifts in the circadian rhythm of locomotor activity of the blowfly, Calliphora vicina. This compound causes phase advances in the early subjective night and phase delays in the late subjective night. This effect is the opposite, but not the mirror image of the phase response curve obtained for 1 h light pulses. This suggests that ecdysteroids might act as entraining agents via the output pathway by feedback to clock neurons in the brain. A computer model based on 12 pacemaker neurons with circadian periods ( values) from short to long without simulated feedback from the ecdysteroid system becomes arrhythmic; with feedback, the oscillators become synchronized to a common period. The possible role of ecdysteroids as endogenous synchronizing agents in the insect circadian system is discussed.     

Mutations in leaf starch metabolism modulate the diurnal root growth profiles of Arabidopsis thaliana

Roots of Arabidopsis thaliana exhibit stable diurnal growth profiles that are controlled by the circadian clock. Here we describe the effects of mutations in leaf starch metabolism on the diurnal root growth characteristics of Arabidopsis thaliana. High temporal and spatial resolution video imaging was performed to quantify the growth kinetics of Arabidopsis wild-type as well as pgm, sex1, mex1, dpe1 and dpe2 starch metabolism mutants grown in three different photoperiods. As a result, root growth patterns of all genotypes displayed characteristic modifications in their diurnal kinetics that were also affected by the photoperiod. To further investigate the role of starch derived substrate deficiency on root growth, the effect of 0.05% extracellular sucrose was studied in 12 h-12 h light-dark cycles.Key words: diurnal root growth kinetics, dpe1, dpe2, mex1, pgm, sex1, starch metabolism, video imagingRoot growth of Arabidopsis thaliana is highly rhythmic with respect to the time of the day.^1–3 In general, root growth rates increase at night while most of the light period is characterized by declining elongation rates. Since a slow oscillation in root growth rate with a periodicity of approximately 24 h persists in free running conditions it was demonstrated that the circadian clock mediates these daily fluctuations.¹ Root growth at night is fueled by the degradation of starch within the leaves. Thus, a correspondence between the time taken to degrade starch reserves and the length of the night is important to optimize growth in C-limiting conditions. Gibon et al. observed a strong correlation between the rate of starch degradation and the relative growth rate when Arabidopsis Col-0 was grown in a range of different photoperiods.⁴ Therefore, to avoid periods of C starvation at the end of the night the circadian clock was postulated to function as a timer that adjusts degradation of starch to the prevailing length of the night.^1,5Root growth strongly depends on the supply of sucrose from the leaves. To investigate the effects of substrate depletion on root elongation at night, 12-day-old seedlings of Col-0, pgm and sex1 growing in a 16 h photoperiod were previously investigated by digital time resolved video imaging.¹ As a result, the diel growth response was strongly modified in pgm and sex1 as compared to the wild-type. Both mutants showed a pronounced inhibition of growth during the night and a gradual recovery of growth during the light period. To substantiate these findings, we here report on the root elongation patterns of additional mutants in starch metabolism, e.g., mex1, dpe1 and dpe2 detected at different photoperiods and elevated external sucrose supply.     

Early- and Late-Emerging Drosophila melanogaster Fruit Flies Differ in Their Sensitivity to Light During Morning and Evening

The authors derived early and late populations of fruit flies showing increased incidence of emergence during morning or evening hours by imposing selection for timing of emergence under 12:12?h light/dark (LD) cycles. From previous studies, it was clear that the increased incidence of adult emergence during morning and evening hours in early and late populations was a result of evolution of divergent and characteristic emergence waveforms in these populations. Such characteristic waveforms are henceforth referred to as “evolved emergence waveforms” (EEWs). The early and late populations also evolved different circadian clocks, which is evident from the divergence in their clock period (τ) and photic phase response curve (PRC). Although correlation between emergence waveforms and clock properties suggests functional significance of circadian clocks, τ and PRCs do not satisfactorily explain the early and late emergence phenotypes. In order to understand the functional significance of the PRC for early and late emergence phenotypes, the authors investigated whether circadian clocks of these flies exhibit any difference in photosensitivity under entrained conditions. Such differences would suggest that the light requirement for circadian entrainment of the emergence rhythm in early and late populations is different. To test this, they examined if early and late flies differ in their light utilization behavior, first by assaying their emergence rhythm under complete photoperiod and then in three different skeleton photoperiods. The results showed that early and late populations require different durations of light during the morning and evening to achieve their EEWs, suggesting that for the circadian entrainment of the emergence rhythm, early and late flies utilize light from different parts of the day. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)