Two <Emphasis Type="Italic">FLOWERING LOCUS T</Emphasis> (<Emphasis Type="Italic">FT</Emphasis>) homologs in <Emphasis Type="Italic">Chenopodium rubrum</Emphasis> differ in expression patterns

FLOWERING LOCUS T (FT) like genes are crucial regulators (both positive and negative) of flowering in angiosperms. We identified two FT homologs in Chenopodium rubrum, a short-day species used as a model plant for the studies of photoperiodic flower induction. We found that CrFTL1 gene was highly inducible by a 12-h dark period, which in turn induced flowering. On the other hand, photoperiodic treatments that did not induce flowering (short dark periods, or a permissive darkness interrupted by a night break) caused only a slight increase in CrFTL1 mRNA level. We demonstrated diurnal oscillation of CrFTL1 expression with peaks in the middle of a light period. The oscillation persisted under constant darkness. Unlike FT homologs in rice and Pharbitis, the CrFTL1 expression under constant darkness was very low. The CrFTL2 gene showed constitutive expression. We suggest that the CrFTL1 gene may play a role as a floral regulator, but the function of CrFTL2 remains unknown.     

Chloroplast development and the synthesis of chlorophyll and protochlorophyllide in Zostera transferred to darkness

Intact plants and isolated leaves of Zostera capricornii Martens ex Aschers were transferred from daylight to darkness. Substantial amounts of chloropyll a and b continued to accumulate in immature and mature tissue in the same ratio as in the light and were incorporated into chlorophyll-protein complexes in the thylakoids. A small amount of protochlorophyllide also accumulated in immature tissue in the dark. Proplastids and immature chloroplasts continued to develop into mature chloroplasts in the dark in the normal manner but prolamellar bodies, which are a conspicuous feature of immature chloroplasts, took longer to disperse than in the light. Protochlorophyllide accumulation and prolamellar-body formation were not correlated. The results indicate that Zostera has a genetic capacity for dark chlorophyll synthesis which is expressed in immature and mature leaf tissue and enables this plant to continue synthesising chlorophyll and assembling chloroplasts at night.Abbreviations Chl chlorophyll - T _o time of transfer to darkness     

Light pulse effect on the locomotor activity rhythm of Talitrus saltator (Montagu) (Crustacea,Amphipoda)

The locomotor activity rhythm of the sandhopper Talitrus saltator (Amphipoda Talitridae) was investigated in Madfoun beach. The rhythm was monitored in individual and group animals during 21 days at constant temperature. During the first two weeks, animals were kept under light–dark cycle (d1–d7) and constant darkness (d8–d14). Light pulses of 2 h were applied, at the end of the experimental night, during the first 3 days of the third week (d15–d18). Then, constant darkness was restored for the rest of the experiment (d19–d21). Results revealed that Talitrus saltator individuals as well as groups concentrated their activities in experimental night under light–dark cycle and in the presence of pulses; whereas, a clear drift of activity is observed under constant darkness. Periodogram analysis showed the presence of circadian component whatever the recording type. An ultradian period was revealed in individual recording whatever the regimen, while for groups, this component appeared only under nLD cycle. Furthermore, the locomotor rhythm is more defined under nLD cycle for individuals and in constant darkness for groups.     

Intracellular phosphorus metabolism and growth of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in dark/light cycles under various redox potential difference conditions

Phosphorus metabolism and growth of M. aeruginosa were studied under three different conditions of diel fluctuation in redox potential. Redox potential in the culture increased in light and decreased in dark in all treatments except one, when cysteine was added in darkness. Total phosphorus content in M. aeruginosa decreased in darkness and increased in light during exponential growth but increased continuously in the stationary phase. Conversely, polyphosphate (PolyP) accumulated in darkness but was lost in the light. Low redox potential in darkness promoted PolyP accumulation. Polyglucose and soluble orthophosphate may provide energy and phosphorus, respectively, for PolyP synthesis. PolyP was important to M. aeruginosa survival during poor growth conditions. If the redox potential difference in the dark/light cycle was large, M. aeruginosa initially grew faster, but soon lost viability.     

Rhabdom size and photoreceptor membrane turnover in a muscoid fly

Summary The cross-sectional area of rhabdomeres in the compound eye of the blowfly, Lucilia, was found to remain constant under 12 h light/12 h dark cyclic lighting, and 10 days constant light or darkness. It was reduced only slightly during 3 h light after 10 days darkness (by 21%), or on exposure to 2h darkness + 1.5 h light after 10 days light (by 10%). Morphological evidence indicates that shedding of photoreceptor membrane during turnover is achieved by an extracellular route, and by pinocytosis from the bases of the microvilli. The photoreceptor membrane shed by both mechanisms appears to accumulate in multivesicular bodies. The amount of photoreceptor membrane shedding, as indicated by numbers of multivesicular bodies, is constant throughout the day and night on cyclic lighting, decreases in constant darkness, but returns to its normal level after an exposure to 3 h light subsequent to 10 days darkness.     

Competition between perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus): the advantage of turning night into day

1. The outcome of interspecific competition for food resources depends both on the competitors’ sensory abilities and on environmental conditions. In laboratory experiments we tested the influence of daylight and darkness on feeding behaviour and specific growth rate (SGR) of two species with different sensory abilities. 2. We used perch (Perca fluviatilis) as a visually orientated, and ruffe (Gymnocephalus cernuus) as a mechano‐sensory oriented predator and tested their growth rates and behaviour under conditions of interspecific and intraspecific competition. Three different foraging conditions were used: food supplied (i) only during the day, (ii) only during the night or (iii) during both day and night. 3. In perch neither SGR nor feeding behaviour were influenced substantially by interspecific competition during daylight. During darkness their foraging behaviour changed markedly and their access to the food source as well as their SGR were negatively affected by the presence of ruffe. 4. Ruffe's foraging behaviour did not change during either day or night with interspecific competition. During the night ruffe's SGR was higher with interspecific competition, probably because of a release from intraspecific competition and the competitive inferiority of perch during the night. 5. Because of its seonsory abilities ruffe feeds predominantly at night, thereby reducing competitive interference from perch.     

CYCLING OF STOMATAL APERTURE IN LEAVES OF PLANTS WITH CRASSULACEAN ACID METABOLISM UNDER CONSTANT CONDITIONS

When leaves of plants with C₃ metabolism are detached and held in darkness, they senesce and the stomata close. Because the relation of senescence and stomatal closure is very close, if not actually causal, the question arose as to whether in the leaves of plants with Crassulacean acid metabolism whose stomata open at night the relationship to senescence would be reversed. Detached leaves of four species of Hoya, floated on water in constant darkness or constant light, were found to show no large differences in stomatal aperture (measured as diffusion resistance) between those in the light or dark, but the aperture changed in a regular circadian rhythm. In some leaves the rhythm was simple, in others the peak showed small secondary peaks, but in all cases the values were nearly the same in the light as in the dark, throughout the cycle. Previous culture of the intact plants under normal day/night conditions gave results similar to those with plants that had had prolonged culture under constant light or darkness. In those cases when the stomata were more open in the dark, the chlorophyll content was greater than when the stomata were more open in the light; but when they were more open in the light, the chlorophyll content showed little difference between light and dark. When the leaves had only their petioles in water they showed greater senescence in the light than in the dark, and the stomata were more tightly closed in the light, especially at the apical ends. All four species of Hoya gave similar results. We deduce that senescence of these leaves is modified by stomatal aperture, and generally in the same direction as in C₃ leaves, but that in continuous light or darkness the primary control over the aperture is the endogenous cycle.     

Rhythms of glycerophospholipid synthesis in retinal inner nuclear layer cells

The present study demonstrates that the biosynthesis of phospholipids in the inner nuclear layer cells of the chicken retina displays daily rhythms under constant illumination conditions. The vertebrate retina contains circadian oscillators and photoreceptors (PRCs) that temporally regulate its own physiology and synchronize the whole organism to the daily environmental changes. We have previously reported that chicken photoreceptors and retinal ganglion cells (RGCs) present significant daily variations in their phospholipid biosynthesis under constant illumination conditions. Herein, we demonstrate that cell preparations highly enriched in inner nuclear layer cells also exhibit a circadian-regulated phospholipid labeling after the in vivo administration of [(32)P]phosphate or [(3)H]glycerol both in animals maintained under constant darkness or light for at least 48h. In constant darkness, there was a significant incorporation of both precursors into phospholipids with the highest levels of labeling around midday and dusk. In constant light, the labeling of (32)P-phospholipids was also significantly higher during the day and early night whereas the incorporation of [(3)H]glycerol into phospholipids, that indicates de novo biosynthesis, was greater during the day but probably reflecting a higher precursor availability at those phases. We also measured the in vitro activity of phosphatidate phosphohydrolase and diacylglycerol lipase in preparations obtained from the dark condition. The two enzymes exhibited the highest activity levels late in the day. When we assessed the in vitro incorporation of [(14)C]oleate into different lysophospholipids from samples collected at different phases in constant darkness, reaction catalyzed by lysophospholipid acyltransferases II, labeling showed a complex pattern of daily activity. Taken together, these results demonstrate that the biosynthesis of phospholipids in cells of the chicken retinal inner nuclear layer exhibits a daily rhythmicity under constant illumination conditions, which is controlled by a circadian clock.     

Influence of gibberellin biosynthesis inhibitors on stem elongation and floral initiation on in vitro chicory root explants under dark and light conditions

Root explants of chicory (Cichorium intybus L.) were cultured in vitro under continuous light or darkness. On a standard medium (no plant growth regulators added), flowering-stems were initiated under continuous light while under continuous dark, vegetative-stems were formed. Different types of GA (gibberellin) biosynthesis inhibitors were added to the culture medium. Paclobutrazol and compounds belonging to the group of cyclohexanetriones clearly reduced flowering-stem growth under light conditions and vegetative-stem growth under dark conditions. Under light conditions, flower bud initiation was not affected. These and other results suggest that GA₁ may be synthesized during the in vitro culture period and that it controls flowering-stem growth but not floral initiation.Abbreviations CCC chlormequat chloride - GA gibberellin - LAB 198 999 3,5-dioxo-4-butyryl-cyclohexane carboxylic acid ethyl ester - BAS 111..W 1-phenoxy-3-(1H-1,2,4-triazol-1-yl)-4-hydroxy-5,5-dimethylhexane     

Effects of carbon source on growth and morphology of <Emphasis Type="Italic">Botryococcus braunii</Emphasis>

The green colonial alga Botryococcus braunii is characterized by the ability to produce and accumulate large amounts of hydrocarbons. We isolated and established an axenic clonal strain of B. braunii B70 and investigated the effects of organic carbon sources, including glucose, mannose, fructose, galactose, or acetate, on growth under light and dark conditions. This algal strain had the capacity to grow photo-, mixo-, or heterotrophically. Growth was promoted substantially following exposure of the algae to glucose or mannose under light exposure. Cells could grow under continuous darkness with glucose or mannose. In the presence of glucose under light or dark conditions, cell and colony size, and the intracellular granules containing oil, were markedly larger than those cultured without glucose.     

Flowering of Pharbitis nil is controlled by an endogenous semidian rhythm

Abstract Flowering of Pharbitis nil after an inductive dark period is greatly influenced by far-red (FR) irradiation during the preceding light period. The response to FR is rhythmic in otherwise constant conditions, and the period of the oscillation is approximately 12 h (i.e. semidian). The rhythm also appears to operate under daily light-dark cycles. The expression of this novel rhythm depends on the time from the beginning of FR pretreatment to the onset of the inductive dark period. The cotyledons are the site of response to both the pretreatment and inductive darkness, and both these conditions must be perceived by the same cotyledon.     

Changes in behaviour and eye-morphology of BoreomysisMegalops G.O. Sars (Crustacea : Mysidacea) following exposure to short periods of artificial and natural daylight

Boreomysis megalops G.O. Sars were collected from 240 m depth using a protective cod-end, which shielded the eyes from light exposure. Animals were divided into groups which were exposed to darkness (DE) or to natural or artificial daylight (LE) for periods of 1–15 min or 4 h. Some animals were thereafter kept in aquaria under simulated habitat light conditions (light/dark cycles). The animals were observed in infra-red (IR) light. DE animals showed a vertical zonation behaviour in the laboratory similar to that obtained from sledge data: i.e. the animals stayed close to the bottom during daytime (light) and spread out vertically at night (darkness).LE individuals showed putative pathological changes both in zonation behaviour in the laboratory and in eye-morphology. The photoreceptor membranes of the six main retinula cells were damaged. The seventh cell was unaffected by light exposures. A correlation was found between the extent of damage to the eye and the degree of modification of vertical zonation behaviour. The groups exposed to the least light showed the smallest changes in zonation behaviour and eye-morphology. The light induced changes were not reversed even after 4 days in the aquarium under simulated habitat light conditions. In conclusion, deep living animals with well-developed and very light sensitive eyes should be protected from daylight during sampling and handling. IR light should be used for observation purposes.     

GROWTH OF BLADES OF NEREOCYSTIS LUETKEANA (PHAEOPHYTA) IN DARKNESS 1

Short term measurements were made of the relative growth rate of the fast growing portions of blades of Ncreocystis luetkeana (Merl.) Post. et Rupr. during exposure to natural daylight and during prolonged darkness. Growth was only slightly, but significantly, faster during the 12 h of daylight than during the 12 h that included 8 h of darkness. Clearly considerable growth occurred at night. In blades amputated 1 cm beyond the zone measured, growth was slower during both night and day. In continuous darkness growth continued for up to 12 days. It was not influenced by amputation of distal blade tissue but it was increased by severance from the bulb and stipe. A mean volume increase of 50% of the blade tissue was recorded. While the organic content decreased, the drop was half that required to support the increase in volume. There was some evidence against translocation. It is possible that cellular biochemical rearrangements allow a light-independent increase in organic material.     

Changes of the diurnal and circadian (endogenous) mRNA oscillations of the chlorophyll a/b binding protein in tomato leaves during altered day/night (light/dark) regimes

Characteristic steady-state mRNA level oscillations were monitored for the chlorophyll a/b-binding (cab) protein in tomato plants grown under the natural day/night (light/dark) regime as well as under constant environmental conditions. This typical expression pattern was altered when plants were transferred to different light/dark regimes. For example, by shifting the light phase by six hours, a change of the time points of maximum and minimum of expression level was monitored, while the principal oscillation pattern remained the same. It appeared that the transition from dark to light is involved in determining the time points of minima and maxima of mRNA accumulation.After exposing tomato plants to an abnormal light/dark periodicity (e.g. six hours of alternating light/dark) an altered oscillation pattern was determined: within 24 hours two maxima of cab mRNA levels were detected. However, this entrained abnormal rhythm was not manifested at the molecular level and the circadian pattern reappeared under constant environmental conditions (e.g. darkness). This result favours the hypothesis that the oscillation pattern of the cab mRNA in tomato plants is not only endogenous but also hereditary.     

Die Wirkung von Beleuchtungsfaktoren und Lichtpunktmustern auf die n?chtliche Zugaktivit?t von Rotkehlchen(Erithacus rubecula)

Zusammenfassung 1. Die nächtliche Zugunruhe setzt auch unter konstanten Lichtbedingungen (Dauerdunkel 0,06 Lux, Dauerhell 250 Lux) etwa mit der Sonnenuntergangszeit ein und erreicht im Frühjahr etwa um 21^h ihr Maximum (etwas später bei Dauerhell).2. Während der Nacht werden vom zugaktiven Rotkehlchen in stärkerem Maße als bei Tag die dunkleren Abteilungen einer Lichtorgel aufgesucht.3. Die höchste Zugaktivität wird bei Beleuchtungsstärken von 1–10 Lux erreicht, aber auch bei völliger Dunkelheit wird noch etwa 7 % der Maximalaktivität gemessen. Sommer-Nachtaktivität erreicht ebenfalls bei ca. 5 Lux ein Maximum, erlischt aber fast völlig bei Beleuchtungsstärken unter 1 Lux.4. Bei dunklem Untergrund ist die gemessene Aktivität bei gleicher Beleuchtungsstärke deutlich geringer als bei hellem Untergrund.5. Niedrigere Tagesbeleuchtungsstärken im Versuchsraum (250 gegenüber 700 Lux) bewirken ein Ansteigen der Zugaktivität in der folgenden Nacht, bei gleichzeitig zunehmender Futteraufnahme während des Tages.6. Einzelne Lichtpunkte wirken aktivitätssteigernd unabhängig von der von ihnen bewirkten Beleuchtungsstärke. Eine größere Zahl von Lichtpunkten, gleichmäßig über die Decke verteilt, hemmt dagegen die Zugaktivität, auch wenn die dabei erreichte Beleuchtungsstärke höher ist als bei einer Diffusionsbeleuchtung, unter der dieselben Tiere eine höhere Aktivität zeigen.

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Nocturnal migratory restlessness in the robin under different light conditions and patterns of light spots

Summary 1. Nocturnal migratory restlessness even under constant LL or DD lighting conditions (250 Lux, 0,006 Lux) starts at the time of sunset, and in spring reaches a maximum at 9 pm under constant dark, and a little later in constant light (Fig. 1).2. At night, during nocturnal restlessness, the birds tend to be more active in the darker parts of a set of differently lighted chambers than during daytime (Fig. 3 b).3. Highest migratory restlessness in spring and autumn is recorded under an illumination of 1 to 10 Lux, though even in total darkness a high level of activity persists. Nocturnal activity in summer also reaches a maximum at an illumination level of 5 Lux, but drops to zero at intensities below 1 Lux (Fig. 4 a).4. In cages painted black the nocturnal activity is lower than in white cages with the same overhead illumination intensity (Fig. 5).5. Low illumination intensity during daytime (250 against 700 Lux) causes high activity during the following night and raises diurnal food consumption considerably.6. A few single light spots (stars) on the ceiling strongly activate migratory restlessness (almost independent of their brightness), while higher numbers of evenly spaced light spots lower the birds activity even though total illumination intensity is higher than under the diffuse control lighting under which the birds show a higher amount of activity (Fig. 7, 8).

     

Flower opening and closing ofOxalis martiana

Flowers ofOxalis martiana open in the morning and close in the afternoon repeatedly for 3–5 days in May–July under natural conditions. Both in light and in darkness, the closed flowers opened in reponse to a rise in temperature (thermonasty), but not under the constant temperatures. Transfer from darkness to light along with temperature rise caused rapid flower opening, and at 20 C or higher temperatures, exposure to light caused flower opening even without changing temperature (photonasty). Therefore, the temperature of the night before opening is critical in determining whether the flower opening under natural conditions depends on thermonasty or photonasty. The opened flowers closed about 8–11 hr after the beginning of opening both under natural conditions and constant light-temperature conditions, which suggests that the time of flower closing is determined by endogenous factors. Length of the perianth increased greatly during opening and slightly during closing. Application of actionomycin D or cycloheximide inhibited both the flower opening and closing, probably by suppressing the perianth growth.     

Influence of experimental illumination and seasonal variation on crossbreeding mating in the snail Biomphalaria glabrata

The crossbreeding activities of the Schistosoma mansoni vector snail Biomphalaria glabrata were counted in a laboratory aquarium throughout the year under two regimes of 12h light: 12h dark from 7 A. M. to 10 P. M. Mating increased significantly in Autumn and Winter and just missed a significant inverse correlation with temperature and a direct one with locomotion. Other similar experiments were carried out to compare mating under various illumination conditions in complete daily cycle measurements. Mating counts decreased under the regimes which submitted snail to a total exposure of 12h light and 12h dark during a daily cycle in the following sequence: 12h light:12h dark alternating hourly with light gradient, 12h light:12h dark, 1h light:1h dark and 12h dark:12h light. Under two constant illuminations, the mating scored less than under the previous conditions, except under 12h dark:12h light. Under darkness the mating count was lower than under light conditions. There was no way to differentiate the night and day rhythms of mating on different days in each regime, except for mating under 12h light:12h dark alternating with light gradient, constant dark and 12h dark:12h light conditions. Mating increased in certain light and temperature conditions, in which the intensities should have an optimum value.     

An investigation of circadian rhythm in Escherichia coli

Background: Persuasive evidence for circadian programs in non-photosynthetic bacteria other than cyanobacteria is still lacking, we aimed to investigate the circadian rhythm of specific growth rate in Escherichia coli ATCC 25922, one of the important prokaryotes. Methods: To grow E. coli under different light and dark conditions. When the growth entered into the stationary phase, we stopped the culture and obtained the viable counts by MTT assay every 3 h. The specific growth rates (SGRs) were calculated and analyzed with cosinor method for potential rhythms. Results: Single cosinor method revealed that the SGR of E. coli displayed rhythmic variations with a period of around 24 h both under light/dark cycles and under constant darkness. The best-fitting periods and best-fitting cosine curves were acquired. Conclusions: The SGR of E. coli (ATCC 25922) in a culture medium with limiting substrates in the stationary and death phases displayed rhythmic variations with a period of around 24 h under light/dark cycles and constant darkness conditions.     

Diurnal regulation of scent emission in rose flowers

Previous studies have shown diurnal oscillation of scent emission in rose flowers with a peak during the day (Helsper in Planta 207:88–95, 1998; Picone in Planta 219:468–478, 2004). Here, we studied the regulation of scent production and emission in Rosa hybrida cv. Fragrant Cloud during the daily cycle and focused on two terpenoid compounds, germacrene D and geranyl acetate, whose biosynthetic genes have been characterized by us previously. The emission of geranyl acetate oscillated during the daily light/dark cycle with a peak early in the light period. A similar daily fluctuation was found in the endogenous level of this compound and in the expression of its biosynthetic gene, alcohol acetyl transferase (RhAAT). The rhythmic expression of RhAAT continued under conditions of constant light or darkness, indicating regulation by the endogenous circadian clock. However, the accumulation and emission of geranyl acetate ceased under continuous light. Our results suggest that geranyl acetate production is limited by the level of its substrate geraniol, which is suppressed under constant light conditions. The emission of germacrene D also oscillated during the daily cycle with a peak early in the light period. However, the endogenous level of this compound and the expression of its biosynthetic gene germacrene D synthase (RhGDS) were constant throughout the day. The diurnal oscillation of germacrene D emission ceased under continuous light, suggesting direct regulation by light. Our results demonstrate the complexity of the diurnal regulation of scent emission: although the daily emission of most scent compounds is synchronized, various independently evolved mechanisms control the production, accumulation and release of different volatiles. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.