Circadian rhythm of cell division in Euglena: effects of random illumination regimen

A persisting, "free-running," circadian rhythm of cell division in autotrophically grown Euglena gracilis is obtained upon placing either an exponentially increasing population or a culture that has been synchronized by a 10:14 light-dark cycle in a random illumination regimen that affords a total of 8 hours of light each 24 hours. These results are interpreted as implicating an endogenous biological clock which "gates" the specific event of cell division in the cell developmental cycle.     

Cell division: a second circadian clock system in Paramecium multimicronucleatum

Light-dark cycles entrain a pattern of division in a population of individually isolated cells cultured in excess nutrients at 14 degrees C. This pattern persists for at least 8 days in continuous dim light. Both clones which do and which do not express a circadian rhythm of mating-type reversals can be entrained. The phase is a clonal characteristic.     

光照周期对尼罗罗非鱼幼鱼昼夜节律调节的作用

为了研究尼罗罗非鱼幼鱼游泳行为在不喂食时是否存在昼夜节律和光照周期的调节作用,设计了光周期为光照(L)∶黑暗(D)=12 h∶12 h,持续的黑暗(DD),持续的光照(LL),光周期为L∶D=6 h∶6 h和光周期为L∶D=2 h∶2 h。结果表明:(1)光周期为L∶D=12 h∶12 h时,尼罗罗非鱼具有明显的昼夜节律,昼夜节律周期为(24. 3±0. 2) h;(2)尼罗罗非鱼的昼夜节律在持续的黑暗和光照下仍然存在,分别为(25. 1±1. 1) h和(25. 6±1. 0) h;(3)光周期为L∶D=6 h∶6 h时,尼罗罗非鱼仍具有明显的昼夜节律(12. 6±0. 5) h;(4)在光周期为L∶D=2 h∶2 h时,尼罗罗非鱼的昼夜游泳行为仍具有明显的昼夜节律,节律周期为(4. 0±2. 0) h。这些结果表明,尼罗罗非鱼具有以24 h为周期的内源性生物钟,但相比与外源性光照调控,内源性的生物钟对罗非鱼的调控较弱,外源性的光照周期才是调节尼罗罗非鱼幼鱼昼夜行为节律的主要因素。     

Indole metabolism in the pineal gland: a circadian rhythm in N-acetyltransferase

The activity of N-acetyltransferase in the rat pineal gland is more than 15 times higher at night than during the day. This circadian rhythm persists in complete darkness, or in blinded animals, and is suppressed in constant lighting. The N-acetyltransferase rhythm is 180 degrees out of phase with the serotonin rhythm and is similar to the norepinephrine and melatonin rhythms. Experiments in vitro indicate that norepinephrine, not serotonin, regulates the activity of N-acetyl-transferase through a highly specific receptor.     

Melatonin: a coordinating signal for mammalian reproduction?

There is a daily rhythm in the production of the pineal hormone melatonin in all mammalian species. Production is stimulated by darkness and inhibited by light. This provides a signal reflecting the changing environmental lighting cycle. In seasonally breeding mammals that use changes in the photoperiod to time their reproductive cycles, temporal signals to the reproductive system are controlled by the daily rhythm in melatonin production.     

Circadian activity rhythm of the deer mouse, Peromyscus: effect of deuterium oxide

Chemical modification of a vertebrate activity rhythm, the circadian (approximately 24-hour) rhythm of Peromyscus leucopus noveboracensis, has been demonstrated. Activity in a running wheel was used to measure the rhythms of mice kept individually in conditions of continuous darkness. Deuterium oxide was presented in the drinking water. The length of the periods of rhythm increased directly and linearly with the increase in concentration of deuterium oxide. There is no threshold for this effect, and the maximum concentration of deuterium oxide (30 percent) that was presented resulted in a 6 percent lengthening of the period of circadian rhythm. The mice reverted to rhythms similar in period length to control values after deuterium oxide was withdrawn from their drinking water.     

Circadian rhythm in pineal tyrosine hydroxylase

Tyrosine hydroxylase is the rate-limiting enzyme in catecholamine synthesis. The rat pineal gland is richly innervated by sympathetic nerves from the superior cervical ganglia. The activity of tyrosine hydroxylase was measured in rat pineal gland at 4-hour intervals over a daily cycle of 12 hours of light (7 a.m. to 7 p.m.) and 12 hours of darkness. The results indicate a circadian rhythm with the maximum activity, at 11 p.m. to 3 a.m., about triple the low values observed at 3 p.m. The pattern is similar in phase to that previously reported for melatonin and hydroxyindole-O-methyl transferase activity.     

Rhythms in pheromone production of the male boll weevil

Male boll weevils, Anthonomus grandis, held in a light regimen of 16 hours of light and 8 hours of darkness released pheromone rhythmically during the 24 hours. The amount released during peaks was typically 20 times the amount released in valleys. The ratio of the two alcohol components of the pheromone also showed a daily rhythm. Under continuous light, both the release of pheromone and the ratio of the two alcohol components were arrhythmic. In darkness, pheromone release was diminished more than tenfold over the 20-day test period.     

Growth of prochlorococcus, a photosynthetic prokaryote, in the equatorial pacific ocean

The cell cycle of Prochlorococcus, a prokaryote that accounts for a sizable fraction of the photosynthetic biomass in the eastern equatorial Pacific, progressed in phase with the daily light cycle. DNA replication occurred in the afternoon and cell division occurred at night. Growth rates were maximal (about one doubling per day) at 30 meters and decreased toward the surface and the bottom of the ocean. Estimated Prochlorococcus production varied between 174 and 498 milligrams of carbon per square meter per day and accounted for 5 to 19 percent of total gross primary production at the equator. Because Prochlorococcus multiplies close to its maximum possible rate, it is probably not severely nutrient-limited in this region of the oceans.     

Circadian clock in photoperiodic time measurement: a test of the Bünning hypothesis

A technique has been developed for effectively separating the direct inductive effect of a light signal from its effect on the phase of the rhythm of sensitivity to photoperiodic induction. With this technique it has been shown that a 75-minute pulse of light per day, when appropriately positioned with respect to the circadian activity cycle of the sparrow Passer domesticus, is sufficient to produce a response normally produced only by long days. The results cannot be interpreted in terms of a requirement of an absolute amount of either darkness or light and offer strong confirmation of Bünning's hypothesis concerning the mechanism of photoperiodic time measurement.     

Daily light sensitivity rhythm in a rodent

Single 10-minute light periods can cause a phase shift in the rhythm of the daily locomotor activity of flying squirrels otherwise maintained in constant darkness. A daily rhythm of sensitivity to these standard light periods was found.     

美花石斛茎尖细胞分裂节律研究初报

采集不同季节、不同时间段的美花石斛茎尖,用品红染色,压片后显微观察,计算茎尖细胞的分裂指数。结果表明,美花石斛茎尖细胞的日分裂高峰为9：00（分裂指数3．3×10^-4）,月分裂高峰为5月。     

Role of seasonality in the evolution of climate during the last 100 million years

A simple climate model has been used to calculate the effect of past changes in the land-sea distribution on the seasonal cycle of temperatures during the last 100 million years. Modeled summer temperatures decreased over Greenland by more than 10 degrees C and over Antarctica by 5 degrees to 8 degrees C. For the last 80 million years, this thermal response is comparable in magnitude to estimated atmospheric carbon dioxide effects. Analysis of paleontological data provides some support for the proposed hypothesis that large changes due to seasonality may have sometimes resulted in an ice-free state due to high summer temperature rather than year-round warmth. Such "cool" non-glacials may have prevailed for as much as one-third of the last 100 million years.     

Resetting the sporulation rhythm in Pilobolus with short light flashes of high intensity

The "clock-controlled" endogenous sporulation rhythm in the fungusPilobolus sphaerosporus has been investigated as part of a comparative study aimed at elucidating characteristic common features of circadian ((1)) rhythms. Pilobolus was chosen for inclusion in this study because of its demonstrated rhythm and sensitivity to light, and because it is a relatively simple plant. It has been shown that a single, high-intensity, 1/2000 second light flash will completely reset (shift the phase of) a rhythm persisting in continuous dim red light at constant temperature, and that one or more transient cycles occur before the phase shift is complete. The significance of these results is discussed.     

黄鳝血清褪黑激素水平日周期性与季节性变化的节律

通过放射免疫测定方法,本文初步研究了黄鳝血清褪黑激素的分泌特性,实验结果表明,黄鳝血清褪黑激素水平具有明显的日周期性与季节性变化节律。白天血清中褪黑激素水平较低,夜间浓度显著升高,比白天值高１－２倍。随着性腺的发育,从卵巢Ⅱ至Ⅳ期,血清中黑激素含量逐渐升高,到排卵前期则急剧下降。排卵期达到雌性阶段的最优值;排卵后期,血清褪黑激素水平又逐渐加回升：间性期则有下降的趋势;雄鱼血清中褪黑激素水平极低。     

黄鳝血清褪黑激素水平日周期性与季节性变化的节律

通过放射免疫测定方法,本文初步研究了黄鳝血清褪黑激素的分泌特性,实验结果表明,黄鳝血清褪黑激素水平具有明显的日周期性与季节性变化节律。白天血清中褪黑激素水平较低,夜间浓度显著升高,比白天值高１－２倍。随着性腺的发育,从卵巢Ⅱ至Ⅳ期,血清中黑激素含量逐渐升高,到排卵前期则急剧下降。排卵期达到雌性阶段的最优值;排卵后期,血清褪黑激素水平又逐渐加回升：间性期则有下降的趋势;雄鱼血清中褪黑激素水平极低。     

Restriction of DNA replication to the reductive phase of the metabolic cycle protects genome integrity

When prototrophic yeast cells are cultured under nutrient-limited conditions that mimic growth in the wild, rather than in the high-glucose solutions used in most laboratory studies, they exhibit a robustly periodic metabolic cycle. Over a cycle of 4 to 5 hours, yeast cells rhythmically alternate between glycolysis and respiration. The cell division cycle is tightly constrained to the reductive phase of this yeast metabolic cycle, with DNA replication taking place only during the glycolytic phase. We show that cell cycle mutants impeded in metabolic cycle-directed restriction of cell division exhibit substantial increases in spontaneous mutation rate. In addition, disruption of the gene encoding a DNA checkpoint kinase that couples the cell division cycle to the circadian cycle abolishes synchrony of the metabolic and cell cycles. Thus, circadian, metabolic, and cell division cycles may be coordinated similarly as an evolutionarily conserved means of preserving genome integrity.     

Variation of carbon partitioning in newly expanded maize leaves and plant adaptive growth under extended darkness

Plants must maintain a balance between their carbon(C) supply and utilization during the day–night cycle for continuous growth since C starvation often causes irreversible damage to crop production. It is not well known how C fixation and allocation in the leaves of crops such as maize adapt to sudden environmental changes. Here, to quantify primary C fixation and partitioning in photosynthetic maize leaves under extended darkness and to relate these factors to plant growth, maize seedlings were subjected to extended darkness(ED) for three successive days at the 6 th leaf fully expanded stage(V6). ED reduced plant growth and leaf chlorophyll levels but not the rate of net CO_2 exchange. As a result of the reduction in photoassimilates, the accumulation of starch and total soluble carbohydrates(TSC) in mature leaves also decreased under ED. However, the percentage of the daily C fixation reserved in mature leaves increased. These transient C pools were largely composed of TSC and were mainly used for consumption by increased nocturnal respiration rather than for transport. As the days went on, both the amount of C accumulated and the percentage of the daily fixed C that was reserved in leaves decreased, which could be largely accounted for by the attenuated starch synthesis in all treatments. The activities of ADPglucose pyrophosphorylase and soluble starch synthase decreased significantly over time. Therefore, this study concluded that both starch and TSC are involved in the coordination of the C supply and plant growth under a sudden C shortage but that they may be involved in different ways. While the ratio of reserved C to daily fixed C increased to maintain blade function under acute C starvation, both the amount and the proportion of C reserved in mature leaves decreased as plant growth continued in order to meet the growth demands of the plant.     

Mechanism of rhythmic synchronous flashing of fireflies. Fireflies of Southeast Asia may use anticipatory time-measuring in synchronizing their flashing

In Thailand, male Pteroptyx malaccae fireflies, congregated in trees, flash in rhythmic synchrony with a period of about 560 +/- 6 msec (at 28 degrees C). Photometric and cinematographic records indicate that the range of flash coincidence is of the order of +/- 20 msec. This interval is considerably shorter than the minimum eye-lantern response latency and suggests that the Pteroptyx synchrony is regulated by central nervous feedback from preceding activity cycles, as in the human "sense of rhythm," rather than by direct contemporaneous response to the flashes of other individuals. Observations on the development of synchrony among Thai fireflies indoors, the results of experiments on phase-shifting in the American Photinus pyralis and comparisons with synchronization between crickets and between human beings are compatible with the suggestion.     

TEMPERATURE-DEPENDENT HISTOTYPIC CHANGES IN WALKER CARCINOSARCOMA IN THE CHORIOALLANTOIS

Solid tumors grew in the chorioallantois of chick embryos after the topical inoculation of ascites tumor cells. The microscopic character of the growth varied depending on the temperature of incubation. At 32.5 degrees C a sarcomatous appearance was prominent; at 37.5 degrees C carcinomatous structure in several alveolar patterns predominated; at 42.5 degrees C growth was that of a "giant cell" carcinoma.