Effect Of Continuous Darkness Research Articles

Morphophysiological dormancy in Smyrnium cordifolium Boiss: Germination requirements and embryo growth

Smyrnium cordifolium Boiss, a biennial medicinal plant, is generally distributed in the Iranian-Turanian phytogeography region. The knowledge about the seed germination and dormancy of this species is limited. S. cordifolium seeds were collected from the Zagros Mountains in Nurabad city, Lorestan province, western Iran. The study was performed based on 9 consecutive experiments. Each experiment was performed as a completely randomized design. Based on a summary of the results, fresh seeds of S. cordifolium (collected in mid-July, 2016) did not germinate after 30 day incubation at different temperature. The seed viability index was recorded 96 ± 1.4%; while the embryo was not observed in 4% of seeds. Therefore, 100% of S. cordifolium viable seeds were considered to be dormant. Germination increased by increasing the stratification period and was affected by temperature regimes. Although germination was not observed between 0 and 4 weeks after incubation, it began at 4 weeks of incubation at 5 °C and peaked at 16 weeks after incubation. After 16 weeks of incubation under photoperiod (12 h light/ 12 h darkness) conditions, germination percentage was recorded 43% at 5 °C, and 8% at 15 °C. In addition, applying 200 ppm gibberellin concentration improved the Percentage germination. The effect of continuous darkness on germination of S.cordifolium seeds was also proved. Seeds which were incubated for 16 weeks at 5 °C under continuous darkness and photoperiod, germinated 71% and 39%, respectively.

CONTINUOUS DARKNESS INDUCES STRUCTURAL CHANGES IN THYROID GLAND OF ADULT MALE RATS

Background The thyroid glands function and structure are influenced by several psychomotor stimulants like: temperature, drugs, chemicals and light. The purpose of this study was to investigate the effect of continuous darkness on the thyroid glands of male rats. Despite so many previous works to explore the effect of exogenous or endogenous melatonin on thyroid, there are few studies dealing with the outcome of progressively increasing phases of darkness on thyroid architecture, according to the available literatures.

Effect of Continuous Darkness on Immune Response (In vivo Assay)

Effect of Continuous Darkness on Immune Response (In vivo Assay)

Development of Acartia bifilosa (Copepoda: Calanoida) eggs in the northern Baltic Sea with specialreference to dormancy

Development of eggs produced by Acartia bifilosa in summer and autumn was studied in the northern Baltic Sea. Resting eggs of the species have previously been found in sediments, and the aim of this study was to reveal the type of dormancy in the eggs. Eggs were incubated at temperatures ranging from 1.5 to 18°C. The effect of continuous darkness on hatching was also tested. Hatching success in the experiments varied between 56 and 97%. Egg development was similar in summer and autumn, indicating that A. bifilosa does not produce diapause eggs in the area. Furthermore, dormancy was not induced at any of the temperatures tested, nor by darkness. Results are compared with those of Castro-Longoria and Williams (Castro-Longoria and Williams, 1999b, J. Plankton Res., 21, 65-84) who studied A. bifilosa in the English Channel, where both production of diapause eggs and arrest of development in the subitaneous eggs at low temperatures occurred. The possible causes of the difference in dormancy strategies in the two areas are discussed.

Diapause in the predacious mites Amblyseius cucumeris (Oud.) and Amblyseius barkeri (Hug.): Consequences of use in integrated control programmes

AbstractThe mites Amblyseius cucumeris and A. barkeri are used in biological control commercial program against Frankliniella occidentalis. The diapause influence is essential to know the efficacy in climatic extreme conditions. The experiments were designed to verify the following: a) the effect of night temperatures on diapause induction; b) the effect of continuous darkness and low temperatures on diapause induction. In the first case A cucumeris at 12°C temperature in ecotophase diapause incidence was 100%. A. barkeri was not affected by 3 night temperatures. In the second case it could be seen that the test conditions did not induce diapause in either case.

Effects of continuous darkness on ERG correlates of disc shedding in rabbit retina

The electroretinogram (ERG) was recorded in the dark from photo-entrained albino rabbits, using a constant-intensity, 500-nm, 50- or 100-msec stimulus at 1-min intervals. Under these conditions, the b-wave of the ERG was previously shown to decrease in amplitude at the time of the morning rod photoreceptor disc shedding event. We have extended our observations to rabbits housed in continuous darkness. The present data show that in constant darkness the change in retinal sensitivity continues to occur, but with a period slightly less than 24 hr. Unilateral dark adaptation, achieved by eyepatching, alters the timing of the event only in the retina of the occluded eye. Thus, the change in retinal sensitivity shares the characteristics of endogenous rhythmicity and intraocular control that have been demonstrated by histologic methods for mammalian rod disc shedding. We also report elongation of rod outer segments in some regions of the albino rabbit retina after continuous darkness.

Effect of continuous darkness on circadian morphological rhythms in pinealocytes of the Chinese hamster, Cricetulus griseus.

Effects of a short-term exposure to continuous darkness on 24-h morphological variations in pinealocytes in the superficial pineal of the Chinese hamster (Cricetulus griseus) were examined. Pinealocytes contained type-1, -2 and -3 synaptic ribbons (SR), which had a central dense structure showing rod-like, various and ring-like profiles, respectively, and the quantity of each type of SR was expressed by SR index. 24-h changes in the type-1 and type-3 SR indices persisted in darkness and thus may be endogenous in nature. As under alternating light and dark (LD) conditions, the type-2 SR indices were almost constant over a 24-h period under continuous darkness, but the indices were larger in animals under darkness than in those under LD conditions. The 24-h variations in the nuclear and cytoplasmic volumes were abolished after exposing animals to darkness for 7 days, suggesting that these rhythms may be regulated exogenously. The amount of condensed chromatin exhibited a circadian change; this rhythm persisted under darkness. The results suggest that 24-h variations in the nuclear and cytoplasmic volumes in pinealocytes of the Chinese hamster are regulated by mechanisms different from those controlling the rhythms in SR and chromatin, and that the changes in the nuclear and cytoplasmic volumes and chromatin are related to the change in synthetic activity of pinealocytes.

The cell cycle of symbiotic Chlorella. II. The effect of continuous darkness.

When green hydra were grown in continuous darkness the mean cell size of their symbiotic algae was smaller than when grown in light and numbers of algae per digestive cell were reduced. The former was due to a reduction in size at which the algae divided, and the latter to a loss of synchrony of algal mitosis with that of digestive cells after transfer to darkness. Eventually, algal mitosis regained synchrony with that of digestive cells. Division synchrony was not lost in reinfected hydra (with lower than normal numbers of algae per cell) transferred to darkness; this, and the observation that synchrony in normal animals transferred to darkness was regained when algal numbers per cell had fallen to a new, lower level, suggested that the initial inhibition of algal mitosis was due to competition for a limited supply of heterotrophically required metabolites. When dark-grown hydra were returned to light there was no delay in algal division and a steady increase in the size of dividing cells, suggesting that the smaller division size in darkness was not due simply to the critical size for division being set at a lower value. In light, algal division size varied with frequency of host feeding, but this had less effect on algal division size in darkness. It is suggested that the critical cell size that algae must attain before being able to complete the cell cycle is the same in light and darkness, but in light mitosis is restricted by some exogenous factor so that algae grow beyond the critical size without dividing. In darkness both algal cell growth and division are dependent on exogenously supplied metabolites, and cell growth rather than the division factor is limiting. The precise nature of the restriction on algal division remains unknown.

A Comparative Study of Germination Responses to Diurnally-Fluctuating Temperatures

(1) Seeds collected from populations of a range of native herbaceous plants in the Sheffield region were subjected to experimental treatments providing a range of amplitudes of diurnal fluctuations in temperature. All experiments involved a photoperiod of 18 h combined in some species with a comparable series of temperature treatments applied in continuous darkness. (2) In the light a stimulation of germination by fluctuating temperature was observed in forty-six of the 112 species tested. The responses varied from those indicating an absolute requirement in all seeds for large (>5 OC) fluctuations (e.g. Rorippa islandica) to polymorphisms (e.g. Carex otrubae) in which some seeds germinated at constant temperatures whilst the remainder responded to small (<5 OC) fluctuations. (3) The capacity to respond to fluctuating temperatures in the light was prominent in species of wetland where it appears to provide a mechanism whereby spring germination may be initiated by increasing irradiance and falling water table. (4) In certain species (e.g. Ranunculus repens) the effect of continuous darkness was to increase the amplitude of temperature fluctuation necessary for germination. Small-seeded species known to form buried seed reserves (e.g. Juncus effusus) were inhibited by darkness and in the absence of light did not respond to fluctuating temperatures. (5) Sensitivity to temperature fluctuations in darkness was observed in species of grassland, wetland and disturbed habitats, and was conspicuous among species forming persistent seed banks. It seems likely that responses to temperature fluctuations in darkness provide mechanisms of depth-sensing by buried seeds and may initiate establishment from seed within canopy gaps. (6) Many of the species found to respond to temperature fluctuations in darkness are successful weeds of arable land or pasture. A polymorphic response to temperature fluctuations may account partially for the unpredictability of appearance of infestations of these weeds. The ability to invade canopy gaps throughout the year is important to the success of many pasture weeds (e.g. Rumex obtusifolius, Ranunculus repens) and is notably absent from the major sown species, Lolium perenne.

Effect of continuous darkness on diurnal rhythms in small vesicles in sympathetic nerve endings of the mouse pineal-quantitative electron microscopic observations.

Quantitative electron microscopic studies on the effect of continuous darkness on the diurnal rhythm of small vesicles in sympathetic nerve endings of the mouse pineal demonstrate that the numerical change of type 1 granulated vesicles, predominant small granulated vesicles, and non-granulated elliptical vesicles seen during the first half of the dark period under diurnal lighting conditions may persist for at least 14 days under continuous darkness. Furthermore, it is found that the alteration in the number of type 1 granulated vesicles and the total vesicle density observed during the light period under diurnal lighting conditions may be lost in mice kept in continuous darkness for 7 days. This result indicates that the type 1 granulated vesicles may be composed of two different populations of vesicles, i.e., granulated vesicles of population 1 and 2, and that the diurnal rhythm in the number of the granulated vesicles of population 1 may be abolished, while that of the granulated vesicles of population 2 may be maintained, under continuous darkness. The diurnal variation in the number of the type 2 granulated vesicles, which constitute a small population of small granulated vesicles, may persist in darkness. Thus, the diurnal rhythm in the number of small granulated vesicles in sympathetic nerve endings of the mouse pineal may be controlled by two different mechanisms, exogenous and endogenous.

Translocation from leaves to fruits of a legume, studied by a phloem bleeding technique: Diurnal changes and effects of continuous darkness

Diurnal changes in the carbohydrates of leaf laminae and fruits and in the bleeding of sugar and amino acids from fruit phloem were followed by successive sampling from a population of Lupinus albus L. plants. Phloem sap was collected for a standard 5 min period from cut distal tips of attached fruits. Daily fluctuations in leaf dry matter resulted largely from changes in starch and sugar. Leaf sugar rose to a maximum in the afternoon, starch to a maximum at, or shortly after, dusk. Leaves lost sugar and starch from dusk to dawn. Phloem bleeding rate varied little over a daily cycle but sucrose levels fluctuated from a noon maximum of 12-13% (w/v) to a dawn minimum of 9-10%. The rhythm of phloem sugar levels matched closely those of fruit and leaf. Phloem amino acid levels fluctuated in phase with that of sucrose: the relative composition of the amino fraction did not vary significantly over the daily cycle. Pulse feeding of source leaves with (14)CO2 at different times in the photoperiod allowed study of the pattern of release of labelled photosynthate to the fruit phloem and the build up and depletion of (14)C starch in leaves. Plants transferred to continuous darkness showed a rapid decline in output and concentration of phloem sap solutes, and translocated nitrogen to their fruits at only one quarter of the rate of control plants retained in natural daylight. The combined data from the experiments showed that the rate of output of sugar from cut phloem of a fruit was directly related to the current level of sugar in leaves. When leaf sugar levels were low (5-10 mg ml tissue water(-1)) sugar in phloem was 10-11 times more concentrated than in source leaves, but at high leaf sugar levels (25-30 mg ml(-1)) this concentration difference was only 3-4 fold.

Effect of continuous darkness on diurnal rhythm in glycogen content in pineal cells of the mouse: a semiquantitative histochemical study.

AbstractThe effect of continuous darkness on diurnal variation of glycogen content in pineal cells of adult mice was investigated by means of a semiquantitative histochemical method. In dark‐maintained mice, a diurnal rhythm in pineal glycogen content persisted for the first 7 days of darkness. After 14 days or longer of continuous darkness, however, a clear relationship between the glycogen content and time of day became less apparent. Reversed conditions of environmental lighting caused a complete reversal of the glycogen rhythm in the pineal as early as the fifth day. When mice that had been kept in reversed conditions of lighting for 7 days were exposed to continuous darkness, the reversed glycogen rhythm also persisted in darkness of 7 and 14 days, but it was abolished by darkness of 28 days. The nuclear density of pineal cells was significantly lower at 9 am than at 9 pm in controls. In dark‐maintained mice, however, no significant diurnal variation in pineal cell size was generally evident except 2 and 3 days after the initiation of darkness.

Rhabdom structure and receptor potentials in single crayfish retinular cells.

AbstractThe effects of continuous darkness and abnormal ionic ratios (excess Ca+ +, Mg+ +, K+, and absence of Na+) on the fine structure of the rhabdoms and on the intracellular retinal receptor potentials were studied in crayfish compound eyes. The normal rhabdom has its constituent microvilli regularly arranged in a characteristic cross‐banded pattern. The normal retinular cell response consists of an initial transient peak and a sustained plateau. After the crayfish were kept for three months in the dark, the regular arrangement of rhabdom microvilli was markedly upset, and receptor potentials of retinular cells in the eye consisted only of the slow phase. The initial phase of the intracellular retinal receptor potential is more labile than the sustained phase (plateau) and was easily abolished if the rhabdom was so strongly affected by continuous darkness, excess Ca+ +, and excess K+ that the fine structural arrangements of microtubules were destroyed. Since receptor potentials were recorded from compound eyes in which rhabdoms were deranged and almost all their microvilli torn off from the retinular cells, transmission of visual excitation from rhabdom to retinular cell soma must be possible without direct membranous connection between them.