Short Light Periods Research Articles

Seasonal reproduction and delayed sexual maturity in mound-building mice Mus spicilegus.

In the mound-building mouse, Mus spicilegus, which is found from Central to Eastern Europe, reproduction is seasonal and limited to spring and summer. In autumn, the mice build voluminous mounds composed of vegetable matter covered with earth, where juvenile animals (autumnal individuals) over-winter in groups without reproducing. Autumnal animals delay reproduction until the next spring when they are 6 months old. The influence and interactions of environmental (short light period and cold temperature (C conditions) compared with long light period and temperate temperature (T conditions)) and social factors (lack of odours from breeding adults (NB conditions) compared with presence of odours from breeding adults (B conditions)) on reproduction and sexual maturation were studied. Forty groups of three autumnal individuals (two males and a female or two females and a male) were placed in four experimental conditions (CB, CNB, TB and TNB), corresponding to interactions between environmental and social factors (n = 10 groups for each condition). Of the 40 groups only one initiated reproduction during the 18 weeks of cohabitation. Subsequently, animals were separated and isolated for 1 month and then paired with unfamiliar partners. Reproduction was monitored for an additional month, and 24 out of 39 females reproduced. In addition, of eight reproducing pairs placed in C conditions and 10 reproducing pairs maintained in T conditions, all but one pair continued reproduction. It was concluded that the delay in reproduction observed in autumnal individuals was the result of the social effects of living in groups as opposed to the environmental conditions of winter.

Photosynthetic induction in saplings of three shade-tolerant tree species: comparing understorey and gap habitats in a French Guiana rain forest.

The photosynthetic induction response under constant and fluctuating light was examined in naturally occurring saplings (about 0.5-2m in height) of three shade-tolerant tree species, Pourouma bicolor spp digitata, Dicorynia guianensis, and Vouacapoua americana, growing in bright gaps and in the shaded understorey in a Neotropical rain forest. Light availability to saplings was estimated by hemispherical photography. Photosynthetic induction was measured in the morning on leaves that had not yet experienced direct sunlight. In Dicorynia, the maximum net photosynthesis rate (A max) was similar between forest environments (ca 4µmol m-2 s-1), whereas for the two other species, it was twice as high in gaps (ca 7.5) as in the understorey (ca 4.5). However, the time required to reach 90% of A max did not differ among species, and was short, 7-11min. Biochemical induction was fast in leaves of Pourouma, as about 3min were needed to reach 75% of maximum carboxylation capacity (V cmax); the two other species needed 4-5min. When induction continued after reaching 75% of V cmax, stomatal conductance increased in Pourouma only (ca 80%), causing a further increase in its net photosynthesis rate. When fully induced leaves were shaded for 20min, loss of induction was moderate in all species. However, gap saplings of Dicorynia had a rapid induction loss (ca 80%), which was mainly due to biochemical limitation as stomatal conductance decreased only slowly. When leaves were exposed to a series of lightflecks separated by short periods of low light, photosynthetic induction increased substantially and to a similar extent in all species. Although A max was much lower in old than in young leaves as measured in Dicorynia and Vouacapoua, variables of the dynamic response of photosynthesis to a change in light tended to be similar between young and old leaves. Old leaves, therefore, might remain important for whole-plant carbon gain, especially in understorey environments. The three shade-tolerant species show that, particularly in low light, they are capable of efficient sunfleck utilization.

The activation state of nitrate reductase is not always correlated with total nitrate reductase activity in leaves

The relation between nitrate reductase (NR; EC 1.6.6.1) activity, activation state and NR protein in leaves of barley (Hordeum vulgare L.) seedlings was investigated. Maximum NR activity (NRA(max)) and NR protein content (Western blotting) were modified by growing plants hydroponically at low (0.3 mM) or high (10 mM) nitrate supply. In addition, plants were kept under short-day (8 h light/16 h dark) or long-day (16 h light/8 h dark) conditions in order to manipulate the concentration of nitrate stored in the leaves during the dark phase, and the concentrations of sugars and amino acids accumulated during the light phase, which are potential signalling compounds. Plants were also grown under phosphate deficiency in order to modify their glucose-6-phosphate content. In high-nitrate/long-day conditions, NRA(max) and NR protein were almost constant during the whole light period. Low-nitrate/long-day plants had only about 30% of the NRA(max) and NR protein of high-nitrate plants. In low-nitrate/long-day plants, NRA(max) and NR protein decreased strongly during the second half of the light phase. The decrease was preceded by a strong decrease in the leaf nitrate content. Short daylength generally led to higher nitrate concentrations in leaves. Under short-day/low-nitrate conditions, NRA(max) was slightly higher than under long-day conditions and remained almost constant during the day. This correlated with maintenance of higher nitrate concentrations during the short light period. The NR activation state in the light was very similar in high-nitrate and low-nitrate plants, but dark inactivation was twice as high in the high-nitrate plants. Thus, the low NRA(max) in low-nitrate/long-day plants was slightly compensated by a higher activation state of NR. Such a partial compensation of a low NR(max) by a higher dark activation state was not observed with phosphate-depleted plants. Total leaf concentrations of sugars, of glutamine and glutamate and of glucose-6-phosphate did not correlate with the NR activation state nor with NRA(max).

Morphological and histochemical changes in the epididymis of hamsters (Mesocricetus auratus) subjected to short photoperiod.

The morphological involution and histochemical changes of the Syrian hamster (Mesocricetus auratus) epididymis induced by a short light period were investigated. Under short-day conditions, the epididymis showed marked morphological changes including a decrease in luminal diameter, disappearance of spermatozoa, increase of interductal tissue, increase of intraepithelial lipofuscin deposits, the presence of phagolysosomes in the principal cells and macrophage-like cells, and a considerable modification of most clear cells. With lectin histochemistry changes were found in the glycoconjugates of principal cells of the regressed epididymis, either a decrease (PNA, WGA, HPA and DBA) or an increase (MAA) in the affinity of lectins to the Golgi area, or a decrease (HPA) or an increase (PNA) in lectin binding to stereocilia. Both morphological and histochemical results showed that, under this light condition, the cauda epididymidis presented the most prominent alterations, and that the epididymis showed increased absorptive activity and a decreased synthesis of glycoproteins. All these changes are probably due to the decrease in testosterone levels.

EFFECT OF PHOTOPERIOD ON EMBRYOGENESIS AND GROWTH RATE IN IDOTEA BALTICA (ISOPODA)

ABSTRACT Photoperiodic effects on the duration of embryo development and on early growth rate in juveniles was carried out in a population of Idotea baltica. Two biological parameters showing seasonal fluctuations in the field were investigated in (a) individuals (G,) born from females collected in nature during mating and then bred in the laboratory, and (b) individuals (G2) born from females of group G,, which had been mated in the laboratory. A longer light period (LD 16:8) reduced embryo development duration, while a shorter one (LD 12:12) increased it. Under the same laboratory conditions, the growth rate in juveniles until the sixtieth day of life was increased by long daylight and reduced by a shorter light period. Seasonal variations observed in the field appeared to depend essentially on day-length regime, since the ecological conditions of the habitat did not show remarkable changes in biotic factors, particularly in the quality and quantity of food available during the year. Sensitivity to photoperiod may represent a strategy used by this species to overcome unfavorable environmental conditions.

Effect of bright light on tolerance to night work.

Fifteen young (mean age 23.4 years) female nurses engaged in a resuscitation unit and working on a fast rotating shift schedule comprising two consecutive night shifts were exposed to short periods (4 x 20 min) of bright light (2350 lx) during their night duty to test a possible positive effect on their tolerance to night work. Two nights with normal lighting (20-380 lx) and two nights with bright light were compared. The following positive effects of bright light upon psychophysical conditions and performance efficiency were noted: in particular, signs of better physical fitness; less tiredness and sleepiness; a more balanced sleep pattern; and higher performance efficiency (letter cancellation test). This result could not be attributed to shifts of the internal clock although the exact cause remains to be determined. In fact, hormonal excretion and body temperature did not show any effect from bright light. In addition melatonin excretion was not suppressed appreciably by the bright light used.

Improved Mesophyll Protoplast Culture and Plant Regeneration in Arabidopsis thaliana (L.) Heynh., Genotype Landsberg Erecta

Summary The response of in vitro cultured Arabidopsis thaliana mesophyll protoplasts was investigated with the aim of characterising the crucial factors that affect plating efficiencies and plant regeneration. We selected the genotype Landsberg erecta, which is frequently used for genetic studies, but which is known to respond poorly in protoplast culture. Factors permitting vigorous vegetative growth of the donor plants, i.e. short light period and avoidance of high temperature, were found to be advantageous. Selection of competent leaves and fractionation of protoplast populations indicated that predominantly protoplasts derived from still expanding, yet not highly immature mesophyll cells were competent of dividing. Plating efficiencies between 6 and 10 % were reproducibly obtained by selecting the appropriate type of mesophyll protoplast and by adjusting the culture medium. A medium rich in organic nutrients and low in mineral content, but supplemented with relatively high concentrations of calcium (50 mM CaCl 2 ) and iron (1 mM FeEDTA) was essential during early stages of protoplast culture. Rapid shoot bud formation and plant regeneration could be obtained by adjusting the constituents of the culture media to permit the growth of dense colonies with cells rich in cytoplasm and by correctly timing the transfer to the respective media.

Laboratory experiments on the effect of light and cover on the behaviour and growth of African catfish, Clarias gariepinus (Pisces: Clariidae)

The effect of different photoperiod regimes, as well as cover in continuous light (24L/0D) and darkness (OL/24D), on the growth rate of larval Clarias gariepinus was evaluated. In addition, a behavioural study of the effect of light on larval and juvenile C. gariepinus was made. The growth rate of larvae was found to increase with shorter light periods, the highest being recorded in continuous darkness (0L/24D photoperiod). Cover was found to enhance the growth rate of larvae reared under a continuous light period, however, the presence of cover did not affect the growth rates of larvae reared in continuous darkness. The behaviour of larval and juvenile catfish differed markedly in continuous light and darkness. When subject to a continuous light period, a strong negative phototaxis, long rest periods interspersed with disturbed activity, refuge seeking behaviour, and increasing incidence of territorial aggression were observed. In continuous darkness, the fish displayed a high level of active swimming with fewer rest periods, and a lower incidence of disturbed rest activity. The level of territorial aggression among fish in continuous darkness gradually declined and became negligible. Higher levels of browsing and airbreathing activity were observed in continuous darkness than in light. The present results, interpreted together with other ecological and anatomical data, demonstrate this species to be primarily a nocturnally active, tactile feeder, with a distinct diet activity pattern. The refuge seeking behaviour observed in the light is interpreted as an adaptation to avoid predators that rely on sight to detect prey. This behaviour, however, appears to promote intraspecific competition for refuges, resulting in a high degree of territorial aggression, and probably an increase in the rate of cannibalism. With regard to fish culture, it is suggested that the rearing of larvae in conditions of continuous darkness or low light intensity is optimal owing to the higher growth rates and apparent reduction of stress observed under these conditions.

Short periods of continuous light can both advance and delay spawning in the rainbow trout

The rainbow trout (Oncorhynchus mykiss) is a seasonally-breeding teleost which typically spawns for a 6-8 week period each year. The consequent seasonality of egg production restricts the profitability of fish farming; year groups of fish all reach marketable size at the same time and farm facilities are either over or under utilised depending on the time of year. Since these problems can be avoided by the production of out-of-season eggs, techniques designed to modify the time of spawning offer considerable commercial advantage. Of the photoperiod regimes available to modify spawning time those utilising continuous light (LL) are particularly attractive because neither time control or blackout are required. However, year-long exposure to LL can produce erratic spawning. This study examines the ability of short (⩽2 months) periods of LL to advance and delay maturation in the rainbow trout.

Short periods of continuous light provide a simple, cheap and predictable method for the production of out-of-season rainbow trout eggs

Short periods of continuous light provide a simple, cheap and predictable method for the production of out-of-season rainbow trout eggs

Diel and seasonal locomotor activity patterns in Arctic charr, Salvelinm alpinus (L.)

One‐year‐old Arctic charr, Sulvelinus alpinus (L.), of the Hornavan strain were tested from February 1985 to January 1986 in an attempt to get an increased understanding of the annual rheotactic behaviour as well as the die1 and seasonal locomotor activity pattern. An annular stream tank equipped with photocells was used to measure the direction of swimming movements as well as the number of passings. From February to late May the locomotor activity was low but increased in July and peaked in September. After November the locomotor activity was again at low winter levels. During the activity peak from July to November the majority ofall movements was directed against the current while no preference for direction was noted during the rest of the year. The high level of swimming movements directed against the current in late summer and autumn may be related to an innate habitat change. From February until June, the charr exhibited a bimodal diurnal activity pattern. In July activity was evenly spread over the whole 24‐ hour period and in August and September activity was again mainly diurnal with a bimodal pattern. In October and November the activity was mainly nocturnal and in December and January activity was concentrated in the short light period. Both annual and die1 activity are discussed in relation to earlier findings in general locomotor activity in Arctic charr and other salmonids.

Light availability and diurnal growth of a green macroalga (Caulerpa cupressoides) and a seagrass (Halophila decipiens)

The effects of daily light period on diurnal growth patterns of a green macroalga [Caulerpa cupressoides v.lycopodium f.elegans (J. Agardh) Weber-van Bosse] and a seagrass (Halophila decipiens Ostenfeld) were investigated in Salt River submarine canyon in the US Virgin Islands in summer 1984. The daily light period, in which quantum irradiance exceeded the light saturation point for photosynthesis of the macroalga and seagrass, was manipulated in situ using lamps and shades. Plant growth was measured every 6 h for 7 d under natural and experimental daily light periods.C. cupressoides grew at the same rate day and night.H. decipiens grew more during the day than at night, a pattern that persisted under continuous light and dark treatments, indicating endogenous control of diurnal growth. Growth vs daily light period curves indicate thatC. cupressoides grew faster thanH. decipiens in short daily light periods, consistent with the observation that the macroalga penetrates to deeper water than the seagrass in Salt River canyon. Overall growth (day + night) ofH. decipiens was unaffected in lengthened light periods and reduced in shortened light periods. Chlorophyll content ofC. cupressoides was not correlated with light availability, while that ofH. decipiens was positively correlated. The alga and seagrass had different diurnal growth patterns but similar overall growth responses to daily light periods. This study shows that diurnal growth patterns are probably under endogenous control, while overall growth is a response to in situ light conditions.

Regulation of Protein Synthesis during Photomorphogenesis of Gametophytes of the Fern Onoclea sensibilis

Gametophytes of the fern Onoclea sensibilis grow as filaments in the dark and in red light and become planar in blue light. Pulse-labeling 4-day-old gametophytes with [(35)S]methionine at different times after transfer to dark, red, and blue light environments revealed higher rates of amino acid uptake and protein synthesis in blue light than in red light or in the dark. Characterization of the extant and newly synthesized soluble proteins by one- and two-dimensional gel electrophoresis showed that the patterns of protein accumulation and synthesis in gametophytes exposed to short periods of red or blue light were qualitatively indistinguishable from those of gametophytes maintained in the dark. However, some striking increases and decreases in the levels of certain polypeptides were noted and these changes were accentuated during continued growth of gametophytes in the different environments. The results show that photomorphogenesis of gametophytes of O. sensibilis is associated with quantitative rather than qualitative changes in the population of mRNAs available for translation.

Intrinsic variability in the frequency of embryonic diapauses of the annual fish Nothobranchius korthausae, regulated by light:dark cycle and temperature

The influence of the light:dark cycle and temperature on the embryonic development, especially diapause, of the annual fish Nothobranchius korthausae was investigated. The variability of the frequency of diapause II during constant L:D cycle and temperature, but at different times of the year, was also studied. In agreement with previous studies it appeared that diapause I does practically not occur in N. korthausae (and other Nothobranchius species), even under sub-optimal conditions which are known to induce diapause II and III. Only at very low temperatures, a first developmental arrest could be induced during the dispersed phase, as well as during the reaggregation phase. Diapause II and III can be induced more easily, by exposing the embryos to low (sub-optimal) temperatures and short light periods (or constant darkness). Both diapauses are inhibited or terminated at high temperature and long light periods (12L:12D). The occurrence of an indirect light:dark response via the adult fishes could not be demonstrated. At moderate temperatures and in constant darkness (or short light periods) considerable variability in diapause II-frequency was observed. This could be an intrinsic feature of annual fish development, constituting a strategy for better survival of the species.

Observed and modelled stomatal responses to dynamic light environments in the shade plant Alocasia macrorrhiza

Abstract. Dynamic responses of stomatal conductance to lightflecks (15 s to 5 min) were observed in the tropical understory plant Alocasia macrorrhiza. Brief observations were also made on step changes in light, flashing light and short low‐light periods (darkflecks) after stomata had reached steady state conductances in high light. Stomata opened substantially even in response to very short lightflecks, with maximal opening being reached about 20 min after the end of the lightfleck. These responses are compared to those of a semi‐mechanistic stomatal model consisting of three steps in series: a biochemical signal which responds directly to light, producing osmotic changes within the guard cells which, in turn, drive the movement of water into the guard cells. The rate of change of each component was assumed to be given by the difference between the current state of that component and the state of the previous component in the series divided by a characteristic time constant for each step. This model allowed excellent description of observed responses to lightflecks, including the fleck‐length dependence of stomatal opening, the lag between the end of the lightfleck and the time of maximal stomatal conductance and the response to multiple flecks. However, agreement with predicted responses to flashing light and darkflecks was poor. Good agreement could be restored by using different time constants for the initial biochemical step, suggesting that the speed of the initial biochemical response is not constant but dependent on the current physiological state of the stomata. For leaves experiencing predominantly low light, punctuated by relatively short and infrequent periods of high light, this model allows good description of the dynamic changes in stomatal conductance.

Single-sample technique for measuring oxygen production and consumption in macrophytic algae

Macroalgae production studies are handicapped by the broad range of variability within experimental replicates. Practically, it is impossible to obtain identical duplicate samples of plant material for the dark and light bottles. A new modification of the oxygen technique, described here, eliminates this difficulty, and also provides an approximation of the respiration in the light bottle. It consists of measurements of dissolved oxygen changes, produced by a single sample of algal biomass, incubated in short alternate periods of light and dark. In this way, each thallus tested provides daily curves of net photosynthesis and respiration. From the data obtained, daily curves of primary productivity are extrapolated.

Water vapor uptake and photosynthesis of lichens: performance differences in species with green and blue-green algae as phycobionts.

Dry lichen thalli were enclosed in gas exchange chambers and treated with an air stream of high relative humidity (96.5 to near 100%) until water potential equilibrium was reached with the surrounding air (i.e., no further increase of weight through water vapor uptake). They were then sprayed with liquid water. The treatment took place in the dark and was interrupted by short periods of light. CO2 exchange during light and dark respiration was monitored continuously. With no exception water uptake in all of the lichen species with green algae as phycobionts lead to reactivation of the photosynthetic metabolism. Further-more, high rates of CO2 assimilation were attained without the application of liquid water. To date 73 species with different types of Chlorophyceae phycobionts have been tested in this and other studies. In contrast, hydration through high air humidity alone failed to stimulate positive net photosynthesis in any of the lichens with blue-green algae (Cyanobacteria). These required liquid water for CO2 assimilation. So far 33 species have been investigated, and all have behaved similarly. These have included gelatinous as well as heteromerous species, most with Nostoc phycobionts but in addition some with three other Cyanophyceae phycobionts. The same phycobiont performance differences existed even within the same genus (e.g. Lobaria, Peltigera) between species pairs containing green or blue-green phycobionts respectively. Free living algae also seem to behave in a similar manner. Carbon isotope ratios of the lichen thalli suggest that a definite ecological difference exists in water status-dependent photosynthesis of species with green and blue-green phycobionts. The underlying biochemical or biophysical mechanisms are not yet understood. Apparently, a fundamental difference in the structure of the two groups of algae is involved.

Plasma ionic calcium regulation by anuran parathyroid glands

1. 1. Plasma ionic calcium ([Ca]i), directly measured by a calcium specific electrode, was measured in 7-day post-operative parathyroidectomized (PTX) frogs ( Rana pipiens) over complete 24 hr light-dark (L-D) cycles during February, June and October. 2. 2. [Ca]i in PTX frogs was depressed about 20% from control levels at each monthly interval, with a maximal depression of plasma total calcium ([Ca]t) in October, and a minimal depression of [Ca]t in June. 3. 3. Over 24 hr L-D cycles [Ca]i is depressed in PTX frogs during the nocturnal period in February with short light periods; but maximally depressed during the light period in June/October with equivalent or long light periods. 4. 4. Hypocalcemia of [Ca]i in PTX frogs is concomitant with a decline in nonprotein-bound calcium in October and February; while protein-bound calcium will increase in February and June. 5. 5. Plasma immunoreactive calcitonin (iCT) decreased from 10.8 ± 7.2, in controls, to 4.8 ± 3.9 ng/ml, in PTX frogs, in October and February with no difference observed in June.

Psoriasis in Children

Psoriasis in children 16 years of age and younger is common. Frequently the disease is associated with a positive family history and often appears as acute guttate psoriasis. Acute guttate psoriasis is seen commonly after streptococcal infection of the upper respiratory tract, but may be associated with other viral and bacterial diseases as well. Acute guttate psoriasis responds well to treatment but often recurs as more typical small- or large-plaque disease. The treatment of childhood psoriasis should be simple and, if the disease is significant, carried out in the hospital. Results are much more impressive in hospitalized patients than in outpatient settings. Topical corticosteroids should be used only for short periods of time, whereas tar, ultraviolet light, and anthralin have much longer beneficial effects.

The turnover of chlorophyll in greening wheat leaves

A method for the estimation of chlorophyll turnover in wheat leaves is presented. This is based on the inhibition of chlorophyll synthesis by treatment of the cut leaves with laevulinic acid (LA), a competitive inhibitor of δ-aminolaevulinic acid dehydratase. The turnover of chlorophyll in young, greening leaves, given short periods of light was a relatively rapid process. However, in seedlings exposed to light for longer periods the turnover became progressively slower, and was measured in days rather than hours.