Reduction In Photoperiod Research Articles

Early hatchery protocols for tetrasporogenesis of the antimethanogenic seaweed Asparagopsis armata

The red alga Asparagopsis armata is an emerging aquaculture-target species due to its application as an antimethanogenic feed ingredient in ruminants, yet information on A. armata reproduction and cultivation is currently lacking. We therefore quantified the effects of temperature, irradiance, nutrients, and photoperiod, and addition of plant growth regulators (PGRs; indole-3-acetic acid, abscisic acid, 1-aminocyclopropane-1-carboxylic acid) on tetrasporogenesis in domesticated A. armata that had been maintained under controlled conditions (18 °C, 12 h light:12 h dark photoperiod) for 18 months prior to experimentation. Tetrasporogenesis was only induced at 5 and 15 µmol photons m−2 s−1 under an 8 h light:16 h dark photoperiod with 3.5 mg nitrogen L−1 and tetraspore release was 28-fold greater at 18 °C compared to 15 °C after 28 days of exposure. After 29 days, tetraspore release and germination rate both declined. All PGR treatments prevented tetrasporogenesis. This study is the first to provide the detail and framework necessary to enable A. armata hatchery development. We conclude that tetrasporogenesis was most likely induced in response to a significant reduction in photoperiod rather than as a result of replicating seasonal environmental conditions, and that temperature played a key role in determining reproductive output. With overall higher tetraspore release and a consistent germination rate of > 90%, we recommend exposing tetrasporophyte biomass to 18 °C, 15 µmol photons m−2 s−1 and 3.5 mg nitrogen L−1 under an 8 h L:16 h D photoperiod for up to 29 days to obtain a reliable supply of tetraspores for seeding onto ropes for transfer to the hatchery phase.

Development of chia plants in field conditions at different sowing-date

The objective of this study was to characterize the development of chia plants sown at different dates, and to determine the relation between the duration of the development cycle and the final number of leaves and the leaf appearance rate on the main stem. A field experiment was conducted in the agricultural year of 2016/2017 in five sowing dates (09/22/16, 10/28/16, 01/03/17, 02/08/17 and 03/24/17) in the edaphoclimatic conditions of the central region of the RS, Brazil. A randomized block design with four replicates was used. For each sowing date, the duration of the vegetative and reproductive phases in days and in °C day (Tb = 11 °C), the final number of leaves and the phyllochron of the main stem were determined. The duration of the vegetative phase of chia plants in days and in ºC day varies between the sowing dates, with shorter duration in late sowings in response to the photoperiod reduction. The vegetative phase represents the largest part of the total development cycle in early sowing dates, being overcome by the reproductive phase in late sowing dates (02/08/17 and 03/24/17). The phyllochron for chia varies from 36.23 (very late sowing) to 59.88 ºC day (early sowing). Later sowing has a smaller final number of leaves accumulated in the main stem due to the shorter duration of the vegetative phase.

Numerical Climatic Analysis of Soybean Development in Sowing Dates in Humid Subtropical Climate

Abstract The objective of this study was to determine the mean duration and the interannual variability of phenological subperiods and total soybean development cycle for 11 sowing dates in the humid subtropical climate conditions of the state of Rio Grande do Sul. Daily meteorological data were used from 1971 to 2017 obtained from the Pelotas agroclimatological station and from 1968 to 2017 from the main climatological station of Santa Maria. The soybean development simulation was performed considering three sets of cultivars of relative maturity groups between 5.9-6.8, 6.9-7.3 and 7.4-8.0, with intervals between the sowing dates of approximately 10 days, comprising September, 21 to December, 31. The data of phenological subperiods duration and total development cycle were subjected to the exploratory analysis BoxPlot, analysis of variance and mean comparison by the Scott-Knott test, with 5% of probability. The development cycle duration is greater in Pelotas than in Santa Maria. There was a decrease in soybean cycle duration from the first to the last sowing date for both locations. The R1-R5 subperiod duration is decreasing from October to December due to photoperiod reduction.

The dark side of nursery photoperiod reduction on summer plantation performance of a temperate conifer: High winter mortality mediated by reduced seedling carbohydrate and nitrogen storage

Planting during summer is considered as a suitable option for forest plantations in regions with a temperate monsoon climate. However, seedlings planted early in the summer are not dormant and experience active growth, which makes them vulnerable to planting stress. The artificial reduction of the photoperiod in the nursery is used to harden seedlings of boreal and alpine tree species for summer planting. Little, however, is known about the effect of artificial reduction of photoperiod with respect to summer planting in temperate monsoon climate tree species.The objective of this study was to assess the effect of length and timing of photoperiod reduction on seedling morphology and physiology attributes in the nursery and on the field performance of Pinus tabuliformis. We applied four photoperiod treatments (6 h, 8 h, 10 h, control) in the nursery on four dates in the summer (June 23, July 3, July 13, and July 23). The nursery and field site were located near Beijing, Northern China. We measured seedling morphology and non-structural carbohydrates and nitrogen concentrations in the nursery and in the field. Additionally, we measured field mortality and plant growth for three years.The reduction of the photoperiod did not have any effect on bud set, but it reduced seedling growth and non-structural carbohydrate concentration, while increasing plant N concentration. A delay in the application of photoperiod treatments increased plant size and the proportion of seedlings that developed buds, and it decreased plant non-structural carbohydrates and nitrogen concentration. High field mortality was typically observed in the winter, and the early application of photoperiod treatments increased winter mortality but enhanced field growth. Mortality during the first winter was negatively related to plant non-structural carbohydrates and nitrogen concentrations at the beginning of the cold season. In contrast, photoperiod had no effect on outplanting mortality and a minor effect on field growth. Field growth in subsequent growing seasons was directly related to the size of the plant at the beginning of the first cold season. However, field growth during the growing season immediately after planting was negatively related to seedling size, and positively related to non-structural carbohydrates and nitrogen concentrations at planting.This study demonstrates that summer planting of container seedlings is feasible for P. tabuliformis, and there is no need to reduce the photoperiod in the nursery before outplanting. Optimizing the planting date during the summer appears to be critical for good mid-term growth and low winter mortality.

Reproductive events and respective faecal androgen metabolite concentrations in captive male roan antelope (Hippotragus equinus).

Understanding the reproductive biology of the roan antelope (Hippotragus equinus) (É. Geoffroy Saint-Hilaire, 1803) is crucial to optimise breeding success in captive breeding programmes of this threatened species. In this study, the pattern of faecal androgen metabolite (fAM) production related to reproductive events (calving or birthing, mating, gestation, and lactation), sexual behaviours as well as environmental cues were studied in captive adult male roan antelope. Faecal sample collection and behavioural observations were carried out from August 2017 to July 2018 for three reproductive males participating in a conservation breeding programme at the Lapalala Wilderness Nature Reserve in South Africa. As a prerequisite, the enzyme immunoassay used in this study was biologically validated for the species by demonstrating a significant difference between fAM concentrations in non-breeding adults, breeding adults and juvenile males. Results revealed that in adults males, the overall mean fAM levels were 73% higher during the breeding period compared to the non-breeding periods, and 85% higher when exclusively compared to the lactation/gestation periods, but only 5.3% higher when compared to the birthing period. Simultaneously, fAM concentrations were lower during the wet season compared to the dry season, increasing with a reduction in photoperiod. With the exception of courtship, frequencies of sexual behaviours monitored changed in accordance with individual mean fAM concentrations in male roan antelope, the findings suggest that androgen production varies with the occurrence of mating activity and may be influenced by photoperiod but not with rainfall.

Influence of photoperiod on morphogenetic processes in near-isogenic lines in PPD genes of soft wheat

Aim. Investigation of the effects of contrast photoperiodic conditions and the state of the Ppd genes (dominant or recessive) on growth and morphogenetic reactions in NILs of soft winter wheat Myronivska 808 and Mercia cultivars. Methods. Experiments were carried out in field and vegetation chamber conditions. NILs were cultivated in contrast photoperiodic conditions: control group plants – in the conditions of a long photoperiod of 16 hours (LD), experimental group plants – in a short photoperiod – 9 hours (SD). The stages of organogenesis, the height of apical growth cones, the number of tillers and biomass of the above-ground part of plants were determined. Results. In our studies, we found that all NILs of both cultivars respond to a photoperiod reduction as typical long-day plants, namely: they have a two-stage of organogenesis delay in development, growth processes are inhibited (growth of the apical cone, formation of tillering shoots and accumulation of plant biomass). It was shown that NILs with the genotypes Ppd-A1a and Ppd-D1a are characterized by accelerated development due to inhibition of growth processes. Conclusions. The genes responsible for controlling the development and photoperiodic sensitivity of soft wheat plants also determine the pace of development, growth and morphogenetic reactions of common wheat plants as in LD photoperiod conditions (16 hours), as well as in SD photoperiod conditions (9 hours).
 Keywords: Triticum aestivum L., Ppd genes, photoperiod, stages of organogenesis, shoot apex.

Extraction of info chemicals inducing the production of resting eggs in cladocerans.

Chemically mediated interactions are widespreadin aquatic ecosystems; this also applies to planktoniccrustaceans [1]. To date, ample data on the effects ofchemical substances secreted by conspecifics or competitors on the morphology, physiology, and behaviorof crustaceans have been accumulated [2]. Understanding the environmental consequences and evolutionary prerequisites of such a phenomenon is hampered, in particular, by an almost complete lack ofinformation on the chemical nature of substancessecreted by crustaceans. The main difficulties in theisolation and identification of these substances arerelated to their low concentrations in the medium,potential synergistic effects, and the absence of methods for determining the target components [3].One of the wellknown examples of chemical interactions in aquatic ecosystems is the stimulating effectof metabolic products of planktonic crustaceans onthe formation of resting eggs by females. The life cycleof many planktonic crustaceans represents an alternation of asexual and sexual reproduction. In favorableconditions, females reproduce by parthenogenesis.When conditions deteriorate, the reproduction typechanges, and females form resting eggs that can survive adverse conditions, including frozen or driedstates. Formation of resting eggs is affected by variousstimuli (reduction of photoperiod and/or temperature, decreased food supply, etc.) signaling about theonset of adverse conditions [4]. One of such stimuli isown metabolic products. For example, it was shownfor several representatives of Rotifera, Cladocera, andCopepoda that metabolic products can cause formation of resting eggs by females of respective species [5].In experiments with a model cladoceran species

Changes of carbon and nitrogen metabolites in white spruce (Picea glauca [Moench] Voss) of contrasted growth phenotypes

The present study documents the changes occurring at the biochemical level in white spruce trees (Picea glauca [Moench] Voss) with contrasted growth phenotypes during the summer period. Full-siblings of tall versus small spruces were grown under controlled conditions at constant day/night temperatures (24/15°C) and exposed to a decreasing photoperiod (15.7–12.2 h) simulating natural photoperiod reduction during the summer in eastern Canada. Growth parameters (stem height and tree biomass) were determined and non structural carbohydrates, soluble proteins and amino acids were quantified in current-year needles and stem, oldest stem and roots from mid-July until the end of September 2006. Sucrose was the main soluble sugar found in all organs, but its concentrations did not significantly change during the summer. In contrast, starch concentrations rapidly declined by the end of the experiment, especially in needles and stems. Both sucrose and starch did not generally differ between growth phenotypes. Total soluble protein significantly accumulated by mid-August (14.4 h of photoperiod) in small trees. Arginine and glutamine were the most abundant amino acids found in spruce organs, and their concentrations strongly increased at 14.4 h of photoperiod, especially in small trees. Our results highlight marked differences in nitrogen metabolism in late summer between contrasted growth phenotypes, especially for arginine, an amino acid typically associated with growth arrest and nitrogen reserve in perennial species. They also reveal that old stems and roots are important storage organs of organic reserves.

Dormancy-associated MADS genes from the EVG locus of peach [Prunus persica (L.) Batsch] have distinct seasonal and photoperiodic expression patterns

Mapping and sequencing of the non-dormant evg mutant in peach [Prunus persica (L.) Batsch] identified six tandem-arrayed DAM (dormancy-associated MADS-box) genes as candidates for regulating growth cessation and terminal bud formation. To narrow the list of candidate genes, an attempt was made to associate bud phenology with the seasonal and environmental patterns of expression of the candidates in wild-type trees. The expression of the six peach DAM genes at the EVG locus of peach was characterized throughout an annual growing cycle in the field, and under controlled conditions in response to a long day–short day photoperiod transition. DAM1, 2, 4, 5, and 6 were responsive to a reduction in photoperiod in controlled conditions and the direction of response correlated with the seasonal timing of expression in field-grown trees. DAM3 did not respond to photoperiod and may be regulated by chilling temperatures. The DAM genes in peach appear to have at least four distinct patterns of expression. DAM1, 2, and 4 are temporally associated with seasonal elongation cessation and bud formation and are the most likely candidates for control of the evg phenotype.

Guar Meal Diets as an Alternative Approach to Inducing Molt and Improving Salmonella Enteritidis Resistance in Late-Phase Laying Hens

Induced molting of laying hens is a practice used by commercial egg producers to increase the productive lifetime of their flock. However, the conventional method of inducing molt, which involves removal of feed, water, or both as well as a reduction in photoperiod to less than a natural day has drawn criticism due to animal welfare and food safety concerns. The objective of this study was to explore the efficacy of diets containing high levels of guar meal (GM) in inducing molt and reducing susceptibility to Salmonella Enteritidis colonization in late-phase laying hens. Late-phase (68 wk old) Lohmann laying hens were either full-fed standard laying hen diets (nonmolted control), induced to molt by feed withdrawal, or full-fed standard laying hen diets containing 20% GM with or without 250 units/kg of mannanase Hemicell supplementation. On the fourth day of treatment, all hens were orally challenged with SE (1.65 × 107 cfu). Hens were killed and evaluated for Salmonella colonization and differences in organ weights 5 d postinoculation. Salmonella Enteritidis present in crop, liver, ovary, and cecal contents were significantly reduced by feeding GM with enzyme supplementation compared with feed withdrawal hens. No significant differences were observed in reproductive tract weights of molted groups, although a difference in liver weight was detected. Results indicate that feeding diets containing 20% GM are as effective as complete feed withdrawal with respect to inducing molt with the added benefit of improved resistance to Salmonella Enteritidis colonization and translocation.

Asymmetric Control of Short Day Response in European Hamsters

The European hamster (Cricetus cricetus) is a circannual species in which the synchronization of the circannual cycle to the natural year occurs during 2 annual phases of sensitivity. Around the summer solstice, the animals are sensitive to a shortening of photoperiod. During this sensitive phase, pronounced changes in circadian output parameters are observed, indicating a different functional state of the circadian system. This special state is assumed to be necessary to develop the extreme sensitivity to short day length in European hamsters during this phase. In natural conditions, the animals are able to recognize the shortening of photoperiod already in mid-July, when the photoperiod is reduced only by 30 min. To investigate the short-day response in sensitive European hamsters on the basis of the 2-coupled oscillator model of Pittendrigh and Daan (1976), daily activity and the reproductive state of European hamsters were recorded after an asymmetrical reduction of photoperiod from long (LD 16:08) to short (LD 08:16) photoperiods. The activity pattern of the animals showed an immediate response to the short photoperiod at the day of transfer when the night was extended only into the evening, but there was a significant delay in the response time when the night was extended into the morning. Thus, the evening oscillator E is more important in inducing the photoperiodic response than the morning oscillator M. Moreover, the broad intragroup variation in the latter conditions strongly suggests that the changes in the activity pattern were endogenously induced and that the animals were not able to recognize a lengthening of the night into the morning. Gonadal regression started in both groups 3 weeks after the change in the activity pattern, indicating that this process is initiated when the circadian system has received the short-day signal either through changes in photoperiod or through the circannual clock.

Change in the effect of constant photoperiods on the rate of sexual maturation in modern genotypes of domestic pullet

1. Data for modern egg-type hybrids reared on constant daylengths show that, as expected, they mature more quickly than earlier genotypes. However, the constant photoperiod which gives earliest sexual maturity has not changed as a result of selection and is 10 h for both early and modern genotypes. 2. Further analysis showed that the rate of delay in sexual maturity for constant photoperiods above 10 h is similar for modern and for early hybrids (+0·29 d for each incremental one hour of photoperiod), the response of modern hybrids below 10 h (+4·22 d for each one-hour reduction in photoperiod) is more than double that of early hybrids (+1·71 d/h).

Effect of a Single Short-Term Reduction in Photoperiod on Photorefractoriness in Turkey Hens

In a prior study, we reported that a high proportion of hens in a winter-laying flock became relatively photorefractory (rPR) early in the reproductive cyand that successive short-term reductions in photoperiod in such hens each initially depressed egg production but then caused a rebound in rate of lay to briefly exceed that of hens that did not exhibit rPR. The present study was conducted to assess rPR in a summer-laying flock and to determine whether a single short-term reduction in day length early in the reproductive cycle might enhance egg production and delay the onset of absolute photorefractoriness (aPR). Control hens received a photoperiod of 16L:8D throughout the experiment. Experimental hens were photostimulated with 16L:8D, received a reduced (but still stimulatory) photoperiod of 11.5L:12.5D for 2 wk beginning 8 wk after photostimulation, and then were returned to 16L:8D for the remainder of the 23-wk test period. Results showed that a single 2-wk reduction in day length shortly after the hens reached peak egg production did not significantly reduce overall flock egg production, but it also did not improve late-season egg production or retard the onset or incidence of aPR. The incidence of rPR was substantially less in this study than we had observed with a winter-laying flock (32.9 vs. 67.1%), but similar proportions of treated hens exhibited the most severe rPR response (a brief but complete cessation of egg production) in both studies (21.1 vs. 24.0%), and all treated hens that subsequently became aPR had shown this severe rPR response to the test photoperiod. We concluded that a core proportion of hens (approximately one-fifth) exhibited a strong rPR response when presented with a reduced photoperiod early in the reproductive cycle, regardless of season of the year, and that such hens were more likely to subsequently exhibit poor egg production or become aPR than flockmates that did not exhibit rPR. Therefore, some indication of the incidence of rPR early in the lay period may have a predictive value for the overall egg production of the flock.

A model for predicting the age at sexual maturity for growing pullets of layer strains given a single change in photoperiod

A model is presented which will predict mean age at first egg (AFE) for pullets of laying strains reared under non-limiting environmental conditions but exposed to a single change in photoperiod during the rearing stage. An initial analysis of 12 previously reported trials involving a wide range of genotypes showed that the response to an increase in photoperiod is not simply the inverse of the response to an equal decrease in photoperiod applied at the same age. Maximum sensitivity to a reduction in photoperiod was found shortly before onset of lay, whereas maximum sensitivity to an increment in photoperiod was observed at around 10 weeks of age. Two experiments were conducted to provide further data. The first compared the effect of 3-h increases in photoperiod from 8 h to 11 h or from 11 h to 14 h with the double increment from 8 h to 14 h and also tested a reduction from 11 h to 8 h, all imposed at 17 weeks of age. AFE was advanced to a similar extent by the changes from 8 to 11 h and from 11 to 14 h (9.8 and 10.9 days respectively). Response to the double increment was not additive: AFE on this treatment was 13.3 days earlier than for constant 8 h controls. Reduction in photoperiod from 11 to 8 h at 17 weeks delayed AFE by 18.7 days compared with constant 11-h controls. In the second experiment, pullets of two strains were transferred from 8 to 16-h photoperiods and from 16 to 8 h at 5, 7, 9, 15, 17 and 19 weeks of age. Controls were kept on constant 8 and constant 16-h days. Transfer from 8 to 16-h photoperiods at 5 weeks of age had no effect on AFE. At 7 weeks there was a bimodal response with some pullets subsequently showing advanced maturity and others not. Maximum stimulation of early maturity (31 days on average for the two genotypes) was obtained at 9 weeks of age and response to stimulation declined linearly with age thereafter. The delay in AFE resulting from a reduction in photoperiod (16 to 8 h) increased linearly between 0 and 15 weeks. At 17 and 19 weeks, the response was bimodal, with some pullets maturing at the same age as long-day controls and others showing delayed maturity. Using all this evidence and some other unpublished data, a model is developed to predict AFE as a function of mean photoperiod and change in photoperiod during the rearing phase. Elements are incorporated to allow for the insensitivity of pullets younger than 50 days to an increase in photoperiod and the effect observed late in rearing when a change in photoperiod comes too late to alter AFE for the most precocious individuals in a flock. Two coefficients are required to adjust for genotype. One describes mean AFE for the genotype when reared on constant daylength and the other defines the rate at which age effects the response to a single change in photoperiod.

Induction of flowering in tropical trees by a 30-min reduction in photoperiod: evidence from field observations and herbarium specimens.

During the late rainy season in October 1997 we observed. over a range of >100 km, the highly synchronous emergence of flower buds in several deciduous tree species of the semi-deciduous tropical forest in Guanacaste, Costa Rica. Synchronous flowering soon after the rapid decline in day length around the September equinox and in the absence of any notable climatic cues suggested flower induction by declining photoperiod. By combining field observations and the analysis of flowering herbarium collections, we established highly synchronous flowering periods with low interannual and latitudinal variation predicted for photoperiodic flower induction for more than 25 tree species and a few herbs. We describe morphogenetic changes at the shoot apex of three species during flower induction and the suppression and induction of flowering in several herbaceous species by experimental daylight extension. The combined observations provide strong, mainly indirect evidence for photoperiodic induction of flowering in many tropical tree species. At low latitudes with annual variation in day length of 1 hour, flower induction must be caused by a decline in photoperiod of 30 min or less. This is the first report of photoperiodic control of flowering in trees.

Effects of photoperiod reduction on rat circadian rhythms of BP, heart rate, and locomotor activity.

The effects of a photoperiod reduction in the entrainment of circadian rhythms of systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and spontaneous locomotor activity (SLA) were determined in conscious Wistar rats by using radiotelemetry. Two groups of seven rats were maintained in a 12:12-h light-dark (12L/12D) photoperiod for 11 wk and then placed in a reduced photoperiod of 8:16-h light-dark (8L/16D) by advancing a 4-h darkness or by advancing and delaying a 2-h darkness for 6 wk. Finally, they were resynchronized to 12L/12D. Advancing a 4-h dark phase induced a 1-h advance of acrophase for SBP, DBP, and HR, but not for SLA. The percent rhythm, amplitude, and the 12-h mean values of all parameters were significantly decreased by the photoperiod reduction. When symmetrically advancing and delaying a 2-h dark phase, a 1 h 20 min delay of acrophases and a decrease in percent rhythms and amplitudes of SBP, DBP, HR, and SLA were observed. Only the 12-h mean values of HR and SLA were decreased. Our findings show that the cardiovascular parameters differ from SLA in phase-shift response to photoperiod reduction and that the adjustment of circadian rhythms to change from 12L/12D to 8L/16D photoperiod depends on the direction of the extension of the dark period.

Effects of Photoperiod Manipulation on Brook Trout Reproductive Development, Fecundity, and Circulating Sex Steroid Concentrations

The goal of this study was to determine the feasibility of conducting reproductive studies with brook trout Salvelinus fontinalis at times other than the normal fall-spawning period. The timing of sexual maturation, fecundity, and concentrations of serum sex steroids (17-β-estradiol, E2; and testosterone, T) in brook trout held under a normal photoperiod were compared with those in brook trout held under an altered photoperiod (initiated in early September). Fish held on a constant long photoperiod (18 h light: 6 h dark) did not reach sexual maturity during the normal fall-spawning time. When these fish were subsequently subjected to a 16-week accelerated photoperiod reduction from 18 h light/d to a day length of 8.5 h, the males and females matured in 8 and 13 weeks, respectively, and spawned successfully in April and May. Overall viability of embryos from this spring spawning was slightly lower than the average viability of control embryos from previous studies with fall-spawning fish in our laboratory; however, hatchability of viable embryos was similar for the spring-spawning fish and those from previous studies. Hormonal profiles of E2 and T were similar for both females and males in fall- and spring-spawning brook trout. These studies demonstrate that photoperiod alterations can be used to manipulate brook trout reproductive cycles for the purpose of conducting studies at times other than the fall.

Variations of light and temperature regimes and resulting effects on reproductive parameters in medaka (Oryzias latipes).

In seasonally breeding fish species, altered fecundity, fertility, and spawning interval are associated with changes in environmental cues such as temperature and photoperiod. To determine quantitative impact of these cues on a suite of reproductive endpoints, groups of medaka (Oryzias latipes; two breeding pairs per group) were subjected to varying photoperiod and temperature regimes. Embryo production ceased after photoperiod reduction from 16L:8D to 8L:16D (at 25 degrees C). A severe decline in production was observed after a temperature decrease of 10 degrees C (25 degrees C to 15 degrees C [16L:8D]). Under reduced photoperiod, histologic analysis showed no mature ova and moderate oocyte atresia in all individuals. However, reduced temperature (15 degrees C) produced only mild oocyte atresia and fewer mature ova. Under both reduced photoperiod and reduced temperature regimes, mature spermatozoa were observed. Offspring viability, along with spawning interval, were not affected by photoperiod reduction. Temperature change had no effect on offspring viability but caused an increase in spawning interval. A shortened photoperiod profoundly affected medaka reproduction, whereas decreased temperature reduced, but did not arrest, fertility; reduced photoperiod decreased fecundity. These findings have important implications for culture of medaka as well as use of this teleost model for reproductive toxicology studies.

Effect of constant and of changing photoperiod on plasma LH and FSH concentrations and age at first egg in layer strains of domestic pullets

1. ISA Brown pullets were transferred from 8 to 14 h or from 14 to 8 h photoperiods at 35 or 56 d of age. Controls were maintained on constant 8 or 14 h photoperiods from day 1. 2. Blood samples were obtained immediately before each daylength change and subsequently at 7 d intervals until 1st egg in the treated groups and at 70 d of age and then at 14 d intervals until 1st egg in the constant photoperiod controls. Plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations were determined using homologous radioimmunoassays. 3. Prior to 16 weeks, LH was consistently higher in birds on constant 14 h photoperiods than in those on constant 8 h, but was down-regulated as birds approached maturity so that LH concentrations in the 2 groups were similar during the final 10 d before the first egg was laid. FSH concentrations rose steadily with age but with a tendency for concentrations to be higher in the 8 h than in the 14 h treatment. Birds on constant 8 h daylengths matured 18.3 d later than those on constant 14 h photoperiods. 4. A 6 h increment in photoperiod given at 35 d or 56 d, resulted in an increase in LH within 7 d in both cases. FSH concentration did not respond to an increase in photoperiod at 35 d but rose following the same increase at 56 d. This was associated with a 3-week advance in sexual maturity, whilst age at 1st egg in birds photostimulated at 35 d was similar to the age with a constant 14 h photoperiod. 5. LH concentration fell when photoperiod was reduced from 14 to 8 h at either 35 or 56 d and remained below the constant 8 h controls for many weeks before rising to a concentration not significantly different from other groups in the final 10 d before 1st egg. FSH concentrations in birds exposed to a decreased daylength at 35 d, although more oscillatory, were similar to the constant 8 h photoperiod controls. In birds exposed to the same decrease at 56 d, FSH concentration initially tumbled but was similar in the 2 groups during the latter stages of rearing; neither differed significantly from the constant daylength controls during the 60 d before 1st egg. Sexual maturity in both groups given a reduction in photoperiod was delayed by about 2 weeks compared with constant 8 h controls. 6. Change in FSH concentration following an increase in daylength was a better predictor of age at 1st egg than change in LH. However, FSH concentrations after 14 weeks of age were rather similar in short day and long day controls and in the 2 groups given reductions in photoperiod at 35 d and 56 d, despite differences of nearly 5 weeks in mean age at 1st egg amongst these 4 treatments.

High frequency of plant regeneration in sunflower from cotyledons via somatic embryogenesis

A plant regeneration methodvia somatic embryogenesis of severalHelianthus annuus L. genotypes was developed. Starting from cotyledonary explants high frequency embryo induction was obtained following several subcultures on defined media. An appropriate cotyledon developmental stage was identified. Etiolated explants and darkness treatment were necessary to obtain somatic embryos in all tested genotypes. After 20-25 days on somatic induction medium containing an auxin:cytokinin ratio of 1:1, the germination of embryos was induced by a reduction of the hormonal ratio (1:2). Shoots were excised from callus and transferred onto a medium containing various vitamins. The range of embryogenesis frequency was 33-72%, depending on the genotype. High frequency of rooting (49-82%) was obtained using a medium supplemented with 0.5 mg/L of ancymidol and by a reduction of photoperiod. A large percentage of somatic embryos developed into normal regenerated plants producing viable seeds.