Long-day Light Research Articles

The early-flowering mutant efs is involved in the autonomous promotion pathway of Arabidopsis thaliana.

The transition to flowering is a crucial moment in a plant's life cycle of which the mechanism has only been partly revealed. In a screen for early flowering, after mutagenesis of the late-flowering fwa mutant of Arabidopsis thaliana, the early flowering in short days (efs) mutant was identified. Under long-day light conditions, the recessive monogenic efs mutant flowers at the same time as wild type but, under short-day conditions, the mutant flowers much earlier. In addition to its early-flowering phenotype, efs has several pleiotropic effects such as a reduction in plant size, fertility and apical dominance. Double mutant analysis with several late-flowering mutants from the autonomous promotion (fca and fve) and the photoperiod promotion (co, fwa and gi) pathways of flowering showed that efs reduces the flowering time of all these mutants. However, efs is completely epistatic to fca and fve but additive to co, fwa and gi, indicating that EFS is an inhibitor of flowering specifically involved in the autonomous promotion pathway. A vernalisation treatment does not further reduce the flowering time of the efs mutant, suggesting that vernalisation promotes flowering through EFS. By comparing the length of the juvenile and adult phases of vegetative growth for wild-type, efs and the double mutant plants, it is apparent that efs mainly reduces the length of the adult phase.

628 Influence of Cooling, Long-day Lighting Regime, and Propagule Type on Flowering of Phlox paniculataL. Cultivars

Rooted terminal cuttings and dormant 1-year-old transplants of Phlox paniculata L. `Ice Cap' and `Red Eyes' were cooled for 0, 4, 8, 12 or 16 weeks and forced under long-day photoperiod provided by incandescent lights as either a night-interruption (2200–0200 hr) or extended-day (1700–2200 hr). The influence of cooling duration, long-day lighting regime, and propagule type on forcing days to flower, flowering stem counts, and flowering stem length was evaluated in a 3 × 2 × 5 factorial experiment. Cooling accelerated flowering and increased stem yield and length. Days to flower for both cultivars decreased and flowering stems and length increased linearly as cooling increased from 0 to 16 weeks, regardless of lighting or propagule type, but cooling for 8 weeks or more was necessary to produce marketable cut flower stems. Extended-day lighting produced longer stems than night interruption, and stem counts were higher among plants grown from transplants, regardless of cooling duration, lighting regime, or cultivar. Flowering stems from rooted cuttings were generally longer than those from transplants. Cut flower stems of `Ice Cap' were longer than those of `Red Eyes', but days to flower and yields for the two cultivars were similar.

Photoperiod and Temperature Influence on Flower Initiation and Development for Euphorbia pulcherrima Grown Under Florida Conditions

Four poinsettia cultivars were grown in glass greenhouses in Gainesville, Fla., in the Fall 1997 to evaluate differences in floral initiation and subsequent development. Three means of regulating photoperiod were 1) natural days 2) long-day lighting to 6 Oct. and then natural days (lights out) 3) long-day lighting to 6 Oct., and then short-day conditions by black cloth for 15 h (black cloth). At 2-day intervals, sample meristems were collected and examined for initiation of reproductive development. Average minimum and maximum temperatures during the first two weeks of October were 22 and 29 °C, respectively, with an average temperature of 25.3 °C. The overall average temperature was 23.2 °C from planting to anthesis. Differences in anthesis dates among cultivars were primarily due to time to initiation vs. rate of development. Under natural days, `Lilo' initiated first on 8 Oct. and `Freedom', `Peterstar', and `Success', followed by 6, 8, and 18 days, respectively. Lights out resulted in `Lilo' initiating 17 Oct., followed by `Freedom', `Peterstar', and `Success' initiating 7, 12, and 15 days later, respectively. Differences between cultivars in time of initiation was reduced under black cloth, where `Lilo' initiated 14 Oct., followed by `Freedom' 2 days later, and `Peterstar' and `Success' 7 days afterward. Initiation was positively correlated to visible bud and anthesis. First color was positively correlated to initiation and visible bud, with the exception of `Lilo'. Growth room studies conducted using various high temperatures and photoperiods indicated similar trends.

Timing of melatonin treatment: differential effects on oestrus and coat growth in goats

AbstractTo avoid winter scarcity of fresh goat milk, simple methods of advancing the season of kidding would be commercially valuable. A combination of long-day light treatment followed by melatonin is successful but other aspects of seasonality including coat growth are also reset. To investigate whether effects on breeding season and coat growth can be dissociated, British Saanen dairy goats (no. = 30) were randomly allocated to one of six groups. Control goats were untreated. Goats in the other five groups received 2 months of treatment with 20 h light: 4 h darkness (20L: 4D) and were then given 3 mg melatonin orally at 16.00 hfor 2 months. The treatments started on 11 January (group 1), 29 March (group 2), 14 June (group 3), 30 August (group 4) and 8 November (group 5). Weekly blood samples were taken for the measurement of progesterone to monitor ovarian activity and prolactin. Side patches (10 cm ×10 cm) were clipped monthly from alternate sides and weighed to measure coat growth. The onset of ovarian activity was advanced from a median date of 15 November in controls to 24 May in group 1 (P < 0·01), 16 August in group 2 (P < 0·05) and 18 October in group 3 (? < 0·05). Groups 4 and 5 showed no significant change in the onset of oestrus (median onset dates 8 November and 1 November, respectively). Group 1 goats came into season again with controls in November. In all except group 5, treatment interacted with time to affect significantly the growth of the coat. The pattern of coat growth was most altered (P < 0·001) in groups 1 and 2. This was associated with effects on plasma prolactin concentrations of light stimulation and melatonin suppression. Group 1 goats resynchronized with control goats to show a coat of normal weight in the winter following treatment. Division of milking goat herds into spring and autumn kidding groups is, therefore, a practical possibility, but effects on overall milk yield require study.

Lupine (Lupinus polyphyllus) Flower in Response to Long-day Photoperiod by Day Extension

Ninety-six uniform plants of each `Russell hybrid' and `Gallery' mix lupines sown 9 June 1995 were randomly assigned to 32 unique treatment combinations. On 14 Dec 1995, plants were either placed in a 17/13°C day/night temperature (DT/NT) greenhouse (COOL) or 22/18°C DT/NT greenhouse (WARM) as controls, or in a constant 4.5°C cooler in the dark for 6, 8 10, or 12 weeks. After cooling, plants were transplanted to #1 nursery cans (2.75 liter) using Sunshine mix #2 and were assigned randomly to the COOL or WARM greenhouse. Greenhouse control plants under natural days were transplanted at intervals similar to cooled plants. Days until visible bud and flowering were analyzed using SAS PROC GLM. Plants receiving long day (LD) flowered 7 to 10 weeks (46 to 70 days) after the start of LD forcing. Buds were visible in 30 to 35 days. Plants receiving natural days (ND) did not flower uniformly unless they were cooled for 12 weeks, yet flowering took longer (8 to 12 weeks) when compared with LD. Unfortunately, LD lighting for the entire forcing period caused excess stretching, so plants finished too tall for quality potted plants. Forcing in a COOL greenhouse delayed flowering about a week compared to the WARM greenhouse.

The Response of Long-day Herbaceous Perennials to a Night-interruption at Low Night Temperatures

A 4-hr night interruption (NI) is an effective way to promote flowering in many long-day herbaceous perennials. Some perennials are grown outdoors in the early spring and often are exposed to low night temperatures. Long days delivered by NI lighting ineffectively promote flowering under low-temperature conditions in some long-day species. The objective of this experiment was to determine the effectiveness of NI long-day lighting treatments delivered at different night temperatures in promoting flowering of several herbaceous perennials. Ten herbaceous perennial species were grown under natural short days augmented with a 4-hr NI. Night temperatures were 2.5, 5, 10, 15, 20, and 25°C with day temperature of 25°C for all treatments. Plants were transferred to 9-hr days at a constant 20°C after 7 weeks of treatment. Results on flowering percentage, date of visible bud and flowering, node count, flower bud count, and plant height at flowering will be presented.

Feeding patterns of S. crassicaudata (Marsupialia:Dasyuridae): role of gender, photoperiod, and fat stores.

Little is known about feeding regulation in marsupials. Sminthopsis crassicaudata is a small nocturnal marsupial, whose tail contains approximately 25% total body fat. We have characterized the effect of gender, photoperiod, food deprivation, and tail removal (lipectomy) on food intake in S. crassicaudata. Males and females maintained in captivity on long-day (LD, 16:8-h light-dark cycle) and short-day (SD, 9:15-h light-dark cycle) light regimens were studied. Feeding patterns under LD and SD photoperiods were initially measured under conditions of ad libitum food supply and then in groups of animals exposed to 24- and 36-h periods of food deprivation. Feeding occurred predominantly in the dark. Females maintained on SD photoperiods for 5 wk ate less (P < 0.005) than females on LD or males on either SD or LD, but this reduction in food intake was not associated with a decrease either in body weight or tail width. After both 24- and 36-h fasts, total food intake in the subsequent 24 h increased (P < 0.001) up to 100% in all groups, with no gender or photoperiod effect. SD females, however, ate less (P < 0.05) than LD females in the first 6 h after refeeding. Tail width decreased (P < 0.05) in all groups of animals after the 36-h fast but only in LD animals after the 24-h fast (P < 0.05). Body weight decreased similarly in all groups of animals after fasting. The effect of tail removal was studied in LD males. The procedure, which was well tolerated, resulted in an initial decrease in body weight (P < 0.005), which recovered within 3 wk. On day 45 in the animals whose tails were removed, body fat was approximately 30% greater than body fat of controls (P < 0.02). No significant increase in food intake occurred after tail removal. These data demonstrate in Sminthopsis crassicaudata 1) a photoperiod and gender-dependent effect on food intake, 2) the ability to regulate the amount and distribution of total body fat, and 3) a dissociation between the regulation of food intake and changes in body fat stores, which suggest alterations in energy expenditure.

Secretion of Luteinizing Hormone During a Forced Molt in Turkey Hens

The secretory pattern of luteinizing hormone (LH) was determined in turkey hens during a forced molt induced by water (1 d) and feed (5 d) restriction and switching the photoschedule from 14 h light (L):10 h dark (D) (long-day) to 6L:18D (short-day), the 1st d of feed and water restriction. Serial blood samples were collected from six hens (every 10 min for 6 h, then every 4 min for 2 h) at four different times during the trial. The first serial bleeding was done at the end of egg laying and 1 d before forced molting was initiated; the second 7 d after the start of forced molting and short-day lighting; the third after 49 d of short-day lighting, and the fourth after 56 d of short-day lighting and 2 d after returning the hens to long-day lighting. Egg production stopped by 5 d after initiation of forced molting. Egg production reinitiated by 34 d (range 22 to 34 d) after returning to long-day lighting. Overall and baseline concentrations of LH were low at the end of egg laying and 7 d after the start of forced molting. Number and amplitude of pulses of LH were also low at these times. Overall and baseline concentrations of LH remained low after 49 d of short-day lighting, with no change in number of LH pulses per 8 h. However, the amplitude of LH pulses was increased at this time in comparison to just after initiation of forced molting. At 2 d after switching to long-day lighting, increases in overall, baseline, and number of pulses of LH were detected. Peak amplitude did not change 2 d after switching to the long-day photoperiod. It was concluded that in turkey hens at the end of a relatively long laying period, baseline LH is low and does not decrease during a forced molt and subsequent reconditioning period. Relatively large increases in circulating LH are induced by exposing the reconditioned hens to the long-day photoperiod of 14L:10D, and this increase was associated with an increase in overall and baseline LH concentrations and LH pulse frequency.

Structural response of the hamster Sertoli cell to hypophysectomy: A correlative morphometric and endocrine study

Reproductively active hamsters were hypophysectomized and examined 6 or 20 days later in a combined morphometric and endocrine study of the Sertoli cell to determine 1) the morphological and endocrine effects of hypophysectomy of both short- and long-term duration, 2) if regression of Sertoli cells after hypophysectomy in a seasonal breeder resembles regression due to seasonal changes, and 3) if effects of hypophysectomy in a seasonal breeder are equivalent to the effects of hypophysectomy in a nonseasonal breeder. Six days after hypophysectomy, at a period when germ cell degeneration is first noted, there was a significant decrease in testis weight, interstitial space, tubule diameter and length, volume of seminiferous tubule, and tubular lumen. There were no significant changes in Sertoli cell nuclear and cytoplasmic volume although cell surface area was decreased significantly. Most organelles exhibited no significant change in volume or surface area except for secondary lysosomes which expectedly increased in volume as the result of phagocytosis of germinal cells. Thus at an early time period when functional changes in germ cells and Leydig cells are clearly evident (Russell et al. [1992] Endocrinology), the Sertoli cell shows minimal changes. Twenty days after hypophysectomy, the cell, nuclear and cytoplasmic volumes and surface area of the Sertoli cells, and volumes and surface areas of nearly all organelles were significantly decreased from values measured in normal and in short-term hypophysectomized hamsters. The exceptions were the total volumes of lipid which increased significantly and lysosomes which were similar to normal but significantly lower than short-term hypophysectomized animals. The long-term hypophysectomized hamster Sertoli cell, like that of the short-day hamster (Sinha Hikim et al. [1989b] Endocrinology, 125:1829-1843) is structurally regressed as a whole rather than exhibiting selective decreases in cellular and subcellular components. The size of the Sertoli cell in pituitary-intact, long- and short-term hypophysectomized animals showed positive and significant correlations with the volumes and surface areas of all its cytoplasmic organelles except the volume of lipid which showed a negative, significant correlation. Comparisons of long-term hypophysectomized hamsters (in long-day light exposure) and short-day exposed animals (Sinha Hikim et al. [1989b] (Endocrinology, 125:1829-1843) suggested that hypophysectomy, in general, resulted in similar, but slightly more severe regressive changes in the testis and germ cell population than those seen during seasonal regression.(ABSTRACT TRUNCATED AT 400 WORDS)

Oestrous activity in three subtropical sheep breeds in Upper Egypt and response to long-day light treatment

SUMMARYOestrous activity in local Rahmani and Ossimi sheep and imported subtropical Awassi sheep at different times of the year in Upper Egypt and the effect of continuous exposure to long-day conditions from July till December on this activity was studied in 1986. The three breeds differed substantially in oestrous activity but differences did not seem to be directly related to latitude of origin. Rahmani ewes from the Nile Delta were mostly cyclic all year round; the percentage coming to oestrus each month never fell below 70%. Ossimi ewes originating from mid-Egypt had a very long breeding season; 74% had an anoestrous period of 68·8 days (v. 27% for Rahmani ewes). All Awassi ewes, except one, had an anoestrous period of 96·5 days on average.Awassi ewes also showed more response to continuous exposure to long days (14 h) than Ossimi ewes, seen in a shorter reaction interval and a greater decrease in the percentage of ewes coming into oestrus (27 and 90% in control and treated Awassi ewes, respectively). The results indicated that changes in daylength, although small in subtropical regions, may be a major factor controlling seasonal changes in reproductive activity in subtropical sheep breeds, the more seasonal breed being more responsive to changes in daylength. The possibility of selection within these breeds for continuous reproductive activity is also indicated.

Temporal Changes in the Pattern of Melatonin Secretion in Sheep Held in Constant Darkness

The pattern of melatonin secretion was investigated in six 2 yr-old Suffolk ewes transferred from a long-day lighting regime (14L:10D) to continuous darkness. During the 9 d in continuous darkness, five of the ewes maintained a characteristic diurnal rhythm in melatonin secretion. However, there was a systematic change in the duration of each episode of melatonin secretion with the result that it extended from 10 h under the entraining lighting regime to about 19 h by the fourth cycle and then contracted to about 14 h by the eighth cycle under continuous darkness. The pattern of individual ewes varied, but overall the time of offset showed a consistent delay each successive day of about 1 h, indicative of control by a pacemaker with a period of greater than 24 h. By contrast, the time of onset tended to occur earlier each day during the first 4 d of continuous darkness, then changed so that after 8 d, it was delayed in all animals compared to the time of onset on d 4. If, as previously postulated, onset is controlled by a separate pacemaker, then this change is accounted for by interaction with the dominant offset control pacemaker; however, control of both onset and offset through a single pacemaker cannot be excluded. The study confirms that the patterns of melatonin secretion developed in sheep held in continuous darkness may be used to gain insight into the activity of the light-sensitive pacemaker centre(s) controlling the offset and onset of pineal function. Further experimentation is required to differentiate whether control is being exerted by one or two or more independent but interacting pacemaker centres.

Phytotron experiments in Pisum

The flowering behavior of 59 Pisum mutants and 228 recombinants was studied in the phytotron in four different photoperiods (continuous light, long-day 18/6 h, short-day 12/12 h, extreme short-day 6/18 h). There was no or little difference in the response of the genotypes to long-day and permanent light, whereas great differences were observed between long- and short-day 12/12 h and between the two short-day trials. About half the genotypes tested were unable to survive or to flower in extreme short-day. Some recombinants, however, had an almost normal development under these unfavorable conditions. Gene fis controls the photoperiodic reaction of the plants: they are unable to flower in short-day. Gene fds negatively influences gene efr for earliness: it causes a strong delay of flowering of efr recombinants in long-day and suppresses the formation of functionable flowers in short-day. Most of the genotypes tested showed a specific reaction to the four photoperiods different from that of the mother variety and the other genotypes. The practical aim of our phytotron experiments is the preselection of Pisum genotypes which might be suited for cultivation in countries with short-day climate.

Etude de l'activité des corps dorsaux de l'escargotHelix aspersaMüller au cours des phases physiologiques de la vie adulte et sous différentes photopériodes / The activity of the dorsal bodies in the snailHelix aspersaMüller as related to photoperiod and to the different phases of the adult life cycle

Summary The dorsal bodies (DB) have been investigated in mature Helix aspersa in different physiological states and in adult animals maintained under short- or long-day light cycles. Morphological criteria as well as a quantitative electron microscopical study do not indicate striking differences in DB cells of snails reared at different photoperiods. Compared with control animals, hibernation causes a reduced activity of the DB, whereas in egg-laying snails, the increase in DB cell size and protein synthesis, the large decrease in the amount of lipids and the mitochondrial changes suggest an activation of DB hormone synthesis.

Effect of vesicular—arbuscular mycorrhizae on growth of Chrysanthemum morifolium Ramat

Benefits of inoculation with the mycorrhizal fungus Glomus fasciculatus (Thaxter) Gerd. Trappe, on growth of Chrysanthemum morifolium ‘Circus’ were determined for varied conditions of N fertilization (375, 1500 or 3000 kg N/ha/year) and irradiance (6 or 800 μE m −2s −1) during lighting long-day treatments. High N fertilization combined with high level of irradiance produced the most mycorrhizal infection. Mycorrhizal infection generally increased C. morifolium height, especially with continuation of long-day lighting to 8 weeks. Mycorrhizae also improved flower, stem and root dry weight for most treatments, particularly the 1500 or 3000 kg N/ha/year fertilization rate and 4- or 8-week long-day light treatments. Although mycorrhizal inoculation increased C. morifolium growth most under extended long-day treatments, only the 2-week duration night lighting resulted in commercially acceptable plant size.

Induction of resting spore germination in Entomophthora aphidis by long-day light conditions

A small proportion of Entomophthora aphidis Hoffmann resting spores produce germ tubes within a few days upon incubation at 20 °C with ample moisture in the dark without chemical treatment or exogenous nutrient. However, the germ tubes do not branch and germ conidia are not produced until after much longer incubation, and then only sparsely. Light periods of 14 h or more in a 24-h day greatly enhance the germination level but seldom result in germination of more than 50% of the spores. Branching of the germ tubes, germ conidia production, and germination of germ conidia all occur rapidly under long-day conditions. The principal germination interval is between 10 and 30 days under the conditions used and it was estimated that the germination level would stabilize after about 60 days. Variability in germination from plate to plate made with the same spore preparation was from about 25 to 50%.

Activité des corpora allata et contrôle photopériodique de la maturation ovarienne chez Locusta migratoria

Locusta migratoria migratoria females of the ‘Kazalinsk’ strain show a sustained inhibition of ovarian maturation when submitted to long-day photoperiodic conditions ( 17 hr 24 hr ). A full ovarian cycle can be initiated at any time throughout adult life by implantation of corpora allata (CA) taken from egg-laying females. Therefore, in inhibited females, the gonadotropic activity of the CA fail to allow normal vitellogenesis. However, if such females receive CA taken from females conditioned in the same way, a full ovarian cycle still occurs. If CA taken from 5-week-old, either mature or immature, females are implanted into 5-day-old females reared without males under long-day lighting, a single ovarian cycle results, no matter what the state of the donor females. The possibility is discussed that in L. migratoria females neurosecretory material may be involved in the functional development of adult CA, whereas the gonadotropic hormone is released from the CA under nervous control, as far as a photoperiod-sensitive strain is concerned.

Photoperiod control of diapause in Daphnia. IV. Light and CO2-sensitive phases within the cycle of activation.

The diapaused embryo of the cladoceran, Daphnia pulex, may require light for terminating the diapause, and a single photocycle may be adequate. In D. pulex the light-refractory phase of diapause may be broken or completed in a variety of environments. In the Supply House strain employed in these studies, the usual low temperature treatment is unnecessary when the embryos are placed in constant darkness in sealed containers. Alternatively, the refractory state in constant darkness may be broken with low 02 and high CO2 tensions. Both modifications were shown to be necessary and in that sequence.A single long-day light signal may terminate the diapause when the embryo passes from the photo-refractory to the photo-sensitive phase. Three kinds of light responses were observed, however. Each relates to the treatment given the embryos prior to light exposure.In one so called internal state the embryo requires one long day or two pulses of light. Scant evidence suggests that the first pulse may be interpreted as either dawn or sunset. In this state there are obviously two photo-inductive phases in each inductive cycle. The embryo may change, however, by "losing" one of the photo-inductive phases. In this condition a single two-hour pulse of light, if given at the appropriate time of a thermocycle, may terminate the diapause.A third internal state is introduced when CO2 is employed to break the refractory phase of diapause. The diapause is terminated by a single two-hour pulse of light, and the embryo is continuously sensitive to the light stimulus. However, the pattern of hatching indicates that activation may occur at restricted phases within the induction cycle.Several roles of CO2 may be deduced from the experimental results. An elevated CO2 tension breaks photo-refractoriness. It also induces a "dark" reaction which may need to be completed before the light may stimulate termination of the diapause. Withdrawal of CO2 after 10 hours prevents activation unless a second light pulse is given immediately thereafter. The apparent deferral of light stimulation suggests a third function of CO2, that of "storing" the light signal until the embryo becomes photo-inductive.The potential roles of CO2 are described in a model of photoperiodism that requires photo-induction at two phases in each daily cycle.