Long-day Response Research Articles

Effects of Temperature and Photoperiod on the Induction of Diapause and the Determination of Body Coloration in the Bean Bug, Riptortus clavatus

Abstract The incidence of diapause and details of body coloration were examined in adults of the bean bug, Riptortus clavatus (Thunberg) (Heteroptera, Alydidae) under various photoperiodic and temperature conditions. The insects showed a long-day photoperiodic response for the induction of diapause at 20, 25 and 30°C. However, some adults at 30°C failed to enter diapause even under short-day conditions. A photoperiodic response that produced light-colored adults under long-day conditions was common among 20, 25 and 30°C, although high temperature increased the proportion of light-colored adults. The photoperiodic response curve for the induction of diapause and that for in the determination of the coloration of the lateral metathorax exhibited a high degree of similarity at 20, 25 and 30°C, supporting a common time-measurement system for these two responses. With respect to the coloration of the ventral metathorax, temperature rather than photoperiod was the major determinant, although an effect of photop...

Role of photoperiod and temperature in the induction of overwintering pupal diapause in the spotted tentiform leafminer, Phyllonorycter blancardella

The role of photoperiod and temperature in the induction of overwintering diapause in Phyllonorycter blancardella (F.) (Lepidoptera: Gracillariidae) was examined in the laboratory and field using leafminers from commercial apple orchards in Ontario, Canada. P. blancardella exhibited a long-day response to photoperiod: long daylengths resulted in uninterrupted development whereas short daylengths induced diapause. The estimated critical photoperiod for diapause induction was L14.25:D9.75. The larvae of leafminers destined to enter diapause took ca. 3x longer to complete development than the larvae of non-diapausing leafminers. The development prolonging effect of photoperiod decreased with decreasing daylength. Temperature modified the diapause inducing effect of photoperiod. At L14.25:D9.75, diapause incidence was similar at 15 and 20 °C but was lower at 25 °C. Photoperiod also altered the normal relationship between development rate and temperature. At L14.25:D9.75, the duration of larval development of diapausing leafminers was similar at 15, 20 and 25 °C. Temperature alone is unlikely to have a role in the induction of diapause because leafminers exposed to natural late summer and fall temperature regimes and L16:D8 did not enter diapause.

Photoperiod-pineal-hypothalamic relay in sheep

Mammals from cold and temperate climates, including many farmed species, utilise the annual cycle in daylength to time the seasonal changes in reproduction, moulting, fattening and other characteristics. These animals have a photoperiodic time-measuring system that encodes information regarding daylength into a hormonal signal, which acts within the brain to coordinate the diverse changes in physiology and behaviour. The neural relay involves the eyes, the suprachiasmatic nuclei (SCN) of the rostral hypothalamus and the pineal gland. The SCN functions as the internal biological clock. It contains neurones expressing endogenous circadian rhythms in electrophysiological activity that are entrained by the periodic photic signals from the 24-h light-dark cycle. The SCN is linked by a sympathetic innervation to the pineal gland, and via this neural pathway regulates the endogenous rhythm in secretion of melatonin. Light acts to entrain the circadian rhythm system and to inhibit the production of melatonin. Melatonin is thus released into the peripheral circulation only at night, and the duration of secretion provides an endocrine index of nightlength and thus daylength. In sheep, timed infusions of melatonin in pinealectomised animals induce biological responses according to the duration of continuous exposure to melatonin. Daily 8-h infusions of melatonin induce long-day responses, while 16-h infusions induce short-day responses. The time of day when these treatments are given has no influence on the response. Exposure of intact animals to artificial photoperiods (non 24-h light-dark cycles or night-interruption protocols) induce effects consistent with the duration hypothesis. The melatonin signal is thought to mediate the multiple effects of photoperiod by affecting the secretion of hormones from the pituitary gland. Placement of micro-implants of melatonin in the mediobasal hypothalamus (MBH) in rams induce a complete spectrum of short-day responses. Two models are presented for the actions of melatonin. One proposes that melatonin acts on dopaminergic and/or opioidergic neuronal pathways within the MBH to influence the release of the peptides and neurotransmitters which normally regulate the pituitary gland. The other proposes that melatonin acts on the adjacent pars tuberalis of the pituitary gland, a tissue with the highest concentration of melatonin receptors, to induce the multiple responses.

Short-day experience is not a prerequisite for the termination of photorefractoriness in the reproductive cycle of baya weaver,Ploceus philippinus

In most photoperiodic avian forms (irrespective of temperate or tropical distribution) including the baya weaver,Ploceus philippinus, seasonal reproduction comes to an end due to the development of a photoperiodically controlled photorefractory phase when birds cease to respond to the stimulatory effect of long days. In the present paper photoperiodic control of the termination of photorefractory phase has been examined by studying the effect of short-day exposure lasting 4–6 months on long-day response of birds. Results indicate that unlike in other photoperiodic birds short-day exposure of winter is not a prerequisite for the termination of photorefractory phase in the reproductive cycle of baya weaver. Artificial long days on the other hand hasten the termination of this phase. Refractory phase in baya weaver, therefore, unlike that in temperate forms, is a temporary state resulting most likely from a sequel of physiological events triggered by long days of spring/summer which temporarily mask the photostimulatory response. Spontaneous termination of photorefractoriness in birds of tropical habitats may have a selective value imparting to the reproductive cycle the necessary elasticity for adaptation to diverse ecological conditions.

Photoperiodic Effect on Diapause Induction and Development in the Predator Orius insidiosus (Heteroptera: Anthocoridae)

Photoperiod influenced nymphal development and diapause induction in a laboratory culture of Orius insidiosus (Say). At 20°C, development of nymphs was significantly faster at a photoperiod of 10:14 (L:D) than at 12:12, 13:11, 14:10, or 15:9. Subsequently, diapause induction exhibited a typical long-day response; nearly 100% of adult females entered reproductive diapause when reared under short photoperiods (10:14 [L:D]), whereas at longer photoperiods (12:12, 13:11, 14:10, 15:9 [L:D]), fewer insects initiated diapause (56.8, 29.7, 5.3, 12.9%, respectively). The critical photoperiod fell between 12:12 and 13:11 (L:D). Duration of the preoviposition period was inversely related to photoperiod.

Metabolic correlates in the working of an insect putative photoperiodic clock

Analysis of the formal properties of photoperiodic systems has emphasized the importance of two discrete phases of nocturnal light sensitivity (the so-called points A and B) in a variety of taxa. This has been exemplified in the lepidopteran, Pieris brassicae, among other species, since the illumination of either of these phases in an otherwise short-day cycle (diapause inducing) gives rise to a long-day effect (development without diapause). In this species, the photoreceptor of diel cycles and the clock-counter system are very likely brain located. Using cytochrome oxidase activity as a marker of energy metabolism, a neuroanatomical base in the brain involved in long-day responses elicited by light at points A and B was investigated.

Effects of melatonin on long-day responses in short-day housed adult Siberian hamsters.

Testis growth is stimulated when short photoperiod-regressed Siberian hamsters are exposed to a lengthening photoperiod, an effect presumably mediated by the pineal gland through a decrease in the peak nocturnal duration of secretion of its hormone melatonin (MEL)(D. S. Carter and B. D. Goldman, Endocrinology 113: 1268-1273, 1983). We examined this stimulatory or "progonadal" effect of MEL in short photoperiod-regressed, adult male Siberian hamsters that were pinealectomized (PINX) and given timed daily subcutaneous 1) injections of MEL (1 or 10 micrograms/day) or saline or 2) infusions of MEL that were "long day-like" (4 h, 10 or 100 ng/day), "short day-like" (10 h, 10 ng/day), or control saline infusions (4 h/day). Photoregressed sham PINX hamsters were transferred to long days at this time. After 5 wk of treatment, 1-microgram MEL-injected hamsters and both groups of 4-h MEL-infused hamsters had stimulatory responses that mimicked those of the long-day-exposed, sham PINX group [i.e., increased testes, body, and epididymal white adipose tissue (EPIWAT) weights, total body fat, EPIWAT lipoprotein lipase activity, and serum prolactin and follicle-stimulating hormone levels]. These effects were not observed in 10-micrograms MEL- or saline-injected and 10-h MEL- or saline-infused hamsters. Thus the peak nocturnal duration of serum MEL is the critical parameter of the MEL secretion profile for stimulating a variety of photoperiodic responses when photoregressed hamsters are exposed to lengthening daylengths.

Pineal and ovarian response to 22- and 24-h days in the ewe.

Melatonin secretion in ewes was entrained by 22-h light-dark cycles whether of long (16L:6D) or short (6L:16D) photoperiod. In photoperiods of 6L:16D, a phase-delay of melatonin secretion was evident, leading to a dark-phase duration shorter than that found in 8L:16D. Early onset of estrus was induced in anestrous ewes kept in 8L:16D, but not 6L:16D, from 22 July compared to controls in natural light. In photoperiods of 16L:6D, the melatonin profile corresponded precisely to the dark phase. Early offset of estrus was induced in estrous ewes kept in both 18L:6D and 16L:6D from 18 December compared to controls in natural light. Thus, when the duration of melatonin secretion was appropriate to the long photoperiod (16L:6D), but with a constantly changing phase position, a long-day reproductive response was found. Activity-rest cycles were not entrained by 16L:6D; thus the synchronization of melatonin and activity-rest cycles does not appear to be essential for the induction of a long-day reproductive response. These results support the hypothesis that the duration, not the circadian-phase position, of melatonin is critical to the induction of photoperiodic effects.

Environmental Control of Flowering in Barley (Hordeum vulgare L.). I. Photoperiod Limits to Long-day Responses, Photoperiod-insensitive Phases and Effects of Low-temperature and Short-day Vernalization

Barley plants were grown at a mean diurnal temperature of 15 °C and reciprocally transferred between different photoperiods (from 16 h d−1 to 8, 10 or 13 h d−1 or vice versa at 4, 8, 16 or 32 d after germination). Ten contrasting genotypes were examined, including seven spring-sown types-Mona, BGS T16-2, Athenais, Emir, Funza, USDA-016525 and S-37, and three autumn-sown types-Gerbel B, Arabi Abiad and Ager. In the latter two all treatments were repeated on plants grown from seeds which had been vernalized at 2 °C for 42 d. The results suggest that, between the critical photoperiod (below which there is a delay in flowering) and the ceiling photoperiod (below which there is no further delay), there is a linear relation between photoperiod and the reciprocal of the time taken to flower (awn emergence). In all genotypes the ceiling photoperiod was ≲, 10 hdd−1; the critical photoperiod was always > 13 hdd−1 often > 14 hdd−1, and sometimes > 16 hdd−1. All genotypes were initially insensitive to long days. At 15 °C this pre-inductive phase typically lasted for 8–10 d after germination in spring-sown types and in vernalized autumn-sown types, but continued for more than 32 d in non-vernalized autumn-sown types. It was followed by an inductive phase, the duration of which depended on photoperiod, being longer in shorter days. Finally, there was a photoperiod-insensitive, post-inductive phase, which probably began about 2 weeks before awn emergence. The low-temperature seed-vernalization treatment considerably hastened awn emergence in Arabi Abiad and in Ager; in Arabi Abiad low-temperature vernalization could be partly replaced by treating young plants with short days (8 or 10 h dd−1). Both low-temperature and short-day vernalization advanced flowering by advancing ear initiation (reducing the duration of the pre-inductive phase), whereas long days stimulated the rate of development following ear initiation.

Photoperiodic control of puberty in the red-legged partridge ( Alectoris graeca chukar)

The photoperiodic control of puberty in birds was studied using hybrid red-legged partridges ( Alectoris graeca chukar). In the wild partridges first breed at about 10 months of age. Males and females were held from hatch on short (8L: 16D) daylengths and then at 3, 4 1 2 , 6, 7 1 2 , 9, and 12 weeks of age groups were transferred to long daylengths (20L:4D) for 3 weeks to test for the photoperiodic induction of gonadal growth. Control groups were maintained on either the short or long daylengths and killed at 3, 9, and 12 weeks of age. Gonadal growth did not occur in either of the control groups, nor in any of the birds photostimulated prior to 6 weeks of age. However, in birds photostimulated after this point gonadal size was increased in a graded manner, this growth being reflected in the plasma and pituitary levels of luteinizing hormone. Similar long-day responses which increased with age were observed in plasma and pituitary levels of prolactin (PRL). In the control birds there was a steady decline with time in plasma PRL, with no change being seen in pituitary PRL. Hypothalamic gonadotrophin-releasing hormone content did not change in birds maintained on 8L-:161) or 20L:4D and was only elevated by photostimulation in the females. Plasma testosterone remained low in all the males except for those transferred to 20L-:4D at 12 weeks. Testicular testosterone content remained low in control birds but was elevated by photostimulation at 6 and 12 weeks of age. Plasma progesterone levels increased with age in control birds and were only elevated by photostimulation at 3 and 4 1 2 weeks of age. These data show juvenile partridges to be completely unresponsive to photoperiodic stimulation and in a condition very similar if not identical to that seen in adult refreactoriness. As in the adults, this refractoriness is progressively dissipated by exposure to short days so that by 9–12 weeks of age the partridges are able to respond maximally to long-day stimulation.

Refractoriness in quail leads to a reduction in the photoperiodic drive on LH secretion.

The hypothesis was advanced that the long-day castration response in quail should become less pronounced in birds made refractory by exposure to long photoperiods. This was tested by pretreating two groups of castrated quail with testosterone for 9 weeks to suppress LH secretion whilst exposing them either to short days or to long days. The castration response was then measured on long days by withdrawing the testosterone and following the subsequent rate of increase in LH secretion. In both groups LH concentrations increased steadily for 7 weeks after removing the testosterone but the rate of increase in the group previously exposed to long days was only 50% of that in the group previously held on short days (P less than 0.025). The long-day castration response in quail not pretreated with testosterone was not altered by retaining the birds for 9 weeks on short days before transfer to long days.

Twenty-four-hour profiles of prolactin and testosterone in ram lambs exposed to skeleton photoperiods consisting of various light pulses.

Individual groups of 6 ram lambs were housed within a controlled environment and exposed to one of 6 photoperiod schedules. Groups I and II received 8 (short day) or 16 (long day) h of continuous light, respectively; Groups III, IV and V were exposed to asymmetrical skeleton photoperiods consisting of a main light period of 7 h followed 9 h later by a light pulse of 1 h, 15 min or 1 min duration, respectively, and Group VI was exposed to a symmetrical skeleton photoperiod consisting of two 1-h light pulses positioned 16 h apart. After 4 weeks of treatment serum concentrations of prolactin and testosterone were measured over 24 h. Long-day responses characteristic of the 16L:8D photoperiod (i.e. elevated prolactin and reduced testosterone) were obtained in each of the asymmetric light-pulse treatment groups, but whereas prolactin was elevated over the full 24 h in lambs exposed to 16L:8D, two prominent nocturnal prolactin releases were largely responsible for the high 24-h mean prolactin values in Groups III, IV and V. Reduced serum testosterone in these same groups could not be attributed to a diurnal pattern of secretion but was associated with an overall decrease in testosterone pulse frequency. Prolactin and testosterone levels in Group IV were intermediate between those observed in lambs exposed to 8 or 16 h of light. In summary, light pulses of short duration (1 min) positioned at 17 h after dawn can produce endocrine changes in lambs similar to those observed in lambs exposed to 16 h of continuous light.

Photoperiodic and temperature responses in the growth and tetrasporogenesis ofGigartina acicularis (Rhodophyta) from Ireland

Gigartina acicularis is an intertidal, perennial red alga which reaches its northern distributional limit in the north-eastern Atlantic on the Irish coast. It has only rarely been found with reproductive structures in the British Isles. Plants isolated vegetatively from field-collected plants near the northern distributional limit in Ireland formed tetrasporangia, the tetraspores of which gave rise to plants which formed gametangia and carposporophytes at 16°C, $$8:\overline {16} h$$ . Sporelings grown from the carpospores of these plants formed tetrasporangia at all daylengths tested (16-8 h) at 13–20°C; but there was a quantitative photoperiodic response in the numbers of plants forming tetrasporangia, and in the numbers of sori formed, at 13–16°C. Only one in 20 plants became fertile at 16°C, $$16:\bar 8h$$ and $$8: \overline {7.5} :1: \overline {7.5} h$$ , but 16 in 20 plants reproduced at 16°C, $$8:\overline {16} h$$ . At 20°C, $$16:\bar 8h$$ and $$8:\overline {16} h$$ , all plants formed tetrasporangia, and formation was most rapid the long-day regime. No tetrasporangia were formed at 9–10°C, regardless of daylength. Apical elongation of these plants also appeared to show a quantitative photoperiodic response at 16°C, 1 h light breaks in a 16 h night giving more or less a long-day response. This effect was apparent about 4 weeks before the formation of the first tetrasporangia. There would therefore appear to be quantitative photoperiodic control of tetrasporogenesis in the Irish strain ofG. acicularis. Temperature and photoperiodic control of reproduction in this species only partially accounts for the observed rarity of reproductive structures in populations of this species near the northern limit of its distribution.

Further studies on the involvement of the circadian system in photoperiodic control of antifreeze protein production in the beetle Dendroides canadensis

The role of circadian rhythmicity in the photoperiodic time measuring processes regulating antifreeze protein production in the beetle Dendroides canadensis was further investigated. Using “T” experiments larvae were exposed to environmental light cycle periods close to the period length of the endogenous circadian oscillator. The following light cycles were employed: light dark 8 13 , 8 14 , 8 16 , 8 18 and 8 19 corresponding to period lengths of 21, 22, 24, 26 and 27 h. Larvae maintained in cycles equal to or less than 24 h displayed a characteristic short-day response, showing significantly ( P < 0.01) greater antifreeze protein activity than did those measured on the day of collection in late summer. In contrast, a long-day response was observed in larvae maintained under a 26- or 27-h light cycle in that antifreeze protein activity did not differ from that measured on the initial collection date. The role of photoperiod and temperature in influencing the photoperiodic timing processes were examined with a series of resonance experiments. The first group consisted of a 24, 36, 48, 60 or 72-h light cycle, each with an 8-h photophase at temperatures of 20 or 17°C. Rhythmic increases in antifreeze protein levels at intervals of 24 h occurred under both temperatures. However, the lower temperature displaced the resonance curve in the vertical direction (i.e. increasing % population response) and reduced the difference between peaks and troughs on the resonance curve. Resonance experiments incorporating a 14-h photophase resulted in low antifreeze protein activity under all conditions except a 36-h light cycle in which a 67% induction was observed. Eight hour resonance experiments were also conducted with D. canadensis collected in early spring to determine whether the circadian system participates in the photoperiodic timing processes influencing the spring termination of antifreeze protein production. Positive resonance results were obtained in that only larvae maintained in cycles of 36 and 60 h displayed significantly ( P < 0.01) lower antifreeze activity when compared to animals on the initial collection date. The combined results emphasize the involvement of the circadian system in the photoperiodic control of antifreeze protein production by D. canadensis during the fall and spring. Furthermore, the induction of antifreeze protein production is a function of light cycle and its waveform (photoperiod). Temperature appears to modify the photoperiodic response in some manner involving the photoperiodic time measuring processes. It is concluded that the photoperiodic response of antifreeze protein production by D. canadensis is dependent upon the entrainment of the circadian system by the light cycle.

The effects of temperature and photoperiod on the induction of diapause in eggs of the Australian plague locust,Chortoicetes terminifera(Walker) (Orthoptera: Acrididae)

AbstractPhotoperiod was shown to be the principal factor regulating the induction of a facultative egg-diapause inChortoicetes terminifera(Wlk.). All developmental stages from first-instar nymphs to immature adults were sensitive to photoperiod. At constant photophases, the insect exhibited a short-day—long-day response, with the upper and lower critical photo-periods for induction approximating to LD 15·5: 8·5 and 11:13, respectively. These correspond to the range of photoperiods experienced by the insect under natural conditions. The maximum inductive response occurred at about the mid-point of this range, i.e. LD 13·5: 10·5. In experiments in which insects experienced a change in photophase at the end of the nymphal stage, the incidence of diapause varied with the direction of change (long to short or short to long) and indicated that diapause induction was prevented by an increase in photophase but enhanced when the photophase was reduced. The size of the inductive response associated with a decrease in photophase appeared to depend less on the size of the decrease than on its position within the inductive range, such that the maximum effects were observed when the sequence of light regimes were close to or spanned the most inductive constant photophase. Temperature was also important in determining the induction of diapause. In the upper portion of the inductive range (15·5 to 12·5 h light), insects subjected to high temperatures or to an increase in temperature during development showed a lower incidence of diapause than those subjected to low temperatures or to a decrease in temperature. In the lower portion of the inductive range, the effects of temperature were reversed, with high temperature or an increase in temperature being more inductive than low temperature or a decrease in temperature.

Eucalyptus Physiology. I. Photoperiodic Responses

Seedlings of selected Eucalyptus species grown under factorial combinations of temperature and photoperiod showed greater response to temperature than to photoperiod. In a few cases maximum growth occurred at an optimum photoperiod of about 12 hr. Growth responses to an increase of low intensity light from 8 to 12 hr were usually of the quantitative, long-day type. The 12 hr optimum was associated with quantitative, short-day responses that may occur with an increase ;n photoperiod from 12 to 16 hr. These optima rarely occurred at more than one growing temperature for any one species or seed source. Such temperature dependence, combined with the small magnitude of the two types of response and with the variability among species, may explain many of the hitherto equivocal results on the effect of photoperiod in Eucalyptus. Long-day responses were more common than short-day responses but whether associated with a photoperiod optimum or not, both response types appeared to be largely unrelated to the latitude and to altitude of the seed source. This contrasts with the behaviour of northern hemisphere vegetation.

The role of neurosecretion in the photoperiodic control of polymorphism in the aphid Megoura viciae.

The location of the photoperiodic mechanism controlling the production of the sexual and parthenogenetic morphs by apterous parents was examined by selectively injuring the brain with an R.F. microcautery. Lesions destroying the Group I neurosecretory cells (NSC) in the protocerebrum abolished the response to changed daylength. Extensive damage to other NSC Groups, to the compound eyes and optic lobes was without effect. It is concluded that the Group I NSC are the effectors, secreting a virginoparapromoting substance; in its absence only oviparae are produced. Areas slightly lateral to the group I NSC are also required for the long-day response, indicating that this is the probable site of the neuronal photoperiodic clock which regulates the release of neurosecretory material (NSM) from the Group I cells.

Photoperiodism and photosynthetic pathways

In a recent paper, Purohit and Tregunna (7) concluded that plants with low carbon dioxide compensation values are either short-day or day-neutral in their photoperiodic requirement for flowering. Although many plants with the C4 pathway of photosynthesis are short-day plants, there are also several Gramineae in which the C4 pathway of photosynthesis is known to be combined with a requirement for, or response to, long days for flowering, such as Paspalum dilatatum, Hyparrhenia hirta, Themeda australis, and Saccharum spontaneum. Consequently, response to short days for flowering is not a constant feature of the C4 pathway, and C4 plants could be selected for a long-day response in areas where this is advantageous.

Diapause in the Australian Flesh Fly Tricholioproctia Impatiens (Diptera: Sarcophagidae).

At a constant temperature of 18�C, exposure of Tricholioproctia impatiens to varied daily photophases resulted in a typical long-day response of diapause induction. A critical daily photophase of 13 h marked the transition between diapause induction and continuous development. At 25�C diapause was supressed with no apparent critical photophase. Diapause occurred at 106 h at 18�C and 48 h at 25�C following pupariation.

Response to light intensity and day-length of two contrasting flower varieties ofAntirrhinum majusL.

SummaryThe effects of day-length and light intensity on the growth rate and leaf number of an early (Pink Ice) and a late (Orchid Rocket) flowering variety of Antirrhinum majus L. have been investigated. Growth rate, as determined by plant height or dry-weight increase, was greater for Pink Ice in all instances. When the two varieties were grown under similar conditions, the leaf numbers prior to flowering attained by Orchid Rocket were always greater than those of Pink Ice. With high light intensity the long-day (LD) responses of both varieties were characterized by leaf numbers which were on average 30 leaves less than the numbers found on plants grown in short days (SD) at high light intensity. Pink Ice exhibited this photoperiodic response to LD irrespective of whether the light intensity was high (26,000 lux) or low (6000 lux), whereas the leaf number of Orchid Rocket only declined in LD when the intensity was high. Plants of this variety grown in low light LD had leaf numbers similar to plants maint...