Subsequent Short Day Research Articles

Effects of photoperiod and slow-release preparations of bromocryptine and melatonin on reproductive activity and prolactin secretion in female goats2

The present study was conducted to investigate seasonal reproductive patterns in a Boer Goat x German Fawn cross and ways to modulate these patterns by injecting slow-release bromocryptine and melatonin preparations. Twenty does were exposed to a light program of alternating periods of 90 long days (LD) followed by 100 short days (SD) twice in succession (LD1, SD1, LD2, SD2). At the beginning of LD2, does were treated as follows: vehicle injection (CTR, n = 7), slow-release bromocryptine (BCR, n = 6), or slow-release melatonin (MLT, n = 7). Blood samples were collected twice weekly, and from October 5 to December 14, 1989, weekly, to be analyzed for progesterone, prolactin, and melatonin. Long days inhibited cyclicity, and short days stimulated it. Prolactin was increased during long days and decreased during short days. High ambient temperature resulted in increased prolactin concentrations. Under long photoperiod, long-acting BCR suppressed prolactin secretion for 68 d, and the estrous season was extended compared with CTR. Under long photoperiod, long-acting MLT increased serum melatonin for 96 d, suppressed prolactin concentration, and substantially lengthened the period of cyclicity compared with the CTR- and BCR-treated groups. The resumption of cyclicity during the subsequent short day period occurred later in MLT- than in CTR- and BCR-treated groups. In conclusion, we modulated the day length-controlled seasonal cyclicity of goats by treating them with injectable slow-release preparations of BCR and MLT, the latter being more effective.

Gibberellins and Stem Growth as Related to Photoperiod in Silene armeria L.

Stem growth and flowering in the long-day plant Silene armeria L. are induced by exposure to a minimum of 3 to 6 long days (LD). Stem growth continues in subsequent short days (SD), albeit at a reduced rate. The growth retardant tetcyclacis inhibited stem elongation induced by LD, but had no effect on flowering. This indicates that photoperiodic control of stem growth in Silene is mediated by gibberellins (GA). The objective of this study was to analyze the effects of photoperiod on the levels and distribution of endogenous GAs in Silene and to determine the nature of the photoperiodic after-effect on stem growth in this plant. The GAs identified in extracts from Silene by full-scan combined gas chromatography-mass spectrometry (GC-MS), GA(12), GA(53), GA(44), GA(17), GA(19), GA(20), GA(1), GA(29), and GA(8), are members of the early 13-hydroxylation pathway. All of these GAs were present in plants under SD as well as under LD conditions. The GA(53) level was highest in plants in SD, and decreased in plants transferred to LD conditions. By contrast, GA(19), GA(20), and GA(1) initially increased in plants transferred to LD, and then declined. Likewise, when Silene plants were returned from LD to SD, there was an increase in GA(53), and a decrease in GA(19), GA(20), and GA(1) which ultimately reached levels similar to those found in plants kept in SD. Thus, measurements of GA levels in whole shoots of Silene as well as in individual parts of the plant suggest that the photoperiod modulates GA metabolism mainly through the rate of conversion of GA(53). As a result of LD induction, GA(1) accumulates at its highest level in shoot tips which, in turn, results in stem elongation. In addition, LD also appear to increase the sensitivity of the tissue to GA, and this effect is presumably responsible for the photoperiodic after-effect on stem elongation in Silene.

One week treatment of immature lambs with long days restores puberty to the normal age

In many mammalian species, photoperiod is an important environmental cue that synchronizes puberty to the appropriate season. The sheep is a short-day breeder, and the female lamb begins reproductive cycles during the short days of autumn at 25-35 weeks of age. Surprisingly, however, lambs reared solely under artificial short days (9L:15D) from birth delay puberty (ca 52 weeks). We have found that 5 or 10 weeks of long days (15L:gD) ending at 22 weeks of age lead to the onset repeated cycles by 35 weeks of age in lambs under short days at other ages. In order to understand the minimum long-day requirements for puberty under subsequent short days, lambs in the present study were challenged with only one week (week 22 of age) of long days. Control lambs received 5 weeks of long days (weeks 17-22). Both groups were housed under short days before and after exposure to long days. Twice weekly blood samples were collected and serum progesterone patterns were used to assess the onset of ovarian cyclicity. Treatment with 1 week of long days effectively synchronized the onset of consecutive cycles to 35 + 0.3 weeks (n=5). This age was similar to the onset of cycles in control lambs (32 + 2 weeks, n=5 of 6) exposed to 5 weeks of long days. These findings raise the possibility that long days, experienced by the spring-born lamb during summer, are necessary for the later onset of puberty during the short days of autumn. The specific requirement for long days may depend upon some critical number of long days at a critical period during development to time the onset of reproductive cycles. (Supported by NIH HD-06471 and HD-11311.)

Effect of Short Days in the Photoperiodic Testicular Response of Japanese Quail

Avian gonadal activity is known to be controlled by photoperiods. In male Japa-nese quail, testicular activity is stimulated by long days and inhibited by short days. However, the photoperiodic testicular response of the quail is not completely under-stood. Thus, I investigated it under various photoperiodic conditions.When birds were reared under continuous light (LL) after hatching, they reached maturation in 6 weeks and maintained large testes as long as they were kept under LL. When birds were transferred from LL to a short photoperiod (8L : 16D), their testes showed considerable involution within 2 weeks. However, when birds received the short day treatment for 5 weeks or longer period prior to the long day treatment, their testes showed resistance to involution in the subsequent short day treatment of both young and old birds. Further, when birds were continuously kept under a short photoperiod, they showed spontaneous growth of their testes 12 weeks after hatching. Adult birds, which experienced sexual maturation under the long photoperiod, also showed spontaneous recrudescence of their testes under a short photoperiod after several weeks in the involuted state. These results clearly indicate that a short photoperiod does not always act to inhibit the testes of the Japanese quail. They also suggest that there is a kind of photorefractoriness against short days.

観賞樹木の生育に及ぼす温周性と光周性の相互影響

Effects of fall chilling on responses of sweet viburnum (Viburnum Awabuki K. Koch) cuttings and Japanese black pine (Pinus ThunbergiiParl.) seedlings to the subsequent daylength and temperature treatments were investigated. The chilling treatments were continued for 70 days at 3°C in the dark from October 15, 1976.1) Shoot emergence of viburnum cuttings was promoted by long days and high ambient temperatures when cuttings were not subjected to fall chilling. The amount of shoot growth was greater in the long day lots than in the short day lots. The higher the ambient temperature, the greater the amount of shoot growth. In the lots receiving the long day and 25°C treatment, the shoot was elongating along a rectilinear growth curve during the entire course of growth measurement.On the other hand, subsequent daylength and temperature treatments had almost no influence on the onset of shoot emergence when cuttings were subjected to fall chilling. As for the shoot growth, responses of viburnum cuttings to photoperiod seemed long-day-dependent in subsequent high temperature regimes, faculative-short-day-dependent in intermediate temperature regimes, and daylength-independent in low temperature regimes. The shoot growth of viburnum cuttings was quite active even under low temperature conditions. The shoots elongated along a rectilinear growth curve under 10°C like under 25°C.2) Shoot emergence of pine seedlings was fairly promoted by long days and high ambient temperatures when seedlings were not subjected to fall chilling. In general, the shoot growth of pine seedlings was stimulated by long days and high ambient temperatures. However, when seedlings were subjected to fall chilling, the onset of shoot emergence was affected only slightly by subsequent daylength and temperature treatments. The shoot growth was greater in the long day lots than in the short day lots. The lower the ambient temperature, the greater the shoot growth of pine seedlings.From the results obtained, it may be concluded that if viburnum cuttings and pine seedlings are subjected to fall chilling, subsequent optimum temperatures for the shoot growth of both species tested tend to shift from higher to lower regimes. Furthermore, both viburnum cuttings and pine seedlings that are subjected to fall chilling may show a markedly flourishing shoot growth under subsequent short day conditions.

Biology of tree-hole mosquitoes: photoperiodic control of development in northern Toxorhynchites rutilus (Coq.)

Carnivorous larvae of the tree-hole mosquito, Toxorhynchites rutilus, were collected from the northern portion of their range. Long days were found to promote rapid growth and metamorphosis from egg to adult; short days retard development during the second and third instars and evoke diapause in the fourth. All larvae exposed continuously to long days from embryos to the third or fourth instar developed without entering diapause. Diapause-averting long days experienced earlier in development could be reversed in at least some individuals by subsequent short days. Among laboratory-reared larvae or those caught early in the fall, the critical photoperiod for the maintenance of diapause is around 13 h of light per day. Among larvae caught in midwinter, diapause is not maintained in all larvae at any photoperiod and in 50% or less of the larvae at photophases shorter than 12.5 h. Winter conditions in the northern part of the range of T. rutilus appear to play a prominent role in the maintenance and termination of diapause.

EFFECTS OF LONG DAY, HIGH TEMPERATURE AND GA3ON FLORAL INDUCTION AND STEM ELONGATION OF SAMOLUS PARVIFLORUS

SUMMARY In Samolus parviflorus Raf. long day induces flowerbud formation and increases stem length directly. Suboptimal induction by long day is completely desinduced by subsequent short day. High temperature, 40°–45°C, when applied during 6 hours in the middle of the light phase of short day, has no flower inducing effect, but when applied in the middle of the dark phase it leads to complete induction. This similarity to Silene armeria L. suggests that also in Samolus parviflorus flower formation depends on two processes: light removes a blocking, darkness has a reblocking effect, but high temperature prevents this reblocking. The inductive effect of GA3 on flower formation was confirmed. Although high temperature in the light does not induce flowerbud formation, while in the dark it induces completely, both applications in combination with GA3 have a pronounced stem elongating effect. Hence S. parviflorus offers another case of separating flowerbud formation and stem elongation.