A CIRCADIAN RHYTHM IN THE LONG-DAY PHOTOPERIODIC INDUCTION OF ERECT AXIS DEVELOPMENT IN THE MARINE RED ALGA NEMALION HELMINTHOIDES1,2

Two isolates of Nemalion helminthoides from the west coast of Ireland showed a heteromorphic life history in which tetraspores formed under short-day conditions on uniaxial, prostrate tetrasporophytes gave rise to uniaxial, prostrate growths similar in morphology to the tetrasporophytes. The induction of multiaxial, erect axes on tetraspore-derived plants was a long-day photoperiodic response. At 11°C, 16:8 h LD, nitrate concentration in the enriched seawater medium had little effect on the numbers of erect exes formed. Induction of erect axes occurred only in daylengths ≥ 12 h, mainly between 7–13° C, and the critical daylength, which generally lies between 14 and 16 h, changed with temperature. Night-breaks (NB) of 1 h light in the middle of 16 h night were ineffective in the promotion of erect axis formation, and day-breaks (DB) of 1 h darkness in the middle of a 16 h day did not inhibit axis formation. Neither continuous light nor NB of 1–1.5 h given at various times during the dark period of an 8:16 h LD cycle promoted the formation of erect axes. At 9° C, equivalent photon exposures (0.69 and 0.34 mol·m^?2) at two different instantaneous photon flux densities resulted in erect axis formation only in the 14 h, 16 h and DB regimes. Photoregimes of 16 h light in combination with dark cycles of various lengths resulted in the maximal promotion of the formation of erect axes in diurnal (22–24 h) and bi-diurnal (44–48 h) cycles, a diminishing response in non-diurnal cycles greater than 24 and 48 h, and a minimal response at 32 h. These data show that the formation of erect axes is a long-day photoperiodic response and provide further evidence for a connection between endogenous circadian rhythms and long-day photoperiodic responses.     

Photoperiodic regulation of receptacle induction in Sargassum horneri (Phaeophyceae) using clonal thalli

We developed a clonal culture of Sargassum horneri to investigate the effect of photoperiod on reproduction in this species. Regenerated vegetative thalli were obtained using lateral branches excised from a thallus grown from a single embryo under short‐day conditions (SD = 10:14 h light : dark cycle). Lateral branches excised from the SD‐regenerated thallus became vegetative thalli that remained in that phase as long as they were cultured under SD. When an excised lateral branch was cultured under long‐day conditions (LD = 14:10 h light : dark cycle), it began to enter the reproductive phase while still less than 50 mm long. Induction of the reproductive phase was accompanied by a distinctive morphological change – suppression of blade formation at the apical region of the branch; elongation of branches without blades was then followed by differentiation of receptacles bearing conceptacles on their surface. Apices of receptacles were able to interconvert between reproductive and vegetative phases, as blades resprouted upon transfer from LD to SD. The critical day length for induction of receptacle formation was between 13 and 14 h; receptacle formation was also induced under SD conditions with night breaks (NBs). These results strongly suggest that reproductive regulation of S. horneri is a photoperiodic long‐day response. NBs with blue and green light were effective for reproductive induction but not with red light. This suggests that blue‐ and/or green‐light photoreceptors are involved in the photoperiodic reproductive response of S. horneri.     

A photoperiodic response mediated by blue light in the brown alga Scytosiphon lomentaria

Summary The crustose phase of Scytosiphon lomentaria (Lyngb.) J. Ag. persists indefinitely in 16 h of white light per day, but produces erect, cylindrical thalli vegetatively in 8-h days. The critical daylength for this short-day (SD) response is sharply defined, and, between 12 and 13 h, differences in daylength of only 15 min produce substantial differences in response. A significant response to SD can be induced by as few as 4 SD cycles, but 10–12 cycles are required to saturate the response and induce more than 90% of the plants to form thalli. The response to SD is completely inhibited by a 1-min light-break with a low irradiance of blue light, given in the middle of a 16-h dark period, but is unaffected by longer periods and higher irradiances of red or far-red light. There is good reciprocity between the irradiance and the length of a light-break with blue light, and 50% inhibition of the response to SD is induced by about 2 nE cm^-2 at 449 nm. All attempts to reverse the inhibitory effects of blue light by subsequent irradiation with another wavelength have so far failed. These results indicate that phytochrome is not the photoreceptor pigment for this response, in spite of the similarity of the response in all other respects to the photoperiodic responses of flowering plants and other algae.Abbreviations and Symbols SD short day - LD long day. Horizontal above number of hours indicates dark period     

Circadian rhythms and the induction of flowering in the long-day grass Lolium temulentum L.

Plants of Lolium temulentum L. strain Ceres were grown in 8-h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8-h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24-h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty-fourth hour. Full flowering was also induced by one 8-h SD beginning 4 or 28 h after the start of a 40-h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so-called ‘displaced short day’ (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 μmol m⁻² s⁻¹, a 4-h light exposure beginning 4 h after the start of a 40-h dark period was sufficient to induce 100% flowering. The flower-inducing effect of a single 8-h DSD was also assessed during a 64-h dark period. Results revealed two maxima at a 20-h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum.     

Changes in the testicular binding of luteinizing hormone and plasma testosterone concentrations in the Djungarian hamster subjected to different photoperiods and temperatures and effects of long-term testosterone treatment on the binding

The effects of artificial photoperiod, temperature, and long-term testosterone treatment on testicular luteinizing hormone (LH) binding were studied in adult male Djungarian hamsters. In hamsters transferred to long-day (LD; 16 hr light, 8 hr dark) photoperiod 8 weeks after adaptation in short-day (SD; 8 hr light, 16 hr dark) photoperiod of 25 degrees C, testicular growth was associated with an increase in the total LH binding per two testes and a decrease in LH binding per unit testicular weight. Plasma testosterone levels reached a peak 47 days after transfer to LD and tended to decrease thereafter, while the testes continued growing. In contrast, when hamsters reared under LD conditions at 25 degrees C for 12 weeks were transferred to SD, testicular regression was associated with a decrease in plasma testosterone and the total LH binding per two testes and an increase in LH binding per unit testicular weight. A significant decrease in LH binding per unit weight compared to SD controls was observed in those hamsters exposed to SD with continuous testosterone treatment. The testosterone treatment tended to induce decrease in the total LH binding. Scatchard plot analyses of the binding suggested that changes in LH binding were due to changes in the number of binding sites. When sexually mature male hamsters were subjected for 8 weeks to two different ambient temperatures (7 degrees C and 25 degrees C) and photoperiods (LD and SD), the difference between the two temperature groups was statistically not significant regarding the weights of testes, epididymides, and prostates; plasma testosterone levels; and LH binding in either LD or SD group. These results suggest that photoperiod is a more important environmental factor than temperature for the regulation of testicular activity and LH receptors and that testosterone reduces the number of LH receptors per unit testicular weight in adult male Djungarian hamsters.     

Growth responses of Matteuccia struthiopteris plants from northern and southern Norway exposed to different temperature and photoperiod treatments

Plants of the fern Matteuccia struthiopteris from northern and southern populations in Norway were studied in a phytotron. Relative growth rate (RGR), growth period, and sporophyll production were measured under different photoperiod (12–24 h) day-length and temperature (9–21 °C) treatments. For the southern plants, there were no significant differences between the different light treatments, but for the northern plants there was a significant (p<0.01) linear increase in the mean maximum RGR with increasing day-length. Small, but statistically significant (p<0.01) differences were found between northern and southern plants when the mean maximum RGR-values were compared. When plants from different origin were exposed to different treatment, there were major differences between the populations in the production of sporophylls (p<0.0001). Southern plants produced in average three times more sporophylls than the northern plants, and they had also higher proportions of fertile plants. Diurnal alternating temperature treatments gave no significant (p>0.05) effect on the mean maximum RGR compared with constant temperatures, but they gave significantly higher production of sporophylls. In general, the northern plants had a higher temperature threshold (approximately 12 °C) for sporophyll production than the southern plants (approximately 9 °C). Plants exposed to 24 h with natural light were generally more often fertile than plants exposed to a shorter photoperiod. The mean maximum RGR-values and time needed to develop the fronds at the 9 °C treatment were fairly equal to those found under natural conditions close to the altitudinal distribution limit of M.struthiopteris in W Norway. In general, the investigation showed that the applied temperature and light treatments affected sporophyll production more than vegetative growth.     

Changes in mRNA level rhythmicity in the leaves ofSinapis alba during a lengthening of the photoperiod which induces flowering

A previous study has shown that mRNAs exhibit complex patterns of diurnal rhythms in their quantity in the leaves ofSinapis alba during an 8 h light/16 h dark short day (SD). In order to determine whether this situation is rapidly modified in plants subjected to an extended light treatment, we have usedin vitro translation and two-dimensional polyacrylamide gel electrophoresis, together with a strict gel comparison procedure giving aP=0.03 certitude level, to analyse the mRNA complement at different times during a 22 h light/2 h dark long day (LD).During this LD, complex changes affected about 10% of the mRNAs. Thirty-four different patterns were observed. Some diurnal rhythms present in SD are not modified by the lengthening of the light period, but most are affected. Moreover, we have shown that some mRNAs presenting a constant quantity under a SD regime show an increase or a decrease during the first hours of the photoperiod lengthening.InSinapis, this LD also induces flowering. All the changes in mRNA quantity detected thus parallel the photoperiodic induction of flowering in the leaves and are quantitative; no mRNA was shown to appear or to disappear.     

Effect of pre-incubation irradiance on survival of cryopreserved gametophytes of Undaria pinnatifida (Phaeophyta) and morphology of sporophytes formed from the gametophytes

Gametophyte strains originating from indigenous sporophytes of Undaria pinnatifida (Harvey) Suringar in Iwate Prefecture, Northeast Japan, were maintained for 9–10 months at 45 μmol photons m⁻² s⁻¹. Before cryopreservation in liquid nitrogen for more than 12 h (1–14 days) using a two-step cooling method with a mixture of cryoprotectants (10% l-proline and 10% glycerol), these were pre-incubated for 2, 4 and 8 months at 15 μmol photons m⁻² s⁻¹. After 1 week of thawing, no surviving gametophytes were detected in the strains without pre-incubation, but both the female and male gametophytes, pre-incubated for more than 4 months, showed high survival rates (43–60% for females and 64–100% for males). This revealed the induction of freezing tolerance by incubation at low irradiance. Thereafter, sporophytes derived from cryopreserved gametophytes and subcultured gametophytes, stored under pre-incubation conditions, were formed from the strain, and a morphological comparison was conducted with 10 characters (stipe length, stipe wet weight, blade length, blade wet weight, blade width, incision depth, blade thickness, sporophyll length, sporophyll wet weight, and sporophyll width). The morphology of the sporophytes formed from the cryopreserved gametophytes corresponded well with that of the subcultured gametophytes from the same strain. The results suggest that the cryopreservation method is applicable for preserving culture stocks of U. pinnatifida to be used in mariculture.     

Pineal-dependent locomotor activity of lamprey,Lampetra japonica,measured in relation to LD cycle and circadian rhythmicity

Summary Locomotor activity of the river lamprey, Lampetra japonica, was investigated under a light-dark (LD 1212) cycle and under continuous dark conditions. Intact lampreys were entrained to the light:dark cycle. They were active mainly in the early half of the dark period and inactive in light period. The light:dark entrainment continued in 72.7% of lampreys after the removal of bilateral eyes, but additional pinealectomy made the entrainment disappear in all lampreys. When lampreys were pinealectomized with their eyes intact, light: dark entrainment was abolished in most cases. The results indicate that the pineal organ of the lamprey is a photoreceptive organ responsible for synchronizing locomotor activity to LD cycle. Under continuous dark conditions, the locomotor activity began to free-run with a period of 21.3 ± 0.9 h (mean ± SD, n = 53). This circadian rhythmicity was not affected by the removal of lateral eyes but was abolished by pinealectomy. The pineal organ appears to function as an oscillator, or as one of the oscillators, for the circadian locomotor rhythm of lampreys.Abbreviations DD continuous dark - LD light:dark     

The effect of temperature and light pulses on the induction of diapause in the Toyama strain of the Indian meal moth, Plodia interpunctella

Abstract.The photoperiodic response in Plodia interpunctella collected at Toyama (36.7°N) was of long-day type and highly sensitive to temperature. The critical photoperiod giving 50% diapause was between 14 and 16 h at 20°C, between 12 and 14 h at 25°C and between 6 and 8 h at 30°C. Effects of night interruption by a 2-h light pulse on the diapause response were examined at 25°C on different background photoperiods ranging from LD 12:12 h to LD 2:22 h. Percentage diapause was very low when the middle portion of dark period was interrupted, so that U- or V-shaped response curves were obtained with background scotophases longer than 12 h. In these curves, the descending slopes were less steep than the ascending slopes. The critical dark period measured from dusk to an interrupting light pulse was about 1.5 h longer than the critical dark period ( c . 10 h) in the normal photoperiodic response. The critical dark period from the interrupting light pulse to dawn, on the other hand, was not parallel to dawn but shorter than the normal critical period in LD 12:12 h and LD 10:14 h and longer than that in LD 7:17 h to LD 4:20 h, indicating that the priming effects of the light pulse might be under the influence of the photophase.     

Photoperiod regulates elicitation of growth promotion but not induced resistance by plant growth-promoting rhizobacteria

For several years, we have noticed that plant growth-promoting rhizobacteria (PGPR), which consistently promote plant growth in greenhouse tests during spring, summer, and fall, fail to elicit plant growth promotion during the midwinter under ambient light conditions. This report tests the hypothesis that photoperiod regulates elicitation of growth promotion and induced systemic resistance (ISR) by PGPR. A commercially available formulation of PGPR strains Bacillus subtilis GB03 and Bacillus amyloliquefaciens IN937a (BioYield) was used to grow tomato and pepper transplants under short-day (8 h of light) (SD) and long-day (12 h of light) (LD) conditions. Results of many experiments indicated that under LD conditions, BioYield consistently elicited significant increases in root and shoot mass as well as in several parameters of root architecture. However, under SD conditions, such increases were not elicited. Differential root colonization of plants grown under LD and SD conditions and changes in leachate quality partially account for these results. BioYield elicited ISR in tomato and pepper under both LD and SD conditions, indicating that although growth promotion was not elicited under SD conditions, induced resistance was. Overall, the results indicate that PGPR-mediated growth promotion is regulated by photoperiod, while ISR is not.     

Photoperiodic and temperature control of diapause induction and colour change in the southern green stink bug Nezara viridula

Abstract. The effect of photoperiod and temperature on the duration of the nymphal period, diapause induction and colour change in adults of Nezara viridula (L.) (Heteroptera: Pentatomidae) from Japan was studied in the laboratory. At 20 °C, the developmental period for nymphs was significantly shorter under LD 10 : 14 h (short day) and LD 16 : 8 h (long day) than under intermediate photoperiods, whereas at 25 °C it was slightly shorter under intermediate than short- and long-day conditions. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when day-length is short and it is unlikely that nymphal development is affected by day-length under summer long-day and hot conditions. Nezara viridula has an adult diapause controlled by a long-day photoperiodic response. At 20 °C and 25 °C in both sexes, photoperiodic responses were similar and had thresholds close to 12.5 h, thus suggesting that the response is thermostable within this range of temperatures and day-length plays a leading role in diapause induction. Precopulation and preoviposition periods were significantly longer under near-critical regimes than under long-day ones. Short-day and near-critical photoperiods induced a gradual change of adult colour from green to brown/russet. The rate of colour change was significantly higher under LD 10 : 14 h than under LD 13 : 11 h, suggesting that the colour change is strongly associated with diapause induction. The incidences of diapause or dark colour did not vary among genetically determined colour morphs, indicating that these morphs have a similar tendency to enter diapause and change colour in response to short-day conditions.     

CIRCADIAN GROWTH RHYTHM IN JUVENILE SPOROPHYTES OF LAMINARIALES (PHAEOPHYTA)1

A circadian rhythm in growth was detected by computer-aided image analysis in 3–4-cm-long, juvenile sporophytes of the kelp species Pterygophora California Rupr. and in seven Laminaria spp. In P. californica, the free-running rhythm occurred in continuous white fluorescent light, had a period of 26 h at 10°or 15°C, and persisted for at least 2 weeks in white or blue light. The rhythm became insignificant in continuous green or red light after 3 cycles. Synchronization by white light-dark regimes, e.g. by 16 h light per day, resulted in an entrained period of 24 h and in a shift of the circadian growth minimum into the middle of the light phase. A morning growth peak represented the decreasing portion of the circadian growth curve, and an evening peak the increasing portion. The circadian growth peak was not visible during the dark phase, because growth rate decreased immediately after the onset of darkness. At night, some growth still occurred at 16 or 12 h light per day, whereas growth stopped completely at 8 h light per day, as in continuous darkness. During 11 days of darkness, the thallus area became reduced by 3.5%, but growth rate recovered in subsequent light–dark cycles, and the circadian growth rhythm reappeared in subsequent continuous light.     

PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)     

CIRCANNUAL GROWTH RHYTHM AND PHOTOPERIODIC SORUS INDUCTION IN THE KELP LAMINARIA SETCHELLII (PHAEOPHYTA)1

Growth and reproduction of laboratory-grown sporophytes of Laminaria setchellii Silva were investigated in a tank system with controlled conditions of daylength, temperature, and nutrients (N and P). A circannual growth rhythm of the frond was detected under constant laboratory conditions. In continuous long-day and night-break conditions the period τ of the free-running rhythm varied between 11.3 and 17.3 months; in short-day conditions the frond grew indefinitely. The growth rhythm of individual plants could be synchronized by a simulated annual cycle of day-length with a period of T = 12 months. The four seasons of the year were simultaneously simulated by phase shifting the annual cycle of daylength by 3, 6, or 9 months in three out of four tanks. The annual growth cycle followed these phase shifts, and initiation of the new blade always started just after the winter daylength minimum. The formation of sori was induced by a genuine photoperiodic short-day reaction in 1- to 2-year-old plants. Sori became, visible 9–14 weeks after transfer of individual plants from long-day to short-day conditions, whereas plants cultured in continuous long-day or night-break conditions remained sterile. Sporophytes with or without blades were able to continue growth or produce new blades in continuous darkness.     

Ixodes rubicundus nymphs are short-day diapause-induced ticks with thermolabile sensitivity and desiccation resistance

The Karoo Paralysis tick, Ixodes rubicundus Neumann (Acari: Ixodidae), is a semi-voltine ixodid that survives stressful environmental conditions using morphogenetic diapause (eggs and engorged nymphs) and desiccation resistance. Both photoperiod and temperature influence diapause induction in the engorged nymph. Ixodes rubicundus nymphs are typical long-day photoperiodic organisms. The critical photoperiod is approximately 13.5 h light, 10.5 h dark, and they display a thermolabile response. The period between detachment and apolysis in engorged nymphs is modified by photoperiod; however, apolysis to ecdysis is not affected by photoperiod. Thus, initiation of development, but not the actual process is controlled by photoperiod. Most engorged nymphs delayed metamorphosis when exposed to short-day regimen (LD 12 : 12 h) after feeding. Nymphs exposed to pre- and post-feeding long-day regimen (LD 14 : 10 h) developed. Times for 50% of nymphs to apolyse when exposed to photoperiods of LD 14 : 10 h, 13.5 : 10.5 h, 13 : 11 h and 12 : 12 h were 28, 36, 40 and 58 days, respectively. Times for 50% of engorged nymphs to ecdyse ranged from 38 to 40 days after apolysis. Nymphs were sensitive to photoperiodic exposures before, during and after feeding. Nymphs exposed to long day (LD 14 :10 h) before and during feeding, moulted at 20 degrees C; however, most exposed to 10 degrees C followed by 20 degrees C (post-feeding) went into diapause. Both short- (10 : 14 h) and long- (14 : 10 h) day exposed engorged nymphs survived 45 days at 0% r.h. (n = 73), but diapause-destined ticks kept at 13 degrees C lost the least mass (29.5+/-9.5%, SD), while nondiapause ticks at 23 degrees C lost the most (48.7+/-8.2%, SD). Termination of diapause and transition to development probably coincides with a definite increase of water vapour uptake by engorged nymphs. Comparatively, I. rubicundus engorged nymphs are more desiccation tolerant than a North-American counterpart, Amblyomma cajennense (Fabricius) (Acari: Ixodidae), which is also semi-arid- to xeric-adapted. Diapause conveys important survival attributes that enable engorged I. rubicundus nymphs to inhabit a semi-arid environment with great temperature extremes, and to synchronize their activity periods with seasons and host utilization patterns.     

Compensatory abilities depending on seasonal timing of thallus excision of the kelp Undaria pinnatifida cultivated in Matsushima Bay, northern Japan

Improved cultivation technology for the kelp Undaria pinnatifida is greatly needed to increase production to meet increasing commercial demand. A previous cultivation trial indicated that the crop yield of U. pinnatifida sporophytes could be increased greatly by thallus excision in late February due to compensatory growth of the remaining tissues. To develop this potential new cultivation technology, it is essential to identify the time period during which this kelp can compensate and its physiological responses to thallus excision. In this study, U. pinnatifida sporophytes were excised at about 30 cm above the meristem at the beginning of January, February, March, and April, respectively. Morphological features, photosynthesis, nutrient uptake, and carbon and nitrogen contents of excised kelps were measured and compared with these parameters in control kelps grown without excision. Both experimental and control kelps were farmed together in Matsushima Bay, northern Japan. The kelps excised in January and February showed significant increases in the lengths and dry weights of the blade, photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents compared with the control kelps, and the growth phase was prolonged for at least 1 month. No significant increases were found in dry weights and carbon and nitrogen contents of sporophylls until early April, which indicated that the maturation period was delayed. At the end of this experiment, the nitrogen contents of sporophyll tissues formed after excisions were significantly lower than those of tissues formed before excisions. In contrast, the kelps excised in March and April showed no significant increases in morphological and physiological parameters compared with control kelps. These results suggest that U. pinnatifida sporophytes exhibited great compensation when excisions were conducted during the growing phase in January and February but not in March and April when the maturation phase had started. The regulation of resource allocation to growth and maturation after thallus excisions in January and February likely results in prolongation of the growth phase and maturation phase in excised kelps.     

Day Length and Temperature Strongly Influence Sexual Reproduction and Expression of a Novel MADS-Box Gene in the Moss Physcomitrella patens

Abstract: The effect of temperature and light conditions on sexual reproduction (sporophyte formation) of in vitro cultures of the moss Physcomitrella patens was analysed. All parameters tested, i.e., temperature, light intensity and day length had a strong impact on the number of sporophytes formed. The highest number of sporophytes, 559 g fresh weight, developed at 15 °C, 8 h light/day with an intensity of 20 μmol/m²/s. In contrast, at 25 °C, as well as with a day length of 16 h per day, the number of sporophytes was drastically reduced. Vegetative growth, determined as fresh weight per petri dish, was impeded under conditions favouring sporophyte formation, probably due to nutrient transfer to the sporophytes. Microscopic documentation of the developing sporophytes revealed that, although archegonia were arranged in bundles at the gametophore apices, usually only one archegonium per gametophore apex developed into a mature sporophyte. From an EST database six novel MADS-box genes were identified which, in phylogenetic analyses, did not cluster with the known groups of higher plant MADS-box genes. One of these genes was represented only as a singleton in a cDNA library specifically derived from gametophore apices and developing sporophytes, and, therefore, designated PpMADS-S. RNA amounts of PpMADS-S were two to three times higher under conditions that stimulate sporophyte development (15 °C, 8 h light per day) when compared to conditions favouring vegetative growth (25 °C, 16 h light per day), indicating a possible function in sexual reproduction of this moss. Thus, an efficient experimental system was established to study sex organ formation, fertilization and embryo development in Physcomitrella.     

Effects of temperature of adults and eggs on the induction of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus

Abstract.  Eggs laid by adult female Dianemobius nigrofasciatus , reared under long-day (LD 16 : 8 h, 25 °C) or short-day (LD 12 : 12 h, 25 °C) conditions from the nymphal stage, are kept at several constant temperatures. At 22.5–30.0 °C, eggs laid by long-day adults show lower incidences of diapause than those laid by short-day adults. In both eggs laid by adults under long-day conditions and those under short-day conditions, the higher the temperature at which the eggs are kept, the lower the incidence of diapause. When eggs of long-day adults are exposed to a low-temperature pulse (10 °C, 24 h) on the day of deposition (day 0), the incidence of diapause increases. The low-temperature pulse on day 1 does not increase the incidence of diapause. By contrast, when the eggs of short-day adults are exposed to a high-temperature pulse (35 °C, 24 h) on day 0 or day 1, the incidence of diapause decreases. The temperature pulses on day 0 are more effective at diapause prevention. Staining of diapause eggs by the Feulgen–Rossenbeck method shows that the eggs enter diapause at the blastoderm stage, which is on day 1 or day 2 at 25 °C. The exposure of adults to long days and higher temperatures prevents the eggs from entering diapause. In D. nigrofasciatus , embryonic diapause is controlled by maternal effects, adult photoperiod and temperature, and egg temperature before or at diapause.