Night Interruption Research Articles

Evolutionary Links Between Circadian Clocks and Photoperiodic Diapause in Insects

In this article, we explore links between circadian clocks and the clock involved in photoperiodic regulation of diapause in insects. Classical resonance (Nanda-Hamner) and night interruption (Bünsow) experiments suggest a circadian basis for the diapause response in nearly all insects that have been studied. Neuroanatomical studies reveal physical connections between circadian clock cells and centers controlling the photoperiodic diapause response, and both mutations and knockdown of clock genes with RNA interference (RNAi) point to a connection between the clock genes and photoperiodic induction of diapause. We discuss the challenges of determining whether the clock, as a functioning module, or individual clock genes acting pleiotropically are responsible for the photoperiodic regulation of diapause, and how a stable, central circadian clock could be linked to plastic photoperiodic responses without compromising the clock's essential functions. Although we still lack an understanding of the exact mechanisms whereby insects measure day/night length, continued classical and neuroanatomical approaches, as well as forward and reverse genetic experiments, are highly complementary and should enable us to decipher the diverse ways in which circadian clocks have been involved in the evolution of photoperiodic induction of diapause in insects. The components of circadian clocks vary among insect species, and diapause appears to have evolved independently numerous times, thus, we anticipate that not all photoperiodic clocks of insects will interact with circadian clocks in the same fashion.

적색광을 이용한 들깨의 개화조절

BACKGROUND: This experiment was conducted to investigate the effects of red light on inhibition of flowering and vegetative growth of perilla (Perilla Frutescens. L). METHODS AND RESULTS: To determine red light intensity for inhibiting floral induction of perilla 6h light plus daylength extension (17:00-23:00) with three different intensity of red lights 0.046, 0.114 and were treated respectively, and control plants were grown under 11(06:00-17:00)/13(17:00-06:00)h light/dark environment. Red(660nm) and far-red(730nm) light were irradiated for night break treatment subsequently to investigate photoreversible flowering response of perilla 'Manchu'. The flowering was inhibited by night break with red light, but sequential far-red light induced floral induction of perilla. Perilla not flowered by red light intensity over . Red light of was irradiated for 6 hours (20:00-02:00) with LEDs device in plastic house. Perilla not flowered and continued the vegetative growth by red light treatment and the plant length, number of leaves, fresh weight, and leaf area of perilla were increased by 3%, 7%, 21%, and 19%, respectively, compared to incandescent control. CONCLUSION: These results showed that red(660nm) light for daylength extension could be used to control flowering and to enhance production of perilla leaf.

Molecular Regulatory Network of Flowering by Photoperiod and Temperature in Rice

Plants have an ability to flower under optimal seasonal conditions to ensure reproductive success. Photoperiod and temperature are two important season-dependent factors of plant flowering. The floral transition of plants depends on accurate measurement of changes in photoperiod and temperature. Recent advances in molecular biology and genetics on Arabidopsis and rice reveals that the regulation of plant flowering by photoperiod and temperature are involved in a complicated gene network with different regulatory pathways, and new evidence and understanding were provided in the regulation of rice flowering. Here, we summarize and analyze different flowering regulatory pathways in detail in rice based on previous studies and our results, including short-day promotion, long-day suppression, long-day induction of flowering, night break, different light-quality and temperature regulation pathways.

Day light quality affects the night-break response in the short-day plant chrysanthemum, suggesting differential phytochrome-mediated regulation of flowering

Chrysanthemum (Chrysanthemum morifolium) is a short-day plant, which flowers when the night length is longer than a critical minimum. Flowering is effectively inhibited when the required long-night phase is interrupted by a short period of exposure to red light (night break; NB). The reversal of this inhibition by subsequent exposure to far-red (FR) light indicates the involvement of phytochromes in the flowering response. Here, we elucidated the role of light quality in photoperiodic regulation of chrysanthemum flowering, by applying a range of different conditions. Flowering was consistently observed under short days with white light (W-SD), SD with monochromatic red light (R-SD), or SD with monochromatic blue light (B-SD). For W-SD, NB with monochromatic red light (NB-R) was most effective in inhibiting flowering, while NB with monochromatic blue light (NB-B) and NB with far-red light (NB-FR) caused little inhibition. In contrast, for B-SD, flowering was strongly inhibited by NB-B and NB-FR. However, when B-SD was supplemented with monochromatic red light (B+R-SD), no inhibition by NB-B and NB-FR was observed. Furthermore, the inhibitory effect of NB-B following B-SD was partially reversed by subsequent exposure to a FR light pulse. The conditions B-SD/NB-B (no flowering) and B+R-SD/NB-B (flowering) similarly affected the expression of circadian clock-related genes. However, only the former combination suppressed expression of the chrysanthemum orthologue of FLOWERING LOCUS T (CmFTL3). Our results suggest the involvement of at least 2 distinct phytochrome responses in the flowering response of chrysanthemum. Furthermore, it appears that the light quality supplied during the daily photoperiod affects the light quality required for effective NB.

Night Interruption and Night Temperature Regulate Flower Characteristics in Cymbidium

We investigated the influences of night interruption (NI) and night temperature on flowering and flower coloration in Cymbidium. Cymbidium 'Red Fire' and 'Yokihi' were grown under a 9 hours photoperiod (control), a 9 hours photoperiod with NI at a low light intensity (LNI) of 3-7 <TEX>${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX>, or a 9 hours photoperiod with NI at a high light intensity (HNI) of 120 <TEX>${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$</TEX> for four hours (22:00-02:00 HR) for 16 weeks during the reproductive growth stage (Experiment 1). Thirty month-old Cymbidium 'Red Fire' plants with initiated flowering buds were placed in four different growth chamber with night temperature set points of 6, 9, 12, or <TEX>$15^{\circ}C$</TEX> for 16 hours (18:00 to 09:00 HR) and a daytime temperature of <TEX>$25^{\circ}C$</TEX> (Experiment 2). In Experiment 1, the numbers of visible buds and flowers increased, and time to flowering decreased in both the LNI and HNI treatments, as compared to the control in both cultivars. Red color in Cymbidium 'Red Fire' increased by both LNI and HNI, as evidenced by an increased <TEX>$a^*$</TEX> in plants grown under these conditions, relative to those grown under the control condition. Number of days to visible buds at 9-<TEX>$15^{\circ}C$</TEX> ranged from 31-34 days, as compared to 39 days at <TEX>$6^{\circ}C$</TEX> in Experiment 2. Although as the temperature increased days to flowering decreased when the plant was grown at <TEX>$15^{\circ}C$</TEX> as compared to 6, 9, or <TEX>$12^{\circ}C$</TEX>, the red color (<TEX>$a^*$</TEX>) also decreased. The number of flowers and percent flowering increased when the night temperature was maintained higher than <TEX>$9^{\circ}C$</TEX>. Therefore, NI treatment and maintaining the night temperature at approximately 9-<TEX>$12^{\circ}C$</TEX> during the winter season after flower spike initiation in the reproductive developmental growth stage improve flower quality and controls flowering time.

Replacing incandescent lamps with compact fluorescent lamps may delay flowering

The natural photoperiod is often modified in the commercial production of floriculture crops to promote or inhibit flowering. In addition, low-intensity lighting is sometimes provided in growth chambers to influence flowering of photoperiodic plants. Incandescent (INC) lamps have been commonly used to provide photoperiodic lighting, but they are being phased out of production because of their energy inefficiency. Here, we compared flowering and morphological responses of two short-day chrysanthemum (Chrysanthemum×grandiflorum) potted varieties and four long-day (LD) plants grown in a controlled environment greenhouse at 20°C with a truncated 9-h day and a 2- or 4-h night interruption (NI) or 6-h day extension (DE) lighting with INC lamps, compact fluorescent lamps (CFLs), or a combination of the two (INC+CFLs). Bulb type had no effect on flowering percentage of campanula (Campanula carpatica ‘Pearl Deep Blue’), coreopsis (Coreopsis grandiflora ‘Early Sunrise’), petunia (Petunia×hybrida ‘Wave Purple Classic’), and rudbeckia (Rudbeckia hirta ‘Becky Cinnamon Bicolor’). Within bulb type, the LD lighting regimen had no effect on flowering percentage, with the exception of chrysanthemum ‘Bianca’, in which the 4-h NI inhibited flowering more than the 2-h NI or 6-h DE treatments. However, petunia that received a 4-h NI or 6-h DE from CFLs flowered 2–3 weeks later than when the lighting treatments were provided by INC lamps. Therefore, complete replacement of INCs with CFLs can delay flowering in some crops such as petunia, whereas a hybrid approach (INC+CFL) or use of lamps that emit far-red light can alleviate this potential problem.

Flower initiation and development in Cymbidium by night interruption with potassium and nitrogen

This study was conducted to investigate the effects of potassium (K) and nitrogen (N) on flower initiation and development when applied in conjunction with night interruption (NI) in Cymbidium ‘Red Fire’. The experimental plants were grown with NI at a low light intensity (LNI) of 3–7 μmol·m−2·s−1 and at a high light intensity NI (HNI) of 120 μmol m−2·s−1 for 4 hours (22:00 to 02:00 HR), whereas control plants were grown under 9 hours photoperiod condition. The concentrations of K and N used in each experiment were 0, 100, 200, and 400 mg·L−1. The plants grown under LNI conditions had 75% inflorescence emergence when 200 mg·L−1 K was supplied, while no inflorescence emerged in control plants, despite the application of K fertilizer. Flower diameter, as well as inflorescence length and diameter increased with an increasing N application up to 200 mg·L−1 under LNI and 400 mg·L−1 under HNI conditions. K fertilization during the adult vegetative stage in Cymbidium grown under LNI artificially induced inflorescence, but the flower quality of the plants decreased relative to those grown under HNI. To improve the flower quality, maintaining N at 200 mg·L−1 and 400 mg·L−1 for plants grown under LNI and HNI conditions, respectively, after inflorescence emergence is recommended.

Effects of time and duration of short-day treatments under long-day conditions on flowering of a quantitative short-day sunflower (Helianthus annuus L.) ‘Sunrich Orange’

The effects of short-day (SD) treatment on differentiation, development and anthesis of flower buds, and on cut flower quality were investigated in a leading cut sunflower (Helianthus annuus L.) cultivar, Sunrich Orange, a quantitative SD plant. Plants were cultivated under long-day (LD) conditions with night interruption lighting from 2200 to 200h. SD treatment (11.5h photoperiod) for 1, 2, or 3 weeks was commenced at the cotyledon, two true leaves, or four true leaves stage. The control plants were grown under LD conditions throughout the experimental period. SD treatment for 1 or 2 weeks promoted flower bud initiation even when delivered at the cotyledon stage (9 days after sowing), indicating that the juvenile phase is very short in this cultivar. Flower differentiation and development were also accelerated by the SD treatment, and resulted in 19–39 days earlier anthesis. The quality of cut flowers was improved by SD treatment to desirable characteristics such as decreased weight, shortened stem and reduced stem diameter. The present study suggests that under LD conditions such as found in summer, SD treatment for 2 weeks from the cotyledon or two true leaves stage can promote LD-delayed flowering of quantitative SD sunflower plants without reducing cut flower quality.

Stimulation of steviol glycoside accumulation in Stevia rebaudiana by red LED light

The aim of this study was to determine whether steviol glycoside accumulation is under phytochrome control. The results indicate that Stevia rebaudiana Bertoni plants grown under short-day conditions showed precocious flowering and stagnation of steviol glycoside accumulation. Long night interruption by red LED light stimulated and sustained the vegetative growth as well as the accumulation of steviol glycosides in the leaves. After 7weeks of treatment, steviol glycoside content was about two-fold higher in LED-treated plants than in the short-day control group. The effects of red LED light were measured both in a greenhouse and in a phytotron, irrespective of cultivar-specific differences. Therefore, it can be concluded that a mid-night interruption by red LED light during short photoperiods provides an easy and inexpensive method to increase vegetative leaf biomass production with an increased steviol glycoside yield.

暗期干扰对棉铃虫两个不同地理种群滞育抑制作用的比较

至今,所测试昆虫的光周期反应均表明,光周期反应对暗期干扰高度敏感,短暂的光脉冲都可在不同程度上逆转长夜效应,抑制滞育的发生。在研究了棉铃虫<em>Helicoverpa armigera</em>泰安种群(36.15°N, 116.59°E)和喀佐种群(41.34°N, 120.27°E)光周期反应的基础上,在滞育诱导的短光周期下(L12:D12 和L9:D15),分别测试了暗期不同时段1h光脉冲对这两个不同地理种群滞育抑制的影响。25和22℃下的光周期反应显示了泰安种群在长暗期11-14 h 的滞育率均显著低于喀佐种群;泰安种群的临界暗长分别为11.7 h和11.5 h,喀佐种群分别为10.5 h和10.3 h,泰安种群均比喀佐种群长1.2 h。在所测试的暗期干扰实验中,除了极少数光脉冲干扰点外,泰安种群蛹滞育率显著低于喀佐种群,但两者的滞育反应曲线基本相似。在短光周期L9:D15下,泰安种群和喀佐种群均显示了光脉冲落入暗期的第9-11小时最有效地抑制了滞育的发生。在短光周期L12∶D12下,泰安种群和喀佐种群在25℃时均显示了光脉冲落入暗期的第3-4小时和第10小时导致了最低的滞育发生;但在22℃时,喀佐种群只在暗期的第3-4小时显示了最高的滞育抑制。这些结果揭示了偏南的泰安种群对暗期干扰的敏感性强于偏北的喀佐种群,但这两个地理种群的最高光敏感位点基本相同。;Photoperiodic time measurement in insects can be affected by interrupting the dark phase of the light dark cycle with short supplementary light pulses. All the photoperiodic responses tested are highly sensitive to night interruption, and the long night effect is reversed by a light break. Most past studies revealed two points of apparent light sensitivity (the so-called A and B peaks), but the response pattern varied considerably among different species. Some species had only one peak (or trough), either A or B. Even the same species may have different patterns of response depending on the experimental conditions. However, it is still not clear whether differences exist in the effect of night-interruption on diapause-averting among different geographic populations. The cotton bollworm, <em>Helicoverpa armigera </em>(Hübner) is one of the most serious crop pests in Asia, Australia, Africa and Europe. The species is distributed across much of China and attacks many host plants. The widely distributed<em> H. armigera</em> encounters a great diversity in climatic conditions in different places and shows different critical day lengths or night lengths (the day length that elicits 50% diapause response) among different geographic populations. In the present study, the photoperiodic response and effects of night-interruption on diapause-averting, in which the scotophases of L9:D15 (Light 9 h:Dark 15 h) and L12∶D12 were interrupted by 1 h light pulse, were investigated at 22℃ and 25℃ in Taian (TA, 36.15°N, 116.59°E) and Kazuo (KZ, 41.34°N, 120.27°E) populations of the cotton bollworm<em> H. armigera</em>. The photoperiodic response curves showed that the incidences of diapause in the scotophases of 11-14 h were significantly lower in the Taian population than in the Kazuo population. The critical night length in the Taian population at 25℃ and 22℃ was 11 h 42 min and 11 h 30 min, respectively, and 1h 20 min longer than that in Kazuo population (10 h 30 min and 10 h 18min). In all night-interruption experiments, the incidences of diapause in almost all positions of light pulse in the Taian population were significantly lower than that in the Kazuo population. However, the diapause response curves were similar in the two populations. Under L9: D15, the incidence of diapause was inhibited most effectively in both the Taian population and the Kazuo populations when the light pulses were placed at 9-11 h in the darkness. Under L12:D12 the incidence of diapause was lowest at 25℃ in both Taian population and Kazuo population when the light pulses were placed at 3-4 h and 10 h in the darkness. However, the Kazuo population only showed a peak of diapaus-averting occurring in 3-4 h in the darkness at 22℃. <br> Our results reveal that effect of night-interruption on diapause-averting is different among different geographic population. The southern Taian population is more sensitive to night-interruption than the northern Kazuo populations, but the most highly photosensitive position is similar for both populations.<br> A light pulse plays two possible roles in photoperiodic time measurement. First it ‘initiates’ or ‘resets’ the clock; this has been called the ‘entraining agent’ or ‘priming agent’. Second it ‘measures’ a critical duration of day or night; this has been called the ‘inductive agent’ or ‘terminating agent’. The present study in <em>H. armigera</em> reveals that a light pulse can reset the process measuring night length, and thus influences the incidence of diapause.

Rapid adjustment in chrysanthemum carbohydrate turnover and growth activity to a change in time-of-day application of light and daylength.

Diel (24h) rhythms are believed to be of great importance to plant growth and carbohydrate metabolism in fluctuating environments. However, it is unclear how plants that have evolved to experience regular day-night patterns will respond to irregular light environments that disturb diurnally-regulated parameters related to growth. In this study, chrysanthemum plants were exposed to a change in the time-of-day application of light followed by short days or long days with a night interruption of light. We observed a clear shift in the diel cycle of sucrose turnover and relative leaf expansion, indicating a resetting of these activities with a temporal trigger in the early morning. The starch pool was relatively stable in long-day plants and marginally affected by the change in the time-of-day application in light followed by long days with a night interruption. This was in contrast with an onset of a daily starch turnover by a shift to short days. These results confirm findings from model species on the complex relationship between carbohydrate metabolism, source-sink relations and growth rate and they shed new light on the dynamic processes during acclimation towards altered environmental responses of plants in fluctuating environments.

Night interruption promotes vegetative growth and flowering of Cymbidium

The effects of night interruption (NI) were examined on the vegetative growth and flowering of Cymbidium ‘Red Fire’ and ‘Yokihi’. Plants were grown under 9/15 h ambient light/dark (control), 9 h ambient light plus night interruption (22:00–02:00 h) with low light intensity at 3–7 μmol m −2 s −1 (LNI) and 9 h ambient light plus NI with high light intensity at 120 μmol m −2 s −1 (HNI) conditions. The number of leaves, leaf length, number of pseudobulbs and pseudobulb diameter increased in both LNI and HNI compared to controls for both cultivars. While none of the control plants flowered within 2 years, 100% of the ‘Yokihi’ and 80% of the ‘Red Fire’ plants grown under HNI condition flowered. In the LNI group, 60% of the plants flowered in both cultivars. Plants in the HNI group showed a decreased time to visible inflorescence and flowering than those in the LNI group. The number of inflorescences and florets were greater in the plants grown under HNI than those in the LNI group. The tallest plants at flowering were in the HNI group in both cultivars. NI with low light intensity can be used effectively to promote flower induction with increased growth rate during the juvenile stage in Cymbidium. To obtain high quality plants, however, NI with high light intensity strategies should be considered.

Constitutive expression of the GIGANTEA Ortholog Affects Circadian Rhythms and Suppresses One-shot Induction of Flowering in Pharbitis nil, a Typical Short-day Plant

GIGANTEA (GI) is a key regulator of flowering time, which is closely related to the circadian clock function in Arabidopsis. Mutations in the GI gene cause photoperiod-insensitive flowering and altered circadian rhythms. We isolated the GI ortholog PnGI from Pharbitis (Ipomoea) nil, an absolute short-day (SD) plant. PnGI mRNA expression showed diurnal rhythms that peaked at dusk under SD and long-day (LD) conditions, and also showed robust circadian rhythms under continuous dark (DD) and continuous light (LL) conditions. Short irradiation with red light during the flower-inductive dark period did not change PnGI expression levels, suggesting that such a night break does not abolish flowering by affecting the expression of PnGI. In Pharbitis, although a single dusk signal is sufficient to induce expression of the ortholog of FLOWERING LOCUS T (PnFT1), PnGI mRNA expression was not reset by single lights-off signals. Constitutive expression of PnGI (PnGI-OX) in transgenic plants altered period length in leaf-movement rhythms under LL and affected circadian rhythms of PnFT mRNA expression under DD. PnGI-OX plants formed fewer flower buds than the wild type when one-shot darkness was given. In PnGI-OX plants, expression of PnFT1 was down-regulated, suggesting that PnGI functions as a suppressor of flowering, possibly in part through down-regulation of PnFT1.

Influence of photoperiod on growth and flowering of dwarf purple loosestrife

This study was conducted to compare the growth and flowering characters of a dwarf purple loosestrife and purple loosestrife (Lythrum salicaria L.), and to determine the optimal photoperiod of dwarf purple loosestrife for forcing cultivation. Dwarf purple loosestrife was grown under natural sunlight (from 08:30 to18:30 HR, 10 h) and additional artificial lighting [0, 2, 3, 4, 6, or 14 h of continual light, or night interruption of 4 h (NI)] in a greenhouse. Growth and development of dwarf purple loosestrife were promoted by 14, 16, or 24 h or NI. The number of lateral shoots and plant height were higher as daylength was extended. However, the number of nodes was not influenced by photoperiod. The number of inflorescences was 0.6, 2.9, 5.0, or 4.2 under 14, 16, or 24 h, or NI, respectively. Also, plants under NI showed more uniform flowering (86%) than those under 14 h (48%). However, plants under 10, 12, or 13 h never produced inflorescences and remained as rosettes throughout the experiment. Therefore, we concluded that dwarf purple loosestrife has a critical photoperiod, 14-h daylength and NI is the effective method to accelerate growth and flowering for forcing cultivation.

The effect of the floral repressorFLCon the timing and progression of vegetative phase change inArabidopsis

Plants undergo two major post-embryonic developmental transitions--the juvenile-to-adult vegetative transition (vegetative phase change) and the adult-to-reproductive transition (flowering). In woody plants, these transitions can be separated by years, but in herbaceous species they are often very close together, making it difficult to differentiate the effects of vegetative phase change and floral induction on vegetative development. To distinguish between these factors, we have compared the vegetative morphology of plants highly expressing the floral repressor FLC (FRI;FLC) with plants mutant for this gene (FRI;flc-3) under both photoinductive (long day, LD and night interruption, NI) and non-photoinductive (short day, SD) conditions. We show that the onset of abaxial trichome production is insensitive to floral induction, but the distribution and overall number of abaxial trichomes, as well as several other leaf traits associated with vegetative change, are strongly influenced by flowering. Most of the major differences in leaf morphology between FRI;FLC and FRI;flc-3 plants grown in LD can be attributed to the early flowering phenotype of FRI;flc-3, because these differences are not apparent in plants grown in SD. These include differences in leaf size, hydathode number and the distribution of abaxial trichomes along the length of the leaf. Leaf shape and the total number of abaxial trichomes are affected by FLC independently of its effect on flowering. Our results demonstrate that the onset and the progression of vegetative phase change are regulated by different combinations of endogenous and environmental factors, and reveal a role for FLC in vegetative development.

Effects of Night-break Treatment Performed Three Times per Week and Exposure to Cold Air on Spinach Growth and Quality in Winter Season

We investigated the combined effects of night-break treatment performed three times per week and subsequent exposure to cold air by opening the greenhouse windows on the growth and quality of December-sown spinach (Spinacia oleracea L.). Plant height and fresh weight increased as a result of the night-break treatment, but plant elongation decreased because of the exposure to cold air. On comparing similar-sized harvests, the sugar concentration (Brix value) and L-ascorbic acid level were significantly higher but the nitrate (NO3-) level was lower in the combined treatment than in the control plants without the night break and exposure to cold air. These results suggest that the combined method of the night break and subsequent exposure to cold air would be effective to produce high-quality spinach without delaying the harvest.

Photoperiodic Flower Induction of Several Kalanchoe Species and Ornamental Characteristics of the Flowering Species

Our objectives in this study were to identify the flowering response of Kalanchoe spp. to photoperiodic treatments and characterize flowering and vegetative characteristics of flowering plants. Twenty vegetatively propagated Kalanchoe spp. were grown under one of four photoperiodic treatments: 1) short days (SD; 8-h photoperiod) for 16 weeks; 2) night interruption lighting (NI; 2000 to 0200 hr) for 16 weeks; 3) SD for 8 weeks then transferred to NI for 8 weeks; or 4) NI for 8 weeks then transferred to SD for 8 weeks. Kalanchoe beauvardii, K. behariensis, K. fedtschenkoi, K. longiflora, K. marmorata, K. marnieriana, K. streptantha, K. tomentosa, and K. vigueridoi did not flower under any treatment. Kalanchoe laetivirens and K. rosei had minimal flowering when exposed to NI followed by SD, whereas K. pumila had minimal flowering when exposed to SD followed by NI. Kalanchoe glaucescens, K. laciniata, K. manginii, K. nyikae, K. rotundifolia, K. uniflora, and K. velutina flowered when exposed to SD for 8 or 16 weeks, and node number below the inflorescence and days to first open flower for these species increased when NI preceded SD. Kalanchoe millotii flowered under a 16-week SD treatment only. No plants flowered when grown under only NI. We classified K. glaucescens, K. laciniata, K. manginii, K. millotii, K. nyikae, K. rotundifolia, K. uniflora, and K. velutina as obligate SD plants. Flower diameter, total flower number, total color index, shoot length, branch number, and leaf length and width varied among species. Based on these ornamental characteristics, we identified K. glaucescens, K. laciniata, K. manginii, K. nyikae, K. uniflora, and K. velutina as potential ornamental flowering potted plants.

Induction and Promotion of Flowering by Heat-Treated Catecholamines inLemna paucicostata

Alkali- and heat-treated norepinephrine, a catecholamine, induced flowering of short-day (SD) plant Lemna paucicostata 151 even under long-day (LD) conditions. Flowering induced with a lower concentration of heat-treated norepinephrine was promoted under SD conditions but inhibited by a night break. The related compounds L-dopa and dopamine also promoted flowering under SD conditions when they were heat-treated.

Sexual difference in the photoperiodic induction of pupal diapause in the flesh fly Sarcophaga similis

The flesh fly Sarcophaga similis enters pupal diapause in response to short days, but averts diapause under long days. This species shows a sexual difference in the photoperiodic induction of diapause, with females having shorter critical daylength than males. Here, we proposed two hypotheses to explain this sexual difference. First, we proposed a sexual difference in the qualitative evaluation of photoperiods. This hypothesis assumes under the external coincidence model that although the photoinducible phase of both sexes locates at late scotophase, in males, it locates at a slightly earlier phase. However, the results of night interruption experiments clearly ruled out this hypothesis. Because we verified that S. similis evaluated photoperiods quantitatively, we next proposed a sexual difference in the quantitative evaluation of photoperiods. This hypothesis incorporates concepts of a hypothetical substance accumulation that shows a diapause-inducing effect and an internal threshold that serves as a reference to determine the diapause/nondiapause developmental program. In long-day exposure experiments and night interruption experiments, females consistently showed a lower incidence of diapause than males. Thus, the present study data satisfactorily meet the second hypothesis, that is a sexual difference in the quantitative evaluation of photoperiods exists in S. similis.

Day/Night Temperatures Influence Growth and Photosynthesis During Containerized Production of Selected Species of Helleborus (Hellebores)

Abstract Containerized seedlings of Helleborus foetidus L. (stinking hellebore), H. niger L. (Christmas rose), and H. ×hybridus L. (Lenten rose) were grown under long-day conditions in controlled-environment chambers for 95 days with 9-hr days of 14, 18, 22, 26, or 30C (57, 64, 72, 79, or 86F) in factorial combination with 15-hr nights of 10, 14, 18, 22, or 26C (50, 57, 64, 72, or 79F). Long-day conditions were provided by a 3-hr night interruption. Growth of each species responded differently to day and night temperatures. Calculated maximum root, top, and total dry weight, and leaf area of H. foetidus occurred with days/nights of 20/15, 18/13, 19/14, and 18/15C (68/59, 65/55, 66/57, and 65/59F), respectively. While night temperature (NT) had no effect on root:top ratio [RTR (root dry weight ÷ top dry weight)], RTR was greatest (0.65) with days of 22C (72F). Helleborus niger had calculated maximum root dry weight and total dry weight with days of 14C (57F) and nights of 16 and 13C (60 and 55F), respectively. Top growth of H. niger decreased linearly as NTs increased for days of 14 or 22C (57 or 72F). Day temperatures (DTs) had no effect on RTR, whereas RTR responded quadratically as NT increased with a calculated maximum RTR at nights of 19C (66F). Leaf area was maximized at days/nights of 14/10C (57/50F). At days of 22 or 26C (72 or 79F), top growth of H. ×hybridus responded quadratically as NT increased with maxima occurring at nights of 18 or 17C (64 or 63F). Root dry weight responded quadratically at days of 14, 22, or 26C (57, 72, or 79F) and calculated maxima occurred with nights of 18C (64F). At days of 22 or 26C (72 or 79F), there were quadratic responses in total dry weight with calculated maximum growth of H. ×hybridus at nights of 18 or 17C (64 or 63F), respectively. For days of 14, 22, or 30C (57, 72, or 86F), there were quadratic responses in RTR with greatest RTR calculated at nights of 15, 18, or 16C (59, 64, or 60F), respectively. There were quadratic responses at days of 22 or 26C (72 or 79F) for leaf area with calculated maxima at nights of 18 or 17C (64 or 63F), respectively. As DTs increased from 14 to 30C (57 to 86F) net CO2 assimilation (PN) of H. ×hybridus also increased linearly whereas increased NTs had no effect on PN. In contrast, stomatal conductance was not impacted by DT or NT.