Experimental control of flowering and vivipary in timothy (Phleum pratense)

Environmental and hormonal control of flowering and vivipary in four Norwegian timothy ( Phleum pratense L.) cultivars has been studied in phytotron and by aseptic culture of inflorescence explants. The critical photoperiod for flowering increased with increasing temperature (12–18°C) and it was 13 to 15 h for the southern and 14 to 16.5 h for the northern cultivars. Diurnal temperature fluctuation significantly stimulated flower formation compared to the corresponding constant temperature treatment. Plants grown in 16-h photoperiod contained normal sexual flowers, but a high percentage of spikes developed in 12- or 14-h photoperiod contained viviparous plantlets. One- to four-weeks in continuous light before treatment with 12-h photoperiod increased the number of spikes per plant, but did not enhance the frequency of vivipary. Experiments with aseptic cultures showed that generative versus vegetative development of timothy inflorescence was affected by plant hormones. Kinetin stimulated the vegetative development and induced proliferation both in inflorescence initials and in spikelets isolated at heading time.     

Cytokinins in photoperiodic induction of flowering in Chenopodium species

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non-inductive for flowering in leaves, stems, roots and apical parts of short-day Chenopodium rubrum and long-day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum , has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far-red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.     

Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid in a long-day plant,Chenopodium murale L., as influenced by photoperiodic flower induction

Chenopodium murale plants, induced to flower by 5 days of continuous light, produced 43% more ethylene than vegetative plants kept under short days (16 h darkness, 8 h light). The 1-aminocyclopropane-1-carboxylic acid (ACC)-induced ethylene production, using saturating ACC concentration (10 mol·m⁻³) was also 55% higher in induced plants. Their ACC and N-malonyl-ACC (MACC) levels were also higher, the former increasing by 56% in both shoots and roots, the latter by 288% and 108% in shoots and roots, respectively. Administration of labeled [2,3-¹⁴C]ACC produced a very similar relative content of ACC and MACC in both treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 66% more ACC than the vegetative ones. The effects of photoperiod on ethylene formation and metabolism in a long-day plant (LDP)C. murale and a short-day plant (SDP)C. rubrum are compared. Ethylene formation seems to be under photoperiodic control in both species, but its role in flower induction remains obscure.     

脱落酸在植物花发育过程中的作用

植物激素脱落酸(ABA)对植物的生长发育具有多方面的调节作用,比如种子休眠、萌发,营养生长,环境胁迫反应等。大量研究显示,ABA也参与了植物的成花调控。影响植物成花调控的环境因子,包括光周期变化、春化作用、干旱等均会导致植物体内ABA代谢的变化。本文从调控植物开花的4条主要途径与植物体内ABA代谢变化之间的相互关系,花芽分化时期ABA在植物叶芽和花芽中的动态分布以及离体培养条件下ABA对花芽分化的影响等方面总结了ABA与植物花发育这一领域的最新研究进展。对ABA在植物成花诱导和花发育中的作用进行了综合分析。     

Role of the Photoperiod Preceding a Flower-Inductive Dark Period in Dark-Grown Seedlings of Pharbitis nil Choisy

Flowering responses to a single photoperiod, of various durationsand irradiances, followed by an inductive dark period were investigatedwith dark-grown seedlings of Pharbitis nil Choisy. The numberof flower buds induced in each plant (NFB) increased with theincrease of both duration and irradiance of the photoperiod.Reciprocity did not hold for this photoresponse within the rangeof 0-16 h and 2.5-10 W-m^-2, NFB depending on the duration ratherthan the irradiance. With lengthening of the dark period followinga photoperiod of 8 h or less, two different phases alternatelyappeared so that NFB sharply increased at 20-24 h and 40-43h after the onset of the photoperiod, then gradually decreased.When the photoperiod was longer than 8 h, NFB sharply increasedat 12–16 h after the end of the photoperiod and remainedaround the saturated value with longer dark periods. Far-redlight given immediately after the photoperiod inhibited flowering,the inhibitory effect being stronger the shorter the photoperiod.This far-red effect is mediated by phytochrome and P_FR seemsto be required during the inductive dark period following ashort photoperiod for floral induction. (Received December 23, 1983; Accepted April 12, 1984)     

Studies on the Photoperiodic Responses in Short-Day Plant Helianthus tubevotus

Plants of Helianthus tuberosus, variety white tuber, were treated with various daylengths of 4, 6, 8, 10, 11, 12, 13, 14, 15, 18 h. for 25 days as soon as six leaves on a plant appeard Irradiation for 6–13 h per day induced the plants to form flower buds and flowering, daylength with 14 h or longer kept the plants in vegetative growth. The experiments showed that this variety of Helianthus tuberosus required short days for flowering and the critical daylength was about 13 h. The plants were treated with short days for different durations. At least 17 days were required, Formation of flower buds and flowering had positive correlation with the number of short days over 17 days. After short-day induction, the shorter the daylength is, the more the flower buds inverted. Long-day treatment after an appropriate period of short days wouid reduce the number of flower and induce new vegetative branches from flowering granehes.     

Aging and flowering of the apex in young Bidens radiata

The response of Bidens radiata Thuill., a short-day plant, to conditions for flower induction changes during the first 96 h after germination: the earlier the induction, the better the flowering response. Flowering is observed without previous vegetative development. An histological study shows that failure to flower is correlated with the development of the primordia of the second node leaves. The antagonism between vegetative and floral development is discussed.     

Exogenously applied melatonin (N-acetyl-5-methoxytryptamine) affects flowering of the short-day plant Chenopodium rubrum

Melatonin ( N -acetyl-5-methoxytryptamine) is an animal hormone synthesized predominantly at night. It often serves as a signal of darkness that regulates circadian rhythmicity and photoperiodism. Melatonin has also been found in algae and higher plants, including the short-day flowering plant Chenopodium rubrum . To test its involvement in plant photoperiodism, melatonin solutions were applied to the cotyledons and plumules of 5-day-old-seedlings of Chenopodium rubrum L., ecotype 374. ³H-labelled melatonin was readily taken up by the plants and was very stable for a period of 37 h from application. Treatment with 100 and 500 µ M melatonin significantly reduced flowering of plants exposed to a single inductive 12-h darkness. Melatonin was efficient only when applied before lights off or during the first half of the dark period. This indicates that melatonin affects some early steps of the transition to flowering. However, it had no effect on the period or phase of a circadian rhythm in photoperiodic time measurement. Melatonin agonists (2-I-melatonin, 6-Cl-melatonin, CGP 52608) and 5-hydroxytryptamine also reduced flowering, whereas 5-methoxytryptamine did not. The results demonstrate that exogenous melatonin is able to influence the early stages of photoperiodic flower induction and/or flower development in a higher plant. Possible mechanisms for this effect are discussed.     

Interrelations of Flowering and Vegetative Growth in Callistephus chinensis (var. Queen of the Market)

In a study of the effect of photoperiod upon the growth andflowering of Calistephus chinensis (var. Queen of the Market)it has been shown that a one-hour night break of low intensityred light given to plants growing in eight hours daylight canhave a number of morphogenetic effects. In the young plant, such a treatment increased the total areaof the leaf surface and the area per unit weight of leaf material,i.e. the specific leaf area. This effect enabled the treatedplants to make greater use of the incident light, for afternine weeks they were at least 25 per cent heavier than comparableplants which had not had the benefit of the night-break treatment.This treatment also caused flower induction and concomitantstem extension, but transfer back into eight-hour days afteran inductive period accelerated further flower development andrestricted stem extension of both the main axis and the laterals.If flower development was delayed by continuing night breaksor by delaying the onset of induction then more flowers wereeventually formed, but in the very prolific treatments flowersize was reduced. The experiment also indicated that the partition of availabledry weight between leaves, stems, and roots followed a definitepattern dependent only upon total plant dry weight. The diversionof dry weight into flowers was strongly accelerated by transferinto eight-hour days after induction but the remaining dry matterstill appeared to be distributed between the vegetative partsalong the general pattern determined by total vegetative weight. Finally the experiment showed that a wide range of plant formsbearing varying amounts of flowers could be obtained by appropriatetransfers between treatments.     

Photoperiod and Temperature Interactions in Growth and Flowering of Strawberry

Growth and flowering of strawberry cultivars were studied in controlled environments. Early cultivars adapted to marginal growing areas in Scandinavia initiated flower buds in all photoperiods including continuous light at temperatures of 12 and 18°C. At 24°C they remained vegetative in photoperiods above 14 or 16 h. The later cultivars ‘Senga Sengana’ and ‘Abundance’ did not initiate flower buds in 24-h photoperiods at any of these temperatures. Their critical photoperiod changed from above 16 h at 12°C to about 14 and 13 h at 18 and 24°C, respectively. It is concluded that at high latitudes temperature is as important as photoperiod in controlling flowering in the strawberry. Stolon formation, petiole elongation, and leaf area growth were stimulated by high temperature and long days, usually with optima at 16 h and 18°C for petiole elongation and 16 h and 24°C for stolon formation. Although growth and flowering responses in general were opposite, the results indicate that they are to some extent independent. The photoperiodic growth responses were mainly of morphogenetic nature. Dry weight of stem and leaves was little influenced by photoperiod when the irradiance was kept constant.     

Timing of reproductive and vegetative development in Saxifraga oppositifolia in an alpine and a subnival climate

Morphogenesis of floral structures, dynamics of reproductive development from floral initiation until fruit maturation, and leaf turnover in vegetative short-stem shoots of Saxifraga oppositifolia were studied in three consecutive years at an alpine site (2300 m) and at an early- and late-thawing subnival site (2650 m) in the Austrian Alps. Marked differences in the timing and progression of reproductive and vegetative development occurred: individuals of the alpine population required a four-month growing season to complete reproductive development and initiate new flower buds, whereas later thawing individuals from the subnival sites attained the same structural and functional state within only two and a half months. Reproductive and vegetative development were not strictly correlated because timing of flowering, seed development, and shoot growth depended mainly on the date of snowmelt, whereas the initiation of flower primordia was evidently controlled by photoperiod. Floral induction occurred during June and July, from which a critical day length for primary floral induction of about 15 h could be inferred. Preformed flower buds overwinter in a pre-meiotic state and meiosis starts immediately after snowmelt in spring. Vegetative short-stem shoots performed a full leaf turnover within a growing season: 16 (+/-0.8 SE) new leaves per shoot developed in alpine and early-thawing subnival individuals and 12 (+/-1.2 SE) leaves in late-thawing subnival individuals. New leaf primordia emerged continuously from snowmelt until late autumn, even when plants were temporarily covered with snow. Differences in the developmental dynamics between the alpine and subnival population were independent of site temperatures, and are probably the result of ecotypic adaptation to differences in growing season length.     

Flowering requirements in Bromus inermis, a short-long-day plant

Smooth bromegrass plants ( Bromus inermis Leyss.) have a dual photoperiodic requirement for flowering. At temperatures ranging from 6 to 24°C, short days (SD) are necessary for primary induction while a transition to long days (LD) is required for initiation of flower primordia, culm elongation and flower development (secondary induction). Critical photoperiods for primary induction (50% flowering) were 13.5 h (15°C) and 12 h (24°C) in the American cv. Manchar and 14.5 and 13 h, respectively, in the Norwegian cv. Löfar. For the secondary induction the respective critical photoperiods were 14 and 15 h in 'Manchar' and 16 and 17.5 h in 'Löar', which also appeared to be better adapted to low temperatures. Low temperature vernalization in LD for up to 16 weeks at 3°C was unable to cause primary induction and temperatures below 12°C also strongly reduced the SD effect. At optimum temperature (15-2TC) 4 to 6 weeks of 8-10 h SD treatments were needed for optimal primary induction effect. A minimum of 8 LD cycles of 24 h were required for complete secondary induction in 'Manchar', while more than 16 cycles were needed in 'Löfar'. Seedlings grown in SD developed a rosette type of growth with shoots growing in a decumbent position, while those in LD grew upright and formed elongated vegetative culms. Rate of leaf initiation was enhanced by about 60% by LD while tillering was promoted by SD.     

Photoperiod and temperature effects on in vitro growth and flowering of P. pusilla, an epiphytic orchid.

Psygmorchis pusilla Dodson and Dressler, an epiphytic orchid, has been shown to be an interesting model to study in vitro flower formation. In the present study, the effects of photoperiod and temperature on vegetative and reproductive development were investigated. Although photoperiod had limited effects on leaf number, an etiolating process was verified in darkness and a higher growth was detected under long days. A positive relationship was observed between long days and floral spike formation. However, plant incubation under 20 h photoperiod or longer days negatively affected floral bud development, inhibiting anthesis and reducing flower longevity. Higher soluble sugar and starch levels were detected in plants cultivated under long days, while chlorophyll and carotenoids contents were negatively affected under these conditions. Plants showed great sensitivity to temperature variations; 27 degrees C being the most adequate for growth, leaf and floral spike formation. Temperatures of 22 and 32 degrees C were not appropriate for in vitro development of P. pusilla.     

Flowering requirements of Scandinavian Festuca pratensis

Flowering requirements of three Scandinavian cultivars of Festuca pratensis Huds, have been studied in controlled environments. At 3 and 6°C, primary induction was independent of photoperiod, while short days (8 h) were more effective than long days (24 h) at higher temperatures. The critical temperature for induction was about 15°C in short days and about 12°C in long days. Saturation of induction required 18–20 weeks of exposure to optimal conditions. At temperatures below 12°C both induction and initiation of inflorescence primordia took place in long days, while a transition to long days was required for inflorescence initiation after primary induction in short days. A minimum of 8 long-day cycles were required for flowering of plants primary induced in short days and saturation of flowering required more than 16 cycles. The critical photoperiod for secondary induction was about 13 h. High temperature (21°C) had some devernalization effect in primary induced plants, suppressing flowering compared with 15°C.     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

Vegetative growth and frost hardiness of cloudberry (Rubus chamaemorus) as affected by temperature and photoperiod

The effect of photoperiod and temperature on growth and induction and development of frost hardiness in cloudberry ( Rubus chamaemorus L.) was examined in two experiments. The photoperiods were 8, 12 or 24 h and the temperatures were 18, 15, 12, 9, 4, 3, –3 or –4°C depending on the experiment. The level of hardiness was expressed as LT₆₆ or LT₅₀ (the lethal temperature for 66 or 50% of the plant material) for percentage of bud break and for the degree of coloring by triphenyltetrazolium chloride for rhizomes. The vegetative growth was clearly affected by daylength; petiole elongation, leaf growth, shoot dry weight and number of shoots per plant were all reduced under short days compared with long days. However, the photoperiod had no significant effect on hardening of buds or rhizomes. Hardening increased with successively decreasing temperatures. To get the maximum hardiness, plants had to be exposed to freezing temperatures.     

不同光周期对西红花开花和花丝品质的效应比较

为筛选促进西红花开花和提高花丝品质的最佳光周期,以3种不同规格(20～25 g、25～30 g、30～35 g)西红花种球为材料,设置4种光周期处理(8 h/16 h、10 h/14 h、12 h/12 h、14 h/10 h),考察光周期对西红花种球鲜重变化、主芽生长、展叶数量、开花后营养物质含量以及花朵性状和花丝品...     

Effects of Temperature and Photoperiod on Flowering in Chickpeas (Cicer arietinum L.)

Factorial combinations of two photoperiods (12 and 15 h), threeday temperatures (20, 25 and 30 °C) and three night temperatures(10, 15 and 20 °C) were imposed on nodulated plants of ninechickpea genotypes (Cicer arietinum L.) grown in pots in growthcabinets. The times to first appearance of open flowers wererecorded. For all genotypes, the rates of progress towards flowering(the reciprocals of the times taken to flower) were linear functionsof mean temperature. There were no interactions between meantemperature and photoperiod but the longer photoperiod increasedthe rate of progress towards flowering. These effects were independentof both radiation integral (the product of irradiance and photoperiod)and the vegetative stature of the plant. Taken in conjunctionwith evidence from work on other long-day species, it is suggestedthat the photo-thermal response of flowering in chickpeas, overthe range of environments normally experienced by the crop,may be described by the equation: 1/f = a+b     

Photoperiodic control of larval diapause in the yellow-spotted longicorn beetle, Psacothea hilaris: analysis by photoperiod manipulation

The photoperiodic control of diapause induction in the larvae of the yellow-spotted longicorn beetle, Psacothea hilaris (Pascoe), was investigated using a west Japan-type population collected from Ino, Kochi Prefecture, Japan. In this population, the larvae expressed a long-day photoperiodic response with a critical daylength between 13.5 and 14 h at 25 °C ; under a long daylength, the larvae pupated after the 4th or 5th instar, while the larvae entered diapause under a short daylength after 2.3 additional molts on average. When the photoperiod was changed from a short (L12:D12) to a long (L15:D9) daylength, pupation occurred in most of the individuals irrespective of the time of the change. When the photoperiod was changed from long to short at 1 or 2 weeks after hatching, all of the larvae entered diapause, whereas when the photoperiod was changed at 5 weeks after hatching or later, most of the larvae pupated. The 2 weeks exposures to a long daylength against a 'background' of a short daylength at various times revealed that the larvae of this insect are most sensitive to the photoperiod from 4 to 6 weeks after hatching.