Dual induction rather than intermediate daylength response of flowering in Echinacea purpurea

Echinacea purpurea cv. Bravado and Magnus have been reported to be intermediate daylength plants (IDP) which flower in response to photoperiods between 13 and 16 h. The present experiments with E. purpurea cv. Bravado show that E. purpurea is actually a dual induction short-long-day plant which flowers promptly and consistently when grown in short day (SD) followed by long day (LD) conditions, but not with the reverse sequence of photoperiods. The flowering response increased with increasing duration of both the SD and the LD treatments. A minimum of 4 weeks of SD followed by 12 LD was required for complete flowering. No flowering occurred in continuous SD or LD, whereas a high proportion of plants flowered in continuous 14-h daylength. However, flowering was more variable in intermediate daylength than after transition from SD to LD. Furthermore, photoperiods between 13 and 16 h could satisfy both the primary SD induction and the secondary LD induction requirements. As a number of dual induction plants, both short-long-day and long-short-day plants, have such an overlapping window of effective photoperiods that can trigger both the SD and LD responses, the rationale for maintaining IDP as a separate and genuine flowering response group is seriously challenged.     

Flowering of contrasting white clover varieties in relation to daylength in controlled environments and in the field

The effect of 12 , 14 and 16 h photoperiods, given consecutively, on flower production in 10 varieties of white clover (Trifolium repens) in controlled environments, is described. The effect of natural daylengths from September to July on the same plants in the field was also studied in the following year. Relationships between morphological and physiological traits and flowering were examined. In controlled environments most plants flowered under the longest days, three times as many in the 16 h daylength as in the 12 h. Larger leaved types had a higher proportion of reproductive plants than did smaller leaved types. Floral initiation was not observed in the field until daylengths were in excess of 15 h. Increasing daylength increased flower production, floret and ovule numbers but did not appear to increase nectar production significantly.     

Phytochrome Regulation of Flowering in the Long-Day Plant, Hyoscyamus niger

A daylength extension with incandescent light is more effective in promoting flowering of long-day plants like Hyoscyamus niger than fluorescent light. A low phytochrome photoequilibrium (Pfr/P_tot), attained by a far-red irradiation at the close of long days under fluorescent light, also promotes flowering. Moreover, if flower initiation processes are initiated by several long days, a low phytochrome photoequilibrium at the end of short, postinduction photoperiods also enhances flowering. The initiation phase of flowering requires Pfr to be present whereas the development phase proceeds more rapidly in the absence of Pfr. Spectral dependence studies, therefore, could be misinterpreted if the initiation and development stages are combined into a single audit of flowering.     

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.     

The Arabidopsis ELF3 gene regulates vegetative photomorphogenesis and the photoperiodic induction of flowering

Flowering in Arabidopsis thaliana is promoted by long-day (LD) photoperiods such that plants grown in LD flower earlier, and after the production of fewer leaves, than plants grown in short-day (SD) photoperiods. The early-flowering 3 ( elf 3) mutant of Arabidopsis , which is insensitive to photoperiod with regard to floral initiation has been characterized. elf 3 mutants are also altered in several aspects of vegetative photomorphogenesis, including hypocotyl elongation. When inhibition of hypocotyl elongation was measured, elf 3 mutant seedlings were less responsive than wild-type to all wavelengths of light, and most notably defective in blue and green light-mediated inhibition. When analyzed for the flowering-time phenotype, elf 3 was epistatic to mutant alleles of the blue-light receptor encoding gene, HY 4. However, when elf 3 mutants were made deficient for functional phytochrome by the introduction of hy 2 mutant alleles, the elf 3 hy 2 double mutants displayed the novel phenotype of flowering earlier than either single mutant while still exhibiting photoperiod insensitivity, indicating that a phytochrome-mediated pathway regulating floral initiation remains functional in elf 3 single mutants. In addition, the inflorescences of one allelic combination of elf 3 hy 2 double mutants form a terminal flower similar to the structure produced by tfl 1 single mutants. These results suggest that one of the signal transduction pathways controlling photoperiodism in Arabidopsis is regulated, at least in part, by photoreceptors other than phytochrome, and that the activity of the Arabidopsis inflorescence and floral meristem identity genes may be regulated by this same pathway.     

Jasmonates Inhibit Flowering in Short-Day Plant Pharbitis nil

The role of jasmonates in the photoperiodic flower induction of short-day plant Pharbitis nil was investigated. The plants were grown in a special cycle: 72 h of darkness, 24 h of white light with lowered intensity, 24-h long inductive night, 14 days of continuous light. At 4 h of inductive night the cotyledons of non-induced plants contained about two times the amount of endogenous jasmonates (JA/JA-Me) compared to those induced. A 15-min long pulse of far red light (FR) applied at the end of a 24-h long white light phase inhibited flowering of P. nil. The concentration of jasmonates at 2 and 4 h of inductive night in the cotyledons of the plants treated with FR was similar. Red light (R) could reverse the effect of FR. R light applied after FR light decreased the content of jasmonates by about 50%. Methyl jasmonate (JA-Me) applied to cotyledons, shoot apices and cotyledon petioles of P. nil inhibited the formation of flower buds during the first half of a 24-h long inductive or 14-h long subinductive night. Application of JA-Me to the cotyledons was the most effective. None of the plants treated with JA-Me on the cotyledons in the middle of the inductive night formed terminal flower buds. The aspirin, ibuprofen and phenidone, jasmonates biosynthesis inhibitors partially reversed the effect of FR, stimulating the formation of axillary and terminal flower buds. Thus, the results obtained suggests that phytochrome system control both the photoperiodic flower induction and jasmonates metabolism. Jasmonates inhibit flowering in P. nil.     

Light requirement,phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois

For dark-grown seedlings of Pharbitis nil capacity to flower in response to a single inductive dark period was established by 24 h white, far-red (FR) or ruby-red (BCJ) light and by a skeleton photoperiod of 10 min red (R)-24 h dark-10 min R. FR alone was ineffective without a brief terminal (R) irradiation, confirming that the form of phytochrome immediately prior to darkness is a crucial factor for flowering in Pharbitis. The magnitude of the flowering response was significantly greater after 24 h FR or white light (WL) (at 18° C and 27° C) than after two brief skeleton R irradiations, but the increased flowering response was not attributable to photosynthetic CO₂ uptake because this could not be detected in seedlings exposed to 24 h WL at 18° C. Photophosphorylation could have contributed to the increased flowering response as photosystem I fluorescence was detectable in plants exposed to FR, BCJ, or WL, but there were large differences between flowering response and photosystem I capacity as indicated by fluorescence. We conclude that phytochrome plays a major role in photoresponses regulating flowering. There was no simple correlation between developmental changes, such as cotyledon expansion and chlorophyll formation during the 24-h irradiation period, and the capacity to flower in response to a following inductive dark period. Changes in plastid ultrastructure were considerable in light from fluorescent lamps and there was complete breakdown of the prolamellar body with or without lamellar stacking at 27 or 18° C, respectively, but plastid reorganization was minimal in FR-irradiated seedlings.Abbreviations BCJ irradiation from photographic ruby-red lamps - FR far-red light - P_fr far-red-absorbing from of phytochrome - P total phytochrome content - R red light - WL white light from fluorescent lamps     

Effects of Temperature and Photoperiod on Flowering in Soya bean [Glycine max (L.) Merrill]: a Quantitative Model

Factorial combinations of five photoperiods (8 h 20 min, 10h, 11 h 40 min, 13 h 20 min and 15 h) and three night temperatures(14, 19 and 24 C) combined with a single day temperature (30C) were imposed on nodulated plants of nine soya bean genotypes[Glycine max (L.) Merrill] grown in pots in growth cabinets.The times to first appearance of open flowers were recorded.For a photoperiod-insensitive cultivar, and for the remainingeight photoperiod-sensitive genotypes in photoperiods shorterthan the critical daylength, the rates of progress towards flowering(the reciprocals of the times taken to flower) were linear functionsof mean diurnal temperature. For all photoperiod-sensitive genotypes,times to flowering in photoperiods longer than the criticaldaylength increased as inverse functions of both increasingphotoperiod and decreasing temperature. A consequence of thesetwo relations is that the critical daylength becomes longerwith higher mean temperatures. In the five photoperiod-sensitivegenotypes which flowered in all environments before the experimentwas terminated (after 150 d) the delays in flowering due tolow temperatures or long photoperiods were limited by a maximumperiod to flowering specific for each genotype. These resultsare discussed in relation to the development of a simple techniquefor the large-scale screening of soya bean germplasm to determinephoto-thermal response surfaces for flowering. Glycine max (L.) Merrill, soya bean, flowering, photoperiod, temperature, screening, germplasm     

Light-quality effects on Arabidopsis development. Red, blue and far-red regulation of flowering and morphology

Arabidopsis thaliana (L.) Heynh. race Columbia plants were grown in red. blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m⁻² s⁻¹) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P_fr/P_tot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P_fr/P_tot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.     

光周期对毕氏海蓬子(Salicornia bigelovii Torr.)开花的影响

对毕氏海蓬子分别进行了不同日照长度处理及不同光周期数的短日照处理,发现:(1)毕氏海蓬子开花的临界日长为15 h;(2)在光照8 h/d处理条件下,毕氏海蓬子开花所需最少光周期数为13;(3)经过13～18个短日照(8 h光照/d)光周期数处理,再移至长日照(17 h光照/d)条件下,有成花逆转现象.     

Role of phytochrome B in organ formation processes in Cucumis sativus L.

The role of phytochrome B in the organogenesis process in the apical and axillary shoot meristems during early ontogenesis stages in cucumber Cucumis sativus L. at photoperiods (day/night) 10/14, 16/8 h, and continuous light in comparison with wild type plants and phytochrome B-deficient mutant (lh-mutant) was investigated. In mutant phytochrome B, deficiency caused inhibition of initiation of leaves both in the main shoot and lateral shoots and increased the number of flower buds (IV stage of organogenesis). With continuous light, the number of lateral shoots and flowers during stage IV of organogenesis in wild-type plants increased twofold in comparison with the mutant. Short-term temperature drops did not induce floral ontogenesis in mutants but increased the number of off-shoots in both experimental variants during a long photoperiod and continuous lighting. We propose that phytochrome B, by increasing the compactness of chromatin, may facilitate coordination of ontogenesis processes with changing environmental conditions.     

Interaction of phytochromes A and B in the control of de-etiolation and flowering in pea

The interactions of phytochrome A (phyA) and phytochrome B (phyB) in the photocontrol of vegetative and reproductive development in pea have been investigated using null mutants for each phytochrome. White-light-grown phyA phyB double mutant plants show severely impaired de-etiolation both at the seedling stage and later in development, with a reduced rate of leaf production and swollen, twisted internodes, and enlarged cells in all stem tissues. PhyA and phyB act in a highly redundant manner to control de-etiolation under continuous, high-irradiance red light. The phyA phyB double mutant shows no significant residual phytochrome responses for either de-etiolation or shade-avoidance, but undergoes partial de-etiolation in blue light. PhyB is shown to inhibit flowering under both long and short photoperiods and this inhibition is required for expression of the promotive effect of phyA. PhyA is solely responsible for the promotion of flowering by night-breaks with white light, whereas phyB appears to play a major role in detection of light quality in end-of-day light treatments, night breaks and day extensions. Finally, the inhibitory effect of phyB is not graft-transmissible, suggesting that phyB acts in a different manner and after phyA in the control of flower induction.     

The Role of Leaves as Inhibitors of Flower Induction in Strawberry: With one Figure in the Text

The effects of various defoliation treatments on flower initiationwere studied in the strawberry var. Talisman, which is a facultativeshort-day plant, with particular reference to differences inthe inductive capacity of leaves of differing maturity. Plants from which all mature leaves had been removed to leaveonly two immature leaves flowered in longer photoperiods thanintact controls, and conversely plants bearing only three fullymature and no immature leaves required a shorter photoperiodfor flower initiation than intact plants. Intact plants in constant darkness and totally defoliated plantsin continuous light both initiated flowers, but intact plantsin continuous light failed to flower. It is submitted that these results provide evidence that thephotoperiodic control of flowering in this plant operates througha flower inhibitor produced in the leaves. They also show that although leaves of any maturity are ableto inhibit flower initiation, under some conditions mature leavesare more inhibitory than immature, and that the inhibitory activityof any leaf decreases with decreasing photoperiod.     

Photoperiodic control of flowering in Dactylis glomerata, a true short-long-day plant

Flowering requirements of three Scandinavian cultivars of Dactylis glomerata L. have been studied in controlled environments. At temperatures ranging from 9 to 21°C optimal flowering required 10 weeks of exposure to short days (SD) followed by exposure to long days (LD). Only a few plants flowered in continuous LD and no primary induction took place in any daylength at 24 or 27°C. However, at a temperature of 3°C primary induction occurred also in 24 h LD, but more than 20 weeks of treatment were required for 100% flowering. The critical photoperiod for secondary induction was about 12–13 h, depending on the latitude of origin of the cultivar. A critical number of 12 to 16 LD cycles was required for 100% flowering, although some plants flowered after only 4 LD. A high proportion of viviparous proliferation resulted from marginal LD induction. Initiation of floral primordia did not take place in SD but required a transition from SD to LD. These results demonstrate that D. glomerata is a true short-long-day plant.     

Flowering responses to altered expression of phytochrome in mutants and transgenic lines of Arabidopsis thaliana (L.) Heynh.

The long-day plant Arabidopsis thaliana (L.) Heynh. flowers early in response to brief end-of-day (EOD) exposures to far-red light (FR) following a fluorescent short day of 8 h. FR promotion of flowering was nullified by subsequent brief red light (R) EOD exposure, indicating phytochrome involvement. The EOD response to R or FR is a robust measure of phytochrome action. Along with their wild-type (WT) parents, mutants deficient in either phytochrome A or B responded similarly to the EOD treatments. Thus, neither phytochrome A nor B exclusively regulated flowering, although phytochrome B controlled hypocotyl elongation. Perhaps a third phytochrome species is important for the EOD responses of the mutants and/or their flowering is regulated by the amount of the FR-absorbing form of phytochrome, irrespective of the phytochrome species. Overexpression of phytochrome A or phytochrome B resulted in differing photoperiod and EOD responses among the genotypes. The day-neutral overexpressor of phytochrome A had an EOD response similar to all of the mutants and WTs, whereas R EOD exposure promoted flowering in the overexpressor of phytochrome B and FR EOD exposure inhibited this promotion. The comparisons between relative flowering times and leaf numbers at flowering of the over-expressors and their WTs were not consistent across photoperiods and light treatments, although both phytochromes A and B contributed to regulating flowering of the transgenic plants.     

Kinetics and time dependence of the effect of far red light on the photoperiodic induction of flowering in wintex barley

Flowering in the long day plant Hordeum vulgare L. var. Wintex barley was enhanced by the addition of far red light to the main light portion of the photoperiod. Far red energy was provided to produce quantum flux ratios (660/730 nm) and phytochrome photoequilibria (Pfr/total phytochrome) equivalent to those reported both beneath a leaf canopy and outside a canopy at twilight. The photoperiodic requirement for long days can be completely eliminated by the addition of far red light. However, both the effect of extending the photoperiod without far red and the addition of far red to 12-hour photoperiods were suboptimal. Maximal stimulation was achieved only when far red was added to continuous light. The duration of the period of maximal apex elongation rate, as well as the reduction of the time required for floral initiation, were saturated by three inductive cycles. When far red energy was provided intermittently during 3 days of continuous light, the ability to respond varied in a circadian manner. This enhancement of flowering by far red appears to be mediated by the “high irradiance response” of phytochrome.     

REPRODUCTIVE PHENOLOGIES IN LOBELIA INFLATA (LOBELIACEAE) AND THEIR ENVIRONMENTAL CONTROL

Flowering and fruiting phenologies of individual plants and flowers of Lobelia inflata, a North American summer annual, were studied in the field and greenhouse to determine whether onset of flowering and fruit maturation were correlated, and the degree to which these reproductive phenologies were influenced by the environment. Within each of two field populations, larger plants flowered earlier and produced more flowers than smaller plants. Onset of flowering was positively correlated with onset of fruit maturation but not perfectly so. Two factors decreased the intensity of this correlation. First, at the flower level, the earlier a flower bloomed, the longer the resulting fruit took to develop. Second, fruit development times varied significantly among individual plants. In the greenhouse, individuals watered more frequently attained greater size and flowered earlier than individuals watered less frequently. Nutrient additions did not affect plant size or onset of flowering. These results indicate that for the summer annual Lobelia inflata, reproductive phenologies are phenotypically correlated, and that timing of reproduction is resource and size dependent, as it is for other monocarpic plant species.     

Seasonal pattern of dry matter allocation in Dactylorhiza lapponica (Orchidaceae) and the relation between tuber size and flowering

A population of the tuberous orchid Dactylorhiza lapponica was sampled from June 2000 to June 2001 in the Sølendet Nature Reserve, Central Norway. Dry matter of aerial shoots, old tubers and new (replacement) tubers was measured, as well as reproductive status during 1999–2001. The biomass of the new tuber was found to continue to increase after the assimilation from photosynthesis had ceased in August. It is suggested that the increase is caused by mycotrophic activity and reallocation of nutrients from the aerial shoots. There was a clear relationship between tuber size and flowering behaviour. Individuals with flower primordia had the largest replacement tuber, whereas those that flowered in the sampling season or remained vegetative throughout 1999–2001 had the smallest. Individuals that flowered in the sampling season had the largest old tuber. Those, which had not flowered for at least two years, but had developed flower primordia, had the second largest, and those that remained vegetative throughout 1999–2001 had the smallest one. Individuals with a replacement tuber less than 0.22 g in October, have a very low probability of flowering the following season. Flowering entails a cost in terms of reduced biomass of the replacement tuber compared to vegetative individuals with old tubers of similar size. Allometric analyses revealed that above-ground biomass and biomass of replacement tubers increased with the biomass of old tubers in vegetative individuals. For generative individuals, however, above-ground biomass was only weakly related to below-ground biomass.