CONTROL OF FLOWER FORMATION BY GROWTH RETARDANTS AND GIBBERELLIN IN SAMOLUS PARVIFLORUS,A LONG-DAY PLANT

The growth retardants AMO–1618 and CCC inhibited flower formation and stem elongation in Samolus parviflorus, a long-day rosette plant, under inductive conditions. The vegetative growth of the plants, as measured by leaf formation, was affected only slightly, or not affected at all. Application of gibberellic acid (GA₃) reversed completely the inhibition both of flower formation and of stem elongation caused by AMO, but relatively larger amounts of GA were required to reverse the CCC inhibition of stem elongation than that of flower formation. When applied under short-day conditions, AMO had no effect on the level of applied GA required for flower induction. When applied following long-day treatment the retardant caused some reduction of flower formation after marginal numbers of long days, but had no effect when enough long days to cause 100% flower formation were given. Other evidence indicates that the growth retardants act by inhibiting the synthesis of endogenous gibberellin. In LD plants, at least part of the action of inductive environmental conditions consists in causing an increase of gibberellin synthesis, supporting the hypothesis that relatively high GA levels are necessary for the production of the floral stimulus in this group of plants, as in long-short-day plants. The experiments with CCC indicate that stem elongation and flower formation in Samolus can be separated, and that the effect of GA on flower formation is not necessarily dependent on its effect on stem elongation.     

The leaf as the site of gibberellin action in flower formation in Bryophyllum daigremontianum

Summary The long-short-day plant Bryophyllum daigremontianum can be induced to flower by transfer from long to short days (LDSD), or by gibberellin (GA) application under SD. Application of GA to mature leaves of intact or partially defoliated plants induces flowering more effectively than when applications are made to the youngest leaf pair and the shoot tip.Mature leaves on de-budded plants in SD are induced to produce floral stimulus by GA application, as demonstrated by grafting LD receptor scions onto the debudded plants, or by grafting SD leaves treated with GA onto receptor stocks in LD. This shows that GA applied to Bryophyllum in SD exerts its flower-promoting effect in the leaves.The minimal number of SD necessary for flower formation in Bryophyllum is approximately 15, both in case of photoinduction by the shift LDSD, and after GA treatment in SD. It is concluded that the LD part of photinduction establishes a high level of endogenous GAs in the leaves which is a prerequisite for production of floral stimulus under subsequent SD.Work supported by the United States Atomic Energy Commission, Contract No. AT(11-1) 1338.     

Auslösung der Blütenbildung durch Cycloheximid im Kurztag bei der Langtagpflanze Hyoscyamus niger

Summary Cycloheximide (CH) was applied selectively either to the shoot apex or by infiltration to the leaves of the long-day plant Hyoscyamus niger in order to investigate whether this inhibitor has an effect on the synthesis of a floral stimulus in the leaves. Treatment of the shoot apex with CH caused inhibition of the photoperiodic induction. In contrast, when CH was applied to leaves, initiation of flowering was observed under short-day conditions. The drug yielded optimum initiating effects at concentrations of 10^-5-3·10^-5 M, inducing flowering of almost 60% of the plants. Daily infiltration over a period of up to 4 days decreased the rate of flower initiation. The effect of CH was shown to be additive to a photoperiodic induction, even to a sub-threshold induction, but not to 2-thiouracil mediated induction. In no case did the presence of additional untreated leaves on the plants suppress CH-mediated flower induction. Treatment of the leaves with chloramphenicol (10^-6-2^-10^-4 M) or puromycin (5·10^-6-2·10^-4 M) caused no initiating response. The results are interpreted to mean that the presence of CH in the leaves may lead to the synthesis of a floral stimulus also under short-day conditions. This finding is similar to that reported previously in the case of the inductive effect of 2-thiouracil.

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Folgende Abkürzungen wurden verwendet 2-TU 2-Thiouracil - CH Cycloheximid - LT Langtag - DL Dauerlicht Herrn Prof. Dr. L. Brauner in Verehrung und Dankbarkeit zum 75. Geburtstag gewidmet.     

Suppression of floral induction inBryophyllum daigremontianum by a growth retardant

Summary Flower formation in the long-short-day plantBryophyllum daigremontianum induced by the shift from long to short day is fully suppressed by applying the growth retardant CCC [(2-chloroethyl)-trimethylammonium chloride]via the roots during short day treatment at a level of at least 1 g per plant. At the same time CCC applications strongly reduce the internode length, but the rate of leaf formation does not seem to be affected. CCC also causes the production of more anthocyanin in the leaves.Gibberellin A₃ appliedvia the apices and youngest leaves at a dose of 1.5 g per plant, completely overcomes the inhibition of flower formation caused by CCC. Ten times higher quantities are needed for a complete reversal of the reduction in stem elongation.The growth retardant CCC seems to keep the level of physiologically active GA below that which is normally required for floral initiation and stem elongation. Thus, the results are in agreement with the hypothesis that a high GA level is necessary for the production of floral stimulus inBryophyllum daigremontianum.With 2 Figures in the TextThis work was supported by the National Science Foundation, grants G-16408 and G-17483.     

Photosynthesis as a function of short day induction and gibberellic Acid treatment in bougainvillea "san diego red"

Short day induction in Bougainvillea “San Diego Red” increases photosynthetic rates in mature leaves; gibberellic acid treatments, which inhibit flowering, cancel the short day effect. These results lend support of a nutritional hypothesis that suggests that in Bougainvillea assimilate supply to the reproductive axis increases before floral initiation and during flower development.     

Auslösung der Blütenbildung bei der Langtagpflanze Hyoscyamus niger im Kurztag durch 2-Thiouracil

Summary Aqueous solutions of 2-thiouracil (TU) were applied selectively either to the growing point or to the leaves of the long-day plant Hyoscyamus niger in order to determine whether this antimetabolite has an effect on the synthesis of the floral stimulus in the leaves. Applications to the growing point were made by means of a small glass tube covering the shoot apex; application to the leaves was performed by vacuum infiltration. In all experiments all leaves except the three youngest fully expanded leaves and the 8–10 youngest primordia were removed before application. Plants were recorded as having initiated flowers when flower primordia were visible under a dissection microscope 5 weeks after the experiment.TU was inhibitory to photoperiodic induction by long-days of 16 hours when applied to the growing point during the second 8 hours of the daily photoperiod. A concentration of 5·10^-3 M of TU fully suppressed flowering without significant inhibition of leaf primordia increment; however, leaves developing from treated primordia had reduced leaf blades. These results are in agreement with findings already published by other investigators.However, when the leaves were infiltrated by TU, the antimetabolite did not inhibit photoperiodic induction but on the contrary initiated flowering even under short-day conditions. This effect was investigated in more detail by repeated daily infiltrations of TU-solutions in concentrations of 10^-5–10^-2 M during the second part of an 8 hour photoperiod up to 5 following days. Even after one single infiltration of a 10^-4 M solution 18% of the treated plants were flowering; the percentage of flowering plants increased with increasing concentrations of TU and number of days of application up to approximately 80%. In no case was a flower initiation of 100% obtained. Leaves developing from primordia after infiltration of the leaves with TU have reduced and deformed leaf blades, indicating that TU is transported to the shoot apex to some extent.Some possible explanations of this inductive effect of TU were tested experimentally. Oxygen uptake of the leaves was not decreased and the respiratory quotient was not affected by TU. Photoperiodic induction is not stimulated by low concentrations of TU when applied to the growing point. Infiltration of the leaves by solutions of 2,4-dinitrophenol (10^-4 M) and sodium azide (10^-3 M) had no inductive effect under short-day conditions; a single complete defoliation (except for the 8–10 youngest primordia) is also not inductive. Under short-day conditions additional leaves remaining on the plant that were not infiltrated by TU decreased the percentage of flowering plants but did not fully suppress flower initiation.From these results it is concluded that TU does not act by inhibition of particular metabolic processes concerned in flower initiation or by inhibition of the synthesis of an inhibitor. We suggest that application of TU may lead to synthesis of a floral stimulus in the leaves under short-day conditions also.     

Changes in diffusible indole-3-acetic acid from various parts of tulip plant during rapid elongation of the flower stalk

In order to chemically identify the putative indole-3-acetic acid (IAA) and to confirm the native source of auxins account for rapid elongation of the floral stalk of tulip, we examined diffusible IAA from various parts of tulip plant during rapid elongation of the flower stalk. IAA was identified in the diffusates collected from the leaves, internodes, and floral organs with gas chromatography (GC)–mass spectrometry. The amount of diffusible IAA from different plant organs followed the order of that the internodes > flower organs > leaves during the period of rapid elongation of the floral stalk. The diffusible IAA from internodes reached its peak amount at different time than did diffusible IAA from the flower. The results obtained indicated that the top internode is probably the major source of auxins account for rapid elongation of the flower stalk.     

Effects of Ring D-Modified Gibberellins on Gibberellin Levels and Development in Selected Sorghum bicolor Maturity Genotypes

Plants of early flowering mutant and wild type genotypes of Sorghum bicolor were treated with ring D-modified gibberellins (GAs), and the effects on endogenous GA levels were determined. The growth and timing of floral initiation in 58M plants grown under 18-h days (which significantly delays floral initiation in this short day plant) following treatment with these compounds, relative to GA₃ and GA₅ treatments, were also investigated. Application of the endo-isomer of C16,17-dihydro-GA₅ (endo-DiHGA₅), the exo-isomer of C16,17-dihydro-GA₅ (exo-DiHGA₅), and C16α,17-dichloromethanodihydro-GA₅ (DMDGA₅) altered GA levels in both genotypes. Each ring D-modified GA significantly inhibited shoot growth while significantly decreasing levels of GA₁ and increasing levels of its immediate precursor, GA₂₀. Gibberellin A₈ levels also decreased. Tillering was not affected by any treatment. For the early flowering genotype 58M, grown under noninductive long days, both dihydro-GA₅ isomers promoted floral initiation while shoot growth was strongly inhibited, and floral development was strongly advanced beyond floral stage 4. Gibberellin A₃ and GA₅, applied under the same conditions, promoted shoot growth slightly and gave ``floral-like' apical meristems that did not develop past floral stage 1. These results suggest that the reduced shoot growth of sorghum, which follows application of those ring D-modified GAs, is due to their inhibiting the 3β hydroxylation of GA₂₀ to GA₁, thereby reducing the GA₁ content. That floral initiation was hastened and floral development promoted in genotype 58M by application of both isomers of DiHGA₅ are in contrast to the effects of other GA biosynthesis inhibitors, which act earlier in the GA biosynthesis pathway, but are consistent with results seen for long day grasses. This suggests that endo-DiHGA₅ and exo-DiHGA₅ may be acting directly in promoting floral initiation and subsequent floral apex development of this short day plant under long day conditions. Received October 3, 1996; accepted January 22, 1997     

Influence of leaves and roots on meristem development inNicotiana tabacum L. cv. Wisconsin 38

The terminal, apical shoot meristem ofN. tabacum cv. Wisconsin 38 normally differentiates into a flower after producing 30 to 40 nodes. The influence of leaves and roots on the regulation of flowering was evaluated by counting the number of nodes produced after removal of leaves or the induction of adventitious roots. Leaf removal has no effect on the number of nodes produced before flower formation. Root induction significantly increases the number of nodes produced before flower formation. The plant behaves as if it were measuring the number of nodes between the meristem and the roots as a means of regulating meristem conversion from vegetative to floral differentiation.     

Requirements for Floral Induction in Contrasting White Clover (Trifolium repens) Populations

Norm, I. B. 1987. Requirements for floral induction in contrastingwhite clover (Trifolium repens) populations.—J. exp. Bot.38: 900–907. Floral initiation and development of four contrasting whiteclover (Trifolium repens) populations was examined after differentinduction treatments (16 h, 5 ?C and 8 h, 5 ?C. The number of reproductive stolons and of reproductive budsper stolon was increased after cold induction. Varietal differencesin response to daylength were large; some varieties respondingbetter to a long day cold period, others to a short day coldperiod while one variety required no induction at all. Whetherthe daylength effect was due to photoperiod, irradiance or totheir interaction was not known. The induction periods had a subsequent effect upon pedunclelength, floret and ovule number. Short days and chilling reducedpeduncle length but increased ovule number, whereas long daysand chilling tended to increase floret number. Nectar concentrationwas highest after short day induction. Key words: White clover, floral initiation, floral induction     

Photoperiodic Responses of Brassica campestris cv. Ceres

The photoperiodic responses of Brassica campestris L. cv. Ceres were investigated to determine the suitability of this plant for further studies on the spectral require ments for floral initiation. This is a long-day plant, sensitive to one inductive photocycle on the fourth day from germination. The flowering response increased with the length and intensity of a single period of supplementary light used to extend an 8-hour daylength and was greatest at 25°C. Application of nitrates retarded floral initiation by about two days under short day conditions, but did not affect the re sponse to one long day. Gibberellic acid induced earlier floral initiation under short day conditions. The photoperiodic response was little affected by omitting the main light period immediately before or after the supplementary light, as long as the intensity of supplementary light was greater than 5000 lux. Short interruptions (5–10 minutes) of a single 16-hour dark period with high energy red or far-red radiation did not promote flowering. When given continuously during a single 16-hour dark period, far-red radiation was more effective in flower promotion than an equal energy of red.     

INFLORESCENCE AND FLOWER DEVELOPMENT IN THE PIPERACEAE. I. PEPEROMIA

Flowers of Peperomia species are the simplest structurally of any of the members of the Piperaceae. The spicate inflorescences form terminally and in axillary position; in each, the apex first is zonate in configuration with a two-layered tunica while 3-4 leaves are initiated. Later, when the inflorescence apical meristem begins bract initiation, the biseriate tunica persists, but zonal distinctions diminish and the apex can be described in terms of a simple tunicacorpus configuration. The inflorescence apex aborts after producing 30-40 bracts in acropetal succession an abscission layer forms across the base of the apex, and the meristem dries and drops off. Bracts are produced by periclinal divisions in T₂ (and occasionally also in the third layer as well); the later-formed floral apices arise by periclinal divisions in T₂ and the third layer. Each floral apex is at first a long transverse ridge in the axil, perpendicular to the long axis of the inflorescence. This establishes bilateral symmetry in the flower, which persists throughout subsequent growth. The floral meristem becomes saddle-shaped, and two stamen primordia are delimited, one at either end and lower than the central floral apex. A solitary carpel is initiated abaxially, and soon forms a circular rim which heightens as a tube with an apical pore. Within the open carpel, a solitary ovule is initiated from the entire remains of the floral apical meristem; it, hence, is terminal in the flower, and its placentation is basal. Carpellary closure in P. metallica results from accelerated growth of the abaxial lip, and the two margins become appressed. Species differ greatly as to whether the abaxial or the adaxial lobe predominates in late stages of carpel development. In P. metallica, the receptive portion of the stigma forms from the shorter lobe which is overtopped. Stigmatoid tissue forms internal to the receptive stigma. The prevailing bilateral floral symmetry, absence of a perianth, and the spicate inflorescence are features which distinguish Peperomia (and Piperaceae) from the magnolialian line of angiosperms.     

The relationship between gibberellin and floral stimulus inBryophyllum daigremontianum

Summary The long-short-day plantBryophyllum daigremontianum initiates flower buds both upon change from long to short day and after gibberellin application in short day only at night temperatures of 11° and 15°C, but not at 19°C.Flowering of receptor scions in long day or short day takes place just as easily when the donor stocks have been induced by the shift from long day to short day or by gibberellin treatment in short day. Leaves taken from gibberellin-induced plants can also function as donors, even better so than photoperiodically induced leaves. Receptor scions induced by gibberellin-treated donors can in turn induce other vegetative scions (indirect induction).Flower formation induced by the change from long day to short day as well as by gibberellin treatment in short day is always associated with an increased length of newly formed internodes.It is concluded that gibberellin and the floral stimulus are not identical, but that gibberellin is a factor which normally limits production of the floral stimulus inBryophyllum under short days, and that the shift from long day to short results in an increase of the gibberellin level in the plant.With 5 Figures in the TextThis work was in part supported by the National Science Foundation, grants G-16408 and G-17483.     

Changes in polyamine pattern are involved in floral initiation and development in Polianthes tuberosa

In the day-neutral plant Polianthes tuberosa (cv. Double) putrescine and spermine in corms at the early floral initiation stage decreased by 26 and 36%, respectively, compared with that in the vegetative stage. In contrast, a sharp increase in spermidine and cadaverine titers in corms was recorded at the early floral initiation stage. However, cadaverine in corms disappeared at the flower development stage. Polyamines in the roots were generally lower than those in the leaves and corms. In no case was the change in endogenous polyamine titers in the roots and leaves associated with floral initiation and flower development in P. tuberosa. Exogenous application of spermidine at 5, 25 or 150 microg per plant at the vegetative stage did not affect flower primordium counts. However, addition of a spermidine synthase inhibitor, cyclohexylamine, at 150 or 250 microg per plant (each dose was applied two times in total at an interval of 4 days) significantly reduced flower primordium counts, indicating that spermidine is involved in floral initiation and floral development in P. tuberosa. In P. tuberosa corms at the vegetative stage arginine decarboxylase activity rises and decreases at the early floral initiation stage. In contrast, ornithine decarboxylase activity reaches the highest level at the early floral initiation stage and declines significantly at the vegetative stage. Results indicate that an increase in spermidine and a transient increase in cadaverine titers in the corms seem characteristic of early floral initiation in P. tuberosa. It is also suggested that a significant reduction in putrescine and spermine in the corms is involved in the early floral initiation in P. tuberosa.     

Gibberellins and the floral transition in Sinapis alba

The putative role of gibberellins in the transition to flowering was investigated in Sinapis alba , a caulescent long-day (LD) plant. It was observed that: (1) physiological doses of exogenous gibberellins (GA₁, GA₃, GA₉) do not cause the floral shift of the meristem when applied to plants grown in short days but have some positive effect on the flowering response to a suboptimal LD; no inhibition was observed in any case; (2) GA-biosynthesis inhibitors (prohexadione-Ca and paclobutrazol) considerably inhibit stem growth but have some negative effect on flowering only when a suboptimal LD is given; and (3) the floral transition induced by one 22-h LD does not correlate with any detectable change in GA content of the apical bud, of the leaves, and of the phloem exudate reaching the apex. Taken together, these results suggest that GAs do not act as a major signal for photoperiodic flower induction in Sinapis .     

High temperature arrest of inflorescence development in broccoli (Brassica oleracea var. italica L.)

High temperature causes unevenly-sized flower buds on broccoli inflorescences. This deformity limits production of broccoli to areas where summer temperatures rarely exceed 30 C. The stage of development sensitive to heat was determined by exposing plants of 'Galaxy' broccoli at varying developmental states to 35 C day temperature for 1 week, and subsequently analysing the head structure. During the high temperature exposure, the development of certain flower buds was arrested. There was no corresponding cessation of bud initiation at the apex. No injury resulted if heat was applied before the reproductive induction, or was their injury to differentiated flower buds. Meristems were affected only if heat was applied during inflorescence production or the floral initiation process. Shorter heat exposures produced little injury, and longer exposures were lethal. The plant's development at this sensitive period still appeared vegetative externally, but the youngest leaves had just begun to reorientate as a consequence of the reduced stem elongation rate. The meristem was less than 1 mm wide, and floral primordia were just forming, still subtended by leaf primordia. The injury was fully expressed by the time the head was first exposed (approximately 5-10 mm wide), though it became more apparent as the head matured. The buds that were delayed in development by the high temperature developed into normal flowers.Key words: Brassica oleracea, broccoli, flowering, heat injury, developmental arrest      

Development of Meristems of Weigela florida Variety 'Bristol Ruby' Following Reproductive Induction in Long Days

Weigela florida variety ‘Bristol Ruby’ has longday requirements for its growth and, in general, for its flowering.Vegetative development, floral initiation and floral organogenesisare described using scanning electron microscopy during photoperiodictreatment in long days, under controlled conditions. Flowering of axillary buds of cuttings has been studied. Theapex of Weigela at the vegetative phase is characterized bya very small hollow meristem. After 9 long days, the meristemenlarges and, after 12 long days, early axillary buds are initiatedin the axils of the leaves, which become bracts. When the numberof long days was increased, flowers were initiated in the budson the induced branches; first at the proximal part of the branchwhere development afterwards slowed down, then on the medianparts of the branch where development was accelerated. Two bracteoles are differentiated soon after floral initiation;first initiation of the calyx required 18 long days. Petals,stamens and ovary were rapidly initiated after that. Weigelaflowers are clustered; the inflorescence ceased growth by abortionof the terminal meristem or by formation of a terminal flower.In axillary buds of the fifth node the formation of the clusterwas completed about 20 days after the beginning of floral induction. Weigela florida ‘Bristol Ruby’, scanning electron microscopic analysis, vegetative meristem, floral development stages, long days induction     

The Exogenous Hormornal Control of the Development of Regenerated Flower Buds in Hyacinthus orientalis

The critical role of exogenous hormone on inducing the initiation of different floral organs in the regenerated flower bud and controlling their numbers was further evidenced. The initiation of the flower buds was first induced from the perianth explants of Hyacinthus orientalis L. cv. White pearl by a combination of 2 mg/L 6-BA and 0.1 mg/L 2,4-D, and then a continuous initiation of over 100 tepals (a flower bud of H. orientalis in situ has only 6 tepals) was successfully controlled by maintenance of such a hormone concentration. However, a change of hormonal concentration (2 mg/L 6-BA and 0-0.000 1 mg/L 2,4-D) caused cessation of continuous initiation of the tepals but gave rise to induction of stamen initiation. Keeping the changed hormone concentrations could successfully control the continuous initiation of over 20 stamens (a flower bud of H. orientalis in situ has only 6 stamens). The experiment showed that the number of identical floral organs in the regenerated flower buds can be controlled by certain defined concentrations of the exogenous hormones, and the amount of the induced identical floral organs has no effect on the differentiation sequence of the different floral organs in the regenerated flower bud. Based on a systematic research on controlling the differentiation of the floral organs from both the perianth explants and the regenerated flower buds by the exogenous hormones in H. orientalis over the past decade, the authors put forward here a new idea on the role of phytohormone in controlling the automatic and sequential differentiation of the different floral organs in flower development. The main points are as follows: 1. the development of flower bud in plant is a process in which all of the floral organs are automatically and sequentially differentiated from the flower meristem. 2. Experiments in vitro showed that the effect of exogenous hormones in controlling the initiation of different floral organs is strictly concentration dependent, i.e., one kind of the floral organ can continuously and repeatedly initiate from the flower meristem as long as it is maintained in that specific concentration of the exogenous hormone which is suitable for the initiation of that particular kind of floral organ. 3. It shows that the flower buds in situ must be automatically able to adjust the endogenous hormonal concentrations just after the completion of the differentiation of one whorl of floral organ to suit the differentiation of the next whorl. Thus, the phytohormone in different concentrations takes after many change-over switches of the organ differentiation and plays a connective and regulatory role between the differentiation of every two whorls of the floral organ. In other words, these change-over switches play the roles of inhibiting the expression of the genes which control the initiation of the floral organs in the first whorl, meanwhile, activating the expression of the genes which control the initiation of the floral organs in the second whorl during the successive initiation of the different floral organs from the flower bud. It results in the automatic and sequential initiation of the various floral organs from the floral meristem.      

Somatic embryogenesis from immature peach palm inflorescence explants: towards development of an efficient protocol

Various factors affect the induction of somatic embryogenesis in peach palm (Bactris gasipaes Kunth). Among these, both the type and level of auxins had the greatest influence on in vitro responses, although the genotype and the developmental stage of the explants also influenced results. Younger inflorescences were more competent to respond to SE induction than more mature inflorescences and the use of a pre-treatment with 2,4-D (200 μM) in liquid MS culture medium also increased the embryogenic capacity, and diminished the development of flower buds. Higher oxidation rates were observed in explants maintained on 2,4-D-supplemented culture medium, while on 300 μM or 600 μM Picloram and Dicamba lower oxidation rates were observed. The progression from floral meristem to flower bud occurred at high frequency when low concentrations of auxins were used, independent of the type. Higher concentrations of Picloram or Dicamba reduced or even inhibited flower bud development. Picloram also enhanced the embryogenic induction rate more than 2,4-D and Dicamba, and among the concentrations evaluated 300 μM Picloram enhanced induction for both genotypes, with significant differences between genotypes. The best combination of variables used the least mature inflorescence (Infl1) from genotype I with the 2,4-D pre-treatment and 300 μM Picloram to generate 5 embryogenic calli from 18 explants; 26 embryos were obtained on average from each embryogenic callus. From these, eighteen embryos converted to plantlets and six of these survived transfer to the greenhouse.