Changes in RNA levels in the shoot apex of Silene during the transition to flowering

Changes in RNA concentration in the shoot apical meristem during induction and the transition to flowering were measured histochemically in Silene coeli-rosa (L.) Godron, a long-day plant. In the apices of plants induced by 7 long days the RNA concentration increased to about 25 per cent higher than in non-induced plants. Three long days did not induce flowering but resulted in a transient rise in RNA concentration. When plants were given long days interrupted by varying numbers of short days successful induction was accompanied by a sustained increase in RNA concentration but those treatments which were not inductive gave only transient increases in RNA. Gibberellic acid had no effect on induction or apical growth rates but increased the RNA concentration by 50 per cent or more in both induced and non-induced plants. Plants induced to flower at 13° C had the same RNA concentration and growth rate at the apex as in non-induced plants at 20° C. Since changes in RNA concentration in the apex could occur without changes in growth rate and without flowering, and induction could occur without a change in RNA concentration or growth rate, it is suggested that the increase in RNA and growth rate which normally occur at the transition to flowering might not be essential for the formation of a flower but may be more closely related to the rapid growth associated with the formation of the inflorescence.Abbreviations LD long day - SD short-day     

Inhibition imposed by developing flowers on further flower-bud initiation in Chamelaucium uncinatum Schau

In Chamelaucium uncinatum, an Australian woody perennial, flower initiation ceases under continuous inductive short-day (SD) conditions after the first flowering flush. The developing flowers were found to be the prime cause of the cessation in flower initiation. Removal of flowering shoots or lowers as soon as the buds appeared resulted in continuous flower formation. Pruning the plants below the young flower buds at the same stage also caused increased flower formation at the tips of the new growth. If pruning was delayed until flower buds were approx. 3 mm in diameter, however, nor further flower initiation took place and the plants, although still under inductive conditions, shifted to vegetative growth. The inhibiting factor is translocated from one branch to another. At least a six-week rest period (a vegetative growth period under long-day conditions) is needed before the plants are able to respond to further SD stimuli.Abbreviations LD long day - SD short day - SE standard error     

Appearance and disappearance of proteins in the shoot apical meristem of Sinapis alba in transition to flowering

Vegetative plants of Sinapis alba L. grown under short days were induced to flower by exposure to one long day or continuous long days. Irrespective of the number of long days, the first flower primordia were initiated by the shoot apical meristem 60 h after the start of the inductive treatment. An indirect histoimmunofluorescence technique was used to search in the apical meristem for three antigenic proteins which had been previously detected by immunodiffusion tests in the whole apical bud (Pierard et al. (1977) Physiol. Plant. 41, 254–258). One protein called protein A, present in the vegetative meristem, increased in concentration during the first 48 h following the start of the inductive treatment. It stayed constant up to 96 h and disappeared completely at a later time. Two other proteins called B and C, absent in the vegetative meristem, appeared in the meristem of induced plants between 30 and 36 h after the start of the inductive treatment and progressively accumulated at later times up to 240 h. These proteins appeared 8 h before the irreversible commitment of the meristem to produce flower primordia (point of no return) was reached and 24 h before start of flower production. These observations support an interpretation of floral evocation as consisting, at least partially, of an early and qualitative change in gene expression.Abbreviations AVB anti-vegetative-bud antiserum - ARB antireproductive-bud antiserum - IgG immunoglobulins G - TRITC tetramethylrhodamine isothiocyanate - GAR IgG goat antirabbit IgG - S₀ IgG non-immune rabbit IgG     

Synchronisation of cell division in the shoot apex of Silene in relation to flower initiation

In plants of Silene coeli-rosa, induced to flower by 7 LD, synchronisation of cell division in 20 per cent or more of the cells in the shoot apical dome was found on the 8th and 9th days after the beginning of induction, during the plastochron before sepal initiation. Synchronisation was inferred from the changes in the proportions of cells with the 2C and 4C amounts of DNA, and changes in mitotic index and labelling index. From the peaks of mitotic index a cell cycle of 10 h was measured for the synchronised cells, half that of cells in the apices of uninduced plants in short days. The faster cell cycle and synchronisation in the induced plants was associated with a shortening, of both G1 and G2, suggesting two control points, while S and M remained unchanged. These results are compared with those from other plants in which synchronisation occurs at the beginning rather than the end of evocation.Abbreviations LD long day(s) - SD short day(s) - S DNA synthesis phase of cell cycle - G1 pre-S interphase - G2 post-S interphase - M mitosis     

Apical Growth and Modification of the Development of Primordia During Re-flowering of Reverted Plants of Impatiens balsamina L

Impatiens balsamina L. was induced to flower by exposure to5 short days and then made to revert to vegetative growth byreturn to long days. After 9 long days reverted plants wereinduced to re-flower by returning them to short days. Petalinitiation began immediately and seven primordia already presentdeveloped into petals instead of into predominantly leaf-likeorgans. However, the arrangement of primordia at the shoot apex,their rate of initiation and size at initiation remained unchangedfrom the reverted apex, as did apical growth rate and the lengthof stem frusta at initiation. The more rapid flowering of thereverted plants than of plants when first induced, and the lackof change in apical growth pattern, imply that the revertedapices remain partially evoked, and that the apical growth patternand phyllotaxis typical of the flower, and already present inthe reverted plants, facilitate the transition to flower formation. Impatiens balsamina, flower reversion, partial evocation, shoot meristem, determination, leaf development     

Flower bud differentiation in Salix pentandra as affected by photoperiod, temperature and growth regulators

Flower bud initiation in seedlings and vegetatively propagated plants of Salix pentandra from different locations has been studied under controlled conditions. In mature plants flower bud formation was induced by 2-chloroethyltrimethylammoniumchloride (CCC) and by short day treatment. The effect of CCC was antagonized by GA₃. The critical photoperiod for flower bud formation was about 18 h for a southern clone (from 49°48'N), but cuttings of a northern ecotype (from 69°39'N) formed flower buds even at 24 h photoperiod. Generally, flower bud formation occurred simultaneously with apical growth cessation. However, apical growth cessation was not a prerequisite for floral initiation and flower buds were also found in elongating plants. Seedlings up to 60 days old did not form flower buds in growth chamber studies. The length of the juvenile phase has not been studied in detail, but cuttings taken from seedlings approximately 20 cm high and 60 days old were able to develop flower buds when treated with CCC. A gradual transition from the juvenile to the mature phase was obtained by repeated pruning of seedlings grown at 18°C and 24 h photoperiod.     

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.     

Changes in adenine-nucleotide content in the apical bud of Sinapis alba L. during floral transition

The total adenylate pool of the apical buds of vegetative plants of Sinapis alba L. continuously grown in short days fluctuates over a 24-h cycle with the minimum occurring at the end of the dark period. In the buds of plants induced to flower by a single long-day treatment, total adenylate pool increases above the control level 16 h after the start of the long day, resulting mainly from a rise in ATP and ADP contents. This occurs 6 h after the increase in the soluble carbohydrate content previously shown to occur in the apical buds of plants induced to flower (Bodson 1977, Planta 135, 19–23). A transient rise of the energy charge occurs 22 h after the start of the inductive long day.Abbreviations LD long day - SD short day     

Photoperiodic control of apical senescence in a genetic line of peas

An early flowering genetic line of peas (Pisum sativum L.), designated G2, has dominant genes at two different loci, both of which function in short days to greatly extend the reproductive phase and thus to delay apical senescence. Long days (18 hours) promote senescence in this line, but the effect is reversible by reinstatement of short days (9 hours) until 3 to 4 days before the apex senesces. The response to photoperiod was quantitative. Increasing the photoperiod from 14 to 18 hours led to a progressive decrease in the number of nodes formed prior to death of the apex. Induction of senescence was determined by the total number of hours of light and darkness rather than by the length of the dark period. Senescence required flower and fruit development as well as long days.     

Stem growth,flower formation,and endogenous gibberellins in a normal and a dwarf strain of Silene armeria

The physiological basis of dwarfism in a single-gene, recessive mutant of Silene armeria L. was investigated through comparison with a normal strain. Exposure of the normal strain to long days led to stem growth and flower formation while similar exposure of the dwarf strain led only to flowering, with very little stem growth. Application of gibberellin A₃ or A₄₊₇ in short days promoted stem elongation in the normal strain, but had a much lesser effect in the dwarf strain. Upon extraction and chromatographic fractionation of the endogenous gibberellins (GAs) in the normal strain of S. armeria, three zones of GA activity were found. An increase in one zone of activity was found in both strains after 1 long day. Neither the quality nor the quantity of the extractable GAs differed greatly between the dwarf and the normal strain. Vegetative dwarf scions, grafted onto fully induced, normal stocks formed flowers, but their growth habit was not changed. Thus, the lack of stem growth in response to long days in the dwarf strain appears to result from a lack of GA sensitivity in the stem tissue of these plants. However, during flower formation dwarf plants did exhibit elongation of the peduncles. This response was suppressed by the growth retardant 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride (AMO-1618), and applied GA₃ could partially overcome this inhibition. Thus, peduncle elongation in the dwarf strain appears to be regulated by endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - LD long day(s) - SD short day(s)     

Factors Affecting the Flowering of Andropogon gayanus Kunth. Responses to Photoperiod, Temperature and Growth Regulators

Andropogon gayanus is a short-day plant with a critical daylengthfor flowering between 12 and 14 h. Flowering is more intenseas the daylength is shortened from 12 h to 8 h, initiation isalso accelerated by increasing durations of short-day treatment.Plants flower more readily with increasing age. The maximumflowering response can be induced by short-day exposure of onlyone expanding leaf. A fixed number of short days distributedamong different groups of leaves on the plant gave less floweringthan the same number given to only one group. Approximately25°C was optimal for flowering. Root removal treatmentsin short day reduced both growth and flowering responses. Application of the growth regulators indol 3yl-acetic acid,abscisic acid, gibberellic acid or dimethylaminosuccinamic acid(B9) was inhibitory to flowering in all cases but gibberellicacid and B9 applied simultaneously had no inhibitory effect.Growth hormone treatments failed to stimulate flower developmentin long day. These results are discussed in relation to the internal mechanismscontrolling growth and flowering.     

Polyamine metabolism,floral initiation and floral development in Chrysanthemum (Chrysanthemum morifolium Ramat.)

In the short-day plant Chrysanthemum (Chrysanthemum morifolium Ramat. variety Pavo) putrescine and spermidine conjugates appeared in the apical bud before the first observable transformation of the meristem into floral structures. These compounds accumulated on floral initiation and well before floral evocation. Spermidine conjugates were predominant during floral initiation whereas free amines did not accumulate to any significant extent. Different associations of amides were observed during floral initiation as compared with the reproductive phase. 3,4-Dimethoxyphenethylamine conjugates (water-insoluble compounds) were the predominant amine conjugates observed during flower development. These compounds decreased drastically after fertilization. In vegetative buds from plants grown in long days polyamine conjugates were very low and appeared as plants aged. We present evidence that ornithine decarboxylase (ODC) regulates putrescine biosynthesis during floral initiation and floral development. When ODC action was blocked by DFMO (-DL-difluoromethylornithine, a specific, irreversible inhibitor of ODC), flowering was inhibited, and free and conjugated polyamines were not detected. This treatment led to a slight enhancement of ADC activity. When putrescine was added, polyamine titers and flowering were restored. A similar treatment with DFMA (-DL difluoromethylarginine, a specific, irreversible inhibitor of ADC) did not affect flowering and the polyamine titers. The results suggest that ODC and polyamine conjugates are involved in regulating floral initiation in Chrysanthemum.Abbreviations ADC arginine decarboxylase - ODC ornithine decarboxylase - DFMA -DL-difluoromethylarginine - DFMO -DL-difluoromethylornithine     

The facultative photoperiodic response in the reproductive development of Amaranthus retroflexus L.: Changes in the dose response during ontogeny

The first inductive (short-day; SD) cycle advanced the initiation of reproductive development, while additional SD cycles progressively reduced the lag phase between the start of induction and initiation. The sensitivity to SD increased during ontogeny in long-days (LD) until even the requirement for the first SD cycle disappeared at the onset of autonomous flowering. In photo-induced plants, the postinitiation rate of elongation of the apex was accelerated as the SD dose was increased, but was progressively slower as the start of induction was delayed closer to autonomous flowering, approaching asymptotically the rate of non-induced controls. The inflorescences were branched in plants growing continuously in LD and unbranched in those growing continously in SD. The subsequent branching of the inflorescence could be repressed by SD at any time prior to autonomous flowering, and the degree of repression increased with the induction dose. After the initial SD cycle, 1–2 additional SD could induce the loss of apical dominance, causing excessive elongation and leaf production in the subjacent branches. Further increase in the SD dose inhibited this elongation by accelerating the transformation of the apices of these branches to the reproductive state.Abbreviations LD long day(s) - SD short day(s) - ContSD continuous short day(s) - RGR relative growth rate     

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.     

GIBBERELLIN-INDUCED INHIBITION OF FLORAL INITIATION IN FUCHSIA

The ‘Lord Byron’ cultivar of Fuchsia hybrida is a long day plant for which GA acts as an inhibitor of flower initiation. At the dosages required to inhibit initiation (0.025 μg per plant) GA also promotes increased stem elongation but causes no other departures from normal development. Similar tests with auxins, antiauxins, kinins, and other substances showed no effect on flower initiation at dosages equivalent to that for GA. At 10- to 100-fold greater dosages, auxins, kinins, and anti-auxins inhibit not only flower initiation but also vegetative development. Thus the effect of GA on flower initiation appears to be unique, although other hormonal substances, such as abscisin, have not been tested. GA-induced inhibition is directly proportional to the dosage applied and inversely to the strength of long day induction (as measured by the number of long days). GA is most effective when applied to the terminal bud rather than to the mature leaves, suggesting that it is active at the site of flower initiation rather than in the leaves. If it is applied after translocation of the floral stimuli from the leaves, GA does not prevent flower initiation. Regardless of the dose applied, GA is less effective if applied later rather than earlier during LD induction. The inhibitory effect persists for several days. For example, an 0.85 μg dosage causes an 8–10-day delay in initiation; lower dosages have reduced effects. GA inhibits flower initiation but has no effect upon flower development. The rate of bud development is the same in GA-treated and control plants. Apparently no more than one to two axillary buds immediately below the apical meristem are receptive to long day-induced floral stimuli from the leaves. Regardless of the daylength conditions axillary buds more basal do not initiate flowers but develop into branch axes. The effect of a long day treatment persists for a very short time, perhaps no longer than the inhibition caused by minimal GA dosage. Thus flower initiation continues for a very short time following the end of long day induction. The significance of these findings is discussed in relation to the many reports of GA-induced inhibition as well as promotion of flower initiation. In particular, the discussion concerns the nation that flower initiation in fuchsia may be controlled by a gibberellin-like transmissible inhibitor.     

Stem elongation and floral initiation on in vitro chicory root explants: influence of photoperiod

Chicory root explants (Cichorium intybus L.) were cultured in vitro under different photoperiods. In complete darkness, strong stem elongation, but no flowering induction was observed. We suggest that this stem elongation could be homologous to the pit growth in chicory heads in vivo. Under a photoperiod of 12 h (LI=±40 E m^–2 s^–1), only vegetative growth was observed. Photoperiods of 16 h or more light a day induced the in vitro explants to develop stems bearing flower buds. When the in vitro cultures were kept in the dark for different durations starting from the first day of culture and afterwards transferred to long-day conditions, 4 days dark were sufficient to cause a decrease in flowering induction. We suggest that during the dark culture, a flowering inhibitory process was started.     

Induction and floral determination in the terminal bud of Nicotiana tabacum L. cv. Maryland Mammoth,a short-day plant

Floral determination in the terminal bud of the short-day plant Nicotiana tabacum cv. Maryland Mammoth has been investigated. Plants grown continuously in short days flowered after producing 31.4±1.6 (SD) nodes while plants grown continuously in long days did not flower and produced 172.5±9.5 nodes after one year. At various ages, expressed as number of leaves that were at least 1.0 cm in length above the most basal 10-cm leaf, one of three treatments was performed on plants grown from seed in short days: 1) whole plants were shifted from short days to long days, 2) the terminal bud was removed and then rooted and grown in long days, and 3) the terminal bud was removed and then rooted and grown in short days. Whole plants flowered only when shifted from short days to long days at age 15 or later. Only rooted terminal buds from plants at age 15 or older produced plants that flowered when grown in long days. Only terminal buds from plants at age 15 or older that were rooted and grown in short days produced the same number of nodes as they would have produced in their original locations while buds from younger plants produced more nodes than they would have in their original locations. Thus, determination for floral development in the terminal bud, as assayed by rooting, is simultaneous with the commitment to flowering as assayed by shifting whole plants to non-inductive conditions.Abbreviations LD long day(s) - SD short day(s) - DN dayneutral     

FLOWER INITIATION IN TOTAL DARKNESS IN A QUANTITATIVE SHORT DAY PLANT, FAGOPYRUM ESCULENTUM MOENCH

The flowering behavior of two cultural varieties of Fagopyrumesculentum Moench aseptically cultured in total darkness wasstudied. The effect on the flower initiation of some chemicalsubstances added to sterilized dry seeds was also investigated.Low temperature was found to be more suitable for flower initiationin buckwheat plants. 2-Thiouracil promoted flower initiationat high temperature in total darkness and inhibited it at anytemperatures examined under light conditions. Sucrose promotedflower initiation at higher temperatures than 15. Lithium chlorideand peptone inhibited flower initiation only at high temperature.Indoleacetic acid, gibberellin and kinetin had no effect onflower initiation in total darkness. It is postulated that in the flowering response the primaryreaction may be connected with the metabolism of sucrose andribonucleic acid. (Received September 21, 1964; )     

Changes in the carbohydrate content of the leaf and the apical bud of Sinapis during transition to flowering

Vegetative plants of Sinapis alba L. were induced to flower by a single long day of 20 h or by a single short day of 8 h starting at an unusual time of the 24-h cycle (displaced short day). The soluble sugar and starch contents of the just-expanded leaf and the apical bud were measured at various times after the start of each of these two photoinductive treatments. Associated with the induction of flowering there were temporary increases in the soluble sugar and starch contents of the leaf and of the bud. These increases were apparent 14 h after the start of the long day and 12 h after the start of the displaced short day. The starch content of the bud increased later. These results indicate that an increase of the soluble sugar content of the bud is required for its transition from the vegetative to the reproductive condition.     

Restricted cell/cell communication in the shoot apex ofSilene coeli-rosa during the transition to flowering is associated with a high mitotic index rather than with evocation

Summary Plants ofSilene coeli-rosa given 5 or more long days (LDs) flowered, even when the LDs were followed by 48 hours of darkness before their return to short days (SDs). The mitotic indices of shoot apices from induced plants shortly after induction were significantly higher than the indices of shoot apices from vegetative plants. Two major mitotic peaks were observed in the shoot apices of plants given 7 long days (LDs) on day 8. One coincided with that reported byFrancis andLyndon (1979).Cell to cell movement was tested in the shoot apices of vegetative and LD treated plants using probes with a molecular size of 749 daltons (fluorescein-hexaglycine) and 847 daltons (fluorescein-leucyl diglutamyl leucine). These probes showed some movement in the shoot apices of both short day (SD) and LD treated plants, but fluorescein-leucyl diglutamyl leucine was immobile in the induced apices of 7 LD plants on day 8 at time intervals which coincided with major mitotic activity in the shoot apex. Symplasmic restriction in the shoot apex was also observed in plants given 8 LDs (i.e., plants not returned to SDs on day 7).In plants that were placed in 48 hours of darkness after the 7 LD treatment or in plants given 5 LDs, there was no strong peak in the mitotic index, even though all these LD treatments resulted in 100% flowering. In such plants no symplasmic restriction was found in the shoot. Thus the symplasmic restriction on day 8 of 7 LD plants is associated with the high mitotic index, but neither of these phenomena is an essential part of the evocation process.Abbreviations F(Glu)₂ L-glutamylglutamic acid conjugated to fluorescein isothiocyanate isomer I (F-) - F(Gly)₆ F-hexaglycine - FLGGL F-leucyl-diglutamyl-leucine - F(PPG)₅ F-the pentamer (propyl-propyl glycine) - LD long day - LDs long days - SD short day - SDs short days