The Influence of Ringing on Bud Development and Flowering in Satsuma Mandarin

Ringing of Satsuma mandarin (Citrus unshiu Marc.) trees showedincreased flowering in the following spring when performed duringSeptember and October, but not during November. Most of theeffect on flowering was due to an enhancement of both bud sproutingand the number of flowering shoots formed per node. In addition,a direct effect of ringing on flower initiation was demonstrated,since the number of vegetative shoots was reduced. The response of the buds to ringing was rapid as demonstratedby changes in bud weight, protein content, and electrophoreticpattern and behaviour when cultured in vitro. Buds from ringedtrees readily flowered in vitro when forced during the winterrest period and flower formation was enhanced by the additionof cytokinin. Buds from control trees formed a smaller numberof flowers in vitro, and flowering was much less enhanced bythe addition of cytokinin. It is concluded that ringing acceleratesflower initiation in the buds and this effect takes place beforethe winter rest period. Key words: Bud sprouting, Citrus unshiu Marc., flower initiation, flowering, in vitro flowering, Satsuma mandarin, ringing     

Flowering in Pisum: the Effect of Age on the Gene Sn and the Site of Action of Gene Hr

Late cultivars of peas behave as quantitative long day plants.The reason that they flower between nodes 20 and 35 under an8 h photoperiod is shown to be because the leaves and maturestem produce a more promotory ratio of the flowering hormonesas they age. Later formed leaves may also start with a slightlymore promotory ratio than the leaves produced at a lower node.The gene Sn controls the production of a flower inhibitor andit is suggested that the activity of this gene in a leaf isgradually reduced as the leaf ages. From grafting experiments,the site of action of the gene Hr is shown to be in the leavesor mature stem and not at the shoot apex. This supports a previoussuggestion that the gene Hr is a specific inhibitor of the ageingresponse of gene Sn. Gene Hr is shown to cause a substantial delay in the floweringnode of decotyledonized plants of genotype If e sn hr undershort day conditions, suggesting that Hr has little effect inthe cotyledons. It is argued that the gene sn is a leaky mutantand that gene Hr does not control a photoperiod response inits own right but has its effect through the Sn locus. From a comparison of intact plants and self-grafts of the lategenotype If e Sn hr it is shown that under the conditions usedphysiological age may be of more importance than chronologicalage in determining flowering in peas. Reasons for the smalleffect of defoliation treatments on flowering are discussedas well as possible reasons for the promotory effect of decotyledonizationon the flowering node of late lines. Pisum sativum L, flowering, ageing, genetic control     

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     

Flowering of Cultivated Green and SAN 9789-Treated Chenopodium rubrum Plants Exposed to White,Blue, and Red Light

Green plants and plants devoid of photosynthetic pigments were compared with regard to their ability to flower under various growth conditions. Green plants of Chenopodium rubrum L. and plants treated with norflurazon SANDOZ-9789 (SAN) were grown on sucrose-containing media with or without hormones (GA₃, BA, IAA, ABA) under short-day photoperiodic or continuous illumination with white, blue, or red light. Green and SAN-treated albino plants produced flowers only under short-day conditions. The flowering of green plants was independent of the presence of sucrose and hormones in the medium as well as of the light quality. The albino plants produced flowers under white and blue light but did not flower in red light. The addition of GA₃ or BA to the medium induced flowering of albino plants exposed to red light. The functional interaction of photoreceptors in the flowering control is discussed.     

Changes in cytokinin activities before,during and after floral initiation in Polianthes tuberosa

The contents of endogenous cytokinin in tuberose corms (Polianthes tuberosa) at vegetative, early floral initiation, and flower development stages were investigated. We also determined the influence of exogenous cytokinin treatment on the corm apex at three different growth stages in relation to floral initiation and development in tuberose. The exogenous cytokinin effectively induced floral initiation and development, especially at the early floral initiation and flower development stages. Endogenous cytokinins were higher in early floral initiation and development stages in comparison to the vegetative stage. During floral initiation stage, the zeatin and dihydrozeatin increased significantly, while the cytokinins, zeatin riboside, dihydrozeatin riboside, ⁶N-(δ²-isopentenyl) adenine, and ⁶N-(δ²-isopentenyl) adenine riboside at consistently low levels. The increase of cytokinin levels in tuberose corms during floral induction suggests a role for cytokinins in tuberose apex evocation. Moreover, these results indicate that cytokinins seem to promote the development of flower buds rather than inducing flowering in tuberose.     

Induction of early flowering in Cymbidium niveo-marginatum Mak in vitro

 Many orchids take several years to flower. We have been able to induce early flowering in the temperate orchid Cymbidium niveo-marginatum Mak in vitro. The combined treatment of cytokinin (6-benzylaminopurine), restricted nitrogen supply with phosphorus enrichment, and root excision (pruning) induced transition of the Cymbidium shoot from a vegetative to a reproductive stage. Nearly 100% of the plants flowered within 90 days only when the combined treatment was applied. When root excision and/or 6-benzylaminopurine were omitted from the combined treatments, flower induction was significantly reduced. The auxin transport inhibitor, 2,3,5-triiodobenzoic acid prevented flowering of Cymbidium in vitro, although auxin (α-naphthaleneacetic acid) itself did not induce flowering. Gibberellic acid markedly delayed flowering in C. niveo-marginatum even when the flower-promoting treatment was applied. Paclobutrazol, an anti-gibberellin agent, totally blocked the inductive effects of either cytokinin or pruning. These observations suggest that concerted actions of auxin, cytokinin, and gibberellin, as well as nutrient concentration and putative promoting/suppressing agents, determine the timing of Cymbidium orchid transition from the vegetative to reproductive stage. Received: 22 July 1998 / Revision revised: 23 November 1998 / Accepted: 2 December 1998     

The role of sucrose and different cytokinins in the in vitro floral morphogenesis of rose (hybrid tea) cv. “First Prize”

Shoots of rose (hybrid tea) cv. “First Prize” were induced to flower in vitro on Murashige and Skoog (MS) medium containing various sucrose concentrations (15, 30 or 45 g l⁻¹) and different phytohormone combinations of different cytokinins [N⁶-benzyladenine (BA); thidiazuron (TDZ) and zeatin] with α-naphthaleneacetic acid (NAA). Results indicate that sucrose is the key factor in floral morphogenesis while cytokinin increases the flowering percentage and helps the normal development of floral buds. From the three cytokinins that were used, BA and zeatin were considered to be more suitable as inductive flowering agents than TDZ. Reduced inorganic and organic salt concentration in MS media had a positive effect on in vitro flowering. The morphology of shoots bearing floral buds varied with different cytokinin treatments. The highest percentage (45%) of flowering was obtained on MS medium supplemented with 3.0 mg l⁻¹ BA, 0.1 mg l⁻¹ NAA and 30 g l⁻¹ sucrose.     

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; )     

The transition to reproductive phase inchenopodium murale L. ecotype 197 - Early flowering long-day plant

Five days of suitable continuous light induced flowering in the majority ofChenopodium murale L. ecotype 197 plants as early as at the phase of the first pair of leaves. At the time of initiation of the 2nd to 4th pairs of leaves the capacity of plants to flower was reduced, the number of flowering plants being significantly lower under the same inductive light treatment. The capacity to flower increased again at the phase of the 5th and the 6th pairs of leaves. Inductive light treatment brought about a marked growth activation of organs present before induction, shoot apex elongation, precocious formation of new leaves and activation of axillary meristems. The course of these changes in plants of different age is demonstrated. The terminal flower developed during 5 short days following inductive light treatment. The paper shows similarities and differences between long-daymutale L. ecotype 197 and short-day C.rubrum L. ecotype 374 grown under practically uniform conditions.     

Blue-light promotion of flowering is absent in hy4 mutants of Arabidopsis

Loss of a blue-light photoreceptor in the hy4 mutants of Arabidopsis thaliana (L.) Heynh substantially delayed flowering (>100 d to flower vs. 40–50 d), especially with blue light exposure from lamps lacking much red (R) and/or far-red (FR) light. Red night breaks were promotory but flowering was still later for the hy4-101 mutant. However, with exposure to light from FR-rich lamps, flowering of all mutants was early and no different from the wild type. Thus, flowering of Arabidopsis involves a blue-light photoreceptor and other, often more effective photoreceptors. The latter may involve phytochrome photoresponses to R and FR, but with little or no phytochrome response to blue wavelengths.Abbreviations HIR high irradiance response - FR far-red - R red - WT wild type     

A possible role for flowering locus T‐encoding genes in interpreting environmental and internal cues affecting olive (Olea europaea L.) flower induction

Olive (Olea europaea L.) inflorescences, formed in lateral buds, flower in spring. However, there is some debate regarding time of flower induction and inflorescence initiation. Olive juvenility and seasonality of flowering were altered by overexpressing genes encoding flowering locus T (FT). OeFT1 and OeFT2 caused early flowering under short days when expressed in Arabidopsis. Expression of OeFT1/2 in olive leaves and OeFT2 in buds increased in winter, while initiation of inflorescences occurred i n late winter. Trees exposed to an artificial warm winter expressed low levels of OeFT1/2 in leaves and did not flower. Olive flower induction thus seems to be mediated by an increase in FT levels in response to cold winters. Olive flowering is dependent on additional internal factors. It was severely reduced in trees that carried a heavy fruit load the previous season (harvested in November) and in trees without fruit to which cold temperatures were artificially applied in summer. Expression analysis suggested that these internal factors work either by reducing the increase in OeFT1/2 expression or through putative flowering repressors such as TFL1. With expected warmer winters, future consumption of olive oil, as part of a healthy Mediterranean diet, should benefit from better understanding these factors.     

A genetic and physiological analysis of late flowering mutants in Arabidopsis thaliana

Summary Monogenic mutants of the early ecotype Landsberg erecta were selected on the basis of late flowering under long day (LD) conditions after treatment with ethyl methanesulphonate or irradiation. In addition to later flowering the number of rosette and cauline leaves is proportionally higher in all mutants, although the correlation coefficient between the two parameters is not the same for all genotypes. Forty-two independently induced mutants were found to represent mutations at 11 loci. The mutations were either recessive, intermediate (co locus) or almost completely dominant (fwa locus). The loci are located at distinct positions on four of the five Arabidopsis chromosomes. Recombinants carrying mutations at different loci flower later than or as late as the later parental mutant. This distinction led to the assignment of eight of the loci to three epistatic groups. In wild type, vernalization promotes flowering to a small extent. For mutants at the loci fca, fve, fy and fpa, vernalization has a large effect both under LD and short day (SD) conditions, whereas co, gi, fd and fwa mutants are almost completely insensitive to this treatment. SD induces later flowering except for mutants at the co and gi loci, which flower with the same number of leaves under LD and SD conditions. This differential response of the mutants to environmental factors and their subdivision into epistatic groups is discussed in relation to a causal model for floral initiation in Arabidopsis thaliana.     

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.     

Flower Formation from Citrus unshiu Buds Cultured In Vitro

Flowers were formed in vitro when buds of Satsuma mandarin (Citrusunshiu Mare) from the summer flush of growth harvested duringthe winter rest period before the onset of flower initiation,were grown on a solid Murashige and Skoog medium supplementedwith sucrose and a cytokinin. Flower development was dependentupon illumination, and was enhanced when a piece of stem wasattached to the bud. The percentage of flowering explants wasalways lower than the percentage of naturally flowering budsin spring, but treatments such as ringing which increase floweringin vitro, increased the number of explants flowering int vitroas well. Citrus unshiu Marc, ‘Satsuma’ mandarin, in vitro flowering, ringing     

The role of hormones on morphogenesis of thin layer explants from normal and transgenic tobacco plants

The organogenic potential of thin layer stem explants of non-reproductive tobacco plants was tested on a hormone-free medium and under various hormonal conditions. A comparison was made between thin layers excised from normal and transgenic plants at the same developmental stage. The transgenic plants were transformed by insertion of TR- and TL-DNA from Agrobacterium rhizogenes 1855 root-inducing plasmid. The aim was to identify hormonal conditions capable of stimulating the expression of the flowering competence present in the differentiated stem tissues at the induced stage before any visible sign of transition to reproductive development. Flower neoformation, observed at the end of the culture period (day 25), occurred on untransformed thin layers only with kinetin treatment. Explants from transgenic plants showed flower bud regeneration on hormone-free medium, indoleacetic acid alone (1 μ M ), kinetin alone (1 μ M ), and most abundantly on indoleacetic acid plus kinetin (1 μ M each). No flower formation was observed on indolebutyric acid plus kinetin (10 μ M and 0.1 μ M , respectively) in both normal and transgenic explants. The latter treatment enhanced rooting instead, above all in the transgenic explants. On hormone-free medium vegetative bud formation was well expressed both by untransformed and transgenic explants, and enhanced by the combined, equimolar concentrations of indoleacetic acid and kinetin.
The results show that cytokinin allows flowering in florally determined stem explants from normal plants. In the transgenic explants, the flowering response increases when indoleacetic acid is added to cytokinin, thus suggesting a role for auxin in enhancing the expression of the florally determined state in thin cell layers of non-reproductive plants.     

Induction of flowering by cytokinins in a short-day plant, Lemna paucicostata

Lemna paucicostata, normally a short-day plant, can be inducedto flower under long-day conditions by providing a cytokininin a medium containing a high level of ferric citrate (5 x 10^–4M).Interestingly, when a cytokinin and EDDHA are present togetherin the medium, flowering is induced even at low levels of iron(10^–5 and 5 x 10^–5M ferric citrate). However, inthe absence of a cytokinin, flowering takes place only undershort days. (Received September 30, 1968; )     

Flower development in the passion fruit Passiflora edulis requires a photoperiod‐induced systemic graft‐transmissible signal

Different organisms use gradual seasonal changes in photoperiod to correctly time diverse developmental processes, such as transition to flowering in plants. Florigen is a systemic signal formed in leaves exposed to specific environmental cues, mainly photoperiodic, and capable of triggering flower induction in several species. Here we show that in Passiflora edulis, a perennial climbing vine, flower initiation occurs throughout the year; however, without long photoperiods, flower primordia show arrested growth and differentiation at an early stage. Our results support the existence of a positive, systemic, graft‐transmissible signal, produced in mature leaves under LDs, that is required for normal flower development beyond sepal formation. Our results also suggest that Gibberellin acts to inhibit flower development. We provide evidence for genetic variation in the response to short photoperiods. A genotype capable of forming developed flowers under short photoperiods produces a positive graft transmissible signal allowing normal flower development under short days in a cultivar which normally aborts flower development under these conditions. We believe these findings contribute towards discovering the chemical nature of this interesting mobile signal involved in 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.     

Characterization of <Emphasis Type="Italic">HoMADS 1</Emphasis> and its induction by plant hormones during <Emphasis Type="Italic">in vitro</Emphasis> ovule development in <Emphasis Type="Italic">Hyacinthus orientalis</Emphasis> L.

To understand the molecular mechanism of ovule development, a MADS box gene,HoMADS 1, has been isolated from the ovule tissues of Hyacinthus. Sequence comparison showed that HoMADS 1 is highly homologous to both class C and D genes. Furthermore, phylogenetic analysis suggests that HoMADS 1 is most likely a class D MADS box gene. RNA hybridization revealed that HoMADS 1 was exclusively expressed in the ovules. Over-expressing HoMADS 1 in transgenic Arabidopsis plants produced ectopic carpelloid structures, including ovules, indicating that HoMADS 1 is involved in the determination of carpel and ovule identities. Interestingly, during in vitro flowering, no HoMADS 1 mRNA was detected in the floral tissues at high level hormones in the media. However, HoMADS 1 mRNA accumulated in the floral tissues when the regenerated flowers were transferred to the media containing low level hormones which could induce in vitro ovule formation. Our data suggest that the induction of HoMADS 1 by plant hormones may play important roles during ovule initiation and development in the regenerated flower. Whether HoMADS 1 expression is also regulated by cytokinin and auxin during ovule development in planta remains to be investigated.