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See detailGene activation cascade triggered by a single photoperiodic cycle inducing flowering in Sinapis alba
D'Aloia, Maria ULg; Tamseddak, Karim; Bonhomme, Delphine ULg et al

in The Plant Journal (2009), 59

Molecular genetic analyses in Arabidopsis disclosed a genetic pathway whereby flowering is induced by the photoperiod. This cascade is examined here within the time course of floral transition in the long ... [more ▼]

Molecular genetic analyses in Arabidopsis disclosed a genetic pathway whereby flowering is induced by the photoperiod. This cascade is examined here within the time course of floral transition in the long-day (LD) plant Sinapis alba induced by a single photoperiodic cycle. In addition to previously available sequences, the cloning of CONSTANS (SaCO) and FLOWERING LOCUS T (SaFT) homologues allowed expression analyses to be performed to follow the flowering process step by step. A diurnal rhythm in SaCO expression in the leaves was observed and transcripts of SaFT were detected when light was given in phase with SaCO kinetics only. This occurred when day length was extended or when a short day was shifted towards a ‘photophile phase’. The steady-state level of SaFT transcripts in the various physiological situations examined was found to correlate like a rheostat with floral induction strength. Kinetics of SaFT activation were also consistent with previous estimations of translocation of florigen out of leaves, which could actually occur after the inductive cycle. In response to one 22-h LD, initiation of floral meristems by the shoot apical meristem (SAM) started about 2 days after activation of SaFT and was marked by expression of APETALA1 (SaAP1). Meanwhile, LEAFY (SaLFY) was first up-regulated in leaf primordia and in the SAM. FRUITFULL (SaFUL) was later activated in the whole SAM but excluded from floral meristems. These patterns are integrated with previous observations concerning upregulation of SUPPRESSOR OF OVEREXPRESSION OF CO1 (SaSOC1) to provide a temporal and spatial map of floral transition in Sinapis. [less ▲]

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See detailCytokinin application to the shoot apical meristem of Sinapis alba enhances secondary plasmodesmata formation.
Ormenese, Sandra ULg; Bernier, Georges ULg; Périlleux, Claire ULg

in Planta (2006), 224(6), 1481-4

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is ... [more ▼]

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is observed 20 h after application within all cell layers (L1, L2, L3) as well as at the interfaces between these layers. Evidence is presented indicating that cytokinin promotes mainly the formation of new secondary plasmodesmata. A similar increase in the frequency of secondary plasmodesmata was observed in the Sinapis SAM during the floral transition induced by a single long day, suggesting that this effect of the long day is mediated by cytokinin. [less ▲]

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See detailAcclimation of Arabidopsis thaliana to long-term CO2 enrichment and nitrogen supply is basically a matter of growth rate adjustment
Tocquin, Pierre ULg; Ormenese, Sandra ULg; Pieltain, Alexandra ULg et al

in Physiologia Plantarum (2006), 128(4), 677-688

The long-term response of Arabidopsis thaliana to increasing CO2 was evaluated in plants grown in 800 mu l 1(-1) CO2 from sowing and maintained, in hydroponics, on three nitrogen supplies: "low," "medium ... [more ▼]

The long-term response of Arabidopsis thaliana to increasing CO2 was evaluated in plants grown in 800 mu l 1(-1) CO2 from sowing and maintained, in hydroponics, on three nitrogen supplies: "low," "medium" and "high." The global response to high CO2 and N-supply was evaluated by measuring growth parameters in parallel with photosynthetic activity, leaf carbohydrates, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) messenger RNA and protein, stomatal conductance (g(s)) and density. CO2 enrichment was found to stimulate biomass production, whatever the N-supply. This stimulation was transient on low N-supply and persisted throughout the whole vegetative growth only in high N-supply. Acclimation on low N-high CO2 was not associated with carbohydrate accumulation or with a strong reduction in Rubisco amount or activity. At high N-supply, growth stimulation by high CO2 was mainly because of the acceleration of leaf production and expansion while other parameters such as specific leaf area, root/shoot ratio and g, appeared to be correlated with total leaf area. Our results thus suggest that, in strictly controlled and stable growing conditions, acclimation of A. thaliana to longterm CO2 enrichment is mostly controlled by growth rate adjustment. [less ▲]

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See detailA physiological overview of the genetics of flowering time control.
Bernier, Georges ULg; Périlleux, Claire ULg

in Plant Biotechnology Journal (2005), 3(1), 3-16

Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as 'primary', but ... [more ▼]

Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as 'primary', but clearly interfere with, or can even be substituted by, less predictable factors. All plant parts participate in the sensing of these interacting factors. In the case of floral induction by photoperiod, long-distance signalling is known to occur between the leaves and the shoot apical meristem (SAM) via the phloem. In the long-day plant, Sinapis alba, this long-distance signalling has also been shown to involve the root system and to include sucrose, nitrate, glutamine and cytokinins, but not gibberellins. In Arabidopsis thaliana, a number of genetic pathways controlling flowering time have been identified. Models now extend beyond 'primary' controlling factors and show an ever-increasing number of cross-talks between pathways triggered or influenced by various environmental factors and hormones (mainly gibberellins). Most of the genes involved are preferentially expressed in meristems (the SAM and the root tip), but, surprisingly, only a few are expressed preferentially or exclusively in leaves. However, long-distance signalling from leaves to SAM has been shown to occur in Arabidopsis during the induction of flowering by long days. In this review, we propose a model integrating physiological data and genes activated by the photoperiodic pathway controlling flowering time in early-flowering accessions of Arabidopsis. This model involves metabolites, hormones and gene products interacting as long- or short-distance signalling molecules. [less ▲]

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See detailA novel high efficiency, low maintenance, hydroponic system for synchronous growth and flowering of Arabidopsis thaliana.
Tocquin, Pierre ULg; Corbesier, Laurent; Havelange, Andrée ULg et al

in BMC Plant Biology (2003), 3(2), 302003

Background: Arabidopsis thaliana is now the model organism for genetic and molecular plant studies, but growing conditions may still impair the significance and reproducibility of the experimental ... [more ▼]

Background: Arabidopsis thaliana is now the model organism for genetic and molecular plant studies, but growing conditions may still impair the significance and reproducibility of the experimental strategies developed. Besides the use of phytotronic cabinets, controlling plant nutrition may be critical and could be achieved in hydroponics. The availability of such a system would also greatly facilitate studies dealing with root development. However, because of its small size and rosette growth habit, Arabidopsis is hardly grown in standard hydroponic devices and the systems described in the last years are still difficult to transpose at a large scale. Our aim was to design and optimize an up-scalable device that would be adaptable to any experimental conditions. Results: An hydroponic system was designed for Arabidopsis, which is based on two units: a seed-holder and a 1-L tank with its cover. The original agar-containing seed-holder allows the plants to grow from sowing to seed set, without transplanting step and with minimal waste. The optimum nitrate supply was determined for vegetative growth, and the flowering response to photoperiod and vernalization was characterized to show the feasibility and reproducibility of experiments extending over the whole life cycle. How this equipment allowed to overcome experimental problems is illustrated by the analysis of developmental effects of nitrate reductase deficiency in nia1nia2 mutants. Conclusion: The hydroponic device described in this paper allows to drive small and large scale cultures of homogeneously growing Arabidopsis plants. Its major advantages are its flexibility, easy handling, fast maintenance and low cost. It should be suitable for many experimental purposes. [less ▲]

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See detailCytokinin levels in leaves, leaf exudate and shoot apical meristem of Arabidopsis thaliana during floral transition
Corbesier, Laurent; Prinsen, Els; Jacqmard, Annie ULg et al

in Journal of Experimental Botany (2003), 54(392), 2511-2517

Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis ... [more ▼]

Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis thaliana has been successfully used to unravel signalling pathways by genetic and molecular approaches, but analyses are still required to determine the physiological signals involved in the control of floral transition. In this work, the putative role of cytokinins was investigated using vegetative plants of Arabidopsis (Columbia) induced to flower synchronously by a single 22 h long day. Cytokinins were analysed in leaf extracts, leaf phloem exudate and in the shoot apical meristem at different times during floral transition. It was found that, in both the leaf tissues and leaf exudate, isopentenyladenine forms of cytokinins increased from 16 h after the start of the long day. At 30 h, the shoot apical meristem of induced plants contained more isopentenyladenine and zeatin than vegetative controls. These cytokinin increases correlate well with the early events of floral transition. [less ▲]

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See detailThe shoot apical meristem of Sinapis alba L. expands its central symplasmic field during the floral transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Bernier, Georges ULg et al

in Planta (2002), 215(1), 67-78

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into ... [more ▼]

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into dorsiventral leaves under the influence of signals from the central zone. During the floral transition the function of the SAM is altered and its peripheral zone starts to form floral structures in a specific pattern. This requires alterations in the signal networks that coordinate the activities of the peripheral and central zone of the SAM. These signal networks are partly housed in the symplasmic space of the SAM. Dye-coupling experiments demonstrate that in the superficial layer of the Sinapis alba meristem this space is radially subdivided. The cells of the central zone are coupled into a symplasmic field, which is shielded from the peripheral zone by the positional closing of plasmodesmata. In the vegetative meristems, most of these central symplasmic fields have a triangular geometry and are relatively small in size. Plants that are induced to flower by exposure to a single long day alter the geometry as well as the size of their central symplasmic field. After two subsequent days under short photoperiod the central symplasmic fields exhibit a circular form. Simultaneously. their size strongly increases both in an absolute sense and relative to the enlarging meristem. The geometric change in the fields is hypothesized to be due to recruitment of extra initial cells, required to support the increase in phyllotactic complexity. The proportional increase in field size is interpreted as an adjustment in the balance between the central and peripheral zone of the SAM, accompanying the shift from leaf production to flower formation. [less ▲]

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See detailC : N ratio increases in the phloem sap during floral transition of the long-day plants Sinapis alba and Arabidopsis thaliana
Corbesier, Laurent; Bernier, Georges ULg; Périlleux, Claire ULg

in Plant & Cell Physiology (2002), 43(6), 684-688

In plants of Sinapis alba and Arabidopsis thaliana, leaf exudate (phloem sap) was analysed during and after a single long day inducing flowering and in control short days. The amounts of carbohydrates and ... [more ▼]

In plants of Sinapis alba and Arabidopsis thaliana, leaf exudate (phloem sap) was analysed during and after a single long day inducing flowering and in control short days. The amounts of carbohydrates and amino acids were measured to estimate the organic C : N ratio. In both species, the C : N ratio of the phloem sap increased markedly and early during the inductive treatment, suggesting that an inequality in organic C and N supply to the apical meristem may be important at floral transition. [less ▲]

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See detailThe control of flowering: do genetical and physiological approaches converge ?
Périlleux, Claire ULg; Bernier, Georges ULg

in O'Neill, S. D.; Roberts, J. A. (Eds.) Plant Reproduction (2002)

Since the early 1990s, Arabidopsis thaliana has been studied as the species of choice of 'flowering geneticists'. Several pathways that either repress or promote flowering have been identified on the ... [more ▼]

Since the early 1990s, Arabidopsis thaliana has been studied as the species of choice of 'flowering geneticists'. Several pathways that either repress or promote flowering have been identified on the basis of (1) the flowering response of different genotypes to environmental factors (vernalization and photoperiod), (2) epistasis analyses, and (3) expression patterns of cloned genes in various backgrounds. Models attempting to include all information have been proposed repeatedly and their complexity is increasing with the bulk of data. In this review, we shall attempt to integrate into this genetical framework the physiological knowledge accumulated on a variety of plants by generations of researchers before the amost overnight breakthrough of Arabidopsis. [less ▲]

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See detailThe flowering process: On the track of controlling factors in Sinapis alba
Bernier, Georges ULg; Corbesier, Laurent; Périlleux, Claire ULg

in Russian Journal of Plant Physiology (2002), 49(4, JUL-AUG), 445-450

The major physiological theories of the control of the flowering process are first presented and their inferences tested in the long-day plant Sinapis alba. Then, the genetic analyses of the control of ... [more ▼]

The major physiological theories of the control of the flowering process are first presented and their inferences tested in the long-day plant Sinapis alba. Then, the genetic analyses of the control of flowering time in Arabidopsis thaliana are also summarized with a brief overview of the several pathways, each including several genes, identified. Clearly, both the experimental data of physiological experiments and the multiplicity of interacting genetic pathways best support the theory of the multifactorial control of flowering. This is further shown by the fact that a critical gene expressed in the shoot meristem at floral transition in S. alba, MADS A (orthologous to A. thaliana SOC1), can be upregulated by a single dose of a cytokinin or a gibberellin, without leading to flowering. This indicates that the floral shift requires upregulation of other genes by other factors. [less ▲]

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See detailN content of phloem and xylem exudates during the transition to flowering in Sinapis alba and Arabidopsis thaliana
Corbesier, Laurent; Havelange, Andrée ULg; Lejeune, Pierre et al

in Plant, Cell & Environment (2001), 24

The involvement of nitrogenous substances in the transition to flowering was investigated in Sinapis alba and Arabidopsis thaliana (Columbia). Both species grown in short days (SD) are induced to flower ... [more ▼]

The involvement of nitrogenous substances in the transition to flowering was investigated in Sinapis alba and Arabidopsis thaliana (Columbia). Both species grown in short days (SD) are induced to flower by one long day (LD). In S. alba, the phloem sap (leaf and apical exudates) and the xylem sap (root exudate) were analysed in LD versus SD. In A. thaliana, only the leaf exudate could be analysed but an alternative system for inducing flowering without day-length extension was used: the displaced SD (DSD). Significant results are: (i) in both species, the leaf exudate was enriched in Gln during the inductive LD, at a time compatible with export of the floral stimulus; (ii) in S. alba, the root export of amino acids decreased in LD, whereas the nitrate remained unchanged - thus the extra-Gln found in the leaf exudate should originate from the leaves; (iii) extra-Gln was also found very early in the apical exudate of S. alba in LD, together with more Glu; (iv) in A. thaliana induced by one DSD, the leaf export of Asn increased sharply, instead of Gln in LD. This agrees with Asn prevalence in C-limited plants. The putative role of amino acids in the transition to flowering is discussed. [less ▲]

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See detailThe Frequency of Plasmodesmata Increases Early in the Whole Shoot Apical Meristem of Sinapis Alba L. During Floral Transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Deltour, Roger ULg et al

in Planta (2000), 211(3), 370-5

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1 ... [more ▼]

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin. [less ▲]

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See detailAre CAB gene expression and flowering under the control of the same clock in Lolium temulentum Ceres ?
Hustin, Cécile; Bernier, Georges ULg; Périlleux, Claire ULg

in Biological Rhythm Research (1999), 30

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See detailPhysiological analysis of the floral transition
Bernier, Georges ULg; Corbesier, Laurent; Périlleux, Claire ULg et al

in Cockshull, K. E.; Gray, D.; Seymour, G. B. (Eds.) et al Genetic and Environmental Manipulation of Horticultural Crops (1998)

This chapter summarizes the changes in contents of the phloem sap that were found at the time of floral induction in different photoperiodic species: Arabidopsis thaliana, Sinapis alba, Lolium temulentum ... [more ▼]

This chapter summarizes the changes in contents of the phloem sap that were found at the time of floral induction in different photoperiodic species: Arabidopsis thaliana, Sinapis alba, Lolium temulentum and Xanthium strumarium. Changes affecting contents in carbohydrates, cytokinins, amino acids, polyamines and inorganis ions are discussed in the context of 'florigen quest'. [less ▲]

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See detailLeaf carbohydrate status in Lolium temulentum during the induction of flowering
Périlleux, Claire ULg; Bernier, Georges ULg

in New Phytologist (1997), 135(1), 59-66

Unifoliated plants of Lolium temulentum L. ev. Ceres, a qualitative long-day grass, were induced to flower by one 24-h long day (LD) or by one 8-h short day (SD) advanced by 1 2 h in the normal regime, so ... [more ▼]

Unifoliated plants of Lolium temulentum L. ev. Ceres, a qualitative long-day grass, were induced to flower by one 24-h long day (LD) or by one 8-h short day (SD) advanced by 1 2 h in the normal regime, so-called 'displaced short day' (DSD). Standard light for SD and DSD was a mixture of fluorescence and incandescence at 400 µmol m2 s-1 whereas the extension period of the 24-h LD was solely incandescence at 10-15 µmol m2 s-1. The DSD system was first characterized by the timings of floral induction, stimulus translocation and apical development. Carbohydrates in the blade tissues and in leaf exudate were analysed comparatively in vegetative and induced plants. Fructans were not detected in the leaf tissues whereas sucrose and starch were found to be present in similar amounts. In SD, their contents exhibited a diurnal fluctuation and were not in large excess. The common change observed during the two inductive treatments was that starch remained at a high level during the LD extension, even though the lighting was unsuitable for photosynthesis, and increased transiently in DSD. Sucrose was the major sugar contained in the leaf exudate. Its content increased when flowering was induced, but not at the same time in the two systems. In LD, sucrose exudation rose when plants were returned to standard light after the inductive cycle, i.e. after the LD stimulus had left the leaf blade. By contrast, during the DSD, sucrose was transported at the same time as the floral stimulus. Results are discussed together with the methods used to time stimulus translocation and their implications. [less ▲]

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See detailBiological clock and photoperiodism in Lolium temulentum Ceres
Périlleux, Claire ULg; Hustin, Cécile; Bernier, Georges ULg

in Journal of Experimental Botany (1997), 48

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See detailDarkness promotes flowering in the absolute long-day requiring plant, Lolium temulentum L. Ceres
Périlleux, Claire ULg; Bernier, Georges ULg; Kinet, Jean-Marie

in Journal of Experimental Botany (1997), 48(307), 349--351

Vegetative plants of the long-day grass Lolium temulentum L. Ceres were exposed to threshold long days or light breaks. Protracted darkness given just afterwards clearly promoted flowering and was weakly ... [more ▼]

Vegetative plants of the long-day grass Lolium temulentum L. Ceres were exposed to threshold long days or light breaks. Protracted darkness given just afterwards clearly promoted flowering and was weakly inductive on its own. The promotive effect of darkness was restricted to floral induction since further apical development was weak. [less ▲]

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See detailChanges in gene expression in the leaf of Lolium temulentum L. Ceres during the photoperiodic induction of flowering
Périlleux, Claire ULg; Ongena, Philippe; Bernier, Georges ULg

in Planta (1996), 200(1), 32-40

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 µmol photons·m-2·s-1, fluorescence ... [more ▼]

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 µmol photons·m-2·s-1, fluorescence + incandescence) with incandescence at 10–15 µmol photonsm -2·s-1. The polyadenylated-RNA complement of leaf blade tissues was analysed at 4-h intervals during the photoperiod extension in LD vs. SD, by using two-dimensional polyacrylamide gel electrophoresis to resolve in-vitro-translated products. Of the 991 spots that were analysed, none appeared or disappeared during the inductive cycle, i.e. no qualitative effect of floral induction was detected, at any time. Sixty-eight spots were found whose intensity was influenced by lengthening of the photoperiod; 50 of them, i.e. ca. 5 of the population analysed, were affected before the end of the extension period and were thus potentially related to floral induction. Many of these RNAs were not quantitatively constant during a 24-h cycle in SD. Seven of them oscillated according to the ‘light-on’ and the ‘light-off’ signals, among which three seemed to be controlled by phytochrome since their relative amount increased under the standard light conditions but decreased under incandescence even faster than in darkness. The large majority of other RNAs varied with a timing that was not clearly driven by the alternation of light and darkness, indicating that genes related to the biological clock may be especially sensitive to the lengthening of the photoperiod. Furthermore, seven spots were observed that underwent a phase-shift in LD, which consisted, for six of them, of a phase advance of 4–8 h. The steady-state level of CAB mRNA was analysed because the CAB gene family (encoding the chlorophyll a/b-binding proteins of the light-harvesting complexes) is known to be controlled both by the biological clock and phytochrome. In SD, the level was high in the light and low in darkness; the fluctuation was conducted by a circadian rhythm. When plants were exposed to the inductive LD, the peak of mRNA accumulation that was expected according to the endogenous rhythmicity was abolished, possibly because of the change in light quality during the LD extension. [less ▲]

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