Utilisation des mutations induites pour l'étude de l'embryogenèse chez le haricot Phaseolus vulgaris L. et deux plantes modèles Arabidopsis thaliana (L.) Heynh. et Zea mays L.

Use of induced mutations in embryogenesis study in bean Phaseolus vulgaris L. and two model plants, Arabidopsis thaliana (L.) Heynh. and Zea mays L.. Breeding of common bean, Phaseolus vulgaris L., through interspecific hybridizations with the species Phaseolus coccineus L. and Phaseolus polyanthus Greenm. as female parents leads to the abortion of immature embryos. Identification of genes required for embryo development could partly explain the abortion of hybrid embryos; induced mutations could thus be an alternative to identify key genes involved in Phaseolus embryogenesis. This paper is a review which shows a few examples of the use of induced mutations in the identification of essential genes for embryogenesis in two model plants, Arabidopsis thaliana (L.) Heyhn. for dicots and Zea mays L. for monocots. In these two species, embryo development mutants have been isolated using insertional mutagenesis and chemical mutagenesis with Ethyl Methane Sulfonate (EMS). Arabidopsis embryo mutants are affected in apical-basal axis polarity, radial pattern and in post-embryonic stages. Some Arabidopsis embryo mutants are defected in auxin signalisation. In maize, defective kernel (dek) mutants are affected in the embryo and the endosperm, while in embryo specific (emb) mutants, only the embryo is affected. In common bean, plants deficient in seed development were isolated using EMS mutagenesis. Embryos inside the seeds fail to growth at different stages of development and show abnormalities mainly in the suspensor and the cotyledons

Pattern formation during de novo assembly of the Arabidopsis shoot meristem

Most multicellular organisms have a capacity to regenerate tissue after wounding. Few, however, have the ability to regenerate an entire new body from adult tissue. Induction of new shoot meristems from cultured root explants is a widely used, but poorly understood, process in which apical plant tissues are regenerated from adult somatic tissue through the de novo formation of shoot meristems. We characterize early patterning during de novo development of the Arabidopsis shoot meristem using fluorescent reporters of known gene and protein activities required for shoot meristem development and maintenance. We find that a small number of progenitor cells initiate development of new shoot meristems through stereotypical stages of reporter expression and activity of CUP-SHAPED COTYLEDON 2 (CUC2), WUSCHEL (WUS), PIN-FORMED 1 (PIN1), SHOOT-MERISTEMLESS (STM), FILAMENTOUS FLOWER (FIL, also known as AFO), REVOLUTA (REV), ARABIDOPSIS THALIANA MERISTEM L1 LAYER (ATML1) and CLAVATA 3 (CLV3). Furthermore, we demonstrate a functional requirement for WUS activity during de novo shoot meristem initiation. We propose that de novo shoot meristem induction is an easily accessible system for the study of patterning and self-organization in the well-studied model organism Arabidopsis

Cytokinin response factors regulate PIN-FORMED auxin transporters

Auxin and cytokinin are key endogenous regulators of plant development. Although cytokinin-mediated modulation of auxin distribution is a developmentally crucial hormonal interaction, its molecular basis is largely unknown. Here we show a direct regulatory link between cytokinin signalling and the auxin transport machinery uncovering a mechanistic framework for cytokinin-auxin cross-talk. We show that the CYTOKININ RESPONSE FACTORS (CRFs), transcription factors downstream of cytokinin perception, transcriptionally control genes encoding PIN-FORMED (PIN) auxin transporters at a specific PIN CYTOKININ RESPONSE ELEMENT (PCRE) domain. Removal of this cis-regulatory element effectively uncouples PIN transcription from the CRF-mediated cytokinin regulation and attenuates plant cytokinin sensitivity. We propose that CRFs represent a missing cross-talk component that fine-tunes auxin transport capacity downstream of cytokinin signalling to control plant development

Programmed cell death and genetic stability in conifer embryogenesis

Somatic embryogenesis, the generation of embryos from somatic cells, is a valuable tool for studying embryology. In addition, somatic embryos can be used for large-scale vegetative propagation, an application of great interest for forestry. A critical event during early embryo differentiation in conifers is the apical basal polarization, which proceeds through the establishment of two embryonic parts: the proliferating embryonal mass and the terminally differentiated suspensor. The development of both parts is strictly coordinated and imbalance causes embryonic defects. The suspensor cells are eliminated by programmed cell death (PCD). In animals, caspase family proteases are the main executioners of PCD. In this work we have used synthetic peptide substrates containing caspase recognition sites and corresponding specific inhibitors to analyse the role of caspase-like activity during early embryo differentiation in Norway spruce (Picea abies L. Karst.). We found that VEIDase is the principal caspase-like activity. This activity is localized specifically in suspensor cells, and its inhibition prevents normal embryo development by blocking the suspensor differentiation. The in vitro VEIDase activity was shown to be highly sensitive to pH, ionic strength, temperature and zinc concentration. In vivo studies with Zinquin, a zinc-specific fluorescent probe, revealed a high accumulation of intracellular free zinc in the embryonal masses and an abrupt decrease in the suspensor. Increased zinc concentration in the culture medium suppresses terminal differentiation and PCD of the suspensor. In accordance, exposure of early embryos to TPEN, a zinc-specific chelator, induces ectopic cell death affecting embryonal masses. This establishes zinc as an important factor affecting cell fate specification during plant embryogenesis. Before somatic embryos can be accepted for clonal propagation it is important to show that the regenerated plants have similar growth to that of seedlings and are genetically uniform. The genetic integrity during zygotic and somatic embryogenesis in Norway spruce and Scots pine (Pinus sylvestris L.) was investigated by comparing the stability of variable nuclear microsatellite loci. The stability varied significantly among families in both species during somatic embryogenesis. Scots pine families showing low genetic stability during establishment of embryogenic cultures had a higher embryogenic potential than those that were genetically more stable. In contrast, embryo development was suppressed in genetically unstable families. The stability of microsatellites was in general higher in zygotic embryos than in somatic embryos. No deviation in growth was observed in somatic embryo plants of Norway spruce carrying mutated microsatellites

North, east, south, west: mapping vascular tissues onto the Arabidopsis root

The Arabidopsis root has provided an excellent model for understanding patterning processes and cell fate specification. Vascular patterning represents an especially interesting process, as new positional information must be generated to transform an approximately radially symmetric root pole into a bisymmetric structure with a single xylem axis. This process requires both growth of the embryonic tissue alongside the subsequent patterning. Recently researchers have identified a series of transcription factors that modulate cell divisions to control vascular tissues growth. Spatial regulation in the signalling of two hormones, auxin and cytokinin, combine with other transcription factors to pattern the xylem axis. We are now witnessing the discovery of increasingly complex interactions between these hormones that can be interpreted through the use of mathematical models

Plant embryogenesis requires AUX/LAX-mediated auxin influx

The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of the auxin influx carriers AUX1 and LIKE-AUX1 (LAX) proteins is not well established. Here, we used chemical and genetic tools on Brassica napus microspore-derived embryos and Arabidopsis thaliana zygotic embryos, and demonstrate that AUX1, LAX1 and LAX2 are required for both shoot and root pole formation, in concert with PIN efflux carriers. Furthermore, we uncovered a positive-feedback loop between MONOPTEROS (ARF5)-dependent auxin signalling and auxin transport. This MONOPTEROS-dependent transcriptional regulation of auxin influx (AUX1, LAX1 and LAX2) and auxin efflux (PIN1 and PIN4) carriers by MONOPTEROS helps to maintain proper auxin transport to the root tip. These results indicate that auxin-dependent cell specification during embryo development requires balanced auxin transport involving both influx and efflux mechanisms, and that this transport is maintained by a positive transcriptional feedback on auxin signalling

Az oszlopos körtemplom és az angolkert — az antikvitás vágyképe és aktualitása. Kerttörténet és művészettörténet

Abstract The paper explores the history of columned rotundas in European landscape gardens with emphasis on three such edifices built in Hungary in the first half of the 19th century. The theme is the temple type called peripteros in architecture history which comprises a colonnade set in a circle around a pagan shrine, modeled on the Temple of Vesta surviving in Tivoli near Rome from the 1st century BC. It appeared in the art of the early modern times as a garden edifice, first in England in the first decades of the 18th century. The need for its modern-time use arose when man turned to the legacy and nature concept of antiquity to support his political, cultural, moral and artistic revival. With its architectural forms and role in the scenery the Temple of Vesta was already an iconic building of antiquity for artists and visitors to Italy well before it was transferred to landscape gardens where it was reborn in the form of a modern artistic phenomenon, incorporated in grand landscape compositions. Garden history registers some 15–20 surviving rotundas of the kind in European landscape gardens. The paper addresses itself to the history, owners, analogies of the rotundas in Stowe, Stourhead, Downhill (GB), Ermenonville, Méréville (F), Kassel (D), Pavlovsk (RUS), Puŀawy, Arkadia (PL), Veltrusy (CZ) and three Hungarian round temples: Hőgyész, Kismarton/Eisenstadt and Alcsút. It looks at their function, interior decoration, implications of the statues as well as their relation to antiquity and to the garden art creations of their own age. Since the architectural form of the rotunda alone was capable of suggesting a connection with antiquity and at the same time represented modernity, the shaping of the specimens are compared to the Tivoli model. In this comparison the interior decoration and its implications might appear secondary. However, its significance lies in the fact that the designation and decoration of a rotunda became an important means for the adaptation of the building, representing the personality and personal affinities of the builder, the expectations of a country or community. When the rotundas with their statues and embellishments depicted political, philosophical programs, they reflected upon the present of the given country and anticipated a future image. For example, Stowe in England symbolizes liberal democracy, Ermenonville in France suggests the importance of science for humanity. In the two Polish rotundas at Puŀawy and Arkadia the enumeration of the relics of Polish and universal culture serves to preserve the unity and memory Poland cut up into three parts. These rotundas carry unusually strong emotional contents, which also characterizes the other colonnaded round temples, including the “Temples of Friendship”(Veltrusy, Pavlovsk, Kassel). Where is the place of the Hungarian rotundas on this spectrum? The first was built by Count Antal Apponyi (1751–1817) at Hőgyész in Southern Hungary, in the garden of his country house (fig. 12). As a leading statesman of the Hungarian Kingdom, he spent a lot of time in his Vienna palace; steeped in music, he was the president of the Vienna Musikverein; also a free mason, he was one of the nominators of Joseph Haydn for his admission to the Vienna lodge. In his garden designed by Viennese masters he had a rotunda surrounded — unusually — by eight columns. The temple was to house the same-size replica of the Medici Venus in marble, made according to family tradition by Giuseppe Ceracchi of Rome, an Italian sculptor favored by European courts. For some time in the 1780s he worked in Vienna and was a member of the same masonic lodge as Apponyi. Later the sculptor became a Jacobin and was guillotined in Paris. The other, far better known rotunda (fig. 13) was ordered by Prince Miklós Esterházy (1764–1833) to be built in the landscape garden (1803—1822) of his mansion in Kismarton (today Eisenstadt, Austria). The large-scale garden and its edifices were planned by the prince's architect from Paris, Charles Moreau. The character of the building has similarities with the rotunda of Méréville in both the shape of the building and the sculptural ornamentation of the interior. Besides, both rotundas were preceded by a painter's picture as a source of inspiration to have a rotunda in a natural setting. In Méréville Hubert Robert, in Eisenstadt Albert Christoph Dies painted a picture in oil (1807, fig. 11). A few years earlier Dies made a series of engravings of picturesque Italian landscapes including the Temple of Vesta in Tivoli (1793, fig. 10). Although the rotunda in Eisenstadt was first to have been dedicated to Neptun, then to Venus, eventually the prince had the magnificent statue of his daughter Leopoldina Esterházy by Antonio Canova inspired by statues of classical antiquity (1805–1819, fig. 17) placed in the temple. The third Hungarian rotunda perished long ago, its memory revived by this paper alone. It was ordered to be built by Archduke Joseph of Habsburg (the brother of Emperor Francis I), the palatine of Hungary. His seat was in the royal castle of Buda, and he had a duly famous landscape garden on Margaret Island in the Danube. In the centre of his rural estates, Alcsút, he had a representative country house erected in a former wasteland and with the help of his court gardener Anton Trost a magnificent landscape garden was created around the house. At the tallest point he had first a monopteros (fig. 21) and later in the first half of the 1840s a peripteros erected (fig. 18) in which he collected the stone relics of a Roman military camp found in the neighborhood and excavated upon his order. Similarly to their European counterparts, the rotundas in Hőgyész, Eisenstadt and Alcsút manifest the changing concept of nature and the attraction to antiquity as a reliable point of reference. The owners chose for their landscape gardens a building type reminding one of ancient Rome while in the interiors all three manifested their personal relations to antiquity through different cultural orientations. That lent the architectural form and spiritual function of the colonnaded rotundas their exceptional harmony — for a short time. In a relatively short time, this harmony began to crumble. Not that the decisions to choose these art works or architectural forms were mistaken: this building type was an up-to-date representative of European landscape gardens all over Central Europe at that time. The world changed around them concerning their function; nearly in the same decades as their construction, new communal forms and spaces of encountering arts, including the art of antiquity had appeared all over Europe: the museum. It emerged as an urban phenomenon, as part of the urban culture, accessible to all, a promoter or means of social integration. The art works — however valuable — collected by private art patronage and displayed in aristocratic residences were gradually obscured and left out of publicity, affecting their subsequent fate. Leopoldina Esterházy's statue disappeared from view for a long time, and for some sixty years now it has been in the Eisenstadt mansion instead of the peripteros. The replica of the Venus de' Medici once at Hőgyész was given to a Budapest museum by the Apponyi family over a century ago (figs. 15, 16) and the round temple was converted into their sepulchral chapel. The rotunda at Alcsút was pulled down in the second half of the 19th century, the Roman relics in the estate of palatine Joseph were transferred to the Hungarian National Museum (fig. 19). Few of the European peripteroi kept their original interior decoration, and those that did relied on the active participation of the official historic garden protection. The art historical significance of the colonnaded round temples lies in their dual function in a decisive art form of the age, landscape architecture: they were pronounced elements of space articulation on the one hand and the representatives of the owners' attitude to antiquity and modernity. That lent them their appeal in and outside England, their adoption and transfer to the continent symbolizing a wide European horizon and the affirmation of the cultural community. The visual power of the formal order of a peripteros still emanates exceptional harmony and solemnity. This even comes through from the garden and landscape photos of visitors to landscape gardens, from the background elements of newly-wed couples or, for that matter, from the rotunda appearing at a dramaturgical culminating point in a new film adaptation of Jane Austen's Pride and Prejudice (2005, featuring Keira Knightley)

Complement to the study of the Indian Paleocene osteoglossid fish genus <i>Taverneichthys</i> (Teleostei, Osteoglossomorpha)

A series of osteological characters of Taverneichthys bikanericus from the continental Paleocene of India are studied, allowing specifying its systematic position within the Osteoglossidae. It is shown that on the basis of its peculiar snout morphology this species occupies an intermediate position between genera such as Chanopsis and Phareodus, which possess a primitive snout with a large dermethmoid reaching the frontals and separating the two nasals from each other, and such as Brychaetus, Musperia, Opsithrissops, Osteoglossum and Scleropages, which exhibit an evolved snout. The latter presents nasals, which are articulated to the frontals, meeting each other on the mid-line, except at their anterior edge, where a small dermethmoid, largely separated from the frontals, is inserted between

A chemical biology approach reveals an opposite action between thermospermine and auxin in xylem development in Arabidopsis thaliana

Thermospermine, a structural isomer of spermine, is produced through the action of ACAULIS5 (ACL5) and suppresses xylem differentiation in Arabidopsis thaliana. To elucidate the molecular basis of the function of thermospermine, we screened chemical libraries for compounds that can modulate xylem differentiation in the acl5 mutant, which is deficient in thermospermine and shows a severe dwarf phenotype associated with excessive proliferation of xylem vessels. We found that the isooctyl ester of a synthetic auxin, 2,4-D, remarkably enhanced xylem vessel differentiation in acl5 seedlings. 2,4-D, 2,4-D analogs and IAA analogs, including 4-chloro IAA (4-Cl-IAA) and IAA ethyl ester, also enhanced xylem vessel formation, while IAA alone had little or no obvious effect on xylem differentiation. These effects of auxin analogs were observed only in the acl5 mutant but not in the wild type, and were suppressed by the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB) and alpha-(phenyl ethyl-2-one)-IAA (PEO-IAA), and also by thermospermine. Furthermore, the suppressor of acaulis51-d (sac51-d) mutation, which causes SAC51 overexpression in the absence of thermospermine and suppresses the dwarf phenotype of acl5, also suppressed the effect of auxin analogs in acl5. These results suggest that the auxin signaling that promotes xylem differentiation is normally limited by SAC51-mediated thermospermine signaling but can be continually stimulated by exogenous auxin analogs in the absence of thermospermine. The opposite action between thermospermine and auxin may fine-tune the timing and spatial pattern of xylem differentiation