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Shoot architecture is a key component of the interactions between plants and their environment. We present a novel model of grass, which fully integrates shoot morphogenesis and the metabolism of carbon (C) and nitrogen (N) at organ scale, within a three-dimensional representation of plant architecture. Plant morphogenesis is seen as a self-regulated system driven by two main mechanisms. First, the rate of organ extension and the establishment of architectural traits are regulated by concentrations of C and N metabolites in the growth zones and the temperature. Second, the timing of extension is regulated by rules coordinating successive phytomers instead of a thermal time schedule. Local concentrations are calculated from a model of C and N metabolism at organ scale. The three-dimensional representation allows the accurate calculation of light and temperature distribution within the architecture. The model was calibrated for wheat (Triticum aestivum) and evaluated for early vegetative stages. This approach allowed the simulation of realistic patterns of leaf dimensions, extension dynamics, and organ mass and composition. The model simulated, as emergent properties, plant and agronomic traits. Metabolic activities of growing leaves were investigated in relation to whole-plant functioning and environmental conditions. The current model is an important step towards a better understanding of the plasticity of plant phenotype in different environments.

International audience; Genetic and epigenetic variations are commonly known to underlie phenotypic plastic responses to environmental cues. however, the role of epigenetic variation in plastic responses harboring ecological significance in nature remains to be assessed. The shade avoidance response (SAR) of plants is one of the most prevalent examples of phenotypic plasticity. It is a phenotypic syndrome including stem elongation and multiple other traits. Its ecological significance is widely acknowledged, and it can be adaptive in the presence of competition for light. Underlying genes and pathways were identified, but evidence for its epigenetic basis remains scarce. We used a proven and accessible approach at the population level and compared global DNA methylation between plants exposed to regular light and three different magnitudes of shade in seven highlyinbred lines of snapdragon plants (Antirrhinum majus) grown in a greenhouse. Our results brought evidence of a strong SAR syndrome for which magnitude did not vary between lines. They also brought evidence that its magnitude was not associated with the global DNA methylation percentage for five of the six traits under study. The magnitude of stem elongation was significantly associated with global DNA demethylation. We discuss the limits of this approach and why caution must be taken with such results. In-depth approaches at the DNA sequence level will be necessary to better understand the molecular basis of the SAR syndrome

International audience; Despite the abundance of cercopithecoids in the fossil record, especially in South Africa, and the recent development of morphometric approaches, uncertainties regarding the taxonomic identification of isolated cranio-dental specimens remain. Because cercopithecoids, nearly always found in stratigraphic association with hominin remains in Plio-Pleistocene deposits, are considered as sensitive ecological and chronological biomarkers, a significant effort should be made to clarify their palaeobiodiversity by assessing additional reliable morphological diagnostic criteria. Here we test the relevance of both molar crown internal structure and bony labyrinth morphology for discrimination of fossil cercopithecoid species. We use microtomographic-based 3D virtual imaging and quantitative analyses to investigate tooth endostructural organization and inner ear shape in 29 craniodental specimens from the South African sites of Kromdraai, Makapansgat, Sterkfontein and Swartkrans and provide the first detailed description of the internal structural condition characterizing this Plio-Pleistocene primate assemblage. Our preliminary results show that enamel-dentine junction morphology could be informative for discriminating highly autapomorphic taxa such as Theropithecus, while semicircular canal shape is tentatively proposed as an efficient criterion for diagnosing Dinopithecus ingens. Further research in virtual paleoprimatology may contribute to the identification of unassigned isolated fossil remains and shed new light on the internal craniodental morphology of extinct primate taxa.

Gonad differentiation is a crucial step conditioning the future fertility of individuals and most of the master genes involved in this process have been investigated in detail. However, transcriptomic analyses of developing gonads from different animal models have revealed that hundreds of genes present sexually dimorphic expression patterns. DMXL2 was one of these genes and its function in mammalian gonads was unknown. We therefore investigated the phenotypes of total and gonad-specific Dmxl2 knockout mouse lines. The total loss-of-function of Dmxl2 was lethal in neonates, with death occurring within 12 hours of birth. Dmxl2-knockout neonates were weak and did not feed. They also presented defects of olfactory information transmission and severe hypoglycemia, suggesting that their premature death might be due to global neuronal and/or metabolic deficiencies. Dmxl2 expression in the gonads increased after birth, during follicle formation in females and spermatogenesis in males. DMXL2 was detected in both the supporting and germinal cells of both sexes. As Dmxl2 loss-of-function was lethal, only limited investigations of the gonads of Dmxl2 KO pups were possible. They revealed no major defects at birth. The gonadal function of Dmxl2 was then assessed by conditional deletions of the gene in gonadal supporting cells, germinal cells, or both. Conditional Dmxl2 ablation in the gonads did not impair fertility in males or females. By contrast, male mice with Dmxl2 deletions, either throughout the testes or exclusively in germ cells, presented a subtle testicular phenotype during the first wave of spermatogenesis that was clearly detectable at puberty. Indeed, Dmxl2 loss-of-function throughout the testes or in germ cells only, led to sperm counts more than 60% lower than normal and defective seminiferous tubule architecture. Transcriptomic and immunohistochemichal analyses on these abnormal testes revealed a deregulation of Sertoli cell phagocytic activity related to germ cell apoptosis augmentation. In conclusion, we show that Dmxl2 exerts its principal function in the testes at the onset of puberty, although its absence does not compromise male fertility in mice., Author summary DMXL2 gene dysfunction underlies various human diseases, including breast cancer, non-syndromic hearing loss, and polyendocrine-polyneuropathy syndrome, demonstrating the large range of potential actions of DMXL2. We show here that Dmxl2 expression is crucial for survival in mice, as neonates die within hours of birth when this gene is inactivated. The transmission of olfactory information is affected, leading to an absence of suckling and impaired feeding. Severe hypoglycemia is also observed in male neonates. We observed Dmxl2 expression in several organs, including the brain, heart and adrenal glands, potentially corresponding to some of the phenotypes observed in Dmxl2-deficient pups. We also described Dmxl2 expression in the reproductive tracts and gonads and showed that Dmxl2 inactivation specifically in the testes has a significant effect on the initial waves of spermatogenesis, resulting in very low levels of sperm production at puberty. Our results suggest that DMXL2 deficits should be considered in men with impaired fertility, as pathogenic variants of this gene may be associated with male infertility in humans.

Drosophila dorsal closure is a key embryonic process during which the dorsal-most epidermal cells called leading edge cells differentiate and act in a coordinated manner to close a transient dorsal hole covered by the amnioserosa in a process reminiscent of wound healing. I showed that JNK and DPP are wired in a network motif called ‘feed-forward loop’ (FFL) that controls leading edge cell specification and differentiation. The DPP branch of the FFL filters unwanted JNK activity that occurs during thermal stress. Next, I focused on the actin cable, a supra-cellular structure produced by the leading edge cells during dorsal closure or wound healing from fly to humans. My data suggest that the actin cable does not provide a major contractile force. Rather, the actin cable balances forces and stabilizes cell geometry so that closure resolves in a perfectly structured and scar-free tissue. The absence of the cable leads to cell shape irregularities as well as patterning and planar cell polarity defects that are reminiscent of scarring. We propose that the cable prevents scaring by acting as a mechanical freeze field that protects fine cellular structures from the major closure forces that operate at tissue level.Altogether, my work brings new insights on the signalling and morphogenesis during dorsal closure., La fermeture dorsale est un événement majeur de l’embryogénèse de la drosophile durant lequel les cellules les plus dorsales de l’épiderme se différencient et agissent de concert pour refermer une ouverture dorsale temporairement recouverte par l’amnioséreuse. Ce processus présente de nombreuses similarités avec la cicatrisation cellulaire. J’ai montré que les voies JNK et DPP forment une boucle cohérente appelée « feed-forward loop » (boucle d’anticipation) qui contrôle la différentiation des cellules de la marge active. La branche DPP de cette boucle filtre les signaux non désirés de la voix JNK quand les embryons sont soumis à un stress thermique. Je me suis ensuite concentré sur le câble d'actine, une structure supra-cellulaire produite par les cellules de la marge active lors de la fermeture dorsale. J’ai montré que le câble d’actine est une structure discontinue qui n’est pas nécessaire pour la fermeture dorsale ou pour la cicatrisation cellulaire. Le câble d’actine homogénéise les forces et stabilise la géométrie cellulaire pour que la fermeture se fasse de manière parfaite et sans cicatrice. Sans le câble, les cellules ont une forme irrégulière, associé à des défauts de patterning et des défauts de polarité planaire qui ressemblent aux défauts que l’on trouve lors de la formation d’une cicatrice. Nous proposons donc que le câble empêche la formation de cicatrice en « congelant » les propriétés mécaniques des cellules afin de les protéger des forces qui agissent au niveau tissulaire lors de la fermeture dorsale.En conclusion, mon travail apporte un regard neuf sur la signalisation et la morphogenèse lors de la fermeture dorsale de l’embryon de Drosophile.

Couturier, Etienne Brunel, Nicole Douady, Stephane Nakayama, Naomi; Premise of the study: How leaf shape is regulated is a long-standing question in botany. For diverse groups of dicotyledon species, lamina folding along the veins and geometry of the space available for the primordia can explain the palmate leaf morphology. Dubbed the kirigami theory, this hypothesis of fold-dependent leaf shape regulation has remained largely theoretical. Using Acer pseudoplatanus, we investigated the mechanisms behind the two key processes of kirigami leaf development. Methods: Cytological examination and quantitative analyses were used to examine the course of the vein-dependent lamina folding. Surgical ablation and tissue culturing were employed to test the effects of physical constraints on primordia growth. The final morphology of leaves growing without steric constraints were predicted mathematically. Key results: The cytological examination showed that the lamina's abaxial side along the veins grows substantially more than the adaxial side. The abaxial hypergrowth along the veins and the lamina extension correlated with the lamina folding. When a primordium was released from the physical constraints imposed by the other primordia, it rapidly grew into the newly available space, while maintaining the curvature inward. The morphology of such a leaf was predicted to lack symmetry in the lobe shapes. Conclusions: The enhanced growth on the abaxial side of the lamina along the veins is likely to drive lamina folding. The surgical ablation provided clear support for the space-filling nature of leaf growth; thus, steric constraints play a role in determination of the shapes of folded leaves and probably also of the final leaf morphology.

Early vigour is an important objective in rice breeding. A previous study reported strong positive effects of development rate (DR, 1/phyllochron) on early growth vigour in two rice panels. This study provided a model-based analysis of DR effects on rice early vigour and underlying source-sink processes during exponential growth, using Ecomeristem model. Relevant model parameters were fitted to panel observations, and their effect on early vigour was quantified. A sensitivity analysis was performed to quantify the impact of model parameters on simulation outputs. The simulated behaviour of a population of virtual genotypes defined by the combination of model parameter values was compared with that of diversity panel. Finally, a simulation experiment was conducted to analyse source-sink adjustments constituting early vigour across a range of DR. Parameters governing structural development, particularly DR, had greater impact on vigour than parameters for resource acquisition. High DR was associated with rapid dry weight accumulation and low transitory carbohydrate reserves in both real and virtual populations. Genotypic DR is thus a major driver of early vigour in rice under stress-free conditions. To evaluate traits contributing to vigour, the capacity of crop models to simulate interactions between structural development and resource acquisition must be improved. (Resume d'auteur)

International audience; Angiosperm microspores are grouped into tetrads before they mature into functional pollen grains. This tetrad stage is an important step in microsporogenesis. Tetrad shapes are diverse across angiosperms, with high levels of variation sometimes occurring within species, reflecting variation in early developmental events of nuclear and cell division (i.e., meiosis and cytokinesis). Among these developmental influences, the shape of the microsporocyte (pollen mother cell; hereafter PMC) is likely to influence tetrad shape. This article presents a test of this hypothesis in 19 species of higher Asparagales with a successive cytokinesis by inferring PMC shape from tetrads observed with epifluorescence microscopy. Sampled species show differences in PMC shape between groups of regular or irregular tetrads at the species level, and there is a strong component of PMC shape variation at the onset of meiosis on resulting tetrad shape, with more elongated PMCs yielding significantly more irregular tetrads.

UMR 1334 AGAP : Equipe AFEF ‘Architecture et Fonctionnement des Espèces fruitières’ ; Team AFFS ‘Architecture and Functioning of Fruit Species’ Correspondance : M. Rakocevic, IAPAR, Rodovia Celso Garcia Cid, km 375, PO Box 481, 86047-902 Londrina,PR, Brazil. Email: miroslava@iapar.br; International audience; Yerba-mate is a subtropical, evergreen, dioecious, South American tree. Sexual dimorphism in photosynthesis, leaf allometry and foliage distribution was hypothesised. Virtual trees (constructed in VPlants software from detailed measurements of plant morphogenesis) of the two genders were compared considering two contrasted cultivation environments and three developmental stages. The total crown volume, leaf area per plant (LA), leaf area index (LAI) and leaf area density (LAD) were calculated. The light interception and photosynthesis were computed from mock-ups in VegeSTAR. Structural sexual dimorphism concerned general plant form, internode length, leaf allometry, leaf surface, pattern of leaf area distribution and LAD. Cultivation environment and developmental stage acted strongly on sex expression of all observed structural parameters and physiological stages. Sexual differentiation in LA and light interception was related to leaves positioned in the lowest layers (150 cm above ground), whereas sexual specialisation in leaf and plant photosynthesis was related to early vegetative and reproductive stages. Several sexual responses strongly depended on the environment, especially light conditions, with opposite effects observed on female and male plants whether they were cultivated in monoculture or in forest understorey, under highlight condition or low-light condition, respectively. Optimised foliage structure and physiology in females may compensate for greater reproductive costs in early developmental stages, but females and males equalise in photosynthetic efficiency after 2-year regrowth

Leaf development entails the transition from a small group of undifferentiated cells to a structure of defined size and shape, highly organized into different cell types with specialized functions. During this developmental sequence, patterning, growth, and differentiation have to be tightly coordinated by intricate regulatory networks in which small RNAs [microRNAs (miRNAs) and trans-acting small interfering RNAs (ta-siRNAs)] have emerged during the last years as essential players. In this review, after having given an overview of miRNA and ta-siRNA biogenesis and mode of action, their contribution to the life of a leaf from initiation to senescence is described. MiRNA and ta-siRNA are not merely regulators of gene expression patterns, but, by acting both locally and at the whole organ scale, they have an essential role in the coordination of complex developmental processes and are fully integrated in genetic networks and signalling pathways.

AtTCP20 is a transcription factor belonging to the Arabidopsis (Arabidopsis thaliana) TCP-P subfamily, characterized by its capacity to bind to site II motifs (TGGGCY). Our aim was to understand the role of AtTCP20 in plant development. The expression pattern of a translational fusion of PromTCP20:CDS20∷GUS∷GFP suggested a function for AtTCP20 in several plant organs and stages of development. The role of AtTCP20 was challenged in planta by inducing expression of AtTCP20 proteins fused with either a transcriptional activator domain (VP16) or a repressor domain (EAR). Expression of both modified proteins led to severe developmental phenotypes. In-depth analysis suggested that AtTCP20 may participate in the regulation of cell expansion, cell division, and cell differentiation. Gene expression profiling in roots and hypocotyls revealed that 252 genes were down-regulated in both organs after induction of the AtTCP20∷EAR repressor gene. Site II motifs (TGGGCY) were underrepresented in their promoters. Conversely, GG(A/T)CCC sequences related to binding sites identified for TCP proteins in rice (Oryza sativa) were overrepresented, and a TCP20 fusion protein was shown to bind to these sequences in vitro. Gene ontology indicated that many targeted genes were involved in cell wall biogenesis and modification during expansion and also encoded numerous transcription factors controlling plant development. Our results are consistent with the previous proposal that AtTCP20 is involved in cell division and growth coordination. Moreover, they further suggest that AtTCP20 also contributes to cell expansion control and indicate a different involvement of this protein in plant morphogenesis depending on the organ and the developmental stage.

UMR DAP équipe AFEF Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; The present study aimed to dissect tree architectural plasticity into genetic, ontogenetic and environmental effects over the first 4 years of growth of an apple F1 progeny by means of quantitative traits loci (QTL) mapping. Both growth and branching processes were phenotyped on the consecutive annual shoots of different axes within a tree. For each studied trait, predicted values (best linear unbiased predictors, BLUPs) of the genotypic (G) effect or its interaction with tree age (G×A) and climatic year (G×Y) were extracted from mixed linear models of repeated data. These BLUPs, which are independent from autocorrelations between repeated measurements, were used for QTL mapping. QTL detection power was improved by this two-step approach. For each architectural process, numerous QTLs were detected and some particularly interesting co-localised in common genomic regions, for internode lengthening, top diameter, and number and percentage of axillary shoots. When several QTLs were detected for a given trait, global models were estimated, which explained a maximum of 40% of the total variance for both internode length and top diameter and 28% for branching. QTLs detected for BLUPs of G×Y effects were interpreted as resulting from the interaction between genetic maximal potential of growth and climatic factors, while those for G×A effects were interpreted in relation to tree ontogeny. Most of the latter ones were found to be concomitant with key development stages during which the trait average started to decrease, but with different magnitudes depending on genotype

UMR DAP, équipe AFEF, Correspondance: costes@supagro.inra.fr Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Genetic control of plant size and shape is a promising perspective, particularly in fruit trees, in order to select desirable genotypes. A recent study on architectural traits in an apple progeny showed that internode length was a highly heritable character. However, few studies have been devoted to internode cellular patterning in dicotyledonous stems, and the interplay between the two elementary cell processes that contribute to their length, i.e. cell division and elongation, is not fully understood. The present study aimed at unravelling their contributions in the genetic variation of internode length in a selection of F(1) and parent genotypes of apple tree, by exploring the number of cells and cell shape within mature internodes belonging to the main axes. The results highlighted that both the variables were homogeneous in samples collected either along a sagital line or along the pith width, and suggest that cell lengthening was homogeneous during internode development. They allowed the total number of cells to be estimated on the internode scale and opened up new perspectives for simplifying tissue sampling procedures for further investigations. Differences in internode length were observed between the genotypes, in particular between the parents, and partly resulted from a compensation between cell number and cell length. However, genetic variations in internode length primarily involved the number of cells, while cell length was more secondary. These results argue for an interplay between cellular and organismal control of internode shape that may involve the rib meristem.

International audience; The influence of dietary vitamins on growth, survival, and morphogenesis was evaluated until day 38 of posthatching life in European sea bass larvae (Dicentrarchus labrax). A standard vitamin mix (VM), at double the concentration of the U. S. National Research Council's recommendations, was incorporated into larval feeds at 0.5%, 1.5%, 2.5%, 4.0%, and 8.0% to give treatments VM 0.5, VM 1.5, VM 2.5, VM 4.0, and VM 8.0, respectively. The group fed the VM 0.5 diet all died before day 30. At day 38, the larvae group fed VM 1.5 had 33% survival, while the other groups, with higher vitamin levels, showed at least 50% survival. The higher the percentage VM in the diet, the lower the percentage of column deformities. High dietary vitamin levels positively influenced the formation of mineralized bone in larvae: the higher the dietary vitamin level, the higher the ossification status. In the larvae group fed at the highest vitamin levels, we observed a temporal sequence of coordinated growth factor expression, in which the expression of bone morphometric protein (BMP-4) preceded the expression of IGF-1, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). In groups fed lower proportions of vitamins, elevated proliferator peroxisome-activated receptors (PPAR-gamma) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-gamma transcripts in larvae-fed diets with a low VM content converted some osteoblasts into adipocytes during the first two weeks of life. This loss of osteoblasts is likely to have caused skeletal deformities.

Crop modeling in support of breeders’ decisions on selection criteria can benefit from the new global focus on phenomics because it provides new information on existing genetic diversity for useful traits. This study attempted an in silico prediction of margins for genetic improvements of early vigor (biomass produced during vegetative growth) and drought resistance combined, based on virtual recombination of several traits (here syn. model parameters) within ranges of trait variation observed in a panel of diverse rice genotypes. The Ecomeristem model was parameterized by multi-parameter optimization procedures applied to observed datasets for 136 rice genotypes. The traits within the observed ranges were then recombined in silico to generate a virtual population of 9000 individuals. Simulations of real and virtual phenotypes under three water treatments, using finite water resources during stress cycles, indicated strong and similar trade-offs between constitutive vigor and drought resistance in both real and virtual, recombinant populations. A substantial margin for potential genetic improvement of vigor with unchanged drought resistance was predicted, drawing chiefly from structural growth and development traits that would increase internal demand for assimilates (larger and thicker leaves, increased leaf appearance rates). Increased vigor would not necessarily require greater photosynthetic potential per se. However, improved drought resistance with unchanged constitutive vigor would require greater water economy (increased photosynthetic potential and limited water use, therefore higher transpiration efficiency) and greater tolerance of leaf extension and gas exchange rates to drought, while tillering ability should be limited in favor of larger and thicker leaves. These results carry significant uncertainty because they predict virtual genotypes and their phenotypes, based on simple assumptions in the model (namely on gas exchange) and in genetics (free, additive trait combinability). But the approach is innovative and may eventually help developing ideotypes drawing from information of existing diversity and integrative modeling of phenotypes.

The qTSN4 was identified as rice QTL (Quantitative Traits Locus) increasing total spikelet number per panicle and flag leaf area but potentially reducing panicle number depending on the environment. So far, this trade-off was mainly observed at grain maturity and not specifically studied in details, limiting the apprehension of the agronomic interest of qTSN4. This study aimed to understand the effect of qTSN4 and of the environment on panicle sizing, its trade-off with panicle number, and finally plant grain production. It compared two high yielding genotypes to their Near Isogenic Lines (NIL) carrying either QTL qTSN4 or qTSN12, two distinct QTLs contributing to the enlarged panicle size, thereafter designated as qTSN. Traits describing C sink (organ appearance rate, size, biomass) and source (leaf area, photosynthesis, sugar availability) were dynamically characterized along plant and/or panicle development within two trials (greenhouse, field), each comparing two treatments contrasting for plant access to light (with or without shading, high or low planting densities). The positive effect of qTSN on panicle size and flag leaf area of the main tiller was confirmed. More precisely, it could be shown that qTSN increased leaf area and internode cross-section, and in some cases of the photosynthetic rate and starch reserves, of the top 3-4 phytomers of the main tiller. This was accompanied by an earlier tillering cessation, that coincided with the initiation of these phytomers, and an enhanced panicle size on the main tiller. Plant leaf area at flowering was not affected by qTSN but fertile tiller number was reduced to an extent that depended on the environment. Accordingly, plant grain production was enhanced by qTSN only under shading in the greenhouse experiment, where panicle number was not affected and photosynthesis and starch storage in internodes was enhanced. The effect of qTSN on rice phenotype was thus expressed before panicle initiation (PI). Whether early tillering reduction or organ oversizing at meristem level is affected first cannot be entirely unraveled. Further studies are needed to better understand any signal involved in this early regulation and the qTSN × Environment interactions underlying its agronomic interest.

In flowering plants, fruit morphogenesis is a distinct process following fertilization resulting in the formation of a specialized organ associated with seeds. Despite large variations in types and shapes among species, fleshy fruits share common characteristics to promote seed dispersal by animals such as organ growth and metabolite accumulation to attract animal feeding. The molecular biology of fruit ripening has received considerable attention, but little is known about the determinism of early fruit morphogenesis and why some fruits are fleshy while others lack flesh. We have identified in grapevine (Vitis vinifera) a mutation we have named fleshless berry (flb) that reduces by 20 times the weight of the pericarp at ripening without any effect on fertility or seed size and number. The flb mutation strongly impaired division and differentiation of the most vacuolated cells in the inner mesocarp. The timing of ripening was not altered by the mutation although the accumulation of malic acid in the green stage was noticeably reduced while sucrose content (instead of hexoses) increased during ripening. The mutation segregates as a single dominant locus. These results indicate that the Flb− mutant is suitable material to advance our understanding of the genetic and developmental processes involved in the differentiation of an ovary into a fruit.

International audience; Leaf development is affected by both internal (genetic) and external (environmental) regulatory factors. The aim of this work was to investigate how leaf growth variables are related to one another in a range of environments. The leaf growth variables of wild-type Arabidopsis thaliana and leaf development mutants (ang4, ron2-1, elo1, elo2 and elo4) were studied under different incident light treatments (light and shade). The leaves studied were altered in various leaf development variables, such as the duration of expansion, relative and absolute expansion rates, epidermal cell size, epidermal cell number and initiation rate. Final leaf area was correlated to maximal absolute leaf expansion rate and cell number, but not to duration of leaf expansion or cell size. These relationships were common to all studied genotypes and light conditions, suggesting that leaf size is determined early in development. In addition, the early variables involved in leaf development were correlated to one another, and initial relative expansion rate was negatively correlated to the duration of expansion. These relationships between the leaf development variables were used to construct a conceptual model of leaf size control.

International audience; Background and Aims To improve the management of grass communities, early plant development was compared in three species with contrasting growth forms, a caespitose ( Lolium perenne), a rhizomatous (Poa pratensis) and a caespitose-stoloniferous species (Agrostis stolonifera). Methods Isolated seedlings were grown in a glasshouse without trophic constraints for 37 d (761 degrees Cd). The appearance of leaves and their location on tillers were recorded. Leaf appearance rate ( LAR) on the tillers and site-filling were calculated. Tillering was modelled based on the assumption that tiller number increases with the number of leaves produced on the seedling main stem. Above- and below- ground parts were harvested to compare biomass. Key Results Lolium perenne and A. stolonifera expressed similar bunch-type developments. However, root biomass was approx. 30% lower in A. stolonifera than in L. perenne. Poa pratensis was rhizomatous. Nevertheless, the ratio of above-ground : below- ground biomass of P. pratensis was similar to that of L. perenne. LAR was approximately equal to 0.30 leaf d(-1) in L. perenne, and on the main stem and first primary tillers of A. stolonifera. LAR on the other tillers of A. stolonifera was 30% higher than on L. perenne. For P. pratensis, LAR was 30% lower than on L. perenne, but the interval between the appearance of two successive shoots from rhizomes was 30% higher than the interval between two successive leaf stages on the main stem. Above- ground parts of P. pratensis first grew slower than in the other species to the benefit of the rhizomes, whose development enhanced tiller production. Conclusions Lolium perenne had the fastest tiller production at the earliest stages of seedling development. Agrostis stolonifera and P. pratensis compensated almost completely for the delay due to higher LAR on tillers or ramets compared with L. perenne. This study provides a basis for modelling plant development

International audience; The present study shows experimentally that primary growth of the native Patagonian Cupressaceae Austrocedrus chilensis (D. Don) Pic.-Serm et Bizz., Fitzroya cupressoides (Molina) I. M. Johnst. and Pilgerodendron uviferum (D. Don) Florin is potentially continuous. External morphological markers of interannual growth limits have been identified for the main axes of these species after several years of observation. Such limits correspond with axis portions in which internodes are relatively short and leaves have a small distal free end forming an acute angle with the axis. The causality of these results and their utility for studying the productivity, adaptation to different environments, population management and conservation of these threatened species are discussed.

International audience; Plant growth‐promoting bacteria (PGPB) have been reported to stimulate root morphogenesis. To improve our knowledge of the PGPB effect, the early modifications of Brassica napus root system architecture induced by the PGPB Phyllobacterium sp. (29‐15) were analysed. Plants were grown in Petri dishes on a vertical medium supplemented with variable doses of Phyllobacterium sp. in gnotobiotic conditions. Root system elementary variables were measured in a nondestructive manner and the distribution of the bacteria throughout the primary root was quantified. Phyllobacterium sp. in doses from 3 × 107 to 3 × 108 colony‐forming units ml−1 significantly promoted B. napus total root length up to 50% by increasing both lateral root density throughout the primary root and growth rate of mature lateral roots. The primary root was progressively colonized by the bacteria from the tip to the base and the number of colonizing cells was positively correlated with the inoculum density. • Relationships between inoculum density, root colonization and root system architecture emphasized the relevance of this approach to specify PGPB effects on plants.

Chapitre 5; International audience; Even though the repetitive and decentralized nature of plant organogenesis confers a large plasticity to plants, their architecture is highly organized throughout ontogeny and at different scales. Growth, branching and flowering constitute the main processes leading to plant architectures and are key determinants of plant productivity, whatever the target product (biomass, flowers, seeds or fruits). Their genetic and genomic study is thus of great interest for breeding purpose. However, progresses have been limited by many constraints resulting from the large size and long-live of trees and therefore the difficult to assess phenotypes on large numbers of individuals for exploring both the genetic effect or genetic by environment interaction. Despite these limitations, significant advances have been recently obtained in quantitative genetics studies performed on architectural traits in forest and fruit trees, and on the physiological and molecular comprehension of mechanisms underlying plant architectural edification. Moreover, tools and methods for describing plant architectures and for exploring genetic and molecular controls have been improved, leading to new perspectives in terms of high-throughput genotyping, phenotyping and genomic studies. In this chapter, we review the genetic, physiological and molecular analyses that have been performed in the last years on tree architecture, with a particular focus on advances realized on tree crops.

The function of the enzyme butyrylcholinesterase (BChE) in the developing and mature brain is still unclear. We have inserted 577 bp of the 5' upstream region plus 106 bp of the exon 1 of the rabbit BChE gene in reverse orientation under control of an SV40 early promoter derivative in an expression vector. This vector was introduced by calcium phosphate-mediated transfection into embryonic chicken retina cells during the first days of reaggregation culture. Depending on the retinal origin, the transfected cell population forms histotypic retina-like spheres, so-called rosetted or stratified retinospheroids. We show that antisense 5'-BChE gene expression decreased the steady-state mRNA level of BChE and the translation of the BChE protein, inhibited proliferation, and accelerated histogenesis in both cellular systems. The pronounced effects of antisense 5'-BChE transfection of spheroids document a key role of BChE during the early reaggregation process of retinal cells, most likely by regulating their growth and differentiation.

Summary • The ability of fluorescent pseudomonads and glomalean fungi to promote plant growth has been reported many times. However, little is known of their effects on root morphogenesis. Growth and root morphogenesis were compared in tomato ( Lycopersicon esculentum ) plants inoculated or not with a model strain of Pseudomonas fluorescens (A6RI) or with the arbuscular mycorrhizal fungus Glomus mosseae (BEG12). • Plants were cultivated in a sandy-loam soil mixed with sand at two different ratios (2 : 1 and 1 : 2), in gnotobiotic conditions. Plant growth was evaluated by measuring root and shoot fresh weight, and various morphometric parameters were compared. • Growth of control plants was less in the 1 : 2 than in the 2 : 1 soil : sand mixture, and root morphogenesis was also significantly altered by soil:sand mixture. P. fluorescens A6RI promoted plant growth and increased total root length, surface area and volume in the more fertile soil:sand mixture (2 : 1) whereas G. mosseae BEG12 did the same in the less fertile soil : sand mixture (1 : 2). • The relevance of differences between the two types of organisms in relation to the environmental conditions favourable for the expression of their beneficial effects is discussed in the context of microbial inoculation.

Bissuel-Belaygue, C., Cowan, A. A., Marshall, A. H., Wery, J. (2002). Reproductive development of white clover (Trifolium repens L.) is not impaired by a moderate water deficit that reduces vegetative growth. I. Inflorescence, floret and ovule production. Crop Science, 42, (2), 406-414. Sponsorship: INRA/ BBSRC/RAGT company (Rodez, France)/European Union (EC Air 3 CT92-0279).

Chondromodulin-I (ChM-I) is an angiogenesis inhibitor isolated from fetal bovine cartilage. Here, we report the nucleotide sequence of chicken ChM-I cDNA. Chicken mature ChM-I had a significantly larger N-terminal hydrophilic domain than its mammalian counterparts. Chicken embryos expressed multiple transcripts (3.3, 2.0 and 1.7 kb in size) due to the alternative utilization of polyadenylation signals, whereas only the 1.7 kb transcripts were detected in mammals. Although confined to cartilage and eye at a later stage of development, whole-mount in situ hybridization revealed the expression of ChM-I mRNA in somites, heart, bronchial arches, roof plate, retina and limb buds. The expression pattern of the gene suggests a role for ChM-I in the morphogenesis during embryonic development.

cept light was severely reduced so that root growth was finally reduced. Effects on leaf growth, biomass accumulation and root morphogenesis associated with the establishment of Key words: Zea mays L., maize, phosphorus, root, root phosphorus (P) deficiency were studied on maize in morphogenesis. order to test the hypothesis that the root system response can be accounted for by the effect of P

The effects of blue light on the growth and development of different branches were studied to determine if variations in the blue light supply modified the horizontal spread of white clover. Cuttings of white clover (‘Huia’) were grown for 56 d in two controlled chambers under conditions similar except for level of blue light (BL). The horizontal spread of white clover was characterised by the phyllochron, internode length and branching or flowering of different axes. The responses to a reduction in BL were different according to axis degree: (1) on the main axis, lowering BL slightly decreased the phyllochron and had no effect on internode length or stolon length; (2) on older primary branches, it decreased their phyllochron, but reduced stolon length due to a reduction in internode length; (3) on secondary branches, it increased the phyllochron and decreased internode length, triggering a strong reduction in stolon length (up to 54%). Moreover, an increase in BL reversed these effects. The switch to lower BL or higher BL had no effect on internode length of primary branches, but triggered changes in internode length of the main axis. These differential effects of variations in BL on the morphogenesis of different branches are discussed in relation to the clonal integration of variations in light composition. Changes in the horizontal spread of white clover induced by BL could play a role, combined with responses to low red:far-red ratio and low photosynthetic photon flux (PPF) in the strategy of horizontal colonisation and shade-avoidance of white clover.

We have investigated the way in which the radiation absorbed by leaves affects the rate of elongation of maize (Zea mays L.) roots. In five repeated growth chamber experiments, plants previously grown at a photon irradiance of 23 mol m–2 d–1 received either 7 or 34 mol m–2 d–1 from day 10 to day 20 after germination. The elongation rate of primary roots steadily decreased for 4 d after reduction in irradiance and then stabilized at 60% of that in plants at high irradiance. The elongating zone was slightly shorter after 2 d at low irradiance, and was further reduced after 8 d. The concentrations of sucrose and glucose in the elongating zone were greatly decreased after 2 d at low irradiance and the gradient of both sugars was suppressed. The longer period at low irradiance affected neither sugar content nor gradient. In the same way, cell production rate was reduced after 2 d at low irradiance and was not appreciably decreased afterwards. The root zone with cell division was shorter in plants at low irradiance, but cell division rate remained nearly constant temporally and spatially, and was unaffected by the irradiance treatment. Our results suggest that primary events after a reduction in irradiance were a change in cell flux and sugar content in the elongating zone. Change in elongation rate was slower and probably the result of a time-related developmental effect, which may be related to the change in cell production.

All aerial parts of a plant are generated by groups of dividing cells called shoot meristems. These structures determine the arrangement and number of the different organs they produce, and, as a consequence the architecture of the plant largely depends on meristem activity. Extensive morphological studies have led to a model which postulates that shoot meristems are organised into functionally and morphologically distinct zones. According to this model, the centre of the meristem is responsible for cell production and meristem maintenance, whereas the periphery will initiate the organ primordia. Recently, genetic analysis allowed the identification of mutants affected in different functions of the meristem and some of the genes involved have now been identified. Meristem function also depends on the strict coordination of morphogenesis at the cellular level, as illustrated by the highly ordered patterns of cell division, division plane alignment and cell expansion observed in many species. Over the past few years, our understanding of the molecular mechanisms that control cell proliferation and growth has progressed significantly. Therefore, we can now start to unravel the networks that link these basic cellular processes to the regulators that control plant development at the level of the whole meristem.

National audience

Five pasture species, very different in their morphological organization (four dicotyledons: Plantago lanceolata, Sanguisorba minor, Ranunculus repens, Taraxacum officinalis and one grass: Dactylis glomerata), were grown as spaced plants in pots, thus excluding competition for light, to study the proportion of senescent leaves. In May, after a 6 month period, the proportion of partially or totally senescent leaves varied from 20% to 80%. Four plant characteristics were important: leaf appearance and senescence rates, leaf lifespan and date and type of flowering. Plantago lanceolata had the longest lived foliage and the smallest proportion of senescent leaves. In contrast, Taraxacum officinalis had the most rapid leaf turnover and Dactylis glomerata had the slowest rate of leaf appearance. Sanguisorba minor and Ranunculus repens were almost identical, with intermediate leaf characteristics in all respects. These results illustrate the fact that the four characteristics studied, and not simply the species' phenology, must be taken into account in order to compare growth between species. The likelihood of these characteristics remaining the same when species are in dense sward is considered.

Because plant cells do not move and are surrounded by a rigid cell wall, cell division rates and patterns are believed to be directly responsible for generating new structures throughout development. To study the relationship between cell division and morphogenesis, transgenic tobacco and Arabidopsis plants were constructed expressing dominant mutations in a key regulator of the Arabidopsis cell cycle, the Cdc2a kinase. Plants constitutively overproducing the wild-type Cdc2a or the mutant form predicted to accelerate the cell cycle did not exhibit a significantly altered development. In contrast, a mutation expected to arrest the cell cycle abolished cell division when expressed in Arabidopsis, whereas some tobacco plants constitutively producing this mutant protein were recovered. These plants had a reduced histone H1 kinase activity and contained considerably fewer cells. These cells were, however, much larger and underwent normal differentiation. Morphogenesis, histogenesis and developmental timing were unaffected. The results indicate that, in plants, the developmental controls defining shape can act independently from cell division rates.

International audience; Understanding the mechanisms of plant adapta- tion to their habitat can help developing relevant conservation politics, which is a crucial issue for several Coffea species. This comes through an understanding of the links between genetic diversity and architectural plasticity. In this study, we investigated the biomass production and allocation strategies of young Coffea trees for nine African species with different countries of origin, that were submitted to a pruning treatment. It revealed that despite large inter-specific differences, the pruning treatment had no influence on biomass production and allocation for these young trees. We propose a theoretical analysis of this result, based on classical modelling hypotheses.

Background Early vigour (biomass accumulation) is a useful but complex trait in rainfed rice (Oryza sativa L). Little is known on trade-offs with drought tolerance. This study explored the relevance of (sugar) metabolic and morphogenetic traits to describe the genetic diversity of rice early vigour and its phenotypic plasticity under drought conditions. A greenhouse experiment was conducted to characterize on a panel of 43 rice genotypes plant morphogenesis and sugar concentration in expanded (source) and expanding (sink) leaves. Results Across genotypes in control treatment, leaf starch concentration was negatively correlated with organogenetic development rate (DR, defined as leaf appearance rate on main stem). Genotypes with small leaves had high DR and tiller number but low leaf starch concentration. Under drought, vigorous genotypes showed stronger growth reduction. Starch concentration decreased in source leaves, by contrast with soluble sugars and with that observed in sink leaves. Accordingly, genotypes were grouped in three clusters differing in constitutive vigour, starch storage and growth maintenance under drought showing a trade off between constitutive vigour and drought tolerance. Conclusions It was therefore suggested that non structural carbohydrates, particularly starch, were relevant markers of early vigour. Their relevance as markers of growth maintenance under drought needs to be further explored. Results are discussed regarding novel process based traits to be introduced in the GRiSP (Global Rice Science Partnership) phenotyping network.

Background: Ergonomic efficiency is in termites maximized by task partitioning among specialized castes. The isopteran caste systems can be classified as either (i) linear, when tasks are performed by pluripotent immatures (pseudergates), retaining the ability to develop into winged imagoes or (ii) bifurcated, with the presence of a true worker caste, which diverges early and permanently from the sexual (nymph/alate) line. Principal Findings: Here, we report on the ontogenetic potentialities of the highly polymorphic sand termite Psammotermes hybostoma. Beside numerous pluripotent pseudergates, constituting the main work force, some larger non-feeding apterous immatures, also occur. These individuals are unable to proceed to the winged imago stage, but store large amounts of fat and also give rise to large soldiers. Soldiers therefore originate from a wide range of apterous instars, consequently being highly polymorphic. Conclusions: The caste system of P. hybostoma is essentially linear, as in other basal Rhinotermitidae, but is distinguished by the late bifurcation leading to large apterous immatures. Because these large worker-like individuals deviate late and do not perform worker tasks, they cannot be considered homologous to the true workers of Termitidae and advanced Rhinotermitidae, but they provide a novel example of the evolution of sterile immatures in termites. © 2012 Bourguignon et al., SCOPUS: ar.j, info:eu-repo/semantics/published

Proper nutrition at first feeding in marine fish larvae is an important factor for successful larval rearing. However, live prey used to feed marine finfish larvae lack essential fatty acids requiring commercial hatcheries to enrich live prey to provide a balanced diet. Currently, the many commercially available enrichments for live prey present considerable differences in their formulas, and compositions of essential nutrients. Since nutritional requirements are species-specific it is necessary to define those enrichments most appropriate for each species in terms of larval development and quality. This study aimed to evaluate the effect of six enrichments on Senegalese sole larval performance including growth, digestive system development and skeletogenesis, to determine whether any of these products are more suitable for Senegalese sole larval rearing. From 8 to 37 days post hatching (dph), larvae were fed Artemia nauplii previously enriched with six different formulae: Easy Selco© (INVE, ES), Easy Selco© (INVE) half diluted with olive oil (ES/2), Multigain© (BioMar, MG), Red Pepper© (Bernaqua, RP), Aquagrow Gold© (ABN, AGG) and Aquagrow DHA© (ABN, AGD), with the last two being diluted by a third with olive oil. The dietary treatments significantly affected larval growth and performance; larvae fed Artemia enriched with AGG presented significantly higher final dry weight (2.0 ± 0.4 mg), growth and intestinal maturation than larvae fed ES-enriched Artemia (final dry weight: 1.1 ± 0.3 mg). Larvae fed the AGG treatment also were those most advanced in metamorphosis and ossification processes. Larvae fed ES/2, RP, AGD and MG treatments presented intermediary values for all these parameters. No significant effect of the dietary treatments was detected in final survival and incidence of skeletal deformities. We conclude that, among the enrichments tested, AGG is the most appropriate for larvae of Senegalese sole. © 2011., This work was funded by the Ministry of Science and Innovation (MICIIN) and the Spanish National Research Council (CSIC) of the Spanish Government (projects AGL2008-03897-C04-01/ACU, AGL2008-03897-C04-04/ACU and PIF-200930I128). M.J. Darias was supported by a Juan de la Cierva post-doctoral contract.

The capacity of preformation and neoformation and the structure of winter buds are vegetative attributes that may vary between plant species and according to ontogenetic stages of the same species. The present study describes and evaluates these features for the four tree species of Proteaceae occurring in Patagonia. In particular, it analyzes the structure and development of the distal buds of the trunk and the preformed or neoformed nature of the organs involved. Two of the species, Embothrium coccineum and Lomatia hirsuta, have scaly buds, in which primordia of green leaves are covered by cataphylls. The shoots of both species may include neoformed organs, more frequently so in juvenile trees. Lomatia ferruginea and Gevuina avellana have naked buds with a low number of primordia; in juvenile and adult trees of both species trunk shoots are entirely preformed. The structure of buds and shoots suggests two different growth modalities of the axes, which would be related to ecological breadth (narrower in the species with naked buds than in those with scaly buds) and distribution area of these species. The considerable morphological differences between the two Lomatia species studied raise the question whether they ought to be included in the same genus. Fil: Magnin, Noel Amaru. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Grosfeld, Javier Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Barthélémy, Daniel. Institut National de la Recherche Agronomique; Francia Fil: Puntieri, Javier Guido. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

International audience; A controlled environment experiment investigated whether the red: far-red (R:FR) ratio of light at the apical bud of the main stolon could alter plant morphogenesis in clonal cuttings of white clover (Trifolium repens L.) The apical bud included the apical meristem, five to six developing leaf primordia with associated axillary bud primordia and stipules and the first emerged folded leaf until development was greater than 0.3 on the Carlson scale. Three light regimes were imposed on the apical bud by collimating light from R or FR light-emitting diodes so that the R:FR ratio of light incident at the apical bud was set at 0.25, 1.6 or 2.1, without significantly altering photosynthetically active radiation. The effect of these light regimes on white clover seedling growth was also tested. At a low R:FR ratio seedling hypocotyl and cotyledon lengths were significantly longer. However, with the cuttings, the light treatments did not alter node appearance rate or internode length of the main stolon, petiole length, area of leaves or total shoot dry matter. There was one significant photomorphogenetic response in the cuttings, a delay of 0.5 of a phyllochron in the appearance of branches from axillary buds in the low R:FR ratio treatment relative to the other treatments. Where branch appearance was delayed plants had fewer branches. This difference could be ascribed solely to a delay in branch appearance as there were no significant treatment effects on either the initiation of axillary bud primordia within the apical bud, the probability of branching or on the rate of growth of branches after appearance. Because treatment of the apical bud induced only one of the many previously observed responses of white clover to a decrease in the R:FR ratio of light, we conclude that other plant organs must also sense the quality of incident light.

The major problems (bad anchorage, water stress, and root disease) with the cropping of the rubber tree (Hevea brasiliensis) are related to the architecture of its root system. So, the morphogenetic properties of the various roots that emerge during the development of the young seedlings are described to improve our understanding of the dynamics of root system architecture. In this study, the development of the root system of 12 seedlings grown for 40 days in root observation boxes has been recorded on a daily basis and analysed. Additional observations were also made on plants grown in pots or in the field for a 60-day period. This analysis of the sequential differentiation of the root system allowed us to distinguish five different root types according to their spatial and temporal location at emergence: (i) taproot, (ii) early first-order lateral roots, (iii) acropetal first-order lateral roots, (iv) late first-order lateral roots, (v) second-order lateral roots. Large variations and close relationship were found within the growth and branching characteristics on one hand, and within anatomical characteristics on the other (number of xylem poles, external diameter, and stele diameter). These between-type variations were also observed, to a lesser extent, among roots from the same type. The continuity of these development characteristics, which were shown to be acquired early, led us to characterize a morphogenetic gradient. This gradient is a reference scale to understand the morphological plasticity of the root system growing in other mediums. Key words: root system, development, morphogenesis, anatomy, root observation box, Hevea brasiliensis.

Hydrangea macrophylla is a ligneous plant that has attracted the attention of many plant breeders and agronomists for the purpose of enhancing its phenotypic plasticity. However, this plasticity was always exploited empirically. Can this plasticity be assessed by a more scientific approach? In this work, the phenotypic variation is analysed via a description of the different development sequences of the plant and by exposing the plant to different contrasted environments. The architectural unit consists of two morphogenetic units: the Vegetative Unit (VU) and the Vegetative and Floral Unit (VFU). They result in four successive development sequences: an organogenetic phase accompanied by continuous growth (sequence A), floral transformation (sequence B), dormancy (sequence C) and flower bloom (sequence D). Under the effect of environmental factors, the formation of the mixed terminal bud (sequence B) provides a considerable source of spatial variability, whereas the absence or presence of dormancy (sequence C) is responsible for a source of temporal variation. The in-depth description of the architectural unit with its morphological components and the characterisation of the four development sequences provide a necessary scientific basis to identify environmental effects on plant development and for the integrated use of its plasticity.; Hydrangea macrophylla est une plante ligneuse présentant une grande plasticité phénotypique qui a suscité l'intérêt de nombreux sélectionneurs et agronomes. Celle-ci a cependant toujours été exploitée de façon empirique.* Peut-on évaluer cette plasticité par une approche plus scientifique ? Dans ce travail, la variation phénotypique est analysée par une description fine des différentes séquences de développement de la plante et par l'exposition de la plante à des environnements contrastés.* L'unité architecturale est composée de deux unités de morphogenèse : l'Unité Végétative et l'Unité Végétative et Florale. Elles résultent de quatre séquences de développement successives : une phase d'organogenèse accompagnée d'une croissance continue (séquence A), la transformation florale (séquence B), la dormance (séquence C) et l'épanouissement floral (séquence D). Sous l'effet des facteurs environnementaux, la formation du bourgeon mixte terminal (séquence B) offre une source de variabilité spatiale forte alors que l'absence ou la présence d'une dormance (séquence C) est à l'origine d'une source de variation temporelle.* La description fine de l'unité architecturale avec ses composantes morphologiques et la caractérisation des quatre séquences de développement est une base scientifique nécessaire pour identifier et localiser les effets de l'environnement sur le développement de la plante et pour l'exploitation raisonnée de sa plasticité.

International audience; Root system architecture adapts to low nitrogen (N) nutrition. Some adaptations may be mediated by modifications of carbon (C) fluxes. The objective of this study was to test the hypothesis that changes in root system architecture under different N regimes may be accounted for by using simple hypotheses of C allocation within the root system of Arabidopsis thaliana. With that purpose, a model during vegetative growth was developed that predicted the main traits of root system architecture (total root length, lateral root number, and specific root length). Different experimental data sets crossing three C levels and two N homogenous nutrition levels were generated. Parameters were estimated from an experiment carried out under medium C and high N conditions. They were then checked under other CxN conditions. It was found that the model was able to simulate correctly C effects on root architecture in both high and low N nutrition conditions, with the same parameter values. It was concluded that C flux modifications explained the major part of root system adaptation to N supply, even if they were not sufficient to simulate some changes, such as specific root length.

International audience; Light quality and, in particular, its content of blue light is involved in plant functioning and morphogenesis. Blue light variation frequently occurs within a stand as shaded zones are characterized by a simultaneous decrease of PAR and blue light levels which both affect plant functioning, for example, gas exchange. However, little is known about the effects of low blue light itself on gas exchange. The aims of the present study were (i) to characterize stomatal behaviour in Festuca arundinacea leaves through leaf gas exchange measurements in response to a sudden reduction in blue light, and (ii) to test the putative role of Ci on blue light gas exchange responses. An infrared gas analyser (IRGA) was used with light transmission filters to study stomatal conductance (gs), transpiration (Tr), assimilation (A), and intercellular concentration of CO(2) (Ci) responses to blueless PAR (1.80 mu mol m(-2) s(-1)). The results were compared with those obtained under a neutral filter supplying a similar photosynthetic efficiency to the blueless PAR filter. It was shown that the reduction of blue light triggered a drastic and instantaneous decrease of gs by 43.2% and of Tr by 40.0%, but a gradual stomatal reopening began 20 min after the start of the low blue light treatment, thus leading to new steady-states. This new stomatal equilibrium was supposed to be related to Ci. The results were confirmed in more developed plants although they exhibited delayed and less marked responses. It is concluded that stomatal responses to blue light could play a key role in photomorphogenetic mechanisms through their effect on transpiration.

Leaves, which play an essential role in plant photosynthesis, share common features such as being flat structures, but also show an impressive variability in their sizes and shapes. Following its initiation in the meristems, leaf development is patterned along three polarization axes to establish its basic architecture. This process is further complicated in the case of compound leaves with the formation of new growth axes. Growth and differentiation must be properly coordinated to regulate the size and the flatness of the leaf. This review provides an overview of the genetic and molecular regulatory networks underlying leaf development, with an emphasis on leaf polarity and the comparison of simple and compound leaves.

The dermomyotome is a transient epithelial sheet that forms from the dorsal aspect of the somite. The dermomyotome gives rise to a variety of tissues, most importantly myotomal muscle and dermis. Despite the central importance of the dermomyotome in the development of amniotes, the question of its existence in lower vertebrates has been lastingly eluded. The combination of single-cell lineage tracing and gene expression analysis has recently led to the identification in fish of a somitic sub-domain that exhibits structural and functional features of the amniote dermomyotome.

Plant sensitivity to mechanical stimuli is obvious when observing the movements of Mimosa pudica leaflets when they are touched [1] or those of the Venus fly trap [2]. It is now well established that other plants are also sensitive to mechanical stimuli even if they do not exhibit such rapid movements [1]. There is a renewal of interest in mechanical stimuli as very important cues for the control of plant growth [3] and morphogenesis [4,5]. This review focuses on mechanosensing in the case of external mechanical loading and its effect on the growth patterns of plant organs (thigmomorphogenesis). The first part of this paper deals with the responses at the whole plant level and their ecological significance. The second part deals with the perception process, with emphasis on the variable that is perceived by the plant. Knowledge about mechanosensors is not presented in great detail because this area of intensive research has been recently reviewed [6,7]. The third part focuses on transduction, i.e., early responses at the cellular level, and particularly focuses on the importance of the kinetics of loading and the kinetics of cellular responses for the interpretation of experimental results. The fourth part focuses on parameters that regulate the mechanosensing process and points out the importance of quantitative studies. Because thigmomorphogenesis and gravitropism are difficult to disentangle, the review ends with data on gravitropism where mechanosensing is involved. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

16 páginas, 12 figuras, 4 tablas., The effects of different levels of vitamin A (VA) in Senegalese sole larval performance and development were evaluated by means of a dietary dose–response experiment using enriched Artemia metanauplii as a carrier of this micronutrient. Larvae were fed from 6 to 27 days post hatch (dph) with enriched Artemia containing graded levels of total VA (1.3, 2.1, 4.5 and 12.9 µg VA mg− 1 DW). The content of VA in live prey directly affected its accumulation in larvae and early juveniles. Retinyl palmitate accumulated during larval ontogeny, whereas retinol showed the opposite trend, decreasing from hatching until 41 dph and then remaining constant until the end of the study. In metamorphic larvae (10 and 15 dph), VA did not affect the number of thyroid follicles or the intensity of the immunoreactive staining of T3 and T4. However, at older stages of development (post-metamorphic larvae: 20, 30, 41 and 48 dph), VA decreased the number of thyroid follicles but increased their mean size and enhanced T3 and T4 immunoreactive staining. A dietary excess of VA did not affect either larval performance in terms of growth and survival or the maturation of the digestive system. However, the most remarkable impact of this morphogenetic nutrient was detected during skeletal morphogenesis. Dietary VA accelerated the intramembranous ossification of vertebral centrums, which led to the formation of a supranumerary haemal vertebra and a high incidence of fused and compressed vertebrae in fish fed 2.1, 4.5 and 12.9 mg VA mg− 1 DW. In addition, VA also affected those structures from vertebrae and caudal fin formed by chondral ossification, leading to defects in their shape and fusions with adjacent skeletal elements. In particular, the caudal fin was the region most affected by the dietary treatments. In order of importance, the bones with more developmental anomalies were the modified neural and haemal spines, epural, hypurals and parahypural. The impact of systemic factors such as thyroidal hormones in skeletogenesis should not be neglected since present results revealed that an excess of dietary VA affected the levels of T3 and T4, which might have affected bone formation and remodelling, leading to skeletal deformities., This work was funded by the Ministry of Education and Culture (MEC) of the Spanish Government (project AGL2005-02478).

Irradiance elicits a large plasticity in leaf traits, but little is known about the modulation of this plasticity by ontogeny. Interactive effects of relative irradiance and ontogeny were assessed on leaf traits for two tropical rainforest tree species: Dicorynia guianensis Amshoff and Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). Eleven morphological and physiological leaf traits, relative to photosynthetic performance, were measured on saplings at three different architectural development stages (ASD 1, 2 and 3) and used to derive composite traits like photosynthetic N-use efficiency. Measurements were made along a natural irradiance gradient. The effect of ASD was very visible and differed between the two species. For Dicorynia guianensis, only leaf mass-per-area (LMA) significantly increased with ASDs whereas for Tachigali melinonii, almost all traits were affected by ASD: LMA, leaf N content and photosynthetic capacity increased from ASD 1 to ASD 3. Photosynthetic N-use-efficiency was not affected by ASD in any species. Leaf traits were severely modulated by irradiance, whereas the degree of plasticity was very similar among ASDs. Only few interactions were detected between irradiance and ASD, for leaf thickness, carbon content, and the ratio Chl/N in T. melinonii and for photosynthetic capacity in D. guianensis. We conclude that ontogenic development and irradiance-elicited plasticity modulated leaf traits, with almost no interaction, i.e., the degree of irradiance-elicited plasticity was stable across development stages and independent of ontogeny in these two species, at least in the early stages of development assessed here., Les traits foliaires varient fortement avec l'éclairement mais également avec l'ontogenèse. Cependant, l'impact de l'ontogenèse sur la plasticité induite par l'éclairement reste mal connu. Les interactions entre ontogenèse et éclairement relatif ont ainsi été étudiées pour des traits fonctionnels foliaires de deux espèces de forêt tropicale humide de Guyane française : Dicorynia guianensis Amshoff et Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). • Onze traits morphologiques et physiologiques foliaires, relatifs aux capacités photosynthétiques, ont été mesurés sur de jeunes arbres ayant atteint trois stades architecturaux de développement successifs (ASD 1, 2 et 3) et utilisés pour en déduire des traits composites. Les mesures ont été réalisées le long d'un gradient naturel d'éclairement en forêt. • L'impact de stades successifs de développement différait entre espèces. Pour D. guianensis, seule la masse surfacique (LMA) a augmenté significativement avec les stades de développement tandis que pour T. melinonii, presque tous les traits foliaires étaient modulés. Pour cette espèce, LMA, teneur en N et capacité photosynthétique ont augmenté de ASD 1 à ASD 3. Par contre, l'efficience d'utilisation de N par la photosynthèse est restée stable entre ASDs. • Les traits foliaires ont été fortement modifiés par l'éclairement mais le degré de plasticité était similaire entre les ASDs. Des interactions entre ASD et éclairement n'ont été observées que pour l'épaisseur, la teneur en C et le rapport Chl/N de T. melinonii ainsi que pour la capacité photosynthétique de D. guianensis. • En dépit de l'effet significatif de l'ontogénèse sur les traits foliaires, seules de très faibles interactions ont pu être détectées avec l'éclairement pour les deux espèces. On peut en conclure que les stades successifs de développement ne modifient pas le degré de plasticité foliaire en réponse à l'éclairement tout au moins dans le cas des stades jeunes pris en compte ici.

UMR LEPSE - Equipe MAPI; International audience; The grapevine (Vitis vinifera L.) shoot is a complex modular branching system, with one primary axis and many secondary axes organised into a repetitive structure of three successive phytomers (P0-P1-P2). P1-P2 phytomers bear one tendril or cluster, whereas P0 phytomers bear no tendrils or clusters. Axis development displays a high variability, due, partly, to trophic competition. The aim of this study was to estimate changes in trophic competition within the shoot, and to relate plasticity in axis development to changes in trophic competition. 'Grenache N.' and 'Syrah' cultivars were grown with two contrasting levels of cluster load. Organogenesis and organ mass were measured during shoot development. Changes in trophic competition were estimated, using the solver functions of the GreenLab model. Internodes and clusters were strong sinks. They affected the shoot development to the same extent, but the internodes showed an earlier effect. The cessation of development of the secondary axis was affected by trophic competition, but the primary axis continued to develop, regardless of trophic competition. Secondary axes differed in sensitivity to trophic competition as a function of two criteria: their type and their size. The most highly developed axes were less affected than the smaller axes, and secondary axes arising from a P0 phytomer were also less affected than secondary axes arising from a P1 or P2 phytomer.