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Plant responses to soil drying and the metabolic basis of drought-induced limitations in stomatal opening are still being discussed. In this study, we investigate the roles of root-born chemical and hydraulic signals on stomatal regulation in wheat genotypes as affected by soil drought and vapour pressure deficit. Twelve consecutive pot experiments were carried out in a glasshouse. Two bread wheat cultivars (Gonen and Basribey) were subjected to drought under high and low vapour pressure deficit (VPD) in a growth chamber. Total dry matter, specific leaf area, xylem ABA content, xylem osmotic potential, xylem pH, root water potential (RWP), stomatal conductance, leaf ABA content and photosynthetic activity were determined daily during 6 days after the onset of treatments (DAT). In the first phase of drought stress, soil drying induced an increase in the xylem ABA with a peak 3 DAT while RWP drastically decreased during the same period. Then the osmotic potential of leaves decreased and leaf ABA content increased 4 DAT. A similar peak was observed for stomatal conductance during the early stress phase, and it became stable and significantly higher than in well-watered conditions especially in high vapour deficit conditions (H-VPD). Furthermore, xylem pH and xylem osmotic potential appeared to be mostly associated with atmospheric moisture content than soil water availability. The results are discussed regarding possible drought adaptation of wheat under different atmospheric humidity., Turkiye Bilimsel ve Teknolojik Arastirma Kurumu [2214]; Universitat Hohenheim, Turkiye Bilimsel ve Teknolojik Arastirma Kurumu, Grant/Award Number: 2214; Universitat Hohenheim

The development of more sustainable remediation techniques has been receiving greater attention, as an alternative to soil excavation plan in urban gardens. An in situ phytoextraction experiment with buckwheat (Fagopyrum esculentum) was performed with a 5 mmol kg−1 citric acid (CA) application. Joint experiments under laboratory conditions were conducted using various cultivars of F. esculentum in two soils with a Pb contamination of either geogenic or anthropogenic origin and various chelate concentrations. Results show that a minimum dose of 50 mmol kg−1 of CA is required to lower soil pH and raise the concentration of mobile Pb–CaCl2 for both soils. Consequently, Pb shoot uptake is increased from 6.3 to 8.9 times depending on soil type. Phytoextraction efficiency is found to be 1.3 to 2.0 times higher in the anthropogenic contaminated soil than in the soil with geogenic Pb. A scale effect has also been identified since Pb root accumulation under laboratory conditions was 2.4 times higher than in the field experiment. Despite an increase in the Pb extraction rate with CA, buckwheat appears to lack the efficiency needed to remove Pb in moderately contaminated soils. The calculated remediation period would last 166 years to remove the mobile Pb fraction.

Inflorescences in the Asteraceae plant family, flower heads, or capitula, mimic single flowers but are highly compressed structures composed of multiple flowers. This transference of a flower-like appearance into an inflorescence level is considered as the key innovation for the rapid tribal radiation of Asteraceae. Recent molecular data indicate that Asteraceae flower heads resemble single flowers not only morphologically but also at molecular level. We summarize this data giving examples of how rewiring of conserved floral regulators have led to evolution of morphological innovations in Asteraceae. Functional diversification of the highly conserved flower meristem identity regulator LEAFY has shown a major role in the evolution of the capitulum architecture. Furthermore, gene duplication and subsequent sub-and neofunctionalization of SEPALLATA and CYCLOIDEA-like genes in Asteraceae have been shown to contribute to meristem determinacy, as well as flower type differentiation-key traits that specify this large family. Future challenge is to integrate genomic, as well as evolutionary developmental studies in a wider selection of Asteraceae species to understand the detailed gene regulatory networks behind the elaborate inflorescence architecture, and to promote our understanding of how changes in regulatory mechanisms shape development.

Orobanche cumana (sunflower broomrape) is an obligatory and non-photosynthetic root parasitic plant that specifically infects the sunflower. It is located in Europe and in Asia, where it can cause yield losses of over 80%. More aggressive races have evolved, mainly around the Black Sea, and broomrape can rapidly spread to new areas. Breeding for resistance seems to be the most efficient and sustainable approach to control broomrape infestation. In our study, we used a population of 101 recombinant inbred lines (RILs), derived from a cross between the two lines HA89 and LR1 (a line derived from an interspecific cross with Helianthus debilis). Rhizotrons, pots and field experiments were used to characterize all RILs for their resistance to O. cumana race F parasitism at three post vascular connection life stages: (i) early attachment of the parasite to the sunflower roots, (ii) young tubercle and (iii) shoot emergence. In addition, RIL resistance to race G at young tubercle development stage was evaluated in pots. The entire population was genotyped, and QTLs were mapped. Different QTLs were identified for each race (F from Spain and G from Turkey) and for the three stages of broomrape development. The results indicate that there are several quantitative resistance mechanisms controlling the infection by O. cumana that can be used in sunflower breeding., Promosol (17, rue du Louvre F-75001 Paris, France) financially supported this work.

International audience; Water de fi cit in fl uences leaf transpiration rate and photosynthetic activity. The genotype-dependent response of the latter has not been assessed in sun fl ower ( Helianthus annuus L.), particularly during the reproductive period when grain fi lling and lipogenesis depend greatly on photosynthate availability. To evaluate genotypic responses to water de fi cit before and after fl owering, two greenhouse experiments were performed. Four genotypes two inbred lines (PSC8, XRQ) and two cultivars (Inedi, Melody) were subjected to progressive water de fi cit. Non-linear regression was used to calculate the soil water de fi cit threshold (FTSWt) at which processes (transpiration and photosynthetic activity) were affected by water de fi cit. In the vegetative growth stage, photosynthetic activity was affected at a lower mean value of FTSWt (0.39) than transpiration (0.55). However, in the reproductive stage, photosynthetic activity was more sensitive to soil water de fi cit (FTSWt = 0.45). We found a signi fi cant ( P = 0.02) effect of plant growth stage on the difference between photosynthesis and transpiration rate thresholds and, a signi fi cant ( P = 0.03) effect of leaf age on transpiration. Such results will improve phenotyping methods and provide paths for integrating genotypic variability into crop models.

Pathogenic, morphological and genetic variation was studied in 35 Plasmopara halstedii(sunflower downy mildew) isolates of different races. Virulence spectrum was analyzed in sunflower hybrids carrying effective Plgenes. Aggressiveness was analyzed in one sunflower inbred line showing a high level of quantitative resistance. There were differences in virulence spectrum for pathogen isolates. Index of aggressiveness was calculated for each isolate and two groups were revealed as more aggressive isolates of 100 and 3xx races, and less aggressive isolates of 7xx races. Significant morphological differences were found in zoosporangia and sporangiophores morphology. Genetic relationships were detected between the pathogen isolates using 12 EST-derived markers. Five multilocus genotypes (MLG) were identified among 35 P. halstedii isolates. Our results did not show a correlation between pathogen variation and both morphological and genetic characteristics. Foi analisada a variação patogênica, morfológica e genética de isolados de 35 Plasmopara halstedii (míldio do girassol) de diferentes genótipos. Investigou-se efetivamente o espetro de virulência em híbridos de girassol com genes de Pl. A agressividade foi analisada num genótipo de girassol, o qual mostrou alto nível de resistência quantitativa. Houve diferenças no espetro de virulência para os isolados patogênicos. O índice de agressividade foi determinado para cada isolado e dois isolados mais agressivos de 100 e 3xx genótipos e isolados menos agressivos de 7xx genótipos foram identificados. Foram encontradas diferenças morfológicas significantes em zoosporangia e na morfologia de esporangióforos. Detectou-se o relacionamento genético entre os isolados do agente patogênico pelos marcadores 12-EST-derivados. Cinco genótipos multilocos foram identificados entre os 35 isolados de P. halstedii. Os resultados não evidenciaram uma correlação entre a variação do agente patogênico e as características morfológicas e genéticas.

Diversity of the level of morphological, pathogenic and genetic characteristics was studied in seven Plasrnopara halstedii (sunflower downy mildew) isolates of seven races namely 100, 300, 304, 314, 710, 704 and 714. All analyses were carried out by using five single zoosporangium isolates per pathogen isolate. Morphological analyses were performed on zoosporangia for P. halstedii single zoosporangium isolates. Aggressiveness criteria were analysed in one sunflower inbred line showing a high level of quantitative resistance. Genetic relationships were detected between the single zoosporangium isolates using 12 EST-derived as SNPs markers. Based on the aggressiveness reaction for the P. halstedii single zoosporangium isolates, there were significant intra and inter-race differences for all criteria studied. Isolates of races 100 and lac were less virulent and more aggressiveness than isolates of races 7xx. There was no relation between morphology of zoosporangia and pathogenic characteristics for 35 single zoosporangium isolates. There was no intra-race genetic variation, but five genetically-identified groups were detected among pathogen isolates of all races. No correlation was detected between EST genotypes on the one hand and both pathogenic traits and morphological characteristics on the other.

The interaction between sunflower plants showing a high level of quantitative resistance and five Plasmopara halstedii (the causal agent of downy mildew) isolates of several races were studied using five single zoosporangium isolates per pathogen isolate. Aggressiveness criteria were analyzed for 25 P. halstedii single zoosporangium isolates. Based on the reaction for the P. halstedii isolates to four sunflower hybrids H1–H4 varying only in their downy mildew resistance genes, there were differences in virulence spectrum in pathogen isolates. Analysis of five single zoosporangium isolates for P. halstedii isolates showed significant variability within pathogen isolate for all aggressiveness criteria but not for all pathogen isolates. The hypothesis explaining the interaction between P. halstedii and its host plant was discussed on the level of pathogenicity.

International audience; Phelipanche ramosa is a major parasitic weed of Brassica napus. The first step in a host-parasitic plant interaction is stimulation of parasite seed germination by compounds released from host roots. However, germination stimulants produced by B. napus have not been identified yet. In this study, we characterized the germination stimulants that accumulate in B. napus roots and are released into the rhizosphere. Eight glucosinolate-breakdown products were identified and quantified in B. napus roots by gas chromatography–mass spectrometry. Two (3-phenylpropanenitrile and 2-phenylethyl isothiocyanate [2-PEITC]) were identified in the B. napus rhizosphere. Among glucosinolate-breakdown products, P. ramosa germination was strongly and specifically triggered by isothiocyanates, indicating that 2-PEITC, in particular, plays a key role in the B. napus–P. ramosa interaction. Known strigolactones were not detected by ultraperformance liquid chromatography–tandem mass spectrometry, and seed of Phelipanche and Orobanche spp. that respond to strigolactones but not to isothiocyanates did not germinate in the rhizosphere of B. napus. Furthermore, both wild-type and strigolactone biosynthesis mutants of Arabidopsis thaliana Atccd7 and Atccd8 induced similar levels of P. ramosa seed germination, suggesting that compounds other than strigolactone function as germination stimulants for P. ramosa in other Brassicaceae spp. Our results open perspectives on the high adaptation potential of root-parasitic plants under host-driven selection pressures.

International audience; Identifying the connections between molecular and physiological processes underlying the diversity of drought stress responses in plants is key for basic and applied science. Drought stress response involves a large number of molecular pathways and subsequent physiological processes. Therefore, it constitutes an archetypical systems biology model. We first inferred a gene-phenotype network exploiting differences in drought responses of eight sunflower (Helianthus annuus) genotypes to two drought stress scenarios. Large transcriptomic data were obtained with the sunflower Affymetrix microarray, comprising 32423 probesets, and were associated to nine morpho-physiological traits (integrated transpired water, leaf transpiration rate, osmotic potential, relative water content, leaf mass per area, carbon isotope discrimination, plant height, number of leaves and collar diameter) using sPLS regression. Overall, we could associate the expression patterns of 1263 probesets to six phenotypic traits and identify if correlations were due to treatment, genotype and/or their interaction. We also identified genes whose expression is affected at moderate and/or intense drought stress together with genes whose expression variation could explain phenotypic and drought tolerance variability among our genetic material. We then used the network model to study phenotypic changes in less tractable agronomical conditions, i.e. sunflower hybrids subjected to different watering regimes in field trials. Mapping this new dataset in the gene-phenotype network allowed us to identify genes whose expression was robustly affected by water deprivation in both controlled and field conditions. The enrichment in genes correlated to relative water content and osmotic potential provides evidence of the importance of these traits in agronomical conditions.

International audience; Understanding what determines the size and composition of fruit, grain and seed in response to the environment and genotype is challenging, as these traits result from several linked processes controlled at different levels of organization, from the subcellular to the crop level, with subtle interactions occurring at or between the levels of organization. Process-based simulation models (PBSMs) implement algorithms to simulate metabolic and biophysical aspects of cell, tissue and organ behaviour. In this review, fruit, grain and seed PBSMs describing the main phases of growth, development and storage metabolism are discussed. From this concurrent work, it is possible to identify generic storage organ processes which can be modelled similarly for fruit, grain and seed. Spatial heterogeneity at the tissue and whole-plant level is found to be a key consideration in modelling the effects of the environment and genotype on fruit, grain and seed end-use value. In the future, PBSMs may well become the main link between studies at the molecular and whole-plant levels. To bridge this phenotype-to-genotype gap, future models need to remain plastic without becoming overparameterized.

[1] Photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are used to constrain global carbon source/sink estimates and partition ecosystem fluxes. Increasingly, the "Keeling plot'' method is being used to determine the carbon isotope composition of ecosystem respiration (delta(13)C(R)) in order to better understand the processes controlling ecosystem isotope discrimination. In this paper we synthesize emergent patterns in delta(13)C(R) by analyzing 146 Keeling plots constructed at 33 sites across North and South America. In order to interpret results from disparate studies, we discuss the assumptions underlying the Keeling plot method and recommend standardized methods for determining delta(13)C(R). These include the use of regression calculations that account for error in the x variable, and constraining estimates of delta(13)C(R) to nighttime periods. We then recalculate delta(13)C(R) uniformly for all sites. We found a high degree of temporal and spatial variability in C-3 ecosystems, with individual observations ranging from -19.0 to -32.6parts per thousand. Mean C-3 ecosystem discrimination was 18.3parts per thousand. Precipitation was a major driver of both temporal and spatial variability of delta(13)C(R), suggesting (1) a large influence of recently fixed carbon on ecosystem respiration and (2) a significant effect of previous climatic effects on delta(13)CR. These results illustrate the importance of water availability as a key control on atmospheric (CO2)-C-13 and highlight the potential of delta(13)C(R) as a useful tool for integrating environmental effects on dynamic canopy and ecosystem processes.