L’imagerie RMN est devenue une technique incontournable, pour l’investigation en recherche agronomique. Le fonctionnement et la qualité des fruits dépendent de multiples paramètres physico-chimiques qui découlent des processus physiologiques, dont les dynamiques sont susceptibles d’être observées à différentes échelles. Le fruit est assimilé à un système complexe qui évolue spatialement et temporellement sous le contrôle de mécanismes mesurables sur des échelles tissulaire, moléculaire et cellulaire. Une difficulté dans l’étude de ces mécanismes est leur localisation dans l’espace du fruit. Les techniques RMN/IRM étant non invasives, peuvent permettre d’accéder à plusieurs types de variables plus difficilement quantifiables (architecture des tissus, variabilités spatiales de la composition, flux entrants et internes au cours de la croissance du fruit) avec des méthodes destructives classiques. Notre contribution est la mise en œuvre d’outils et de techniques de mesures quantitatives par imagerie RMN capables d’apporter des réponses sur les propriétés physiologiques et morphologiques des produits agronomiques afin d’améliorer leur qualité.

In this paper, we report the synthesis of monodisperses and size controlled (6 and 18 nm) magnetic nanoparticles (NPs), from the pyrolysis of iron oxyhydroxide with oleic acid in high temperature solvents. The SQUID measurements revealed that the iron oxide nanoparticles exhibit a superparamagnetic behavior at room temperature. In order to evaluate the potential application of these NPs in Nuclear Magnetic Resonance (NMR) imaging, we investigated using 1 H NMR spectroscopy the modifications of T1 and T2 relaxation times at a magnetic field (4.7 Tesla) for different concentrations of NPs. The following transverse (r2 ) and longitudi- nal (r1 ) relaxivities were found : (r2 = 17.85 mM −1 s−1 , r1 = 6.90 mM −1 s−1 ) and (r2 = 9.20 mM −1 s−1 , r1 = 4.30 mM −1 s−1 ) for a nanoparticle size 18 and 6 nm, respectively. These results confirm that these magnetic NPs present a high con- trast enhancement capacity and have both high r1 and r2 relaxivities responsible for positive or negative enhancement properties. This effect increases with the nanoparticle size. We also developped a new recognition motif (coating) of sac- charide type (Rhamnose) for targeting at the tissular and cellular levels biological models (plants) in order to track the flow of the water and saccharide (main drivers of plant growth) in NMR imaging. Moreover, we demonstrated that this saccahride motif provides a good biocompatibility and biodistribution in physiological medium.

Understanding the controlling factors of fruit quality development is challenging, because fruit quality is the result of the interplay between physical and physiological processes that are under the control of genes and the environment. Although process-based models have been used to make significant progress in understanding these factors, they to a large extent ignore the shape and internal structure of the fruit. To help investigate effects of fruit shape and internal structure on quality, the aim of this work is to create a 3D virtual fruit model that integrates fruit structure and function with growth governed by environmental inputs. For this purpose, we are creating a modelling pipeline that includes the following steps: creation of a 3D volumetric mesh of the internal and external fruit structure, calculation of the fruit’s physical properties from the resulting mesh, and integration of aspects of fruit physiology into the 3D structure. We have applied this pipeline to study tomato fruit (Solanum lycopersicum) by constructing 3D volumetric meshes from two images of perpendicular fruit slices and from MRI data, and integrating water and carbon transport processes into one of these meshes. To illustrate the tomato model, we performed a simulation of one season’s of the fruit’s growth, and compared the results with an already published process-based tomato fruit model. The results of the two models were in general agreement, but our model provided additional information on the internal properties of the fruit, such as a gradient in sugar concentration. Once the model is calibrated and evaluated, our approach will be suitable for studying the effects of internal fruit heterogeneity and overall shape on fruit quality development.

Two essential functions in determining fruit quality are the transport and accumulation of water and dry matter to various fruit tissues. Since water and carbon are delivered to fruit tissues through a complex vasculature system, the internal fruit structure and pattern of vasculature may have a significant impact on their distribution within the fruit. The aim of this work is to provide methods for generating fruit structure that can be integrated with models of fruit function and used to investigate such effects. To this end, we have developed a modelling pipeline in the OpenAlea platform that involves two steps: (1) generating a 3D volumetric mesh representation of the entire fruit, and (2) generating a complex network of vasculature that is embedded within this mesh. To create the 3D volumetric mesh, we use reconstruction algorithms from the 3D mesh generation package of the Computational Geometry Algorithms Library. To generate the pattern of vasculature within this volumetric mesh, we use an algorithmic approach from PlantScan3D software that was designed to reconstruct tree architecture from laser scanner data. We have applied our modelling pipeline to generate the internal and external geometry of a cherry tomato fruit using Magnetic Resonance Imaging data as input. These kinds of applications of our pipeline demonstrate its ability to create species-specific models of fruit structure with relatively low effort. In another work, the volumetric meshes will be combined with models of function to form integrative computational fruit models, which will help to investigate the effects of fruit structure on quality.

The principle of NMR is based on the detection of the magnetization originating from the spin of atomic nuclei. The spin is polarized by a static magnetic field and excited by radiofrequency pulses (wavelength about one meter), that tilt the axis of the magnetization. When the magnetization returns to equilibrium, with a classical receiving antenna, we detect the electromagnetic field. This contribution, we propose the use of a micrometer-sized probe positioned in the vicinity of the object of interest, at a distance shorter than the wavelength of the radiated NMR signal. Our microprobe presents innovative characteristics: a capacitive coupling (electric field component) and reduced dimensions for an accurate positioning, which ensure the detection of NMR signal from the sample.

Le principe de la RMN/IRM est basé sur la détection du spin d’un noyau atomique par exemple le 13C, 31P et le proton 1H soumis à des impulsions radiofréquences. Le signal RMN (champ magnétique) est détecté par une antenne de réception (bobine) via un couplage inductif. Dans notre cas, nous utilisons une sonde de taille micrométrique que nous positionnons à une distance sublongueur d’onde de l’objet. Nous sommes donc en champ proche et donc dans les conditions de détection des ondes évanescentes. Notre dispositif nouveau dans la RMN/IRM collecte du champ proche électrique à travers un couplage capacitif et non inductif comme cela se fait classiquement. Ce système a une détection localisée au voisinage de sa pointe.