Abstract
Today, understanding how plants respond to water stress is essential to meet the challenge of developing new cultivars and new irrigation strategies, consistent with the maintenance of crop productivity with the evidence of global warming. In this context, the study of plant /water relations is of central interest for modeling plant and organ responses to biotic and abiotic constraints. Paradoxically, there are very few direct and non-invasive methods to quantify and measure the level and the flow of water in plants.For this purpose, we report on the development of an innovative methodology based on low-field Nuclear Magnetic Resonance Relaxometry (NMR). A dedicated NMR device to perform NMR measurements on living plants has been built in a climatic chamber that allows a control and careful modification of environmental parameters during experimentation over reliable periods of time at the laboratory. In parallel, complementary NMR imaging at high magnetic field to study, the anatomy, water content, phloem and xylem transport in sorghum plants were performed. The combination of these approaches allows us to determine innovant eco-physiological biomarkers and to design new experiments in the laboratory and even in the fields.One particular interesting result concertns the investigation of the spatial distribution of water stems (node and inter node) from low field NMR Relaxometry and 3D high resolution MRI images. The modification of the NMR relaxation parameters during dynamic diurnal cycle will be presented in normal and abiotic stress conditions. A direct application permits to extract eco-physiological biomarkers which allows to explore and model water fluxes during water stress and to analyze their impact on the development of sorghum plant. Our ultimate goal is to perform these NMR studies directly in the fields. Thus, a home made portable NMR device, working at 336kHz(8mT) is presented. The development and optimization of the homogeneity of a resistive magnet and Radio Frequency coils, NMR pulse sequences in order to respect the versatility and thermal conditions to maintain the plant intact are described in details. Finally we will present our investigations conducted with this device in the laboratory, in the greenhouses and in sorghum fields.