PhD Position on NMR/MRI in agronomy Montpellier/Avignon

PhD project: Combining NMR-MRI developments and modeling approach for the multi-scale integration of plant water and carbon fluxes in response to water and heat stress in tomato

Host laboratories:

BioNanoNMRI (CNRS-UM2 Montpellier) and Plantes et Systèmes de culture Horticoles, INRA Avignon

PhD supervisors: G. Vercambre, N. Bertin (PSH) - C. Goze-Bac (BioNanoMRI) – J-L Verdeil (CIRAD)

                In the context of climate change, plants are prone to repeated periods of abiotic stress, among which thermal and water stresses intensively threaten crop productivity. In such context, plants have to tightly control their water and carbon status throughout growth and development processes, which represent a pivotal response for short- and long-term adaptation to environmental challenges.

                The objective of this thesis is in a first step to validate experimentally an in silico model taking into account the hydric and carbon state from the intracellular level to the whole plant. For this, various multi-scale techniques of NMR and MRI will be implemented for the measurements necessary for the validation and calibration of the model. In a second step a model / experiments approach will characterize the impact of hydric and thermal stresses on the growth of the plant.

                The candidate needs training in ecophysiology and he / she must be willing to commit himself / herself to working with physicists and performing MRI and NMR measurements.

Starting date: before the 1st of January 2017

Location: Montpellier / Avignon

Gross salary: about 1757€

G. Vercambre         gilles.vercambre@inra.fr
N. Bertin                 nadia.bertin@inra.fr
C. Goze-Bac            christophe.goze@umontpellier.fr
J-L Verdeil               jean-luc.verdeil@cirad.fr

Detailed description:

In the context of climate change, plants are prone to repeated periods of abiotic stress, among which thermal and water stresses intensively threaten crop productivity. In such context, plants have to tightly control their water and carbon status throughout growth and development processes, which represent a pivotal response for short- and long-term adaptation to environmental challenges. Multi-scale process-based models are appropriate tools for integrating knowledge from the gene to the plant (Struik et al., 2005), predicting the behavior of complex systems such as plant organs in fluctuating environments (Génard et al., 2007; 2010) and analyzing gene-environment interactions (Bertin et al., 2010). An integrated functional-structural model of tomato plant has been developed in PSH. This model connects the plant architecture, the spatial carbon assimilation and transpirational fluxes, and water and carbon transfers within the plant (Naja et al. 2009). So the model is able to map the local supply of resources and its variation within the plant architecture in response to environmental conditions (temperature, light and humidity) and endogenous parameters (water potential and phloem sap concentration). This model has been recently combined with a fruit model and the integrated model describes the diurnal fluctuations in carbon and water fluxes from the cell to the plant scale (Baldazzi et al. 2013). Until now, the model has not been validated since experimental data are missing, in particular concerning cellular/tissue hydraulic and diffusion properties, spatial and temporal distribution of water and carbon transfers in the plant. Indeed local endogenous resource availability and transport within intact plants are difficult to measure because only a few suitable techniques exist. Yet dedicated Nuclear Magnetic Resonance (NMR) spectroscopy, relaxometry and Imaging (MRI) equipment and methods are now available to study cell water balance, cell-to-cell, phloem and xylem transport in large potted plants (Van As 2007). They offer exciting possibilities for the physiological mapping of whole plants at high spatial and temporal resolution. Moreover recent progress in the development of small-scale portable NMR devices will allow soon routine measurements of xylem and phloem sap flows in intact plants or assessment of dynamic changes in the absolute water content of fruit or leaves. In this context, we propose to combine NMR measurements and integrative modeling of carbon and water fluxes among the tomato plant components in order to explicitly examine many aspects of plant functions in response to environmental stresses. The interactions and dialogue between model and MRI measurements is expected to boost our capacity to integrate and validate both approaches and to go beyond the limits of current approaches in plant ecophysiology

So the PhD student will have to collect data and information to further develop the integrated plant model. He/She will perform new experiments using lab NRM-MRI tools (BionanoMRI groups) and portable systems. He/she will also perform in silico experiments with the model in order to analyze the plant plasticity under an extended range of environmental conditions and to propose crop systems or conditions optimizing yield, quality and environmental issues.

The objectives are to:

  1. Collect data and information on the cellular components of plant tissue hydraulics that will be used to calibrate the model. Objectives are to estimate hydraulic and diffusion properties along the xylem and phloem pathways.
  2. Measure by MRI, water fluxes (and carbon fluxes if allowed by project developments) throughout the plant architecture in response to water and heat stresses thanks to multiple sensors placed at different heights in the plant. Experiments will be performed under controlled environments (climatic chamber). The plant/tissue/organ water and carbon status will be assessed in parallel (same plants or other plants grown under similar conditions), with more common sensors and ecophysiological methods during the experiment (water and osmotic potentials, sap flow, conductance, fluorescence) or after the experiment by destructive measurements (carbon and water allocation among organs).
  3. Include new knowledge in the plant model.

iv)    Perform in silico experiments with the model. This part of the work could be run at the beginning of the project to address key-questions about the determinants of plant response to water and heat stress. And then, at the end of the project, the model will allow analyzing the plant plasticity under a wide of environmental stresses.