Rarefaction of fossil resources, impact of fuel production and use on global warming, and pollution have led to a search for technologies that generate renewable and environmentally safe alternatives such as biodiesel. At present, two major renewable carbon sources were explored for this purpose, plant and microorganism oil biomass (essentially storage of lipid triacylglycerol, TAG). The main challenges are (1) increase oil content (2) modification of the fatty acid (FA) profile of TAG in these organisms, to better fit requirements for each specific use (for example, chemical uses). Over the last decade, there has been tremendous interest in improving both aspects. In all organisms, storage lipids are packaged into specialized structures called lipid bodies. They contain a core of storage neutral lipids surrounded by a monolayer of phospholipids, and numerous proteins which vary strongly according to the species. In particular, structural hydrophobic proteins stabilize the interface between lipid core and cellular aqueous environment (PAT proteins, apolipoproteins, oleosins). We developed a genetic approach using Saccharomyces cerevisiae to obtain heterologous expression of Arabidopsis thaliana lipid body proteins: oleosin AtS3 or caleosin AtClo1. These transformed yeasts overaccumulated lipid bodies, leading to a specific increase of storage lipids. These lipid bodies harbor a high level of oleosins. These cells or their purified lipid bodies were exposed to the Soleil synchrotron lights to understand the dynamics of lipid storage and carbon fluxes by measuring the biochemical changes on single cells using FTIR microspectroscopy on SMIS beamline to obtain structural data on whole cellular organelle and on oleosins inserted in lipid bodies using Sychrotron Radiation Circular Dichroism (SRCD) on DISCO beamline