Jeudi 07 avril 2011 – Amphi 206 (Cœur d’Ecole) à 14h00

Louis Grillet

(Doctorant B&PMP-équipe Transport & Signalisation Fer)

Deciphering iron transport into the seed with combined approaches of physiology, genetics, analytical chemistry and imaging

Although Iron is one of the most abundant elements on earth, 1.6 billion people are affected by anemia, a disease caused by Fe deficiency. In most of diets or soils quantity of Fe is sufficient, however the bioavailability is low which is why studying the speciation of Fe  (i.e. its redox status and ligands) is of compulsory importance.
In plants, iron transport and homeostasis has been intensely studied, and the uptake mechanisms by plant roots from soils is known in detail, as well as the induction of those mechanisms by iron deficiency.
However, only little information is available regarding to the speciation, the circulation of iron within plants and eventually the seed loading. The aim of my thesis is to gain an insight into those issues by using combined approaches of analytical chemistry, elemental imaging and molecular physiology.
This study started with the chemical analysis of embryo sac liquid sampled from developing pea seeds. The embryo sac liquid, also known as liquid endosperm, originates from maternal tissues and is delivered to the developing embryo for its nutrition. The chemical analysis revealed that iron was mainly under its oxidized ferric state and bound to citrate and malate in this compartment. In dicot plants, it is well established that iron is transported under its reduced ferrous state by ZIP proteins, and this led us to investigate the presence of a ferric-chelate reductase activity at the embryo surface. This activity was found to be high under both iron-limiting and iron-sufficient treatment, contrasting with the well-known iron-regulated root reductase activity. This result suggested a new model for embryo iron uptake in dicot plants and we are currently studying the importance of this reductase activity for Fe acquisition by the embryo. Candidate genes that fulfill this function are investigated in the model species Arabidopsis thaliana by reverse genetics.
The second part of this study focuses on the subcellular localization of iron in developing pea embryos. Previous work has shown that in cells of pea embryos iron is mainly localized in the nuclei, contrasting with the vacuolar localization described in Arabidopsis embryos. This nuclear localization was confirmed by elemental imaging (PIXE and XRF) and further work is still going on to get an insight on the role of this pool of iron.