séminaire d'agroécologie - lundi 3 novembre

Chlorophyll breakdown and stay-green mutantst l

Stefan Hörtensteiner, Institute of Plant Biology, University of Zurich

Lundi 3 novembre 2008 à 11 heures, salle de conférences de l'INRA

During leaf senescence, chlorophyll is broken down in a multistep pathway to colorless products, which are stored in the vacuole of senescing cells. Key reactions of the pathway are the hydrolysis of the lipophilic phytol moiety of chlorophyll, in order to render breakdown products more water soluble, and porphyrin ring opening, which is responsible for the loss of green color. Chlorophyll breakdown is tightly associated with other processes of senescence such as loss of photosynthetic activity and expression of senescence-related genes. Another key process of senescence is the degradation of proteins, in order to remobilize nitrogen from senescing tissues. Absence of early steps of chlorophyll degradation prevents the release of pigments from chlorophyll binding proteins and their degradation. At the same time other senescence parameters proceed normal in these mutants, thus resulting in non-functional “stay-green” phenotypes. Many such stay-greens mutants have been identified in crop species. In contrast, absence of enzymatic reactions acting later in the pathway, cause the accumulation of free photodynamic chlorophyll breakdown intermediates. As a consequence these mutants exhibit early cell death phenotypes.