Metabolic reprogramming during leaf senescence is affected by chloroplast redox state modification

ANABELLA F. LODEYRO; MOHAMMAD R. HAJIREZAEI; MARTÍN MAYTA; NÉSTOR CARRILLO

Rosario

Simposio; Second Latin American Metabolic Profiling Symposium; 2016

LAMPS-Network

Senescence is a genetically programmed sequence of biochemical and physiological changes that comprise chloroplast dismantling and degradation of macromolecules such as proteins, nucleic acids and lipids (1) in order to mobilize nutrients from senescing leaves to other parts of the plant, such as younger leaves, developing seeds or storage tissues. Hence, it is vital for plant survival and reproduction. The primary physiological purpose is the recycling of N-containing compounds (e.g. amino acids) and sugars, which mainly derive from chloroplasts (2). Therefore, senescence involves substantial metabolic reprogramming, and metabolite profiling analysis has been used to characterize plants with delayed senescence (3). Transgenic tobacco plants expressing the electron carrier protein flavodoxin (Fld) from Anabaena in their chloroplasts (pfld plants) display a ?stay-green? phenotype in leaves and lower reactive oxygen species accumulation in the organelle during leaf senescence. Under environmental stress conditions, Fld has been shown to preserve central metabolic pathways presumably by acting as an electron donor for critical reactions in the chloroplast (4, 5). To evaluate if a similar role is played during senescence we determined the presence and quantity of several amino acids, soluble sugars, starch and phosphorylated metabolites involved in primary processes in young and senescent leaves from wild-type and transgenic lines. Fld expression in chlororplasts was able to delay the inhibition of central metabolic routes in senescent leaves, as reflected by higher levels of key aminoacids and phosphorylated sugars. Sucrose levels were also higher and starch and monosaccharides were lower in pfld plants. Additionally, several forms of citokinins (CKs) and auxins (two important senescence-related phytohormones) were measured. No differences were observed for auxins in old leaves of all lines. Instead, transgenic pfld lines displayed higher levels of a major active CKs form and lower levels of a major CKs reserve form. Taken together, the results indicate that signals responding to chloroplast redox state modulate the progress of metabolic changes during leaf senescence.