CONICET | Buscador de Institutos y Recursos Humanos

Leaf development can be divided into several processes: i) initiation of primordia, ii) growth by cell proliferation, iii) growth by post-mitotic cell expansion, and iv) senescence. Several reports indicate that reactive oxygen species (ROS) play signaling roles in both the early steps of leaf development, and in leaf senescence, but neither their mechanism(s) of action nor their subcellular source are completely clarified. Noteworthy, the onsets of cell proliferation and senescence represent extreme stages of leaf development with a feature in common, an imperfectly assembled photosynthetic electron transport (PET) chain, which is in the process of formation in the first case and of collapse in the second. Non-functional PET leads to runaway ROS production, and in this sense both early leaf development and senescence resemble the oxidative components of stress physiology and responses. A plastid-targeted flavodoxin (Fld) can increase tolerance to multiple stresses in plants by acting as a general antioxidant specific for chloroplasts. Therefore, Fld-expressing lines can be used as tools to probe the role played by chloroplast-generated ROS in different processes undergone by plants, and to distinguish them from ROS produced in other compartments. In plants grown under controlled conditions, leaves of the Fld transformants showed a decrease in leaf size caused by a repression of cell expansion, whereas cell proliferation was unaffected. Likewise, Fld expression significantly delayed senescence. The ?stay-green? phenotype was reflected by extended preservation of leaf pigments and photosynthetic activity. Taken together, the results indicate that chloroplast-generated ROS are involved in both leaf development and senescence.