title: Investigation on cell death in the megagametophyte of Araucaria bidwillii Hook. post-germinated seeds.
abstract: The megagametophyte of the Araucaria bidwillii seed is a storage tissue that surrounds and feeds the embryo. When all its reserves are mobilized, the megagametophyte degenerates as a no longer needed tissue. In this work we present a biochemical and a cytological characterization of the megagametophyte cell death. The TUNEL assay showed progressive DNA fragmentation throughout the post-germinative stages, while DNA electrophoretic analysis highlighted a smear as the predominant pattern of DNA degradation and internucleosomal DNA cleavage only for a minority of cells at late post-germinative stages. Cytological investigations at these stages detected profound changes in the size and morphology of the megagametophyte nuclei. By using in vitro assays, we were able to show a substantial increase in proteolytic activities, including caspase-like protease activities during the megagametophyte degeneration. Among the caspase-like enzymes, caspase 6- and 1-like proteases appeared to be the most active in the megagametophyte with a preference for acidic pH. On the basis of our results, we propose that the major pathway of cell death in the Araucaria bidwillii megagametophyte is necrosis; however, we do not exclude that some cells undergo developmental programmed cell death.
authors.affiliation: Department of Biology, University of Pisa, Via Luca Ghini 5, 56126 Pisa, Italy. scasani@biologia.unipi.it
authors.forename: Simone
authors.initials: S
authors.lastname: Casani
authors.forename: Debora
authors.initials: D
authors.lastname: Fontanini
authors.forename: Antonella
authors.initials: A
authors.lastname: Capocchi
authors.forename: Lara
authors.initials: L
authors.lastname: Lombardi
authors.forename: Luciano
authors.initials: L
authors.lastname: Galleschi