Female gametophyte development in Aristolochia labiata Willd. (Aristolochiaceae)

Piperales are an extremely diverse angiosperm lineage in terms of female gametophyte structure and, as such, an excellent candidate for comparative investigations of developmental evolution. In Piperales, Aristolochiaceae are sister to clades in which several divergent patterns of female gametophyte development are prevalent. Outgroup comparisons and explicit analyses of character evolution demonstrate that Polygonum-type female gametophyte development and structure in Aristolochiaceae appears to represent the plesiomorphic condition from which the divergent ontogenies of Piperales evolved. Here, we present detailed analyses of female gametophyte development in Aristolochia labiata that combine light and confocal microscopy with three-dimensional computer reconstruction. Our reconstructions demonstrate that, at the two-nucleate stage of development, separation of nuclei to opposite poles of the female gametophyte does not appear to be dependent on vacuolar expansion as generally hypothesized. We also found a decrease in antipodal volume following formation of the secondary nucleus. Our data provide a baseline for future efforts to describe developmental modifications responsible for evolutionary transitions in female gametophyte ontogeny throughout Piperales. (C) 2008 The Linnean Society of London.