POLLEN-STIGMA CAPTURE IS NOT SPECIES DISCRIMINANT WITHIN THE BRASSICACEAE FAMILY

The capture of pollen on the stigma surface is the first stage of inte ractions following the initial contact of the male gametophyte with th e female tissues. In order to analyse pollen adhesion, we used a biome chanical assay based on Archimedes flotation of pollinated pistils to measure the forces necessary to detach pollen populations from stigmas . A considerable homogeneity of early pollen-stigma adhesion in intra- and interspecific situations among the Brassicaceae was observed. On the contrary, pollina tion of Brassica oleracea stigmas by pollen from species of more distantly related families showed a significantly low er level of pollen adhesion. Crosses involving interspecific pollinati ons among the Brassicaceae are not blocked at the stage of pollen capt ure but rather at later stages of pollination such as hydration, germi nation or penetration of the pollen tube into the style. This control is not totally stringent, confirming the potential risk of escape of t ransgenes from cultivated Brassicaceae crops to their allied adventice s through interspecific pollination. (C) Academie des sciences/Elsevie r. Paris.