INFLUENCE OF INTRAOVULAR RESERVES ON OVULE FATE IN APRICOT (PRUNUS-ARMENIACA L.)

In many plant species with multiovulate ovaries, a considerable reduct ion in the number of ovules takes place. However, the underlying physi ological causes are not clear. In Prunus spp., although flowers presen t two ovules, usually only one seed is produced. We have followed the development and degeneration of the two ovules in apricot (Prunus arme niaca L.) and examined the extent to which carbohydrates within the ov ule might be involved in determining the fate of the ovule. While the primary ovule grows in the days following anthesis, growth of the seco ndary ovule is arrested. Starch distribution along the different ovula r tissues exhibits several changes that are different in the two ovule s. Primary ovule growth is inversely related to starch content and thi s growth takes place independently of pollination since it occurs in t he same way in pollinated and unpollinated flowers. In the secondary o vule, starch disappears simultaneously from all ovular structures and callose is layered at the chalazal end of the nucellus. The size of th e secondary ovule does not change significantly from anthesis to degen eration, and callose starts to accumulate 5 days after anthesis. Likew ise, this process occurs independently of pollination, These results a re discussed in terms of the implications of the starch content of ovu les in fertilization success and ovule fate.