The arrest of development of useless reproductive organs in the unisexual flower of Vitis vinifera ssp silvestris

Sex differentiation of unisexual flowers of monoecious and dioecious species is an interesting problem of developmental biology. At early stages of development the flowers of the great majority of these species are hermaphrodite and the expression of organ identity genes follow the same pattern described for hermaphrodite flowers (Hardenak et al. 1994; Ainsworth et al. 1995). At a crucial moment, however, a particular genetic control, involved in the arrest of development of stamen or pistil, becomes operative. With the aim of understanding this mechanism, which probably involves the programmed death of specific target cells, we are studying the crucial events related to this phenomenon in the dioecious species Vitis vinifera ssp silvestris, the wild grape. Here we describe the development of wild grape male and female flowers, focusing our attention on the moment of transition from hermaphrodite to unisexual development, through SEM analysis and cytological observations. The reconstruction of the morphological events leading to the sex differentiation and the definition of the most important steps are, in fact, a necessary premise to attempt the study of the genetic control of this phenomenon.