Programmed cell death drives male sterility in Opuntia

Male and female flowers in the dioecious Opuntia stenopetala (Cactaceae) initiate development as hermaphrodites, but at maturity only the stamens of the male flowers remain functional. Flores-Rentería et al. use SEM and histological observations to study the cellular events behind anther formation and detect programmed cell death (PCD) in anthers of both male and female flowers, but the patterns differ in time and space. Functionally male individuals develop viable pollen, and normal development involves PCD on each layer of the anther wall, which occurs progressively from the inner to the outer layer. In contrast, functional female individuals abort anthers by premature and spatially displaced PCD. They conclude that PCD could be a widespread mechanism in the determination of functionally dioecious species.