Developmental differences between male and female flowers in the dioecious plant Silene latifolia

Abstract

In order to identify the earliest visible differences between male and female flowers of the dioecious angiosperm Silene latifolia, the early stages of floral development were compared between male and female plants using scanning electron microscopy and thin section analysis. To simplify the comparison, the development was divided into defined stages from the appearance of the floral meristem to the end of meiosis. Both sexes begin flower development in a common manner resembling the development of hermaphroditic flowers. The first gender-specific differences are seen at stage 5, when the stamen primordia appear in flowers of both sexes. The undifferentiated space left in the center of the floral meristem after the stamen primordia emerge is much smaller in male flowers. Subsequently, the male gynoecium primordium that emerges there at stage 6 forms as an undifferentiated rod much different in appearance from the five carpel primordia formed in female and hermaphroditic flowers at the same stage. Female flowers continue to resemble hermaphrodites until the end of stage 7, when stamen development is arrested after the anthers become distinguishable from the filaments. In contrast to the rudimentary gynoecia of male flowers, which continue to grow throughout flower development, the arrested stamens of female flowers degenerate as the gynoecium matures. Differences in the timing of residual organ arrest support genetic evidence that the developmental program leading to suppression of gynoecium development in male flowers is independent of the program that arrests stamen development in female flowers.