Gynoecium development and the heterotopic shift of stigma in Apocynaceae

Abstract

The Apocynaceae possess a great floral diversity and pollination systems related to extremely elaborate flowers with high degree of synorganization between parts of a same whorl and between different whorls. Comprehending the alterations of the development processes that resulted in this degree of morphological differentiation would help to understand this group's evolution and its phylogenetic relationships. The developmental study creates important data about the floral's morphological diversity through the discovery of key innovations and, in Apocynaceae, many evolutionary trends are related to their flowers. One of the first observed variations is the modification of the stigma position and its function. This occurred prematurely in the group's evolutionary history and can be accessed through the study of basal genera, and for that, this work aims to analyses flowers of two basal genera closely related (Aspidosperma and Tabernaemontana), each one with different position and function of the stigmas. This study will use floral meristems, floral buds in different stages of development and adult flowers through structural and ontogenetic analyses in light microscopy and scanning electron microscopy. In addition, artificial pollinations will be performed to verify the region of pollen tubes penetration in the gynoecium. The results obtained will be compared with the ones in the literature and an evolutionary hypothesis on the stigma heterotopic evolution will be proposed for the group and its consequent establishment in a sub-terminal position in four of their five subfamilies. (AU)