Functional diversity of style head in Apocynaceae and its implications for pollen dispersal

• Grant number: 23/15463-8
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Effective date (Start): May 01, 2024
• Effective date (End): April 30, 2028
• Field of knowledge: Biological Sciences - Botany - Plant Morphology
• Principal Investigator: Diego Demarco
• Grantee: Danielle Maximo Fonseca e Silva
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Apocynaceae is a family that stands out for having a huge morphological diversity, the most elaborate flowers among the eudicots and the largest number of glands in the same structure, which are involved in the production of compounds related to defense or pollination. Among the floral glands, only two are ubiquitous in the family: laticifers and style head. The style head is an expansion of the style apex covered by a secretory epidermis, formed by postgenital fusion of the apex of the carpels that, in a few genera, corresponds to the stigma. The secretion produced by this gland is related to the transfer of pollen during pollination, being one of the main responsible for the morphological evolution of the group. In derived subfamilies, the style head is differentiated into five secretory zones alternating with the anthers, where different cells from the same secretory tissue produce different secretions that give rise to structures with different composition and shape. Despite its evolutionary importance for the group, we have almost no information about the subcellular diversity of these secretory cells related to the metabolic or functional evolution of this gland in the family. Therefore, new studies are needed to better understand the cellular activities of this secretory tissue. This project aims to comparatively study the structure, ultrastructure and histochemistry of the cells and organelles of this tissue involved in the production of different secretions, relating them to the different functions of the stylet head. Structural analysis will be carried out using light microscopy and material embedded in paraffin. Histochemical and chemical analyses using GC-MS and HPLC will be carried out to detect the main chemical classes of secretion and transmission electron microscopy will be performed to identify the secretory activity of the cells. Considering the functional diversity of the style head in different genera of Apocynaceae, it is expected to find distinct subcellular structures in cells whose function is only to produce a secretion for adhesion and in cells that also serve as a receptive surface. (AU)