Transmitting tissues in Apocynaceae: structural and evolutionary aspects of the pollen tube guidance

• Grant number: 24/23299-6
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: June 01, 2025
• End date: April 30, 2029
• Field of knowledge: Biological Sciences - Botany - Plant Morphology
• Principal Investigator: Diego Demarco
• Grantee: Amarylis Lins Torres
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Apocynaceae is a highly diverse family that exhibits the greatest degree of floral synorganisation among eudicots. The high level of morphological complexity in their flowers is largely attributed to numerous connations and adnatations between floral organs, resulting in highly specialised pollination mechanisms. Associated with the diverse modes of pollen dispersal, the gynoecium shows significant variation across different infrageneric groups. A common characteristic of all Apocynaceae is the presence of the style head, an expanded structure at the apex of the gynoecium, formed through postgenital fusion of the styles. However, the structural organisation of the style head and the degree of carpel fusion vary within the family, which impacts the structure and function of the transmitting tissues. These tissues are responsible for guiding and nourishing pollen tubes as they travel from the stigma to the micropyle of the ovules. Studies on transmitting tissues in Apocynaceae are scarce, particularly regarding the ultrastructural aspects of their cells. Therefore, this study aims to analyse the transmitting tissues in the three sections of the gynoecium (stigma, style, and ovary) across different species of Apocynaceae. Six species from various clades, selected based on the distinct morphologies of their gynoecia, will have their floral buds fixed, embedded, and sectioned for structural and histochemical analysis of the transmitting tissues under light microscopy. Additionally, these tissues will be examined ultrastructurally and cytochemically using transmission electron microscopy to investigate the secretion mechanisms of their cells. Micromorphological analyses will also be conducted under scanning electron microscopy to compare the varying gynoecium morphologies with the types of transmitting tissues identified. Through these analyses, this study aims to understand the structure and function of the transmitting tissues and their variations in relation to the evolutionary history of Apocynaceae.