Style head in Apocynaceae: a very complex secretory activity performed by one tissue

Area of Science:

• Botany
• Plant Anatomy
• Evolutionary Biology

Background:

• Nuptial glands exhibit diverse forms linked to pollination mechanisms.
• Flower complexity increases with pollen transfer specificity.
• Apocynaceae flowers display extreme specificity due to synorganization and floral glands.

Purpose of the Study:

• Investigate the functional complexity of floral glands, particularly in the style head of Apocynaceae.
• Characterize the different types of style heads and their associated secretions.
• Analyze the evolutionary alterations in secretory tissues and pollen dispersal mechanisms.

Main Methods:

• Comparative morphological analysis of floral glands across Apocynaceae.
• Histochemical analysis of secretions from different style head types.
• Examination of pollen aggregation and stigma position in relation to secretory structures.

Main Results:

• Apocynaceae style heads exhibit four types with varying functional complexity.
• Secretions in types I-III are fluid, aiding pollen adherence to pollinators.
• Type IV secretions solidify into a 'translator' apparatus, comprising a rigid core and caudicles for pollinia attachment.

Conclusions:

• The style head in Apocynaceae, especially type IV, demonstrates extreme functional complexity in pollen dispersal.
• Evolutionary adaptations in secretory cells and secretion properties facilitate precise pollen transfer.
• The 'translator' mechanism in type IV represents a highly specialized adaptation for pollination.