Attachment-based mechanisms underlying capture and release of pollen grains

Abstract

Successful insect pollination can be achieved by a sequence of numerous attachment and detachment events at various biological surfaces. However, the quantitative measurements of pollen adhesion on biological surfaces have been poorly studied so far. We performed atomic force microscopy adhesion measurements of pollen on two most important floral parts for Asteraceae in a course of pollination: the stigma and style of Hypochaeris radicata plant . The results indicated distinct adhesive properties of them—the pollen adhesion on stigmatic surfaces drastically increased over prolonged contact time, while the pollen adhesion increase on stylar surfaces was rather restrained. Based on the observation with cryo-scanning electron microscopy, we explained the experimental results by the presence of morphological features in form of flexible stigmatic papillae that may play a crucial role in enhancing both capillary attraction and van der Waals forces. The distinct adhesive properties seemingly originate from the unique adhesive tasks that each of the floral parts requires to achieve successful pollination. The insights into the adhesive interaction between pollen and the floral parts, obtained in the present study, may lead to better understanding of pollination mechanisms, which are strongly related to our food production. Additionally, the novel pollen adhesive mechanisms learned from the stigma of the studied Asteraceae plant can inspire biomimetic designs of spontaneous gripping systems.