Interactions of pollen-stigma interface in fruit trees: A multiscale analysis of adhesion mechanisms

Inspired by sophisticated adhesion strategies in nature, physicochemical properties of pollen from three widely distributed fruit species (apple, pear, and kiwifruit) are investigated, and an novel adhesion mechanism for fruit tree pollination is proposed. Through simulation and measurement of natural pollination process, adhesion force between pollen and stigma is quantified, with its constituent components deduced theoretically. Herein, composition and hygroscopic capacity of pollenkitt from three species reveal that while van der Waals forces dominate the adhesion between two biological interfaces, the presence of pollenkitt confers an increased binding strength as relative humidity rises. At the microscale, pollen surfaces are characterized, and biological model between pollen surface microstructure and stigma papillae is investigated to reproduce the natural pollination adhesion system. Following the discovery of strikingly similar ridge structures in two Rosaceae pollen species and dense microprotuberances on kiwifruit pollen, various mechanical models of these microstructures with papillae as well as artificial substrates are established. Furthermore, based on electrostatic properties of pollen, the electrostatically enhanced adhesion effect is explored through theoretical analysis and experimental validation. Collectively, this research elucidates a bioadhesion mechanism underlying fruit tree pollination, providing application potential for research in agricultural science and technology, biomedicine, and ecological environment.