Characterizing the intrinsic parameters, mass, volume and density, of single pollen grains as a base for mechanical analysis of pollen adhesion.

This study combines own experimental data with an extensive literature research to characterize the average single pollen grain mass, volume and density as parameters for future force measurements on pollen. The analysis of pollen grain mechanical properties and adhesion and detachment forces is important to understand the process of pollination in general. However, it requires knowledge of pollen grain mass, volume and density. Despite their importance for research, mass and density have rarely been measured directly, but there is vast data about pollen grain size and shape. Thus, an average value of pollen grain density can provide an estimation of single grain mass for a given volume. However, in this study, we directly measured mass and volume of pollen grains from five anemophilous species by using the weigh-and-count approach and the projected-particle-area approach. This data was used to calculate the density for fresh and dry grains. Furthermore, we combined these results with an extensive literature research to provide a range for the average density of pollen from eudicots, monocots and gymnosperms. We found an uncertainty of up to ± 30% for density calculation, as well as some significant differences between the three plant groups. Methodical details and side effects that can influence pollen grain parameters are discussed. This study is an attempt to extend existing geometrical data about pollen size with the physical parameters, such as mass and density, to provide a background for further biomechanical analysis of pollen grains and pollination process.