Chemistry and morphology of dried-up pollen suspension residues



Pollen grains are covered with lots of different biochemical compounds, like proteins, saccharides and lipids, which are only loosely attached to the pollen. Therefore, they can be separated from the pollen by suspending them in water. Since these compounds play a key role in many atmospheric processes (e.g. cloud condensation nucleation, ice nucleation, aerial allergen exposure), their separation and analyzing are of interest.

The chemical composition of whole pollen grains is compared by both Raman and infrared spectroscopy with material that could be extracted from pollen with water. The dominant signals in the pollen grain Raman spectra are those from sporopollenin and carotenoids. These bands decrease in the washing water spectra, since sporopollenin is high molecular and thus is not extractable. The released material shows in turn a chemical composition that differs significantly between species, what is quite expected, since they differ even in the optical properties of their aqueous suspensions. The FTIR spectra show some additional bands to appear in comparison to the Raman spectra.

Furthermore, we investigated the pollen rupturing and material release in the aqueous suspensions by drying them up and picturing the residues with a scanning electron microscope. We saw that corn pollen ejected loads of micrometer-sized organelles, which are most likely starch granules. The more the pollen disrupted, the more the measured samples were covered with an amorphous film, which consists of the extracted pollen material, like lipids, sugars, and proteins – the same substances we detected by spectroscopy. Copyright © 2013 John Wiley & Sons, Ltd.