26 Feb 2021

26 Feb 2021

Review status: this preprint is currently under review for the journal BG.

Subpollen particles (SPP) of birch as carriers of ice nucleating macromolecules

Julia Burkart1, Jürgen Gratzl1, Teresa M. Seifried2, Paul Bieber2, and Hinrich Grothe2 Julia Burkart et al.
  • 1Faculty of Physics, University of Vienna, 1090 Wien, Austria
  • 2Institute of Materials Chemistry, TU Wien, 1060 Wien, Austria

Abstract. Within the last years pollen grains have gained increasing attention due to their cloud forming potential. Especially the discovery that ice nucleating macromolecules (INM) or subpollen particles (SPP) obtained from pollen grains are able to initiate freezing has stirred up interest in pollen. INM or SPP are much smaller and potentially more numerous than pollen grains and could significantly affect cloud formation in the atmosphere. However, INM and SPP are not clearly distinguished and explanations on how these materials could distribute in the atmosphere are missing. In this study we focus on birch pollen and investigate the relationship between pollen grains, INM and SPP. According to the usage of the term SPP in the medical fields we define SPP as the starch granules contained in pollen grains. We develop an extraction method to generate large quantities of SPP and show that INM are loosley attached to SPP. Further, we find that purified SPP are not ice nucleation active: after several times of washing SPP with ultrapure water the ice nucleation activity completely disappears. To our knowledge this is the first study to investigate the ice nucleation activity of isolated SPP. To study the chemical nature of the INM we use fluorescence spectroscopy. Fluorescence excitation-emission maps indicate a strong signal in the protein range (maximum around λex = 280 nm and λem = 330 nm) that correlates with the ice nucleation activity. In contrast, with purified SPP this signal is lost. We also quantify the protein concentration with the Bradford assay. The protein concentration ranges from 77.4 μg mL−1 (Highly concentrated INM) to below 2.5 μg mL−1 (purified SPP). The results indicate a linkage between ice nucleation activity and protein concentration. Even though purified SPP are not ice nucleation active they could act as carriers of INM and distribute those in the atmosphere.

Julia Burkart et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Reviewer comment on Burkart et al. 2021', Anonymous Referee #1, 03 Apr 2021
    • RC3: 'Reply on RC1', Anonymous Referee #2, 08 Apr 2021
      • AC3: 'Reply on RC3', Julia Burkart, 13 May 2021
    • AC1: 'Reply on RC1', Julia Burkart, 13 May 2021
  • RC2: 'Comment on bg-2021-8', Anonymous Referee #2, 08 Apr 2021

Julia Burkart et al.

Julia Burkart et al.


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Latest update: 29 Jul 2021
Short summary
Extracts of birch pollen grains are known to be ice nucleation active and thus impact cloud formation and climate. In this study we develop an extraction method to separate subpollen particles from ice nucleating macromolecules. For the first time we show that pure subpollen particles are not ice nucleation active. Our results illustrate that the ice nucleating macromolecules can be washed off the subpollen particles and that the ice activity is linked to the presence of proteins.