Demystifying and Unravelling the Factual Molecular Structure of the Biopolymer Sporopollenin

Abstract

<p></p><p>Sporopollenin is a natural, highly cross-linked biopolymer composed of carbon, hydrogen, and oxygen, which forms the outer wall of pollen grains. Sporopollenin is resilient to chemical degradation.<sup> </sup>Because of this stability, its exact chemical structure and the biochemical pathways involved in its biosynthesis remains a mystery and unresolved.<sup> </sup></p> <p>We have identified and characterized the molecular structure of the clean, intact sporopollenin using soft ionization mass spectrometric and nuclear magnetic resonance techniques. These analyses showed that sporopollenin contained a poly(hydroxyacid) dendrimer-like network, which accounted for the sporopollenin empirical formula. In addition, the identified hydroxy acid monomers contained a beta diketone moiety, which most probably accounts for the known antioxidant activity of sporopollenin. Moreover, our elucidation studies allowed us to identify a unique circular polyhydroxylated tetraketide polymer. This polymer acted as the rigid backbone on which the poly(hydroxyacid) network can be built, forming the scaffold of the spherical sporopollenin exine.</p><br><p></p>

Quantifying the impact of chemicals on stable carbon and oxygen isotope values of raw pollen

“…Raw pollen differ from fossilized pollen, because decomposition of structurally weak pollen wall components and pollen wall coatings leaves only the sporopollenin layer of fossil pollen intact (Loader and Hemming, 2000). Sporopollenin, the main component of a pollen wall, is a highly resistant biopolymer approximately consisting of C 90 H 150 O 33 (Brooks and Shaw, 1978;Loader and Hemming, 2004;Fraser et al, 2014;Li et al, 2019;Mikhael et al, 2019) and the proportion of sporopollenin within raw pollen of different species ranges between 55 and 85% (Nelson, 2012). Additional to sporopollenin, the outer wall of raw pollen contains lipids, proteins and in some cases pollenkitt, whereas the inner pollen wall is composed of pectin, cellulose and hemicellulose (Fan et al, 2019).…”