<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>