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Sporopollenin is a biological polymer found as a major component of the tough outer (exine) walls of plant and pollen grains. It is chemically very stable (one of the most inert among biopolymers) and is usually well preserved in and . The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from (for example) lake sediments to provide useful information to palynology about plant and fungal populations in the past. Sporopollenin has found uses in the field of paleoclimatology as well. Sporopollenin is also found in the cell walls of several taxa of green alga, including Phycopeltis (an ) and Chlorella.
are dispersed by many different environmental factors, such as wind, water or animals. In suitable conditions, the sporopollenin-rich walls of pollen grains and spores can persist in the fossil record for hundreds of millions of years, since sporopollenin is resistant to chemical degradation by organic and inorganic chemicals.
In 2019, thioacidolysis degradation and solid-state NMR was used to determine the molecular structure of Pinus rigida sporopollenin, finding it primarily composed of polyvinyl alcohol units alongside other aliphatic monomers, all crosslinked through a series of acetal linkages. Its complex and heterogeneous chemical structure give some protection from the biodegradative enzymes of bacteria, fungi and animals. Some aromatic structures based on p-Coumaric acid and naringenin were also identified within the sporopollenin polymer. These can absorb ultraviolet light and thus prevent it penetrating further into the spore. This has relevance to the role of pollen and spores in transporting and dispersing the gametes of plants. The DNA of the gametes is readily damaged by the ultraviolet component of daylight. Sporopollenin thus provides some protection from this damage as well as a physically robust container.
Analysis of sporopollenin from the Lycopodiaceae Lycopodium in the late 1980s have shown distinct structural differences from that of flowering plants. In 2020, more detailed analysis of sporopollenin from Lycopodium clavatum provided more structural information. It showed a complete lack of aromatic structures and the presence of a Macrocycle backbone of polyhydroxylated tetraketide-like monomers with pseudo-aromatic 2-pyrone rings. These were crosslinked to a poly(hydroxy acid) chain by ether linkages to form the polymer.
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