Sporopollenin

Sporopollenin is a chemically resistant biopolymer that forms the outer wall, or exine, of pollen grains and many plant spores. It is among the most durable natural polymers, providing protection during dispersal and contributing to the durability of the pollen and spore walls in harsh environments. Sporopollenin also occurs in the walls of some algal spores.

The precise chemical composition of sporopollenin is not fully understood. It is believed to be a heterogeneous, cross-linked polymer derived from a combination of lipid-like and phenolic constituents. The matrix is thought to incorporate long-chain aliphatic units and aromatic residues, linked through various bonds, resulting in a highly resistant, three-dimensional network. This complexity makes definitive structural characterization challenging.

Functionally, sporopollenin serves to shield genetic material from desiccation, UV radiation, chemical attack, and enzymatic degradation. Its robustness helps pollen and spores survive transport through air and water, and it contributes to the distinctive sculpturing of pollen grains observed under microscopy. Its stability also preserves pollen in the geological record, supporting palynology, paleobotany, and studies of plant evolution.

Research on sporopollenin employs techniques such as infrared spectroscopy, solid-state nuclear magnetic resonance, and pyrolysis coupled with chromatography–mass spectrometry to probe its composition and properties. Despite advances, the detailed molecular architecture remains an active area of study due to the polymer’s extreme resilience.