sporopollenin

SEM image of pollen grains

Sporopollenin is a major component of the tough outer (exine) walls of spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns (see image at right), allowing material recovered from (for example) lake sediments to provide useful information to palynologists about plant and fungal populations in the past.

The chemical composition of sporopollenin is not exactly known, due to its unusual chemical stability and resistance to degradation by enzymes and strong chemical reagents. Analyses have revealed a mixture of biopolymers, containing mainly long chain fatty acids, phenylpropanoids, phenolics and traces of carotenoids. Tracer experiments have shown that phenylalanine is a major precursor, but other carbon sources also contribute. It is likely that sporopollenin derives from several precursors that are chemically cross-linked to form a rigid structure.

Electron microscopy shows that the tapetal cells that surround the developing pollen grain in the anther have a highly active secretory system containing lipophilic globules. These globules are believed to contain sporopollenin precursors. Chemical inhibitors of pollen development and many male sterile mutants have effects on the secretion of these globules by the tapetal cells.

References

• Boavida LC, Becker JD, & Feijó JA. (2005) The making of gametes in higher plants. Int. J. Dev. Biol. 49: 595-614. [1]

• Guilford WJ, Schneider DM, Labovitz J, Opella SJ (1988) High-Resolution Solid-State C-13 NMR-Spectroscopy of Sporopollenins from Different Plant Taxa. Plant Physiology 86 (1): 134-136. [2]