Exine fanzine

The astonishing texture richness found in pollen surface when observed at the microscopic level may resemble the beautiful artwork of a painter or a terrific nightmare. We may think that such diversity parallels the variable morphology and architecture present throughout the plant kingdom. However, recent discoveries identifying some biochemical steps involved in the synthesis and deposition of the compound sporopollenin, the main component of the outer wall of the pollen cell (exine), argue for the presence of a limited number of responsible enzymes highly similar in different species. What is then the molecular origin of such diversity?

If deposition of sporopollenin is roughly identical in non-related organisms, then funny forms are more likely due to previous structural features of pollen plasma membrane, as undulations or the particular distribution of receptor proteins, which are not known up to date.

Exine sporopollenin is one of the most resistant natural products, evolutionarily “designed” to protect reproductive microspores from drought and mechanical damage. In fact, pollen longevity due to the strong exine layer has been employed to support creationists theories, based on fossil pollen grains hypothetically found in geological substrates formed millions of year before the appearance of flower plants (http://creation.com/fossil-pollen-in-grand-canyon-overturns-plant-evolution).

For scientific reading, see: Ariizumi T, Toriyama K. (2011) Genetic regulation of sporopollenin synthesis and pollen exine development. Annu Rev Plant Biol. 62: 437-460.