Airborne pollen: A brief life

The transfer of pollen, whether it is transported by insects or carried by the wind, from floral anther to recipient stigma is the critical reproductive event among higher plants. In this scenario, the pollen grain functions as a fully constituted life-cycle stage, capable of growth (albeit limited) and delivery of gametes. Pollen is prepared for this role by an intricate developmental process with dual sources of structural elements and chemical constituents, including allergens. The resulting complexity relates, at least in part, to the requirements of an unforgiving recognition process at stigmatic surfaces and of active growth before the achievement of gametic union. Recently, the basic participants in pollen-stigma interactions have been defined, and they provide a striking counterpoint to human histocompatibility concerns. Pollen development offers a useful tableau in terms of which to reexamine forces affecting pollen prevalence and their interactions. Development also provides clues to the sources and significance of more minute bioaerosols now known to carry pollen allergens.