Is the quantity of orbicules released by Dactylis glomerataand Cynosurus echinatus(Poaceae) big enough to play an allergenic role?

Abstract

Orbicule characteristics of Dactylis glomerataand Cynosurus echinatus(Poaceae) were investigated using light (LM), scanning electron (SEM) and transmission electron microscopy (TEM). Based on SEM micrographs, the number of orbicules per 100 µm2 of the locule wall surface was determined in both dehisced and undehisced anthers and was further compared statistically. A total of 100 pollen grains were examined using SEM in search for orbicules attached to the pollen exine. Orbicules were not found distributed freely in the anther locules. They were attached to the locule wall surface through sporopolleninous fibrils, the orbicule wall being firmly embedded in, and often in continuity with the thin layer of sporopollenin lining each locule. The orbicule density on the locule wall surface of both the dehisced and undehisced anthers did not differ significantly. Only a few orbicules were seen attached to the pollen exine in both species. It is concluded that orbicules are not easily removed from the surface of the locule wall and, consequently, that the number of orbicules emitted from the two grass species is too low to play a significant role in triggering allergic diseases.