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

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.http://www.informaworld.com/10.1080/0017313070144806

Changes in Cell Wall Structure During Rhizoid Formation of Silvetia babingtonii

We examined the ultrastructure of the cell wall and immunolocalization of alginates using specific antibodies against M-rich alginates and MG blocks during rhizoid formation in fucoid zygotes, Silvetia babingtonii. The thallus region of 24-h-old zygotes had a cell wall made of three layers with different fiber distribution. In the 12-h-old zygotes, three layers in the thallus were observed before rhizoid formation, namely the inner, middle, and outer layers. During rhizoid elongation, only the inner layer was apparent close to the rhizoid tip area. Immunoelectron microscopy detected M-rich blocks of alginate on the inner half of the cell wall, irrespective of the number of layers in the thallus and rhizoid regions. The MG blocks were seen to cover a slightly wider area than M-rich alginate blocks. It was suggested that parts of M in mannuronan would be rapidly converted to G, and MG-blocks are generated. Transcriptome analysis was performed using 3 -, 10 -, and 24-h-old zygotes after fertilization to examine the relationship between gene expression and alginate synthesis over time. The expression of two mannuronan C5-epimerase homologs that convert mannuronic acid into guluronic acid in alginates was upregulated or downregulated over the course of the examination