Developmental stages of the pollen grains in Ash tree (Fraxinus excelsiorL.)

Fraxinus excelsior is a common tree belongs to the Oleaceae family which is commonly found in the vegetation of most areas of Iran, especially Tehran province. According to the reports of allergenicity of olive family and homology between genera and species of this genus and high level of seasonal sensitivity to ash pollens, accurate knowledge of pollens is essential.In this research we investigated the pollen grains developmental characteristics of pure male flowers F. excelsior. The flowers and buds, in different developmental stages, were removed, fixed in FAA70, stored in 70% ethanol, and following dehydration and embedding in paraffin, the specimens were sliced by a rotary microtome. Staining was carried out with PAS and contrasted with Hematoxylin and prepared specimens were studied under a light microscope. Also, to be observed pollen structure was examined by SEM and FESEM electron microscopy.The results indicated that consist of two stamens and anthers were four pollen sacs and pollen tetrads types were tetragonal and cubic. Pollen grains, when shed had three colpes and Striped-mesh ornaments and/or be observed along with orbicules of different sizes on the surface. The pollen grains, in this plant, are spherical in polar view and fusiform in equatorial view; mature pollens are prolate, tricolporoidate with furrows disposed along polar axis. The disposition of the microspore in the tetrads is tetrahedral. The pollen grains are 2-celled when shed. Scrutiny cell and tissue of pollen grains can help in more thorough investigation on applications of aerobiology and identification of pollen allergens.