Abstract
Pollen development in Enkianthus perulatus (Ericaceae, Enkianthoideae) was investigated by transmission electron microscopy. Pollen grains of E. perulatus disperse as monads. The mode of deposition and dissolution of the callose wall and separation of the four microspores derived from each microspore mother cell is similar to that of the genus Orthilia (Ericaceae, Monotropoideae), which produces monad pollen. The primexine matrix was deposited as a fibrillar surface coat on the four microspores within the callose wall. Radially-directed pro-columellae appeared first in the primexine matrix, followed by the pro-tectum and foot layer, and the primexine is differentiated into the tectum, columellae, and foot layer after callose dissolution. In the future apertural region, primexine is absent in the initial colpus region, whereas a thick primexine matrix is formed in the os region. The process of exine and aperture development is similar to that of Orthilia and Pyrola (Ericaceae, Monotropoideae) and Vaccinium (Ericaceae, Vaccinioideae). Except for the apertural region, intine deposition inside the endexine takes place after the first mitosis of microspores. Ubisch bodies were found on the surface of degenerating tapetal layer. We could not observe any trinucleate pollen grains, though previously reported in Enkianthus.
