Developmental changes in the aperture during pollen grain ontogeny in Olea europaea L.

Changes in both size and form of the structures making up the apertural region, a modified part of the pollen grain wall, were studied during development in Olea europaea L. The very young microspores initially show thickening of the endexine around the apertural zone. This is followed by the appearance of an exinous oncus and subsequently an intinous oncus. The intinous oncus contains tubules derived from evaginations of the plasmalemma. These tubules increase in number and diameter during development.