Mechanism of exine rupture in hydrated taxoid type of pollen

Abstract

The taxoid type of pollen has a pore in the exine, plugged by an opercule-like structure, the operculoid, as seen under scanning electron microscope. In light microscopy a bulge at the surface of the exine is evident only when using a fluorochrome (calcofluor). The bulge, which is part of the intine, appears fluorescent in mature pollen grains. In water, it disappears progressively within one to two minutes. It is assumed that the operculoid is ejected because of the swelling of the intine in the apertural region following contact with water. Therefore, the exine aperture constitutes a passage for the water to penetrate towards the whole intine. The mucilagenous substance of the intine is hydrated and dilated and causes the bursting of the exine which is left in the medium. The mode of exine rupture in the pollen of Cupressus arizonica and Juniperus communis was studied and a possible explanation of the function of the apertural structure is proposed.