Exine development in Stangeria eriopus (Stangeriaceae):: ultrastructure and substructure, sporopollenin accumulation, the equivocal character of the aperture, and stereology of microspore organelles

It has been found that in Stangeria eriopus all the main characters of the ectexine appear within the tetrad period, whereas the lamellated endexine appears at the beginning of the free microspore period. The framework of the exine the plasma membrane glycocalyx - appears first and consists of closely packed cylinder-like units 120-150 nm in diameter, oriented perpendicularly to the microspore plasma membrane. The main character of the glycocalyx framework is its dynamism: the units are capable of building up throughout the period of exine development. Sporopollenin acceptor particles occur distributed alongside the walls of the cylinder-like units, bringing about a corresponding sporopollenin accumulation and the appearance of long-alveolate exine pattern with cylindrical alveolae. The sporal origin of sporopollenin in Stangeria is most probable; the initial accumulation of this polymer apparently occurs in the form of microglobules. Microspores have rather proximal than distal apertures; at the distal pole a pseudosulcus appears in a very unusual way, the whole process looks like an attempt of the formation of the distal aperture. Quantitative data on the dynamics of the volume density, and absolute volume of the cell components of the developing microspores have revealed the degree of organelle participation during the main processes taking place in the cells. They have revealed an important role of the plasma membrane movements, and contribution of the endoplasmic reticulum and Golgi apparatus to the establishment of the sporoderm. (C) 2002 Elsevier Science B.V. All rights reserved.