Sporoderm development and substructure in Magnolia sieboldii and other Magnoliaceae: an interpretation

The developmental events in the periplasmic space and the cytoplasm of microspores of Magnolia sieboldii during microspore ontogeny have been traced with transmission electron microscopy in detail and compared to some developmental stages of other members of Magnoliaceae. We show that in mature pollen grains some important features, such as a columellate infratectum and a lamellate endexine, are not evident and highlight the importance of ontogenetic studies for the proper evaluation of exine structure. One of our aims was to find out whether the sequence of sporoderm developmental events represents the sequence of self-assembling micellar mesophases, the initiation of which is genetically controlled. Another aim was to consider substructural models of exine by John Rowley and his other chief ideas, and to analyse how these ideas concur with micellar hypotheses of exine development.