Ultrastructural characteristics of pollen development in Vitis vinifera L-(cv. Sangiovese)

Ultrastructural studies on the development of microspores to ripe pollen (c v. Sangiovese) showed that the diploid microsporocyte undergoes meiosis in order to form a tetrad of microspores sticked together by a callose wall. A fter callose digestion, 4 independent microspores were released. With succe ssive growth, the single nucleus of each microspore undergoes an asymmetric al division forming the bicellular pollen grain (vegetative cells containin g the generative cells). Only after pollination and pollen tube growth the two sperms will be formed. The mature pollen of Sangiovese is tricolpate; t he exine is scabrate-verrucate in the equatorial zone and foveolate in the polar region.