A comparative light and electron microscopic study of microspore and tapetal development in male fertile and cytoplasmic male sterile oilseed rape (Brassica napus)

Abstract

The cytological development of male cells and the tapetum of male fertile and combined cytoplasmic triazine-resistant cyto-plasmic-genetic male sterile (ctr) lines of B. napus L. was studied using light, scanning electron, and transmission electron microscopy. Development of the cytoplasmic-genetic male sterile anther was similar to the normal anther up to and including meiotic prophase I. After this stage, degeneration of the microspore mother cells occurs within the callose walls, and tetrads of microspores are not formed. These degenerating microspore mother cells appear to develop numerous endoplasmic reticulum derived vesiculated structures, which may be involved in lysis of organelles. Degeneration occurs simultaneously with a proliferation of the tapetum, which eventually fills the anther locule. It is not clear whether the abortion of the microspore mother cells during meiosis stimulates proliferation of the tapetum or whether the proliferating tapetum actually interferes with microspore development thereby causing degeneration. Dilated endoplasmic reticulum cisternae containing crystalline-like deposits, and plastids with osmiophilic bodies, are frequent in cells of the proliferated tapetum of cytoplasmic-genetic male sterile anthers.