Ultrastructure of Megasporogenesis in Beta vulgaris
栽培甜菜大孢子发生的超微结构

Megasporogenesis of Beta vulgaris (2n=18) is of the Polygonum type. Megasporocytes contain nuclear vacuoles before meiosis and synaptonemal complexes at the early stage of meiosis. Redifferentiation of cytoplasmic components occurs, and callose is deposited in the wall during meiosis. The dyad formed in Meiosis I was wrapped by thick callose. The chalazal cell in the dyad contains many organelles, and mitochondria and plastids showing regular shapes, considered a sign of the end of redifferentiation. The micropylar cell in a dyad always degenerates quickly, and only chalazal one finished meiosis II to form two unequal-sized megaspores . The two unequal-sized megaspores plus a micropylar cell in the dyad formed a triad, and the callose disappeared in the chalazal end of the megaspore cell that developed into a functional megaspore.