Ultrastructure of inoculated anthers in relation to the frequency of induction of pollen callus in anther culture of Oryza sativa L.

Abstract

The formation of pollen callus was induced when rice anthers, which contained microspores in the mid-uninucleate and late-uninucleate stage, were cultured. The ultrastructure of the microspores was also examined in the anthers in vivo. The amount of mitochondria and rough endoplasmic reticulum in the microspores increased and their nuclei and nucleoli enlarged from the early stage to the mid-uninucleate and late-uninucleate stages, resulting in an increase of the cell activities. Morphology of plastids changed from ring-shaped plastids and plastids containing starch grains to ordinary proplastids. Microbodies also appeared in the microspores. Cell organelles in the tapetal cells of the anther wall gradually underwent degenerative changes during this period. After the favorable stage for anther inoculation in vitro, the pollen cells showed the first pollen mitosis and the vegetative cells started to differentiate into mature storage cells which accumulated starch grains. However, the ultrastructure of the tapetal cells did not change significantly during this period. Based on these results, it was suggested that the above-mentioned ultrastructural changes reflected the ability of the rice pollen cells to undergo dedifferentiation in anther culture.