DNA synthesis and cytoplasmic differentiation in tapetal cells of normal and cytoplasmically male sterile lines of Petunia hybrida.

A new method is described by which tapetal cells may be isolated from anthers of cytoplasmic male sterile (CMS) and fertile lines of Petunia hybrida. Using a combination of stereometry and Feulgen densitometry it has been possible to chart DNA synthesis and nuclear division with great precision within these cells. Results are presented which show CMS lines both to synthesize far less DNA than the fertiles and also to undergo less cell division. These differences in DNA kinetics and cytokinesis are obvious long before any differences between sterile and fertile lines may be detected in the meiocyte mass. In addition to these difference in nuclear behaviour, the tapetal cells of CMS lines also synthesize far lower levels of rough endoplasmic reticulum than do their fertile counterparts. Again, this difference is evident at a very early stage of anther development when all other cell components, including mitochondria and plastids, appear normal. These data are discussed in terms of the very special differentiation undergone by tapetal cells in angiosperms, and the conclusions drawn are considered in the perspective of current hypotheses proposed to explain the operation of CMS.