The proposed study is part of an on-going project to determine the cellular basis of cytoplasmic inheritance in alfalfa. This species is one of a few in which there is a predominance of male plastid transmission to the offspring, and for which considerable genetic data are available. Plastid transmission is under genetic control, and genotypes have been characterized as strong,intermediate or weak male or females, according to their plastid transmission frequencies. To date the PI's laboratory has used quantitative, three dimensional ultrastructure, along with a DNA-specific fluorochrome, to analyze generative cells and sperm cells of strong and weak male lines. The first objective of the proposed research is to compare the egg cells of strong and weak females to determine whether egg composition before fertilization is a determining factor in plastid inheritance, as preliminary data suggest. Further studies will analyze fertilized eggs (zygotes) and early embryos in order to follow the specific fates of male and female plastids during these critical stages of embryogenesis. This research will complement other studies utilizing techniques of classical and molecular genetics, and promise to be invaluable for providing cytological explanations for observed patterns of cytoplasmic organelle inheritance in an economically important plant.
