| Pandey has reported extensively on an unusual genetic phenomenon he called "egg transformation". When compatible pollen was treated with genetically lethal dosage of gamma-radiation (100,000 rad), and used as "mentor pollen" to overcome self-incompatibility of several Nicotiana species, some genetic characters were found to be transferred from the radiation-"killed" pollen to non-hybrid progeny. Observed transformants were fertile, cytogenetically normal, and had maternal phenotypes except for those specific traits transferred from the donors. Heavily irradiated pollen was believed to discharge its radiation-fragmented DNA (chromatin) into the embryo sac and bring about the transformation of the egg. The frequency of gene transfer was reported to be over 50%, and happened for all three characters Pandey studied--self-incompatible specificities, flower color, and pollen color.;The purpose of this research was to determine the validity of Pandey's observations, to elucidate the underlying mechanisms, and to investigate the relevance of "egg transformation" to plant breeding. A comprehensive set of reasonable hypotheses, including different potential transforming mechanisms and selective mechanisms were postulated, and several plant species with different reproductive mechanisms were selected to test these hypotheses. Plant species studied were tomato, pea, apple, rapeseed, and Nicotiana species, including various stocks from Dr. Pandey. Treatments included pollinations with soley irradiated donor pollen, with a mixture of irradiated donor and normal self pollen, with a mixture of normal donor and self pollen, and double pollinations with irradiated donor pollen and normal self pollen, using different time intervals to separate the two pollinations. A total of 6,210 pollinations were made, and 17,522 seedlings representing 87,750 potential transformational events were screened. In no case was an unambiguous transformant recovered. This research was unable to confirm or expand upon the findings of Dr. Pandey, or elucidate the mechanisms underlying such phenomena. Alternative explanations for Pandey's data were postulated. This approach to gene transfer by using irradiated pollen appears to be of little practical use to plant breeders. |
