Abstract:Studies on the formation of the pre-developed embryo of rice(Oryza sativa L.)rariety(PDER)indicate that PDER is diploid,with chromosome number 2n=24. About 50% of the embryo sacs of this variety can give rise to embryo from unfertilized egg cells.The seeds so formed show higher germination rate and produce more vigorous plants.Some of the megasporocytes do not undergo meiosis but divide mitotically to give rise to diploid embryo sacs indicating that PDER is an apomictic type of plant showing diploid pargthenogenesis(diplospory).The apomictic embryo sacs have the following characteristics:1.The transition period from the archesporial cell to the megaspore mother cell is much prolonged.Thecytoplasm of the archesporial cell and the megaspore mother cell appears less dense in comparison with that of the surrounding nucellus cells.2.After the second mitotic division the megasporocytes give rise to three uniserially arranged cells.Two cells near the micropylar end degenerate.The cell near the chalazal end becomes the functional megaspore.In some embryo sacs all three cells degenerate resulting in the formation of degenerated embryo sacs.3.The functional megaspore divides three more times(mitotically)to give rise to an 8nucleate embryo sac.The 8-nucleate embryo sac produces seven cells similar to those seen in normal(i.e.non-apomictic) embryo sacs.The morphology of the synergids is,however,slightly different.In the apomictic embryo sacs the synergids appear much elongated and they do not tightly surround the egg cell.
