Y.G. Lu and X.D. Liu

Plant Molecular Breeding Research Center, South China Agriculture University, Guangzhou, China

Many mutants for floral development have been found and intensively studied in higher plants. The most useful information from these studies is from the model plant Arabidopsis thaliana. Rice has a highly specialized floral structure. Each embryo sac has only one egg cell. A spontaneous mutant, polyembryonic rice APIV, was found in which there were more than one egg cells in embryo sac, in some florets. The number of egg cells was different among different embryo sacs. In this poly-egg apparatus embryo sac, three eggs were in majority. They could be further divided into three types, namely, “5-2-1” type (there were three eggs and two synergids in the micropyle end, two polar nuclei above the eggs, and one group of antipodals in the chalazal end (Fig. 1-b and Fig. 2-A), “6-2-0” type (there were three eggs, two synergids, and one group of antipodals in the micropyle end, two polar nuclei above the eggs (Fig. 1-c and Fig. 2-B), and “5-3-0” type (there were three eggs and two synergids in the micropyle end, two polar-nuclei and one group of antipodals above eggs (Fig. l-d and Fig. 2-C), based on the whole structure of embryo sac. Besides the poly-egg apparatus embryo sacs, a new variant embryo sac, referred to as “double set of embryo sac”, was also found in APIV. There were egg cells far from micropylar end in the “double set of embryo sac” (Fig. 1-e and Fig. 2-D). According to the genetic analysis, gametophytic genotypes, rather than sporophytic ones probably controlled the production of poly-eggs. Genetic polymorphism for the structure of embryo sac was found in a single-panicle of APIV. Fertilization and development of the poly-egg apparatus resulted in polyembryony in APIV. It is considered that APIV is a useful material for molecular study of the development of female gametophyte in rice.