Cytological Evidence of Seed-forming Embryo Development in Polyembryonic Ovules of Facultatively Apomictic Guineagrass (Panicum maximum Jacq.)

抄録

Seven facultatively apomictic accessions of guineagrass (Panicum maximum) were studied cytologically for clarifying the mechanisms of seed-forming embryo development in poly-embryonic ovules. The continuous observations of ovules before and after anthesis under the condition of open-polination, indicate that 1) The first AESIC appeared is located dominantly in micropylar end (Chen and Kozono 1994), and the percentage of mature embryo sacs in micropylar end was higher than that in the other end; 2) The rates of the ovules contained developed embryo sacs in micropylar end at 4-days after anthesis were 33%-91% comparable to 0%-2% of that in the other ends; 3) The embryo of the developed sac in micropylar end, in final, became a seed-forming embryo, and in contrast, the other sacs, were crowded out to chalazal end and degenerated at 10 or more days after anthesis. From the above results, it can be concluded that the AESIC-derived embryo sac in micropylar end, in most of the cases, has temporal dominant in embryo sac mature, and has the positional dominant in fertilization and subsequent development of embryo sac when compared with the sacs in the other end in polyembryonic ovules. We, therefore, suggest that the degrees of sexuality or apomixis can be estimated based on the frequency of sexual and apomictic embryo sacs in the micropylar end by means of embryo sac analysis in present generation, even without progeny test. The other types of embryo sac development were also investigated and discussed.