Cytology and Quantitative Analysis of Aposporous Embryo Sac Development in Guineagrass (Panicum maximum Jacq.).

Abstract

Seven facultatively apomictic accessions and three obligately sexual accessions of guineagrass (Panicum maximum) were studied cytologically and quantitatively for clarifying the mechanisms of appearance of aposporous embryo sac initial cell (AESIC) and apomictic embryo sac formation by using ovary length as an index. The observations of AESIC appearance and their development indicates that most of ovules in apomictic accessions contain several AESICs, and the number of AESICs increased as the ovary grew before anthesis. That is, several AESICs in the same ovule did not differentiate synchronously, but instead, they seemed following a continuous course and appeared one by one during the period from after megasporegenesis to the first AESIC-derived embryo sac maturity. It was also found that the higher the frequency of apospory was, the greater the number of AESICs was, and the longer the duration of AESIC appearance should be. This result will produce the information on sampling of the materials used for the apomixis gene isolation program. The type of embryo sacs in same ovules of apomictic plants were also distinguished and discussed.