Classification and Seed Set of Varied Embryo Sacs of Autotetraploid Rice*

Abstract

Autotetraploid strains which are developed from diploid individuals by colchicine treatments exhibit high variation rates of embryo sacs. Abnormal embryo sacs frequently occur in the spikelets of main panicles and the first tillers 1~2 d before heading, leading to obvious decreases in the degrees of normal embryo sacs among the strains. The varied embryo sacs are classified into four types according to their different structures and origins: Degenerated embryo sac (DES), structure variation (SV), apomixis (Apo) and antipodal cell proliferation (ACP). The DES exhibits small embryo sac or no embryo sac, with the former showing a small sac and the latter showing no sac. The SV includes deletion, duplication and location variation, which suggests the occurrence of the variations of the eight nuclei, seven celled embryo sacs of the Polygonum type. The Apo occurs at very low frequency and includes antipodal embryo and egg embryo. The ACP frequently occurs in autotetraploid rice that leads to the increase in diversity of the embryo sacs and simultaneously influences seed germination. The Pearson’s correlation analysis shows that seed set is contributed by three main parts: normal embryo sac, small embryo sac with normal pattern and embryo sac with antipodal proliferation. These embryo sacs may be highly fertile and account for 72.44%, 15.12%, 12.44% of seed set, respectively. The NES is negatively related to seed set at the P0.01 level and the LV negatively related to seed set at the P0.05 level, which suggests strong stress on seed set by the two types.