Embryo sac abortion is one of the major reasons for sterility in indica/japonica hybrids in rice. To clarify the causalmechanism of embryo sac abortion, we studied the female gametophyte development in two indica/japonica hybrids viaan eosin B staining procedure for embryo sac scanning using confocal laser scanning microscope. Different types ofabnormalities occurred during megasporogenesis and megagametogenesis were demonstrated. The earliest abnormalitywas observed in the megasporocyte. A lot of the chalazal-most megaspores were degenerated before the mono-nucleateembryo sac stage. Disordered positioning of nucleus and abnormal nucellus tissue were characteristics of the abnormalfemale gametes from the mono-nucleate to four-nucleate embryo sac stages. The abnormalities that occurred from theearly stage of the eight-nucleate embryo sac development to the mature embryo sac stage were characterized by smallersizes and wrinkled antipodals. Asynchronous nuclear migration, abnormal positioning of nucleus, and degeneration ofegg apparatus were also found at the eight-nucleate embryo sac stage. The abnormalities that occurred during femalegametophyte development resulted in five major types of abnormal embryo sacs. These abnormal embryo sacs led toabnormal fertilization. Hand pollination using normal pollens on the spikelets during anthesis showed that normal pollenscould not exclude the effect of abnormal embryo sac on seed setting.
Yu-Xiang Zeng Chao-Yue Hu Yong-Gen Lu Jin-Quan Li Xiang-Dong Liu
By using the laser scanning confocal microscope and plastic (Leica 7022 historesin embedding kit) semi-thin sectioningtechnique, comparative studies on the development of endosperm were carried out between autotetraploid and diploid rices. Aboutone third of the ovaries in the autotetraploid showed normal endosperm development as those in the diploid. In these ovaries, one ofthe polar nuclei would fuse with the sperm nucleus, and the primary endosperm nucleus formed and underwent the first division in 4hours after pollination; the anticlinal wall began to grow centripetally between the free nuclei starting from the wall ingrowths of theembryo sac near the micropylar end, and some of the phragmoplasts formed transformed into periclinal walls. In addition, some of thecell wall situated in the middle of the endosperm appeared to originate from phragmoplasts, whereas others seemed to developrandomly without the obvious formation of phragmoplasts. Cellulose began to accumulate in the wall of aleurone cell layer at 6 daysafter pollination. The cellulose wall of the cells of the aleurone cell layer appeared to have completely formed within 7 to 8 days afterpollination. On the other hand, about two thirds of the ovaries in the autotetraploid showed abnormality in endosperm developmentwith various types, such as non-fertilization, abnormal fertilization, endosperm development-delay and non-synchronization in thedevelopment of cellulose wall of cells of the aleurone layer. These abnormalities usually resulted in decreased seed setting inautotetraploid rice.
WANG LanLIU Xiang-dongLU Yong-genFENG Jiu-huanXu Xue-binXu Shi-xiong （S. Y. Zee）
The structures of mature embryo sacs in 13 genetic stock lines of autotetraploid rice (Oryza sativa L.), including indica, japonica and javanica, were studied by using the whole-mount stain-clearing laser scanning confocal microscopy (WCLSM). Among the 13 autotetraploid rice, the majority of ovaries possess normal polygonum-type embryo sacs, while a few ovaries were characterized by abnormal embryo sacs. The abnormalities of embryo sacs could be classified into six categories, i. e. no female germ unit, abnormal polar nuclei, embryo sac degeneration, no egg apparatus, small embryo sac and ‘double set’ of embryo sacs. The frequency of abnormal embryo sac in japonica (26.6%) was higher than that in indica (19.34%). In addition, the major abnormalities in each autotetraploid line varied, suggesting that the abnormalities may be related to the genotypes of the varieties.
Guo Hai-bin FENG Jiu-huan Lu Yong-gen LIU Xiang-dong
