Abstract: 【Objective】Through the observations of different varieties of walnut seed oil body development processes and the analyses of the mature cotyledon oil body characteristics, we aimed at finding walnut seed oil body synthesis initiation time and location, understanding the relationship between the oil rate and the differences in the cotyledon oil of the seeds of different varieties and deepen the understanding of Xinjiang early fruit walnut seed cell ultrastructure.【Method】The oil content were tested by a fat analyzer. The ultrathin sections of resin embedded seeds were observed by a Transmission Electron Microscope (TEM). 【Result】 Juglans regia ‘Wen185’ and J. regia ‘Xinxin2’seeds were used as materials. The results showed that, in the embryo, the cell can be distinguished from each other and organelles such as vacuole, nucleolus, chloroplast, starch grain, endoplasmic reticulum, and mitochondrion, the Golgi’s body appeared in each cell after 30 days after flowering (DAF). The number of endoplasmic reticulum were increased after 50 DAF. The tip of the double membrane of endoplasmic reticulum began to be inflated and oil bodies were observed after 60 DAF. The number of oil bodies increased gradually until the fruit matured. The number of endoplasmic reticulum decreased after 90 DAF and organelles disappeared after 110 DAF. The period of organelles which were observed in the cotyledon was later than the embryo. In the period of seed maturity, cells consisted of oil bodies and protein bodies in the cotyledon. The sizes and shapes of the oil bodies were different. Most of oil bodies showed an elliptical or irregular shape. The J. regia ‘Wen185’ had more oil content than J. regia ‘Xinxin2’. Also, it was found that the mean size of the oil bodies of the cotyledons for J. regia ‘Wen185’ was significantly different from the oil bodies of the cotyledons for J. regia ‘Xinxin2’. J. regia ‘Wen185’ has less number of oil bodies per cell than J. regia ‘Xinxin2’. J. regia ‘Wen185’ has larger oil bodies than J. regia ‘Xinxin2’. 【Conclusion】These results provide that oil bodies were originated from the endoplasmic reticulum. The period of organelles which were observed in the cotyledon was later than in the embryo. The length and total sum of the areas of the oil bodies correlate well with the oil content of walnut of Juglans regia ‘Wen185’ and J. regia ‘Xinxin2’.

Key words: walnut, seed, embryo, cotyledons, oil bodies formation