Observation And Characterization Of Oil Body Biogenesis And Distribution In Brassica Napus L. Ovules After Flowering

Brassica napus L. is an important oil crop in China. Most of the oil from B. napus is stored in oil bodies. In this study, the biogenesis of oil bodies and variations in the gene expression levels of oil body proteins and fatty acid synthesis transcription factors were characterized during embryogenesis using ultrastructural observations and quantitative polymerase chain reaction. When comparing the fluorescence intensities of Nile red staining in embryos at various stages, increasing numbers of oil bodies were observed in B. napus embryos after the globular embryo stage. Oil bodies were observed in early embryos in the embryo itself and in suspensors at 9-11 days after pollination (globular embryo stage) using ultrastructural analyses. There were more oil bodies in embryos at the torpedo-shaped embryo stage than at the heart-shaped embryo stage. In addition, the gene expression levels of oil body proteins, including oleosins, steroleosins, and BnCLO1, but not BnCL03, increased during the heart-shaped embryo stage and these elevated levels were maintained during the subsequent developmental stages. The expression levels of fatty acid synthesis transcription factors (BnLEC1, BnL1L, BnWRI1, and BnFUS3) increased during the early stages and decreased during the later stages, while their peak expression times differed. Expression of BnLEC1 was the first to peak, followed by BnL1L,BnWRI1, and BnFUS3. We characterized oil body formation during the early embryonic development of B. napus, including the first examination of oil bodies in globular embryos. We also documented numerical variation in oil bodies during early embryogenesis, which was consistent with the gene expression levels of oil body proteins and fatty acid synthesis transcription factors.