Ultrastructural and electrophoretic analyses of viviparous and normal seeds in hybrid rape (Brassica napus L.)

Hybird rape (Brassica napus L.) "Qinyou 2" and its three-line parents, Shan2A, Shan2B and KenCl, were used for this experiment. Transmission electron microscopic (TEM) analysis of cotyledon cells and electrophoretic analyses of esterase and peroxidase isoenzymes in viviparous and normal seeds were carried out. One unique band of peroxidase (Rm=0.49) was found in viviparous seeds as compared to normal seeds, but no significant differences in esterase isoenzymes were observed between normal and viviparous seeds, suggesting that there were proteins unique to the embryogenesis pathway of normal seeds and others to the germinative pathway of viviparous seeds. TEM analysis indicated that the size of oil bodies in cotyledon cells of normal seeds was greater than that of viviparous seeds. No significant differences in the size and number of protein bodies were observed between cotyledon cells of normal and viviparous seeds. The size of plastids in cotyledon cells of normal seeds was larger than that of viviparous seeds. The results of TEM analysis also provided strong evidence for previous experiments indicating that seed vivipary resulted in reduced oil content and increased soluble sugar content, while vivipary had no significant effect on protein content in Brassica napus seeds. Therefore, it is suggested that the decrease in viviparous seed yield is mainly responsible for reduction in seed oil content at late development stage.