A comparative study of the seed structure between resynthesized allotetraploid and their diploid parents

Brassicaceae is at the forefront of evolution because of its frequent hybridization. Hybridization is responsible for the induction of widespread genetic and phenotype changes, making it important in agricultural production. In this study, we obtained resynthesized allotetraploid Brassica napus by performing interspecific crossing of B. rapa × B. oleracea combined with embryo rescue. We applied light microscopy and electronic microscopy to analyze the microstructure and ultrastructure of seeds of diploid parents and their allotetraploid progeny. Results showed that pigments in the seed coat were mainly distributed in the palisade layer. B. rapa presented the highest amount of pigment followed by B. napus and B. oleracea. B. napus had the thickest palisade layer followed by B. rapa and B. oleracea. The seed coat microsculpturing in B. rapa and B. napus was characterized as reticulate or reticulate-foveate, whereas that in B. oleracea was observed to be rugose and sulcate. The area index of the protein body was higher in central meristematic cells than in parenchyma cells. By contrast, the area index of the oil body was the lowest in central meristematic cells. Protein bodies were found to be heterogeneous with crystal globoids in two diploid parents and resynthesized allotetraploid progenies. Oil bodies consisted of large and small oil bodies, the sizes of which differed between two parents and allotetraploid progenies. Small oil bodies were spheroid, whereas large oil bodies were ovoid in shape. The quantity of oil bodies indicated that oil bodies were spheroid in two parents, ranging in size from 0.12 to 1.18 μm. In comparison, the size of large oil bodies in allotetraploid progenies exceeds 2.0 μm. These findings suggest that the anatomy of resynthesized allotetraploid seeds remarkably differs from that of two diploid parents, and these differences definitely affect the nutritional components of rapeseeds.