Seed development and oil body dynamics of tree peony

Abstract

This study aims to reveal the developmental process and structure of seeds and oil bodies of tree peony, to provide a scientific basis for the development and utilization of such woody oil plants. In this study, the fruits of P. ostii were selected as the research material to examine the changes during the development of fruits and seeds, the structural changes of the endosperm, embryo, and the seed coat along with the accumulation process of the oil bodies. Besides, using transmission electron microscopy the process of the oil body synthesis was closely observed. The resultant karyotype of the endosperm indicated that the seed changes from liquid to gel and finally becomes solid, filling the entire interior section of the seed at maturity. When the endosperm was in the liquid state, the intracellular oil body was closely attached to the cell membrane. In the gelatinous state, the oil body was concentrated around many small vacuoles, in the matured stage, the endosperm cells were filled with oil bodies, and the number of oil bodies reached the highest number. The oil bodies in the endosperm cells were synthesized in the endoplasmic reticulum. During the gelatinous period of the endosperm cells, the smaller oil bodies had lower electron density when observed under the electron microscope, while the larger ones had a ring-shaped structure with lower electron density, and there were multiple lipid droplets with high electron density aggregated in the central part. In the solid state of the endosperm, the oil body matured into a spheroid with uniform size and electron density. During the shrinkage period of the seed, the number of oil bodies in the endosperm cells decreased along with a decrease in the electron density.