Structure and Permeability Characterization of Sinojackia xylocarpa Hu drupe, based on High-field Magnetic Resonance Imaging, Scanning Electron Microscopy, Transmission Electron Microscopy, Paraffin Section Detection
Authors: WU YU , Shen Bao 
Published: February 2020

• Background Sinojackia xylocarpa Hu is the first new genus published by a Chinese botanist, which belongs to the genus Sinojackia Hu of Styracaceae[1]. It is a national key second-class endangered species [2]. It is only distributed in the area near the area of Nanjing city, Jiangsu Province. The wild plants are almost extinct because of the deep dormant habit of seeds and artificial destruction. At present, there are only a few cultivations in botanical gardens in Nanjing, Shanghai and Hangzhou [3]. In addition, the Sinojackia xylocarpa Hu tree has white and lovely flowers, and shaped like hammer fruits, which have very special features and high ornamental value[4] (Fig. 1). Due to the lack of an in-depth understanding of the biological characteristics and dormancy causes of its seeds, the progress of artificial breeding is very slow. Therefore, in order to protect this endangered tree species, it is necessary to carry out research on the dormant mechanism and reproduction of seeds. In this paper, the MRI, SEM, TEM and PSD test methods were used to study the structure and permeability characteristics of the drupe, and explore the mechanical and permeability barriers of peel, seed shell and the contents of endosperm [5, 6]. According to the experimental results, we found important reasons for seed dormancy, and put forward suggestions for how to break the dormancy, in order to provide a theoretical basis for the seed large-scale reproduction of Sinojackia xylocarpa Hu tree.• Result We observed the water channel and distribution through MRI in the imbibition phase, and found that the fruit handle hole and the fruit tip are the main entrance for water to enter the drupe. After entering the drupe, water penetrated into the peel along with the vascular bundle. This illustrated that the exocarp, the mesocarp, and the endocarp are all with good permeability characteristics. The SEM, TEM, and PSD showed that the shell was highly lignified and corky, and there were a large number of high electronic dense substances in the endosperm. This demonstrated that the shell and the endosperm have poor permeability and caused mechanical barriers to seed germination.• Conclusion The peel has good water permeability but has mechanical obstacles. The hard seed shell caused mechanical obstacles, and the permeability is poor. Neither the peeled seeds nor the seeds with partial endosperm germinated, but the embryos germinated normally. It can be speculated that dense seed coats and endosperms with high-fat content may cause mechanical obstacles. And the endosperm has poor water permeability. It can be seen that mechanical barriers and water permeability problems are the main reasons for the dormancy of the Sinojackia xylocarpa Hu drupes. Therefore, it is particularly important to remove mechanical barriers and permeability barriers of the drupes. Next, we will explore how to reduce the mechanical barriers and permeability barriers of the pericarp, seed shell, seed coat, and endosperm by sulfuric acid treatment, and accelerate the process of dormancy release by low-temperature stratification.These main limiting factors of drupe germination will provide a theoretical basis for understanding the root cause of its dormancy, and put forward targeted opinions on the research direction of breaking the dormancy of Sinojackia xylocarpa Hu drupes, and provide a scientific basis for further exploring how to release dormancy and expand seeding and reproduction. It also will have great significance for the phylogenetic of the entire benzoin family.