Abstract:

Objective: This study aims to analyze the dynamic changes of morphological structure and physiological characteristics of Cinnamomum migao seed embryos during germination to reveal the mechanism of natural regeneration barrier, so as to provide a theoretical basis and technical support for the breeding and application. Method: In this study, the naturally germinating C. migao seeds were used as test materials. The morphological changes of embryo and microscopic changes of cotyledon cells, and physiological changes such as the contents of endogenous hormones and storage substances, and antioxidant enzyme activities in C. migao seeds at four different germination stages of dry seed (GZ, seeds without absorbing water), imbibed seed (XS, absorb water to full imbibition), fissure seed (LK, seed coat fissure after imbibition), and germinated seed (MF, radicle protruding the seed coat after imbibition). Result: At the dry seed stage, there were abundant oil bodies in the cotyledon cells of C. migao seeds. The oil bodies began to be consumed at the stage of XS, decreased significantly at the stage of MF, and subsequently, the oil structure disappeared. With seed germination, starch and lipid gradually degraded to supply energy. There was no significant difference in starch content between the stage XS and stage GZ. The starch content decreased significantly in the stage LK and stage MF, while the fat content decreased rapidly after the seed water absorption stage. On the contrary, the soluble protein content and POD activity significantly increased, while the soluble sugar content first decreased and then increased during the germination process of seeds. MDA content and SOD activity first increased and then decreased, reaching a peak at the stage LK, while CAT activity maintained a stable status after a sharp increase at stage XS. ABA and JA contents showed a decreasing trend, and IAA、GA₃、CTK and BR contents showed an increasing trend during the germination process. At the same time, the ratios of ABA/GA₃ and ABA/IAA significantly decreased, while ETH and SA contents increased significantly at stage LK. From stage GZ to stage MF, starch content was highly significantly negatively correlated with soluble sugar content, and highly significantly positively correlated with fat content. The content of soluble protein was highly significantly positively correlated with the activities of SOD and POD, and significantly positively correlated with CAT activity. ABA content was highly significantly negatively correlated with GA₃, IAA, CTK and BR content, significantly negatively correlated with ETH content, but significantly positively correlated with JA content. Conclusion: Starch and lipid are important storage substances which provide essential material and energy during the germination of C. migao. CAT and SOD play a key role in balancing MDA contents, while POD significantly promotes seed germination. The growth of radicle, hypocotyl and germ is mainly affected by endogenous hormones ETH and SA. The increase of GA₃ content and the decrease of ABA content are the critical to promote the germination of C. migao seeds.

Key words: seed germination, storage substances, endogenous hormone, antioxidant enzymes