Effects of storage substances and endogenous hormones on seed germination and seedling formation of Quercus variabilis

Objective This paper aims to analyze the germination and emergence characteristics of large, medium and small seeds of Quercus variabilis, and elucidates the physiological mechanisms, by which seed storage substances and endogenous hormones affect its germination and emergence characteristics. From the perspective of seed specifications, the regeneration strategy of Q. variabilis was clarified.

Method The single-seed mass of 5 000 collected seeds was measured, and classified into three size grades, i.e. large (Ⅰ), medium (Ⅱ), and small (Ⅲ). Then they were subjected to artificial climate cultivation in a growth chamber to observe the germination and seedling dynamics. The soluble sugar and starch content, soluble protein content, content of gibberellin (GA₃), abscisic acid (ABA), and indoleacetic acid (IAA) were measured using enzymatic, coomassie brilliant blue G-250 staining, high-performance liquid chromatography (HPLC) methods, respectively. Principal component analysis was used to explore the main factors influencing seed germination and seedling emergence.

Result (1) The number of seeds of Q. variabilis Ⅰ, Ⅱ and Ⅲ accounted for 23.82%, 42.78% and 33.40%, respectively. There were significant differences in the average content of starch, soluble protein, and ABA among three size grades. The average starch content of Ⅰ seeds was 2.02 and 2.37 times of Ⅱ and Ⅲ seeds, the average soluble protein content of Ⅰ seeds was 1.05 and 1.87 times of Ⅱ and Ⅲ seeds, and the ABA content in Ⅰ seeds was 0.86 and 0.60 times of Ⅱ and Ⅲ seeds, respectively. (2) Seed germination and emergence experiment showed that the cumulative germination percents of Ⅰ, Ⅱ and Ⅲ seeds were 91%, 84% and 77%, and the cumulative emergence percents were 90%, 81% and 70%, respectively. The proportion of germination but not emergence accounted for 1%, 3% and 9%, respectively. The days from germination to the end of emergence for Ⅰ, Ⅱ and Ⅲ were 17, 18 and 23 d, respectively. (3) Principal component analysis showed that seed germination and seedling emergence were affected not only by seed reserves, but also by plant hormones, especially the content of ABA and soluble protein.

Conclusion The proportion of large-sized seeds in Q. variabilis is small, with fast germination and emergence rates, while small-sized seeds are the opposite. There is a trade-off between resource allocation and germination characteristics. The differences in germination and emergence of seeds of different sizes are influenced by storage substances and plant hormones. Therefore, when artificially cultivating seedlings, first grading the seeds before sowing can improve the uniformity of the seedlings and reduce the labor cost of picking and grading seedlings.