Abstract

Korean Hackberry (Celtis koraiensis Nakai), an ornamental, deciduous tree, lacks species resources, and low germination percentage also prevent the exploitation. Thus it becomes necessary to investage the mechanism of seed dormancy. This research explored the effect of plant hormone and seed coat (endocarp and testa) on seed germination. Endogenous hormone concentration, protein content, total soluble sugars, total starch and amino acids during germination were studied and the germination recorded with different seed coat treatments. Four seed lots were evaluated: (i) fresh; (ii) imbibed; (iii) germinated; (iv) non-germinated seeds. In seeds treated with gibberellic acid (+GA₃), the rate of germination was higher than in untreated (control) seeds. Exogenous GA₃ also promoted the generation of endogenous GA₃, increasing the total bioactive gibberellins (GA) in the embryo during germination relative to the control. Endogenous abscisic acid (ABA) concentration decreased during germination, however, the GA/ABA ratio was consistently higher in germinated than non-germinated seeds. The GA₃ treatment had a significant effect on the GA/ABA ratio. One-trans-zeatin riboside (ZR) and indole-3-acetic acid (IAA) content increased in germinated seeds. From dormancy to germination, the seeds of Korean Hackberry underwent changes in protein content, decreasing in germinated seeds, while concentrations of total soluble sugars and amino acids increased. In addition, germination was higher in seeds with the covering layers removed. The results suggest that germination of Korean Hackberry seeds is controlled by plant hormones and is also affected by the seed coat.

Key words: Abscisic acid, gibberellic acid, germination, indole-3-acetic acid, one-trans-zeatin riboside, storage substances.