Abstract:

Grown for both its fine timber and medicinal use, Cyclocarya paliurus is a monotypic genus of Juglandaceae, and is an endemic plant to China. However, the seeds remain deeply dormant in natural condition. In order to assess the dormancy mechanism of the seeds, a germination test of both isolated embryos and seeds were conducted with different treatments, and water and gas permeability of the husk, as well as the bioassay and identification of extracts from different seed fractions were measured. The results showed that C. paliurus seed scarcely had embryo dormancy, and the dormancy of the seed was mainly attributed to its pericarp and seed coat. The mechanical and permeability barrier of pericarp and seed coat had a negative effect on germination to a certain extent, but seed dormancy of C. paliurus was mainly due to the inhibitory substances in the pericarp. The bioassay results indicated that the inhibitors were distributed in all the fractions of the seeds, and the inhibition activity was found as the following: pericarp>seed coat>intact seeds>embryo. Methanol extract of the pericarp was further separated by the method of systemic solvents, and a bioassay of the separated fractions showed that the ether phase had the strongest inhibitory effect. Analysis of GC-MS revealed that the maximal component in ether phase of the pericarp was vanillic acid, accounted for 35.09%. The results from this study systematically illustrated the dormancy mechanism of C. paliurus seeds for the first time, and would provide some theoretical bases for breaking the seed dormancy in practice.

Key words: Cyclocarya paliurus, seed dormancy, embryo culture in vitro, permeability of husk, inhibitors