Abstract:

Objective: In this study, the seasonal variation in particle morphology, membrane fatty acid composition and molecular weight of gutta-percha was investigated, and the correlation between particle morphology, and fatty acid composition and molecular weight of gutta-percha was also analyzed, which would lay a theoretical foundation for further elucidating the biological function of Eucommia ulmoides gum particles and revealing the mechanism of E. ulmoides gum synthesis. Method: The rubber particles from leaves growing on the new branches of 10-year-old E. ulmoides were collected from June to November, and the morphological differences of rubber particles at different growth stages were observed by using light microscope and electron microscope, and the composition and content of fatty acid in rubber particles were also analyzed by gas chromatography-mass spectrometry (GC-MS). Meanwhile, the characteristic parameters of rubber particles were determined by size-exclusive chromatography (SEC). The relationships between the morphology, fatty acid composition of rubber particles, as well as molecular weight and molecular weight distribution of rubber particles were investigated. Result: 1) The results showed that the rubber particles size in E. ulmoides leaves increased gradually with the passage of months (from June to November), and the average diameter was 3.99 μm in June and increased to 6.7 μm in November. The proportion of small rubber particles (d<5 μm) decreased from 65.91% in June to 19.09% in November, while the proportion of large rubber particles (d≥5 μm) increased from 34.09% in June to 80.91% in November. 2) Fatty acid determination showed that 26, 30 and 26 kinds of fatty acids were detected in rubber particles of E. ulmoides leaves in August, October and November, respectively, with 15 saturated fatty acids being the same. The palmitic acid (C16:0) had the highest content, followed by tetracyclonic acid (C24:0). Meanwhile, seven unsaturated fatty acids were found to be unique to the rubber particles of E. ulmoides leaves collected in October, and three unsaturated fatty acids including myristicoleic acid (C14:1), trans-linoleic acid (C18:2n6t) and α-linolenic acid (C18:3n3), were found to be unique to the rubber particles of E. ulmoides leaves collected in August and October. 3) Determination of characteristic parameters of gutta-percha indicated that the molecular weight distribution peaks of gutta-percha in leaves collected in June, July, August, September, October and November were 3, 6, 6, 3, 5 and 3, respectively. Additionally, the molecular weight distribution value (D) of E. ulmoides rubber from June to November varied from 2.18 to 6.00, indicating that the molecular weight difference of E. ulmoides rubber in leaves in June was small and concentrated, while the molecular weight difference of E. ulmoides rubber in leaves in November was large and scattered. Conclusion: With the passage of months, the size of E. ulmoides rubber particles gradually increases, and rubber particles in different months contain a few of special fatty acids which are dependent on the growth period. The molecular weight of gutta-percha increases with the passage of months and tends to be stable. In the early stage (from June to August), most of the molecules with little molecular weight difference have been found, while in the late stage (from September to November), most of the molecules with large molecular weight difference have been found.

Key words: Eucommia ulmoides, rubber particles, morphology, fatty acids composition, molecular weight