杜仲叶胶颗粒形态、脂肪酸组成及胶分子量季节变化

Seasonal Dynamics of Morphology,Fatty Acid Composition and Molecular Weight of Gum Particles in Eucommia ulmoides Leaves

【目的】解析杜仲胶颗粒形态、膜脂肪酸组成及杜仲胶分子量的季节变化规律,分析胶颗粒形态差异和脂肪酸组成与杜仲胶分子量的相关性,为进一步阐明杜仲胶颗粒生物学功能、揭示杜仲胶合成机制提供参考。【方法】以10年树龄杜仲成株新枝上6—11月叶片胶颗粒为材料,利用光镜和电镜观察不同生育期叶片杜仲胶颗粒形态差异,结合气相色谱-质谱联用仪(GC-MS)分析胶颗粒脂肪酸组成与含量变化以及利用分子排阻色谱(SEC)测定杜仲胶特征参数,探讨杜仲胶颗粒形态与胶颗粒脂肪酸组成以及杜仲胶分子量和分子量分布间的相互联系。【结果】1)叶片胶颗粒粒径总体表现为随月份推移而逐渐增大。6月份平均直径为3.99μm,到11月份时增加到6.7μm。小胶颗粒(d<5μm)数量占比从6月份的65.91%降至11月份的19.09%,而大胶颗粒(d≥5μm)数量占比从6月份的34.09%增至11月份的80.91%;2)脂肪酸测定表明,8、10、11月份叶片杜仲胶颗粒中分别检测到26、30和26种脂肪酸,且有15种饱和脂肪酸相同,以棕榈酸(C16:0)含量最高,二十四碳酸(C24:0)次之。同时,发现有7种不饱和脂肪酸为10月份特有,而3种不饱和脂肪酸(肉豆蔻油酸(C14:1)、反式亚油酸(C18:2n6t)和α-亚麻酸(C18:3n3))为8和10月份特有;3)杜仲胶特征参数测定表明,叶片中杜仲胶分子量的分布峰在6、7、8、9、10、11月份分别有3、6、6、3、5、3个。另外,6—11月份的杜仲胶分子量分布值变化在2.18~6.00,说明叶片中杜仲胶分子量在6月份差异小、分布集中,而在11月份差异大、分布零散。【结论】杜仲胶颗粒的粒径随月份推移逐渐增大,且大粒径占比逐渐升高。不同月份杜仲胶颗粒中除含有少数对生育期有依赖的特有脂肪酸。杜仲胶分子量随月份推移而增加并趋于稳定,且早期(6—8月)以分子量差异不大的胶分子居多,而后期(9—11月)以分子量差异较大的胶分子居多。

【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 3.99μm in June and increased to 6.7μm in November.The proportion of small rubber particles(d<5μm)decreased from 65.91%in June to 19.09%in November,while the proportion of large rubber particles(d≥5μm)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)andα-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.