Study On The Traits Of Oleoresin Exudation And The Structural Characteristics Of Secretory Canals In The Trunk Of Sindora Glabra

Terpenoids are the most abundant compounds in secondary metabolites of plants,which are widely used in medicine,health,industry and agriculture;therefore,it has become one of important fields in the plant research and utilization to explore plant resources rich in terpenoids and to improve their terpene yield.As one of plants rich in terpenoids,Sindora glabra Merr.ex de Wit,belongs to the Caesalpiniaceae family and is endemic to the province of Hainan,China.The tree is called as “balsam tree” due to the high content of oleoresin in the tree trunk when wounded,serving a great potential utilization in developing inter and external medicine and professional care products.Up to date,some progresses have been made in the investigation of natural resources and the production of oleoresin for S.glabra;however,the characteristic and mechanism on oleoresin exudation have not been well understood and the methods to identify the exudation trait rapidly are still lacking,which restrict genetic improvement and utilization of germplasm resources of S.glabra.Hence strengthening the oriented breeding and promoting the development and utilization of germplasm resources are pressing.In this paper,four natural distribution areas of Jianfengling(JFL),Bawangling(BWL),Diaoluoshan(DLS),Wuzhishan(WZS)and 140 wild individuals of S.glabra in Hainan were selected to carry out studies on change patterns of oleoresin exudation varied with time,space and diameter class,on biological characteristics of oleoresin secretion,on the development of secretory canals and changing rules in the charactersitcs of secretory canal among distribution areas,DBH classes and radial direction,and on the relationship between secretory structure characteristics and oleoresin production,based on trunk perforation and oleoresin collection,core section making and analysis on chemical composition of different oleoresin samples.The results were as follows:Significant differences were observed in the oleoresin yield among different distribution areas,diameter classes and individuals.Annual yield,monthly yield,dry season and rainy season yield of oleoresin varied significantly among four distribution areas.Changing rule of oleoresin yield among four areas was DLS>BWL>JFL>WZS in general,with the significant differences of the yield between DLS,BWL and JFL,WZS.Totally,annual oleoresin yield increased first with the increasing diameter class with the peak value at 66-80 cm DBH class,and then decreased when the DBH was higher than 80 cm.Annual oleoresin yield at 66-80 cm DBH class was 775.1 g/tree,signicantly higher than that at the former three DBH classes.Change pattern of oleoresin yield among DBH classes also depended on distribution areas;annual oleoresin yield in JFL and WZS increased with DBH class while that in DLS and BWL increased first and then decreased later with DBH class.Annual oleoresin yield of different individuals fluctuated violently from 2.0 to 3808.8 g/tree.Annual oleoresin yield of individuals related to distribution areas,ranging from 2.0 to 2265.7 g/tree in JFL,29.5 to 3808.8 g/tree in DLS,6.6 to 2191.3 g/tree in BWL,and 5.8 to 550.1 g/tree in WZS.The distribution of oleoresin-secreting grade for different individuals in JFL and WZS displayed anti J-type while that in DLS and BWL was parabolic.Oleoresin yield in different seasons and years fluctuated to varied extent.Generally,oleoresin yield during rainy season was higher than that in dry season,and that in the first year was also higher than in the second year.However,there were no significant differences in different seasons and years.Basically,oleoresin yield showed a decreasing trend with time passing after trunk perforation.The duration of oleoresin exudation for different individuals was dependant on distribution areas and DBH classes;the duration of oleoresin exudation in DLS and BWL areas was mostly 4 to 8 months while that in JFL and WZS areas were mostly 0 to 3 months,indicating that the substainability of oleoresin exudation in the former two areas was higher than in the latter two areas.The individuals with DBH of 20~50 cm in JFL and WZS areas displayed high sustainability of oleoresin exudation,so did for those of all DBH classes in WZS and BWL.Chemical components of oleoresin samples from different individuals were the same,covering 18 kinds of sesquiterpenes and resin acids,but the relative content of them varied greatly.α-Copaene,β-caryophyllene and resin acids were the main components of S.glabra oleoresins,and relative content of these three component varied from 19.6% to 54.4%,from 7.04% to 41.6%,and from 4.85% to 29.9% respectively among individuals.Relative content of chemical components of oleoresin samples was different among distribution areas,and there were significant differences of relative content for α-Copaene,β-caryophyllene,α-humulene,aromadendrene and α-amorphene among distribution areas.The trunk wood presented only axial secretory canals in the secondory xylem,which distributed along the marginal parenchyma bands delimited growth layers and arranged in a tangential direction.They originated in the cambial zone from the initially parenchyma cells derived from fusiform initials or ray initials.The secretory canals were formed by schizolysigenesis and the process of development could be divided into five stages,namely initial stage,formative stage,expanding stage,mature stage and senescent stage.At the initial stage,four initials were arranged in a radial direction and had dense cytoplasm and clear visible nucleus.At the formative stage,after the middle lamella degraded and the initials separated,the canal space appeared.At the expanding stage,the secretory lumen can be enlarged by tangential extension and anticlinal and periclinal division of the living epithelial cells.The fusion between two adjacent axial canals resulted from the separation of radial cells.At the mature stage,secretory canals were constituted by a locally biseriate epithelium,lumen and sheath cells.Mature secretory canals had 7 to 19 epithelial cells and their diameter varied from 19 to 167 μm.The epithelium composed of thin-walled cells and thick-walled cells,the proportion of parenchyma cells at this stage was 66.7%.At the senescent stage,partial epithelial cell walls degraded,some cell cavities filled with gum,and the tylosoids can be seen.Structural characterstics of seretory canals in four distribution areas were quite different in term of the tangential diameter of secretory canals(SCTD),the area of secretory canals(SCA),the density of secretory canals(SCD),the total area of secretory canals(SCTA),the frequency of secretory canals(SCF),the total tangential diameter of secretory canals(SCTTD)and the frequency of marginal band(MBF),ranging from 55 to 61 μm,1212 to 1324 μm2,2.1 to 2.7 number/mm2,2529 to 3806 μm2/mm2,5.6 to 6.1 number/mm,208 to 345 μm/mm,and 0.36 to 0.48 number/mm,respectively.Except for SCA,the other six indicators of secretory canals were significantly different among distribution areas.SCTD,SCD and MBF increased with the increasing DBH class where SCTD of 66~80 cm DBH class were significantly higher than that of the other three classes.Differences of SCA,SCTA and MBF varied to some extent among DBH classes,but did not reach the significant level.SCTTD of 66~80 cm DBH class were significantly higher than that of 31~50 cm and 51~65 cm DBH classes.Differences of SCTD among DBH classes in JFL,DLS,BWL and WZS were also significant.There were significant differences of the structural characteristics of secretory canals among radial direction.From pith to cambium,SCTD,SCA,SCTA showed an increasing tendency while MBF changed irregularly.The differences of structural characteristics of secretory canals were significant among individuals possessing different levels of oleoresin exudation.SCTD,SCA,SCTTD of high yield individuals were higher than those of low yield individuals in JFL,DLS and BWL.Annual oleoresin yied correlated to SCTD,significantly and positively in JFL,DLS and BWL,and it also correlated to SCA significantly and positively in DLS and BWL.SCTD and SCA were the effective indicators to represent the oleoresin exudation for S.grlabra trees.