Studies On The Comparision Of Structures And Their Accumulation Of Chemical Components And The Development Of Secretory Canals In Six Medicinal Plants Of Bupleurum L.

Bupleurum L.is a genus of perennial herbaceous plants in Umbelliferae.Bupleurum chinense DC.and Bupleurum scorzonerifolium Willd.were recorded as prescribed plants of traditional medical herb Bupleuri Radix in Chinese pharmacopoeia(2005),the main medical parts were their roots.For different habits and different resource supplies, Bupleurum smithii Wolff.var.parvifolium Shan et Y.Li.and Bupleurum yinchowense Shan et Y.Li.were also for medical uses in different areas.The main medical components were saikosaponin,flavonoid and essential oils.In present study,anatomical methods such as wax-slides,thin sections and ultra-thin sections,histochemical and phytochemical methods were used to study the six plants in Bupleurum L.,such as B.chinense DC.,B.scorzonerifolium Willd.,B.yinchowense Shan et Y.Li,B.longiradiatum Turcz.var.porphyranthum Shan et Y.Li.,B.smithii Wolff.var.auriculatum Shan et Y.Li and B.longicaule Wall.ex Dc.var.giraldii.Wolff.Firstly,development of the secretory canals distributed in the root,stem and leaf were studied,and in a while,production,transportion and accumulation process of essential oils were investigated.Secondly,in order to provide theoretical evidences for identificating crude drugs,the structures of organs and distribution of the secretory canals in six plants of Bupleurum L.were systematically studied.Finally,the comparision on accumulation of the total saikosaponin and flavonoid in the root,stem,leaf and fruit of six plants in Bupleurum L.were studied.The results are as follows:The secretory structures distributed in the six plants of Bupleurum L.were formed by cell wall separation,i.e.,schizogenous.They located in pericycle and secondary phloem of root,phloem and pith of stem,phloem and over xylem of the vein;in addition,they were also distributed in bract,petal and mesocarp.The size,number of the secretory canals and the number of the secretory cells in different species showed some differences.Development of the secretory canals distributed in the vegetative organs of Bupleurum chinense DC.was studied.The results showed that the secretory canal in root pericycle was developed from a group of pericycle cells.The secretory canals in root secondary phloem initiated from the outer derivative cells of the vascular cambium.The secretory canals presenting in phloem of stem and leaf originated from two or three exterior layers of protophloem cells in the procambium bundles.The secretory canals in the stem pith and above the leaf xylem were developed from ground meristem.The lumens of these secretory canals were formed by cell wall separation,i.e.,schizogenous. Histochemical tests showed that these secretory canals contained essential oils and were also important distribution sites.Development of secretory canals in vegetative organs of Bupleurum chinense DC.and the accumulation of essential oils were investigated by electron microscopy(TEM) analyses.The secretion mechanism of the essential oil was also discussed.The results indicated that the plastid,ground substances of cytoplasm and mitochondria took part in the biosynthesis of oil or oil precursor.The endoplasmic reticulum involved in the transport of essential oil to the secretory lumen.At latter stages of development of secretory cells,numerous different sized vesicles fused with the plasmalemma along the boundary between two neighbor secretory cells and secreted the substance into the wall. Thus,the wall between two neighbor secretory cells near the lumen became loosely structured.Then,the wall lined the lumen near two neighbor secretory cells extruded numerous grey vesicles with various sizes on the side facing the lumen,and release these vesicles into the lumen.This phenomenon has not been reported in the literature.As a result,the manner of secretion in secretory canals of Bupleurum chinense DC.appeared to be exocytosis.The structures of root,stem and leaf of the six plants in Bupleurum L.were similar to normal structures of herbaceous plants in dicotyledon.The secondary structures of root were composed of periderm,pericyclic parenchyma cells and secondary vascular tissues from the outer to inner,and the fibers distributed around the vessels were showing certain differences.The structures of stem between six plants were similar,composed of epidermis, cortex,vascular tissues,for the course of cell wall lignification of parenchyma cells which origined from interfascicular cambium,the xylems of stem were connected as a ring.The leaf consisted of epidermis,mesophyll and vascular tissues,B.scorzonerifolium Willd.was bifacial leaf,but isobilateral leaf in other five plants.Different structure characters about the six plants in Bupleurum L.may supply certain academic evidences for species identification.The inner structures of bract were similar to that of leaf The shapes and the inner structures of six plants were also similar,were composed of lower and upper epidermis and the inner parenchyma cells,there also existed a vascular bundle in the middle part.The stamen was composed of anther and filament,the mature anther consists of four pollensacs; filament consisted of epidermis,ground tissues and a vascular bundle.The ovary of the pistil was under the perianth,composed of two carpels jointed from the lower part with two locules and a ovule in each locule.The fruit was cremocarp,it could be separated into two groups according to shapes of fruit arris.Histochemistry of several plants in Bupleurum L.showed that saikosaponin could produce characteristic colors when were stained with special test reagents,according to this,we could use it to test saikosaponin.The results showed that saikosaponin was commenly present in root,stem,leaf and fruit.In the root,saikosaponin was mainly distributed in phloem,vascular cambium and xylem near vascular cambium.In stem,it was distributed in epidermis,collenchyma in the cortex,cortex,the vascular cambium in the vascular bundles and parenchyma cells in phloem.In leaf,it was distributed in epidermal cells,mesophyll,phloem of the vein and vascular cambium.Studies showed that saikosaponin was also present in the winter sprouts,espeicilly in undifferentiated organs. In fruit,saikosaponin mainly located in endosperm,pericarp.In addition,saikosaponin was also present in the secretory canals of root,stem,leaf and fruit in several plants of Bupleurum L.The content of total saikosaponin and flavonoid in the root,stem,leaf and fruit of six plants in Bupleurum L.showed great differences in fruit mature time.The contents of total saikosaponin in both the root and leaf of B.smithii var.auriculatum were higher than those of two medical plants included in Chinese Pharmacopoeia,so it was suggested that B.smithii var.auriculatum was a better medicinal plant should be explored.Otherwise,The contents of total saikosaponin in the root and fruit of B.longicaule var.giraldii were high too.In addition,the fruit of B.scorzonerifolium Willd.showed higher total saikosaponin content,so it could be concluded that not only its roots but also its fruits could be used for distilling total saikosaponin.Further more,the leaf and fruit of B.longicaule var.giraldii had the highest content of total flavoniond among the six plants of Bupleurum L.,and its stem also had more one,so B.longicauIe var.giraldii should be a better one for exploring total flavoniond.From above all,it was proposed that the overground and underground parts of the medicinal plants should be explored respectively according to the needs,which could be greatly significant for exploitation of the medical resources properly.