Anatomical Study On The Root And Stem Of Bupleurum Dracaenoides

Bupleurum dracaenoides was a new species which was discovered in the Jinsha River Basin in the southwest of China and published by the Chinese botanistsin in recent years.Currentty,we know it is the largest perennial shrub with distinctive woody stem in Bupleurum.This species not oily has the significant scientific value for studying the geological historical change and the evolution of biota because of its special habitat,but also has great potential for medicinal efficacy.In addition,because the distribution range and the population quantity of Bupleurum dracaenoides is narrow and spare,it needs to be protected in the scientific and effective way.Therefore,It is necessary to study the basic biology of Bupleurum dracaenoides comprehensively and deeply.In this study,the anatomical structure of the roots and stems of Bupleurum dracaenoides was researched,and its relative species-Bupleurum candollei,the accompanying species-Bupleurum longicaule var.amplexicaule,Bupleurum hamiltonii were comparative studied.Combining the results of anatomical observation,the relationship between the anatomical structure and the environment,and the degree of lignification were discussed in this paper.The main results were as follows:1.The primary structure of the root of Bupleurum dracaenoides is similar to other known species in Bupleurum,which consists of epidermis,cortex and vascular cylinder.The primary xylem is diarch,and its development process is exarch.The secondary structure of the root consists of periderm,pericycle parenchymal cells and secondary vascular tissue.The secondary growth of Bupleurum dracaenoides was obvious,it can form a developed secondary structure.The area of the secondary xylem in the annual root accounted for 65.8%the cross section of the root,and the area of the secondary xylem accounted for 72.67%the cross section of the perennial root.2.The primary structure of the stem of Bupleurum dracaenoides is also composed of three parts,from outside to inside,which are epidermis,cortex and vascular cylinder,respectively.18 vascular bundles arranged in a ring in the stem cross section.The vascular bundles of Bupleurum dracaenoides are collateral bundle.Each vascular bundle in the cross section wsa"V" shape.There were a amount of vessels in the primary xylem.The development process of the primary xylem in stem is endarch.The center part of stem is the developed pith.The secondary structure of stem is composed of periderm,cortex,secondary vascular tissue and pith.The secondary growth of stem of Bupleurum dracaenoides was very active,so the whole secondary vascular tissue was a completely closed ring.There were a number of vessels and wood fiber in the secondary xylem which occuped the majority of cross-section area in the stem.There was a obvious "flower ring"pith primedullary zone in the stem,which was different from other species of Bupleurum.3.The growth and development regularities of the root and stem of Bupleurum dracaenoides were as follows:During the first three months of growth,the root and stem had only the primary structure.At fourth month,a small part of the cells in the roots and stems had recovered the splitting ability,being the first part of vascular cambium.It was the beginning of secondary growth.At sixth month,it was found that a complete vascular cambium were formed in the root and stem,which the secondary growth started being active.From then on,the root and stem produced a large number of secondary organizations.One year later,it had fully developed secondary structure in the root and stem.4.The secondary structure of root and stem of Bupleurum dracaenoides are developed,resulting for the the activities of vascular cambium and cork cambium.Especially,it was formed perderm which was the secondary protective tissue.It is accordance with the structural characteristics of perennial woody plants.But the secondary structure of Bupleurum candollei,Bupleurum longicaule var.amplexicaule,and Bupleurum hamiltonii were not developed without perderm in the stem.They were proved the growth characteristics of perennial herbaceous plants.5.The woody degree of the stem and the root of Bupleurum dracaenoides is much higher than Bupleurum candollei,Bupleurum longicaule var.amplexicaule,and Bupleurum hamiltonii.The ground part of the stem of Bupleurum dracaenoides was lignified entirely.The ground part of stems of Bupleurum candollei and Bupleurum hamiltonii were turned out to occur lignification,but the degree of lignification were lower.About a distance of 25mm of the ground part of stem of Bupleurum candollei and about a distance of 6mm of the ground part of stem of Bupleurum hamiltonii were lignified.This study showed that,the area ratio of secondary xylem in the stem of Bupleurum dracaenoides was the largest.The area ratio of the secondary xylem among four species in the order of high to low was:Bupleurum dracaenoides>Bupleurum candollei>Bupleurum hamiltonii>Bupleurum longicaule var.amplexicaule.6.In the primary structure of the Bupleurum dracaenoides,the proportion of cortex and vascular column area of the root and stem were larger,and the pith in stem was developed.In the secondary structure,there were periderm and a large number of parenchyma cells in root and stem.In the outer diameter of the vascular cylinder of the stem distributed sclerenchyma.The conducting tissue of Bupleurum dracaenoides in roor and stem were developed.According to the feature of the root and stem structure of Bupleurum dracaenoides described above,it was found that the structure may be related to the special habitat with drought,barren soil and so on.This species shows a strong drought resistance through enhancing the ability of water storage and water retention.