Eucommia ulmoides Oliv. (Eucommiaceae)
Distribution and Significance
Eucommia {Eucommia ulmoides) is a deciduous tree belonging to the family Eucommiaceae. As a mature tree, it is 20 m in height and 40 cm in diameter at breast height and has a chromosome number of 2n = 34. It is a gynodioecious plant, which shows characteristically a white filamentous natural polymer, gutta-percha, when a piece of the bark or folded leaf is pulled apart.
Wild species are vertically distributed in the warm and humid zone in the southeastern part of the Chinese continent at sea level (300-1300 m). As a medicinal raw material, it has been cultivated in the southeastern region of China at 500-1100 m sea level, and recently it has also been cultivated in Japan, Taiwan, and Korea. Further, it is known to have originated from the Tertiary period, and many species of Eucommiaceae have been found among Pliocene fossil plants, from which it is known to be distributed all over the world (Chinese Agricultural Encyclopaedia 1989).
Eucommia, mainly its bark, is used as a medicinal herb material for tonics and hypotensive drugs, which is specified in the Japanese Pharmacopoeia. Further, its leaves are used as a basis for beverages. Gutta-percha, which is contained in the plant body (approx. 10%) and is resistant to acids and alkalies, is used extensively in electrical insulation and as filling material in dentistry. Further, its wood which is solid and hard, is used for construction, furniture, and farming tools.
Eucommia was first recorded as a medicinal plant in the Shinnohonsokyo, an ancient book published in China around 100 a.d., in which Eucommia is classified as one of the Johon (an efficacious drug which is less harmful to human beings). It was also introduced in typical medicinal books, such as Meiibetsuroku, Honsokumoku, etc., where its pharmacological and clinical effects, known for over 2000 years, were reported. The major pharmacological effects include: (1) hypotensive, (2) diuretic, (3) tonic, (4) analgesic, and (5) sedative actions.
Propagation and Cultivation
Generally, seed propagation has been employed. A high fertility rate can be obtained by collecting seeds from a 10-20 year old mother tree and sowing them in spring or autumn. Although propagation by layering is also feasible, vegetative propagation is expensive as propagation by cutting is rather difficult.
The germination rate was as low as 10% in the case of natural sowing, however, it rose to 60% when seeds were immersed in water, and reached 80% when the seed coat was peeled off. Seedlings are cultivated for year after sowing. They are planted at intervals of 10 cm on a high ridge.
In winter or spring, 1-year seedlings are planted at 2.5-3 m intervals. The bark, used as a raw material for crude drugs, is cropped by peeling it off a cut tree cultivated for 15-20 years. The 1-year seedlings are planted at a distance of 2.5-3 m and pruned at 40 cm above the ground in order to induce the growth of lateral branches in 2 years; leaves to be used in beverages are cropped from the epinasty branches after 3 years.
Medicinal Components of Eucommia
According to reports, the chemical components of Eucommia have been analyzed and identified as iridoid, lignan, and phenyl propane compounds. In particular, those noted as a single compound revealing pharmacological effects during animal tests: pinoresinol diglucoside (PRDG), syringaresinol diglucoside (SRDG), geniposidic acid (GA), and aucubin, which are reported to have hypotensive, psychogenic, hypokinesis preventive, and cholagogic activities.
Marketability of Eucommia
The market for pharmaceuticals extracted from plants in Japan is divided into two groups, namely, the ethical and the nonprescription drugs. Sales in 1991 were reported to be 145 000 million yen for ethical drugs and ca. 170 000 million yen including nonprescription drugs (Nikkei Biotechnology Annual Report 1992); 0.03% of the drugs are believed to contain Eucommia. Beverages sold in the health food market in 1992 amounted to 130 000 million yen, thus, its market scale is assumed to be about 200 000 million yen for Eucommia products, including drugs.
Summary
Eucommia ulmoides Oliv. (Eucommia) is a medicinal tree originating in China, which is known for its physiological activity as a hypotensive drug. The authors studied its propagation and in vitro production of secondary metabolites, and obtained the following results.
Propagation by Tissue Culture
For propagation of Eucommia by tissue culture, the epicotyl of seed after germination was the best explant material, in particular, with addition of 0.1-5 mg/1 BA to the B5 medium. Rooting was noted at a rate of 60% after immersion in 100 ppm NAA, and all of those rooting could be acclimatized. However, when shoots, mature bark, cambiums, or the parenchyma cells from the mature plant were used as explant, only callus formation was noted.
Production of Secondary Metabolites
As explant, a young shoot was employed. Callus induction was produced in B5 medium supplemented with 0.5 mg/1 BA and 0.5 mg/1 NAA. The establishment of a cell line was promoted by selecting cultured cells superior in shearing resistance and growth rate using the shake culture. The cell line was then scaled up stepwise, and at the level of 2000 ml, transferred to a closed, continuous culture in the tank. At a scale of 5000 ml, the cultured cell mass reached 2100 g after incubation for 110 days, starting from a fresh weight of 3 g. Thus, closed, continuous culture in the tank is considered useful for the production of secondary metabolites from cultured cells. The contents of the active ingredients in the cultured cells revealed less than half that in the parent body (bark, leaves), when assayed by HPLC after fractionation by gel filtration. Iridoids and lignans were also formed in cell cultures.
Selections from the book: Medicinal and Aromatic Plants VIII (1995).
