The genus Cornus (family Cornaceae) consists of about 40 species, nearly all of which are native to the northern hemisphere. The name dogwood is a corruption of dagwood or dagger wood because the daggers (for skewering meat) were made from the wood of some sorts (another tradition also exists that the extract of the barks was used for the treatment of skin disease in dogs). Cornus plants, with flower clusters surrounded by large, spreading, petal-like bracts, have great decorative merit for garden and landscape trees. C. florida (eastern flowering dogwood) and C. nuttallii (western flowering dogwood) are especially popular trees in North America.
Cornus kousa of Japan and Korea is also often used as a garden tree; the clusters of flowers and the brilliant red leaves in autumn look attractive under city conditions. The varieties C. kousa chinensis (from China), which is not botanically very distinct from the typical species, and C. kousa Milky Way, which blooms unusually freely, occur in Japan. C. capitata, whose four bracts turn yellow, often decorate the mountainside (evergreen forests) in the Himalayas.
For medicinal use, C. offtcinalis Sieb. et Zucc, native to China, is often employed. The extract of the dried fruits, containing organic acids (malic acid, tartalic acid, gallic acid, etc.) and fatty oils (palmitic acid, oleic acid, etc.) is a popular tonic, an astringent, and a hemostatic in East Asian countries. The fruits (cornus fruits) have been often one of the ingredients in traditional prescriptions for preventing and improving symptoms of aging, including pollakiuria and cataract.
Some other dogwood species provide food for wildlife); for example, the fruits of C. mas L. can be used to make jelly. The bark of some species also yields a compound that can be substituted for quinine.
Cornus plants are also rich in tannins, which can be classified into two large groups, i.e., hydrolyzable and condensed tannins. Some chemical investigations, particularly on this medicinal plant have clarified the major polyphenol constituents of the plant to be hydrolyzable tannins, the metabolites of gallic acid.
Establishment of Cultures
Multiplication of Cornus plants by axillary shoot proliferation is currently the most commercially valuable method for micropropagating selected cultivars. Young branches of C. kousa chinensis, C. kousa Milky Way, and C. capitata Mountain Moon were collected and sterilized by usual methods. The axillary buds and shoot apices were cut off and placed on BW medium under illumination. Successful proliferation of shoot tissues was obtained. The proliferated shoots fill the culture bottle (450 cm3, containing 90 ml medium) in 2-3 months of culture.
Active and vigorous rooting in in vitro plants is important for obtaining healthy plantlets which will be harvested and successfully acclimatized for field planting. In vitro root formation of these plants was obtained on BW medium containing NAA, indole-3-butyric acid (IBA), and active charcoal. Within 1-2 months of culture, (100%) rooting occurred.
The proliferated shoots with well-developed roots, after acclimatization by the usual method (gradually reducing humidity and increasing light intensity), were successfully transplanted to pots. Thus, in vitro propagation techniques are very useful for the rapid mass production of selected clonal plants of Cornus.
Cornus kousa (Dogwood): Summary and Conclusion
Cornus species, such as C. kousa chinensis, C. kousa Milky Way, C. kousa Gold Star, G. kousa Satomi, G. kousa Snowboy, G. capitata Mountain Moon, c. drummodii Eddie’s White Wonder, and G. offtcinalis generally contain hydrolyzable tannins in which the major component is 1,2,3,4,6-penta-O-galloyl-β-D-glucose. In some varieties (+)-catechin and related pro-anthocyanidin (condensed tannin) are also produced.
In three species, G. kousa chinensis, G. kousa Milky Way, and G. capitata Mountain Moon, micropropagation through shoot proliferation, rooting in in vitro, and transplantation to pots was successful. The tannin profiles in these shoot cultures were different from those of the whole plant tissues; the major compound observed in vitro plants was lowest molecular weight galloyglucose β-glucogallin. This result also suggested the suitability of shoot cultures of Cornus plants for the study of gallic acid metabolism.
Callus and cell suspension cultures of G. kousa produce phenolics similar to those observed in the intact plant. Especially the contents of flavan 3-ols and procyanidin were relatively high in the callus cultures. With the determination of several culture conditions, G. kousa calli were clarified to be usable for biosynthetic study of condensed tannins as well as for their production.
Selections from the book: “Medicinal and Aromatic Plants X”, (1998).