Distribution and Importance of the Plant
At least 34 species of the genus Uncaria (tribe Cinchonea, subtribe Mitragyninae Havil, family Rubiaceae) are widely distributed in Africa, tropical America, tropical and subtropical Asia (). About 14 species have been reported in Malaysia. Uncaria species are characterized by the presence of hooks on the nodes lying opposite leaves with interpetiolar stipules and a head-shaped inflorescence. It is a woody climber the stems of which are square-shaped, bearing ovate leaves with five to seven lateral veins. The midribs are typically pubescent with long straight hairs, although sometimes only finely pubescent with glabrous laminae.
A typical young and an adult Uncaria elliptica plant (woody climber) are shown in Figs. 1 and 2, respectively. This plant was originally found growing among Hevea trees in a large rubber plantation near Kuala Lumpur, Malaysia. The identity was determined with the help of Dr. C.E. Ridsdale and Dr B.A. Krukoff, Botanists of Malesian Botany, Leiden.
In open land, the Uncaria plant grows as a bush, also thriving well in the forest or cleared jungles. Some of the species commonly found in Malaysia, Sri Lanka, India, Burma, Thailand, Cambodia, and Indonesia include Uncaria gambier (Hunt) Roxb., Uncaria elliptica R. Br. ex G. Don, Uncaria longiflora (Poir) Merr., and Uncaria callophylla Bl. ex North.
Flavonoids and Alkaloids in Uncaria
The Uncaria elliptica plant has been reported to contain several flavonoids such as the glycoside rutin, the aglycone (—)-epicatechin (), and ( + )-catechin was reported to be present in Uncaria gambir ().
Various Uncaria species also contain several types of alkaloids. The alkaloids isolated from the different species were mainly the heteroyohimbines and oxindoles (). The species Uncaria borneesis, Uncaria longiflora var. longiflora, and Uncaria longiflora var. pteropoda are particularly rich in alkaloids of the oxindole type, namely, corynoxeine, rhyncophylline, and pteropodine (). The yohimbine alkaloids (e.g., pseudoyohimbine) were reported to be found in Uncaria borneesis and Uncaria callophylla (). Uncaria callaphylla is also unique in that it contains the dimeric indole alkaloid, callophylline, which is made up of the gambirine and pseudoyohimbine moieties (). Uncaria elliptica of Thailand has been reported to contain several types of indole alkaloids such as rauniticine pseudoindoxyl, 19-epi-ajmalicine, and 3-iso-rauniticine (). The Uncaria gambir of Malaysia contained the indole alkaloid gambirine (). The Uncaria thwaitessi of Sri Lanka was reported to contain triterpenes such as uncaric acid, diacetyl uncaric acid, and ursolic acid ().
Pharmacological and Medicinal Use
Several species of Uncaria have been used as folk medicine and as a source of tannins (). Recently, several reports have described the use of the Uncaria as a traditional medicine for the treatment of hypertension (). The alkaloid gambirine isolated from Uncaria gambier was reported to affect the vegetative nerves of the uterus ().
Most of the Uncaria species are not available commercially, therefore, the plant is conventionally propagated through stem cuttings. In this method, a portion of a stem, root, or leaf is cut from the parent plant. The cuttings are then placed under certain favorable environmental conditions and induced to form roots and shoots, thereby producing a new independent plant which is usually an exact reproduction of the parent plant. For species that can be propagated by cuttings, this method has numerous advantages. Many new plants can be started in a limited space from a few stock plants. The method is inexpensive, rapid, and simple. In addition, special techniques in grafting and budding have also been used for some species.
Many of those “hard-to-root” plant species will usually require the treatment of the cuttings with growth regulators in order to increase the percentage of cuttings that form good quality roots, and to increase uniformity of rooting (). Auxins such as indole-3-butyric acid (IBA) and oe-naphthalene acetic acid (NAA) have been found to be reliable in stimulating adventitious root production in a large number of plant species.
We examined the effects of growth regulators and other physical factors such as light and dissolved air on the formation of root on the stem cutting, hence establishing a rooting protocol for the propagation of Uncaria elliptica.
In general, there are three major methods for applying growth regulators to stem cuttings for the induction of root formation: (1) the quick dip or concentration dip; (2) prolonged soaking; and (3) powder methods. Preliminary attempts to utilize the quick dip and the powder methods were unsuccessful and not pursued further. Therefore, only the prolonged soaking method was utilized and investigated in greater detail in our present study.
Stem cuttings obtained from the Uncaria elliptica plant were separated into five groups and placed in several test solutions () for varying lengths of time (6, 24, 48, 72, 96, and 120 h) at ambient temperatures (26±2°C). After the incubation period, the stems were transferred to deionized water (about 5 cm depth) and the water level replenished daily. The container was covered with black paper. After 18 days of culture in deionized water, the number of visible roots formed were counted. The test substances, namely, IBA, NAA, and indole acetic acid (IAA) were dissolved in ethanol and the solutions diluted with deionized water. The final ethanol concentration was 0.1-0.4% and each test solution by itself had no significant effects on adventitious root formation. Each stem cutting had six fully developed uppermost leaves, unless otherwise stated. Various concentrations of auxins were added to the test solutions and their effect on root formation studied ().
The rooting efficiency between lateral and terminal shoots was compared. The influence of the number of leaves on the rooting response was also tested. A series of cuttings was prepared as follows: (1) apex with two uppermost leaves; (2) apex with four uppermost leaves; and (3) apex with six uppermost leaves. The cuttings were treated with IBA (10 µM) and NAA (10 µM).
The effect of light on the formation of roots from the cutting was also investigated. A white fluorescent lamp of about 4000 lx (16-h daily exposure) was used. The black paper covering the test containers was removed to expose the submerged portion of the stem to light. The effect of dissolved air on the formation of the roots was studied by sparging air bubbles through the test solution using an aquarium aeration pump. The number of roots formed after 18 days of culture was counted.
The rooting response of the cuttings of Uncaria elliptica was found to depend upon the auxin concentration and duration of the treatment. This phenomenon is also observed in other species, e.g., Pinus radiata () and Mains pumica (). IBA and other auxins had to be present for several days in order to stimulate rootings (). Twenty-four-hour treatment with these auxins had no effect and resulting only in a rather small stimulation. The fact that synthetic auxins such as IBA and NAA are much more stable than IAA may explain the difference in response to IAA and similar concentrations of synthetic auxin.
The rooting response was maximum at 10 µM for both IBA and NAA when applied singly (). IBA is, however, more potent than NAA. The synergy between these two compounds was also maximal when they are applied together at 10 µM ().
Light was found to be unfavorable for Uncaria elliptica root formation ().
Lack of dissolved air and attached leaves resulted in a slightly lower efficiency of root formation. However, though the availability of dissolved air did enhance root formation, it was not very important and therefore not implemented in the rooting protocol () which was established for the future propagation of Uncaria elliptica in plantations for the production of the flavonoids rutin and/or (—)-epicatechin.
A callus cell line was established using the natural variation of cells induced by different growth regulators. The identification or selection of a high-yielding cell line for both rutin and (—)-epicatechin have not been successful. Within the time frame of the present study, only (—)-epicatechin-producing calli were found. With this (—)-epicatechin-producing cell line, it was hoped that, by varying the different physical and culture conditions, the level of (—)-epicatechin could be enhanced and the production of rutin induced.
Rutin, the major flavonoid found in the source plant, was not detected under the present culture conditions. The ability of the callus to synthesize (—)-epi-catechin but not rutin appeared to favor the concept that when more than one flavonoid derivative is simultaneously formed in a vegetative plant tissue, the accumulation of the simplest form in callus or cell cultures is preferred over the more highly oxidized flavonoids ().
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.