An Introduction to the Yew (Taxus) and a Detailed Explanation of Its Planting Methods
The yew, also known as Taxus, is likewise called red cypress pine. A national first-class rare and protected tree species, the yew is a shallow-rooted plant, with an inconspicuous taproot and well-developed lateral roots. It is recognized worldwide as an endangered natural rare anti-cancer plant. It is an ancient tree species left over from the Quaternary glaciation, with a history of 2.5 million years on Earth. Because under natural conditions the yew grows slowly and has poor regenerative capacity, for a long time no large-scale yew raw material forest base has been established anywhere in the world.
Because the yew's extract (TAXOLPACLITAXEL) paclitaxel has a unique anti-cancer mechanism, Dr. BRODER, director of the U.S. National Cancer Institute, called paclitaxel, after doxorubicin and cisplatin, a new type of anti-cancer drug of the past fifteen years regarded as effective against many kinds of cancer with few side effects. Beginning in the 1980s, the United States, the United Kingdom, Russia, South Korea and China all carried out in-depth research one after another. The United States was the first to apply the research results in medical clinical practice and achieved remarkable clinical results in treating various cancers. From then on humanity made a new breakthrough in the field of anti-cancer. Therefore, up to now and for a considerable time to come, the most advantageous weapon for humanity in its fight against cancer can only be paclitaxel.
Apart from its important medicinal value, the yew's unique appearance and its vivid evergreen foliage also make it a rare and valuable landscaping tree species.
In front of the United Nations headquarters in New York; in front of Buckingham Palace in the United Kingdom; and on the square of the White House in the United States, the beautiful figure of the yew can be seen. We hope the yew's medicinal value can not only benefit humanity, but also that in the near future the beautiful and noble yew can make Beijing, host of the 2008 Olympic Games, even more beautiful and even more splendid.
At present, many domestic yew cultivation enterprises are developing a series of yew products. For example, yew bonsai can be pruned into umbrella shapes, pagoda shapes, round shapes, etc. There are also yew health cups, yew handicrafts, yew health products, and so on.
The State Forestry Administration once issued clear instructions on the currently carried-out "Yew Project": "The yew is a first-class protected tree species of our country, with both good ecological benefits and extremely high economic value. The state supports vigorously establishing yew forests within an appropriate scope, and all sectors of society participating in afforestation and greening undertakings in various forms such as contracting, leasing, auctioning and joint-stock cooperation should be advocated and encouraged."
Although our country's yew resources account for more than half of the world's total compared with other countries, they are still far from sufficient given the world's demand for paclitaxel. Since 1992, when the U.S. Food and Drug Administration (FAD) approved paclitaxel as a drug for treating advanced cancer, excessive felling of our country's wild yew resources has become increasingly serious, and wild yew resources have suffered severe damage. Moreover, many biological characteristics of the wild yew also restrict the development of natural communities. According to statistics: the annual number of cancer cases worldwide is more than 10 million; if paclitaxel is extracted at 0.006%----0.06%, the annual consumption of yew bark would be 700----1000 tons. Even if all the world's yew bark were completely harvested, it could only meet short-term needs. Furthermore, methods for artificially synthesizing or chemically synthesizing paclitaxel are still at the laboratory stage. Therefore, artificially propagating and expanding yew resources and establishing yew timber forest bases for medical raw materials is extremely urgent.
Several current propagation methods for yew seedlings
1. First, the seedling cultivation method
The preservation of yew resources and the rapid propagation of seedlings are the foundation for solving the construction of paclitaxel timber forests, and establishing large-area artificial yew forests on a large scale is the key to solving the paclitaxel raw material problem. When propagating seedlings with yew seeds, attention must be paid to the storage method of the seeds; mixed storage with sand or temperature-controlled treatment has a very good effect on sprouting after overwintering and on breaking dormancy habits. Before sowing, the seed coat must be rubbed and damaged, the seeds soaked in warm water, and treated with chemicals and hormones. Shading after emergence is the key to seedling cultivation; it can prevent high-temperature scorching of the seedlings and maintain moisture, with a light transmittance of 40% being appropriate. The emergence rate of both Japanese yew (Taxus cuspidata) and southern yew (Taxus wallichiana var. mairei) can reach 70---80%, and the emergence temperature is required to be above 15°C.
The dynamic growth of seedling-grown plants is as follows: the plant height and stem thickness of seedling-grown plants grow slowly in the first two years after emergence, with plant height generally increasing by about 10CM per year, and growth accelerating after one year following transplanting. From 3---5 years, the annual increase can reach 20---30CM.
2. Tissue culture propagation of yew
Tissue culture makes use of the totipotency and clonability of plant cells. Young stems, needles, bark, cambium, aril, embryos and so on of yew plants are used as explants for culture research.
(1). Select excellent yew varieties, such as high-quality organs of Japanese yew (with relatively high paclitaxel content) as explants, inoculate them into culture medium, and through steps such as callus formation, rooting and shoot cluster formation, a large number of tissue-cultured seedlings can be obtained in the laboratory. After substrate transplanting, hardening off and inspection for disease prevention, they become production seedlings.
(2). The ratio of early to late callus formation in yew differs among different species and among different plants of the same species. At the same time, it is related to factors such as explant type, sampling site and collection season, light conditions and medium type. On induction medium, Japanese yew, southern yew and Yunnan yew can all form callus. However, the formation situation also differs depending on the yew species and plant.
Research shows that a certain degree of hydrolyzed casein (CA) can promote callus growth in Japanese yew and southern yew, but a concentration greater than 0.5% is unfavorable to the formation and accumulation of paclitaxel.
However, when the concentration is greater than 1%, it can promote the healing of callus and the formation of new growth points without affecting the accumulation of paclitaxel.
By comparison, 2,4D is also beneficial to callus formation and can also increase the induction rate. In 2,4D medium the callus is fresh in color, large, loose and soft, and induction of yew callus is relatively easy. However, other medium additives, such as cell suspension culture, B5 medium and the carbon source sucrose, can also increase the paclitaxel content. But the glucose in high-concentration sucrose inhibits the synthesis of paclitaxel. At the same time, galactose significantly promotes cell growth.
GIBSON's research shows that, whether in cell suspension culture or in inducing callus cell growth and the formation of paclitaxel content, dark conditions are better than light conditions.
Regardless of the variety and part used in tissue culture, cells with strong proliferative capacity from the middle layer must be selected for composition (surface cells contain large amounts of starch granules, while central cells are enucleate and prone to differentiating into tubular molecules). This is conducive to forming intercellular cell chains and filaments, thereby forming large cell clusters and facilitating the signal transmission of small substances between cells. In this way yew cells exist in the form of cell clusters, producing functional cell bodies, promoting the regionalization of cell clusters and the differentiation of cell functions; this is the prerequisite for making the yew produce metabolites.
3. Artificial cutting propagation of yew
As yew resources dwindle day by day and demand grows day by day, rationally utilizing the yew and developing the yew brooks no delay. Under the policy of "ensuring medicinal use and strictly prohibiting timber use," branch and leaf utilization should be carried out more effectively. Against the backdrop of the provincial government's "Yew Project," afforestation and tree planting by the whole people should be actively advocated. While protecting existing wild yew resources, artificial cutting propagation and planting of yew is currently still the most effective and most practical means.
The Weihe Forestry Bureau has for many years carried out active exploration in this area and accumulated quite rich practical experience. And in 1984 it was the first nationwide to succeed in artificial clonal cutting propagation of yew. It also established the world's first artificial yew forest. At present, Weihe has the world's largest yew seedling base, and its yew seedling quantity accounts for 1/5 of the world's total yew.
For yew cutting propagation, softwood cuttings are better in spring and hardwood cuttings are better in autumn. Generally, low-tunnel shading treatment is needed when cutting. The general cutting survival rate can reach more than 70%. While conventional cuttings are only about 3%--20. The shading rate should be no less than 60%. Careful rooting treatment should be done at the base of the cuttings. At the beginning, humidity should be kept intermittently at about 75---85%. Avoid water loss caused by strong winds.
Factors affecting the cutting survival rate generally include: tree age, temperature, chemical treatment concentration, substrate, season, humidity, variety and other human factors. Data show that the highest cutting survival rates of several yews are generally: Japanese yew 95%, southern yew 95%, Yunnan yew 90%, Chinese yew 86%.
During the rooting process in the first year, the above-ground part of the cutting seedling grows slowly, but rooting is rapid and lateral roots are well developed. After transplanting in the second year, further shading treatment and seedbed management are needed. By ensuring corresponding environmental conditions, growth accelerates. Growth is fastest in summer and slow in winter and spring. At this time attention should be paid to temperature changes; long-term dryness can cause growth inhibition or sudden death. However, after the seedlings are strengthened in the seedbed, the afforestation survival rate of the yew is very high. There is very little death, and growth is rapid.
Applying the cutting method is the most effective way to solve the shortage of yew resources and accelerate the construction of medicinal yew forests. At the same time, judging from the current market situation: starting from the second year after cutting, the annual seedling price, so long as it is not subject to major interference, will multiply in value every year. In recent years, some enterprises and individuals with financial strength have begun to invest in this project one after another, and some enterprises or individuals who acted quickly have long since seized the business opportunity of the yew and joined the ranks of millionaires and ten-millionaires.