Eucommia Ulmoides. Report, Only Eucommia Ulmoidesand Brous
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IAWA Bulletin n.s ., Vol. 9 (4), 1988: 375-383 DIFFERENTIATION OF SECONDARY XYLEM AFrER GffiDUNG by Li Zhengli (Lee Chenglee) and Cui Kerning Department of Biology, Peking University, Beijing, China Summary Under favourable growth season and by after. Three years after girdling, the regener suitable technical means, regeneration and ated bark has the same thickness as nearby continuous growth of new bark after girdling nongirdled trees. has been observed in many trees. Differen The bark of Eucommia is a very important tiation of the secondary xylem varies after traditional Chinese medicine which has an arteficial treatment. Thus , the authors con anti-hypertensive and metabolic regulatory ef sider that (1) under appropriate conditions feet. Thus the adoption of extensive girdling most trees could be girdled on a large scale obviously alleviate the short supply of this with subsequent new bark regeneration and drug. continued growth, (2) after removal of the Since 1979, the authors in collaboration phloem the living cells of the secondary xy with some other laboratory workers have car lem, i.e., wood parenchyma cells, may func ried out various trials on girdling of a variety tion in transporting nutrients from the tree of trees and woody herbaceous plants and crown downwards, and (3) finally, after gir have found that under suitable conditions dling or when cultured in vitro, both imma many trees and woody herbaceous plants can ture xylem and phloem can dedifferentiate be girdled, after which they resume normal into meristematic tissue that further develops growth similar to the nearby upper or lower vascular tissue. bark (Li & Cui 1983; Lu et at. 1987; Li et ai. Key words: Girdling , xylem differentiation, 1988). Eucommia ulmoides. For the past nine years the authors have also investigated the differentiation of sec ondary xylem after girdling and tentatively Introduction proposed that the xylem can transport nutri It has been a general concept that a tree, if ents downwards when the bark is removed completely girdled, sooner or later will die over a long part of the stem. In the present eventually due to the blockage of nutrients report, only Eucommia ulmoidesand Brous from the upper portion of the excision. Al sonetia papyrifera are emphasised for anato though some authors have reported that trees mical description. after natural or artificial damage to the bark could grow continuously for a certain period of time (Noel 1970), normal growth after ar Materials and Methods tificial girdling in a very large number of trees Large-scale girdlings of the trees were car in China has not been reported previously. ried out within the last ten days of June (Li In recent years, many trees of Eucommia et al. 1981) with the following procedures. ulmoides Oliv. are cultivated for medicinal Firstly two circular incisions were made purpose in some provinces of China, such through the bark about 1 or 2 metres apart. as Shandong, Hubei, Sichuan and Guizhou . Then the bark was vertically slit from the top These trees can all be girdled on a large scale downward (Fig. I), so that the separated bark (1-2 m in length) and about 96% of their was easily removed as a whole piece (Fig. girdled trunk can regenerate new bark in a 2). After the bark was removed , the exposed short period and then grow normally there- surface should be protected from any touch- Downloaded from Brill.com10/05/2021 10:27:21PM via free access 376 IAWA Bulletin n.s., Vol. 9 (4),1988 Downloaded from Brill.com10/05/2021 10:27:21PM via free access Li Zhengli & Cui Keming - Xylem differentiation after girdling 377 ing or else the regenerated new bark would together to form a more or less complete fail to grow at the site of touching. Usually zone. This newly formed cambial zone pro the exposed trunk was loosely wrapped with duced xylem towards the inside and phloem a semi-transparent plastic sheet immediately towards the outside in the same way as nor after girdling, the upper and lower ends of mal cambium. One year later the newly the wrapped sheet were tied up with strings formed bark of the girdled portion appeared (Fig. 3). similar to the surrounding bark (Fig. 4). Several experimental procedures were also It is really surprising that the main trunk carried out on the girdled tree trunks such as of the Eucommia tree in the Laoshan area excision of the tree crown ; application of could usually be girdled over a length of one ethrel, 2,4-D, NAA, GA and NAA + GA at to two metres and that regeneration of bark various concentrations to the exposed sur took place normally where plastic sheet wrap face; application of mechanical injury to the ping was not compulsory. However, in the exposed surface and cultivation of immature Eucommia trees from elsewhere in China and xylem and phloem in vitro etc. All samples in all other species , wrapping with plastic for microscopic observations were taken just sheet immediately after girdling was neces after girdling and at some time later. Materials sary; otherwise the exposed surface of the were prepared by the conventional paraffin trees usually dried out and eventually caused methods. the death of the whole tree. Observations The effect ofplastic wrapping on new bark formation . Differentiation of newly formed bark after As mentioned above, it is necessary to girdling wrap the exposed trunk of Eucommia trees The girdled trunk of Eucommia grown in with plastic sheet after girdling in most areas Laoshan mountains of Shandong Province, of China. In these girdled Eucommia trees, did not need to be wrapped up with plastic the types of plastic sheet, whether semi-trans sheet after exposure. Within 24 hours after parent or black, influenced tissue differen girdling, it formed a surface layer which pro tiation of the newly formed bark (Li et al, tected the immature xylem immediately un 1982). After being wrapped, several cell lay derneath against drying (Li et al. 1981; Li & ers adjacent to the surface of the trunk formed Cui 1983). loose callus cells outwards. New cambium One week later, the ray cells of immature formed about two weeks earlier in the trunk xylem swelled, proliferated and spread later wrapped with semi-transparent plastic sheet ally under the surface layer. They gradually than it did in stems wrapped with black plas joined together with the neighbourhood ray tic sheet. However, after either type of plastic cells and were also mixed with some other sheet was removed one month after girdling, cells derived from the immature xylem. Soon the constituents of the regenerated barks as afterwards a cork layer appeared near the sur they continued to grow was about the same face and a newly formed vascular cambium as that of the original bark. appeared deeply in the callus. Three to four In the tree trunk of Eucommia as well as months after girdling, the cambium cells in other trees, the regenerative processes and divided tangentially and gradually joined tissue differentiation of the newly formed Fig. 1. Girdling of the bark of Eucommia ulmoides. - Fig. 2. The large piece of bark imme diately after girdling. - Fig. 3. The girdled trunk of Eucommia wrapped with plastic sheet. Fig. 4. One year after girdling of the Eucommia trunk. The demarcation of the new bark is arrowed . Downloaded from Brill.com10/05/2021 10:27:21PM via free access 378 lAWA Bulletin n.s., Vol. 9 (4), 1988 Downloaded from Brill.com10/05/2021 10:27:21PM via free access Li Zhengli & Cui Keming - Xylem differentiation after girdling 379 barks were quite similar after being girdled cambium and acceleration of bark growth, the and wrappedin plastic sheets. Various amounts therapeutic effectiveness of this newly form of developing xylem cells were tom off dur ed bark for medicinal use as compared with ing girdling. The ray cells located near the that of the ordinary bark still needs further in surface became swollen (Fig. 5, r). vestigation. One week after girdling, the swollen ray cells closely grouped near the surface into a Effect of bark grafting on the traumatic shape of a bell rim. Eventually these cells be girdled trunk came mingled with the other immature xylem Although it is evident that the trunk of cells to form callus (Fig. 6, ca) which gradu Eucommia can be girdled and can regenerate ally increased and enlarged to a certain extent. a new bark during favourable growth season Two weeks after girdling, cell arrange and by suitable experimental procedure, the ment near the surface became somewhat reg exposed surface became traumatic due to ular. This might be considered as a very early poor wheather conditions or careless han stage of phellogen. Some deep-seated, flat dlings leading to cessation of new bark for meristematic cells, as seen in cross sections, mation and death of the tree (Li et al. 1984). gradually appear (Fig. 7, arrows). These flat Once the ringed surface was damaged, it was cells might reflect the early vascular cambium possible to rescue the girdled trunk by cov cells which later produce phloem outwards ering or grafting a piece of new bark taken and xylem inwards. from another Eucommia tree (Li et al. 1983). The differentiation of a cork layer is very conspicuous one month after girdling (Fig. 8, The role of the tree crown in new bark for p). The cells of the deep-seated vascular cam mation bium also proliferate forming a zone of cam The starch grains stored in the ray cells of bium (Fig. 8, c) that produces phloem out xylem play an important role for the initiation wards (Fig. 8, ph) and xylem inwards (Fig.