|Title||A Study on Breeding Tetraploids and Comparison of Laticifers of Euphorbia Tirucalli L.|
Euphorbia tirucalli L., Euphorbiaceae,the genus Euphorbia, namely milk-bush,is a succulent cactus-like shrub originating from Africa and now can be found in Hainan Island, Xishuangban-na,Taiwan,Hongkong of China. As a kind of ornamental plant, it is used as a kind of peculiar tree in the botanical garden,vegetation garden and exhibition center of popularized science for its leafless stem. All parts of the plant ooze large quantities of a milklike sap called latex. The shrub is called “petroleum plant” because it produces a hydrocarbon materials very much like gasoline,including alkanes,diterpenoids,triterpenoids,steroids etc. As a kind of tropical plant, E.tirucalli L. is sensitive to low temperature. In this experiment, researches on polyploid induce of Hainan and Holland E.tirucalli L. have been done in order to raise its adaptation in Chongqing. Besides, the researches on laticifer distribution in the stem and comparison of laticifer between diploid and tetraploid have been done.The suitable medium for propagation is 3/4MS + ZT 0.6 mg/L (pH=5.8).And an average propagation coefficient is found to be 2.90 for Hainan material and 2.22 for Holland material, respectively. The suitable medium for rooting is 1/2MS+NAA0.5 mg/L(pH=5.8) and the rooting rate is 100%.In order to induce tetraploid, five methods have been put to the experiment simultaneously, namely i ) sprinkling colchicine in meristrm, ii) stem segment drenching and cuttage outdoors.iii) mixing culture with colchicine, iv ) immersing stem segment and step-generation,and v ) precultivation and sprinkling colchicine and step-generation. The best method is found to be the 5th method:precultivation for 3d and then sprinkling colchicine for 24h,which yields the inducing rate of 72.22% and the survival rate of 60.00%, respectively. As a result,3 pure tetraploid Hainan E.tirucalli L. were obtained by cutting the clump sprout constantly,.Chromosome identification shows that the diploid chromosome of these two materials is 2n=2X=20, while that of the tetraploid is 2n=4X=40.Morphologically, the stems of the tetraploid become stronger,the leaves become longer,broader and thicker, and the color gets darker than that of the diploid,though the leaf index declines. Compared with the characteristic of the stoma of the diploid, the guard cells of the tetraploid become longer and broader;the number of the stomas declines and the chloroplast number increases. Electronic microscope suggests that the stomas in the stem epidermis of diploid is distributed along the axle of the stem in the form of two bands and the stomas are sunk, while the stomas in the stem epidermis of tetraploid are irregularly distributed and the stomas are slightly raised. Careful measurement under the microscope shows that the diameter of the stoma in Hainan tetraploid stem epidermis increases by 10.4Î¼m, the Holland tetraploid increases by 8.5Î¼m. In the winter of 2005, a comparative experiment on the cold-resistance between Hainan diploid and tetraploid was conducted. Results show that all the diploid died and the death rate is 100%, while the survival rate of tetraploid is 20%.Results of the experiment of POD gel electrophoresis indicate that there is no remarkable difference in number and colour between Holland diploid and tetraploid,and that the number of pedigrees of Hainan tetraploid is three moer than that of diploid, and three of the pedigrees become darker in colour.Laticifer distribution and number were studied in Hainan diploid and tetraploid E. tirucalli L.. The laticifers are non-articulated. Primary laticifers are distributed mainly between the xylem and phloem and in the pith of 2-year-old stems as well. Secondary laticifers are multi-branched and distributed irregularly in the phloem. Terminal laticifers are present beneath the cortex (or periderm). Primary laticifers increase in number and diameter with stem growth. But the diameter grows within a certain limit while the number keeps increasing to relieve the sap pressure. Compared with diploid, the number of the primary laticifers of tetraploid decreases by 5.5 and 10.7 in the newborn and the 1-year-old stems, respectively, and their diameter decreases by 8.4Î¼m and 9.6Î¼m, respectively.
|Keywords||colchicine, Euphorbia tirucalli L., laticifer, tetraploid,|
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