Studies On Morphology, Structure And Metabolism Of Taxus Chinensis Var. Marei Under Supplementary UV-B Radiation

The principal ultraviolet radiation absorbance occurs in the stratospheric ozone layer in earth's atmosphere. The destruction of this layer, which is caused by ozone depletion, has lead to an increase in solar UV-B radiation (280-320 nm) reaching the Earth's surface and produced potentially biological effect for plants in the earth.In this thesis, the effects of different dose and treatment time of supplementary UV-B radiation on the Taxus chinensis var. marei grown in the greenhouse were studied. The dose of supplementary UV-B radiation were 3.25μw·cm-2·nm-1(low dose) and 9.76μw·cm-2·nm-1(high dose), and the radiation time were 10d (short term),30d (transition period) and 60d (long term), individually. Then, the responses of morphous, physiology, biochemical and ultrastructural of T. chinensis var. marei responses to supplementary UV-B radiation were investigated. We revealed the adapted mechanism of this plant to UV-B radiation in the cell and subcellular level and optimized the best UV-B radiation conditions to promote the growth of T. chinensis var. marei and the accumulation of taxol.The main results are as follows:1. There were noticeable effects of supplementary UV-B radiation in morphous and biomass of T. chinensis var. marei. Meanwhile, a noticeable distinction among different UV-B radiation dose and different time were also observed. After the long and low dose UV-B radiation treatment, the leaf area, secondary branch length, secondary branch numbers and biomass were increased; the root:shoot was decreased. However, the leaf area, secondary branch length and biomass were all reduced in long and high dose UV-B radiation. The low dose UV-B radiation was better to the growth of T.chinensis var. marei, but the high dose UV-B radiation was adverse.2. There were noticeable effects of supplementary UV-B radiation to the leaf ultrastructure of T. chinensis var. marei, and also noticeable distinction among different UV-B radiation dose and different time. The stomata density and aperture, cell wall of epidermic cell and appendages of the leaf of T. chinensis var. marei under long and low dose UV-B radiation were markedly increased. However, the stomata density under long and high dose UV-B radiation was reduced, and there were more particulate matter in substomatic chambers. Besides, the chloroplasts were twisting, distorted, the arrangement in the lamellae of the grana and stroma was loose, disordered, bulged and produced cavity, the volume and numbers (high dose) of osmiophilic grain were increased apparently by supplementary UV-B radiation.3. The hydroxyl free radicals and MDA content were notably increased under short UV-B radiation; and the active of anti-oxidant enzymes and UV-B absorbing substances were improved to resist to oxidation stress. There were no remarked changes between low dose UV-B radiation and CK, but there were still seriously damage under high dose UV-B radiation.4. There were noticeable effects of supplementary UV-B radiation to photosynthesis, physiology and metabolism of T. chinensis var. marei, and noticeable distinction among different UV-B radiation dose and different time. The net photosynthetic rate, Fv/Fm, Fv/Fo and soluble sugar were raised markedly. However, the net photosynthetic rate, Fv/Fm, Fv/Fo and soluble sugar were descended remarkably, but the protein content was increased remarkably.5. There were noticeable effects of supplementary UV-B radiation to the taxanes content in the leaves of T. chinensis var. marei, and based on the correlative analysis of three taxanes content, we found that the increase of taxol content maybe mainly come from the bioconversion of 7-xyl-10-DAT in short term UV-B radiation, but which maybe mainly come from the bioconversion of 7-xyl-10-DAT and 10-DAB long term UV-B radiation.The main conclusions are as follow:(1) There are observably effects of supplementary UV-B radiation to the morphology, physiology, biochemical and ultrastructural of T. chinensis var. marei. However, the plant could adapt to the UV-B radiation by changes of morphous architecture, increase of actives of anti-oxidant enzymes, UV-B absorbing substances and waxes content to resist to the UV-B stress. (2) Long term and low dose UV-B radiation could promote the stomata density and aperture, net photosynthetic rate, fluorescence parameters (Fv/Fm and Fv/Fo) to increase remarkably, and then the biomass is raised markedly. But the Long term and high dose UV-B radiation could injure the chloroplast configuration, inhibit net photosynthetic rate and fluorescence parameters(Fv/Fm and Fv/Fo), and then the biomass is reduced markedly (3) Supplementary UV-B radiation could promote notably the bioconversion of the combined taxol (7-xyl-10-DAT) and the precursor of taxol (10-DAB) to taxol. (4) The long term and low dose UV-B radiation are the best conditions to promote the growth and the accumulation of taxol.