Effects Of UV-B Radiation On Physiological And Taxol Synthesis Of Taxus Chinensis

Taxus chinensis(Taxus chinensis(Pilger)Rehd.var.mairei(Lemee et Levl.)Cheng et L.K.Fu)is rich in paclitaxel and is the main target tree species for artificial cultivation of Taxus chinensis resources.To investigate the effects of environmental UV-B radiation enhancement on photosynthetic growth and taxane content of Taxus mairei,and to explore the regulation mechanism of UV-B radiation on taxol synthesis in Taxus mairei needle leaves.In this study,the photosynthetic parameters,endogenous hormone content,leaf character,taxane content and the expression of key genes in synthesis pathway of Taxus mairei under different ultraviolet B(UV-B,280-320 nm)radiation intensity were analyzed.Furthermore,it provides a theoretical basis for the construction of Taxus paclitaxel forest oriented ecological cultivation technology system.The main results are as follows:(1)With the of UV-B radiation dose increasing and the extension of treatment time,the plant height,leaf weight and branch weight average of Taxus chinensis were decreased.Plant height was positively correlated with photosynthetic parameters Pn,Gs and Ci(p<0.05).With the UV-B radiation intensity increasing,the content of Pn and photosynthetic pigment increased first and then decreased.Under high-dose UV-B treatment,the qP,YII and ETR increased first and then decreased,and the NPQ increased significantly at the beginning of the experiment(p<0.05).UV-B radiation significantly decreased the content of IAA(p<0.05)and increased the content of ABA(p<0.05).Short-term UV-B treatment significantly increased the content of 6-BA,while significantly decreased it after 24 h treatment(p<0.05).In the meanwhile,there was a significant positive correlation between IAA and gas exchange parameters such as Pn,Gs,Ci and Tr(p<0.01).(2)Long-term high-dose UV-B radiation decreased leaf length,leaf width,leaf area,leaf thickness and leaf water content,and induced stomatal collapse,epidermal cell wilting and inhibition of photosynthesis in the needles of Taxus mairei,moreover the leaf traits were positively correlated with gas exchange parameters(p<0.05).The epidermis appendages of Taxus mairei needles were flakiness under CK treatment.With the UV-B radiation dose increasing,the epidermal appendages were fractured seriously and became rod-shaped.Low dose of UV-B radiation exposed(T1 treatment)significantly increased the total wax weight of Taxus mairei needles(p<0.05),in the meanwhile the component contents of wax showed alkanes>alcohols>esters>phenols>ethers under UV-B stress.(3)The improved CTAB-LiCl method can effectively extract high purity and integrality RNA from the needles of Taxus mairei.The ratio of OD260/OD28 was in the range of 1.8-2.0.The method had clear electrophoretic detection bands of 28s and 18s and higher RNA yield.(4)The expression of paclitaxel side chain synthesis pathway gene Pam,CoA-ligase was significantly correlated with 3 h UV-B treatment(p<0.01),and the expression of Pam was significantly correlated with the upstream synthesis pathway gene Hmgr,Tat,T5ah,Ts and Dbat expression(p<0.01),while positively correlated with the expression of Bapt and Dbtnbt in downstream synthesis pathway(p<0.01).The expression of CoA-ligase was significantly correlated with the Tat(p<0.01),T5ah and Ts(p<0.05).The high expression of CoA-ligase genes was positively correlated with the Baccatin III content of taxanes(p<0.01).(5)Elevated UV-B radiation had increased the contents of taxane compounds(10-deacetybactine III,Bakatin III and paclitaxel).Compared with CK,the taxol yield per plant increased by 70.3%(T1),89%(T2)and 76.3%(T3)after UV-B treatment for 24 h.Increasing environmental UV-B radiation could rapidly regulate the expression of key genes in taxol synthesis pathway of Taxus mairei,and effectively increase the taxol content.However,long-term high-dose UV-B radiation could lead to severe yellowing of conifers and decrease of gas exchange parameters,and yet the photosynthesis was inhibited and the needles would be injured obviously.Therefore,low intensity(6.51 ?w·cm-2)of UV-B irradiation for a short time(within 3 h)could effectively increase the contents of paclitaxel and other medicinal active substances,to increase the economic benefit of Taxus mairei forest.