Growth、Physiological、and Biochemical Characteristics And Camptothecin Content Responses Of Camptotheca Acuminata Seedlings To Light Intensity

Our study set 4 different treatment groups( namely:100% light intensity(PAR, 1500±30 μmol m-2 s-1)(non-shaded, control), 25% irradiance(75% shaded), 50% irradiance(50% shaded) and 75% irradiance(25% shaded).). One-year-old C. acuminata seedlings were studied on the effects of growth, Chlorophyll content, photosynthetic parameters, chlorophyll fluorescence parameters and photosynthetic apparatus after treatment 60 days; while CPT content, key enzyme activity and gene expression involed in CPT synthesis, exploring how C. acuminate adapts to different light environment, in order to provide theoretical foundation for leaf-produing plantation industry. The main results are as follows:(1) The seeding height increment and total biomass of C. acuminata seedling responsed differently under different light intensity, the growth and biomass were inhibited under both high and low irradiance. And the leaf area was increased under low irradiance.(2) Chlorophyll a, chlorophyll b, chlorophyll(a+b) and carotenoids content all increased with the descend of light intensity, while the increase in photosynthetic rate Gs, Tr mediated with light intensity increasing from 25% to 75%, indicated plant increase Chl content in order to promote photosynthetic rate under low light intensity. But photosynthetic rate and Chl content decreased under full light, while Ci was on the contrary, indicated more light energy caused Chlorophyll degradation, resulted in derease in photosynthetic rate. And the descend of Chla/b with the decrease of light intensity indicated that more chlorophyll b to absorb light energy under low light intensity. And the higher Fv / Fm, Fo, Fm, ΦPS Ⅱ, q P under 75% light intensity suggested higher PS Ⅱ photochemical efficiency under this light intensity.(3) Under 25% and full light intensity, the MDA content, REC, O2.- production rate and H2O2 content were higher than other treatment, suggested C. acuminata seedlings suffered light deficiency and inhitition. And superoxide dismutase(SOD), catalase(CAT) activities and POD activity were lower than other light intensity, indicated that POD, SOD and CAT had an effect on the removement of ROS, but could not work when serious.(4) Light intensity had an influence on the development of stoma and chloroplast. The high and low irradiance prejudice the development of stoma and chloroplast..Under low irradiance, C. acuminata seedlings decrease burden of light reaction center, while decrease water loss under high light, by decreasing stoma density. High and low irradiance resulted in chloroplast deformation and grana lamella disorder.(5) The decend of irradiance and extension of treatment time promoted the increase of CPT content, equally TSB and TDC activity change. Thereby, gene expression of tsb, tdc1 and tdc2 change with it. But, CPT yield is to the maximine under 50% irradiance after treatment 60 days, due to the growth was inhibited under 25% light intensity.