Effects Of Light Quality On Physiological And Biochemical Characteristics And Accumulation Of Camptothecin In Camptotheca Acuminata Decne Seedlings

With the method of plastic pots in the controlled environment room, and by setting 4 different treatment groups, one-year-old Camptotheca acuminata(C. acuminata) seedlings were studied on the effects of growth, photosynthetic and physiological-biochemical characteristics under different light quality(white, blue, yellow and red light), to study how light quality effects the physiological-biochemical characteristics and camptothecin yield, enzymatic activity, and the expression of camptothecin biosynthesis-related genes. Manipulating light quality can be an effective means to achieve the higher camptothecin yield in medicinal plantation. Through the determination and analysis of the various indexes in the experiments, the main results are as follows:(1) the growth of Camptotheca acuminata seedlings were quite different under different light quality after 45 d. In general, the total biomass, leaf area(LA), specific leaf area(SLA) and seedling height of plants were the greatest when grown under red light, and lowest under blue light( BL).Compared with white light, as time increased, red light gradually increased young leaf biomass, while yellow and blue light gradually decreased young leaf biomass.(2) Compared with white light, MDA and REC content of seedling leaves were significantly decreased under red light treatment, which proved that red light reduced the incidence of ROS, slowed the membrane lipid peroxide. Antioxidant enzymes activity like SOD, CAT and POD of seedling leaves were increased significantly under the BL and YL, which may be uesd to remove ROS and relieve lipid peroxidation, thus to protect plants. The different levels of antioxidant enzyme activity under different light quality suggest that the protection mechanism under different light quality is different.(3) Proline and soluble protein content of Camptotheca acuminata seedlings significantly increased under blue and yellow light, which may play a protective role against the photo-oxidation. While proline and soluble protein content of Camptotheca acuminata seedlings significantly decreased under red light, which indicated that red light promoted the development of Camptotheca acuminata seedlings.(4) Compared with white light, red light significantly increased values of Pn、Gs、Ci and Tr while blue light significantly decreased values of Pn、Gs、Ci and Tr, which indicated that the different influences of different light quality on the photosynthetic of Camptotheca acuminata seedlings. At the same time, red light promoted the synthesis of chlorophyⅡs while blue and yellow light significantly decreased chlorophyⅡs content.(5) In this study, values of Fv/Fm and ETR were significantly increased under RL, suggesting that RL increased the efficiency of photosynthesis in C. acuminata. While values of Fv/Fm, q P, ETR and PSII were significantly reduced under BL and YL treatments, suggesting that BL and YL induced an inhibition of PSII electron transport. In our study, we also observed that BL and YL significantlyincreased the NPQ of plants. These results indicated that the protection of PSII against over excitation through regulating of photo-protective mechanism under BL and YL.(6) The lower density and almost closed stomata under BL may protect plants against light insufficiency.Meanwhile, the larger pore area of stomata in leaves under RL can optimise the uptake of CO2 and thus leads to better photosynthesis. The results of stomata scanning under different light quality also confirm that the growth, gas exchange, stomatal aperture and density are correlated in the plant development.(7) More thylakoids were observed in the grana of leaves under RL than WL, BL and YL. RL promoted the development of chloroplasts, grana and stroma lamellae. This was associated with the higher photosynthetic rates of plants under RL, which meant that at least RL treatment was conducive to the plant growth. Meanwhile, the swollen chloroplast and irregular shape of grana with decreased lamellae and disorganization of thylakoid membrane system in plants under YL at least suggested that YL was harmful to the development of chloroplasts.(8) The highest values of CPT content were observed under BL conditions, followed by yellow light,red light, and white light. Among the four light environments, CPT yield was the highest in plants grown under RL. Furthermore, activities of TSB and TDC as well as the relative expression of genes of TSB, TDC1, and TDC2 were significantly increased on 45 d under BL as compared with the WL. The gene expression levels are notably correlated with CPT content in Camptotheca acuminata leaves. The results indicated that RL was effective for inducing the production of camptothecin in Camptotheca acuminata seedling leaves.