The Effects Of Ultraviolet-B On Physiological Traits And Quality In Postharvest Flowers Of Medical Chrysanthemum And Its Mechanism

The ozone layer thinning resulted in the increase of ultraviolet-B(UV-B, 280–320 nm) radiation on the earth’s surface. Enhanced UV-B radiation can affect secondary metabolism processes in plants, and increase secondary metabolites content. Most of active ingredients in medicinal plants are secondary metabolites. However, active ingredients concentrations in medicinal plants are not high enough to have a health-promoting effect, which limits development of medicinal plants to some extent. The paper, medicinal chrysanthemums as tested materials, mainly studied the effects of UV-B radiation on physiological traits, active ingredients and differential proteomic in postharvest flower of medicinal chrysanthemum, and optimized the determination of chlorogenic acid in chrysanthemum flower using ultrasonic extraction and spectrophotometry. The results as followed:1. The paper optimized the determination of chlorogenic acid in chrysanthemum flower using ultrasonic extraction and spectrophotometry by the single factor and orthogonal experiments. The optimal conditions were:(1) extraction solution was 80% methanol and ultrasonic extraction was 30min;(2) the concentration and dose of ferric chloride chromogenic agent were 0.02 mol/L and 0.25 m L, respectively. The developmed method is simply, accurate and sensitive with high repeatability which can be used for the extraction and determination of chlorogenic acid in medicinal chrysanthemum.2. The effects of enhanced UV-B radiation on physiological traits, active ingredients, nutritional ingredients and secondary metabolism enzymes were related to radiation intensity. The experiment included six levels of UV-B radiation(UV0, 0 μW cm-2; UV50, 50 μW cm-2; UV200, 200 μW cm-2; UV400, 400 μW cm-2; UV600, 600 μW cm-2 and UV800, 800 μW cm-2). Enhanced UV-B radiation significantly increased hydrogen peroxide content(except for UV50), but did not evidently affect malondialdehyde content in flowers. Chlorophyll b and total chlorophyll content were significantly increased by UV600 and UV800. UV400 and UV600 significantly increased anthocyanins, carotenoids and UV-B absorbing compounds content, and the activities of phenylalanine ammonia lyase(PAL) and cinnamic acid-4-hydroxylase(C4H) over the control. The relationships between UV-B radiation intensities and the activities of secondary metabolism enzymes were best described by a second-order polynomial. The R2 values for UV-B radiation intensities and the activities of PAL, C4 H and 4CL were 0.8361, 0.5437 and 0.8025, respectively. Enhanced UV-B radiation significantly increased total vitamin C, chlorogenic acid and flavone(except for UV800) content. The results indicated that enhanced UV-B radiaiton could promote secondary metabolism processes in postharvest flowers, and increased active ingredients content. In the experimental conditions, the optimal UV-B radiation intensity was between UV200-UV600.3. The effects of enhanced UV-B radiation on physiological traits, active ingredients, nutritional ingredients and secondary metabolism enzymes were also related to radiation time. The experiment included six levels of UV-B radiation time: 0, 15, 30, 60, 120 and 180 min. The shorter UV-B radiation(15 min) significantly increased the hydrogen peroxide(H2O2) in postharvest flowers, whereas the longer UV-B radiation(180) significantly decreased H2O2 content. Malondialdehyde, UV-B absorbing compounds and chlorophyll a content were not affected by UV-B radiation time. When radiation time was 15, 30, 60 and 120 min, UV-B radiation significantly increased chlorogenic acid and flavone(except for 15 min) content in flower. The relationships between UV-B radiation intensities and the activities of secondary metabolism enzymes were best described by a second-order polynomial. The R2 values for UV-B radiation intensities and the activities of PAL, C4 H and 4CL were 0.7883, 0.5742 and 0.5628, respectively. The results indicated that it was most beneficial to improve the quality of chrysanthemum flower when UV-B radiation time was 30-120 min.4. Two-dimensional gel electrophoresis(2-DE) was utilized to analyze differential proteomic in flowers with or without UV-B radiation. Results indicated that a total of 43 protein spots(>1.5-fold difference in volume) were detected, including 19 spots with a decreasing trend and 24 spots with an increasing trend. 19 differentially expressed protein spots were successfully indentified by MALDI-TOF MS. The indentified proteins were classified based on functions and the majority included those involved in photosynthesis, respiration, protein biosynthesis and degradation and defence.This study further broadened the field of UV-B radiation, supplied a simple and environmental-friendly method to improve active ingredients content in postharvest flower, and partially revealed that UV-B mediated the physiological changes in postharvest flower from protein level. This will effectively promote the development of medicinal plant resources.